Assessment of Drought Tolerance Indices in Confectionary Sunflower (Helianthus anuus L.) Landraces of Iran

This research was conducted to evaluate the response of 56 landraces of confectionary sunflower to drought stress based on grain yield and drought tolerance indices in experimental field of Agricultural and Natural Resources Research center in West-Azerbaijan provinec in 2012-2013 cropping season. The genotypes were evaluated in three separated rectangular 7 × 8 lattice design with two replications in three irrigation treatments including optimum irrigation, moderate and severe stress where irrigation was done after depletion of 50%, 70% and 90% of available water (water between field capacity and permanent wilting point), respectively. Ten drought tolerance indices including stress susceptibility index (SSI), tolerance index (TOL), relative drought index (RDI), abiotic tolerance index (ATI), stress susceptibility percentage index (SSPI), yield stability index (YSI), sensitive drought index (SDI), relative decrease in yield index (RDY), modified stress tolerance index in optimum irrigation (M_PSTI) and modified stress tolerance index in moderate and severe stress (M_sSTI)  were calculated based on grain yield under well-watered (Y_P), moderate drought stress (Y_S-mild) and severe drought stress (Y_S-severe) conditions. Grain yield in mild and severe stress conditions was significantly and positively correlated with RDI, YSI, M_sSTI and M_PSTI. Grain yield in well-watered (YP) conditions was significantly and positively correlated with SSI, TOL, ATI, SSPI, SDI, RDY, M_sSTI and M_PSTI. Grain yield in mild and severe stress conditions was significantly and negatively correlated with SSI. Results of this study showed that in moderate drought stress conditions the indices M_sSTI and M_PSTI can be used as the most suitable indicators for screening drought tolerant cultivars. Therefore, to select drought tolerant cultivars in severe drought stress conditions, it is suggested to use M_sSTI and M_PSTI indices because these indices supports stable and high yield in both non-stress and stress conditions. Based on cluster analysis, the studied landraces were grouped in 3 clusters in each one of water treatment conditions. According to the proposed indices and grain yield under severe drought stress, landraces 2, 7, 12, 25, 29 and 49 as resistant genotypes and landraces 3, 11, 13, 16, 27, 42 and 46 were classified as semi tolerant native genitypes and other landraces were susceptible.