Identification of Quantitative Trait Loci (QTL) for Gray Leaf Spot Resistance, Maturity, and Grain Yield in a Semi-tropical Recombinant Inbred Population of Maize.
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2005-04-12
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Abstract
Identification of QTL can aide in future breeding objectives by allowing breeders either to improve a line through targeted introgressions or assist in forward breeding strategies. Such analyses may be particularly helpful in integrating exotic germplasm into a breeding program. The percentage of tropical maize germplasm grown in U.S. farmers' fields is almost nonexistent. Tropical germplasm in maize (Zea mays L.) is a valuable resource to decrease the dependence upon a limited genetic base currently used to produce commercial hybrids, extend selection limits for grain yield, and to provide an insurance function against emerging biotic and abiotic stresses. Results of research presented in this dissertation support these recommendations.
Experiments were conducted to evaluate 143 S4:5 recombinant inbred lines (RILs) resulting from a cross between NC300, an all-tropical, temperate adapted line, and B104, a stiff stalk line. The 143 RILs were topcrossed to the Lancaster tester FR615xFR697 and randomly subdivided into two sets. The two sets were evaluated for resistance to GLS disease and yielding ability in three and eight North Carolina environments, respectively. Spatial trends were examined in the GLS trials. Significant (P ≤0.01) trend effects were fitted in five of the six set-by-environment combinations, which led to improved analyses within and across environments for both sets.
Ninety-three and eighty-two percent of the RILs in topcrosses (RILT) were significantly (P = 0.05) more resistant to GLS when compared to the mean of the commercial checks for set 1 and 2, respectively. Twenty-one RILs from both sets did not differ significantly (P = 0.05) for grain yield when compared to the mean of the commercial checks. RIL 2070 yielded significantly (P = 0.05) higher when compared to one commercial check, HC33.TR7322. RIL 1991 was rated the most resistant entry in set 1 and also did not differ from the mean of the commercial checks for grain yield.
The RILs were genotyped at 94 simple sequence repeat loci, and a linkage map was constructed that included nine chromosomes. Composite interval mapping was used to map QTL for GLS resistance, days to fifty-percent pollen shed (DTP), and grain yield. QTL associated with GLS rating were identified at individual environments on chromosomes 1, 4, and 8. One QTL located on chromosome 4 was associated with GLS resistance from the combined analysis across environments and explained 24.5% of the phenotypic variation on an entry-mean basis. A multi-locus model was constructed that involved four marker main effects and a significant epistatic interaction that together accounted for 35.0% of the phenotypic variation. Associations between GLS and maturity have been observed previously. The genetic correlation between GLS rating and DTP in this population was 0.46. A genomic region significantly associated with DTP corresponded to a region associated with GLS resistance on chromosome 8. Further, linked GLS-rating and DTP QTLs occurred together on chromosomes 1, 4, and 8.
QTL associated with grain yield were identified on chromosomes 1, 3, 7, and 9. In the combined analysis across the 2003 environments the NC300 allele had an increasing effect of 0.15 t ha-1 for the QTL on chromosome 1 and explained 11.0% of the phenotypic variation on an entry-mean basis. The QTL detected on chromosome 3 was from the combined analysis across all environments. The B104 allele had an increasing effect of 0.20 t ha-1 on chromosome 3 and explained 31.0% of the phenotypic variation. B104 also had alleles associated with an increasing effect for other grain yield QTLs identified on chromosomes 7 and 9.
These experiments collectively demonstrated the potential that tropical maize germplasm has to improve grain yield and resistance to GLS via conventional or marker-assisted selection strategies.
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qtl, maturity, gls resistance
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Degree
M
Discipline
Curriculum and Instruction
