Evaluation of Drought Tolerance in Sugar Beet O-Type Lines

One objective of drought resistance breeding of sugar beet is to introduce cultivars with lower yield loss under drought stress. The evaluation of O-type lines is known as a determining stage of sugar beet breeding for introducing hybrid cultivars with the favorable genetic trait. The present study investigated 29 sugar beet O-types (with different levels of drought tolerance) as well as a tolerant foreign cultivars as control (IR7) and sensitive genotype (191) and the genotypes 30908, 31290, 31291 and 31292 as well as forage beet bulk 7221 in a split-plot experiment on the basis of a Randomized Complete Block Design (RCBD) with four replications. It was carried out in Motahari Research Station (Lat. of 35 59' N., Long. of 51 06' E., and Alt. of 1300 m.) in 2012. The main plot was devoted to stress (at two levels of normal irrigation and stress application) and the sub-plots were devoted to 36 studied lines and cultivars. Under both conditions, the plots were normally irrigated until thinning and plant establishment and then, they were irrigated on the basis of about 270 and 80-90 mm evaporation from evaporation pan under normal and stress conditions, respectively. The plots were composed of one 8-m-long row with inter-row spacing of 50 cm. It was found that drought stress (SI = 0.72) resulted in the reduction of canopy ground covering from 57 to 38% and accelerated green ground cover from 81 to 67 days after sowing (DAS). In addition, drought stress increased wilting score (3.17) and plants death score (1.90) as compared to normal conditions (1.54 and 1.50, respectively). In response to drought stress, mean root, raw sugar, and white sugar yield and gross and net sugar contents were decreased by 59, 72, 76, 33 and 43%, respectively and root Na content and molasses sugar were significantly increased by 23 and 13%, respectively. The significance of the effect of genotype and the interaction between stress and genotype on crop quantitative traits shows the wide diversity of genetic material in terms of the response to drought stress. According to Fernandez's theory, 8 genotypes (3, 35, 32, 5, 34, 13, 26 and 36) were ranked in Group A (high yielding under normal and stress conditions). Also, the comparison of 16 tolerance indices revealed that eight indices (GMP, HM, K2STI, SNPI, STI, YI and YS) successfully recognized the eight genotypes categorized in Group A although the coefficients of correlation between tolerance indices and raw sugar yield under normal and stress conditions showed the superiority of SSPI, ATI, MP, TOL, GMP, STI, RDY, K2STI, HM, YI, K1STI, SNPI and DI. Finally, The most tolerant o-types were 3 (O.T.110-25), 5 (O.T.110-09), 13 (O.T.110-29) and 26 (O.T.110-17), respectively.