Effects of linkage and Epistasis on intergeneration correlations in self-pollinated species
In breeding for self-pollinated crop cultivars, early generation testing and selection (EGT) is desirable because it allows for more resources to test superior lines and helps avoid the loss of desirable alleles that would occur if EGT is delayed. However, high intergeneration correlations (IGCs) are required for effective EGT. This study is conducted to determine the effects of linkage and epistasis on IGCs. The covariance between genetic means of lines at early and late selfing generations with both linkage and epistasis is derived. Intergeneration correlations are calculated for different levels of coupling and repulsion linkages and for 10 nonepistatic and epistatic models. Intergeneration correlations are moderate to high in the presence of only additive and dominance effects at unlinked and nonepistatic loci but can be very low (<0.2) in tight repulsion linkages or some allelic and nonallelic effects. Epistasis may mimic or counteract the effects of linkage on changes in IGCs. Thus linkage or epistasis can be an important cause of low IGCs and such genetic causes cannot be changed through testing of more environments. This study points out the need to consider both genetic and nongenetic causes of low IGCs when evaluating the efficiency of EGT in self-pollinated species.