ADVANCED-BACKCROSS MAPPING OF COTTON QTLS

¹ Department of Soil and Crop Sciences, Texas A&M University, College Station, TX 77843-2474.

² Department of Crop and Soil Science, University of Georgia, Athens GA 30602

³ Universite catholique de Louvain, Croix du Sud 2/10, 1348 Louvain-la-Neuve, Belgium.

Genetic mapping and extraction of valuable quantitative traits from exotic germplasm often are hampered by the presence of many undesirable and deleterious alien alleles in the early generations. The development of advanced-backcross populations can mitigate these difficulties by reducing the number of deleterious or undesirable alien alleles during backcrossing before the populations are evaluated. This approach was employed to develop 24 independently derived interspecific advanced-backcross populations of cotton, from a cross between the recurrent parent Gossypium hirsutum TAMCOT 2111 and G. barbadense Pima S6. Twenty-four BC3F1 plants were selfed, generating a total of 3,662 BC₃F₂ progeny, ranging from 33 to 191 per family. The extent of introgression and the chromosomal locations of G. barbadense donor chromatins retained in the 24 BC₃F₁ plants were assessed using 262 RFLP markers selected for even coverage of the cotton genome. A subset of 127 RFLP markers were found sufficient to monitor all of the introgressed regions, and were used to genotype all 3,662 BC₃F₂ individuals. The BC₃F₂ were evaluated in the field for their agronomic and fiber quality traits. Many genomic regions were identified by QTL analysis to be associated with agronomic (such as yield) and fiber quality traits (such as fiber length, strength and maturity). While most QTLs were detected in the families where common markers were segregating, occassional QTLs was detected only in selected families, suggesting the need for testing multiple lineages in advanced-backcross design.