Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2012
Publication Date: 12/5/2012
Citation: Schramm, E.C., Nelson, S.K., Kidwell, K.K., Steber, C.M. 2012. Increased ABA sensitivity results in higher seed dormancy in soft white spring wheat cultivar ‘Zak’. Theoretical and Applied Genetics. 126(3):791-803 Available: http://link.springer.com/article/10.1007/s00122-012-2018-0/fulltext.html. Interpretive Summary: This paper describes the isolation of new alleles that can be used to increased the grain dormancy of wheat varieties with white kernels. White wheat is more prone than red white to problems with preharvest sprouting of mature grain when rain occurs prior to harvest. Soft white wheat is valued for making cookies and hard white wheat is gaining in popularity for making bread due to better flour extraction rates and due to the fact the whole wheat bread made from hard white wheat is not bitter tasting. Preharvest sprouting of white wheat has been linked to lack of seed dormancy. This paper demonstrates that the seed dormancy of white wheat can be increased by selecting for increased sensitivity to the plant hormone ABA. Promising new germplasm, especially Zak ERA8, has been developed for use by breeding programs.
Technical Abstract: As a strategy to increase the seed dormancy of soft white wheat, mutants with increased sensitivity to the plant hormone abscisic acid (ABA) were identified in mutagenized grain of soft white spring wheat ‘Zak”. Lack of seed dormancy is correlated with increased susceptibility to preharvest sprouting in wheat, especially those cultivars with white kernels. ABA induces seed dormancy during embryo maturation and inhibits the germination of mature grain. Three mutant lines called Zak ERA8, Zak ERA19A, and Zak ERA19B (Zak ENHANCED RESPONSE to ABA) were recovered based on failure to germinate on 5 µM ABA. All three mutants resulted in increased ABA sensitivity over a wide range of concentrations such that a phenotype can be detected at very low ABA concentrations. Wheat loses sensitivity to ABA inhibition of germination with extended periods of dry after-ripening. All three mutants recovered required more time to after-ripen sufficiently to germinate in the absence of ABA and to lose sensitivity to 5 µM ABA. However, an increase in ABA sensitivity could be detected after as long as three years of after-ripening using high ABA concentrations. The Zak ERA8 line showed the strongest phenotype and segregated as a single semi-dominant mutation. This mutation resulted in no obvious decrease in yield and is a good candidate gene for breeding preharvest sprouting tolerance.