PHYSIOLOGICAL RESPONSE AND SEED YIELD OF SPRING RAPESEED GENOTYPES UNDER OPTIMUM AND DROUGHT STRESS CONDITION

In order to study the effect of water deficit in generative growth period on agronomical characteristics and growth indexes in rapeseed (Brassica napus L.)genotypes, a field experiment was conducted in split-plot design on randomized complete block design with four replications at field experimental of Seed and Plant Improvement Institue, Karaj in 2002/3. There were two factors, irrigation at two levels (irrigation after 80 mm evaporation from class “A” pan as control and water stress from stem elongation stage until physiological maturity) as main plots and spring genotypes in ten levels: Ogla, 19-H, Hyola 401 (Canada), Hyola 401 (Safiabad), Hyola 401 (Borazjan), Hyola 420, Syn-3, Option 500, Hyola 308 and Quantum, as sub plots. Agronomical characteristics such as pod length, number of pods in plant, number of grains per pod, 1000- seed weight, seed yield were studied. Furthermore, physiological characteristics such as proline, chlorophyll, relative water content (RWC) were studied too. Results showed that the water interruption since stem elongation stage, had undesirable effect on growth activities, yield and yield components.Among yield components, decreasing 1000-seed weight (8%) and specially number of grains per pod (11.3%) had the most proportion in decreasing seed yield. Among genotypes, Syn-3, 19-H, Hyola 420, Hyola 401 (Canada) and Hyola 401 (Borazjan), produced more seed yield than the others, but the lowest seed yield belonged to Hyola 308. In water stress condition, cultivars had higher content of proline, whereas the relative water content and chlorophyll a, b and total chlorophyll were lower. Water stress condition, increased the ratio of chlorophyll a/b and this resulted from more decreasing in chlorophyll b in comparision with chlorphylla. The amounts of proline in leaves showed the degree of stress- induced injury and it was not related to drought stress tolerance. Also, the decreasing of relative water content was more in sensitive varieties. On the basis of the results it is concluded that Syn-3, 19-H, Hyola 420, Hyola 401 (Borazjan) and Hyola 401 (Canada) with higher stress tolerance index (STI) had better compatibility to water stress and could produce greater seed yield in both conditions (normal irrigation and drought stress), in contrast with the cultivars listed above, Hyola 308 had the most sensitivity to water stress.