THEORETICAL COMPARISON OF RECURRENT SELECTION METHODS FOR THE IMPROVEMENT OF SELF-POLLINATED CROPS

Choosing a recurrent selection strategy depends on the resources of th e breeder and on the efficiency of the possible selection schemes. An experimental comparison is difficult and time consuming, but a theoret ical comparison may provide some guidelines. This study was conducted to compare theoretically the efficiency of different recurrent selecti on methods of improving the line value of a population, in this case, of self-pollinated crops. We considered five methods that are well ada pted to breeding autogamous species: single-doubled-haploid descent se lection with a 4-yr (SDH1) or 5-yr cycle (SDH2); selection on S-1 fami ly (S-1); selection on S-2 bulk (S2B) and on S-2 family (S2F); and two other methods-selection on half-sib progeny (HSP) and on full-sib Fam ily (FSF)- used for the improvement of per se or combining ability val ues. Analytical expressions for the corresponding expected genetic adv ances (per growing season) were derived and compared according to the values of the narrow sense heritability and the variance components in an inbred system. SDH1 always appeared as the most efficient method, SDH2 and S2F were the next best methods for realistic values of parame ters. S-1 efficiency was restricted to very high heritabilities and ad ditive variances, Gain due to higher gene fixation in the St families balanced the short cycle of S-1. As the proportion of nonadditive and environmental effects increased, SDH2 became more efficient than S2F, and S2F more efficient than S-1, S2B was always the least efficient ex cept when the possibility to reduce the between-plot environmental var iance through a larger plot size was taken into account, In that case, S2B could be more efficient than S2F for medium to low heritabilities . HSP and FSF appeared only marginally as the second or third most eff icient methods. SDH is the best method to improve autogamous crops eve n though cycle length is 5 yr; however, if haplo-diploidization techno logies are not available or are too expensive, a selection scheme base d on SI family may be the most economical method.