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CROP BREEDING & GENETICS

QTL Analysis and Epistasis Effects Dissection of Fiber Qualities in an Elite Cotton Hybrid Grown in Second Generation

National Key Lab. of Crop Genetics and Germplasm Enhancement, Cotton Research Institute, Nanjing Agricultural Univ., Nanjing 210095, ChinaM

^* Corresponding author (cotton{at}njau.edu.cn).

The purpose of the research presented here was to explore the genetic basis of cotton (Gossypium hirsutum L.) fiber quality traits through quantitative trait locus (QTL) analysis and epistasis effects dissection, and further discuss the mechanism of heterosis. An immortalized F₂ population was developed by intercrossing Xiangzamian 2–derived recombinant inbred lines (RILs) (XZM2). Fiber quality traits were investigated in F₁ and F₂ generations of hybrid XZM2, its two parents, and the immortalized F₂ population in multiple environments in China. The low level of heterosis in XZM2 and in the immortalized F₂ population suggested a lack of dominant and dominant x dominant interaction. In general, the low correlations of genotypic heterozygosity with trait performance and midparent heterosis showed that heterozygosity was not always advantageous for performance, and they excluded overdominance as a major genetic basis of heterosis. A total of 50 QTLs for fiber quality were identified by single-locus QTL analysis. Although partial dominance and overdominance were detected, additive genetic variance was predominant. Common QTLs were detected both in the homozygous RILs and in the heterozygous immortalized F₂ populations. Additionally, single-locus heterotic effects and epistasis effects at the two-locus level were detected. Our results indicated that additive gene action was the primary mechanism responsible for genetic variability in fiber quality traits. Additionally, we found that single-locus heterotic effects and epistasis effects contributed to heterosis of fiber quality traits in XZM2.

Abbreviations: AA, additive-by-additive effects • AD, additive-by-dominance effects • DA, dominance-by-additive effects • DD, dominance-by-dominance effects • FB, fiber yellowness • FE, fiber elongation • FL, fiber length • FMAT, fiber maturity • FMIC, micronaire • FR, fiber reflectance • FS, fiber strength • FSFI, short fiber index • FUR, fiber uniformity ratio • PV, phenotypic variation • QTL, quantitative trait locus • RIL, recombinant inbred line