Article

Bacillus subtilis and Vermicompost Suppress Damping-off Disease in Psyllium through Nitric Oxide-Dependent Signaling System

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Abstract

Fusarium oxysporum is one of pathogens causing the damping-off disease of Plantago psyllium in Iran. A greenhouse experiment was conducted to assess the effect of Bacillus subtilis and vermicompost singly and in combination on control of Fusarium–induced damping-off in psyllium. The results showed that vermicompost or B. subtilis, significantly increased the growth of psyllium seedlings and both were effective biocontrol agents against F. oxysporum. Among treatments at least damping-off incidence was recorded in combination of 50% vermicompost and B. subtilis. Results for the first time exhibited that vermicompost as well as B. subtilis induced systemic resistance through nitric oxide (NO) signaling and their combined application further than their individual treatments induced development of plant defense related enzymes including β-1,3-glucanase (GLU), phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO) and the activities of antioxidant enzymes (ascorbate peroxidase, catalase, superoxide dismutase and peroxidase) and also more effectively reduced lipid peroxidation in psyllium leaves. These findings suggested potential of B. subtilis in promoting plant growth as well as inducing systemic resistance in the host plants, was enhanced by vermicompost application.

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Agrochemicals which ushered in the ‘green revolution’ in the 1950-60’s, boosted food productivity, but at the cost of environment and society. It increased food production but also destroyed the ‘physical, chemical and the biological properties’ of soil over the years of use. It killed the beneficial soil organisms and also impaired the power of ‘biological resistance’ in crops making them more susceptible to pests and diseases. No farmland of world is free of toxic pesticides today. Over the years it has worked like a ‘slow poison’ for the soil and society. According to UNEP and WHO nearly 3 million people suffer from ‘acute pesticide poisoning’ and some 10 to 20 thousand people die every year from it in both the developed and the developing countries. Organic farming by earthworms (Sir Charles Darwin’s ‘friends of farmers’) can provide a sustainable and also highly economical solution to the various problems created by the destructive agrochemicals in farm production. Earthworms vermicompost are scientifically proving to be an ‘extraordinary powerful growth promoters and protectors’ for crops (5-7 times over other bulky organic fertilizers and 20-40 % higher over chemical fertilizers). They are rich in NKP, micronutrients, beneficial soil microbes like ‘nitrogen-fixing’ and ‘phosphate solubilizing’ bacteria, ‘mycorrhizal fungi’, humus and growth hormones – auxins, gibberlins and cytokinins. It has very high ‘porosity’, ‘aeration’, ‘drainage’ and ‘water
Article
Rhizoctonia solani damping-off and root rot diseases are frequent in impatiens crops in Buenos Aires. Their control is based in fungicide use. In a sustainable nursery production, beneficial microorganisms that develop in organic amendments may suppress diseases and promote plant growth. The aim of this work was to evaluate the effect of different proportions of vermicompost on the growth and health of patience-plant (Impatiens wallerana). The experiment was carried out in a polyethylene greenhouse. Treatments were defined as follows: infested substrate, substrate, sterilized substrate, vermicompost, and vermicompost mixed with infested substrate at 75, 50 and 25% by volume. Seeds of I. wallerana were sown in plugs containing the different substrates. Percentage of healthy seedlings was evaluated since emergence, and growth parameters were recorded at day 51. The concentration of pathogen in the different treatments was estimated at the beginning and end of the experiment. Treatments with 100-75% of vermicompost showed important increases of leaf area, plant height and fresh and dry weight of aerial and subterranean organs. Root length was not modified by compost addition. Vermicompost at 75% provided slight control of damping-off caused by R. solani.
Article
Vermicomposting is a process in which earthworms are used to convert organic materials into humus-like material known as vermicompost. A number of researchers throughout the world found that the nutrient profile in the vermicompost is generally higher than traditional compost. In fact, vermicompost can enhance soil fertility physically, chemically and biologically. Physically, vermicompost-treated soil has better aeration, porosity, bulk density and water retention. The chemical properties such as pH, electrical conductivity and organic matter content are also improved for better crop yield. Nevertheless, the enhanced plant growth could not be satisfactorily explained by improvements in the nutrient content of the soil, which means that other plant growth influencing materials are available in the vermicomposts. Although vermicomposts have been shown to improve plant growth significantly, the application of vermicomposts at high concentrations could impede the growth due to the high concentrations of soluble salts available in the vermicomposts. Therefore, vermicomposts should be applied at moderate concentrations in order to obtain maximum plant yield. This review paper discussed in detail the effects of vermicompost on soil fertility physically, chemically and biologically. Future prospects and economy on the use of organic fertilizers in agriculture sector were also examined.
Article
Muskmelon (Cucumis melo L.) wilt caused by Fusarium oxysporum f. sp. melonis leads to severe economic losses. A bio-organic fertilizer (BIO) fortified with an antagonistic strain of Bacillus subtilis Y-IVI was used to control this disease. Pot experiments were carried out to investigate the efficacy and to elucidate biocontrol mechanisms for the disease. BIO significantly reduced the disease incidence. Population of F. oxysporum in plant shoots of the BIO treatment were about 1000-fold lower than the control. Population of Y-IVI remained high in muskmelon rhizosphere of the BIO treatment during the experiment. Concentration of antifungal lipopeptides, iturin A, in the BIO treatment was significantly higher than other treatments. Ten days after transplantation, the salicylic acid content in BIO-treated plant leaves was significantly higher than control. In conclusion, BIO effectively controlled muskmelon wilt, possibly because the antagonistic microbes effectively colonize the plant rhizosphere and shoots to preclude pathogen invasion. Furthermore, Y-IVI produces antifungal lipopeptides in the rhizosphere.
Article
Four Pseudomonad strains were used with or without vermicompost amendment to see their performance on potato plant growth and yield along with suppression of common scab of potato. Two locations in the Varanasi district of India were selected as they had been under potato cultivation for the past one decade and the scab pathogen was well established. Among the various treatments, the Pseudomonad strain R1 when applied with vermicompost gave the best plant growth and yield along with maximum reduction in scab incidence and scab index. The strain R1 was later identified as Pseudomonas mosselii. The treatment also showed maximum activities of the antioxidant enzyme peroxidase (POX) and the first enzyme of the phenylpropanoid pathway phenylalanine ammonia lyase (PAL) in a pot experiment till 72 h after pathogen challenge and then declined thereafter. Interestingly the activities of both POX and PAL were higher in the potato tuber peels, the active site of pathogen interaction, than in the potato leaves. The results revealed the potential of P. mosselii strain R1 in promoting plant growth as well as inducing antimicrobial mechanisms systemically in the host plants facilitated by the organic amendment in the form of vermicompost.Graphical abstractResearch highlights► Pseudomonas mosselii reduced common scab incidence and index in potato. ► P. mosselii increased peroxidase and PAL activities in tuber peel. ► Performance of P. mosselii enhanced by vermicompost. ► P. mosselii and vermicompost in combination increased tuber yield.
Article
Antifungal compounds in the culture filtrate from Bacillus subtilis NSRS 89-24 that inhibited the growth of Pyricularia grisea and Rhizoctonia solani were mainly heat stable as the filter sterilized culture filtrate showed higher activity than an autoclaved one. The heat stable and labile components were due to an antibiotic and a β-1,3-glucanase, respectively. This β-1,3-glucanase was purified and characterized. Glucanase activity in the culture medium of B. subtilis NSRS 89-24 was inducible in the presence of 0.3% chitin, reaching a maximum on day 5. After purification, activity was associated with a protein of molecular mass of approximately 95.5 kDa by both gel filtration and native PAGE. Two major bands of Mr 64.6 and 32.4 kDa were revealed by SDS–PAGE. The enzyme had a Km of 0.9 mg/ml, and Vmax of 0.11 U, the optimal pH was 6.5–9.5 and was stable up to 50 °C. Both the pure enzyme and the antibiotic extract from the culture filtrate of the B. subtilis separately inhibited R. solani and P. grisea with MIC values of 12.5 and 6.25 mU/ml and 3.13 and 1.56 μg/ml, respectively. The glucanase enzyme in combination with the antibiotic showed a strong synergistic inhibitory effect on the hyphal growth of both fungi.
Article
Biological control of soil-borne pathogens comprises the decrease of inoculum or of the disease producing activity of a pathogen through one or more mechanisms. Interest in biological control of soil-borne plant pathogens has increased considerably in the last few decades, because it may provide control of diseases that cannot or only partly be managed by other control strategies. Recent advances in microbial and molecular techniques have significantly contributed to new insights in underlying mechanisms by which introduced bacteria function. Colonization of plant roots is an essential step for both soil-borne pathogenic and beneficial rhizobacteria. Colonization patterns showed that rhizobacteria act as biocontrol agents or as growth-promoting bacteria form microcolonies or biofilms at preferred sites of root exudation. Such microcolonies are sites for bacteria to communicate with each other (quorum sensing) and to act in a coordinated manner. Elicitation of induced systemic resistance (ISR) by plant-associated bacteria was initially demonstrated using Pseudomonas spp. and other Gram-negative bacteria. Several strains of the species Bacillus amyloliquefaciens, B. subtilis, B. pasteurii, B. cereus, B. pumilus, B. mycoides, and B. sphaericus elicit significant reductions in the incidence or severity of various diseases on a diversity of hosts. Elicitation of ISR by these strains has been demonstrated in greenhouse or field trials on tomato, bell pepper, muskmelon, watermelon, sugar beet, tobacco, Arabidopsis sp., cucumber, loblolly pine, and two tropical crops (long cayenne pepper and green kuang futsoi). Protection resulting from ISR elicited by Bacillus spp. has been reported against leaf-spotting fungal and bacterial pathogens, systemic viruses, a crown-rotting fungal pathogen, root-knot nematodes, and a stem-blight fungal pathogen as well as damping-off, blue mold, and late blight diseases. This progress will lead to a more efficient use of these strains which is worthwhile approach to explore in context of biocontrol strategies.
Article
A photo-induced cyclic peroxidation in isolated chloroplasts is described. In an osmotic buffered medium, chloroplasts upon illumination produce malondialdehyde (MDA)—a decomposition product of tri-unsaturated fatty acid hydroperoxides—bleach endogenous chlorophyll, and consume oxygen. These processes show (a) no reaction in the absence of illumination; (b) an initial lag phase upon illumination of 10–20 minutes duration; (c) a linear phase in which the rate is proportional to the square root of the light intensity; (d) cessation of reaction occurring within 3 minutes after illumination ceases; and (e) a termination phase after several hours of illumination. The kinetics of the above processes fit a cyclic peroxidation equation with velocity coefficients near those for chemical peroxidation.The stoichiometry of MDA/O2 = 0.02, and O2Chlbleached = 6.9 correlates well with MDA production efficiency in other biological systems and with the molar ratio of unsaturated fatty acids to chlorophyll. The energies of activation for the lag and linear phases are 17 and 0 kcal/mole, respectively, the same as that for autoxidation. During the linear phase of oxygen uptake the dependence upon temperature and O2 concentration indicates that during the reaction, oxygen tension at the site of peroxidation is 100-fold lower than in the aqueous phase.It is concluded that isolated chloroplasts upon illumination can undergo a cyclic peroxidation initiated by the light absorbed by chlorophyll. Photoperoxidation results in a destruction of the chlorophyll and tri-unsaturated fatty acids of the chloroplast membranes.
Article
Recognition of an avirulent pathogen triggers the rapid production of the reactive oxygen intermediates superoxide (O2-) and hydrogen peroxide (H2O2). This oxidative burst drives crosslinking of the cell wall, induces several plant genes involved in cellular protection and defence, and is necessary for the initiation of host cell death in the hypersensitive disease-resistance response. However, this burst is not enough to support a strong disease-resistance response. Here we show that nitric oxide, which acts as a signal in the immune, nervous and vascular systems, potentiates the induction of hypersensitive cell death in soybean cells by reactive oxygen intermediates and functions independently of such intermediates to induce genes for the synthesis of protective natural products. Moreover, inhibitors of nitric oxide synthesis compromise the hypersensitive disease-resistance response of Arabidopsis leaves to Pseudomonas syringae, promoting disease and bacterial growth. We conclude that nitric oxide plays a key role in disease resistance in plants.
Article
Reactive oxygen species are believed to perform multiple roles during plant defense responses to microbial attack, acting in the initial defense and possibly as cellular signaling molecules. In animals, nitric oxide (NO) is an important redox-active signaling molecule. Here we show that infection of resistant, but not susceptible, tobacco with tobacco mosaic virus resulted in enhanced NO synthase (NOS) activity. Furthermore, administration of NO donors or recombinant mammalian NOS to tobacco plants or tobacco suspension cells triggered expression of the defense-related genes encoding pathogenesis-related 1 protein and phenylalanine ammonia lyase (PAL). These genes were also induced by cyclic GMP (cGMP) and cyclic ADP-ribose, two molecules that can serve as second messengers for NO signaling in mammals. Consistent with cGMP acting as a second messenger in tobacco, NO treatment induced dramatic and transient increases in endogenous cGMP levels. Furthermore, NO-induced activation of PAL was blocked by 6-anilino-5,8-quinolinedione and 1H-(1,2,4)-oxadiazole[4,3-a]quinoxalin-1-one, two inhibitors of guanylate cyclase. Although 6-anilino-5,8-quinolinedione fully blocked PAL activation, inhibition by 1H-(1,2,4)-oxadiazole[4, 3-a]quinoxalin-1-one was not entirely complete, suggesting the existence of cGMP-independent, as well as cGMP-dependent, NO signaling. We conclude that several critical players of animal NO signaling are also operative in plants.
Nitric oxide functions as a signal in plant disease resistance
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  • Y Xia
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Searching ISR determinants from
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Effect of sodium nitroprusside on responses of
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  • Roohollahi
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Effect of vermicompost on growth
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  • Golmohammadi
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Searching ISR determinants from Bacillus subtilis IAGS174 against Fusarium wilt of tomato
  • V Akram
  • T Anjum
  • V. Akram