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United States Department of Agriculture

Agricultural Research Service

Title: Genetic and physiological analysis of an irradiated bloomless mutant (epicuticular wax mutant) of sorghum

Authors
item Burow, Gloria
item Franks, Cleve
item Xin, Zhanguo

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 16, 2007
Publication Date: January 16, 2008
Citation: Burow, G.B., Franks, C.D., Xin, Z. 2008. Genetic and physiological analysis of an irradiated bloomless mutant (epicuticular wax mutant) of sorghum. Crop Science. 48:41-48.

Interpretive Summary: Sorghum (Sorghum bicolor Moench.) is considered as one of the most drought tolerant and water efficient crop species under intensive agriculture production systems. A distinctive feature of sorghum is the production and deposition of visible bloom or epicuticular wax in the abaxial side of the leaf and sheaths in the wild type condition. However, while increased epicuticular wax has been associated with drought response, its role has been inconclusive. In this study, we characterized a bloomless mutant (KFS2021 developed via gamma irradiation) using a combination of genetic and physiological approaches and provided evidence for the important contribution of epicuticular wax in reducing night transpiration. Phenotypic segregation for bloomless trait in an F2 population developed from a cross between KFS 2021 and BTx623, suggest that in this cross, the mutation is a result of single recessive nuclear gene mutation. Physiological characterization of parents and F2 progenies suggest that bloomless genotypes had significantly higher seedling water loss rate but decreased frequency of guttation. Bloomless genotypes exhibited greater cuticular permeability (measured based on chlorophyll leaching in 80% ethanol) than bloom progenies. More important, bloomless genotypes consistently showed 3 to 6- fold higher night time transpiration based on measurement of night time conductance. A genetic correlation of traits in the F2 generation revealed the association of nighttime stomatal conductance with a number of physiological traits assayed in the study. Taken together these results provide evidence that bloom in sorghum could play a vital role in decreasing nighttime transpiration which can have important implications in the water efficiency for sorghum. This study also demonstrates that sorghum could serve as a unique genetic and physiological system for the study of the epicuticular wax pathway that could provide important information for the possible transgenic manipulation of this complex pathway in grasses.

Technical Abstract: Sorghum (Sorghum bicolor (L).Moench.) is one of the most drought tolerant and water efficient grass species. A distinctive feature of sorghum is the profuse deposition of epicuticular wax or bloom on the abaxial side of the leaf and sheaths which has been proposed as a possible trait contributing to drought stress tolerance. However, the role and contribution of epicuticular wax to drought tolerance has been inconclusive. In this study, we characterized a bloomless mutant (KFS2021 developed via gamma irradiation) using a combination of genetic and physiological approaches and provided evidence for the contribution of epicuticular wax in reducing night transpiration. Phenotypic segregation for bloomless trait in an F2 population developed from a cross between KFS 2021 and BTx623, suggest that in this cross, the bloomless phenotype is a result of mutation in a single nuclear recessive gene. The bloomless parent and F2 progenies had lower frequency of guttation, more leaky cuticular layer (measured based on chlorophyll leaching in 80% ethanol) and higher rate of seedling water loss than the wild type and bloom progenies. More important, bloomless progenies consistently showed 3 to 6- fold higher night time transpiration based on measurement of night time conductance. Genetic correlation analysis of traits showed significant associations which indicate the important role of epicuticular wax in the various physiological traits analyzed in this study. Taken together our results suggest that sorghum epicuticular wax or bloom may enhance water use efficiency by depressing night time water loss.

Last Modified: 8/22/2014
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