evaluation of drought tolerance in rapeseed varieties based on physiological and agronomical characteristics at yazd region

in order to study of drought stress on physiological and agronomicalcharacteristics of rapeseed varieties, an experiment was carried out as split plot basedon randomized complete block design with three replications at yazd region duringof 2011-2012. irrigation treatments was designed in two levels as main plot includingirrigation after 80 mm evaporation from evaporation pan, class a (control treatment)and drought stress as withholding irrigation from flowering stage, and varieties lilian,cooper and savannah as sub plots. sampling stages was done 7, 12 and 26 days aftertreatment. the results indicated that drought stress significantly decreased thestomatal conductivity, relative water content (rwc), plant height, silique per plant,1000 grain weight and grain yield, whereas, in comparison with control spad valuewas higher. lilian indicated the higher stomatal conductivity (196 mmol m-2 s-1) andrwc, silique per plant (300 silique), 1000 grain weight (4.06 g) and grain yield(1411 kg.ha-1). in this study, geometric mean productivity (gmp) and stresstolerance index (sti) had the high correlation with grain yield in normal and droughtstress conditions. also, bi-plot diagram based on two principal componentsindicated that lilian variety with higher gmp and sti indices in addition with highergmp and sti both in stress and non stress environment had the highest grain yield.