Browsing by Author "Kuhlman, Leslie Charles"
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Item Investigation of a xenia effect for yield caused by the waxy gene in grain sorghum(Texas A&M University, 2005-11-01) Kuhlman, Leslie CharlesSorghum grain with a waxy endosperm is more digestible and has a higher feeding efficiency compared to sorghum grain with a non-waxy (or normal) endosperm. However, waxy sorghums (Sorghum bicolor (L.) Moench) yield 10-15% less than normal sorghum and the cause of the yield reduction is unclear. The objective of this research is to determine if the yield decrease could be due to the waxy phenotype itself. The waxy phenotype is an example of a xenia effect, where the pollen not only contributes to the genotype of the resulting hybrid, but also immediately influences the phenotype of the resulting seed. Sterile hybrids under different pollination types, and different genotypes of fertile hybrids, both resulted in hybrids that produced different ratios of waxy phenotype seed. The effects on yield and 500 kernel weight were investigated in Weslaco, College Station, and Halfway, Texas over two years. Yields of sterile heterozygous waxy hybrids under waxy pollination, which produced an average 27% waxy seed over all environments, were nearly identical to homozygous nonwaxy hybrids that produced 0% waxy seed. Average 500 kernel weights for the same hybrids were not different. Grain yields for the fertile hybrid genotypes were significantlydifferent. Hybrids which produced 100% waxy seed yielded significantly less than hybrids which produced 25% waxy seed. Upon further examination, hybrids that were produced from waxy F1 endosperm seed (wxwxwx) had significantly worse stand and panicle number per plot means than did hybrids from nonwaxy F1 endosperm seed (Wxwxwx). Grain yields adjusted for panicle number showed no significant differences. The average 500 kernel weights between hybrids with different amounts of waxy phenotype grain did not significantly differ. The yield effect seen in this population was the result of waxy endosperm hybrid seed displaying significantly poorer stand establishment than nonwaxy endosperm hybrid seed. These data do not support a xenia yield effect due to the waxy gene.Item Sorghum introgression breeding utilizing S. macrospermum(2009-05-15) Kuhlman, Leslie CharlesSorghum has been improved by plant breeders for yield, biotic and abiotic stress resistance, as well as quality traits by using germplasm from within the species. Interspecific hybridization can greatly increase the amount of genetic variation available to plant breeders for improvement. Interspecific hybrids between sorghum and the 19 species in the tertiary gene pool have, until recently, not been successful. The Australian species, S. macrospermum, was recently successfully hybridized with sorghum by using germplasm homozygous for the iap allele, which eliminated reproductive isolation barriers. The objectives of this research were to evaluate the potential for use of S. macrospermum in an introgression breeding program, determine the map position of the Iap locus, and backcross the iap allele into elite Texas A&M germplasm. Interspecific hybrids between S. bicolor and S. macrospermum revealed moderate levels (2.6 II per PMC) of allosyndetic recombination, indicating that introgression through genetic recombination is possible. Genomic relationships were sufficient to assign S. macrospermum the genomic formula AAB1B1YYZZ, Y and Z remain unknown. In backcrosses to S. bicolor using the female interspecific hybrid gamete and embryo rescue, BC1F1 plants were recovered. They had high chromosome numbers (2n = 35-70) and were male-sterile but three plants set backcross seed. Ninety-five percent of BC2F1 plants were 2n = 20 chromosomes and 75% of them contained S. macrospermum introgression. BC2F1 plants carried between 0-18.5% S. macrospermum introgression; in total 26% of the S. macrospermum genome was detected in the BC2 generation. Three types of introgression germplasm were created: alien addition lines; alien substitution lines; and introgression lines. Recombinant chromosomes, containing S. macrospermum introgression sites, were identified in multiple introgression lines. The Iap locus was genetically mapped to sorghum chromosome 2 (SBI-02), flanking AFLP markers were 2.1 and 2.7cM away, one AFLP marker shared the same map position (0.0cM). A genetic stock, Tx3361, was created which has iap iap genotype and improved agronomic qualities such as short plant height, white seed color, non-pigmented testa, no awns, reduced lodging, early maturity, and backcross segregation of male-sterility (ms3). This research shows that S. macrospermum is now available to plant breeders for sorghum improvement.