Allelic changes in bread wheat cultivars were associated with long-term wheat trait improvements

Abstract

Genetic impacts under selective breeding of agricultural crops have been frequently investigated with molecular tools, but inadequate attention has been paid to assess genetic changes under longterm genetic improvement of plant traits. Here we analyzed allelic changes with respect to wheat trait improvement in 78 Canadian hard red spring wheat cultivars released from 1845 to 2004 and screened with 370 mapped SSR markers. The improvements in quality, maturity, yield, disease, stem rust, leaf rust, sawfly resistance, and agronomy were considered. A total of 154 (out of 370) loci with significant allelic changes across 21 chromosomes were detected in the 78 wheat cultivars separated into improved versus non-improved groups for eight traits. The number of significant loci for improving a trait ranged from four for quality to 68 for yield and averaged 35. Many more loci with significant allelic reduction for improving a trait were detected than those with significant allelic increase. Selection for early maturity introduced more alleles, but improving the other traits purged more alleles. Significantly lower numbers of unique alleles were found in the cultivars with improved traits. The distributions of unique allele counts also varied greatly across the 21 chromosomes with respect to trait improvement. Significant SSR variation between two cultivar groups was observed for improvement in seven traits, but not in stem rust. The proportional SSR variation residing between two groups ranged from 0.014 to 0.118. The proportional SSR variations within the improved cultivar groups consistently were much lower than those within the non-improved groups. These findings clearly demonstrate the association between allelic changes and wheat trait improvements and are useful for understanding the genetic modification of the wheat genome by long-term wheat breeding.

Genetic diversity reduction in improved durum wheat cultivars of Morocco as revealed by microsatellite markers

“…The proportional SSR variations within the improved 1990s and 2000s temporal groups were consistently far lower than those within the older cultivars developed before the 1990s. These findings are clearly in line with observations by Fu and Somers, (2011) which demonstrate the association between allelic changes and wheat trait improvements, and are useful for understanding the genetic modification of the wheat genome by long-term wheat breeding. The exotic durum lines currently being deployed in breeding programs will enhance the genetic base of the cultivar in Morocco.…”

Genetic Differentiation in Response to Selection for Water-Soluble Carbohydrate Content in Perennial Ryegrass (Lolium perenne L.)

“…Changes in allele frequencies during selection are commonly associated with decreases in allelic richness [18]. Loss of alleles, along with increases in the homozygosity of the remaining alleles, was observed in the GRASP selection experiment for most of the markers showing a significant LOSITAN selection effect.…”

“…Other workers have also demonstrated that SSR markers can be less neutral than might be expected during selection experiments. In wheat, long-term improvement (from 1845 to 2004) of a range of quality and productivity traits resulted in significant allelic changes in nearly half the SSRs tested [18]. In maize, there were changes in the allele frequencies of SSRs during selection; some markers were flanking known QTL but others were spread across the genome [19].…”

A study of genetic diversity among Indian bread wheat (Triticum aestivum L.) cultivars released during last 100 years

“…This has been possible due to modifications of plant genomes through selective breeding or due to directional and focused selections of target genes/QTLs (Allard 1999). This selection is believed to increase the (Zeng and Cockerham 1990;Walsh 2005;Fu and Somers 2011). However, the details of the effects of selective breeding on plant genome remains poorly understood and several questions remain unanswered (Fu 2006;Fu et al 2010;Fu and Somers 2011).…”