Preharvest sprouting (PHS), germination of mature grain while still on the mother plant, occurs when conditions become cool and wet before harvest. The hydrolytic enzyme ?-amylase, induced during germination, mobilizes starch into simple carbohydrates to fuel seedling growth. Because this enzyme activity in flour causes poor end-use quality, sprouted grain sells at a severe discount. The falling number (FN) test measures ?-amylase activity in wheat meal or flour in the wheat industry. Seed dormancy, the inability to germinate even under favorable conditions, contributes about 60--80 % of genetic PHS tolerance. Red wheat varieties have higher seed dormancy and PHS tolerance than white. To improve white wheat, a genome-wide association study (GWAS) examined the genetic architecture of PHS tolerance in 469 soft white winter wheat accessions. Based on FN after natural or artificial rain, the GWAS identified 9 QTL (QFN.wsu), of which 4 co-localized with known PHS QTL and 3 with known FN/quality QTL. Based on visible sprout in spike-wetting tests, the GWAS identified 34 QTL (QPHS.wsu), of which 19 co-localized with known PHS loci and genes such as MOTHER OF FLOWERING TIME (TaMFT) and mitogen-activated protein kinase kinase 3 (TaMKK3-A). PHS tolerance in white wheat can result from higher sensitivity to the seed dormancy-inducing hormone abscisic acid (ABA). Enhanced Response to ABA (ERA8 ) is a semi-dominant ABA hypersensitive mutant, resulting in increased seed dormancy and PHS tolerance in the soft white spring wheat 'Zak'. The ERA8 locus was mapped to a large region of chromosome 4A relative to mutagen-induced SNPs in a Zak/ZakERA8 backcross population using bulk segregant analysis (BSA) of exome sequence from BC 3F2:3 wild-type and mutant DNA. Fine mapping using mutagen-induced SNPs in additional backcross lines localized ERA8 to a 4.5 Mb region containing 70 predicted genes. The only mutagen-induced coding region mutation strongly linked to ERA8 (LOD 16.51) resulted in a missense mutation in MKK3-A, a gene involved in Arabidopsis ABA signaling. Natural variation in wheat and barley MKK3 was previously shown to control seed dormancy and PHS tolerance.