FAMILY PER SE RESPONSE TO SELLING AND SELECTION IN MAIZE BASED ON TESTCROSS PERFORMANCE - A SIMULATION STUDY

Determining the appropriate number of lines to retain across generatio ns during inbred line development in maize (Zea mays L.) is crucial fo r efficient allocation of resources. Although the primary interest dur ing line development is performance of testcross progeny, genetic info rmation on Lines per se adds to basic understanding of the genetic res ponse of maize to inbreeding and selection. The objective of this rese arch was to compare genetic responses of families per se to varying se lection intensities across early generations of selfing in maize. A FO RTRAN program simulating a stochastic genetic model with 30, 40, and 3 0% additive, dominant, and over-dominant loci, respectively, and a ran dom environmental effect was used to compare varying combinations of s election intensities across generations. In the simulation, individual plants were evaluated on the basis of testcross progeny performance u sing multiple testers and environments. Individual plants correspondin g to top performing testcross progenies were selected as parents for s uccessive generations. Within each generation, phenotypic and genetic means of families per se increased with increased selection intensitie s. Response to selection in any given generation was not dependent on selection intensity used in the previous generation. Percent homozygos ity and frequency of superior alleles increased as selection pressure intensified. Few original plants contributed to retained families with only approximately 5% of S-0 plants appearing in pedigrees of selecte d S-4 families. Retaining few but larger families resulted in increase d genetic values of families per se, compared with saving a large numb er of smaller families, even though selection was based on testcross p erformance.