Asian Research Thesis Index

Abstract

Sorghum (Sorghum bicolour L. Moench) productivity is greatly affected by drought which is a major abiotic stress factor around the world. Sorghum being an important crop that is used as human food, animal feed as well used for industrial purposes, is widely grown throughout the world. This important crop is considered more tolerant to drought. However, pre-flowering stage of sorghum plant is more sensitive to drought stress and as a result causes severe reduction in grain yield due to the influence on plant reproductive organs and processes. The availability of genetic variation and effectiveness of selection within the genotypes, are factors that greatly improves drought stress resistance. Additionally, markers assisted selection procedures to identify genetic factors involved in plant responses to drought stress facilitate pyramiding of favourable alleles in breeding programs. In sorghum, drought stress at pre-flowering stage is more common but limited studies have been conducted considering this stage. Therefore, the goal of this study is to investigate the effects of drought stress at pre-flowering stage and to determine variations in different traits i.e. pollen fertility in sorghum core collection. In addition, experiments were performed to map chromosomal regions controlling these traits. Also, selected accessions were screened at seedling stage to analyse polymorphisms for selected drought controlling genes. The sorghum core collection consisting of 107 sorghum accessions from Africa and Asia were evaluated under drought stress at pre-flowering stage. Under drought stress the average leaf drying score (LDS) ranged from 5 to 85% among accessions. Pollen fertility (POFE) was measured by acetocarmine staining which showed significant differences among accessions under drought stress. Drought susceptibility index (DSI) was also calculated which showed difference in yield under drought stress and well water conditions. Based on different selection criteria including leaf drying score (LDS), pollen fertility (POFE) and drought susceptibility index (DSI) the sensitive and tolerant accessions were selected, which can be used for the improvement of drought tolerance in sorghum in breeding programs. In this study, association analysis was used to map Quantitative Trait Loci (QTLs) associated with drought stress. Using 98 SSR markers data the association analysis was performed and 17 QTLs were identified residing on chromosomes SBI-01, SBI- x 02, SBI-04, SBI-08, SBI-09 and SBI-10 under well water conditions. While under drought stress, 9 QTLs were identified on chromosomes SBI-01, SBI-02, SBI-03 and SBI-10. On chromosome SBI-02, two QTLs identified were physically localized and were homologous for genes encoding DNA binding and ATP binding proteins. The identification and analysis of these QTLs could help in dissecting genetic and physiological basis of drought tolerance in sorghum. Experiment was also conducted to analyse eight sorghum accessions that were exposed to osmotic stress produced by polyethylene glycol. The accessions showed varied response to drought tolerance at seedling stage in terms of root length and root dry weight. The most promising drought tolerant accessions showed greater root length and root dry weight. The same accessions were also screened for selected drought controlling genes i.e. NAC1, DHN1, WRKY11 and BADH to identify polymorphisms among drought sensitive and tolerant accessions. Furthermore, no polymorphism was found among accessions for different genes primers at genomic level revealing that these genes expressed only under stress conditions. Further analysis must be carried out to investigate the expression pattern of these genes as well as to determine their functional and biological importance in sorghum drought tolerance. The work presented in this thesis is devoted to identify and study various traits that are associated to drought tolerance in Sorghum. This thesis discusses in detail the phenotypic evaluation of different drought controlling traits as well as genetic analysis to identify the chromosomal regions responsible for expression of these traits.

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