Genetic dissection of the relationships between grain yield components by genome-wide association mapping in a collection of tetraploid wheats

Increasing grain yield potential in wheat has been a major target of most breeding programs. Genetic advance has been frequently hindered by negative correlations among yield components that have been often observed in segregant populations and germplasm collections. A tetraploid wheat collection was evaluated in seven environments and genotyped with a 90K SNP assay to identify major and stable quantitative trait loci (QTL) for grain yield per spike (GYS), kernel number per spike (KNS) and thousand-kernel weight (TKW), and to analyse the genetic relationships between the yield components at QTL level. The genome-wide association analysis detected eight, eleven and ten QTL for KNS, TKW and GYS, respectively, significant in at least three environments or two environments and the mean across environments. Most of the QTL for TKW and KNS were found located in different marker intervals, indicating that they are genetically controlled independently by each other. Out of eight KNS QTL, three were associated to significant increases of GYS, while the increased grain number of five additional QTL was completely or partially compensated by decreases in grain weight, thus producing no or reduced effects on GYS. Similarly, four consistent and five suggestive TKW QTL resulted in visible increase of GYS, while seven additional QTL were associated to reduced effects in grain number and no effects on GYS. Our results showed that QTL analysis for detecting TKW or KNS alleles useful for improving grain yield potential should consider the pleiotropic effects of the QTL or the association to other QTLs.提升小麦籽粒产量潜力始终是多数育种项目的核心目标。然而，产量组分间普遍存在的负向关联，常阻碍遗传改良进程，这类现象在分离群体与种质资源库中已被频繁观测到。本研究针对一套四倍体小麦（tetraploid wheat）种质资源库，在7个环境下开展表型鉴定，并采用90K单核苷酸多态性（Single Nucleotide Polymorphism, SNP）分型检测进行基因分型，旨在筛选调控每穗粒数（kernel number per spike, KNS）、千粒重（thousand-kernel weight, TKW）及每穗籽粒产量（grain yield per spike, GYS）的主效且稳定的数量性状位点（Quantitative Trait Locus, QTL），同时从QTL层面解析产量组分间的遗传关联。全基因组关联分析共检测到与KNS、TKW、GYS分别相关的8个、11个和10个QTL，上述位点均至少在3个环境、2个环境及环境均值中表现出显著效应。调控TKW与KNS的多数QTL位于不同的标记区间，提示二者的遗传调控机制相互独立。在8个KNS相关QTL中，3个可显著提升GYS；而另外5个QTL所增加的籽粒数，会因籽粒重量降低而被完全或部分代偿，因此对GYS未产生显著影响或仅带来微弱增益。类似地，4个稳定QTL与5个提示性QTL可提升TKW，进而使GYS显著增加；另有7个QTL则会降低籽粒数，且对GYS无明显效应。本研究结果表明，若要通过筛选TKW或KNS相关等位基因以提升小麦籽粒产量潜力，开展QTL分析时需充分考虑QTL的多效性，或是其与其他QTL的协同关联效应。