Quantitative trait loci associated with lodging, stem strength, yield, and other important agronomic traits in dry field peas
Smitchger, Jamin A.
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In pea, lodging changes canopy structure, increases disease pressure, reduces yield, and reduces harvest efficiency. In order to discover the quantitative trait loci (QTLs) influencing lodging resistance and other important agronomic traits in pea, a recombinant inbred line (RIL) population was created from a relatively wide cross between the commercial variety Delta and an unnamed pea variety. The RIL population was grown for 6 site-years in Bozeman and Moccasin, MT, USA, and phenotypic data was collected for 22 quantitative morphological traits and seven categorical traits which were thought to be associated with lodging resistance. Genotypic data was derived from genotype by sequencing, microsattelite markers, and cleaved amplified sequence tagged sites. QTL analysis identified a total of 135 putative QTLs for the 22 traits examined in the study. There were 12 specific regions where 115 QTLs co-located, indicating that as few as 12 genes may be responsible for multiple pleiotropic effects. Ten QTLs were found for lodging resistance. Due to the large amount of phenotypic data collected, the putative mechanism of lodging resistance was determined for each QTL. In nearly every case, lodging resistance was associated with reduced plant height, a change in tendril number, or increased stem strength. This conclusion was supported by mathematical modeling. Branch number, which determines the number of tendrils per plant, was also positively associated with lodging resistance during all site-years, indicating that increasing tendril number also increases lodging resistance. Yield was controlled by eight QTLs. All QTLs for yield had pleiotropic effects on lodging resistance and yield per plant. Seed size was not correlated with yield, and a model was created which explained why no association between yield and seed size was found. The pleiotropic effects and utility of the QTLs discovered in this study are discussed. The results of this study further refine the ideotype for pea, and can be used for marker assisted selection in this crop.