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Biological strategies for disease management in strawberry growing (Fragaria spp.)
Abstract
The strawberry is a crop of high economic, nutritional and medicinal value. However, it is highly susceptible to attack by pathogens; thus, one of the principal challenges in the development of crops and post-harvest fruits is the management of diseases, mostly fungi followed by bacterial problems, nematodes, and some viruses. The management of these disorders is based on the use of a broad array of products for crop protection that are commonly called pesticides, which generate high risks to humans and environmental health, affect the safety of the fruits and increase production costs. In this sense, there is a need to find alternatives for integrated disease management. One of the most-studied strategies in recent years has been the use of microbial antagonists with the aim of regulating plant pathogen populations in crops. The broad range of organisms used against various pathological targets, the possibility of including them before and during crop establishment and even during post-harvest, and their multi-functionality as not only biological control agents but also as promoters of plant growth and bio-fertilizers make the inclusion of this biological strategy in integrated disease management attractive to producers who must adapt to the demands of consumers for cleaner and safer products that increase every day.
... There are many post-harvest fungal diseases that cause damage to strawberries and have a negative impact on its yield. Anthracnose is one of the most important diseases and is caused by species of the genus Colletotrichum (Cano, 2013), such as Colletotrichum gloeosporioides (Penz.) Penz. ...
... Hay diversas enfermedades fúngicas postcosecha que afectan a la fresa y ejercen un efecto negativo en su rendimiento. La antracnosis es una de las enfermedades más importantes y es causada por especies del género Colletotrichum (Cano, 2013), como Colletotrichum gloeosporioides (Penz.) Penz. ...
Plant diseases with a negative impact on strawberry yield (Fragaria ananassa), such as anthracnose and fruit rot, are mainly controlled using pesticides, which can cause harmful effects; thus, new control alternatives for fruit decay are needed. Chitosan is a compound already evaluated for fungal disease control at post-harvest. The aim of this study was to evaluate the in vitro and in vivo control activity of chitosan against post-harvest fungal strawberry pathogens, such as Colletotrichum gloeosporioides, Colletotrichum acutatum, Fusarium oxysporum and Phytophthora sp. The experimental design was completely random, with at least three repetitions for each chitosan treatment (5, 7.5, 10 and 15 mg mL 1). The data obtained were transformed with the x 0 5. function. A variance analysis (p0.05), and a Tukey's test (p0.05) were conducted using the SAS software. In vitro bioassays showed the anti-fungal effects of chitosan (5, 7.5, 10 and 15 mg mL 1) against all pathogens tested, which are related to the inhibition of mycelial growth and spore germination. The best results were observed in F. oxysporum and Phytophthora sp. with 100% of mycelial growth and spore germination inhibition. In vivo bioassays showed that strawberry fruit inoculated with mycelium or spores, and then immersed in chitosan (7.5, 10 and 15 mg mL 1), displayed a significant reduction (p0.05) in disease severity index after two treatments: 1) exposure for 7 d at 22.0 °C, and 2) for 3 d at room temperature (252.0 °C). The best results were observed in fruit treated with 15 mg mL 1 chitosan, which showed a disease severity range of 1-1.2 for fruit RESUMEN Las enfermedades con efecto negativo en el rendimiento de la fresa (Fragaria ananassa), como la antracnosis y la pudrición del fruto, se controlan principalmente con el uso de pesticidas que pueden generar efectos nocivos; así, nuevas alternativas se requieren para controlar la descomposición del fruto. El quitosano es un compuesto ya evaluado para el control de enfermedades fúngicas en postcosecha. El objetivo de este estudio fue evaluar la actividad in vitro e in vivo del quitosano frente a los patógenos fúngicos de la fresa en postcosecha, como Colletotrichum gloeosporioides, Colletotrichum acutatum, Fusarium oxysporum y Phytophthora sp. El diseño experimental fue completamente al azar, con al menos tres repeticiones para cada tratamiento con quitosano (5, 7.5, 10 y 15 mg mL 1). Los datos obtenidos se transformaron con la función x 0 5. . Un análisis de varianza (p0.05) y la prueba de Tukey (p0.05) se realizaron con el software SAS. Los bioensayos in vitro demostraron los efectos antifúngicos del quitosano (5, 7.5, 10 y 15 mg mL 1) contra todos los patógenos evaluados, los cuales están relacionados con la inhibición del crecimiento micelial y la germinación de las esporas. Los mejores resultados se observaron en F. oxysporum y Phytophthora sp., con una inhibición del 100% en el crecimiento micelial y la germinación de esporas. En los bioensayos in vivo, la fresa inoculada con micelio o esporas y luego sumergida en quitosano (7.5, 10 y 15 mg mL 1), presentó una disminución significativa (p0.05) en el índice de severidad de la enferme-dad después de dos tratamientos: 1) exposición durante 7 d a 22.0 °C, y 2) exposición durante 3 d a temperatura ambiente (252.0 °C). Los mejores resultados se observaron en los frutos tratados con 15 mg mL 1 de quitosano, con un intervalo de severidad de la enfermedad de 1-1.2 para los frutos inoculados con micelio y de 1-1.6 con esporas. Estos resultados demuestran
Antagonistic microorganisms have been used as biological control agents for several postharvest diseases of fresh fruits. These microorganisms can be isolated from the surface of fruits or leaves. In order to properly use this type of microorganism, it is important to understand the action mechanisms involved in biocontrol activities which would allow a more secure development of the application processess and a base to select new and efficient strains. Basic biochemistry and molecular studies are required in order to elucidate the effect of antibiosis, nutrient competition, and the induction of resistance. In almost all biocontrol systems, a single biocontrol agent is applied. However it has been suggested the need to evaluate the effect of several combination of antagonists to assure an adequate disease control, reducing rates and minimizing the use of synthetic products, considering that the use of additives improve the effect of antagonist microorganisms.
Turechek, W. W., Peres, N. A., and Werner, N. A. 2006. Pre- and post-infection activity of pyra- clostrobin for control of anthracnose fruit rot of strawberry caused by Colletotrichum acutatum. Plant Dis. 90:862-868. The effect of pre- and post-infection-period applications of pyraclostrobin (Cabrio EG) on the development of anthracnose fruit rot was characterized in a controlled-climate study and vali- dated in field studies in New York and Florida. Plants of the day-neutral cv. Tristar were inocu- lated with C. acutatum and placed into mist chambers at 14, 22, or 30ºC. The plants were re- moved from the chambers after 3, 6, 12, or 24 h of misting and placed on greenhouse benches to allow disease development. The fungicide pyraclostrobin was applied to the berries at a concen- tration equivalent to 168 g a.i./ha at 3, 8, 24, and 48 h prior to inoculation and exposure to their wetting period, or 3, 8, 24, and 48 h following inoculation and exposure to their wetting period. All pyraclostrobin treatments suppressed disease compared with the corresponding untreated control treatments. The highest incidence of disease occurred on plants exposed to the longest wetness durations (12 and 24 h) or highest temperature treatments (22 and 30ºC). Post-infection applications of pyraclostrobin provided significant control when applications were made within 3 and often up to 8 h after wetting, but generally were less effective than protective sprays. We further tested the ability of pyraclostrobin to control anthracnose when applied as a protectant or as an after-infection application in inoculated field plots exposed to a short (8 h) or long (24 h) wetting period in Florida and in New York. In three of the four experimental plots, disease con- trol equivalent to or better than the protective spray was achieved when pyraclostrobin was ap- plied up to 24 h after infection for long and short wetting periods. In the remaining plot, condi- tions for disease development were exceptionally favorable. The protective treatment provided approximately 75% control, whereas the best post-infection treatment provided only 50% con- trol. Our study indicates that for short wetting events, such as those associated with seasonal thunderstorms, growers can wait until after such an infection event before applying pyraclos- trobin and achieve control equivalent to a protective application.
In a previous report, it was described that strawberry plants pre-treated with an avirulent isolate of Colletotrichum fragariae (M23) acquired resistance to a virulent isolate of Colletotrichum acutatum (M11) causing anthracnose. In this report we present evidence that the eliciting activity can be found not only in conidial extracts but in culture supernatants of the avirulent pathogen as well. Plants of the cv. Pájaro treated with the culture filtrate (CF) derived from M23, 3days prior to the inoculation with M11 showed significantly reduced disease severity as compared to control plants and the disease was completely suppressed when plants were pre-treated 7days before the challenge inoculation with M11. The same effect was achieved when a single leaf was sprayed with CF, suggesting that the resistance acquired is systemic. Control treatments showed that none of the active extracts inhibited the growth of the virulent pathogen, indicating that the protection effect was due to the induction of a defense response. The latter was confirmed by the accumulation of reactive oxygen species (e.g. hydrogen peroxide, superoxide anion) and the deposition of lignin and callose, usually associated to plant defense, after the CF treatment. Experiments carried out with other strawberry cultivars treated with CF showed that also protected them against different virulent isolates, suggesting that the response observed is cultivar-nonspecific. These outcomes indicate that the protection against anthracnose in strawberry involves a phenomenon of induced resistance (IR) by action of defense-eliciting molecules produced by M23.
Crop phenology and epidemiological information were used to design a reduced use fungicide program for control of Botrytis fruit rot in winter annual strawberry. Fungicide spray programs during early and late periods of the season using high and low rates of captan were evaluated with or without second peak bloom applications of fenhexamid during the 1999-2000 and 2000-2001 seasons. During the early harvest period, low rates of captan were as effective as high rates for controlling Botrytis fruit rot and maintaining yield. Late in the season, treatments with fenhexamid over the peak bloom period significantly improved control of Botrytis fruit rot and increased marketable yield. Application of both captan and fenhexamid during the second peak bloom did not reduce Botrytis fruit rot incidence or improve yield compared with fenhexamid alone during this time period. Late season applications of captan may be reduced or eliminated when bloom applications of fenhexamid are being applied without affecting Botrytis fruit rot control. The study generated new recommendations for use of low-rate applications of captan during the early season and applications of fenhexamid during the second peak bloom period for winter annual strawberry production in Florida.
Soft rotting (Rhyzopus stolonifer) and black rotting (Mucor spp., Aspergillus niger and Pythium spp.) are the most common post harvesting strawberry (Fragaria spp.) diseases, generating great losses. During many years synthetic fungicides have been used to control these pathogens, but their development of resistance to these products has been demonstrated, following to the fact that they represent a potential environmental and human health risk. This has lead to the search of natural alternatives such as the use of vegetal extracts and microbial antagonists, being Trichoderma harzianum the antagonist most widely used as biological control. The purpose of this study was to determine the antagonist effect of T. harzianum over some post strawberry harvesting pathogens and determine their mechanism of action. The strawberry samples were transported to the laboratory in the same packages in which they were sold, and then were placed in germination chambers, controlling humidity to obtain a rapid development of the fungi present in the fruit. We identified the following fungi: Rhyzopus stolonifer, Mucor spp., Penicillium digitatum, Rhizoctonia solani, Aspergillus niger and Phytium spp., which were tested for antagonism, using the T. harzianum. The growth speed of the biocontroller was greater than that of the post harvest fungi (p<0,01) and at 96 hours of incubation the Petri dish was completely covered, and the encounter area between them showed that the action mechanism of the biocontroller was of the mycoparasitic type. T. harzianum turned out to be an excellent in vitro controller of post strawberry harvest fungi.
Strawberry powdery mildew is a serious disease and its control is based on chemical fungicides. The efficacy of alternatives to chemical fungicides was evaluated and their integration into strategies against strawberry powdery mildew to reduce pesticide residues on fruits was also tested. Bicarbonates and mineral oils were poorly effective. Biocontrol agents (BCAs), like Ampelomyces quisqualis, Bacillus subtilis and Trichoderma harzianum T39, controlled the disease, but to a lesser extent than chemical fungicides. When BCAs were alternated with chemicals, a significant reduction of chemical fungicide residues was achieved while maintaining good powdery mildew control. None of the tested strategies increased populations of the pest Tetranychus urticae, nor had side effects on the beneficial predatory mite Amblyseius andersoni populations and, consequently, they can be regarded as safe for the ecological balance of arthropods in strawberry greenhouses.
Azospirillum species are free-living nitrogen-fixing bacteria commonly found in soil and in association with roots of different plant
species. For their capacity to stimulate growth they are known as plant growth-promoting bacteria (PGPB). In this work, we
demonstrate the natural occurrence and colonization of different parts of strawberry plants by Azospirillum brasilense in the cropping area of Tucumán, Argentina. Although bacteria isolations were carried out from two strawberry cultivars,
e.g., Camarosa and Pájaro, attempts were successful only with the cultivar Camarosa. Whereas different strains of Azospirillum were isolated from the root surface and inner tissues of roots and stolons of the cultivar Camarosa, we have not obtained
Azospirillum isolates from the cultivar Pájaro. After microbiological and molecular characterization (ARDRA) we determined that the isolates
belonged to the species A. brasilense. All isolates showed to have the capacity to fix nitrogen, to produce siderophores and indoles. Local isolates exhibited
different yields of indoles production when growing in N-free NFb semisolid media supplemented or not with tryptophan (0.1mgml−1). This is the first report on the natural occurrence of A. brasilense in strawberry plants, especially colonizing inner tissues of stolons, as well as roots. The local isolates showed three important
characteristics within the PGPB group: N2-fixation, siderophores, and indoles production.
Background and aims
Azospirillum brasilense REC3 is a plant growth-promoting and siderophore-producing bacterium isolated from strawberry. Colletotrichum acutatum M11 is the causal agent of anthracnose, an important disease in strawberry crop. The aim of this study was to characterize
at the biochemical and molecular level, the systemic resistance induced by A. brasilense on pathogen-challenged strawberry plants.
MethodsPhytopathological tests were performed; the content of phenolic compounds was determined spectrophotometrically; callose depositions
in leaves by aniline blue staining; salicylic acid (SA) content in leaves by HPLC; and defense-related gene expression [pathogenesis-related
proteins (FaPR1), chitinases (FaChi2-1; FaChi2-2) and glucanase (FaBG2-2)] by RT-PCR.
Results
A. brasilense REC3 reduced anthracnose symptoms on pathogen-challenged plants, and the effect became greater as the elapsed time between
bacterial inoculation and fungal infection increased. Biochemical and transcriptional studies revealed a transient accumulation
of SA and the induction of defense-related genes, suggesting further that this response is related to structural cell wall
modifications as consequence of the observed increase in phenolic compounds and callose deposition.
ConclusionsThe plant growth-promoting bacterium A. brasilense REC3 participates actively in the induction of systemic protection on strawberry plants against anthracnose disease caused
by C. acutatum M11.
KeywordsAnthracnose–
Azospirillum brasilense
–
Colletotrichum acutatum
–Induced protection–Strawberry plant
Azospirillum brasilense (strains REC3, RLC1, PEC5) were root inoculated in strawberry plants of the cultivars ‘Milsei’, ‘Selva’ and ‘Camarosa’ to
assess plant growth-promoting effects. The bacteria were able to promote plant growth (expressed as root length, root area,
and dry weight of root and shoot), depending on the genotypes of plants and bacteria used, whereas the stolon production (3–4)
depended only on the strawberry cultivar. To explain whether root exudates plays any role on the growth-promotion observed
herein, total protein and sugar were determined, and chemotaxis properties were evaluated. The strains showed positive chemotaxis
toward the root exudates, being influenced by the total sugars content, suggesting that the latter plays an important role
in the chemotaxis effect and may contribute to enhance the root capacity to recruit azospirilla from rhizosphere, thus improving
the growth-promoting effect exerted by these bacteria.
Three commercial Trichoderma products (Trichodex, Binab TF WP, and Rootshield) and the laboratory strain T. harzianum P1 were sprayed weekly onto greenhouse-grown strawberry plants during the flowering period in an attempt to reduce fruit disease caused by Botrytis cinerea and Mucor piriformis. None of the treatments affected the marketable yield of strawberries. Laboratory tests showed that at the mean temperature of the greenhouse (12°C), formulated conidia of the various Trichoderma strains required up to 96 h to germinate, and conidia of B. cinerea and M. piriformis isolated from greenhouse strawberries required 11 and 16 h, respectively. Furthermore, the commercially formulated conidia were much more subject to fungistasis under nutrient stress in vitro than were fresh conidia of the same strains. This nutrient sensitivity was not revealed when assaying germination on a standard nutrient-rich laboratory medium. Formulated conidia were also inferior to fresh conidia in capacity to colonize senescent strawberry leaves. We conclude that not only were the Trichoderma strains tested unable to germinate as quickly as B. cinerea and M. piriformis at the ambient temperatures of the greenhouse, but also that the commercially formulated conidia lost the capacity to germinate on and effectively colonize nutrient-poor natural substrates. These findings may be relevant not only to the lack of disease control shown in the present application but also to the inconsistent performance of these products reported in other trials.
Multimicrobial inoculation has been proposed as a way of protecting plants against environmental stress and increasing the sustainability of plant production. To study these possibilities in a micropropagation system, microplants of strawberry, Fragaria × ananssa, were inoculated or left uninoculated with five microorganisms (Glomus mosseae BEG29, Bacillus subtilis M3, Trichoderma harzianum DB11, Pseudomonas fluorescens C7r12 and Gliocladium catenulatum Gliomix®), used either singly or in dual mixtures in the presence or absence of the strawberry diseases crown rot (Phytophthora cactorum) and red stele (P. fragariae). Finnish light Sphagnum peat was used as the growth substrate in the experiments. Seven experiments were performed as two to three months pot experiments in greenhouses of research laboratories in Finland and Belgium and in a nursery in Finland. In most experiments, the inoculated microorganims were detected at sufficient densities four weeks after inoculation. Exceptions were T. harzianum and G. mosseae which were detected at insufficient densities in several experiments. This might have been due to the biological and/or nutritional properties of the peat. None of the microorganisms or their mixtures caused significant growth-promoting effects in more than two experiments. Dual inoculation did not increase growth more than inoculation with single organisms. B. subtilis was the most promising growth promoting microorganism. Most of the microbial treatments decreased crown rot shoot symptoms as well as the numbers of oospores in the roots when the experiment was performed in autumn. In the summer experiment with conditions more favourable for strawberry growth, no disease control was obtained, but some of the microorganisms increased the severity of crown rot. No microbial treatment decreased shoot symptoms of red stele, but the degree of root necrosis was slightly decreased by B. subtilis and G. mosseae + G. catenulatum. The numbers of oospores of P. fragariae in strawberry roots were not decreased by any treatment, but several treatments increased them. Both growth promotion and disease control considered, the single microorganisms T. harzianum, G. catenulatum and B. subtilis as well as the mixture T. harzianum + G. catenulatum were the most promising treatments in this study. However, the great variation between experiments indicates that more studies are needed for optimization of the whole plant–substrate–microorganism system. The importance of microbial inoculation for ensuring subsequent growth in the field also needs to be studied.
Many authors have reported interactions between strawberry cultivars and pathogenic microorganisms, yet little is known about the mechanisms triggered in the plant. In this paper we examine the participation of the salicylic acid (SA) signaling pathway involved in the response of Fragaria x ananassa cv. Pájaro plants to pathogens. Strawberry plants were challenged with the virulent strain M11 of Colletotrichum acutatum, or with the avirulent strain M23 of Colletotrichum fragariae which confers resistance to the former. Our study showed that the isolate M23 induced a temporal SA accumulation that was accompanied with the induction of PR-1 gene expression in strawberry plants. Such events occured after the oxidative burst, evaluated as the accumulation of hydrogen peroxide and superoxide anion, and many hours before the protection could be detected. Similar results were obtained with exogenously applied SA. Results obtained supports the hypothesis that strawberry plants activate a SA mediated defense mechanisms that is effective against a causal agent of anthracnose. In contrast, plants inoculated with M11 did not show oxidative burst, SA accumulation or PR1 gene induction. This is the first report about a defense response signaling pathway studied in strawberry plants.
Anthracnose, caused by the fungus Colletotrichum acutatum is one of the most important diseases in strawberry crop. Due to environmental pollution and resistance produced by chemical fungicides, nowadays biological control is considered a good alternative for crop protection. Among biocontrol agents, there are plant growth-promoting bacteria, such as members of the genus Azospirillum. In this work, we demonstrate that under iron limiting conditions different strains of A. brasilense produce siderophores, exhibiting different yields and rates of production according to their origin. Chemical assays revealed that strains REC2 and REC3 secrete catechol type siderophores, including salicylic acid, detected by thin layer chromatography coupled with fluorescence spectroscopy and gas chromatography-mass spectrometry analysis. Siderophores produced by them showed in vitro antifungal activity against C. acutatum M11. Furthermore, this latter coincided with results obtained from phytopathological tests performed in planta, where a reduction of anthracnose symptoms on strawberry plants previously inoculated with A. brasilense was observed. These outcomes suggest that some strains of A. brasilense could act as biocontrol agent preventing anthracnose disease in strawberry.
Strawberries are produced in much of the world with practices that many consider unsustainable. These include soil fumigation, the use of plastic, a high water requirement, and dependency on pesticides to produce high quality fruit. In addition, strawberry fruit quality is inconsistent in the marketplace, and the product is often unaffordable to poorer segments of the population. Many of the problems inherent in our production systems simply reflect an absence of design around certain guiding principles. No one set out to deliberately design an input-intensive, environmentally expensive production system for strawberries, it just evolved as growers and researchers responded to problems with short-term solutions. Researchers are now challenged to design and build strawberry production systems that follow certain guiding principles that include the use of renewable and recyclable resources, the use of products and practices that do not cause environmental damage, practices that do not harm communities of people, and systems that are economical. Eight critical questions are presented that, when answered, will help provide the building blocks for a more sustainable design. Our legacy as a worldwide community of researchers could be one of entrenchment as we fine-tune current production systems, or it could be one of creative design as we develop and introduce novel production systems that sustain soils, farms, communities, and the environment far into the future.
The effects of mycorrhizal fungi have traditionally been considered within the rather narrow perspective of their effects on the mineral nutrition of individual plants. Most biologists are familiar with the idea that these symbiotic fungi may improve plant uptake of dissolved mineral nutrients. What other effects do these symbionts have? Research during the past 20 years has increasingly viewed symbiotic mycorrhizal associations between plants and fungi within a wider, multifunctional perspective. New molecular methods have been applied to investigate mycorrhizal fungal communities (Bruns & Bidartondo, 2002) and greater attention has been paid to their possible effects at the level of the plant community. As we have acquired greater knowledge about fungal species diversity, so we have become more aware of the potential functional diversity of mycorrhizal fungi. The new multifunctional perspective includes mobilisation of N and P from organic polymers, possible release of nutrients from mineral particles or rock surfaces via weathering, effects on carbon cycling, interactions with myco-heterotrophic plants, mediation of plant responses to stress factors such as drought, soil acidification, toxic metals and plant pathogens, as well as a range of possible interactions with groups of other soil microorganisms.
The control activity of Rhodotorula mucilaginosa, alone or in combination with phytic acid (PA) on gray mold spoilage and natural spoilage of strawberries was investigated. R. mucilaginosa as stand-alone treatment significantly reduced the disease incidence of gray mold spoilage of strawberries at 20 °C, and the combination of R. mucilaginosa and PA at the concentration of 4 mol/ml and 6 mol/ml were more effective than R. mucilaginosa alone treatment. In vitro test showed that PA at the concentration of 4 mol/ml and 6 mol/ml significantly enhanced the inhibition of the growth of Botrytis cinerea on PDA. PA at all the tested concentrations enhanced the growth of R. mucilaginosa in NYDB media. PA at the concentration of 4 mol/ml slightly increased the population growth of R. mucilaginosa in strawberry wounds at the first day at 20 °C, and slightly increased the population growth of R. mucilaginosa in fruit wounds at 4 °C at the whole storage time. The combination of R. mucilaginosa and PA at the concentration of 4 mol/ml was the most effective treatment in controlling the natural spoilage of strawberries following storage at 4 °C for 20 d followed by 20 °C for 5 d.
Tolerance to fusarium wilt, caused by Fusarium oxysporum f, sp. fragariae (Fof), in strawberry (Fragaria×ananassa Duch., cv. Nohime) plants infected with arbuscular mycorrhizal (AM) fungi (Gigaspora margarita, Glomus fasciculatum, Gl. mosseae, Gl. sp. R10, Gl. aggregatum) was estimated under capillary watering conditions. Thirty days after Fof inoculation, the incidence of fusarium wilt ranged from a minimum of 22.2% in Gl. mosseae plot and a maximum of 100% in non-AM one ; the incidence varied, depending on AM fungal species. Incidence and severity of browned vessels and roots became lower in AM plots than in non-AM one. Non-diseased and diseased AM plants had higher dry weight of shoots and roots than did diseased non-AM plants. No significant difference in phosphorus concentration in plants appeared between non-AM and AM plots 11 weeks after AM fungus inoculation (just before Fof inoculation) and 30 days after Fof inoculation. These findings suggest that tolerance to fusarium wilt occurred in AM fungusinfected strawberry plants, and the effect had less association with phosphorus concentration in plants.
This study evaluated Sporidiobolus pararoseus (Sp) strain YCXT3 as biocontrol agent of Botrytis cinerea (Bc), the causal agent of strawberry gray mold disease. Efficacy of live yeast cells and volatile organic compounds (VOCs) of Sp in suppression of Bc on strawberry fruits was determined. Results showed that in dual cultures of Sp and Bc on potato dextrose agar at 20 °C, Sp did not inhibit mycelial growth of Bc. However, inoculation of the yeast cell suspensions of Sp (1 × 105 or 1 × 106 yeast cells ml−1) on strawberry fruits resulted in reducing the disease incidence from 96–100% in the control treatment to 39–50% in the Sp treatment and the disease severity index from 5.1–7.0 in the control treatment to 1.1–1.9 in the Sp treatment. We found that the VOCs from the Sp cultures on yeast extract peptone dextrose agar were highly effective in inhibiting both the conidial germination and the mycelial growth of Bc. A total of 39 VOCs, including 2-ethyl-1-hexanol, were identified in cultures of Sp using GC–MS. Authentic 2-ethyl-1-hexanol was found to have strong anti-fungal activity against Bc with the IC50 values of 1.5 and 5.4 μl l−1 for conidial germination and mycelial growth, respectively. The VOCs from the Sp cultures were effective in suppression of gray mold disease under the air-tight conditions. This study suggests that the strain YCXT3 of Sp is a promising agent for control of Bc and production of VOCs is a valid biocontrol mechanism for this yeast strain.
In this study, chlorine dioxide (ClO2), sodium hypochlorite (NaClO), hydrogen peroxide (H2O2), citric acid (C6H8O7) and ethanol (EtOH) were applied to strawberry fruit using a fogger with an ultrasonic aerosol generator that can produce spheres at 1.2 μm in diameter. Fruit were treated at room temperature for 30 min while with the fogger operating and for an additional 30 min in the fog consisting of disinfectants. Treated fruit were stored at 1 °C for 5 days and an additional 2 days at 20 °C. The percentage of infected fruit and microorganism populations on the surface of the fruit and in the storage air were evaluated to determine the efficacy of treatments. Chlorine dioxide, hydrogen peroxide, sodium hypochlorite, citric acid and ethanol significantly reduced the percentage of infected fruit. The percentage of decay was reduced to 14.5% from 83.2% by the hydrogen peroxide treatment at 2000 μL L−1 and to 32.5% by sodium hypochlorite at 2000 μL L−1 in the first experiment. In addition, all chemicals significantly reduced the total number of microorganisms on the fruit surface and in the storage atmosphere. Hydrogen peroxide at 2000 μL L−1 achieved approximately a 2 log reduction on the surface microorganism population in the first experiment. The study showed that application of disinfectants by fogging was effective in reducing postharvest diseases of strawberry.
The effect of benzo-thiadiazole-7-carbothioic acid S-methyl ester (BTH), at 0.2g/l, on antioxidant enzymes, radical-scavenging activity and decay development in strawberry (Fragaria×ananassa Duch.) fruit, was investigated. The results showed that BTH treatment enhanced the activities of antioxidant enzymes, including superoxide dismutase, ascorbate peroxidase, and glutathione reductase. The treatment increased the contents of phenolic and anthocyanin in strawberry fruit, as well as radical-scavenging capacity, expressed as 1,1-diphenyl-2-picrylhydrazyl and superoxide radical values and reducing power. The treatment also decreased the development of decay compared to control fruit. These results indicated that BTH might increase the disease resistance of strawberry fruits by enhancing their antioxidant systems and their free radical-scavenging capabilities.
Rhodotorula glutinis was evaluated for its activity in reducing postharvest gray mold decay of strawberry caused by Botrytis cinerea in vitro and in vivo. In the test on PDA plates, R. glutinis significantly inhibit the growth of B. cinerea. Spore germination of pathogens in PDB was greatly controlled in the presence of living cell suspensions. Rapid colonization of the yeast in wounds was observed during the first 3 days at 20°C, and then the populations stabilized for the remaining storage period. On strawberry wounds kept at 4°C, the increase in population density of R. glutinis was lower than those kept at 20°C, but continued over 8 days after application of the antagonist until it reached a high level. Number of inoculated strawberry fruit treated with 1×108CFU/ml washed cell suspension of R. glutinis was 10% after 2 days at 20°C, compared to 100%, respectively, in the control. Washed cell suspensions of yeast controlled gray mold better than yeast in culture broth. Treatment of wounds with autoclaved cell cultures or cell-free culture filtrate did not prevent decay. The concentrations of antagonist had significant effects on biocontrol effectiveness: the higher the concentrations of the antagonist, the lower the disease incidence regardless of whether the fruit was stored at 20°C for 2 days or 4°C for 7 days. At concentrations of R. glutinis 1×109CFU/ml, the incidence of gray mold was reduced by 94.7 or 95%, respectively, compared with control, after storage at 20°C for 2 days or 4°C for 7 days, respectively. R. glutinis significantly reduced the natural development of decay of fruit following storage at 20°C for 3 days or 4°C for 5 days followed by 20°C for 3 days.
Biological control of powdery mildew on strawberry leaves by Penicillium oxalicum applications was achieved on different cultivars and lines in growth chambers and in open-field nurseries. Growth chamber conditions were more conducive to the development of natural infection of powdery mildew on the various cultivars and lines than plants cultivated in open-field nurseries. Penicillium oxalicum-treated strawberry cultivars and lines showed a significant reduction in the amount of powdery mildew in growth chamber (except for Ventana) and open-field nursery experiments. These results indicate that P. oxalicum may be an effective treatment for biological control of strawberry powdery mildew in open-field nurseries of strawberries.
Clonostachys spp. were isolated from soil samples, and living and dead leaves of different plant species. Twelve isolates which sporulated well when cultured on agar media were compared regarding the capacity of establishing and suppressing Botrytis cinerea in leaves of Rosa hybrida ‘Sandra,’ Fragaria×ananassa ‘Dover,’ Lycopersicon esculentum ‘Kada,’ and Eucalyptus globulus. The isolates established in leaves of each plant species, but leaf area with conidiophores (SFCA) varied with the stage of leaf development. In rose, SFCA varied from 3.0 to 13.9% on senescing leaves and 3.4 to 10.0% on green leaves. SFCA was higher in young leaves of E. globulus and tomato (1.4–15.6% and 1.4–8.0%, respectively) than on senescing leaves (0.8–3.5% and 1.0–5.2%, respectively). In strawberry, SFCA varied from 0.7 to 6.2% on completely expanded leaves. Clonostachys rosea isolates reduced B. cinerea sporulation on leaves of rose (81.0–97.4% reduction), strawberry (87.6–96.8%), E. globulus (63.7–89.7%), and tomato (100% reduction). Four isolates of C. rosea were selected based on high levels of SFCA and suppression of B. cinerea. When leaf discs of the four hosts inoculated with these C. rosea isolates were challenged with isolates of B. cinerea of variable levels of aggressiveness, SFCA and pathogen suppression varied with the combination. Efficiency of C. rosea isolates in suppressing sporulation of B. cinerea varied among hosts but was always above 80%. The four selected Brazilian isolates of C. rosea are potential biocontrol agents for Botrytis blight management in Brazilian agricultural systems.
Wild strawberry (Fragaria vesca) microplants were inoculated at establishment in the glasshouse with the commercial inoculants Endorize IV, Vaminoc and Glomus mosseae. After 2 weeks, plants were transferred to control peat-based growth substrate and Suppressor®, a commercial peat substrate amended with chitin-containing shellfish waste. Percentage root length colonisation (%RLC) by Vaminoc and G. mosseae, but not Endorize IV, was stimulated significantly after 4 weeks growth in the amended substrate but there were no significant differences for any of the inoculants at 8 weeks. Runner production in Vaminoc-inoculated plants was unaffected by either growth substrate. Runner production was significantly reduced in Endorize IV and G. mosseae treatments in the control growth substrate, other growth parameters were not significantly affected.Disease resistance to red core was increased by growth of the Vaminoc-inoculated plants for 4 weeks in Suppressor® before challenge in control compost. Neither Vaminoc inoculation nor growth in Suppressor® resulted in increased disease resistance.
In order to identify fungi pathogenic to strawberry fruit and the relationship with cultivars and crop management, five postharvest samples were taken; three from the region of Zamora, Michoacan, Mexico, in december, 2001, as well as in february and may of 2002, on cultivars Camarosa and
More than 80 disease biocontrol products are on the market worldwide, but none of these contain mycor rhizal fungi. This is despite ample evidence that both arbuscular mycorrhizal fungi and ectomycorrhizal fungi can control a number of plant diseases. A procedure for successful development of disease biocontrol agents in general is used as a background to examine the potential for achieving commercial mycorrhizal biocontrol agents. This includes (i) selection and screening; (ii) characterization involving identification, studies of modes of action and ecophysiology, as well as inoculum production, formulation, application and shelf life; (iii) registration. The last stage is problematic for mycorrhizal fungi, as currently they can be sold as plant growth promoters without any form of costly registration, even though in some instances they may actually function to some extent through biocontrol activity. The significance of this approach is discussed, and some possible ways of enhancing biocontrol by mycorrhizas are considered.Key words: arbuscular mycorrhizas, ectomycorrhizas, biological disease control, soilborne pathogens, modes of action, ecology.
Clonostachys rosea is effective to control of Botrytis cinerea on strawberry, although is highly susceptible to ultraviolet radiation and has reduced ability to antagonize a pathogen in solar radiation conditions. The objective of this work was to evaluate the ability of an isolate of C. rosea, previously selected for its tolerant to UV-B radiation, to control B. cinerea on strawberry leaves in controlled experiments. Leaf discs of 1 cm diameter were placed on Petri dishes and each received 20 μL of a C. rosea LQC 62 concentrations (104, 105, and 106 conidia mL−1). They were then exposed to UV-B irradiance 600 mW m−2 (0, 2.1, 4.2, and 6.3 kJ m−2), and after radiation, half of the discs were inoculated with an aliquot of 10 μL B. cinerea (105 conidia mL−1). The colonization of fungi on the leaf disc was measured with diagrammatic scale formation of conidiophores. The presence and sporulation of C. rosea on leaf disc was influenced by the dose of UV-B radiation and the conidial concentration of antagonist. The incidence and severity of B. cinerea on leaf discs were inversely correlated to presence and sporulation of C. rosea. The growth of the pathogen was higher in the lower C. rosea concentration. The highest concentration of C. rosea (106 conidia mL−1) reduced the incidence and severity by 91% and 98% of B. cinerea on strawberry leaf discs. The UV-B radiation reduced the ability of C. rosea to control B. cinerea. The higher dose of UV-B reduced the presence and sporulation of C. rosea by 20% and 42%, respectively. Consequently, the incidence of B. cinerea increased twice and the severity was three-folder higher. Taken together this data means that, for the development of biological control agents based products, the effect of UV-B should be considered on the efficacy studies.
The influence of arbuscular mycorrhizal fungi (AMF) colonization on free amino acid concentrations in strawberry (Fragaria × ananassa Duch., cv.Nohime) plants was investigated using two AMF species [Glomus mosseae (Gm), Gl. aggregatum (Ga)] under phosphorus-supplemented (+P) or non-supplemented (−P) conditions. Ten weeks after AMF inoculation, mycorrhizal plants showed higher values in dry weight of both shoots and roots than did non-mycorrhizal ones among most of the treatments. Shoots and roots of mycorrhizal plants had greater phosphorus concentrations in −P plots, while in +P plots, P concentrations differed little among the inoculation treatments. AMF colonization was greater in plants inoculated with Gm than in plants inoculated with Ga. Total amino acid concentration was higher in most of the plants inoculated with Gm than in non-mycorrhizal ones regardless of P treatment. Serine, glutamic acid, glycine, alanine, leucine and GABA were higher in both mycorrhizal plants in −P plots than in non-inoculated plants. In +P plots, threonine and isoleucine concentrations were greater in both mycorrhizal plants than in non-inoculated ones. Asparagine, glutamic acid, glycine, citrulline, GABA and arginine were greater in plants inoculated with Gm than in non-mycorrhizal ones. These findings verified that inoculation with AMF increases total amino acid concentrations and concentrations of specific amino acids in strawberry plants with or without phosphorus supplementation, though the effects varied with species of mycorrhizal fungus.
The influence of chitin on the efficacy of Rhodotorula glutinis in controlling postharvest grey mould of strawberries and the possible mechanisms involved were investigated. The results showed that the antagonistic activity of R. glutinis harvested either from the culture media of NYDB amended with chitin at 0.5% or from the culture media in which chitin was the sole carbon source (NYCB) was improved greatly compared with that without chitin. The application of R. glutinis cultivated in the culture media of the chitin-supplement (0.5%) induced higher β-1,3-glucanase activity and reduced more MDA content of strawberries compared with that R. glutinis cultivated in the NYDB. Moreover, the control efficacy of the cell-free filtrate of the chitin-supplement culture media (0.5%) and NYCB were higher than that of cell-free culture filtrates of NYDB in 2 days incubation, with the associated high level of chitinase activity.
For increasing the shelf life of strawberries during storage, bioactive coatings were applied using modified polysaccharides of chitosan. First, antimicrobial tests were performed with selected essential oils to evaluate their antimicrobial capacities against moulds and total flora isolated from strawberries. Red thyme (RT) and oregano extract (OR) were found as strong bioactive agents against moulds and total flora isolated from strawberries, whereas limonene (LIM) and peppermint (PM) had lower antimicrobial properties. These essential oils were also used as bioactive compounds which were sprayed onto strawberries and evaluated for their potential to increase shelf life during storage at 4 °C. RT, PM and LIM were found to be more efficient preservative agents for strawberries during 14 days of storage. Finally, chitosan was functionalized by acylation with palmitoyl chloride to increase its hydrophobicity, to ensure a controlled release and improve its stability and adhesion to the fruit product. LIM and PM were incorporated into the modified chitosan to create bioactive edible coatings and these were tested for their ability to extend the shelf life of fresh strawberries during storage. Formulations based on modified chitosan containing LIM and Tween®80 were shown to perform better than other formulations.
Se efectuó un ensayo en condiciones controladas utilizando hongos formadores de micorrizas arbusculares (HFMA) nativos, provenientes de un suelo rizosférico de Pennisetum clandestinum de la Universidad Nacional de Colombia (Bogotá), mante- niéndolos en plantas de Brachiaria decumbens creciendo sobre sustrato arenoso suple- mentado con solución nutritiva. Se evaluaron diferentes tratamientos: plantas con inóculo de HFMA, plantas con Trichoderma harzianum, plantas con HFMA+T. harzianum y plantas control no inoculadas, con el fin de determinar las posibles interacciones entre dichos microorganismos, así como su efecto sobre el crecimiento de B. decumbens. La presencia de T. harzianum disminuyó la colonización radicular por HFMA, aunque no afectó la cantidad de esporas de HFMA/g suelo seco, en tanto que la población de T. harzianum (UFC/g suelo seco) disminuyó significativamente en presencia de HFMA. Estos resultados mostraron que existen interacciones entre HFMA y T. harzianum que afectan tanto el desarrollo de HFMA como la densidad poblacional de T. harzianum. Los valores obtenidos para los parámetros del crecimiento de la planta evaluados sugie- ren que el efecto de la interacción entre los microorganismos sobre la planta hospe- dera es de tipo neutral.
Individually, arbuscular mycorrhizal fungi (AMF), drought stress, and root damage can alter terrestrial plant performance but the joint effects of these three factors have not been explored. Because AMF can improve water relations, colonization by these root symbionts may increase the host’s tolerance of drought especially when roots have been compromised by herbivory. This full factorial study examined effects of AMF, water deficit, and artificial root herbivory in three genotypes of wild strawberry, Fragaria virginiana Duchesne that originated from the same restored tallgrass prairie as the AMF inoculum. Drought stress and root damage altered allocation to roots vs. shoots but the effects were not additive and the interaction did not depend on AMF treatment. Effects of AMF were absent with one exception: root damage significantly reduced belowground mass only in plants inoculated with AMF. Although drought stress did not interact with the AMF treatment, both drought stress and root damage reduced the abundance of arbuscules, and especially vesicles, and colonization varied among genotypes. Failure to detect strong effects of AMF on host growth could be due to variable responses of individual AMF species summing to no net effects. Functionally, AMF were primarily commensals of strawberry in this study.
Biological control agents for plant diseases are currently being examined as alternatives to synthetic pesticides due to their perceived increased level of safety and minimal environmental impacts. Fungal biological control agents have several mechanisms of action that allow them to control pathogens, including mycoparasitism, production of antibiotics or enzymes, competition for nutrients and the induction of plant host defences. While effective in the control of plant diseases, these mechanisms may pose risks to non-target species including mycorrhizal and saprophytic fungi, soil bacteria, plants, insects, aquatic and terrestrial animals, and humans. Non-target effects including mycoparasitism of mycorrhizae, reduction in plant root colonisation by mycorrhizal fungi, disorders in commercial mushrooms and nodulation by Rhizobium spp., and changes in plant growth have been associated with fungal biological control agents, such as Trichoderma spp. Also, the genera Trichoderma and Gliocladium have been linked to respiratory disorders and shellfish toxicity in humans, respectively. Biological control agents, such as Pythium oligandrum, Talaromyces flavus, Coniothyrium minitans and Ampelomyces quisqualis have modes of action which may pose risks to non-target fungi, bacteria, plants and animals. There is need for future research into ecological impacts associated with the release of any biological agent and methods of determining possible non-target effects. Adequate monitoring and the use of molecular techniques to identify and follow the movement of biological control agents are needed to examine and mitigate negative biological impacts.
Closed (recirculating) growing systems provide a greater potential for the dispersal of water-borne plant pathogens and disease expression compared to open (run-to-waste) systems. Here we studied the effects of three soilless growing systems (open, closed, and closed with slow sand filtration) on the dispersion of Phytophthora cactorum propagules and the severity of the crown rot disease in strawberry (Fragaria × ananassa Duch.). The plant-growth medium used was coir fiber. The three growing systems showed the same density of P. cactorum propagules in the water drained from the growing media. However, propagules of this pathogen were not detected by the baits in the filtered solution recovered from slow sand filtration. In all systems Phytophthora propagules dispersed from the inoculated plant to adjacent uninoculated plants. At the end of the first crop no differences in the severity of crown rot were found between the different systems of crop culture. However, at the end of the second crop cycle, crown rot in the closed soilless system without slow sand filtration was more severe than in the other two systems. These results demonstrated that the commercial potential of slow sand filtration to prevent propagule dispersal and hence suppress crown rot in strawberry crops grown in a closed culture system.
Growth, development and nutrient status of micropropagated. Fragaria×ananassa cv. Elvira (strawberry) in response to inoculation with nine species of arbuscular mycorrhizal (AM) fungi from three different genera was investigated. The nine species of AM fungi were Glomus clarum, G. etunicatum, G. intraradices, Gigaspora rosea, G. gigantea, G. margarita, Scutellospora calospora, S. heterogama and S. persica. No positive shoot growth responses to AM fungal inoculation were observed. Root growth enhancements were observed for plants colonised by G. intraradices and G. margarita. Shoot and root growth depressions were observed for G. rosea and all species of Scutellospora. Furthermore, individual isolates of AM fungi had unique effects on the mineral status of the strawberry plants. In general Mn and Mg concentrations were significantly increased within the shoot tissue of plants colonised by all isolates of AM fungi. Moreover, plants colonised by G. clarum and G. rosea, had significantly increased concentrations of 7 and 9 out of the 12 mineral nutrients within the shoot tissue, respectively.
Gray mold, caused by Botrytis cinerea, is an important strawberry disease. As gray mold control is difficult, there is a need to evaluate integrated methods to successfully manage the disease. The efficiency of integrating Clonostachys rosea sprays, fungicide sprays, and crop debris removal to manage gray mold was evaluated in field experiments conducted in 2006 and 2007. Leaf colonization by C. rosea (LAC), average number of B. cinerea conidiophores (ANC), gray mold incidence in both flowers (Iflower) and fruits (Ifruit), and yield were evaluated weekly. In both years, LAC was higher in the treatments with no fungicide. When compared to the check, ANC, Iflower and Ifruit were most reduced in treatments that included C. rosea sprays. Maximal reductions were achieved with the combination of C. rosea sprays, fungicide sprays and debris removal (96.62%, 86.54% and 65.33% reductions of ANC, Iflower and Ifruit, respectively). Otherwise, maximal yield (103.14% increase as compared to the check) was achieved with the combination of the three treatments. With just C. rosea sprays, ANC, Iflower and Ifruit were reduced by 92.01%, 68.48% and 65.33%, respectively, whereas yield was increased by 75.15%. Considering the individual effects, application of C. rosea was the most efficient treatment. Chemical control was effective only in plots without debris removal. Elimination of crop debris was the least effective method in reducing gray mold incidence in both flowers and fruits. The integrated control approach enhanced the efficacy of the individual methods of gray mold control and provided high strawberry yield. An important component of this integrated approach it the biological control with C. rosea.
Increasing loss of conventional fungicides due to pathogen resistance and general unacceptability in terms of public and environmental risk have favoured the introduction of integrated pest management (IPM) programmes. Induction of natural disease resistance (NDR) in harvested horticultural crops using physical, biological and/or chemical elicitors has received increasing attention over recent years, it being considered a preferred strategy for disease management. This article reviews the enhancement of constitutive and inducible antifungal compounds and suppression of postharvest diseases through using elicitors. The effect of timing of pre- and/or postharvest elicitor treatment and environment on the degree of elicitation and the potential for inducing local acquired resistance, systemic acquired resistance and/or induced systemic resistance to reduce postharvest disease is discussed. The review highlights that more applied and basic research is required to understand the role that induced NDR can play in achieving practical suppression of postharvest diseases as part of an IPM approach.
Leaf surfaces of plants are colonized by microbes, although the ecological roles of most of these epiphytes are unknown. Eleven non-pathogenic bacteria were isolated from strawberry (Fragaria x ananassa) plants and tested for their ability to interact with plant volatiles and the phytopathogenic fungus Botrytis cinerea. None of the bacterial epiphytes produced antimicrobial compounds. Light microscopic and SEM analysis of F. x ananassa leaf surfaces showed that capitate glands are densely colonized by microorganisms. Benzyl alcohol, 2-phenylethanol, R,S-linalool and nonanal were identified as major volatiles emitted by intact strawberry leaves, while R,S-linalool and nonanal were released by the capitate glands. The isolated epiphytes cannot utilize these leaf volatiles as sole carbon source, but some of the bacteria metabolize them, e.g. to the corresponding acids. However, the leaf volatiles have a stronger inhibitory effect on different strains of the plant pathogenic fungus B. cinerea than on the isolated epiphytic bacteria. In co-culture experiments, B. cinerea strains suppress the proliferation of epiphytes but low concentrations of 1–5 ppm of R,S-linalool, 2-phenylethanol and in particular nonanal significantly enhance the progeny of a number of epiphytic bacteria, while the growth of B. cinerea strains is retarded. Thus, native volatile compounds can affect population dynamics of epiphytes and the phytopathogenic fungus. Our findings have significant implications for pest management notably on the use of antagonistic bacteria as biocontrol agents.
Arbuscular mycorrhizal fungi (AMF) show significant potential for biocontrol of Phytophthora spp., but there is little evidence for the mechanisms involved in the process. This study establishes that microorganism free exudates from roots colonised by AMF result in significantly less sporulation of P. fragariae than those from uncolonised plants. Experiments in vitro showed that after 48 h in the presence of exudates from strawberry roots colonised by Glomus etunicatum and G. monosporum, sporulation of P. fragariae was reduced by ca 67% and 64% relative to sporulation in the presence of uncolonised roots. After 72 h sporulation was reduced by 83% and 89% respectively. These data were then confirmed in an in vivo system in which Phytophthora fragariae was inoculated into the mycorrhizosphere of either uncolonised strawberry plants or those colonised by G. etunicatum. A similar trend was observed, with a 69% reduction in sporulation of P. fragariae after 72 h in the mycorrhizosphere of colonised plants relative to sporulation in the mycorrhizosphere of uncolonised plants.
Headspace volatile substances (VS) produced by Streptomyces platensis F-1 were preliminarily identified using GC–MS. The effects of VS released by S. platensis F-1 on the control of leaf blight/seedling blight of rice caused by Rhizoctonia solani, leaf blight of oilseed rape caused by Sclerotinia sclerotiorum and fruit rot of strawberry caused by Botrytis cinerea, as well as on the growth of these three pathogenic fungi, were investigated. Results showed that sixteen volatile compounds were tentatively identified in 1-week-old cultures of S. platensis F-1 grown on autoclaved wheat seeds. They could be chemically grouped into alcohols, esters, acids, alkanes, ketones and alkenes. The most abundant composition in volatiles of S. platensis F-1 is geosmin, an earthy-muddy–smelling compound. Two antifungal compounds, phenylethyl alcohol and (+)-epi-bicyclesesquiphellandrene, were detected in the volatile profile of S. platensis F-1. Consistent fumigation of healthy tissues of rice, oilseed rape and strawberry to VS of S. platensis effectively reduced the incidence and/or the severity of leaf blight/seedling blight of rice (R. solani), leaf blight of oilseed rape (S. sclerotiorum) and fruit rot of strawberry (B. cinerea). A significant (P < 0.05) suppression of the mycelial growth of R. solani, S. sclerotiorum and B. cinerea by the VS of S. platensis was observed. The potential of using VS of S. platensis F-1 as a biofumigant to control plant fungal diseases is discussed.
An in vitro tripartite culture system was used to monitor the effect of arbuscular mycorrhizal (AM) symbiosis on host plant water relations. We hypothesized that the root colonization by Glomus intraradices Schenck and Smith modifies the water’s status, the control of water losses and the osmotic relations of leaves and roots of micropropagated strawberry (Fragaria ananassa Duch. cv. Kent) plantlets, under in vitro conditions of high humidity. Strawberry plantlets, AM or non-AM, disposed in a randomized complete block design, were assessed in order to measure relative water content (RWC) of leaf discs, roots and complete plants, leaf stomatal conductance (Gs), leaf and root osmotic potentials (ΨπL, ΨπR), chlorophyll fluorescence parameters Fv/Fm, fresh, dry and turgid weights and mineral content. Although ΨπL, ΨπR, Gs and RWC of foliar discs were not affected by the fungal inoculation, the RWC of the complete plants was 11% higher in AM colonized plantlets compared to non-AM ones. This significant increase of RWC of whole plants was not related to an improved mineral nutrition nor growth stimulation of mycorrhizal plantlets. This is the first report that AM colonization enhances the RWC of entire strawberry microplants under axenic well-watered conditions. We have concluded that this effect is related to a higher water content in AM root systems not paralleled to a dilution in the root osmotic potential, ΨπR, suggesting that mycorrhizal roots must have a higher concentration of water soluble compounds or a different distribution in the cell compartments than non-AM roots.
Gray mold, caused by Botrytis cinerea, is an important strawberry disease in Brazil. As a component of a disease management program, we have been evaluating pathogen biological control with Clonostachys rosea, and selected four isolates as potential antagonists to B. cinerea. In 2006 and 2007, under field conditions, we compared the efficiency of the four C. rosea isolates (applied once or twice a week) with a weekly spray of procymidone alternated with captan in controlling gray mold. Following the applications and up to harvest, we evaluated weekly: leaf area colonization by C. rosea (LAC), average number of B. cinerea conidiophores on leaves (ANC), incidence of gray mold on both flowers (Iflower) and fruits (Ifruit), incidence of latent infections on fruits (Ilat), and yield. The applications of C. rosea twice a week provided higher LAC (16.97%), smaller ANC (10.28; 78.22 in the check treatment, sprayed with water), smaller IFlower (10.02%; 50.55% in the check treatment), and smaller IFruit (5.95%; 25.10% in the check treatment). Yield ranged between 3490 and 3750 g plot−1 with applications of C. rosea twice a week and between 1740 and 1910 g plot−1 in the check treatment. Ilat was 20% in the check treatment and less than 10% in the other treatments. Based on this 2-year study, at least two weekly applications of C. rosea are required for a successful gray mold management program.
Plants can be induced to develop enhanced resistance to pathogens by treatment with a variety of biotic and abiotic inducers. The resistance induced is broad spectrum and can be long-lasting, but rarely provides complete disease control, with most inducing agents reducing infection between 20 and 85%. One possible reason for this is that plants in the field are already induced through their continual interactions with the biotic and abiotic environment. This article looks briefly at the evidence for biotic and abiotic induction of resistance and then considers whether plants that are already induced are in any way compromised in their ability to respond to agents that induce resistance. Knowledge of the extent to which plants are already induced in the field and the extent to which resistance can be further induced by application of resistance-inducing agents is likely to be important for effective use of induced resistance in practical crop protection.
The plant kingdom is colonized by a diverse array of endophytic bacteria which form non-pathogenic relationships with their hosts. When beneficial, such associations can stimulate plant growth, increase disease resistance, improve the plant’s ability to withstand environmental stresses (e.g. drought), or enhance N2 fixation. Crop sequences can favour the build-up of advantageous associations of bacterial endophyte populations leading to the development and maintenance of beneficial host-endophyte allelopathies. Utilization of rhizobacteria in sustainable crop production systems will require strategies to create and maintain beneficial bacterial populations within crops (endophytes) and as well in the soils surrounding those crops.
Postharvest diseases cause considerable losses to harvested fruits and vegetables during transportation and storage. Synthetic fungicides are primarily used to control postharvest decay loss. However, the recent trend is shifting toward safer and more eco-friendly alternatives for the control of postharvest decays. Of various biological approaches, the use of antagonistic microorganisms is becoming popular throughout the world. Several postharvest diseases can now be controlled by microbial antagonists. Although the mechanism(s) by which microbial antagonists suppress the postharvest diseases is still unknown, competition for nutrients and space is most widely accepted mechanism of their action. In addition, production of antibiotics, direct parasitism, and possibly induced resistance in the harvested commodity are other modes of their actions by which they suppress the activity of postharvest pathogens in fruits and vegetables. Microbial antagonists are applied either before or after harvest, but postharvest applications are more effective than preharvest applications. Mixed cultures of the microbial antagonists appear to provide better control of postharvest diseases over individual cultures or strains. Similarly, the efficacy of the microbial antagonist(s) can be enhanced if they are used with low doses of fungicides, salt additives, and physical treatments like hot water dips, irradiation with ultraviolet light etc. At the international level, different microbial antagonists like Debaryomyces hansenii Lodder & Krejer-van Rij, Cryptococcus laurentii Kufferath & Skinner, Bacillus subtilis (Ehrenberg) Cohn, and Trichoderma harzianum Rifai, are being used. Biocontrol products like Aspire, BioSave, and Shemer etc., have also been developed and registered. Although the results of this technology are encouraging, we need to continue to explore potential uses on the commercial scale in different corners of the world.
By virtue of their physiological adaptability and metabolic versatility, bacteria in plant root zones are a key agent of change in soil agroecosystems. Interactions between plant root systems and rhizobacteria have a profound effect on crop health, yield, and soil quality. Through the selective release of exudates and leachates plants activate and sustain specific rhizobacterial communities in the root zone. In turn, root zone bacteria are able to generate a wide array of secondary metabolites which can have a positive influence on plant growth; enhancing the availability of minerals and nutrients, improving nitrogen fixation ability, decreasing susceptibility to frost damage, improving plant health through the biocontrol of phytopathogens, inducing systemic plant disease resistance, and facilitating plant establishment, growth and development. The benefits from root zone bacterial biodiversity are moot in managed agroecosystems, where community complexity is minimized, and ecosystem stability is often disrupted for the purpose of disease control and yield maximization. The complexity of plant–soil–microbial interactions are so varied, that a complete understanding of all the relationships involved is unlikely to be achieved, even in a production monoculture. Nevertheless, the consequences of beneficial biological interactions that stimulate crop yields and improve plant health can be evaluated relatively simply and a number of general management strategies can be devised accordingly.
The potential of using Rhodotorula glutinis alone or in combination with salicylic acid (SA) for the control of postharvest Rhizopus rot of strawberries, and their effects on enzyme activities of fruits were investigated. The combination of R. glutinis (1 × 108 CFU ml−1) with SA (100 μg ml−1) resulted in a significant reduction in the disease incidence and lesion diameter of Rhizopus rot on the strawberry fruits at 20 °C and 4 °C, and more so than with SA or yeast alone. SA at the concentration of 100–1000 μg ml−1 significantly inhibited spore germination of Rhizopus stolonifer. About 100 μg ml−1 of SA did not inhibit the growth of the antagonistic yeast, and could significantly increase the population growth of R. glutinis in strawberry wounds at 20 °C. SA, combined with R. glutinis, increased the activity of strawberry host defence enzymes (POD) and cell wall lytic enzymes (β-1,3-glucanase).