evaluation of drought tolerance in some rapeseed cultivars based on stress evaluation indices

water deficient is one of the most important limiting factors in rapeseed (brassica napus l.) production in arid and semiarid areas speciallyiran, which is the best approach to deal with the introduction of resistant and compatible varieties to drought stress. the response of fourteen rapeseed cultivars to water stress was studied in a split plot experiment based on complete randomized block design with 3 replications at experimental field ofuniversitycollege of agricultural and natural resourcesuniversity oftehran. cultivars were planted as subplots within the moisture regime as main plots. drought stress in flowering stage was provided by irrigation stop until soil water potential met -1/5 mp. irrigation of drought stressed plots in grain filling stage was stopped completely after grain filling began. the results showed that drought stress at grain filling did not significantly affect on yield, while stress on flowering stage decreased seed yield by 51.2% through speeding up the maturity (8.8 days compared to normal condition) and reduction of height (19.5%), root length (26.7%) and biological yield (46%). mean productivity (mp), geometric mean productivity (gmp) and stress tolerance index (sti) were the most suitable indices showing the highest correlation with yield under both stress and normal conditions. based on mp, gmp and sti and also biplot technique, okapi and pf7045-91 (sarigol) were determined as the most tolerant cultivars while hyola 60 being the most sensitive.