Arbuscular mycorrhizal fungi (Glomus intraradices) and diazotrophic bacterium (Rhizobium BMBS) primed defense in blackgram against herbivorous insect (Spodoptera litura) infestation.

In the changing scenario of agriculture, plants are exposed to various biotic and abiotic stresses. Induction of both constitutive and inducible defense systems was noticed in plants exposed to stress. As a major defense response, production of phenolics and superoxide radicals quenching enzymes is accelerated in plants under stress. These metabolites production intensified further when arbuscular mycorrhizal fungi (AMF) infected plants are subjected to stress. With this background, we conducted experiments to explore the impacts of Glomus intraradices and Rhizobium on the stimulation of defense in blackgram against Spodoptera litura. Uninoculated plants accumulated considerable quantity of defense metabolites like phenolics, lignin and superoxide radicals quenching enzymes such as superoxide dismutase, peroxidase, catalase, phenylalanine ammonium lyase, and polyphenol oxidase constitutively. While production of these defense metabolites primed strongly due to G. intraradices inoculation. These defense responses augmented further when G. intraradices colonized plants were exposed to S. litura. Though the combined inoculation with G. intraradices and Rhizobium improved the defense response, the effect was more pronounced due to single inoculation with G. intraradices. Results of in vitro leaf feeding bioassay showed that the feeding capacity of S. litura reduced (36.32%) significantly due to feeding G. intraradices infected plants. These outcomes revealed that tolerance against S. litura in blackgram could be primed by mycorrhizal inoculation. This is the first report to state that G. intraradices besides improving nutrient use efficiency, also accelerates defense response in blackgram against S. litura. Hence, AMF could be recommended as a bioprotectant against S. litura in blackgram.