No abstract

The improvement of cotton fiber quality has become more important because of changes in spinning technology. Stable quantitative trait loci (QTLs) for fiber quality will enable molecular marker-assisted selection to improve fiber quality of future cotton cultivars. A simple sequence repeat (SSR) genetic linkage map consisting of 156 loci covering 1,024.4 cM was constructed using a series of recombinant inbred lines (RIL) developed from an F 2 population of an Upland cotton (Gossypium hirsutum L.) cross 7235 · TM-1. Phenotypic data were collected at Nanjing and Guanyun County in 2002 and 2003 for 5 fiber quality and 6 yield traits. We found 25 major QTLs (LOD ‡3.0) and 28 putative QTLs (2.0 < LOD < 3.0) for fiber quality and yield components in two or four environments independently. Among the 25 QTLs with LOD ‡ 3, we found 4 QTLs with large effects on fiber quality and 7 QTLs with large effects on yield components. The most important chromosome D8 in the present study was densely populated with markers and QTLs, in which 36 SSR loci within a chromosomal region of 72.7 cM and 9 QTLs for 8 traits were detected.

Root-knot nematodes Meloidogyne incognita (Kofoid and White) can cause severe yield loss in cotton (Gossypium hirsutum L.). The objectives of this study were to determine the inheritance and genomic location of genes conferring root-knot nematode resistance in M-120 RNR, a highly resistant G. hirsutum line with the Auburn 623 RNR source of resistance. Utilizing two interspecific F(2) populations developed from the same M-120 RNR by Gossypium barbadense (cv. Pima S-6) cross, genome-wide scanning with RFLP markers revealed a marker on Chromosome 7 and two on Chromosome 11 showing significant association with the resistant phenotype. The association was confirmed using SSR markers with the detection of a minor and a major dominant QTL on Chromosome 7 and 11, respectively. Combined across the two populations, the major QTL on Chromosome 11 Mi-C11 had a LOD score of 19.21 (9.69 and 9.61 for Pop1 and Pop2, respectively) and accounted for 63.7% (52.6 and 65.56% for Pop1 and Pop2, respectively) of the total phenotypic variation. The minor QTL locus on Chromosome 7 Mi ( 1 ) -C07 had a LOD score of 3.48 and accounted for 7.7% of the total phenotypic variation in the combined dataset but was detected in only one population. The allele from the M-120 RNR parent contributed to increased resistance in the Mi-C11 locus, but surprisingly, the Pima S-6 allele contributed to increased resistance in the Mi-C07 locus. The M-120 RNR allele in the Mi-C11 locus, derived from the Auburn 623 RNR, is likely to have originated from the Clevewilt 6 cultivar. Results from this study indicated that the SSR marker CIR316 may replace the laborious greenhouse screening in breeding programs to identify genotypes resistant to M. incognita.

Most agronomic traits of cotton (Gossypium hirsutum L.) are quantitatively inherited and affected by environment. The importance of epistasis as the genetic basis for complex traits has been reported in many crops. In this study, a linkage map was constructed by means of a recombinant inbred line (RIL) population derived from 72353TM-1. Main effects, epistatic effects, and environmental interaction effects of quantitative trait loci (QTLs) controlling fiber and yield component traits were determined by mixed linear model based QTL mapping in two to four environments. Sixteen main effect QTLs for 12 traits and 19 digenic interaction QTLs for 12 traits were detected. The amount of variation explained by the QTLs of main effect was larger than the QTLs involved in epistatic interactions. Among seven QTLs having QTL 3 Environment (QE) interaction effects, five produced significant additive effects and two did not, but only one interaction showed significant additive 3 additive 3 environment (AAE) interaction effects. Some QTLs with large effects detected in specific environments could be associated with environmental response elements.