ANALYSIS OF THE DIALLEL MATING DESIGN FOR MAIZE INBRED LINES

One of the assumptions required to estimate genetic parameters by use of the diallel mating design is that the genes in the parents are inde pendently distributed. The objective of this study was to test the val idity of this assumption. Diallel experiments including a fixed sample and a random sample of parents were conducted in maize (Zea mays L.). For the fixed sample, an eight-parent diallel among selected inbred l ines was produced (original diallel). Ninety-six unselected inbred lin es derived from a population, developed by intermating for five genera tions crosses of the original diallel, were used to produce 12 eight-p arent diallels (random diallels). Diallels were evaluated in a replica tion-within-sets randomized incomplete block design in six environment s. Estimates of additive (sigma(A)(2)) and dominance (sigma(D)(2)) var iances from the pooled random diallels were significantly different fr om estimates of sigma(A)(2) and sigma(D)(2) in the original diallel fo r about half the traits. For six traits, the average level of dominanc e was overestimated in the original diallel relative to the pooled ran dom diallels. The estimated average level of dominance for grain yield was two times greater in the original diallel than in the pooled rand om diallels. Estimates of sigma(A)(2) seemed to be affected more than estimates of sigma(D)(2) by repulsion phase linkages. Non-independent distribution of genes causes differences in sigma(A)(2) and sigma(D)(2 ). The diallel mating design should only be used to estimate genetic p arameters when the parents of the diallel have been randomly selected from a population in linkage equilibrium.