Effect of moisture stress on chlorophyll accumulation and nitrate reductase activity at vegetative and flowering stage in Avena species

The genus Avena comprises about seventy species, a few are cultivated like Avena sativa and Avena byzantina are the main oats grown for fodder and grain purpose. Drought stress is one of the major causes for crop loss world wide, reducing average yields with 50% and over (Wang et al. 2003). Under such stress, water deficit in plant tissue develops, thus leading to a significant inhibition of photosynthesis. At vegetative stage all the seven species of Avena grouped under three categories in response to the extent of moisture stress. The group one comprised of three species viz. A. brevis, A. marocana and A. sterilis showing the maximum stress up to 16 th day from the day with holding the water. The second group comprised of 3 species (A. strigosa, A. vaviloviana and A. abyssinica) showing tolerance up to 12 th day and the third group in which the stress tolerance goes up to 9 th day includes only one species i.e. A. sativa. In group one with highest stress tolrance, A. sterilis considered to be the highest drought tolerant species in terms of minimum decrease in chlorophyll and carotene content even subjected to longest stretch of drought spell, followed by A. strigosa in gorup two at vegetative stage. Flowering stage six species showed tolerant to drought up to 5 days wheras A. sterilis showed extent of drought tolerance up to 4 days. There was less decrease in chlorophyll and carotene accumulation in A. marocana followed by A. abyssinica under waterstress at flowering stage of crop growth therefore considered to be drought tolerant species during flowering stage. The minimum decrease in NRA was recorded in A. brevis followed by A. abyssinica and A. vaviloviana at vegetative stage whereas at flowering stage minimum decrease was observed A. vaviloviana followed by A. marocana and A. sativa indicating variations in NRA under moisture stress at different stages of plant growth.