evaluation of drought tolerance indices in determining sugar beet genotypes under early season drought stress conditions

this study was conducted over a three-year period (1998, 1999 and 2000) to evaluate some drought tolerance indices and their relations with sugar yield in some sugar beet genotypes under early season drought and non-drought conditions. the experimental design was a split plot with a randomized complete block. the main plots consisted of two irrigation regimes: non-stress and water stress in early season. subplots consisted of nine sugar beet genotypes. six genotypes were common in three years. the indices that were studied include difference between white sugar yield in stress condition and non-stress condition, ratio of white sugar yield in stress condition to non-stress condition, stress susceptibility index, mathematical and geometric mean of white sugar yield in stress and non-stress conditions and stress tolerance index. the mathematical and geometric mean of white sugar yield in stress and non-stress conditions predicted white sugar yield in stress and non-stress conditions better than other indices. the results showed that applying the ratio of white sugar yield in stress to non-stress conditions and mathematical mean white sugar yield simultaneously in stress and non-stress conditions were useful for determining suitable genotype in each condition (stress and non-stress). also when we emphasis for finding suitable genotypes in drought stress, the ratio of white sugar yield in stress condition to non-stress and white sugar yield of genotypes in stress condition must be used together. among six common genotypes, mstc2 and 7233.p3 were introduced as drought tolerance sources in breeding program.