عنوان مقاله [English]
For evaluation of drought tolerance of sugar beet genotypes by assessment of the drought tolerance indices under mild and severe stresses, furrow irrigated field experiments were carried out at Zarghan Research Station in 2002 and 2004, and at Motahari Research Station (located inKaraj) in 2002, 2003, and 2004. The experimental design was split plot, with a randomized complete block arrangement with four replications. The irrigation treatments as main plots consisted of non-stress, mild stress (75% of the water applied in non-stress), and severe stress (50% of the water applied in non-stress), and sub plots were composed of 10 genotypes. Based on the potential sugar yield (SYp) and stressed sugar yield (SYs), some quantitative criteria of drought tolerance such as mean productivity (MP), tolerance index (TOL), geometric mean productivity (GMP), harmonic mean (HARM), stress susceptibility index (SSI), yield loss ratio (S), and stress tolerance index (STI) were calculated. The positive and significant correlations of SYp and SYs with different water stress indices showed that (a) in Zarghan, under mild and severe stress conditions, STI, MP, GMP and HARM, and (b) in Karaj, under mild stress condition, STI, MP, GMP, and HARM, and under severe stress condition, STI, GMP, and HARM were the best indices that could be used to determine the tolerant genotypes. By considering these indices, and high values SYp and SYs, and also the multivariate biplot display, the most tolerant genotypes were identified as (a) 7221-I-79 and MST261*W-7221-I-79 in Zraghan under mild stress condition, (b) 7221-I-79 in Zraghan under severe stress condition, (c) MSTC2*W-7221-I-79 and 7221-I-79 in Karaj under mild stress condition, and (d) MSTC2*W-7221-I-79 and BP-Mashhad in Karaj under severe stress condition. Distributions of the genotypes in the biplot display indicated the presence of genetic diversity among the genotypes for drought tolerance.