Chromosome regions between centromeres and proximal crossovers are the physical sites of major effect loci for yield in potato: Genetic analysis employing meiotic mutants

Abstract

Meiotic mutant (2n) gametes formed by first-division restitution without crossover (FDR-NCO) are expected to be superior to FDR with crossover (FDR- CO) because they transmit to the progeny, without disruption by recombination, almost 100% of the parental genotype. FDR-CO transfers ≃80% of the parental heterozygosity and a large fraction of the epistatic interactions. Another genetic expectation associated with both FDR gametes is their equivalence for the phenotypic expression of traits controlled by genes residing between centromeres and proximal crossover sites. This set of unique cytogenetic features of FDR mutants was employed here as a tool to infer physical location of quantitative trait loci controlling total tuber yield (TTY) in potato. Two assays were conducted to verify the superiority of FDR- NCO over FDR-CO gametes for TTY by using progenies from 4x-2x factorial crosses. Male clones were 2n-pollen producers by either FDR-CO or FDR-NCO mechanisms. Compared with the 4x parents, TTY of the progenies ranged from 41% to 175% (i.e., high-parent heterosis). However, no significant TTY differences were observed between FDR-CO and FDR-NCO families. In addition, the size of variance components of males was smaller than females and near zero. Our results reinforce the hypothesis that genes controlling yielding ability have a predominant physical location between centromeres and proximal chiasmata. Quantitative trait loci in chromosome regions with reduced levels of recombination may provide a partial explanation for the slow progress in increasing TTY through conventional 4x-4x crosses and for the often high degree of heterosis obtained by introgressing genetic diversity via 4x-2x crosses in potato.