Xu, Jiale (2014-12). Transmission Rates of Gossypium mustelinum and G. tomentosum SNP Markers in Early-generation Backcrosses to Cotton. Master's Thesis.
Gossypium hirsutum L. is the most widely cultivated cotton species in the genus Gossypium. The genetic diversity of G. hirsutum is considerably restricted, so it is highly desirable to introgress germplasm of related species to expand opportunities for genetic improvement. Successful interspecific introgression efforts require the transmission of alien genes into the cultivated species and homologous recombination. Transmission distortion can restrict or preclude gene transfer, and reduced rates of homologous recombination can reduce or preclude recovery of desirable genetic products. Marker-based analysis of specific chromosome segments and loci during early generations of backcrossing can reveal general and locus-specific features of alien germplasm transmission and recombination with the recurrent parent, and help guide decisions for expanded analysis, subsequent backcrosses and analogous efforts with other donors.
Interspecific monosomic hybrids were used to localize pre-validated single nucleotide polymorphism (SNP) markers in six target chromosomes. Eventually, 67 SNPs were used to analyze transmission rates. In the present research, each "breeding situation" was defined as a unique combination of cross direction, backcross generation and cross location. Twelve G. hirsutum backcross populations were derived under different breeding situations, six from each of two alien donors, G. mustelinum and G. tomentosum. KASP analysis of the SNPs revealed the presence or absence of specific donor loci and segments in 784 individuals of the 12 populations, and was used to determine transmission rates.
Linkage groups were constructed based on segregation ratios in BC1F1 populations for each donor. The average transmission rate of germplasm from G. tomentosum was similar to but higher (3%) than G. mustelinum, indicating a closer relationship of G. tomentosum with G. hirsutum. Several markers exhibited strongly distorted transmission relative to other loci of the respective linkage groups in specific populations. Several loci exhibited significant differences due to cross direction and cross location. Analysis of the BC3F1 populations revealed the crosses from field environments were relatively favorable for transmission of alien germplasm and greenhouse environments for loss of alien germplasm. Multiple comparisons based on general linear model (GLM) for effects of breeding situations on transmission rates revealed generation and location significantly affected transmission of G. mustelinum germplasm, whereas cross direction, location and generation affected transmission of G. tomentosum germplasm.