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Suppression of Fusarium wilt of banana by combining acid soil ameliorant with biofertilizer made from Bacillus velezensis H-6
Abstract
Fusarium wilt is one of the most serious banana diseases. It is caused by the soil-borne pathogen Fusarium oxysporum f. sp. cubense (Foc). The key accepted reasons for disease break-outs are the increasing number of pathogens in soil and gradual soil acidification according to published reports. Few studies have reported management methods to control these two aspects at the same time. In this study, a novel improved biological control method, combined acid soil ameliorant (ASA) with biofertilizer (BIO), was applied to manage Fusarium wilt under greenhouse conditions. A biocontrol agent, Bacillus velezensis H-6, was isolated and used for producing biofertilizer BIO6 for pot experiments. Combined ASA with BIO6 (treatments OBIO6 and ABIO6) showed greater biocontrol efficacy compared with individual treatments by 63.3% and 66.7%, respectively. They also increased rhizosphere soil pH from 4.50 to 4.89 and 5.52, respectively. Correlation analysis showed that the Foc population and Fusarium wilt disease incidence (DI) were both significantly (P < 0.05) negatively correlated with ∆pH in the rhizosphere, contents of NH4-N and organic matter (OM), and populations of bacteria and actinomycetes. Furthermore, ∆pH was significantly positively correlated with content of OM and populations of bacteria and actinomycetes, while it was negatively correlated with content of NO3-N and population of fungi. In conclusion, our novel improved biological control method revealed a greater potential to control Fusarium wilt of banana, and the effect might be a result of improving soil acid-alkali conditions to decrease the density of pathogen and manipulating the soil microbial community.
... En particular algunas especies de B. velezensis han mostrado cierta efectividad en la reducción de la incidencia de F. oxysporum en plántulas de banano, velezensis have shown some effectiveness in reducing the incidence of F. oxysporum in banana seedlings, under greenhouse conditions (Cao et al., 2018), and especially the incidence of FocR4T in plants of Cavendish banana var. Brazil (Huang et al., 2019). This agrees with that report from Segura-Mena et al. (2021) who mention that the en condiciones de invernadero (Cao et al., 2018), y de manera especial la incidencia de FocR4T en plantas de banano Cavendish var. ...
... This agrees with that report from Segura-Mena et al. (2021) who mention that the en condiciones de invernadero (Cao et al., 2018), y de manera especial la incidencia de FocR4T en plantas de banano Cavendish var. Brazil (Huang et al., 2019). Lo anterior concuerda con lo reportado por Segura-Mena et al. (2021) quienes mencionan que la utilización de bacterias benéficas/antagonistas son parte de prácticas de manejo del suelo para use of beneficial/antagonistic bacteria are part of soil management practices to reduce the incidence and severity of diseases caused by Fusarium. ...
... The results obtained suggest that B. subtilis and B. sonorensis could potentially be evaluated in greenhouse and later in the field, to be considered in the future as part of a management program against FocR2 and against FocR4T, before an eventual introduction of it; either through bacterization practices of plantain vitroplants before their establishment in the field or in the preparation of biofertilizer formulations that could be applied once the crop is established in the field, as has already been reported by Kavino and Manoranjitham (2018) and Huang et al. (2019). ...
There are three races of Fusarium oxysporum f. sp. cubense (Foc) that affect bananas and plantains, though the Cavendish group banana cultivars are resistant to Foc race 1 (FocR1) and Foc race 2 (FocR2). However, there are no effective control methods for the Tropical Race 4 (R4T). The foregoing makes it necessary to generate biological control strategies for FocR2 fungal model that is present in Mexico, forecasting the potential introduction of FocR4T into our country. In vitro inhibition was evaluated of bacterial strains Bacillus subtilis (BASU), B. velezensis (BAVE), and B. sonorensis (BASO) against three isolates of FocR2 (MIC17188, MIC17191 and MIC17192), obtained from plant samples collected in three banana production sites in the states of Puebla, Michoacán and Oaxaca. At 14 days, the strain BASU had in average high inhibition (55.1%) in comparison to BAVE and BASO strains (45.8 and 21.7%, respectively) against the three fungal strains mentioned before. In addition, the in vitro inhibition of Paenibacillus sp. (BSP 1.1) and Serratia sp. (AC35) was also evaluated by considering three pre-inoculation timings; the strain BSP1.1 showed high inhibition (80.1%) when pre-inoculated individually seven days before the fungus and at seven days of confrontation.
... In a previous study, we proposed a novel biocontrol method by combining the application of acid soil ameliorant and biofertilizer made from Bacillus velezensis H-6 and organic material, it showed greater efficacy than individual applications (Huang et al., 2019b). Some reports indicated that the complex phenomenon of disease suppression could not simply be attributed to a single antagonist but is most likely governed by a complex microbial community via changes in abiotic soil properties and an abundance of microorganisms (Mendes et al., 2011;Pane et al., 2013). ...
... According to the reported studies, lots of the control methods were mainly focused on pathogen inhibition, such as rotation, chemicals, and biocontrol agents (Ahammed & Yang, 2021;Kutawa et al., 2021;Zhang et al., 2014), rarely paying attention to the soil environment. In the present study, combining the application of acid soil ameliorant (ASA) and biofertilizer (BIOs) was proved to be an effective way to enhance the suppression on Fusarium wilt of banana compared with previous study (Huang et al., 2019b). It was an improvement approach to control diseases in the acid soil region because it was focused on both soil properties adjustment and pathogen inhibition. ...
... It therefore could conclude that the increase of MDA indicated highly lipid peroxidation, which caused antagonism to the pathogen. Higher biocontrol efficacy was observed on Fusarium wilt of banana by the biofertilzer made from a mixed microbial community, compared with the application of individual antagonist H-6 in a previous study (Huang et al., 2019b). The results were in agreement with Grosch et al. (2012), who found that compared to the single application, the co-inoculation of Trichoderma viride strain GB7 and Serratia plymuthica strain 3Re4-18 resulted in an improved biocontrol efficacy. ...
Fusarium wilt of banana is caused by the soil-borne pathogen Fusarium oxysporum f.sp. cubense (Foc). To increase the suppression activity, an improved mixed microbial community (a mixture of antagonists H-1, H-5, H-6, and H-7) was prepared for biofertilizer production, and underlying disease suppression mechanisms were determined. The results from pot experiments indicated that the biocontrol efficacies of organic acid soil ameliorant in combination with biofertilizer (OBIOs) and inorganic acid soil ameliorant in combination with biofertilizer (ABIOs) were 70.0% and 73.3%, respectively. OBIOs and ABIOs treatments also significantly increased the soil pH from 4.50 to 4.92 and 5.57. Real-time PCR analysis revealed that the densities of bacteria and actinomycetes increased, while those of fungi decreased, in the rhizosphere soil and/or fresh plant stems. The fermentation of antagonists H-1 and H-7 showed significant antagonistic effects on pathogens by increasing the malonaldehyde (MDA) concentration while reducing the ergosterol and protein concentrations and pectinase activities. The suppression efficacy of different treatments was significantly (P < 0.05) positively correlated with the ∆pH, the bacteria/fungi ratio, NH4-N, organic matter, and dissolved organic carbon, whereas it was negatively correlated with the pathogen density and NO3-N. In conclusion, the combination of acid soil ameliorant with biofertilizer showed a greater potential to control Fusarium wilt of banana, and the effect might result from improving the soil acid-alkali conditions and the toxicological effect on the pathogen.
... Controlling measures such as using resistant cultivars (Gonçalves et al., 2019), fungicides and soil fumigation (Nel et al., 2007), as well as crop rotation (Wang et al., 2015) have been employed. However, biological control appears as a new, highly promising, strategy for controlling Foc, mainly due to its advantages in relation to the safety and conservation of the environment (Huang et al., 2019). ...
... Bacillus are able to efficiently compete for nutrients in the soil, increasing their microbial mass, releasing of various antimicrobial substances, root colonization and the strains ability in using nutrients for their own growth, thus affecting the Foc development (Fu et al. , 2017;Huang et al., 2019;Palyzová et al., 2019). It is noteworthy that the amount and composition of the root exudates produced by plants vary depending on the species, cultivar, age of individual plants, and on the external abiotic and biotic factors (Haichar et al., 2014). ...
... These results are determined by Bacillus acting, in an antagonistic way, directly against phytopathogens, which comprises antibiosis mechanisms, where one organism harms the other, such as the following: production of antimicrobial substances, formation of volatile compounds, as well as the competition for nutrients and space (Palyzová et al., 2019;Huang et al., 2019). Foc accumulation results in the segregation of toxins that attack the banana tree roots, spreading to the pseudostem and leaves, thus resulting in the Fusarium wilt. ...
The aim of this study was to evaluate the controlling effect of Bacillus spp. on Fusarium oxysporum f. sp. cubense
(Foc) activity under greenhouse conditions. Two experiments were set up, with the first consisting of one Bacillus application
on the substrate, with Foc addition seven days later; two Bacillus applications at a seven-day interval on the substrate and Foc
application seven days after the last Bacillus application; and Bacillus applied to the substrate at the same time as Foc. After
14 days of incubation of the substrate infested with Foc and Bacillus, banana seedlings of the Prata-Anã cultivar were planted
in tubes. In the second experiment, the application interval was the same as the pre-inoculation experiment, but with Fusarium
inoculated first and then transferring bacteria to the substrate. The results of both experiments demonstrated that the Bacillus
spp. application after the Fusarium installation, with and without time interval, proved to be the best biocontrol of this disease in
Prata-Anã plants
... The inductive effect of Fusarium populations due to acid pH has been reported in Fusarium oxysporum f. sp. cubense (Huang et al., 2019) and Fusarium oxysporum f. sp. fragariae. ...
... greater than 3%) is widely accepted as a condition of suppressive soils that favors competition or inhibition of Fusarium spp. due to beneficial microorganisms (Orr and Nelson, 2018;Huang et al., 2019). In this investigation, Trichoderma spp. ...
... El efecto inductivo de poblaciones de Fusarium con pH ácido se ha reportado en Fusarium oxysporum f. sp. cubense (Huang et al., 2019) y Fusarium oxysporum f. sp. fragariae. ...
Wilt and dry bud rot of the agave (Agave tequilana var. azul) are diseases of high economic impact for this crop. The implication of Fusarium spp. in both diseases at a regional context was determined in this research. Root and soil samples were collected from 40 commercial plantations located in 13 counties at Los Altos, Jalisco an important cultivation region of agave azul in Mexico; Inoculum charge, as a Fusarium Index was obtained base on colony units (Fusarium vs total fungi) and its relationship with pH and organic matter were estimated from each sampling plantation. A total of 109 isolates were morphologically characterized as Fusarium spp. of which 25 were selected for molecular identification with ITS and EF-1a. The selection considered symptomatology, macro and microscopic characters and prevalence of colony types observed in vitro in Komada, Sabouraud, SNA and CLA media. The cultural and morphological characters evaluated were mycelial coloration, size, shape and septation of macro and microconidia, and length and number of phialides. Five species were associated with wilt and/or dry bud rot within three phylogenetic complexes: F. oxysporum of the Fusarium oxysporum species complex (FOSC) with 56% (46.2 % soil y 66.7 % root) regional representation; F. solani, F. falciforme and Fusarium sp. of Fusarium solani complex (FSSC) (40%); and Fusarium sp. of Fusarium fujikuroi complex (FFSC) (4%). MO and pH correlated inversely with Fusarium Index (r 2=0.68-0.70). It is postulated that wilt and dry bud rot of blue agave constitute a syndrome in which several Fusarium species are associated and parasitically specialized. A single isolate per each species complex was found associated specifically to each or both symptoms. Most isolates were associated to wilting with prevalence of F.oxysporum.
... Existing Cavendish cultivars are extremely vulnerable to the disease. The extensive use of chemical fertilisers and the monoculture of bananas, both of which are defining characteristics of industrial farming, facilitate the spread of TR4 pathogens (Bubici et al., 2019;Huang et al., 2019). ...
... The successful framing of Taiwan's banana export market, as discussed, is associated with using fertilisers and agrochemicals, which increase soil acidity and create a more favourable environment for the TR4 fungus to thrive (c.f. Huang et al., 2019;Segura-Mena et al., 2021). Farmers we spoke with in the fields stated that soil fertility is the most critical factor in the management of TR4. ...
This paper examines the making and remaking of Taiwan's banana export market in response to the devastation caused by an outbreak of a novel infectious plant disease, Fusarium wilt disease Tropical Race 4 (TR4, Fusarium oxysporum f. sp. Cubense). Taiwan was the world's fourth-largest exporter of bananas in the 1960s before the collapse of the market in the early 1970s. While scholars have drawn on actor-network theory-inspired performativity approach to understand the role of non-human actants in market-making, insufficient attention has been given to the distinct impacts of microbes on cases such as that of Taiwan's banana export market. Microbes' creative and ever-evolving qualities constantly present challenges related to the control and containment of such non-human entities, for which no pre-existing or universally applicable solutions exist. Consequently, there is a lack of research that provides useful frameworks to understand such disease -plagued markets. To bridge this gap in the literature, we examine the remaking of Taiwan's banana export market in the aftermath of the TR4 crisis using a case study approach and develop the notion of pathological markets. Inspired by recent scholarship on biosecurity and related care practices, we outline two characteristics that shape pathological markets: (a) speculative and pro-biotic care practices and (b) the rescaling of market organisations. The results of the fieldwork conducted as part of the present study in laboratories, government offices and on banana farms lead us to contend that the growth and development of particular microbes in multispecies environments such as Taiwan's banana farms constantly pose significant challenges for market farming. Moreover, to co-exist with the threats posed by the growth and development of microbes such as those which cause Fusarium wilt disease TR4, growers in Taiwan's banana export market rely heavily on probiotic and speculative care practices.
... The alternative would be to optimize the principle of low prevalence with the pathogenic knowledge at the haplotypes level and their regional prevalence levels. This also implies a thorough knowledge of the physico-chemical and biological mechanisms of suppressive soil to operate on the soil health as a mitigation strategy (Fang et al., 2012;Huang et al., 2019). For example, neutral-alkaline pH and organic matter greater than 2.5 do not promote high Fusarium indexes (FI) in soils where agave is grown in Jalisco and are considered low inductive soils (López-Bautista et al., 2020). ...
... La alternativa sería optimizar el principio de baja prevalencia con el conocimiento patogénico a nivel de haplotipos y sus niveles de prevalencia regional. Así mismo, implica el profundo conocimiento de los mecanismos físico-químicos y biológicos de supresividad de suelos para operar sobre la salud de suelo como estrategia de mitigación (Fang et al., 2012;Huang et al., 2019). Por ejemplo, pH neutros-alcalinos y materia orgánica superiores a 2.5 no favorece altos índices de Fusarium spp. ...
p>Esta investigación tuvo como objetivos identificar la especie(s) de Fusarium asociada(s) a hijuelos comerciales de Agave tequilana y desarrollar una metodología para cuantificar la carga de inóculo en hijuelos provenientes de plantaciones madre de Jalisco con inductividad epidémica diferencial al síndrome marchitez y pudrición seca del cogollo (SMAP). La finalidad fue proporcionar criterios para la certificación de plantaciones madre. La fase de campo se realizó entre marzo-mayo 2018 y 2019 en 21 plantaciones comerciales en 14 municipios de Los Altos, Sur y Valles de Jalisco. Se estimó el número de plantas enfermas (PE) y severidad SMAP (S) en 63 y 200 plantas/plantación mediante App-SIVEA para 2018 y 2019 respectivamente. Se desarrolló y aplicó el método CIFUSAG en 7055 hijuelos y 46 656 colonias fungosas obtenidas de 2364 siembras de lavado basal de la ‘piña’, secciones de tejido interno y macerado total de hijuelo. Unidades formadoras de colonia de Fusarium spp. (Fsp) y hongos totales (HT), purificación, monospóricos, caracterización morfológica y cultural se realizó con los medios Komada, agua-agar, Sabouraud, SNA y Sabouraud, respectivamente, diferenciando 557 aislados. La mayor inductividad epidémica en Los Altos significó moderado Índice de Fusarium [(IF) = (?Fsp) / (?HT)] (0.30 y 0.40) y Fsp (20 y 72UFC) respecto al Sur que tuvo valores más altos (0.69, 0.50; 23, 84UFC, respectivamente) (Tukey p=0.05). Calibre de hijuelo no tuvo influencia en IF y Fsp (p=0.183). IF y Fsp de lavado basal no estuvieron correlacionadas con S de plantas madres (r2 = 0.036 y 0.13), mientras que PE únicamente se correlacionó con Fsp (r2 =0.94). La carga de inóculo obtenida por lavado fue superior al de tejido interno con un total de 17,828 UFC (93%) e IF=0.42. Análisis molecular con el gen EF-1a evidenció asociación de 23 cepas con cuatro complejos filogenéticos: Fusarium oxysporum , F. fujikuro i, F. solani y F. incarnatum-equiseti con identidad superior al 98%. El hijuelo comercial de Agave tequilana constituye un factor de dipersión de al menos cuatro especies de Fusarium spp. en el rango de 3.3±3 y 6.83±4.2 UFC/hijuelo.</p
... Shen et al. (2013) have studied that inoculation of compost or enrichment with rhizosphere microbes is known to be more efficient in controlling soil-borne pathogens than the use of microbes or compost alone. Recently, a combination of microbes and compost has also been studied in the management of diseases caused by Fusarium (Fu et al., 2016(Fu et al., , 2017Huang et al., 2019). Enrichment of compost with beneficial microbes is carried out as an effort to increase the benefits of compost in increasing soil fertility (Andrade et al., 2021). ...
Shallot (Allium cepa var. aggregatum.) is a horticultural plant that is widely consumed in the world. However, the productivity of shallots in Indonesia is still relatively low, if compared to the actual optimum production potential of shallot. Shallot cultivation in Indonesia often experiences many problems. One of the problems is twisted diseases caused by Fusarium sp. This research aimed to study the effect of the application of organic material enriched with Bacillus in suppressing the development of twisted disease of shallot. This study was arranged in Randomized Complete Block Design (RCBD) with 5 treatments namely (A) compost + Bacillus velezensis isolate B-27, (B) compost + Bacillus cereus isolate RC76, (C) B. velezensis isolate B-27+B. cereus isolate RC76+compost, (D) compost + Trichoderma asperellum and (E) control (compost 1 ton/ha) with 5 replications on glasshouse treatment and 3 replications on field treatment. The results showed that the combination of B. velezensis in compost effectively reduced the incidence of twisted disease, the number of Fusarium spp. colonies, and the number of infected bulbs by Fusarium sp. Besides, the combination of compost with microbial agents showed better results than compost single treatment.
... Soil bacteria exhibit remarkable responsiveness to soil management practices, while using of organic fertilizers especially biofertilizer amendment has been reported to alter soil bacterial community composition and structure (Huang et al., 2019a). A related research highlighted the distinctive bacterial communities harbored by biofertilizers (Liu et al., 2021). ...
... Soil bacteria exhibit remarkable responsiveness to soil management practices, while using of organic fertilizers especially biofertilizer amendment has been reported to alter soil bacterial community composition and structure (Huang et al., 2019a). A related research highlighted the distinctive bacterial communities harbored by biofertilizers (Liu et al., 2021). ...
The southern area of China, particularly Guangxi region, contributes significantly to the nation's sugar industry. Nevertheless, this region faces challenges due to excessive use of nitrogen fertilizer in sugarcane cultivation, leading to land degradation. Biofertilizers (BF) signifies an important turning point in this challenging scenario globally. However, there is few literature on the co-application of biofertilizers (BF) and nitrogen (N) fertilizers and their effect on sugarcane rhizosphere microbial community, soil chemical properties, and above-ground growth. This study employed the combination of six different treatment in a netted greenhouse experiment and the results showed a significant variations in sugarcane biomass, soil chemical properties and rhizosphere bacterial community. Further, in comparison to the control and only N fertilization, the combined application of biofertilizer and nitrogen (BF+N) significantly affected the rhizosphere microbes as per the Shannon and Chao1 index (p < 0.05). The altered relative abundance of microbes significantly affected soil chemical properties, including pH, total carbon, total nitrogen, ratio of carbon and nitrogen, ammonium nitrogen, and nitrate-nitrogen. Ternary plot analysis further showed the enriched bacterial genera i.e., Burkholderia, Sphingomonas, Meosrhizobium, Rhizobacter, Nitrospirae, and Dyella, as a result of BF amendment. Redundancy analysis also validated the results and showed that soil organic matter, total carbon, and its ratio to nitrogen and ammonium nitrate were the key edaphic factors in altering the microbial community of sugarcane rhizosphere. In conclusion biofertilizer (1500 kg.ha − 1) combined with 150 kg.ha − 1 of urea (BF2) could be an effective strategy for enhancing sugarcane growth, reducing chemical fertilizers, and moving towards sustainable soil environment in continuous sugarcane cropping system.
... Furthermore, B. velezensis UR1 proved ineffective in controlling F. solani, as fungal filaments and spores proliferated and covered the bacterial cells. In the context of F. solani, each spore in the soil represents a pathogenic unit, and a higher number of pathogenic units contributes to increased disease prevalence in the soil 33 . Inhibiting pathogen growth and sporulation are critical for effective disease control, but the effectiveness of each strain may vary. ...
Biocontrol agents are safe and effective methods for controlling plant disease pathogens, such as Fusarium solani, which causes dry wilt, and Pectobacterium spp., responsible for potato soft rot disease. Discovering agents that can effectively control both fungal and bacterial pathogens in potatoes has always presented a challenge. Biological controls were investigated using 500 bacterial strains isolated from rhizospheric microbial communities, along with two promising biocontrol strains: Pseudomonas (T17-4 and VUPf5). Bacillus velezensis (Q12 and US1) and Pseudomonas chlororaphis VUPf5 exhibited the highest inhibition of fungal growth and pathogenicity in both laboratory (48%, 48%, 38%) and greenhouse (100%, 85%, 90%) settings. Q12 demonstrated better control against bacterial pathogens in vivo (approximately 50%). Whole-genome sequencing of Q12 and US1 revealed a genome size of approximately 4.1 Mb. Q12 had 4413 gene IDs and 4300 coding sequences, while US1 had 4369 gene IDs and 4255 coding sequences. Q12 exhibited a higher number of genes classified under functional subcategories related to stress response, cell wall, capsule, levansucrase synthesis, and polysaccharide metabolism. Both Q12 and US1 contained eleven secondary metabolite gene clusters as identified by the antiSMASH and RAST servers. Notably, Q12 possessed the antibacterial locillomycin and iturin A gene clusters, which were absent in US1. This genetic information suggests that Q12 may have a more pronounced control over bacterial pathogens compared to US1. Metabolic profiling of the superior strains, as determined by LC/MS/MS, validated our genetic findings. The investigated strains produced compounds such as iturin A, bacillomycin D, surfactin, fengycin, phenazine derivatives, etc. These compounds reduced spore production and caused deformation of the hyphae in F. solani. In contrast, B. velezensis UR1, which lacked the production of surfactin, fengycin, and iturin, did not affect these structures and failed to inhibit the growth of any pathogens. Our findings suggest that locillomycin and iturin A may contribute to the enhanced control of bacterial pectolytic rot by Q12. Fungal pathogens, such as Fusarium solani (FS) 1,2 , and bacterial pathogens, including Pectobacterium carotovo-rum (PC) 3,4 , P. atrosepticum (PA) 5-8 , and Xanthomonas campestris (XC) 9 , play a significant role in global plant diseases, causing root rot (dry and soft), leaf spots, and blackleg in both forest and crop ecosystems 1,7,10. The use of chemical fungicides and bactericides for disease management has adverse effects on human health and the environment. Consequently, there is an increasing reliance on biological agents to mitigate the negative impact of agrochemicals. The rhizosphere represents a competitive environment where microorganisms vie for resources to ensure their survival 11. While beneficial microorganisms are widely used in agriculture to control plant diseases, their inconsistent performance and a lack of sufficient safety data have limited the adoption of many promising biopesticides 12. Thus, there is an urgent need to identify bacteria that not only promote plant growth but also consistently demonstrate effective biological control mechanisms. Genome mining of microorganisms can provide valuable insights into the molecular-level mechanisms involved. Plant growth-promoting rhizobacteria (PGPR) employ various mechanisms for biocontrol. In addition to secondary metabolites that directly act against plant pathogens 13 , induced systemic resistance (ISR) and rhizospheric colonization are key OPEN
... Firstly, the replication types for S. spontaneum and S. hybrid R570 were different; the former was mainly based on the WGD/segmental duplication type, while the latter was mainly based on the proximal duplication ( Figure 5B). Tandem duplication plays a major driver, accompanied by more tandem gene microarrays [48]. The expansion of plant GLRs in different species is not consistent, and the different types of duplication present in intraspecific genes may also allow subgenus genes to evolve in different directions [13]. ...
The plant glutamate receptor-like gene (GLR) plays a vital role in development, signaling pathways, and in its response to environmental stress. However, the GLR gene family has not been comprehensively and systematically studied in sugarcane. In this work, 43 GLR genes, including 34 in Saccharum spontaneum and 9 in the Saccharum hybrid cultivar R570, were identified and characterized, which could be divided into three clades (clade I, II, and III). They had different evolutionary mechanisms, the former was mainly on the WGD/segmental duplication, while the latter mainly on the proximal duplication. Those sugarcane GLR proteins in the same clade had a similar gene structure and motif distribution. For example, 79% of the sugarcane GLR proteins contained all the motifs, which proved the evolutionary stability of the sugarcane GLR gene family. The diverse cis-acting regulatory elements indicated that the sugarcane GLRs may play a role in the growth and development, or under the phytohormonal, biotic, and abiotic stresses. In addition, GO and KEGG analyses predicted their transmembrane transport function. Based on the transcriptome data, the expression of the clade III genes was significantly higher than that of the clade I and clade II. Furthermore, qRT-PCR analysis demonstrated that the expression of the SsGLRs was induced by salicylic acid (SA) treatment, methyl jasmonic acid (MeJA) treatment, and abscisic acid (ABA) treatment, suggesting their involvement in the hormone synthesis and signaling pathway. Taken together, the present study should provide useful information on comparative genomics to improve our understanding of the GLR genes and facilitate further research on their functions.
... In addition, this bacterial strain BSP.1.1 produces auxins and indole as "bacterization practice" of micropropagated banana plantlets for inducing more protection before their establishment in field conditions. In this regard, protection of micropropagated banana plantlets against Foc has been achieved by inoculating with Bacillus subtilis and Pseudomonas fluorescens (Kavino & Manoranjitham, 2018), or by applying a biofertilizer formulation consisting of Bacillus velezcensis which showed high biocontrol efficacy against FocR4T (Huang et al., 2019). The later suggests the utilization of beneficial/antagonistic bacteria as part of wider soil management practices for reducing the incidence and severity of Fusarium wilt disease (Segura-Mena et al. 2021). ...
There are three races of Fusarium oxysporum f.sp. cubense (Foc) that significantly affect commercial banana plantations. Most banana cultivars are very susceptible to infection by tropical race 4 of Foc (FocR4T); in contrast, some banana varieties (Cavendish group) are resistant to FocR1 and FocR2. Therefore, it is necessary to develop combined management strategies for controlling the imminent arrival of FocR4T in Mexican plantations. This research evaluated, under in vitro conditions, the effect of seven antagonist bacterial strains, six systemic fungicides, and a fourth generation quaternary ammonium salt on the mycelial development of five Foc strains isolated from banana plantations at Puebla, Michoacan and Oaxaca states (Mexico). Paenibacillus sp. (BSP 1.1) resulted in the highest antagonistic effect (46.6% inhibition) towards the five Foc strains, followed by Serratia sp. (AC35) with 26.6% fungal inhibition. Tebuconazole applied in doses of 50, 100 and 500 μg mL−1 of active ingredient inhibited fungal growth by 100%, whereas Carbendazim and Benomyl delivered 99% fungal inhibition. A high dose of fourth generation quaternary ammonium salts (1250 μg mL−1) caused fungal growth inhibition of 100% and 98.5% after 5 and 8 days post inoculation, respectively. Overall, Paenibacillus sp. (BSP 1.1) and Serratia sp. (AC35) were the most effective bacterial strains; moreover, the application of certain doses of systemic fungicides such as Tebuconazol (50 μg mL−1), Carbendazim and Benomyl (>500 μg mL−1), and ammonium quaternary salts at doses of 1250 μg mL−1 may be considered as alternatives for preventing dissemination, or for using them as part of FocR4T control and sanitary programs.
... Combined application of B. velezensis H-6 with acid soil ameliorant (ASA) suppressed the incidence of Foc race 4 up to 63.3% to 66.7%. Besides, it also enhanced growth promotion in banana plants (Huang et al., 2019). Furthermore, Wang et al. (2013) reported that B. amyloliquefaciens W19 acted in synergy with organic fertilizer to reduce the incidence of Fusarium wilt other than plant growth promotion. ...
Fungicides play an immense role in quenching the infection of Panama wilt in banana. However, the use of fungicides and the monoculture of banana cultivars have resulted in the development of new races like race 4 which challenges scientists across the globe to identify new candidates for biological suppression of Fusarium oxysporum f.sp. cubense (Foc). Hence, attempts were made to dissect the endophytes from resistant banana cultivar YKM5 (Yengambi–AAA) to suppress Foc KP (race 4) infecting cv. Karpooravalli (ABB; Pisang Awak). Among the various endophytes, Bacillus velezensis YEBBR6 inhibited the mycelial growth up to 63% over control and hyper-parasitized the mycelium of Foc KP. Scanning electron microscope analysis revealed the ramification by B. velezensis over the hyphae of Foc KP leading to lysis. Analysis of VOCs/NVOCs compounds from the zone of inhibition, confirmed the presence of unique biomolecules including linoelaedic acid, nonanol, acetylvaleryl, 5–hydroxyl methyl furfural, clindamycin, allobarbital, 3-thiazolidine carboxamide, azulene, aminomorpholine, procyclidine, campholic acid, 3 amino-4 hydroxy phenyl sulfone, 3–deoxy mannoic lactone, hexadecanoic acid, oleic acid, and dihydroacridine of an antifungal and antimicrobial nature. Considering the diverse antimicrobial property, biohardening of micropropagated banana cv. Karpooravalli (ABB) with a liquid formulation of B. velezensis YEBBR6 (8 × 108 cfu/ml) and challenge inoculation with Foc KP promoted plant growth compared to uninoculated control. Besides, incidence of Fusarium wilt was reduced by 100% over inoculated control in greenhouse conditions. Furthermore, the expression of transcription factors and defense genes WRKY, MAPK, CERK 1, LOX, and PAL increased by several folds compared to inoculated and healthy control and thus suppressed Fusarium wilt of banana cv. Karpooravalli (ABB). Also, cytoscape analysis of defense genes indicated the coordinated expression of various other genes associated with it. Hence, our study confirmed the scope for exploring B. velezensis on a commercial scale for the management of Fusarium wilt race 4 causing wilt across genomes of banana.
... Soil acidification which is caused by long-term excessive and irrational use of chemical fertilizer, especially nitrogen fertilizer in banana plantation results in the proliferation and spread of banana wilt pathogens [10,19,20]. Increasing soil pH will be a possible measure to decrease the incidence of banana wilt. ...
The purpose of this study was to determine the effect and mechanism of alkaline fertilizer, bio-control fungi, and their synergistic application on control of Fusarium Tr4 incidence. Synchronized use of the alkaline fertilizer and biocontrol fungi eliminates rhizome browning and reduces the incidence rate of banana Fusarium wilt. The incidence of yellow leaves (ratio of yellow leaf to total leaf) and disease index in +Foc Tr4 CF treatment were the same (65%), while incidence of yellow leaves and disease index in +Foc Tr4 AFBCF were 31% and 33%, respectively. Under the stress of Foc Tr4 infection, the synergistic utilization of the alkaline fertilizer and biocontrol fungi would raise the activities of peroxidase, catalase and superoxide dismutase in banana roots. The root activity of banana was also increased. As a result, the banana height and stem diameter increments, shoot and root dry weight, accumulation of N, P and K in banana plants had been increased. The efficacy of the synergistic application of alkaline fertilizer and biocontrol fungi was not only reducing Foc Tr4 pathogen colonization and distribution in banana plants, but also preventing tylosis formation in vascular vessel effectively. Therefore, the normal transport of water and nutrients between underground and aboveground is ensured.
... Bacillus amyloliquefaciens FZB42 has been reported as a promising agent to reduce soil-borne plant pathogens (Borriss, 2020). Examples include control of Fusarium wilt in banana by using Bacillus velezensis H-6 as a biofertilizer (Huang et al., 2019). ...
Biofertilizers are the substances containing variety of microbes having the capacity to enhance plant nutrient uptake by colonizing the rhizosphere and make the nutrients easily accessible to plant root hairs. Biofertilizers are well known for their cost effectiveness, environment-friendly nature, and composition. These are effective alternatives to the hazardous synthetic fertilizers. This chapter covers various types of microbial biofertilizers pronouncing symbiotic and free-living nitrogen-fixers, phosphorus-solubilizer and mobilizers, their formulations, applications of few commercially available biofertilizers toward sustainable agriculture, and recent approaches to develop next-generation biofertilizers.
... The novel biofertilizer (BIO) is mixture of organism Bacillus velezensis H-6 and organic substrate (cattle manure compost + peanut bran 9:1 w/w). This novel BIO increases the soil pH, adds organic matter to soil, manipulates soil bacteria and actinomycetes, and controls pathogen causing fusarium wilt [270]. ...
Biofertilizer is an eco-friendly alternative to chemical fertilizer for a sustainable agriculture. The microbial inoculants help in growth directly or indirectly by fixing nitrogen (N), by solubilization of phosphorus (P) and potassium (K), by secreting siderophores, antibiotics, enzymes, antifungal, and antibacterial substances, and by releasing plant growth promoting hormones to enhance productivity and adaptabilty to overcome biotic and abiotic stresses. Many microorganism like Cyanobacteria, Azotobacter, Azospirillum, Bacillus sp., Pseudomonas sp., Actinomycetes, Paenibacillus, Rhizobium , arbuscular mycorrhiza fungi (AMF), and microalgae are applied in the preparation of biofertilizers. The microbes are cultivated at mass scale at high cell density (10 ⁹ cells/ml) and mixed with carrier materials such as lignite, coal, charcoal, filter mud, vermiculite, mineral soils, oils cakes, and coir waste for delivery as biofertilizers. Optimizing of biofertilizer by coinoculation of like bacteria with other bacteria, rhizobium with rhizobacteria, and bacteria with fungus would be a more appropriate approach to enhance growth and yield in terms of number of grains, number of leaves, shoot and root length, shoot and root fresh and dry weight, etc. Development of new genetic engineering microbes, nano-biofertlizers supported with studies like bioinformatics, genome mining, and and genome sequencing is discussed as the need of the future to improve biofertilizer efficacy.
... The soil organic matter content was determined using the dichromate digestion method. The pH was measured in a soil:H 2 O (1:2.5) solution [21]. Since the cation exchange capacity (CEC) was less than 160 mmol/kg, the soil samples could be classified as Ferallsols according to the WRB (World Reference Base for Soil Resources) [22]. ...
Fusarium oxysporum f. sp. cubense race 4 (Foc4) has significant impacts on banana production. Foc4 conidia can survive for many years in the soil, making control difficult. Thus, the inhibition of the conidia that serve as a continual source of inoculum in soil should be an effective way to control banana Fusarium wilt. In this paper, we first investigated the activities of polydimethylsiloxane-polymethacrylate block copolymers containing quaternary ammonium salts (PDMS-b-QPDMAEMA, labeled SixQ5) against Foc4 with microbroth dilution and toxicity plate assays. Then, the environmental behavior of these compounds, i.e., their adsorption and migration in soils, was further studied. Later, the effect and duration of SixQ5 on Foc4 in soil and the effects of SixQ5 on soil microbial diversity were evaluated. In addition, we conducted pot experiments to study the effect of Si5Q5 on banana Fusarium wilt. The results showed that SixQ5 showed a good inhibitory effect on Foc4, was easily adsorbed by the soil and was relatively immobile in soil. The inhibitory effect of SixQ5 on Foc4 was maintained for 30 d under continual inoculation of Foc4 into the soil (Foc4 addition every 2 d), and SixQ5 remained active in the soil for 90 d with Foc4 addition every 10 d. Soil microbial population analysis revealed that the culturable total fungal and bacterial populations increased and the culturable actinobacterial population decreased SixQ5 with addition. Pot experiments showed that Si5Q5 can reduce Foc4 infection in banana seedlings and does not harm banana seedlings. The stability and inhibitory effects on Foc4 demonstrate the potential application of SixQ5 in banana fields to prevent Foc4 conidial infection in the long term.
... Recently, some studies have evaluated combinations of antagonistic microbes and compost in controlling Fusarium wilt (Fu et al., 2016(Fu et al., , 2017Huang et al., 2019). Changes to the soil microbial community are considered as the main mechanism through which bio-organic fertilizer promotes soil suppression of disease (Shen et al., 2013;Huang et al., 2017). ...
Biological control agents (BCAs) are considered as one of the most important strategies for controlling Fusarium wilt, and bioorganic fertilizer, in particular, has been extensively investigated. However, little is known regarding how a biocontrol microorganism affects the suppression mechanisms when combined with different amendments. In this study, a pot experiment was performed using banana plants to investigate the different mechanisms by which the biocontrol bacterium Bacillus velezensis HN03 (isolated from our laboratory) and amendments suppress Fusarium wilt. The incidence of banana wilt was decreased under HN03 and was reduced further when HN03 was combined with compost, particularly wormcast. In the suppression of Fusarium wilt, HN03 was found to influence the soil environment in various ways. HN03 increased the peroxidase level, which improves plant defense, and was highest when combined with wormcast, being 69 times higher than when combined with cow dung compost. The high accumulation of Mg and P in the “HN03 + wormcast” and Zn and Mn in the “HN03 + cow dung” treatments was negatively correlated with disease incidence. Furthermore, HN03 re-established the microbial community destroyed by the pathogen and further increased the level of suppression in the wormcast. HN03 also enhanced the functional traits of the soil, including defensive mechanism-related traits, and these traits were further enhanced by the combination of HN03 + wormcast.
... Delivery systems for inputs and seed are also often deficient where small growers predominate. Research to develop such ICDM approaches centers on healthy soils with capacity to suppress disease build-up and crop management to (Huang et al., 2012), and integrated systems approaches (Haddad et al., 2018;Huang et al., 2019) already provide evidence for the potential of this strategy. Basic knowledge on Foc populations, cultivar susceptibility, and more advanced quantitative diagnostic tools should underlie the applied management approaches. ...
The spread of Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4), causal agent of Fusarium wilt of banana (FWB), has been projected to reach 17% of the global banana-growing area by 2040 equaling 36 million tons of production worth over US$10 billion. This potential loss has fueled (inter)national discussions about the best responses to protect production and small-scale growers’ livelihoods. As part of a multi-crop ex ante assessment of returns on research investments conducted by the CGIAR Research Program on Roots, Tubers, and Bananas (RTB) from 2012 to 2016, four FWB research options were assessed: (i) improved exclusion, surveillance, eradication, and containment (ESEC) measures to reduce Foc TR4 spread, (ii) integrated crop and disease management (ICDM) to facilitate production of partially FWB resistant cultivars on Foc-infested soils, (iii) conventional breeding of FWB-resistant cultivars (CBRC), and (iv) genetically modified (GM) FWB-resistant cultivars (GMRC). Building on a risk index (Foc scale) predicting the initial occurrence and internal spread of Foc TR4 in 29 countries, an economic surplus (ES) model, cost-benefit analysis, and poverty impact simulations were used to assess impact under two adoption scenarios. All options yield positive net present values (NPVs) and internal rates of return (IRRs) above the standard 10% rate. For the conservative scenario with 50% reduced adoption, IRRs were still 30% for ICDM, 20% for CBRC, and 28% for GMRC. ESEC has IRRs between 11 and 14%, due to higher costs of capacity strengthening, on-going surveillance, farmer awareness campaigns, and implementation of farm biosecurity practices, which could be effective for other diseases and benefit multiple crops. The research investments would reach between 2.7 million (GMRC) and 14 million (ESEC) small-scale beneficiaries across Asia/Pacific, Sub-Saharan Africa, and Latin America/Caribbean. The options varied in their potential to reduce poverty, with the largest poverty reduction resulting from CBRC with 850,000 and ESEC with 807,000 persons lifted out of poverty (higher adoption scenario). In the discussion, we address the data needs for more fine-grained calculations to better guide research investment decisions. Our results show the potential of public investments in concerted research addressing the spread of Foc TR4 to yield high returns and substantially slow down disease spread.
... Biocontrol organisms (or their natural by-products) have been shown to have adverse effects on various plant diseases. For example, Bacillus sp. is one of several candidates (Huang et al. 2019;Shoda 2019). There are commercially available biocontrol products derived from Bacillus sp. for soil-borne diseases including the product "Serenade" containing B. amyloliquefaciens (Matzen et al. 2019). ...
Pythium myriotylum is a destructive soil-borne phytopathogen, causing yield losses in ginger and many other crops. Environmental and regulatory concerns drive the need to find biological alternatives to conventional pesticides used to manage P. myriotylum. Trans-cinnamic acid (TCA) alone, and fermentation broth from strains of symbiotic bacteria of eight species of entomopathogenic nematodes alone, and in combination with TCA, were tested for their effect on zoospore germination and mycelial growth of P. myriotylum. TCA significantly inhibited mycelial growth. Fermentation broths from seven of the eight strains of symbiotic bacteria directly inhibited mycelial growth, especially those isolated from Steinernema feltiae (strain SN) and S. riobrave (strain 7–12). Moreover, adding TCA significantly increased the inhibitory effect on mycelial growth of the fermentation broths of seven of the strains tested. All bacteria fermentation broths showed inhibitory effects on zoospore germination. However, TCA alone was not inhibitory to zoospore germination but was inhibitory to mycelial growth. Antimicrobial effects on mycelial growth and zoospore germination were proportional to the concentration of symbiotic bacteria isolated from S. feltiae (strain SN). These results show that TCA and symbiotic bacteria of entomopathogenic nematodes may have potential to provide biorational control of P. myriotylum.
... Meanwhile, each of the treatments suppressed FWD to some extent, and the DB + 40dp treatment was the most effective. It has previously been shown that supplementing fertilizers with spores of an antagonistic microbe such as Bacillus subtilis or P. polymyxa is beneficial in terms of promoting growth (Suliasih & Widawati, 2018), controlling FWD (Huang et al., 2019), and raising yield (Schütz et al., 2017). Indirani, Jayakumar, and Latha (2000) reported that dazomet fumigation improved the growth, yield, and quality of tomato and Mark and Cassells (1999) found that dazomet fumigation enhanced the strawberry productivity. ...
Sustained monoculture often leads to the inhibition of plant growth, the decrease of the soil microbial diversity, and changes in soil microbial community composition, particularly to the accumulation of soil‐borne pathogens. In this study, we conducted field experiments to investigate the practical effects of tilling the soil down to a depth of 40 cm (40dp) in combination with dazomet (D) soil fumigation and/or the application of a bio‐organic fertilizer (B) on chrysanthemum growth, with a focus on the potential mechanisms underlying the responses of the soil microbiome. The growth indices of chrysanthemum were significantly (p < .05) increased in the DB + 40dp treatment compared to that in other treatments. The weighted and unweighted UniFrac distances in the principal coordinate analysis (PCoA) revealed that soil bacterial and fungal community compositions were separated according to the treatments. The abundance of genera potentially expressing growth promotion, such as Pseudomonas and Bacillus, was increased in the DB + 40dp treatment. In addition, the combined DB + 40dp treatment enhanced the activities of catalase, urease, sucrase, and β‐d‐glucosidase, and significantly increased the levels of available nitrogen, phosphorus, and potassium in the soil. The redundancy analysis (RDA) implied that the composition of the microbiome was correlated to soil enzymatic activities and soil potassium availability in the rhizosphere soil of chrysanthemum plants. Our findings suggest that the DB + 40dp treatment is a better strategy for improving chrysanthemum growth and regulating the rhizosphere microbiome in monoculture soils than the methods presently employed by commercial chrysanthemum producers.
... The decrease in Fusarium abundance could be related to the higher N total and pH values in AOF plots. Previous studies have shown the sensitivity of Fusarium spp. to increases in ammonia and pH (Deltour et al., 2017;Huang et al., 2019;Zakaria, 1980). None of the studied variables affected root-inhabiting pathogen richness, although their relative abundance was highest in the AOF treatment. ...
Application of organic fertilisers to soil prevents erosion, improves fertility and may suppress certain soil-borne plant pathogens, but it is still unclear how different trophic groups of fungi and oomycetes respond to long-term fertilisation treatment. The objective of the study was to examine the effect of different fertilisation regimes on fungal and oomycete pathogen- and mycorrhizal symbiont diversity and community structure in both soil and roots, using PacBio SMRT sequencing. The field experiment included three fertilisation treatments that have been applied since 1989: nitrogen fertilisation (WOM), nitrogen fertilisation with manure amendment (FYM) and alternative organic fertilisation (AOF), each applied at five different rates. Soil samples were collected three times during the growing season, while root samples were collected during the flowering stage. There was no influence of the studied variables on soil and root pathogen richness. Contrary to our hypothesis, pathogen relative abundance in both soil and roots was significantly higher in plots with the AOF treatment. Furthermore, richness and relative abundance of arbuscular mycorrhizal (AM) fungi decreased significantly in the AOF treatment. Permutational analysis of variance (PERMANOVA) demonstrated the effect of fertilisation treatment on pathogen community composition in both soil and roots. Our findings indicate that organic fertilisers may not always benefit soil microbial community composition. Therefore, further studies are needed to understand how fertilisation affects mycorrhizal mutualists and pathogens.
Trichoderma spp. has the ability to inhibit fungal plant pathogens through several mechanisms like the production of hydrolytic enzymes, mycoparasitism, coiling, and antibiosis and is therefore recommended as a potential and native biocontrol agent for effective control of soil-transmitted diseases. Various species of Trichoderma, like T. virens, T. asperellum, T. harzianum, etc., have been explored for their biocontrol activity against phytopathogens. There are different Trichoderma species and strains with respect to plant pathogens. Efforts have been made to develop effective and efficient methods, such as microencapsulation use of different polymers, adjuvants, or carriers, to increase the shelf-life and efficacy of Trichoderma formulations. The crucial aspects for the success of a biocontrol agent include developing and validating formulations, improvement in shelf-life, cost-effectiveness, easy accessibility, improved delivery systems, broad spectrum in action, robust performance (biocontrol), and integrative strategies for sustainable disease management. This review focuses on recent developments in the isolation, identification, preservation, substrates, consortium, quality control, mass production, delivery methods, field performance, registration, and commercialization of Trichoderma formulations for strategic development of next-generation multifunctional biological control formulations.
In the global marketplace, agriculture plays an important role. However, diseases produced in plants mostly affect the financial system. Pest occurrence and climatic changes are the leading trouble that the banana plant leaf faces, which influences the quality of fruit and crop yields. To predict the leaf disease symptoms in an early stage, the automatic banana leaf disease detection technique is more significant. The traditional deep neural network methods used in banana plant leaf detection need more parameters and utilize complex architectures. To address such problems, modified generative adversarial networks–modified faster region-based convolutional neural networks with fuzzy (MGAN–MFRCNN with Fuzzy) is proposed for identifying banana leaf disease. The most effective framework in deep learning is GAN. The autoencoder is incorporated within the fundamental GAN design for developing a modified GAN model; it is used for data augmentation. To perform feature extraction from high-resolution networks, an MFRCNN is used in our proposed method. The improved and more accurate classification scores are obtained by combining fuzzy with the ensemble model. The experimentation is carried out using a banana plant leaf dataset in which the healthy leaf, xanthomonas-affected leaf, and sigatoka-affected leaf diseases are detected and classified. The proposed model reached 98% accuracy, 97% precision, 96% F1-score, 98% specificity, and 98% sensitivity, which is better than other existing methods.
The introduction of legumes into rotations can improve nitrogen use efficiency and crop yield; however, its microbial mechanism involved remains unclear. This study aimed to explore the temporal impact of peanut introduction on microorganisms related to nitrogen metabolism in rotation systems. In this study, the dynamics of diazotrophic communities in two crop seasons and wheat yields of two rotation systems: winter wheat – summer maize (WM) and spring peanut → winter wheat – summer maize (PWM) in the North China Plain were investigated. Our results showed that peanut introduction increased wheat yield and biomass by 11.6% (p < 0.05) and 8.9%, respectively. Lower Chao1 and Shannon indexes of the diazotrophic communities were detected in soils that sampling in June compared with those sampling in September, although no difference was found between WM and PWM. Principal co-ordinates analysis (PCoA) showed that rotation system significantly changed the diazotrophic community structures (PERMANOVA; p < 0.05). Compared with WM, the genera of Azotobacter, Skermanella, Azohydromonas, Rhodomicrobium, Azospirillum, Unclassified_f_Opitutaceae, and Unclassified_f_Rhodospirillaceae were significantly enriched (p < 0.05) in PWM. Furthermore, rotation system and sampling time significantly influenced soil properties, which significantly correlated with the top 15 genera in relative abundance. Partial least squares path modeling (PLS-PM) analysis further showed that the diazotrophic community diversity (alpha- and beta-diversity) and soil properties (pH, SOC and TN) significantly affected wheat yield. In conclusion, legume inclusion has the potential to stabilize diazotrophic community structure at the temporal scales and increase subsequent crop yield.
Globally, the production of bananas (Musa sp. L.) often suffers from various environmental challenges. Among them, biotic stress-induced disease caused by phytopathogenic soil microorganisms is the most threatening factor. Fusarium oxysporum f. sp. cubense Foc Tropical Race 4 (Foc-TR4) is an important soil-borne fungus triggering the severe disease, Fusarium wilt (Panama disease) in bananas. Following infection in a wide variety of bananas, strain Foc-TR4 harshly reduced their cultivation. Herein, we have summarized the present scenario of Fusarium wilt disease. Numerous challenges have been proposed by researchers to control the Panama disease as well as to improve banana production. Primarily aiming at increasing disease tolerance to bananas and improving their cultivation, various management strategies like crop rotation, burning of rice husks, biological soil disinfection, and use of chemical fungicides have been developed. However, these chemical and cultural practices have several drawbacks and therefore not often used. Plant growth-promoting (PGP) bacteria offer one of the most environmentally friendly, effective, safe, and economically sound solution to combat the Panama disease. Apart from growth promotion, this PGPR prevents phyto-pathogen-induced diseases. The recent chapter highlights the utilization of beneficial and antagonistic PGPR and their efficacy against diseases, and bacterial-mediated mechanisms involved in managing Panama disease. Induced systemic resistance (ISR), production of antibiotics, extracellular enzymes, cyanogenic compounds, siderophores, and other antifungal metabolites are the main mechanisms involved in PGPR-induced disease suppression. It will be possible to build or select sustainable management techniques to prevent or aid to minimize Fusarium wilt incidence in banana plantations using the scientific knowledge gathered in this research. The use of indigenous PGP rhizobacteria in plant disease control is gaining popularity as environmental and health concerns underscore the need for a more sustainable agriculture system.KeywordsPanama diseaseFusarium oxysporum f. sp. cubenseTropical Race 4Biological control agents (BCAs)PGPRInduced systemic resistanceRhizobacteria
Advances in production systems always aim at finding alternatives to improve crop productivity. One of the recent practices adopted in commercial banana and plantain plantations refers to the application of liquid fertilizers in bunches in order to increase productivity. This research aimed at verifying whether the use of biofertilizers based on pure vinasse or associated with other chemical fertilizers would provide morphophysiological changes in fruits or increase the productivity of ‘Terra Maranhão’ plantain cultivars. In order to carry out this project, a randomized block design with 6 treatments and 3 replicates was set up in a commercial crop and the postharvest production and quality characteristics of ‘Terra Maranhão’ plantain fruits were evaluated. The results showed that the morphophysiological characteristics of freshly harvested fruits that impact productivity such as the fruit weight and bunch weight were affected by treatments, as the postharvest characteristics of ripe fruits were little affected by the application of fertilizers in bunches, except for the SST content. It could be concluded that the crop yield increased significantly by 17% when using mixture of vinasse, potassium chloride and urea; however, this treatment caused significant reduction of 1.3 ºBrix compared to control.
Covering: Focus on 2015 to 2020Plant and soil microbiomes consist of diverse communities of organisms from across kingdoms and can profoundly affect plant growth and health. Natural product-based intercellular signals govern important interactions between microbiome members that ultimately regulate their beneficial or harmful impacts on the plant. Exploiting these evolved signalling circuits to engineer microbiomes towards beneficial interactions with crops is an attractive goal. There are few reports thus far of engineering the intercellular signalling of microbiomes, but this article argues that it represents a tremendous opportunity for advancing the field of microbiome engineering. This could be achieved through the selection of synergistic consortia in combination with genetic engineering of signal pathways to realise an optimised microbiome.
The plant pathogenic fungus Fusarium oxysporum f. sp. passiflorae (FOP) causes severe losses to the Brazilian passiculture. As a soil inhabitant, the fungus spreads at the micro spatial scale (microspread) via mycelial growth and colony expansion. The pathogen expansion rate is affected by the spatial distribution of inoculum sources available, as well as by environmental factors. The objective of this study was to model the in vitro dynamics of FOP by simulating its microspread, under the effect of pH and osmotic potential, in controlled physical environments formed by agar sites spatially distributed in a triangular lattice. An additional experiment evaluated the effect of a heterogeneous environment on FOP microspread. This setting was represented by different fractions of sites with high and low nutritional content. A percolation theory was used to determine the limits of pathogen spread where critical distances are associated with a critical probability of site colonization. The logistic dose-response model was fitted to growth curves with the parameters estimated based on non-linear regression. We found that nutritional state of sites affected FOP microspread. In particular, a heterogeneous environment reduced their rate of microspread and consequently could reduce epidemic progress rate. This study contributes new biological knowledge and information to further improve disease management.
Long-term greenhouse vegetable cultivation commonly incurs soil-borne diseases, which seriously threaten the sustainability of greenhouse production system. Rhizomicrobiome plays an important role in ensuring plant health and driving soil nutrient cycling. However, how rhizomicrobiome respond to the occurrence of soil-borne disease is still not completely clear. Increasing knowledge involved would benefit to the prevention of soil-borne disease in intensive greenhouse production by providing the insight into soil microbial ecology. Herein, with the help of a continuously cultivated greenhouse cucumber field, soil physicochemical and biochemical properties and the abundances (quantitative real-time PCR) and communities (high-throughput amplicon sequencing) of bacteria, fungi, ammonia-oxidizing archaea (AOA) and bacteria (AOB) in the rhizosphere of healthy and Fusarium-diseased cucumbers were investigated. Diseased cucumber rhizosphere had significantly higher available nutrient contents and acidity compared to healthy cucumber rhizosphere, but significantly lower microbial activity and nitrification capacity. Although there was no significant difference in the abundances of bacteria, fungi, AOA and AOB, diseased cucumber rhizosphere had more abundant Fusarium oxysporum. For bacteria, only community richness in diseased cucumber rhizosphere was significantly lower than that in healthy cucumber rhizosphere, whereas for fungi both community richness and Shannon diversity were significantly lower. Community structures of bacteria, fungi, AOA and AOB all significantly differed between healthy and diseased cucumber rhizosphere. Particularly, healthy cucumber rhizosphere had more abundant beneficial microbes (Bacillus and Penicillium) and putative biocontrol microbes (Mycothermus) as well as Nitrosospira briensis Clade-related AOB. These results revealed significantly different rhizomicrobiome between Fusarium wilt diseased and healthy cucumbers under long-term intensive greenhouse cultivation, and suggested that rhizomicrobiome may play an important role in the occurrence of Fusarium wilt disease of cucumber. The findings obtained here also provided potential directions towards the prevention of soil-borne diseases and the improvement of N turnover in diseased soil by manipulating rhizosphere microbiome.
MicroRNAs (miRNAs) are a class of endogenous non-coding small RNAs that regulate targeted mRNAs by post-transcription; thus, miRNAs are considered post-transcription regulators. Although numerous miRNAs have been found in model plants, information on miRNAs in banana is limited. In this study, 139 members in 38 miRNA families were determined by sequencing the small RNA (sRNA) transcriptomes of Fusarium wilt-resistant and susceptible banana varieties, and six out of eight new miRNAs were confirmed by RT-PCR. According to the sRNA transcriptome data and qRT-PCR verification, some miRNAs were differentially expressed between Fusarium wilt-resistant and susceptible banana varieties. A total of 293 and 31 target genes were predicted based on the draft maps of banana A genome and Fusarium oxysporum (FOC1, FOC4) genomes, respectively. Two important pathogenic genes in F. oxysporum genomes, namely, feruloyl esterase gene and proline iminopeptidase gene, were targeted by banana miRNAs. These novel findings may provide a new strategy for preventing and controlling Fusarium wilt in banana.
Over 50 years ago, banana export plantations in Panama were ruined by Fusarium wilt race 1 (Foc. R1) since the popular cultivar Gros Michel is susceptible to Foc. R1 [1]. Fortunately, the resistant cultivar Cavendish replaced Gros Michel as the world biggest commercial fruit after ten years' research and development. Due to its good economic profit, banana industry develops very fast recently in China. Unfortunately, Fusarium oxysporum f. sp. cubense tropical race 4 (TR4) brought disaster to Cavendish plantation since 1996. Most of traditional banana planting zones of Guangdong and Hainan provinces were infected by Foc. TR4 to the end of 2009. In order to fight against Foc. TR4, here we tried to investigate the cost-benefit and disease resistance of six banana cultivars (Cavendish Baxijiao, Dajiao, Guangfen No. 1, Fenzha No. 1, Gongjiao, Haigongjiao) planted in China Foc. Zones. Comparisons were conducted on their economic characteristics, cost, benefit, as well as the advantage and disadvantage and their application in rota-tion. Generally, supposing the investment of 2200/ha. Rotation of these cultivars can maintain the biodiversity as well as improve the sustainable development of banana industry.
Fusarium wilt is one of the most serious diseases of banana plants caused by soil-borne pathogen Fusarium oxysporum f.sp. cubense (FOC). In this study a pot experiment was conducted to evaluate the effects of different bio-organic fertilizers (BIOs) on Fusarium wilt of banana, including the investigations of disease incidence, chitinase and β-1,3-glucanase activities of banana plants, and FOC populations as well as soil rhizosphere microbial community. Five fertilization treatments were considered, including chemical fertilizer containing the same N, P and K concentrations as the BIO (control), and matured compost mixed with antagonists Paenibacillus polymyxa SQR-21 and Trichoderma harzianum T37 (BIO1), Bacillus amyloliquefaciens N6 (BIO2), Bacillus subtilis N11 (BIO3), and the combination of N6 and N11 (BIO4). The results indicated that the application of BIOs significantly decreased the incidence rate of Fusarium wilt by up to 80% compared with the control. BIOs also significantly promoted plant growth, and increased chitinase and β-1,3-glucanase activities by 55%–65% and 17.3%–120.1%, respectively, in the banana roots. The population of FOC in the rhizosphere soil was decreased significantly to about 104 colony forming units g−1 with treatment of BIOs. Serial dilution plating and denaturing gradient gel electrophoresis analysis revealed that the application of BIOs increased the densities of bacteria and actinomycetes but decreased the number of fungi in the rhizosphere soil. In general, the application of BIOs revealed a great potential for the control of Fusarium wilt disease of banana plants.
BACKGROUND
The lack of reliable prediction tools for evaluation of the level and specificity of compost suppressiveness limits its application. In our study, different chemical, biological and microbiological parameters were used to evaluate their potential use as a predictor parameter for the suppressive effect of composts against Fusarium oxysporum f. sp. melonis (FOM) and Phytophthora capsici (P. capsici) in muskmelon and pepper seedlings respectively. Composts were obtained from artichoke sludge, chopped vineyard pruning waste and various agro-industrial wastes (C1: blanched artichokes; C2: garlic waste; C3: dry olive cake).RESULTSCompost C3 proved to offer the highest level of resistance against FOM, and compost C2 the highest level of resistance against P. capsici. Analysis of phospholipid fatty acids isolated from compost revealed that the three composts showed different microbial community structures. Protease, NAGase and chitinase activities were significantly higher in compost C3, as was dehydrogenase activity in compost C2.CONCLUSION
The use of specific parameters such as general (dehydrogenase activity) and specific enzymatic activities (protease, NAGase and chitinase activities) may be useful to predict compost suppressiveness against both pathogens. The selection of raw materials for agro-industrial composts is important in controlling Fusarium wilt and Phytophthora root rot. © 2014 Society of Chemical Industry
Our previous work demonstrated that application of a bio-organic fertilizer (BIO) to a banana mono-culture orchard with serious Fusarium wilt disease effectively decreased the number of soil Fusarium sp. and controlled the soil-borne disease. Because bacteria are an abundant and diverse group of soil organisms that responds to soil health, deep 16 S rRNA pyrosequencing was employed to characterize the composition of the bacterial community to investigate how it responded to BIO or the application of other common composts and to explore the potential correlation between bacterial community, BIO application and Fusarium wilt disease suppression. After basal quality control, 137,646 sequences and 9,388 operational taxonomic units (OTUs) were obtained from the 15 soil samples. Proteobacteria, Acidobacteria, Bacteroidetes, Gemmatimonadetes and Actinobacteria were the most frequent phyla and comprised up to 75.3% of the total sequences. Compared to the other soil samples, BIO-treated soil revealed higher abundances of Gemmatimonadetes and Acidobacteria, while Bacteroidetes were found in lower abundance. Meanwhile, on genus level, higher abundances compared to other treatments were observed for Gemmatimonas and Gp4. Correlation and redundancy analysis showed that the abundance of Gemmatimonas and Sphingomonas and the soil total nitrogen and ammonium nitrogen content were higher after BIO application, and they were all positively correlated with disease suppression. Cumulatively, the reduced Fusarium wilt disease incidence that was seen after BIO was applied for 1-year might be attributed to the general suppression based on a shift within the bacteria soil community, including specific enrichment of Gemmatimonas and Sphingomonas.
Strawberry (Fragaria × ananassa) is one of the most important berry crops worldwide. Fusarium wilt poses a serious threat to commercial strawberry production worldwide and causes severe economic losses. Our previous surveys suggested that soil pH, soil amendment with organic matter and/or crop rotation could offer opportunities for improved management of strawberry disease. Studies were conducted for the first time to determine the effects of soil pH, soil amendments with manure compost and crop residue, and crop rotation on the severity and impact of Fusarium wilt on strawberry. At soil pH 6.7, plants showed the least severe disease and the lowest reductions in shoot and root dry weight (DW) of plants from disease, significantly lower than those of plants in acidic soil at pH 5.2 or 5.8. In soil amendment with manure compost at 5.0 %, plants showed the least severe disease and the lowest reductions in shoot and root DW of plants from disease, significantly lower than those of plants in the other three levels of manure compost. In soil amendment with crop residue at 2.5 % or 5.0 %, shoot and root disease of plants and reductions in shoot and root DW of plants from disease were significantly lower than those of plants in soil without crop residue or excessive crop residue amendment at 10.0 %. Plants in soil rotated with tomato not only showed the least severe disease but also showed the lowest reductions in shoot and root DW of plants from disease, significantly lower than those of plants in soil continuously planted with strawberry without rotation or rotated with capsicum. Soil pH, soil amendment with manure compost or crop residue, and crop rotation, all significantly reduced the severity and impact of Fusarium wilt on strawberry. There is great potential for manipulating soil pH, adding soil organic amendments and utilizing crop rotation, not only to successfully manage Fusarium wilt on strawberry, but to do so in a sustainable way without current reliance upon chemical fumigants.
Fusarium wilt, caused by Fusarium oxysporum f. sp. cucumerinum J. H. Owen, results in considerable yield losses for cucumber plants. A bio-organic fertilizer (BIO), which was a combination of manure composts with antag-onistic microorganisms, and an organic fertilizer (OF) were evaluated for their efficiencies in controlling Fusarium wilt. Application of the BIO suppressed the disease incidence by 83% and reduced yield losses threefold compared with the application of OF. Analysis of microbial communities in rhizosphere soils by high-throughput pyrosequencing showed that more complex community structures were pres-ent in BIO than in OF treated soils. The dominant taxonomic phyla found in both samples were Proteobacteria, Firmi-cutes, Actinobacteria and Acidobacteria among bacteria and Ascomycota among fungi. Abundance of beneficial bacteria or fungi, such as Trichoderma, Hypoxylon, Tritir-achium, Paenibacillus, Bacillus, Haliangium and Strepto-myces, increased compared to the OF treatment, whereas the soil-borne pathogen, Fusarium, was markedly decreased. Overall, the results of this study demonstrate that the appli-cation of the BIO was a useful and effective approach to suppress Fusarium wilt and that the high-throughput 454 pyrosequencing was a suitable method for the characteriza-tion of microbial communities of rhizosphere soil of cucumber.
fragments ofgenescoding for 16SrRNA,allthesame length, bydenaturing gradient gelelectrophoresis (DGGE).DGGE analysis ofdifferent microbial communities demonstrated thepresenceofup to10distinguishable bandsintheseparation pattern, which were mostlikely derived fromas many different species constituting these populations, andthereby generated a DGGE profile ofthepopulations. We showedthatitispossible toidentify constituents which represent only1%ofthetotal population. Withanoligonucleotide probespecific fortheV3region of16SrRNA ofsulfate-reducing bacteria, particular DNA fragments fromsome ofthemicrobial populations couldbe identified byhybridization analysis. Analysis ofthegenomic DNA fromabacterial biofilm grown underaerobic conditions suggests thatsulfate-reducing bacteria, despite their anaerobicity, were present inthis environment. Theresults we obtained demonstrate thatthis technique willcontribute toour understanding ofthegenetic diversity ofuncharacterized microbial populations. Onlyan estimated 20%ofthenaturally occurring bacteria havebeenisolated andcharacterized so far(22). Selective enrichment cultures fail tomimictheconditions thatpartic- ularmicroorganisms require forproliferation intheir natural habitat. Furthermore, many microorganisms areboundto sediment particles andarethusnotdetected byconventional microscopy. Molecular biological techniques offer new opportunities fortheanalysis ofthestructure andspecies composition of microbial communities. Inparticular, sequencevariation in rRNAhasbeenexploited forinferring phylogenetic relation- ships among microorganisms (23) andfordesigning specific nucleotide probes forthedetection ofindividual microbial taxainnatural habitats (2,10). Thesetechniques havealso beenapplied todetermining thegenetic diversity ofmicro- bialcommunities andtoidentifying several uncultured mi- croorganisms (9,21). Theyconstitute thecloning ofriboso- malcopy DNA (21) or polymerase chainreaction (PCR)- amplified ribosomal DNA (rDNA)(9)followed bysequence analysis oftheresulting clones. Here, we present a new approach fordirectly determining thegenetic diversity ofcomplex microbial populations. The procedure isbasedon electrophoresis ofPCR-amplified 16S rDNAfragments inpolyacrylamide gels containing alinearly increasing gradient ofdenaturants. Indenaturing gradient gel electrophoresis (DGGE)(6), DNA fragments ofthesame length butwithdifferent base-pair sequencescan besepa- rated. Separation inDGGE isbasedon theelectrophoretic mobility ofa partially meltedDNA molecule inpolyacryl- amidegels, whichisdecreased compared withthatofthe completely helical formofthemolecule. The melting of fragments proceeds indiscrete so-called melting domains:
The composition of the soil microbial community can be altered dramatically due to association with individual plant species, and these effects on the microbial community can have important feedbacks on plant ecology. Negative plant-soil feedback plays primary roles in maintaining plant community diversity, whereas positive plant-soil feedback may cause community conversion. Host-specific differentiation of the microbial community results from the trade-offs associated with overcoming plant defense and the specific benefits associated with plant rewards. Accumulation of host-specific pathogens likely generates negative feedback on the plant, while changes in the density of microbial mutualists likely generate positive feedback. However, the competitive dynamics among microbes depends on the multidimensional costs of virulence and mutualism, the fine-scale spatial structure within plant roots, and active plant allocation and localized defense. Because of this, incorporating a full view of microbial dynamics is essential to explaining the dynamics of plant-soil feedbacks and therefore plant community ecology.
More effective ways of applying biocontrol products should be developed based both on the characteristics of the biocontrol
agents and the normal practices of the agricultural producer. A new system was developed to improve the biocontrol efficacy
of Fusarium wilt for watermelon production, and this system was tested in pot and field experiments. Biocontrol was achieved by applying
a novel bioorganic fertilizer product (BIO) to Fusarium-infested soil. The best biocontrol was obtained by application of a bioorganic fertilizer, BIO, into soil during the nursery
phase of watermelon seedling followed by a second application to Fusarium-infested soil when watermelon seedlings were transplanted. In comparison with the controls, the incidence of the disease
was reduced by 60–100% in the pot experiment and by 59–73% in the field experiment when the BIO was applied during the nursery
stage. After application of BIO during the nursery stage, the number of colony-forming units of Fusarium oxysporum in rhizospheric soil was significantly (P<0.05) inhibited compared to the controls. An invitro experiment showed that the antagonist Paenibacillus polymyxa in the BIO could effectively colonize the rhizosphere of watermelon and proliferate along the extending plant roots. This
inhibited growth of Fusarium oxysporum in the rhizosphere of watermelon and protected the watermelon roots from attack by the pathogens. The method used for biocontrol
Fusarium wilt disease in watermelon should be a useful strategy to improve field efficacy of other biocontrol agents.
KeywordsBioorganic fertilizer (BIO)-Nursery application-
Fusarium wilt-Watermelon-
Paenibacillus polymyxa
Verticillium wilt is the most devastating disease of cotton in China and a challenge for producers to find effective means of control. Here, we report the effects of different organic amendments on the incidence of this disease and on the rhizosphere microflora of cotton plants. Seven organic amendments were evaluated for their suppressive effect on cotton Verticillium wilt caused by Verticillium dahliae Kleb. The results showed that organic amendments applied to soil reduced disease severity in both inoculated pots and naturally infested cotton field plots. The most effective control was achieved with crab shell (chitin), soybean stalk and alfalfa, and in pots the efficacy was 72%, 60% and 56% for vascular tissues, respectively. Rice chaff gave moderate control, while poultry manure, peanut cake and wheat straw showed a weak suppressive effect with efficacy of 21%, 28% and 11% for vascular tissues, respectively. Organic amendments increased the population size of rhizosphere microbes (including fungi, bacteria and actinomycetes), which varied at the different ages of the cotton plants. The organic materials with the best biocontrol capacity strongly stimulated the proliferation of antagonists to V. dahliae in the rhizosphere. However, poultry manure, peanut cake and wheat straw caused only small changes in the total numbers of microflora and the percentage of antagonists was lower. Extracts from organic amendments were highly inhibitory to V. dahliae. The changes undergone by rhizosphere microbes after the addition of organic amendments may contribute to suppression of cotton wilt and help to explain the protective effect of the amendments. The results indicate that application of organic amendments is an effective control measure against cotton Verticillium wilt.
To construct a new recombinant strain of Bacillus velezensis that has antifungal and insecticidal activity via the expression of the insecticidal Bacillus thuringiensis crystal protein, a B. thuringiensis expression vector (pHT1K-1Ac) was generated that contained the B. thuringiensis cry1Ac gene under the control of its endogenous promoter in a minimal E. coli-B. thuringiensis shuttle vector (pHT1K). This vector was introduced into a B. velezensis isolate that showed high antifungal activities against several plant diseases, including rice blast (Magnaporthe grisea), rice sheath blight (Rhizotonia solani), tomato gray mold (Botrytis cinerea), tomato late blight (Phytophthora infestans), and wheat leaf rust (Puccinia recondita), by electroporation. The recombinant B. velezensis strain was confirmed by PCR using cry1Ac-specific primers. Additionally, the recombinant strain produced a protein approximately 130 kDa in size and parasporal inclusion bodies similar to B. thuringiensis. The in vivo antifungal activity assay demonstrated that the activity of the recombinant B. velezensis strain was maintained at the same level as that of wild-type B. velezensis. Furthermore, it exhibited high insecticidal activity against a lepidopteran pest, Plutella xylostella, although its activity was lower than that of a recombinant B. thuringiensis strain, whereas wild-type B. velezensis strain did not show any insecticidal activity. These results suggest that this recombinant B. velezensis strain can be used to control harmful insect pests and fungal diseases simultaneously in one crop.
We describe a new molecular approach to analyzing the genetic diversity of complex microbial populations. This technique is based on the separation of polymerase chain reaction-amplified fragments of genes coding for 16S rRNA, all the same length, by denaturing gradient gel electrophoresis (DGGE). DGGE analysis of different microbial communities demonstrated the presence of up to 10 distinguishable bands in the separation pattern, which were most likely derived from as many different species constituting these populations, and thereby generated a DGGE profile of the populations. We showed that it is possible to identify constituents which represent only 1% of the total population. With an oligonucleotide probe specific for the V3 region of 16S rRNA of sulfate-reducing bacteria, particular DNA fragments from some of the microbial populations could be identified by hybridization analysis. Analysis of the genomic DNA from a bacterial biofilm grown under aerobic conditions suggests that sulfate-reducing bacteria, despite their anaerobicity, were present in this environment. The results we obtained demonstrate that this technique will contribute to our understanding of the genetic diversity of uncharacterized microbial populations.
The objectives of the research were to investigate short-term dynamics of bacterial populations in soil after a disturbance in the form of fresh organic matter incorporation and to investigate how these dynamics are linked to those of some environmental parameters. To reach these objectives, soil bacterial populations, mineral nitrogen, pH, and redox potential (ROP) were monitored daily for 1 month after incorporation of clover-grass (CG) plant material in microcosm experiments. Colony-forming units (CFUs) and direct microscopic counts of FDA-stained and FTTC-stained bacteria increased immediately after incorporation of the plant material, dropped within 2 days, and fluctuated thereafter. Harmonics analysis demonstrated that there were significant wavelike fluctuations with three or four significant peaks within 1 month after incorporation of clover-grass material. Peaks in CFUs were 1-2 days ahead of those in direct counts. Ammonium (NH4) concentrations increased from the start of the experiments until nitrification commenced. Nitrate (NO3) concentrations dropped immediately after plant incorporation, and then rose monotonically until the end of the experiments. There were no wavelike fluctuations in NH4 and NO3 concentrations, so that bacterial fluctuations could not be attributed to alternating mineral N shortages and sufficiencies. pH levels rose and declined with NH4 levels. ROP dropped shortly before NH4 concentrations rose, and increased before NH4 concentrations decreased; there were no regular fluctuations in ROP, so that temporary oxygen shortages may not have been responsible for the observed fluctuations in bacterial populations. Thus, for the first time, regular wavelike dynamics were demonstrated for bacterial populations after perturbation by addition of fresh organic matter to soil, and several potential reasons for the death phase of the fluctuations could be excluded from further consideration.
Combining chemical fertilizer with organic fertilizer is an important management strategy for maintaining soil fertility and disease suppression. Banana is an important cash crop in tropical regions and is severely threatened by Fusarium wilt disease. Little is known about the effects of combined fertilization on rhizosphere soil properties and disease suppression in tropical regions in China. In this study, the effects of combined fertilization on rhizosphere soil properties and the development of banana Fusarium wilt disease were assessed based on key components of soil chemical and biological properties. With chemical fertilization (CF) only, the soil urease, SOC and available nutrients contents were increased continuously, while the soil bacterial diversity, pH, and acid phosphatase activities were initially increased, and then decreased with increasing NPK application rate. Under low NPK application rate (25% CF), the OM addition was more effective in increasing soil bacterial diversity, pH, available nutrients, urease and acid phosphatase activities than NPK fertilization only. However, excessive OM addition had negative effect on soil available P and K content under high NPK application rate (100% CF). The T6 treatment of 50% CF + 500 organic matter (OM) had the highest integrated score among the treatments. Path coefficient analysis revealed that soil bacterial diversity plays the most important role in improving soil integrated score. The disease index was significantly and negatively linear correlated with the integrated score (r = −0.92, P < 0.01). These results demonstrate that an appropriate combination of organic and inorganic fertilizer application is effective at improving soil fertility and reduced disease incidence of banana.
Significant soil pH decrease has been reported in Chinese croplands in response to enhanced chemical fertilizer application and crop yields. However, the temporal and spatial variation of soil acidification rates across Chinese croplands is still unclear. We therefore assessed trends in soil acidification rates across provincial China for the period 1980-2010 by calculating inputs-outputs of major cations and anions in cropland systems. Nitrogen (N) induced proton production increased from 4.7keqH(+)/ha/yr in 1980 to a peak of 11.0keqH(+)/ha/yr in 1996 and remained nearly constant after 2000 at a rate of approximately 8.6keqH(+)/ha/yr. The proton production induced by crop removal increased from 1.2 to 2.3keqH(+)/ha/yr. The total proton production thus increased from 5.9 to 10.9keqH(+)/ha/yr in the 30years. As a result, the actual acidification rate, reflected by (base) cation losses, accelerated from 2.3 to 6.2keqH(+)/ha/yr and the potential acidification rate, reflected by phosphorus accumulation accelerated from 0.2 to 1.3keqH(+)/ha/yr. The national averaged total acidification rates were thus estimated to increase from 2.6 to 7.6keqH(+)/ha/yr in the past 30years. The highest soil acidification rate occurred in the Jiangsu Province with a rate of 17.9keqH(+)/ha/yr, which was due to both high N application rates and high base cation removals by crops and crop residues. The combination of elevated N inputs and decreased N use efficiency (NUE) in response to those N inputs, thus enhancing the nitrate discharge, were the main reasons for the accelerated acidification in Chinese croplands. Considering the expected growth of food demand in the future, and the linkage between grain production and fertilizer N consumption, a further acceleration of soil acidification can thus be expected, unless the N inputs is reduced and/or the NUE is increased substantially.
Microbial diversity in rhizosphere soil considered as important factors for agricultural productivity. Proteomic approach in Fusarium wilt infected and healthy rhizosphere soils of tomato provided the role of microbial protein involved for the development of disease as well as resistance. In this study, two different rhizosphere soils of tomato were collected analyzed through metaproteomic approach to determine the microbial protein abundance. The result of 2D-PAGE from both the soils revealed that, totally 11 differentially proteins were expressed and they were identified through MALDI-TOF. The identified proteins were originated from bacteria, fungus and plant. The functions of proteins showed that they were involved in resistance of tomato plant. Quantification of fungal pathogen inoculums from the both soils were formed by qPCR analysis. The result of qPCR analysis in soils revealed that Fusarium wilts infected soil contained more amount of Fungal ITS, Fusarium genus and F. oxysporum inoculums than healthy soils. Hence, our result suggests that due to the activity of beneficial microbial proteins in healthy soil, protected the tomato plants from wilt disease under the field conditons. Likewise, qPCR analysis clearly demonstrated the requirement of pathogen inoculums for the development of Fusarium wilt disease in tomato. Thus, the current study concludes that exploitation of microbial protein functions unravels the role of microbes including unculturable bacteria's for the development of resistance in plants against pathogens. In the other hand, early detection of pathogen by qPCR at minimal population level helps to develop management strategies before infection.
Previous studies demonstrated that the Chryseobacterium sp. WR21 could effectively control the bacterial wilt disease caused by Ralstonia solanacearum through effective root colonization. The strain WR21 exhibited a low level of DNA homology with Chryseobacterium strains DSM 15235T (24.1%), DSM 17724T (24.8%), and DSM 18014T (10.4%), suggesting that WR21 may represent a novel species, for which the name Chryseobacterium nankingense sp. nov. is proposed. The in vitro competition experiments with strain WR21 indicated it significantly inhibited growth of the pathogen in co-culture with six of nine tested nutrients (e.g. root exudates) that could be utilized by strain WR21 and R. solanacearum. Similar trends were observed in co-culturing experiments using tissue exudates of tomato. A positive relationship (r = 0.785) was noticed between the differences in the average growth rate of both strains and the disease suppression effects. In conclusion, Chryseobacterium nankingense sp. nov. WR21 exhibits antagonism through nutrient competition that might be used for achieving biocontrol of Ralstonia solanacearum induced wilts. © 2017 International Organization for Biological Control (IOBC)
BAC03 is a novel Bacillus velezensis strain previously studied for biological control of scabby diseases caused by Streptomyces scabies. To optimize its efficacy in disease control, different application strategies of BAC03 were investigated in this study, including timing, frequency, and concentrations of BAC03. BAC03 was either used for seed tuber treatment, foliar application or drenching in potting mix infested with S. scabies. Neither foliar application nor seed treatment affected disease severity. BAC03 applied five days before planting significantly reduced S. scabies population and completely suppressed radish scab, but the later BAC03 was applied the less effective it was. BAC03 at 105 CFU cm−3 potting mix or higher concentrations was effective in reducing radish scab. Increasing the frequency of BAC03 application did not increase the efficacy on disease reduction. BAC03 also increased the biomass of radish roots and leaves whether the pathogen was present or not.
One of the most destructive diseases of banana is Fusarium wilt or Panama disease, caused by the soilborne fungus Fusarium oxysporum f. sp. cubense (Foc). Foc is widespread in almost all banana-growing areas and cannot be effectively controlled by chemical or biological measures. Fusarium wilt could potentially be managed by the promotion of soil disease suppressiveness, but little is known how soils attain a higher level of disease suppression and how crop management can impact on this. Banana cultivar (cv.) Maçã, a cultivar highly susceptible to Foc race 1, was grown on a farm managed as agroforestry system in Pedra Dourada, Brazil, where Foc race 1 is present in soil. At some locations on the farm banana plants of cv. Maçã stayed productive, while on others it succumbed rapidly. We hypothesized that the differences in disease severity on the farm could be attributed to different levels of soil disease suppressiveness. In this study, we assessed the level of disease suppression of the different locations and elucidated potential factors that could promote disease suppression in soil. Patches with confirmed presence of Foc race 1 were sampled and tested for Fusarium wilt suppression in greenhouse assays. The plant community composition, soil abiotic properties and soil microbial community of the different locations were compared. Locations with a higher level of disease suppression were characterized by a low density of the susceptible cv. Maçã, a high diversity of other banana varieties, a higher clay content, higher pH and lower soil cover by graminoids. Banana cv. Ouro was only present in the three most suppressive patches. The results of this study suggest that in soils with favorable abiotic properties, a good plant arrangement, in which cv. Maçã is grown in mixed stands with other banana varieties, can help to promote Fusarium wilt suppression.
Many of the areas dominated by acid sulfate (AS) soils in southern China have been reclaimed for rice cultivation and represent an important source of agricultural production and food security for the local population. In this study, we examined the abundance and partitioning of Fe, Mn, Zn, Cu, and Al in both rice paddy fields and uncultivated fields by using a six-step sequential extraction procedure. Rice cultivation significantly reduced acidity levels at soil depths of 0–100 cm, but acidity at depths of 100–140 cm increased significantly. A substantial loss of Mn in the oxide and acidified soil layer (0–100 cm) compared to the underlying parent material was observed, but there were few changes in the concentrations of Fe and Zn throughout the soil profile. However, both Cu and Al were substantially enriched in the superficial soil (0–40 cm) compared to the underlying subsoil (40–140 cm). In general, leaching of Fe, Mn, and Al was higher in the paddy fields because of intensified irrigation and flood conditions, whereas accumulation of Cu, mainly in the form of “acid soluble” and “crystalline iron oxide” Cu, was higher in the paddy fields than in the uncultivated fields. The most marked declines in metal concentrations occurred in the “labile” and “acid soluble” fractions, as a result of rice cultivation, which increased leaching of the readily mobilized “labile” and “acid soluble” fractions of heavy metals in these soils.
The rapid development of biogas production will result in increased use of biogas slurry (BS) as organic fertilizer. However, side effects such as suppression of soilborne diseases are not yet well investigated and understood. Therefore, the objectives of the study were to evaluate the effects of biogas slurry application on suppression of Fusarium wilt disease of watermelon and its relationship with soil chemical and microbiological properties. Pot and field experiments were conducted to compare effects of biogas slurry application on Fusarium wilt disease suppression of watermelon in soil with a moisture content of 60% water holding capacity (WHC) or flooded continuously. Fusarium wilt was significantly suppressed in soil from biogas slurry amended plots. Biogas slurry flooding enhanced the degree of suppression in the pot experiment. Moreover, the biogas slurry treatment also significantly suppressed Fusarium wilt in the field with a disease index of 33.2% compared with 69.6% in water treatment. Biogas slurry strongly reduced the pathogen population in rhizosphere soil. The populations were decreased by 43.1% and 95.9% in the biogas slurry moist and flooding treatments, respectively. Biolog data indicated that average well color development (AWCD) and Shannon-weaver index were increased significantly in biogas flooding treatment. Principal component analysis showed that Fusarium wilt was negatively correlated with NH4+-N, available K (AK), water-soluble carbon (DOC), water soluble nitrogen (DON) and phenolic acid (PA) contents in soil and positively correlated to soil pH and soil redox potential (Eh). Microbial communities, in general, did not significantly correlate with disease suppression.
Bacillus velezensis G341 can suppress plant pathogens by producing antagonistic active compounds including bacillomycin D, fengycin, and (oxy) difficidin. The complete genome sequence of this bacterium was characterized by one circular chromosome of 4,009,746bp with 3,953 open reading frames. The genome contained 36 pseudogenes, 30 rRNA operons, and 95 tRNAs. This complete genome sequence provides an additional resource for the development of antimicrobial compounds.
Copyright © 2015. Published by Elsevier B.V.
Continuous cropping with banana results in an enrichment of Fusarium oxysporum f. sp. cubense race 4 (FOC) in soil, causing the soil-borne disease Fusarium wilt. Crop rotation has been an effective method of controlling various soil-borne diseases. However, no information is currently available concerning variations in soil microbial community structure in banana crop rotations. Thus, the influence of two-year crop rotation systems of pineapple–banana and maize–banana on the population density of FOC and soil microbial community structure was investigated to identify which rotation system is more effective in FOC suppression and differences in microbial community composition among different rotations. Bacterial and fungal communities were interrogated by pyrosequencing of the 16 S RNA gene and the internal transcribed spacer (ITS) region. The pineapple–banana rotation was more effective than maize–banana in reducing FOC abundances and suppressing Fusarium wilt disease incidence. Allelopathic effects of pineapple root exudates on FOC were not observed. Greater fungal community variations than bacterial were identified between the two rotation systems, suggesting that fungal communities may play a more important role in regulating FOC abundances. Furthermore, in the pineapple–banana rotation, Acidobacteria, Planctomycetes, Chloroflexi phyla, Gp1, Gp2 and Burkholderia bacterial genera increased while the fungal phyla Basidiomycota, (esp. Gymnopilus) increased and Sordariomycetes decreased. Such changes may be important microbial factors in the decrease in FOC.
This study combined the micro‐cross‐section cultural system with in vitro mutagenesis induced by ethyl methanesulphonate (EMS) to screen for fusarium wilt‐resistant lines of Brazil banana (Musa spp., AAA). The results indicated that the optimum EMS concentration and duration for the treatment of micro‐cross‐sections cut from the pseudostem of tissue‐cultured plantlet were 300 mm and 60 min, respectively. Under the optimal treatment, an average of 2·2 regenerated shoots were produced from each explant. One hundred regenerated plantlets were used for screening for fusarium wilt‐resistant lines by the early screening technique. The initial disease symptom – yellowing in lower leaves of susceptible plantlets – was observed 2 weeks after inoculation. After 2 months, only six plants survived – the putative fusarium wilt‐resistant lines. The fusarium wilt pathogen Fusarium oxysporum f. sp. cubense race 4, was identified in the preliminary test field by a SCAR marker technique. Of the six putative resistant lines, five survived the preliminary field test. The regenerated plantlets from these five fusarium wilt‐resistant lines were subjected to early screening again, where they showed markedly reduced disease incidences compared with regenerated plantlets of Brazil banana (control). It was concluded that EMS‐induced mutation of banana through the micro‐cross‐section cultural system is potentially useful for banana improvement.
Fears rise for Latin American industry as devastating disease hits leading variety in Africa and Middle East.
Bacterial wilt caused by Ralstonia solanacearum is one of the most serious tobacco diseases worldwide. Brevibacillus brevis (L-25) and Streptomyces rochei (L-9) with strong inhibitory effects on R. solanacearum in vitro were isolated from the rhizosphere of a healthy tobacco plant in a severely wilt-diseased field. Pot and field experiments were conducted to evaluate the biocontrol effect of the isolated antagonists alone and in combination with organic fertilizer. In pot experiment, the control efficacy was 92.3–100 % in the treatments applied with L-25 and L-9 alone or together with organic fertilizers. When bioorganic fertilizer containing L-9 and L-25 was applied to the soil in field condition, the control efficacies were 95.4 and 30.0 in the Anhui and Guizhou field plots, respectively. The counts of bacteria and actinomycetes in rhizosphere soil were significantly increased (p ≤ 0.05) under all antagonist applications compared with CK (PR). In contrast, fungal and R. solanacearum densities in the rhizosphere soil applied with antagonists were much lower than the CK (PR) rhizosphere. Combined application of the two antagonists had better effect than single antagonist treatments. The antagonists were more effective when they were combined with organic fertilizer as compared with the antagonistic strains only. These results allow us to conclude that a combination of the biocontrol agents, L-25 and L-9, together with organic fertilizers can effectively control bacterial wilt by affecting soil microbial structure.
Cotton Verticillium wilt is a destructive soil-borne disease affecting cotton production. In this study, application of bio-organic fertilizer (BIO) at the beginning of nursery growth and/or at the beginning of transplanting was evaluated for its ability to control Verticillium dahliae Kleb. The most efficient control of cotton Verticillium wilt was achieved when the nursery application of BIO was combined with a second application in transplanted soil, resulting in a wilt disease incidence of only 4.4%, compared with 90.0% in the control. Denaturing gradient gel electrophoresis patterns showed that the consecutive applications of BIO at nursery and transplanting stage resulted in the presence of a unique group of fungi not found in any other treatments. Humicola sp., Metarhizium anisopliae, and Chaetomium sp., which were considered to be beneficial fungi, were found in the BIO treatment, whereas some harmful fungi, such as Alternaria alternate, Coniochaeta velutina, and Chaetothyriales sp. were detected in the control. After the consecutive applications of BIO at nursery and transplanting stage, the V. dahliae population in the rhizosphere soil in the budding period, flowering and boll-forming stage, boll-opening stage, and at harvest time were 8.5 × 102, 3.1 × 102, 4.6 × 102, and 1.7 × 102 colony-forming units per gram of soil (cfu g−1), respectively, which were significantly lower than in the control (6.1 × 103, 3.4 × 103, 5.2 × 103, and 7.0 × 103 cfu g−1, respectively). These results indicate that the suggested application mode of BIO could effectively control cotton Verticillium wilt by significantly changing the fungal community structure and reducing the V. dahliae population in the rhizosphere soil.
Soil pH is an important factor affecting the availability of soil nutrients that impact plant growth. Given the susceptibility of soil pH to excessive fertilization and the widespread use of manures, it is essential to examine the influence of soil pH on the distribution and availability of soil nutrients. We sampled and analyzed brown soils from pear orchards in thirteen towns in Wendeng county. Samples were obtained from areas along or between rows of trees at specified distances and depths. The results showed that the soil pH fluctuated from 4.06 to 6.59 in October 2008 and from 4.24 to 7.57 in April 2009. The quantity of soil samples with pH below 5.50 increased by 34.6%. Analysis of the soil pH for samples obtained along the rows of trees showed that the pH decreased as the depth increased (except for the range 5.5 to 6.0); soil pH in the samples obtained between the rows of trees demonstrated different trends. The average organic matter (O.M.) content as well as the N (NH4+) and available P, K, Cu, Zn, Fe, and Mn contents in the samples collected in October 2008 were higher than those observed in April 2009. Conversely, the values for other available nutrients were lower than those in the samples collected in April 2009. The available nutrients and organic matter (O.M.) content in different pH ranges varied. The soil pH was significantly or very significantly correlated with N (NH4+ and NO3-), available K, Cu, Fe, and exchangeable Ca for the October 2008 samples, while a significant or very significant correlation existed between N (NH4+), available P, Zn, exchangeable Ca, and exchangeable Mg for the April 2009 samples. The correlations between soil pH and the amounts of available nutrients and organic matter (O.M.) along the rows of trees in September 2009 were nearly consistent with those between the rows.
Several soil characteristics have been studied in relation to Fusarium wilts in field plots of banana plantations of Gran Canaria Island (Spain). Principal component analysis has been applied to soil chemical parameters, the aim being to determine the possible relationships between the apparition and development of the Fusarium wilts and soil characteristics. The results seem to indicate that there is a relationship between the disease incidence and the values of some parameters like pH, cation exchange capacity (CEC), sodium (Na) in solution, and iron (Fe); pH, CEC, and Na values were significantly smaller in areas affected by the disease. However, the values of Fe extracted with DTPA and Fe associated with fulvic acids were significantly higher in disease affected areas; the same tendency was observed in the values of total carbon (C) and nitrogen (N) in the different areas. Other parameters studied, like exchangeable cations, Fe‐oxalate, etc., have not showed either differences or general tendencies. These results seem to suggest that the absence and/or presence of disease could be controlled partly for the chemical characteristics of the different soil areas of the same field plot.
Different formulations of Bacillus subtilis were prepared using standard laboratory protocols. Bacillus subtilis survived in glucose and talc powders at 8.6 and 7.8 log10 CFU/g, respectively, for 1 year of storage at room temperature compared with 3.5 log10 CFU/g on a peat formulation. Glasshouse experiments using soil and seed treatments were conducted to test the efficacy of B. subtilis for protecting lentil against the wilt disease caused by Fusariumoxysporum f. sp. lentis. Seed treatments with formulations of B. subtilis on glucose, talc and peat significantly enhanced its biocontrol activity against Fusarium compared with a treatment in which spores were applied directly to seed. The formulations decreased disease severity by reducing colonization of plants by the pathogen, promoting their growth and increased the dry weight of lentil plants. Of these treatments the glucose and talc-based powder formulations were more effective than the peat formulation and the spore application without a carrier. It was shown that the B. subtilis spores applied with glucose were viable for longer than those applied with other carriers. Seed treatment with these formulated spores is an effective delivery system that can provide a conducive environment for B. subtilis to suppress vascular wilt disease on lentil and has the potential for utilization in commercial field application.
The existence of soils that are naturally suppressive to diseases induced by soilborne plant pathogens provides good opportunities
to study situations where biological control is effectively working. In most cases, suppressiveness is fundamentally based
on microbial interactions between the pathogen and some populations of the saprophytic microflora. However, these biotic interactions
are dependent on the abiotic characteristics of the soil. In the case of soils suppressive to fusarium wilts, it is obvious
that pH and the nature of the clays are important factors interacting with the microbial populations responsible for suppressiveness.
Competition for nutrients, mainly carbon and iron, has been demonstrated to be one of the mechanisms by which suppressive
soils control fusarium wilts. Populations of non-pathogenic Fusarium oxysporum and fluorescent Pseudomonas spp. are, at least partly, responsible for competition for carbon and iron, respectively. Moreover, these antagonistic populations
have other modes of action which can contribute to their biocontrol activity. Strains of both non-pathogenic F. oxysporum and P. fluorescens are being developed as biocontrol agents. Studies of suppressive soils suggest biological control could also be achieved
by enhancing the natural level of suppressiveness that exists in every soil.
A detailed study (involving in vitro bioassays, greenhouse and field trials) was carried out to develop an integrated approach to control fusarium wilt of banana. Eight biocontrol agents were screened against Fusarium oxysporum f. sp. cubense in vitro. Among these, the Pfm strain of Pseudomonas fluorescens showed maximum growth inhibition of the pathogen and a compatible reaction with extracts of neem cake. Similar effects were shown by T. viride and T. harzianum, P.fluorescens; these agents were used further to verify efficacy under greenhouse conditions using various methods of application. Among the methods tested, soil application of biocontrol agents proved to be most effective against the wilt disease and associated vascular discolouration. Soil application of talc formulation of P. fluorescens at 10 g/plant had the least effect when measured by wilt index and vascular discolouration index. Other methods, viz., sucker dipping corm injection and capsule application showed a significant reduction in wilt index and vascular discolouration. In field trials, there were 15 treatments including soil application, sucker dipping in spore suspension, basal application of neem cake, in all possible combinations, together with chemical and uninoculated control. Two field trials in two locations each were conducted during 2000–2001 and 2001–2002 to test its efficacy. The treatment: basal application of neem cake at 0.5 kg/plant+sucker dipping in spore suspension of P. fluorescens for 15 min+soil application of P. fluorescens at 10 g/plant at 3.5 and 7 months after planting showed the greatest suppression of wilt disease and this was on par with basal application of neem cake at 0.5 kg/plant+soil application of P. fluorescens at 10 g/plant at 3.5 and 7 months after planting. Other treatments also showed significant effects in reducing wilt incidence.
Studies of induced systemic resistance using strains of plant growth-promoting rhizobacteria (PGPR) have concentrated on the use of individual PGPR as inducers against multiple diseases of a single crop. To date, few reports have examined the potential of PGPR strain mixtures to induce systemic resistance against diseases of several different plant hosts. The objective of this study was to select mixtures of compatible PGPR strains with the capacity to elicit induced systemic resistance in four hosts. The specific diseases and hosts tested in this study included: bacterial wilt of tomato (Lycopersicon esculentum) caused by Ralstonia solanacearum, anthracnose of long cayenne pepper (Capsicum annuum var. acuminatum) caused by Colletotrichum gloeosporioides, damping off of green kuang futsoi (Brassica chinensis var. parachinensis) caused by Rhizoctonia solani, and cucumber mosaic virus (CMV) on cucumber (Cucumis sativus). To examine compatibility, seven selected PGPR strains were individually tested for in vitro antibiosis against all other PGPR strains and against three of the tested pathogens (R. solanacearum, C. gloeosporioides, and R. solani). No in vitro antibiosis was observed among PGPR strains or against pathogens. Twenty-one combinations of PGPR and seven individual PGPR were tested in the greenhouse for induced resistance activity. Results indicated that four mixtures of PGPR and one individual strain treatment significantly reduced the severity of all four diseases compared to the nonbacterized control: 11 mixtures reduced CMV of cucumber, 16 mixtures reduced bacterial wilt of tomato, 18 mixtures reduced anthracnose of long cayenne pepper, and 7 mixtures reduced damping off of green kuang futsoi. Most mixtures of PGPR provided a greater disease suppression than individual PGPR strains. These results suggest that mixtures of PGPR can elicit induced systemic resistance to fungal, bacterial, and viral diseases in the four hosts tested.
The ability of an organic amendment to suppress soil-borne disease is mediated by the complex interactions between biotic and abiotic soil factors. Various microbiological and physicochemical soil properties were measured in field soils with histories of receiving 4 or 5 years of spring additions of paper mill residuals (PMR), PMR composted alone (PMRC), PMR composted with bark (PMRB), or no amendment under a conventionally managed vegetable crop rotation. The objectives of this study were to (i) determine the residual and re-amendment effects of the organic materials on root rot disease severity; (ii) determine the influence of amendment type on the structure of bacterial communities associated with snap bean roots grown in these soils; and (iii) quantify the relative contributions of microbiological and physicochemical properties to root rot suppression in the field and greenhouse. While all amendment types significantly suppressed root rot disease compared to non-amended soils in both environments, only soils amended with PMR or PMRB sustained suppressive conditions 1 year after the most recent amendment event. Disease severity was inversely related to microbial activity (fluorescein diacetate assay) in recently amended soils only. Terminal restriction fragment length polymorphism (T-RFLP) analysis of the 16s rRNA gene was performed to obtain bacterial profiles. Principal component analysis (PCA) of terminal restriction fragments (TRFs) revealed general differences in bacterial community composition (PC1) among amendment types, and specific TRFs contributed to these differences. Correlation and multiple regression analyses of the measured soil variables revealed that the composition of root-associated bacterial communities and the amount of particulate organic matter—carbon in bulk soils imparted independent and relatively equal contributions to the variation in disease severity documented in the field and greenhouse. Together, our findings provide evidence that disease suppression induced by annual PMR inputs was mediated by their differential effects on bacterial communities and the amount and quality of organic matter in these soils.
Fusarium wilt is considered one of the most important diseases of bananas. The disease can only be managed by using resistant cultivars and by preventing its introduction into new fields. The objectives of this study were to evaluate newly available fungicides, in vitro and in vivo, for their efficacy against the responsible pathogen Fusarium oxysporum f.sp. cubense, and to evaluate surface sterilants that could be used for sterilization purposes. Of the fungicides, prochloraz and propiconazole significantly inhibited mycelial growth at concentrations of 1 and 5 μg ml−1, respectively. Benomyl and the demethylation-inhibiting fungicides significantly reduced the disease severity of Foc when applied as a root dip treatment, showing disease reduction up to 80.6%. The results also demonstrated that certain quaternary ammonium compounds are effective as sterilants against Foc and should replace the ineffective sterilants that are currently being used. Further field evaluations of the fungicides are required.
Members of the genus Bacillus are known to produce a wide arsenal of antimicrobial substances, including peptide and lipopeptide antibiotics, and bacteriocins. Many of the Bacillus bacteriocins belong to the lantibiotics, a category of post-translationally modified peptides widely disseminated among different bacterial clades. Lantibiotics are among the best-characterized antimicrobial peptides at the levels of peptide structure, genetic determinants and biosynthesis mechanisms. Members of the genus Bacillus also produce many other nonmodified bacteriocins, some of which resemble the pediocin-like bacteriocins of the lactic acid bacteria (LAB), while others show completely novel peptide sequences. Bacillus bacteriocins are increasingly becoming more important due to their sometimes broader spectra of inhibition (as compared with most LAB bacteriocins), which may include Gram-negative bacteria, yeasts or fungi, in addition to Gram-positive species, some of which are known to be pathogenic to humans and/or animals. The present review provides a general overview of Bacillus bacteriocins, including primary structure, biochemical and genetic characterization, classification and potential applications in food preservation as natural preservatives and in human and animal health as alternatives to conventional antibiotics. Furthermore, it addresses their environmental applications, such as bioprotection against the pre- and post-harvest decay of vegetables, or as plant growth promoters.
ABSTRACT The world's oldest ecosystems are found in the tropics. They are diverse, highly evolved, but barely understood. This and subsequent papers describe diseases of tropical, perennial plants that are caused by Fusarium spp. Many of these are economically significant, difficult to manage, and of scientific interest. Some represent coevolved patho-systems (e.g., Panama disease, tracheomycosis of coffee, fusariosis of pineapple, and Fusarium wilt of oil palm), whereas others may be new-encounter diseases or are caused by generalist pathogens (cushion gall of cacao). New vector relationships are evident in other pathosystems (e.g., mango malformation), and two or more pathogens have been shown to cause some of the diseases (Panama disease and tracheomycosis of coffee). More work on these pathosystems is warranted as they could reveal much about the evolution of plant pathogens and the important diseases they cause.
Gene expression in fungi by ambient pH is regulated via a conserved signalling cascade whose terminal component is the zinc finger transcription factor PacC/Rim1p. We have identified a pacC orthologue in the vascular wilt pathogen Fusarium oxysporum that binds the consensus 5'-GCCAAG-3' sequence and is proteolytically processed in a similar way to PacC from Aspergillus nidulans. pacC transcript levels were elevated in F. oxysporum grown in alkaline conditions and almost undetectable at extreme acidic growth conditions. PacC+/- loss-of-function mutants displayed an acidity-mimicking phenotype resulting in poor growth at alkaline pH, increased acid protease activity and higher transcript levels of acid-expressed polygalacturonase genes. Reintroduction of a functional pacC copy into a pacC+/- mutant restored the wild-type phenotype. Conversely, F. oxysporum merodiploids carrying a dominant activating pacCc allele had increased pacC transcript and protein levels and displayed an alkalinity-mimicking phenotype with reduced acid phosphatase and increased alkaline protease activities. PacC+/- mutants were more virulent than the wild-type strain in root infection assays with tomato plants, whereas pacCc strains were significantly reduced in virulence. We propose that F. oxysporum PacC acts as a negative regulator of virulence to plants, possibly by preventing transcription of acid-expressed genes important for infection.
Bacillus species as a group offer several advantages over other bacteria for protection against root pathogens because of their ability to form endospores, and because of the broad-spectrum activity of their antibiotics. The objectives of this work were to determine the ability of strains of Bacillus to inhibit Fusarium verticillioides growth and fumonisin B(1) accumulation in vitro, and to evaluate the ability of the best bacterium for preventing rhizosphere and endorhizosphere colonization by F. verticillioides. Bacterial populations from the maize rhizoplane were obtained, and the capacity of ten Bacillus strains to inhibit fungal growth and fumonisin B(1) accumulation in vitro was assayed. According to these results, B. subtilis CE1 was selected as the best antagonist for testing maize root colonization of F. verticillioides. Bacillus subtilis CE1 at 10(8) and 10(7) CFU ml(-1) inocula was able to reduce rhizoplane and endorhizosphere colonization of F. verticillioides in greenhouse trials. The strain B. subtilis CE1 could be a potential biological control agent against F. verticillioides at the root level.
Detection, identification and quantification of plant pathogens are the cornerstones of preventive plant disease management. To detect multiple pathogens in a single assay, DNA array technology currently is the most suitable technique. However, for sensitive detection, polymerase chain reaction (PCR) amplification before array hybridization is required. To evaluate whether DNA array technology can be used to simultaneously detect and quantify multiple pathogens, a DNA macroarray was designed and optimized for accurate quantification over at least three orders of magnitude of the economically important vascular wilt pathogens Verticillium albo-atrum and Verticillium dahliae. A strong correlation was observed between hybridization signals and pathogen concentrations for standard DNA added to DNA from different origins and for infested samples. While accounting for specific criteria like amount of immobilized detector oligonucleotide and controls for PCR kinetics, accurate quantification of pathogens was achieved in concentration ranges typically encountered in horticultural practice. Subsequently, quantitative assessment of other tomato pathogens (Fusarium oxysporum, Fusarium solani, Pythium ultimum and Rhizoctonia solani) in environmental samples was performed using DNA array technology and correlated to measurements obtained using real-time PCR. As both methods of quantification showed a very high degree of correlation, the reliability and robustness of the DNA array technology is shown.
The extent of soil microbial diversity is seen to be critical to the maintenance of soil health and quality. Different agricultural practices are able to affect soil microbial diversity and thus the level of suppressiveness of plant diseases. In a 4-year field experiment, we investigated the microbial diversity of soil under different agricultural regimes. We studied permanent grassland, grassland turned into arable land, long-term arable land and arable land turned into grassland. The diversity of microbial communities was described by using cultivation-based and cultivation-independent methods. Both types of methods revealed differences in the diversities of soil microbial communities between different treatments. The treatments with higher above-ground biodiversity generally maintained higher levels of microbial diversity. Moreover, a positive correlation between suppression of Rhizoctonia solani AG3 and microbial diversity was observed. Permanent (species-rich) grassland and grassland turned into maize stimulated higher microbial diversities and higher levels of suppressiveness of R. solani AG3 compared with the long-term arable land. Effects of agricultural practices on Bacillus and Pseudomonas communities were also observed and clear correlations between the levels of suppressiveness and the diversities of these bacterial groups were found. This study highlighted the importance of agricultural management regime for soil microbial community structure and diversity as well as the level of soil suppressiveness.
Regulation and function of root exudates
- D V Badri
- J M Vivanco
Effectiveness of alkaline fertilizer on the control of banana Fusarium wilt and regulation of soil acidity in banana orchard
- X L Fan
- J Li