| A purpose of this thesis study was to improve our understanding of the genetics of cold, salt and drought tolerance during seed germination and reproductive stages in tomato. Hybridizations were made between a stress-sensitive L. esculentum tomato breeding line (NC84173, maternal and recurrent parent) and a stress-tolerant accession (LA722) of the wild tomato species L. pimpinellifolium and BC1, BC1S1 (self-pollinated progeny of the BC1 individuals), BC1S 2 and BC1S3 were generated. Quantitative trait loci (QTLs) controlling the rate of seed germination under different stress and nonstress conditions were identified across BC1S1 and BC1S3 generations using interval mapping and single-marker analysis. QTLs for cold and salt tolerance in the BC1S1 generation were previously reported (Foolad et al. 1998a & b). QTLs for drought tolerance and comparative mapping of QTLs for cold, salt and drought tolerance and nonstress seed germination across generations are presented here.; Two classes of QTLs were identified: those that affected germination rate under both nonstress and stress conditions (referred to as “stress-nonspecific” QTLs) and those that affected germination rate only under stress conditions (referred to as “stress-specific” QTLs). Heritability estimates, calculated based on regression of BC1S3 family means on BC1S1 family means, ranged from 0.41 (for cold stress) to 0.45 (for drought stress). Heritability of the rate of seed germination under control conditions was estimated to be 0.04. The results indicate that cold-, salt-, and drought-stress tolerance genes are moderately heritable, and thus reasonable progress in enhancing tolerance to these stresses is expected by phenotypic selection and breeding.; A second part of this thesis was the investigation of genotypic variations in pollen tolerance to cold stress in tomato. Fourteen accessions, representing three Lycopersicon species, were grown to maturity under control (22°C day/18°C night) and low-temperature (14°C day/9°C night) conditions, and pollen were collected from individual plants.; Overall, the results in this study indicate the potentials for improving tomato for cold, salt and drought tolerance during seed germination and cold tolerance during pollen production and pollen germination stages. (Abstract shortened by UMI.)... |
