A QTL Analysis of White Clover Seed Production

Abstract

White clover (Trifolium repens L.) exhibits complex inheritance of seed production potential. Genome maps allow plant breeders to dissect the genetic control of complex traits into discreet factors with Mendelian inheritance, each of which is called a quantitative trait locus (QTL). A pair‐cross between two highly heterozygous white clover genotypes created an F1 mapping population (n = 182) used to investigate the genetic control of seed yield (SY) and three component traits: inflorescence density (ID), yield per inflorescence (YI), and thousand‐seed weight (TSW). Analysis of 3 yr of field data from a replicated trial in the primary seed production region of New Zealand indicated no strong correlations among the component traits. The ANOVA indicated significant genotype, year, and genotype × year effects for SY, ID, and YI; and genotype and genotype × year effects for TSW. Using genotype data for 209 microsatellite loci in the allotetraploid genome, the multiple QTL model analysis resulted in the discovery of 23 QTLs related to seed production in white clover. Both parent plants harbored beneficial alleles for SY and the three component traits. A region of the genome at the distal end of linkage group D2 was implicated in a number of traits related to seed production, and was strongly implicated in the control of YI and SY. The central region of linkage group C2 was strongly implicated in the control of ID and SY. Parent trait values were similar for ID, yet the population was highly variable for this trait and segregated for multiple QTLs, indicating the utility of this experimental design for QTL discovery in crosses among heterozygous individuals with similar phenotypes. Most QTLs were dominant, suggesting suitability for marker‐assisted selection (MAS) in white clover.