Genetics of drought tolerance and associated traits in sorghum
Abstract
Sorghum (Sorghum bicolor (L.) Moench) is one of the most drought tolerant crop species. Significant variation for drought tolerance, however, exists among sorghum germplasm. Progress in breeding for drought tolerance has been limited by the complexity of the trait. In sorghum, we recognize drought tolerance at certain physiological stages. Drought at the pre-flowering stage occurs when the sink size is being determined. Post-flowering drought reduces the ability of a plant to fill the panicle and causes premature senescence. This study utilized 98 recombinant inbred (RI) lines derived by single seed descent from a cross of TX7078 (pre-flowering drought tolerant/post-flowering drought susceptible) by B35 (pre-flowering drought susceptible/post-flowering drought tolerant). The lines and the parents were evaluated under pre-flowering drought stress, post-flowering drought stress and full irrigation in 1992, 1993 and 1994. An array of agronomic and morphological measurements were recorded under each irrigation treatment. With these data, indices were developed for pre-flowering and post-flowering drought tolerance. In another study, each line was crossed onto two unrelated A-lines. The lines and hybrids were evaluated at Lafayette, Indiana under no stress and under moisture stress environments in Texas for 2 yr. Several stability measures were calculated on the lines and hybrids. Several agronomic and yield components were measured in the Lafayette trials. Quantitative trait loci (QTL's) for drought and agronomic traits were identified by restriction fragment length polymorphism (RFLP) and by random amplified polymorphic DNA (RAPD) marker techniques. Significant variation for drought responses were observed among the set of RI lines under each stress treatment. The indices were related to grain yield under the stress environments, but were negatively correlated with yield under the nonstress conditions. Stability of the RI lines was not reflected in stability of the hybrids unless the stability measure was correlated with grain yield. The same stability measures were associated with seed number. In the combining ability analysis, general combining ability effects were significant for all variables. Specific combining ability was important for yield and yield components, especially at the Texas environments. Molecular marker analysis identified chromosomal regions important for yield and other agronomic variables across environments. Molecular marker analysis also indicated genetic relationships among the variables measured.
Degree
Ph.D.
Advisors
Ejeta, Purdue University.
Subject Area
Agronomy|Genetics|Molecular biology
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