Estimation of heterosis and heritability of drought stress tolerance in test cross genotypes of sugar beet

Introduction Drought stress conditions are the most important factors in yield reduction of crops in the world. Breeding of cultivars with high tolerance to these stresses and satisfactory yielding are considerable. In order to evaluate the resistance of test cross hybrids of sugar beet (12 hybrids and two control cultivars) to water stress (200 mm evaporation of A class pan) in field conditions were used randomized complete block design with three replications in Khorasan Razavi Agricultural and Natural Resources Research and Education Center. Materials and methods This experiment was carried out in 2015 in a randomized complete block design with 14 test cross genotypes of sugar beet includes six monogerm hybrids (mono s1, mono s2, mono s3, mono s4, mono s5 and mono s6) and six multigerm hybrids (multi s1, multi s2, multi s3, multi s4, multi s5 and multi s6) with two control cultivars (Pars and Motahar) in three replications. In this research, traits such as root yield, sugar yield, sugar content of root, leaf number, temperature difference between leaf and air, succulence index, leaf relative water content, specific leaf weight, leaf color score, leaf growth score, postural leaf, root growth score and ratio of length to width of root were measured. Data were analyzed using SAS 9.1 software. After standardizing data, cluster analysis for sugar yield was done with WARD method and Square Euclidean distance coefficient. Factor analysis was performed using the software Minitab version 15. The analysis of variance on test data and comparison to the middle of the LSD test was performed at the 5% and 1% level. Results and discussion The results showed that there were significant differences (p≤0.01) between studied genotypes for all traits except for temperature difference between leaf and air, postural leaf, root growth score and ratio of length to width of root. The control cultivars of sugar beet (Pars and Motahar) did not showed superior than the other genotypes for most of traits studied and those have the average values of traits. Multi s5 genotype showed superiority for root yield, succulence index, leaf relative water content, specific leaf weight, leaf growth score and root growth score than the other genotypes and in other words, has a high potential for drought tolerance. The highest heritability (89.40 %) estimated for leaf number, suggested that the influence of environmental effects on this trait. The highest standard heterosis in hybrid Multi s5 was obtained for most of studied traits. In this research, there were significant positive correlations between root yield and sugar yield. Significant and positive correlations were observed between root yield and root growth score. While, significant and negative correlations were obtained between root yield, sugar content of root and leaf number. The dendrogram generated from the cluster analysis for sugar yield classified genotypes into three main groups. Factor analysis led to five loading factors which explained 91.3 percent of total variation. Conclusions In general, the results showed that there are considerable variations in yield, morphological and physiological traits among test cross genotypes of sugar beet due to the potential for drought tolerance in them.