Understanding the Genetic Basis of Spike Fertility to Improve Grain Number, Harvest Index, and Grain Yield in Wheat Under High Temperature Stress Environments

Abstract

Moderate heat stress accompanied by short episodes of extreme heat during the post-anthesis stage is common in most US wheat growing areas and causes substantial yield losses. Sink strength (grain number) is a key yield limiting factor in modern wheat varieties. Increasing spike fertility (SF) and improving the partitioning of assimilates can optimize sink strength which is essential to improve wheat yield potential under a hot and humid environment. A genome-wide association study (GWAS) allows identification of novel quantitative trait loci (QTLs) associated with SF and other partitioning traits that can assist in marker assisted breeding. In this study, GWAS was performed on a soft wheat association mapping panel (SWAMP) comprised of 236 elite lines using 27,466 single nucleotide polymorphisms (SNPs). The panel was phenotyped in two heat stress locations over 3 years. GWAS identified 109 significant marker-trait associations (MTAs) (p ≤ 9.99 x 10−5) related to eight phenotypic traits including SF (a major component of grain number) and spike harvest index (SHI, a major component of grain weight). MTAs detected on chromosomes 1B, 3A, 3B, and 5A were associated with multiple traits and are potentially important targets for selection. More than half of the significant MTAs (60 out of 109) were found in genes encoding different types of proteins related to metabolism, disease, and abiotic stress including heat stress. These MTAs could be potential targets for further validation study and may be used in marker-assisted breeding for improving wheat grain yield under post-anthesis heat stress conditions. This is the first study to identify novel QTLs associated with SF and SHI which represent the major components of grain number and grain weight, respectively, in wheat.

Genetic dissection of heat-responsive physiological traits to improve adaptation and increase yield potential in soft winter wheat

“…S3A_ 609909640 was associated with SPAD and CT and had a negative allelic effect on CT and a positive allelic effect on SPAD (Table 3). Interestingly, we detected five significant MTAs on chromosome 3A (S3A_12554694 and S3A_12554700), 5A (S5A_590056740), 6B (S6B_ 149148874), and 7D (S7D_18808932) for PTs, which were associated with GY and other yield related traits in our previous study [10]. Seventy-five out of 500 MTAs were expressed in multiple environments and were considered as stable MTAs (Table 4).…”

“…Population structure analysis of the SWAMP was performed in our previous study using 27,466 high quality GBS-derived SNP markers (minor allele frequency; MAF > 0.05 and missing data < 20%) [10]. Briefly, these SNP markers were distributed throughout the A (9958, 36%), B (9,968,~36%) and D (6,954,~25%) genomes.…”

“…LD was computed using the "LDcorSV" package in R to determine the approximate marker density required for GWAS [10]. The LD decay below the line of critical value (r 2 = 0.2) was estimated at 1182, 1920 and 2916 bp for ranges of 30,000, 40,000, and 50,000 bp, respectively, across the whole genome (Additional file 7).…”

“…Genetic improvement of yield under HT via direct selection is hindered by the quantitative nature of grain yield and large genotype by environment interaction. Optimizing carbohydrate partitioning using traits such as spike fertility (SF), internode partitioning, and spike organ partitioning is essential to overcome sink limitations and increase harvest index (HI) [10,11]. Although higher grain yield potential of wheat has been largely a result of increased HI under HT, increased biomass and crop adaptation are equally important.…”

Genetic characterization and deployment of a major gene for grain yield on chromosome arm 1BS in winter wheat

“…To maximize the grain yield of the winter wheat cultivars by conventional plant breeding and biotechnology is vital to wheat improvement of the most important economic trait (Rajaram 2005;Ray et al 2013). Numerous quantitative trait loci (QTLs) or genomic regions have been mapped for yield traits by genetic analyses on segregated biparental populations, such as recombinant inbred lines (RILs) and doubled haploid (DH) lines, as well as association analyses on germplasm from landraces to modern varieties and breeding lines (Zhang et al 2010;Bennett et al 2012;Liu et al 2012;Mir et al 2012;Bordes et al 2014;Cui et al 2014;Zanke et al 2014a, b;Gao et al 2015;Lopes et al 2015;Guo et al 2016;Zhai et al 2016;Assanga et al 2017;Liu et al 2018;Ma et al 2018;Pradhan et al 2019). Clustered QTLs were also found on the short arm of chromosome 1B, where pleiotropic effects on yield per plant, spikes per plant, spike length, grains per spike, thousand grain weight, and dry matter were observed (Quarrie et al 2005;Wang et al 2009;Sukumaran et al 2015;Zhai et al 2016).…”