Response of maize (Zea mays L.) genotypes to excess soil moisture stress: morpho-physiological effects and basis of tolerance

Experiments were conducted during kharif (summer rainy) season in 1999 and 2000 under controlled environment (glass-house) followed by field condition to assess the effects of excess soil moisture (ESM) stress on maize (Zea mays L.), extent of genetic variability and to assess the morpho-physiological/metabolic basis of stress tolerance. Six genotypes, having different genetic background and known for their reactions to waterlogging stress, have been used in this study. Seedlings were raised in disposable plastic cups (250 cm^3) under completely saturated soil conditions, transplanted in field 20 days after planting and again exposed to waterlogging stress at knee-high stage for 7 days. ESM stress severely affected growth, biochemical composition and metabolic activities, both at early stage and kneehigh stage. There was good similarity in the response of genotypes to ESM stress at two growth stages. Genotypes with early adventitious rooting, partial stomatal closure, <5.0 days anthesis-silking interval, increased root NAD+alcohol dehydrogenase activity and high starch accumulation in stem tissues showed good tolerance to ESM stress. Most of these morpho-physiological traits associated with ESM tolerance were common in both pre-existing and induced (pre-hypoxia/anoxia) tolerance. The results show that hypoxia/anoxia pre-treatment enhances tolerance to waterlogging conditions in maize. However, genetic heritability of such induced tolerance needs to be worked out. It may be concluded that ESM tolerance was mainly based on the stress avoidance mechanism by anaerobic metabolic and alternative arrangement like brace root development to avoid anoxia condition.