Delineation of interspecific epistasis on fiber quality traits in Gossypium hirsutum by ADAA analysis of intermated G. barbadense chromosome substitution lines

Genetic diversity is the foundation of any cropimprovement program, but the most cultivated Uplandcotton [Gossypium hirsutum L., 2n = 52, genomic formula2(AD)] has a very narrow gene pool resulting fromits evolutionary origin and domestication history. Cultivarsof this cotton species (G. hirsutum L.) are prized for theircombination of exceptional yield, other agronomic traits,and good fiber properties, whereas the other cultivated52-chromosome species, G. barbadense L. [2n = 52,genomic formula 2(AD)], is widely regarded as havingthe opposite attributes. It has exceptionally good fiberqualities, but generally lower yield and less desirableagronomic traits. Breeders have long aspired to combinethe best attributes of G. hirsutum and G. barbadense, buthave had limited success. F hybrids are readily created andlargely fertile, so the limited success may be due to crypticbiological and technical challenges associated with theconventional methods of interspecific introgression. Wehave developed a complementary alternative approach forintrogression based on chromosome substitution line, followedby increasingly sophisticated genetic analyses ofchromosome-derived families to describe the inheritanceand breeding values of the chromosome substitution lines.Here, we analyze fiber quality traits of progeny familiesfrom a partial diallel crossing scheme among selectedchromosome substitution lines (CS-B lines). The resultsprovide a more detailed and precise QTL dissection of fibertraits, and an opportunity to examine allelic interactioneffects between two substituted chromosomes versus onesubstituted chromosome. This approach creates newgermplasm based on pair wise combinations of quasi-isogenicchromosome substitutions. The relative geneticsimplicity of two-chromosome interactions departs significantlyfrom complex or RIL-based populations, in whichhuge numbers of loci are segregating in all 26 chromosomepairs. Data were analyzed according to the ADAA geneticmodel, which revealed significant additive, dominance, andadditive-by-additive epistasis effects on all of the fiberquality traits associated with the substituted chromosomeor chromosome arm of CS-B lines. Fiber of line 3-79, thedonor parent for the substituted chromosomes, had thehighest Upper Half Mean length (UHM), uniformity ratio,strength, elongation, and lowest micronaire among allparents and hybrids. CS-B16 and CS-B25 had significantadditive effects for all fiber traits. Assuming a uniformgenetic background of the CS-B lines, the comparativeanalysis of the double-heterozygous hybrid combinations(CS-B 9 CS-B) versus their respective single heterozygouscombinations (CS-B 9 TM-1) demonstrated that interspecific epistatic effects between the genes in thechromosomes played a major role in most of the fiberquality traits. Results showed that fiber of several hybridsincluding CS-B16 9 CS-B22Lo, CS-B16 9 CS-B25 andCS-B16 9 TM-1 had significantly greater dominanceeffects for elongation and hybrid CS-B16 9 CS-B17 hadhigher fiber strength than their parental lines. Multipleantagonistic genetic effects were also present for fiberquality traits associated with most of the substituted chromosomesand chromosome arms. Results from this studyhighlight the vital importance of epistasis in fiber qualitytraits and detected novel effects of some cryptic beneficialalleles affecting fiber quality on the 3-79 chromosomes,whose effects were not detected in the 3-79 parental lines. © Springer-Verlag (outside the USA) 2011.