ESTIMATING GENETIC PARAMETERS OF AGRONOMIC AND QUALITY TRAITS IN A DIALLEL CROSS OF SUGARBEET

Knowledge of genetic characters of agronomic and quality traits and their heritability in sugarbeet (Beta vulgaris L.), is the most important requirement for breeding high yielding varieties and good processing of this strategic crop. For this reason, fifteen hybrids from a diallel cross of six multigerm, diploid inbred lines (S4) of sugarbeet were studied to determine the combining ability, gene action, heterosis, and heritability of thirteen technological and agronomical characteristics. Six parental lines and their F1 s (twenty one genotypes) were evaluated in a randomized complete block design with four replications in Kooshkak Agricultural Research Center in 1996. Data were analyzed with method II and mix-model B of Griffing. Haymanʹs method was also used for graphical and genetical analysis. Significant differences were observed between genotypes for all traits except alkalinity. General combining ability (GCA) mean squares were significant for all traits. However, specific combining ability (SCA) mean squares were significant only for root yield, sugar percentage, impure sugar yield, recoverable sugar yield and white sugar yield. Significant ratio of GCA/SCA mean squares for sugar percentage showed that additive variance was more important. Non- sucrose components were controlled by additive gene action and had the maximum additive variance. Additive variance accounted for 54% and 75% of total genetic variance for root yield and sugar percentage, respectively. A significant negative correlation was observed between yield and technological characters. Test for validity of diallel assumptions showed epistasis effect for root yield, impure sugar yield, white sugar yield, recoverable sugar yield, potassium and mollasses sugar percentages. The frequency of dominant genes was more than the recessive genes in sugar percentage, purity, recoverable sugar percentage, white sugar and potassium percentage. Broadsense heritability varied between 0.38 for white sugar yield to 0.73 for potassium percentage. White and recoverable sugar percentage, and white and recoverable sugar yield showed similar genetic expression. Parent 6 had more recessive genes, while , parents 1, 2 and 5 had more dominant genes.