Biochemical and physiological responses of rice as influenced by Alternanthera paronychioides and Echinochloa colona under drought stress

Rice crops experience biotic (weeds) and abiotic stress (drought) at early in the season when the plants are most susceptible to weed competition, which results in oxidative stress in rice. Oxidative stress is an important factor that could decrease plant yield. The main aim of this study was to investigate the biochemical, physiological, and yield responses of rice in the presence of its major weeds (Echinochloa colona (L.) Link. and Alternanthera paronychioides A. St.-Hil.) during the critical competitive period (25 days after sowing) under drought stress and identifying the differential sensitivity of rice towards the weeds. In the presence of weeds, the rice physiological, biochemical attributes and yield of rice are negatively affected under drought, which was evident by a decline in relative water content, membrane stability index, antioxidant enzymes, non-enzymatic oxidants and chlorophyll content linked with the accumulation of reactive oxygen species (ROS). However, the extent of reduction in these traits of rice was greater and the accumulation of ROS was higher in the presence of E. colona than A. paronychioides, indicating a higher sensitivity towards E. colona under drought stress. The highest accumulation of MDA was observed under drought due to A. paronychioides (38.66 mu g g(-1) FW) and E. colona (66.21 mu g g(-1) FW) interference. Besides this superoxide content increased by 6.81 mu mol g(-1) FW and 8.36 mu mol g(-1) FW in the presence of A. paronychioides and E. colona, respectively under drought stress. This oxidative stress significantly reduced the yield. Overall, our study provides the characterization of trait responses of rice to biotic (weeds) abiotic stresses (drought) at the physiological and biochemical level and can serve as starting point for further in-depth research.