Load of deleterious genes and stability of performance in maize

The objective of the present study was to assess the effect of the load of deleterious genes on the potential yield per plant and stability of perform ance of maize (Zea mays L.) inbreds and hybrids grown in the isolation envi ronment. The load of deleterious genes was estimated indirectly by (1) the mean yield per plant, (2) the coefficient of variation (CV) of single-plant yields, (3) the formula of the best-parent heterosis, and (4) the departur e from normality of the frequency yield distributions. The materials used w ere the inbreds B73 and Mo17 and their hybrid, as well as two sets of S lin es (named A and B) and their hybrids. The latter inbreds and hybrids were d erived through honeycomb selection starting from the F-2 of the commercial single-cross hybrid PR 3183. The results showed that recycled A and B S-6 l ines had 3.7 to 8.3 times greater potential yield per plant compared with B 73 and Mo17, 1.6 to 2.3 times lon;er CV values, and more normal yield distr ibutions. AxB hybrids had average potential yield per plant 1113 g, CV 30%, and best-parent heterosis 196%, compared with the values of the B73xMo17 h ybrid that were 449 g: 38% CV, and 562% best-parent heterosis respectively. The main effect of efficient recycling is the replacement of deleterious g enes by favorable additive alleles that increase the yield and stability of inbreds, and transmit their favorable effects to the hybrids. The general conclusion was that the best way to eliminate deleterious genes and improve inbred line and hybrid performance, is selection in the isolation environm ent for high potential yield per plant on the basis of the mean yield, and for stability of performance on the basis of reduced CV. Selection for comb ining ability early in the program leads to the preservation of deleterious genes on account of evaluation under heterozygosity.