Endophytic fungus Piriformospora indica mitigates moisture stress in rice by modifying root growth

We examined the drought mitigating effects of endophytic root colonization by the beneficial fungus Piriformospora indica in rice plants under varying moisture stress. In a randomized block design, P. indica colonized and non-colonized rice under different levels of moisture stress viz., ideal/non-stress, mild, moderate, severe, very severe and extremely severe stress; created by manipulating the irrigation levels based on the depth and frequency, were evaluated for growth, yield, rooting parameters, and nutrient uptake under non-flooded rice growing conditions. Growth promotive and stress protective effects were noticed in the colonized plants on the number of productive tillers, filled grains per panicle and grain yield under extremely severe stress with an enhancement of 73, 18 and 37 % respectively over control. They also had 26 and 21 % higher rooting depth than the control plants at 60 days after transplanting and harvest respectively, under severe stress which could have ensured better performance of the inoculated plants in terms of growth and yield. Colonization by the beneficial fungus also enhanced production of lateral roots contributing to 44 % higher root volume, resulting in higher area for water and nutrient absorption under severe stress. Endophyte mediated modification of the root architecture improved acquisition of phosphorus, an element directly linked to plant health under stress, by the plants under both severe stress and non-stress situations. Colonization also enhanced the water use efficiency of the plants, a factor influenced by root spread and volume, to 29 % compared to that in the non-colonized plants under severe stress.