Quantitative trait loci for water-soluble carbohydrates and associations with agronomic traits in wheat

Several environmental factors including drought and disease can reduce leaf area and photosynthesis during grain-filling to decrease grain yield and kernel weight of cereal crops. Water-soluble carbohydrates (WSC) accumulated around anthesis can be mobilised to assist in filling of developing grains when post-anthesis assimilation is low. Cultivar differences support opportunities to select for high WSC but little is known of the extent or nature of genetic control for this trait in wheat. Three wheat mapping populations (Cranbrook/Halberd, Sunco/Tasman, and CD87/Katepwa) were phenotyped for WSC and other agronomic traits across multiple environments. The range for WSC concentration (WSC-C) was large among progeny contributing to moderate-to-high narrow-sense heritabilities within environments (h(2) = 0.51-0.77). Modest genotype x environment interaction reduced the correlation of genotype means across environments (r(p) = 0.37-0.78, P < 0.01) to reduce heritability on a line-mean (h(2) = 0.55-0.87) basis. Transgressive segregation was large and genetic control complex, with 7-16 QTLs being identified for WSC-C in each population. Heritability was smaller (h(2) = 0.32-0.54) for WSC mass per unit area (WSC-A), reflecting large genotype x environment interaction and residual variance with estimating anthesis biomass. Fewer significant QTLs (4-8) were identified for this trait in each population, while sizes of individual genetic effects varied between populations but were repeatable across environments. Several genomic regions were common across populations including those associated with plant height (e.g. Rht-B1) and/or anthesis date (e.g. Ppd1). Genotypes with high WSC-C were commonly shorter,flowered earlier, and produced significantly (P < 0.01) fewer tillers than those of low WSC-C. This resulted in similar yields, lower final biomass, and fewer grains per m(2), but greater dry weight partitioning to grain, kernel weight, and less grain screenings in high compared with low WSC-C genotypes. By contrast, lines high for WSC-A produced more fertile tillers associated with similar or greater anthesis and maturity biomass, grain number, and yield, yet similar kernel weight or size compared with genotypes with low WSC-A. The data support an important role for WSC-A in assuring stable yield and grain size. However, the small effects of many independent WSC QTLs may limit their direct use for marker-aided selection in breeding programs. We suggest using molecular markers to enrich populations for favourable height and anthesis date alleles before the more costly phenotypic selection among partially inbred families for greater WSC-A.