Determination of Genetic Parameters of Quantitative and Qualitative Traits of Sugar Beet in Drought and Normal Conditions

Improving crop yield under drought stress conditions is one of the most important goals of plant breeding. Drought tolerance is usually evaluated by plant yield under low water stress, but due to the influence of other traits under stress conditions, this trait alone cannot indicate drought tolerance of genotypes. Therefore, it is better in breeding programs to identify drought tolerance traits of genotypes and guide programs based on yield and other important physiological and biochemical traits. Determining the values of genetic variance and the additive part and the dominance of genetic variance in controlling traits under both normal and stress conditions is the basis for deciding how to use germplasms in different conditions, which researchers use based on different methods to estimate them. The aim of this study was to estimate the genetic parameters of quantitatively yielding and qualitative traits of sugar beet under drought and normal stress conditions for use in breeding programs.

To determine the genetic parameters of different quantitative and qualitative traits of sugar beet, two series of genotypes full-sib and hybrid (resulting from the meeting of some of full-sibs as paternal lines and two lines SC C2 and SC 261 as maternal lines) were studied under both drought and normal conditions, in Motahari's Research, Karaj in 2017. After testing, different physiological and qualitative traits of genotypes were measured in two environments and finally genetic parameters were calculated.

In full-sib experiment under stress conditions, sodium content, potassium/sodium ratio, nitrogen content, alkalinity coefficient, syrup purity, molasses sugar, leaf area, shoot fresh weight, shoot dry weight, root dry weight, root mass ratio, and root/stem ratio had more genetic variance than environmental variance, so they also had higher broad sense heritability. Therefore, due to high genetic variance, these traits can be used in breeding and selection programs. Under normal conditions, the amount of genetic variance was low in all traits and consequently, the general heritability was low. In hybrid experiment under stress conditions for sugar yield traits, sodium content, sodium/potassium ratio, nitrogen content, and leaf area, and normal conditions for sugar yield and sodium/potassium ratio there was high genetic variance and broad-sense heritability was observed above 0.5. Therefore, these traits can be considered for breeding and selection programs. In drought conditions, the highest heritability was related to potassium content 0.77, molasses sugar 0.65, extractable sugar percentage 0.48, syrup purity 0.44, and sodium content and relative water content with 43, respectively. So, these traits were controlled to varying degrees by additive effects. Under normal conditions, pure sugar with 0.4 and sodium with 0.44 showed the highest heritability.

The results showed that the genetic parameters calculated in the stress environment cannot be generalized to the non-stress environment. As a result, studying the genetic characteristics of lines and hybrids under different environments is inevitable so that the estimation of gene function can be more accurate.  In both environments, the narrow-sense heritability of root yield was low but in sugar yield was moderate. So, in improving root yield, hybrid products can be used, and in sugar yield, selection can be used in long and term generations, as well as hybrid production.