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Title: Wheat ABA-insensitive mutants result in reduced grain dormancy

item SCHRAMM, ELIZABETH - Washington State University
item NELSON, SVEN - Washington State University
item Steber, Camille

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/29/2012
Publication Date: 3/31/2012
Citation: Schramm, E., Nelson, S.K., Steber, C.M. 2012. Wheat ABA-insensitive mutants result in reduced grain dormancy. Euphytica. 188(1),35-49. Published online March 31, 2012.

Interpretive Summary: The control of seed dormancy and germination is very important in cereal crops where excessive dormancy leads to problems with uneven stand establishment, and insufficient seed dormancy can result in pre-harvest sprouting (PHS), or seed germination on the mother plant. Wheats with white seed coat color are more likely than wheats with red seed coat color to suffer from pre-harvest sprouting when cool rainy conditions occur prior to harvest. This problem causes economic losses to farmers when the grain is graded as animal feed. Pre-harvest sprouting tolerance is linked to insufficient seed dormancy. Seed dormancy is induced by the plant hormone abscisic acid (ABA). This study isolated mutants with reduced ABA sensitivity in hard red spring Scarlet, and found that such mutants are not completely non-dormant but loose dormancy more rapidly than normal Scarlet. This tells us that ABA response is important for maintaining dormancy, and suggests that such mutants might be used to improve the germination/emergence of red wheat planted soon after harvest without abolishing initial preharvest sprouting tolerance.

Technical Abstract: This paper describes the isolation of wheat mutants in the hard red spring Scarlet resulting in reduced sensitivity to the plant hormone abscisic acid (ABA) during seed germination. ABA induces seed dormancy during embryo maturation and inhibits the germination of mature seeds. Wheat sensitivity to ABA gradually decreases with dry after-ripening. Scarlet grain normally fails to germinate when fully dormant, shows ABA sensitive germination when partially after-ripened, and becomes ABA insensitive when after-ripened for 8 to 12 months. Scarlet ABA-insensitive (ScABI) mutants were isolated based on the ability to germinate on 5 'M ABA after only 3 weeks of after-ripening, a condition under which Scarlet would fail to germinate. Six independent seed-specific mutants were recovered. ScABI1, ScABI2, ScABI3 and ScABI4 are able to germinate more efficiently than Scarlet at up to 25 'M ABA. The two strongest ABA insensitive lines, ScABI3 and ScABI4, both proved to be partly dominant suggesting that they result from gain-of-function mutations. The ScABI1, ScABI2, ScABI3, ScABI4, and ScABI5 mutants after-ripen more rapidly than Scarlet. Thus, ABA insensitivity is associated with decreased grain dormancy in Scarlet wheat. This suggests that ABA sensitivity is an important factor controlling grain dormancy in wheat, a trait that impacts seedling emergence and pre-harvest sprouting resistance.