COMPARISON OF SELECTION STRATEGIES AND OPTIMIZATION CRITERIA IN HYBRID MAIZE BREEDING WITH DOUBLED HAPLOIDS

摘要

In hybrid maize (Zea mays L.) breeding, doubled haploids (DH) are increasingly replacing conventionally developed inbred lines. We considered two breeding schemes with selection based on the evaluation of testcross progenies of DH lines in two stages (DHTC) and of S, families in the first stage and of DH lines within S, families in the second stage (S1TC-DHTC). For both breeding schemes, we considered different selection strategies with or without optimum index at second stage and uniform or variable sizes of crosses and S, families. Our Objectives were to (1) determine the optimum number of test environments as well as the optimum number and sizes of parental crosses and S, families for various variance component ratios and (2) identify the Superior selection strategy for each breeding scheme with respect to the selection gain (Delta G) and the probability to Select superior genotypes (P(q)) as well as to minimize their standard deviation. Breeding scheme S1TC-DHTC had larger Delta G and P(q) but a higher standard deviation of Delta G than DHTC. For breeding scheme S1TC-DHTC, strategies with selection among all DH lines led to larger progress than the strategy with sequential selection among and within crosses and S-1 families. The results for both optimization criteria in strategies with variable numbers Of S, families and DH lines within crosses and S, families were larger than with uniform numbers. With decreasing contributions of the genetic variance, the number of test locations Should be increased at the expense of the test candidates in both breeding schemes. Further, Our Study showed that a lower standard deviation of the expected Values for both optimization criteria were feasible Without a significant loss in Delta G Or P(q) with an increased number of test locations.