In order to study the genetics of resistance to Cercospora leaf spot (CLS) and bolting in sugar beet, nine parental lines and their Fi hybrids were formed in a diallel cross pattern. The genotype main effect plus genotype X environment interaction (GGE) biplot and Griffing's method II diallel scheme were used for analysis. Combining ability, gene action and heterosis were estimated for these two important traits. The biplot displayed the most important entry by tester patterns of the data and allow^ed the information to be extracted visually. Using this technique, different genetic aspects were clearly visualized. The biplot analysis indicated that the first two principal components explained 74% (59% and 15% by PCI and PC2, respectively), and 75% (42.36% and 32.64% by PCI and PC2, respectively) of the variation for resistance to CLS and bolting, respectively. Based on GGE biplot presentation and Griffing's diallel Genotype 436 presented the largest positive GCA, indicating contribution towards susceptibility. Also 7112-36 and RR607 showed the largest negative GCA for bolting percentage, indicating contribution towards resistance to bolting, and 436 presented the largest positive GCA, indicating contribution towards susceptibility to bolting. The results indicated tbat the SB-FIROZ x 261 Fi hybrid showing negative heterosis for bolting percentage, so these genotypes possess at least some different resistance genes, which were expressed in the hybrids and led to the observed effects. Results were coherently presented by biplot and Griffing's diallel analyses. However, the GGE biplot method is recommended because of its powerful capability to visualize the results of entry by tester (diallel) data.
AdditionalAbbreviations: ATC = Average tester coordinate, CLS = Cercospora leaf spot, GCA = General combining ability, GGE = Genotype main effect plus genotype x environment interaction, MPH = Mid-parent heterosis, RCBD = Randomized complete block design, SCA = Specific combining ability, SREG = Site regression.