Higher Seed Dormancy and ABA Sensitivity Improves Wheat Preharvest Sprouting Tolerance

Many white wheat cultivars are susceptible to preharvest sprouting, the germination of mature grain on the mother plant when rain occurs before harvest, due to insufficient seed dormancy.  However, cultivars with high seed dormancy have problems with poor germination and emergence if sown within 6 to 8 weeks of harvest.  Thus, the breeding goal is to have sufficient seed dormancy at maturity to prevent sprouting, but to lose dormancy rapidly through 6 to 8 weeks of after-ripening during dry storage.  Two approaches are being taken to improve preharvest sprouting tolerance without adverse effects on emergence.  The first is to deploy ENHANCED RESPONSE TO ABA8 (ERA8), a wheat mutant isolated for increased sensitivity to the dormancy hormone ABA in soft white wheat.  The second approach is to perform genome wide association mapping for seed dormancy and seedling emergence within white winter wheat breeding programs.  The increased ABA sensitivity in the Zak ERA8 line is associated with increased seed dormancy compared to wild type soft white spring Zak.  However, Zak ERA8 loses dormancy fairly quickly, within about 8 weeks of after-ripening.  Zak ERA8 showed improved PHS tolerance based on spike wetting tests over 3 field environments.  While the effect Zak ERA8 on germination and field seedling emergence were not statistically significant, future work will examine whether a small decrease in germination capacity impacts grain yield.