Effect of recombination in the parent populations on the means and combining ability variances in hybrid populations of maize (Zea mays L.)

Abstract

Recombination of selected genotypes plays a key role in plant breeding for generating new base populations. We investigated the influence of recombination in two parent populations on the means and combining ability variances of their hybrid population by (1) quantitative genetic theory and (2) experiments with maize. The two parent populations were founded by four early flint and four early dent inbred lines, respectively. Each population was studied in three generations: Syn-0, the four inbred lines themselves; Syn*-1, the six intrapool single crosses (SC); and Syn*-2, the three intrapool double crosses (DC). Four interpool hybrid populations were created: (1) all 16 SC and (2) all 36 DC were produced from generations Syn-0 and Syn*-1, respectively, (3) 168 biparental progenies (BIP) of type flint x dent (female x male), and (4) 168 BIP of type dent x flint were produced according to NC-design I with randomly sampled plants of generation Syn*-2. The half-sib and full-sib families obtained in this manner were evaluated for grain yield, dry matter concentration and plant height. According to theoretical results, differences in the population means of these hybrid populations indicate the presence of various types of epistasis. Changes in combining ability variances from SC to DC reflect different levels of parental inbreeding (F = 1 vs F = 0), whereas changes from DC to BIP only reflect the effects of recombination and are attributable to covariances between additive and dominance effects caused by linkage disequilibrium in the Syn-0 generations. The experimental results showed a significant decline in yield from DC to BIP due to a loss of gene combinations with favourable epistatic effects. Estimates of sigma(2)(GCA) attributable to flint or dent lines decreased or remained unchanged from SC to DC, but generally increased in the BIP populations. The consequences of these trends for developing improved interpool hybrids are discussed.

Unlocking the Genetic Diversity of Maize Landraces with Doubled Haploids Opens New Avenues for Breeding

“…Actually, in agreement with a high degree of recombination within the open-pollinated landraces, the rapid decrease of LD observed in the DH lines derived from landraces in comparison to the EF lines (Table 4) supports a high number of new haplotypes within the DH lines. While the introgression of new haplotypes in elite material disrupts gene combinations with positive epistatic effects [45], it also breaks negative trait associations due to linkage [46] and releases new genotypic variation. Further, the rapid decay of LD together with high genotypic variances and absence of population structure within the populations of DH lines derived from landraces enables high resolution association mapping in such germplasm.…”

Effect of recombination in the maize breeding population with exotic germplasm on the yield stability

“…Different number of generations of intermating, depending on recurrent selection method and the selection intensity, are interposed so that linkage equilibrium is at least partly restored before initiating the next selection cycle (Melchinger et al 2003). Winkler et al (2003) noted that genetic linkage is broken down more effectively by randomly mating an F 2 population for a small number of generations.…”

Quantitative Trait Loci for Grain Yield and Adaptation of Durum Wheat (Triticum durum Desf.) Across a Wide Range of Water Availability

“…Overall, negative epistatic effects prevailed in the RILs in comparison to the average performance of the two parental cvs. The presence of negative epistatic interactions in the nonparental genotypes is a common feature for GY, particularly in mapping populations derived from inbred elite materials (Li et al 1997Luo et al 2001;Melchinger et al 2003). In the Kofa 3 Svevo population, the two major QTL for GY and PH on chrs.…”