Advanced Backcross Quantitative Trait Locus Analysis Of Fiber Elongation In A Cross Between Gossypium Hirsutum And G. Mustelinum

In an effort to explore the secondary gene pool for the enhancement of upland cotton (Gossypium hirsutum L.) germplasm, we developed advanced-generation backcross populations by crossing G. hirsutum (PD94042) and Gossypium mustelinum Miers ex Watt (AD4-8), then backcrossing to the G. hirsutum parent for three cycles. Genome-wide mapping revealed intro-gressed alleles at an average of 13.8% of loci in each BC3F1 plant, collectively representing G. mustelinum introgression in 80.9% of the genome. Twenty-one BC3F1 plants were selfed to generate BC3F1 families of 127 to 160 plants per family (totaling 3203 plants), which were field-tested for fiber elongation and genetically mapped. One-way ANOVA detected 15 non-overlapping quantitative trail loci (QTLs) distributed over 12 chromosomes. Individual loci explained from 10.0 to 25.24% of phenotypic variance. Nine stringent QTLs were detected in one-way ANOVAs and composite interval mapping; two of the nine QTLs explained more than 20% of variance and one was detected in four different families simultaneously with similar additive effects. Although the G. mustelinum parent does not produce spinnable fiber, G. mustelinum alleles contributed to increased fiber elongation for three of the nine stringent QTLs and five of the 15 total QTLs. Two-way ANOVA detected significant (P < 0.001) among-family genotype effects and genotype x family interactions, suggesting that the phenotypic effects of some introgressed chromosomal segments are dependent on the existence of other chromosomal segments. Gossypium mustelinum alleles that contribute to increased fiber elongation are of great interest to be further exploited in cotton breeding.