Preharvest Sprouting Tolerance in White Wheat, Avoiding the Falling Number Blues.

Preharvest sprouting is the germination of wheat grain (caryopses) on the mother plant when moist cool conditions occur before harvest. α-amylase induction during sprouting can cause starch degradation, leading to problems with poor end-use quality. Farmers loose money when grain is discounted for α-amylase damage measured by the Hagberg-Perten Falling Number (FN) test. Several factors are associated with preharvest sprouting susceptibility including lower grain dormancy, white kernel color, open spike morphology, and lower accumulation of or sensitivity to the dormancy hormone ABA (abscisic acid). Dormancy can prevent the germination of mature grain under conditions that would normally induce germination or sprouting. Dormant grain acquires the ability to germinate through dormancy-breaking treatments such as cold stratification (moist chilling) and dry after-ripening (storage as a dry seed). White grain mills better and has better flavor in whole-grain products than red wheat. Thus, our focus is on genetic strategies to improve preharvest sprouting resistance in white wheat cultivars. This will be done using: 1) sources of sprouting tolerance in northwest cultivars characterized using the spike-wetting test and FN testing of sprouted grain, and 2) selection for alleles providing increased grain dormancy as a result of increased ABA sensitivity.

ABA signaling appears to be a key determinant of sprouting tolerance in white wheat. While red kernel color is associated with higher dormancy, preharvest sprouting susceptibility and resistance occur in both red and white wheat cultivars. ABA hormone sets up dormancy during grain maturation, prevents germination of dormant grains, and can block germination when applied to seeds. ABA hypersensitivity from the ERA8 allele provided higher seed dormancy and preharvest sprouting tolerance in soft white spring Zak. Cereals are unusual in that ABA sensitivity is lost with dormancy loss through after-ripening and cold stratification. Higher sprouting tolerance in white wheat was associated higher ABA sensitivity following dormancy-breaking treatments.