Impact of Spodoptera litura Attack on Chlorophyll and Biomass Content of Vigna mungo Colonized with Arbuscular Mycorrhizal Fungi and Rhizobium

The first and foremost response of plants to any external stimuli, including herbivorous insect attack is the generation of reactive oxygen species, which majorly occurs in the chloroplast followed by mitochondria, peroxisomes, cell membrane, and cell wall. Under these circumstances, the photosynthetic efficiency of the plant system dramatically influences the plant biomass and yield. Although arbuscular mycorrhizal fungi (AMF), Glomus intraradices and Rhizobium improve plant growth through nutritional modes, their impact on protecting chloroplast from herbivore-induced damage is not yet explored. In this regard, experiments were carried out to examine the changes in chlorophyll composition (Chl a & b), and biomass production of Rhizobium and AMF inoculated plants infested with Spodoptera litura. Among various treatments, AMF and Rhizobium inoculated plants showed higher chlorophyll a and b than un-inoculated control. Upon the herbivore attack, there was a drastic reduction in the chlorophyll content (a & b) in all the treatments. However, the reduction in chlorophyll content upon S. litura attack was lesser in plants inoculated either with AMF or in the combination of AMF and Rhizobium. Similarly, these microbial inoculants protected the plants from S. litura damage by sustaining the biomass productivity. These results highlight the synergistic effects of AMF and Rhizobium in protecting the black gram plants from herbivore-induced damage.