Microorganisms under natural habitats live in communities and some provides benefits to plant. Further, microbes when introduced to soil as consortium and interact with a host plant, partially mimic the natural soil conditions. The current research trend has therefore oriented towards investigating the role of small microbial consortia in promoting plant growth and health against various invading pathogens. This is a paradigm shift from the original investigations involving a single microbe. In the recent past, information on various mechanisms by which microbial consortia promoted plant growth and triggered defense responses in host plants during pathogen ingress have become available. It was also unveiled that microbes in small consortia enhance the defense signaling cascades leading to enhanced transcriptional activation of several metabolic pathways. However, an additive or synergistic effect is not achieved every time a microbial consortium is used. With progress in time a sizable understanding on microbial consortium-induced plant defense responses had been reached. Further generation of information on host's responses to pathogenic challenge in the presence of diverse microbial consortia at functional level is underway. In this review, we have presented the outcomes of small microbial consortia used so far to protect crop plants from various pathogens. We have also provided possible explanations for reduction in diseases when a microbial consortium was used, compared the effects of microbes when used alone as well as in consortium, possible shortcomings for not obtaining desired outcome from the introduced consortia, and provided the rationale for development of effective microbial consortia capable of inducing enhanced systemic resistance. Finally, we have suggested some potential biotechnological applications to sustain the effect of microbe-induced defense responses in host plants.

Microbial consortium-mediated plant defense against phytopathogens: Readdressing for enhancing efficacy

Management of tomato diseases caused by Fusarium oxysporum

Aims: To evaluate the potentiality of three rhizosphere microorganisms in suppression of Sclerotinia rot in pea in consortia mode and their impact on host defence responses.



Methods and Results: Pseudomonas aeruginosa PJHU15, Trichoderma harzianum TNHU27 and Bacillus subtilis BHHU100 from rhizospheric soils were selected based on compatibility, antagonistic and plant growth promotion activities. The microbes were used as consortia to assess their ability to trigger the phenylpropanoid and antioxidant activities and accumulation of proline, total phenol and pathogenesis-related (PR) proteins in pea under the challenge of the soft-rot pathogen Sclerotinia sclerotiorum. The triple-microbe consortium and single-microbe treatments showed 1·4–2·3 and 1·1–1·7-fold increment in defence parameters, respectively, when compared to untreated challenged control. Activation of the phenylpropanoid pathway and accumulation of total phenolics were highest at 48 h, whereas accumulation of proline and PR proteins along with activities of the antioxidant enzymes was highest at 72 h.



Conclusions:  The compatible microbial consortia triggered defence responses in an enhanced level in pea than the microbes alone and provided better protection against Sclerotinia rot.



Significance and Impact of the Study:  Rhizosphere microbes in consortium can enhance protection in pea against the soft-rot pathogen through augmented elicitation of host defence responses.

https://sfamjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2672.2011.05220.x

Microbial consortium-mediated reprogramming of defence network in pea to enhance tolerance against Sclerotinia sclerotiorum.

Plant beneficial microbes (PBMs), such as plant growth-promoting bacteria, rhizobia, arbuscular mycorrhizal fungi, and Trichoderma, can reduce the use of agrochemicals and increase plant yield, nutrition, and tolerance to biotic-abiotic stresses. Yet, large-scale applications of PBM have been hampered by the high amounts of inoculum per plant or per cultivation area needed for successful colonization and consequently the economic feasibility. Seed coating, a process that consists in covering seeds with low amounts of exogenous materials, is gaining attention as an efficient delivery system for PBM. Microbial seed coating comprises the use of a binder, in some cases a filler, mixed with inocula, and can be done using simple mixing equipment (e.g., cement mixer) or more specialized/sophisticated apparatus (e.g., fluidized bed). Binders/fillers can be used to extend microbial survival. The most reported types of seed coating are seed dressing, film coating, and pelleting. Tested in more than 50 plant species with seeds of different dimensions, forms, textures, and germination types (e.g., cereals, vegetables, fruits, pulses, and other legumes), seed coating has been studied using various species of plant growth-promoting bacteria, rhizobia, Trichoderma, and to a lesser extent mycorrhizal fungi. Most of the studies regarding PBM applied via seed coating are aimed at promoting crop growth, yield, and crop protection against pathogens. Studies have shown that coating seeds with PBM can assist crops in improving seedling establishment and germination or achieving high yields and food quality, under reduced chemical fertilization. The right combination of biological control agents applied via seed coating can be a powerful tool against a wide number of diseases and pathogens. Less frequently, studies report seed coating being used for adaptation and protection of crops under abiotic stresses. Notwithstanding the promising results, there are still challenges mainly related with the scaling up from the laboratory to the field and proper formulation, including efficient microbial combinations and coating materials that can result in extended shelf-life of both seeds and coated PBM. These limitations need to be addressed and overcome in order to allow a wider use of seed coating as a cost-effective delivery method for PBM in sustainable agricultural systems.

/pdf/seed-coating-a-tool-for-delivering-beneficial-microbes-to-4yr5i5do3t.pdf

Seed Coating: A Tool for Delivering Beneficial Microbes to Agricultural Crops

Vegetable crops are frequently infected by fungal pathogens, which can include seedborne fungi. In such cases, the pathogen is already present within or on the seed surface, and can thus cause seed rot and seedling damping-off. Treatment of vegetable seeds has been shown to prevent plant disease epidemics caused by seedborne fungal pathogens. Furthermore, seed treatments can be useful in reducing the amounts of pesticides required to manage a disease, because effective seed treatments can eliminate the need for foliar application of fungicides later in the season. Although the application of fungicides is almost always effective, their non-target environmental impact and the development of pathogen resistance have led to the search for alternative methods, especially in the past few years. Physical treatments that have already been used in the past and treatments with biopesticides, such as plant extracts, natural compounds and biocontrol agents, have proved to be effective in controlling seedborne pathogens. These have been applied alone or in combination, and they are widely used owing to their broad spectrum in terms of disease control and production yield. In this review, the effectiveness of different seed treatments against the main seedborne pathogens of some important vegetable crops is critically discussed.

https://www.d3a.univpm.it/sites/www.d3a.univpm.it/files/d3a/Lavori%20scientifici/Mancini%20and%20Romanazzi%2C%202014%20Pest%20Management%20Science.pdf

Seed treatments to control seedborne fungal pathogens of vegetable crops

Evaluation of arbuscular mycorrhizal fungus, fluorescent Pseudomonas and Trichoderma harzianum formulation against Fusarium oxysporum f. sp. lycopersici for the management of tomato wilt

U.S. Singh

Papers

Evaluation of arbuscular mycorrhizal fungus, fluorescent Pseudomonas and Trichoderma harzianum formulation against Fusarium oxysporum f. sp. lycopersici for the management of tomato wilt