Drought tolerance is an important agronomic trait but the genetic and physiological mechanisms that condition its expression are poorly understood. Molecular genetics and quantitative trait loci analysis provide a new and powerful approach to understand better the inheritance and expression of this trait. The purpose of this study was to use molecular markers to identify genetic loci associated with the expression of pre‐flowering drought tolerance in sorghum [Sorghum bicolor (L.) Moench]. Two genotypes with contrasting drought reactions, TX7078 (pre‐flowering tolerant, post‐flowering susceptible) and B35 (pre‐tiowering susceptible, post‐tlowering tolerant), were selected as parents for a sample of recombinant inbred (RI) lines. Ninety‐eight RI lines were evaluated in two different years under conditions of pre‐tlowering drought and full irrigation. This information was used to quantify the drought tolerance of each line. The population was also genotyped with 150 RAPD and 20 RFLP markers that mapped to 17 linkage groups. By means of these markers, six regions of the genome were found to be specifically associated with pre‐flowering drought tolerance. Eight additional regions were more generally associated with yield or yield components under fully irrigated conditions. Several loci were associated with the expression of drought tolerance under both mild and severe drought stress conditions.
No abstract
Glycinebetaine (N,N,N‐trimethylglycine; betaine) accumulates in many species of the Poaceae and Chenopodiaceae. This accumulation is thought to be a metabolic response to osmotic stress which protects enzymes during heat and dehydration. Glycinebetaine deficient mutations have been identified and their genetic control elucidated in cereal crops including barley (Hordeum vulgare L.) and maize (Zea mays L.) The objective of this study was to determine the mode of inheritance of newly identified glycinebetaine deficient lines of sorghum [Sorghum bicolor (L.) Moench], Crosses were made between three high glycinebetaine (>20 μmol gfw−1) and three glycinebetaine deficient (<1 μmol gfw−1) varieties from which F1, F2, and backcross progenies were generated. A colorimetric assay was used to screen leaf samples collected from field grown parental, F1, and segregating progenies for glycinebetaine levels. Reciprocal F1 plants in each cross were not significantly different from each other. Approximately one‐fourth of the F2 plants in each cross exhibited the glycinebetaine deficiency, supporting the theory of single gene inheritance. Backcrosses to deficient parents segregated 1:1 for deficiency, further supporting this hypothesis. Gene action was primarily additive based on generation mean analysis of high and low parents, F1 progenies, and backcrosses to the respective parents. A small degree of dominance for glycinebetaine production was exhibited in the F1 generation.
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