Evaluation of agronomic traits and drought tolerance criteria in some Brassica species under stress and irrigation conditions.

To evaluate the agronomic characteristics in 16 cultivars of three Brassica species ( rape , mustard , turnip) and to determinate the best stress tolerance indices, a field experiment was conducted based on randomized complete block design with three replications under stress and irrigated conditions at the Dryland Agricultural Research Station, Kermanshah during 2004-05. The results exhibited significant differences between and within Brassica species for the studied characters. In this study, the shortest days to flowering and maturity in turnip species, the highest plant height in mustard species, the maximum no. of pods/plant in two mustard and turnip species, the maximum no. of seeds/pods, pod length, and seed weight in rape species was observed, respectively. Rape and mustard cultivars had the highest and lowest seed oil content, respectively. However, the highest oil and seed yield were belonged to mustard cultivars. The correlation coefficients between no. of pods/plant with yield other components were negatively significant that indicated genotypes with high pod number such as mustard and turnip cultivars have short pod length, low no. of seeds/pods and seed weight. Yield of Brassica cultivars was not correlated with any single yield component. Seed oil content and also oil yield in irrigation condition positively correlated with stress condition. the highest geometric mean (GM), stress tolerance (STI), mean productivity (MP), and harmonic mean (HM) belonged to mustard species, the least tolerance (TOL) and stress susceptibility (SSI) indices and the highest drought response index (DRI) related to turnip species. The indices GM, STI, MP, and HM were positively correlated with oil and seed yield in both conditions, therefore those were the best indices for evaluation of Brassica cultivars. Based on the above indices , winter rape cultivars Parade, Opera , Amica and mustard cultivars J98/102/51/5, Landrace, and Lethbridge were superior to the other cultivars.