Altered physiological response in drought stressed rice plants upon root colonization with the beneficial endophytic fungus Piriformospora indica under field conditions

We studied the physiological and biochemical responses of rice plants colonized by the root endophytic fungus Piriformospora indica under varying moisture stress levels that consisted of ideal (non-stress), mild, moderate, severe, very severe, and extremely severe stress imposed by altering depth of irrigation and frequency, in a summer field crop. Colonization by P. indica exhibited distinctive drought defensive effects characterized by the enhanced production of proline, which contributed to improved plant resilience to drought stress, alleviating the harmful oxidative stress. In colonized plants that were under extremely severe stress, proline levels in leaf tissues rose by 18% during panicle initiation (PI) and by 21% during the flowering stage, compared to the uninoculated plants. P. indica colonization also enhanced the relative leaf water content and cell membrane stability in plants. Under extremely severe stress, colonized plants displayed improved cell membrane stability (57% and 48%) at PI and flowering, representing 29% and 8% improvement, respectively, over the non-colonized plants under stress. Endophyte colonized plants demonstrated increased resistance to drought stress with enhanced chlorophyll stability when compared to stressed plants that were not colonized. Fungal colonization also enhanced the growth and resilience of rice plants under drought, resulting in a remarkable 37% increase in grain yield compared to non-colonized plants.