Evaluation of Drought Tolerance in Cultivars of Three Oilseed Brassica Species

To evaluate the agronomic characteristics in three Brassica species (rape, Indian mustard, and turnip) and to determine the best stress tolerance indices, 16 brassica cultivars were studied under controlled conditions in -0.6 Mpa of stress and as well under field (either stressed or irrigated) conditions at the Dryland Agricultural Research Station, Kermanshah during 2004-05. The results showed significant differences among and within Brassica species for the studied traits. Under controlled conditions, maximum germination (Gmax) as well as Germination Rate Index (GRI) were recorded for rape species. Based on the above characteristics, rape cultivars Parade, and Comet were superior to the others. Under field conditions, the fewest number of days to flowering and maturity were observed in turnip species, the highest plant height in mustard species, the maximum no. of pods per plant in the two mustard and turnip species, and finally the maximum no. of seeds per pod, pod length, and seed weight were recorded in rape species. Rape and mustard cultivars contained the highest and the lowest seed oil contents, respectively. The highest oil and seed yield belonged to rape and mustard cultivars. The correlation coefficients between no. of pods per plant and other yield components were negatively significant that indicating genotypes of high pod number such as mustard and turnip cultivars possess short pod lengths, low no. of seeds per pod as well as low seed weights. Yield of Brassica cultivars was not correlated with any single yield component. Seed oil content and oil yield under stressed irrigation conditions were positively correlated with the stress. The highest geometric mean (GMP), stress tolerance (STI), Mean Productivity (MP), and harmonic mean (Harm) belonged to rape and mustard species. The least tolerance (TOL) and stress susceptibility (SSI) indices as well as the highest Drought Response Index (DRI) belonged to turnip species. The indices GMP, STI, MP, and Harm were positively correlated with oil yield in both experimental conditions, therefore those were determined as the most suitable indices for evaluation of Brassica cultivars. Based on the above indices, rape cultivars Parade, Opera, Amica and mustard cultivars J98/102/51/5, Landrace, and Lethbridge were recognized as superior to the other cultivars.