BGS 753, Quantitative seed dormancy 2, Qsd2

Seed dormancy 2 = SD2 (6).
Quantitative seed dormancy 1 = Qsd2 (18).

Monofactorial recessive for rapid loss of dormancy in wild barley (14); previously identified as a dominant QTL in cultivated barley for seed dormancy (4, 5, 6, 9, 22, 23).
Located in chromosome 5HL (6, 23); the qsd2 locus is in terminal region of 5HL near RFLP marker MWG851 (5); qsd2 is in a 0.8-cM interval between molecular markers MWG851D and MWG851B (4); the main QTL for dormancy is near RFLP markers ABC57 CDO506 (1, 11); the Qsd2 locus is in the terminal region between 196.6 and 197.5 cM (15).

Malting and dormancy testing are conducted under conditions unfavorable for germination of barley. Wild barley (Hordeum vulgare subsp. spontaneum) is a winter annual for which germination must be prevented until soils is cool and moist. To break dormancy experimentally, kernels are placed, after imbibition for 24 to 48 hours, in near freezing temperatures for 3 to 5 days. Dormancy in wild barley is established by the recessive allele at the Qsd1 locus, which encodes for an alanine aminotransferase (AlaAT) (19). Dormancy is maintained in wild barley until favorable conditions for seedling establishment exist by a recessive allele at the Qsd2 locus, which encodes for Mitogen-activated Protein Kinase Kinase 3 (MKK3) (14). Domestication resulted in a partial loss of dormancy; however, more dormancy is retained in cultivars grown as winter barley (19). The Qsd2 locus is the second quantitative seed dormancy locus involved in maintenance of post-harvest grain dormancy (6, 23). Dominant QTL at the Qsd2 locus in 5HL caused reduced seed germination following grain harvest (2, 4, 5, 6, 14, 15). Alleles in the terminal region of 5HL are associated with many malt quality parameters in the Harrington/TR306 DH progeny (3, 9, 13). In the Chebec (PI 606292)/Harrington DH progeny, extract and diastatic power levels were associated with alleles in 5HL (1) and also with α-amylase activity and free amino acids (11). The Qsd2 allele of Baronesse was associated with higher yield and inferior malt quality in backcross-derived lines (20). Higher lipoxygenase (LOX) content, which affects foam stability and beer flavor, was associated with more dormant alleles at the Qsd2 locus (10); however, it is possible that closely linked loci are involved in the dormancy/malt quality associations (5, 10). The Qsd2 locus 5HL has been associated with rapid release of after-ripening dormancy in the non-dormant parent (16, 17) and preharvest sprouting (22, 24). The N260T substitution in Mitogen-activated Protein Kinase Kinase 3 allele of wild barley decreases MKK3 kinase activity and increases dormancy (14). A large number of sequence variations in the MKK3 were identified, but their relationships with dormancy levels were reported as variable (14).

The rapid dormancy release allele at the Qsd2 locus in wild barley H206 was named Qsd2-OK (Qsd2.c) (14); the slow dormancy release allele (from Azumamugi) of MKK3 with the N260T was named Qsd2.AK (Qsd2.d), which likely arose in northeastern China and was established as a major allele in cultivars from southeastern China, Korea, and Japan (14); many other sequence variants in MKK3 (Qsd2) are present in wild and cultivated barley accessions (14).

Wild type alleles were considered recessives (14); the Qsd2.c series of allele symbols is suggested for the recessive variants present in Hordeum vulgare subsp. spontaneum; sequence changes in cultivars produce dominant variants (14), which were placed in the Qsd2.d group of alleles. Cultivars with strong dormancy alleles at the Qsd2 locus: included Steptoe (CIho 15229) (6, 23), TR306 (3, 24), Chebec (1, 11), Stirling (2, 5), Baronesse (20); dormancy QTL were detected in Chevron (CIho 1111) and Morex (CIho 15773) (12); Harrington (1, 3, 5), Haruna Nijo (14, 15), Flagship (7), and AC Metcalfe (25, 26) have a non-dormant allele at the Qsd2 loci.

qsd1.c in the wild barley accession H602; a series of sequence variants (qsd1.c alleles) in wild barley accessions; Qsd1.d variants associated with a range of dormancy levels in barley cultivars.

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J.D. Franckowiak. 2018. Barley Genet. Newsl. 48:184-187.