Evaluating Seed Dormancy and Preharvest Sprouting Resistance of an ABA Hypersensitive Mutant ZakERA0.

To examine the role of hormone sensitivity in determining wheat seed dormancy and preharvest sprouting tolerance, this study examined the effect of an ABA hypersensitive mutation on the kinetics of after-ripening, hormone sensitivity, and preharvest sprouting tolerance of soft white spring Zak.  Seed dormancy refers to the temporary inability of a seed to germinate after maturity, and is alleviated by after-ripening during dry storage.  Sufficient seed dormancy is a crucial genetic characteristic needed to prevent pre-harvest sprouting when rain induces germination prior to harvest.  Sprouting induces alpha-amylase, compromising quality through conversion of starch to sugar and low Falling Numbers.  The hormone abscisic acid (ABA) is required to induce dormancy during plant embryo maturation, and inhibits alpha-amylase.  In contrast, the hormone gibberellic acid (GA) induces seed germination and alpha-amylase.  The ABA hypersensitive mutant, ZakERA0 (Enhanced Response to ABA) was generated to improve seed dormancy and sprouting tolerance.  To compare the seed dormancy and hormone sensitivity of Zak and ZakERA0, an after-ripening time course was conducted in which germination index with and without ABA and GA was determined.  ZakERA0 required 10 weeks to after-ripen, whereas Zak required 4 weeks.  Higher seed dormancy in ZakERA0 was associated with lower sensitivity to GA when freshly harvested.  ZakERA0 also required longer after-ripening to loose ABA sensitivity than normal Zak.  Moreover, PHS tolerance among soft white wheat was correlated with higher ABA sensitivity and lower GA sensitivity.  This suggests that hormone sensitivity can be used in selecting for preharvest sprouting tolerance.