Response of different species of Brassica to water deficit

Development of drought-tolerant cultivars is hampered by a lack of effective selection criteria. In this research, response of 36 genotypes of rapeseed from seven species of Brassica including B. napus, B. rapa, B. juncea, B. carinata, B. oleracea, B. nigra and B. fruticulosa was assessed under three moisture levels (no stress, mild stress and intense stress) in the field during 2011-2012. Five drought-tolerance indices were calculated: stress tolerance (TOL), stress susceptibility index (SSI), mean productivity (MP), geometric mean productivity (GMP) and stress tolerance index (STI). Increasing water stress levels caused significantly more reductions in the seed yield of all species. Species B. napus had the highest yields in normal and intense stress conditions while B. carinata showed better performance in mild stress condition. Correlation coefficients revealed that among drought tolerance indices, GMP, STI and MP are superior criteria for selecting high-yield genotypes under stress and non-stress conditions. B. napus and B. carinata were the most drought tolerant while B. rapa and B. oleracea were the most susceptible species of Brassica based on yield potential. Application of principle component analysis (PCA) for distinguishing drought and susceptible species are discussed.