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University of Queensland (2010)

GENOTYPIC VARIABILITY IN STRUCTURE AND FUNCTION OF SORGHUM ROOT SYSTEMS

Vijaya Singh

Titre : GENOTYPIC VARIABILITY IN STRUCTURE AND FUNCTION OF SORGHUM ROOT SYSTEMS

Auteur : Vijaya Singh

Grade : Doctor of Philosophy (PhD) 2010

Université de soutenance : University of Queensland

Résumé
Sorghum is a major dryland cereal crop in areas with low and unpredictable rainfall, and improvements in root related drought adaptive traits may be advantageous. There is little information available about the extent of genetic variation in root architecture in sorghum and the potential for manipulating this variation to improve the tolerance of sorghum in water limiting conditions. A lack of simple and efficient root screening methods has hindered the progress. In this study we employ a screening method developed to investigate genetic variation in root architecture, with a particular focus on nodal root angle. A diverse range of sorghum inbred lines and hybrids were studied to explore the extent of genetic variation in this trait and the nature of its genetic control. The encompassing nodal root angle of sorghum inbred lines varied from about 15º to 50º. While the heritability for nodal root angle was high, the significant specific combining ability limited predictability of expression in hybrids. Genetic variation among inbred lines and hybrids in nodal root angle was largely distinct from other plant size traits, such as shoot and root mass, and plant leaf area. Variability in these plant size traits in hybrids was associated with the female parent and significant general combining ability. Selected contrasting sorghum genotypes varying in nodal root angle (wide, intermediate and narrow) at the seedling stage were then grown in large root observation chambers. The chambers were watered to field capacity prior to sowing and no further water was added. Although there were no significant differences among entries in total soil water used or water use efficiency, the genotype SC170-6-8 (wide angle) had a tendency of greater proportion of its total water extraction at distance from the plant due to the broader spatial pattern of its root system. Conversely, the genotype B923296 (narrow angle) had a greater tendency of water extraction from depth immediately below the plant. These findings were consistent with observed differences in root system architecture among the entries. Although further research is needed to more clearly quantify these differences in water extraction capabilities, this finding has implications for seedling nodal root angle as an indicator for specific adaptation in water-limited environments. A genetic linkage map for the RIL population of the cross (B923296 x SC170-6-8) with contrasting nodal root angle was constructed on a subset of lines based on DArT (Diversity Arrays Technology) and SSR markers. This was used to identify two QTL for nodal root angle on chromosomes SBI-05 and SBI-09. They were independent of QTL associated with plant size and could be used in a molecular breeding strategy to optimize sorghum root architecture for better accessibility of available water in a target environment.

Mots-clés : Sorghum bicolor ; root architecture ; root screening ; nodal root angle ; genetic variation ; root chambers ; water extraction ; QTL

Présentation

Page publiée le 11 juillet 2017