Physiological, Agronomical and Morphological Reactions of Sugar Beet Populations in Water Stress

To identify the tolerant sugar beet genotypes from the physiological and morphological viewpoints, and to increase the water use efficiency (WUE), furrow irrigated field experiments were carried out at the Zarghan research station in the years 2002 and 2004, and at the Motahari research station (located in Karaj) in the years 2002, 2003, and 2004. The experimental design was split plot, with a randomized complete block arrangement with four replications. The irrigation treatments as a main plots consisted of: non-stress, 75% of the applied water in non-stress as mild stress, and 50% of the applied water in non-stress as severe stress, and sub plots were composed of 10 genotypes. Based on the potential sugar yield (SYp) and stress 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 results showed that water stress significantly affected the top yield, root yield and sugar yield in Zarghan whereas all characteristics were not affected in Karaj. Maximum yields and WUE were obtained on the non-stress treatment, and these decreased as the intensity of water stress increased in Zarghan. In Karaj maximum yields were obtained on the non-stress treatment, and these decreased as the intensity of water stress increased. Genotype significantly affected the quantitative and qualitative characteristics in both locations. Comparisons made between the 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 a mild stress condition, STI, MP, GMP, and HARM, and under a severe stress condition, STI, GMP, and HARM were the best indices that could be used to determine the tolerant genotypes. Regarding these indices, and high SYp and Sys, and also the multivariate biplot, the most tolerant genotypes were identified as (a) 7221-I-79 and MST261-W-7221-I-79 in Zraghan under a mild stress condition (b) 7221-I-79 in Zraghan under a severe stress condition (c) MSTC2-W-7221-I-79 and 7221-I-79 in Karaj under a mild stress condition (d) MSTC2-W-7221-I-79 and BP-Mashhad in Karaj under a severe stress condition. Distributions of the genotypes in the biplot space indicated the presence of genetic diversity among the genotypes for water stress.