Response of different species of Brassica to water deficit

Development of drought-tolerant cultivars is hampered by a lack of effective selectioncriteria. In this research, response of 36 genotypes of rapeseed from seven species of Brassicaincluding B. napus, B. rapa, B. juncea, B. carinata, B. oleracea, B. nigra and B. fruticulosa wasassessed under three moisture levels (no stress, mild stress and intense stress) in the field during2011-2012. Five drought-tolerance indices were calculated: stress tolerance (TOL), stresssusceptibility index (SSI), mean productivity (MP), geometric mean productivity (GMP) andstress tolerance index (STI). Increasing water stress levels caused significantly more reductionsin the seed yield of all species. Species B. napus had the highest yields in normal and intensestress conditions while B. carinata showed better performance in mild stress condition.Correlation coefficients revealed that among drought tolerance indices, GMP, STI and MP aresuperior 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 themost susceptible species of Brassica based on yield potential. Application of principlecomponent analysis (PCA) for distinguishing drought and susceptible species are discussed.