Mapping quantitative trait loci for bread making quality and agronomic traits in winter wheat under different soil moisture levels
El-Feki, Walid Mohamed Roushdy
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Drought is a major abiotic stress that affects wheat (Triticum aestivum L.) production in many regions of the world. Identifying quantitative trait loci (QTL) controlling important traits such as quality and yield components in winter wheat under reduced soil moisture may help develop cultivars improved for those traits. Our main objective was to identify QTL affecting quality and agronomic traits under fully irrigated and reduced soil moisture conditions. A population of 185 doubled haploid (DH) lines derived from a cross between CO940610 and 'Platte' was grown in replicated field trials in Fort Collins and Greeley, Colorado, USA in 2007-08 and 2008-09. At each location, two side-by-side trials were planted; one trial was grown under moderate moisture stress ("dry") and one under fully irrigated ("wet") conditions, for a total of four environments. Fifteen quality traits were evaluated under both irrigation treatments: mixograph parameters, single kernel characteristics, polyphenol oxidase activity, and flour color. Seventeen agronomic traits comprising phenological parameters, morphological traits, yield and yield components, pre-harvest sprouting, normalized difference vegetation index, and drought susceptibility index were evaluated. Moderate to high heritability estimates were observed for most of the quality traits, indicating that a large part of the expression of these traits is genetically controlled. Heritability of yield-related traits was low to moderate indicating the greater effect of environmental conditions on these traits. Moisture stress affected most of the quality and agronomic traits. Grain yield was reduced by 795.8 kg ha-1 (21.4%) at Fort Collins, and by 704.0 kg ha-1 (18.7%) at Greeley in the dry treatments. All kernel characteristics (kernel weight, kernel diameter, and kernel hardness), test weight, and grain protein concentration had higher mean values (P<0.05) under limited irrigation compared to the full irrigation treatments in both years. Thirty-one linkage groups spanning 2,083 cM and covering the 21 chromosomes were constructed from 221 microsatellite, diversity array technology, sequence-tagged-site, and protein markers. The composite interval mapping option of QTL Cartographer software was used in a genome-wide scan to estimate the location and effect of QTL associated with the evaluated traits. A total of 251 QTL were identified on 25 linkage groups representing 19 chromosomes. Individually, the QTL explained from 3.7 to 68.4% of the phenotypic variation, and when combined in multiple-locus models for a given trait and environment, they accounted for up to 73.8% of the phenotypic variation. Regions on chromosomes 1A, 2B, 6A, 7B, and 7D contained QTL for multiple traits. The QTL clusters on linkage groups 2B.1 and 7D.2 seem likely to coincide with the photoperiod response gene Ppd-B1 and vernalization locus Vrn-D3. Genomic regions on chromosomes 1AL, 1BL, 1DL, and 7BS contained QTLs for multiple bread making quality traits. The 1AL, 1BL, and 1DL QTL most likely indicate the effects of the Glu-A1, Glu-B1, and Glu-D1 loci. The 7BS QTL region may reflect a novel quality locus or loci. The co-localization of QTL for multiple quality traits suggests that the effects may be due to pleiotropy. Distribution of QTL for quality traits was relatively balanced between irrigation treatments; 67 QTL (54.7%) were detected under full irrigation and 56 QTL (45.5%) were identified under limited irrigation. For agronomic traits, 64 QTL (50.0%) were detected under full irrigation and 62 (48.4%) under limited irrigation. In general, the same QTL for most of the quality and agronomic traits were detected in both soil moisture levels. This indicates that the same set of genes controls these traits regardless of the degree of moisture, at least within the range of moisture sampled in this study. This finding is convenient for wheat breeders, who do not need to modify their selection schemes based on the moisture stress of target environments. Colocalized QTL for grain yield in the dry treatment and drought susceptibility index were identified on chromosomes 5B and 7B at Greeley. These regions deserve additional attention to determine the basis of these drought-adaptive traits. After validation, the identified QTL may facilitate marker assisted breeding strategies or high resolution mapping leading to map-based cloning for the benefit of winter wheat breeding programs.