Increased grain dormancy in white-grained wheat by introgression of preharvest sprouting tolerance QTLs

Abstract

White-grained wheat cultivars have long been recognized to be less resistant to preharvest sprouting (PHS) than the red-grained ones. Previously two QTLs for grain dormancy, QPhs.ocs-3A.1 (QPhs-3AS) and QPhs.ocs-4A.1 (QPhs-4AL) were identified in a highly dormant Japanese red wheat, Zenkoujikomugi (Zen). Aiming at improvement of PHS tolerance in white-grained wheat, the introgression effect of these two QTLs in a white-grained population consisting of 40 recombinant inbred lines (RILs) developed from a cross between Zen and whitegrained Spica was examined here. Random 20 RILs with red grains were also developed from the same cross and used as a control population. The RILs were grown in the field and in the glasshouse to evaluate the grain dormancy by germination test. Several SSR markers closely linked to the QPhs-3AS and QPhs-4AL were used to estimate the alleles at the QTLs. Dormancy variation in the RILs was significantly associated with the differences for grain color and the alleles at QPhs-3AS over several years. Although allelic variation was detected in a SSR marker closely linked to QPhs-4AL there was no difference in germination data between the Zenallele and the Spica-allele groups. As expected, the red-grained RILs with the Zen allele at QPhs-3AS were the most dormant. Some white-grained RILs with the Zen allele at QPhs-3AS showed higher dormancy compared to the red-grained RILs with the alternative allele. These results demonstrated that introgression of the QPhs-3AS gene could contribute to the increased grain dormancy in white-grained wheat.

Characterization of Quantitative Trait Loci Controlling Genetic Variation for Preharvest Sprouting in Synthetic Backcross-Derived Wheat Lines

“…MLM identified two QTL on chromosome 4A ( Figure 3, which is in agreement with previously reported results about the presence of two QTL on chromosome 4A; Kato et al 2001;Mares et al 2005;Kottearachchi et al 2006), however, the genomic location of these QTL varies. The discrepancies could be due to the use of different PHS-resistant sources in the different studies, varying methodologies of assessing PHS, or the use of different marker densities.…”

“…Other color-independent major genomic regions associated with PHS resistance were identified on chromosome 4A, which has been reported in previous studies (Kato et al 2001;Mares et al 2005;Kottearachchi et al 2006). When comparing the level of dormancy between synthetic wheat, Syn37 and its tetraploid (durum variety, Altar84) and diploid (Ae.…”

“…We used three PHS indexes (GI, SI, and VI) jointly in a single study across three environments to characterize QTL for PHS response and then applied the knowledge to select for both red-and white-grained PHS-resistant lines. In all previous studies these indexes were used only individually to map PHS/seed dormancy QTL (Kato et al 2001;Flintham et al 2002;Kulwal et al 2005;Mares et al 2005;Kottearachchi et al 2006;Tan et al 2006). It appeared in this study that GI and VI are the best predictors of resistance to PHS compared to SI, which has subjective aspects when scoring sprouting of susceptible materials after artificial wetting.…”

“…The exposure of grains to wet conditions at ripening triggers a sequence of physiological processes, which among others include the release of hydrolytic enzymes such as a-amylase. Due to the increase in amylase activity, grain carbohydrate reserves will be hydrolyzed, which results in bread wheat quality attributes being affected causing for example sticky crumb and collapsed loaves (Kottearachchi et al 2006). The financial losses to growers are even greater when grains germinate in the head while attached to the mother plant.…”

“…Therefore both seed dormancy and PHS are complex traits controlled by many genes or quantitative trait loci (QTL) (Paterson and Sorrells 1990;Mares 1996;Flintham et al 2002). In wheat, QTL associated with PHS resistance have been identified spanning all 21 chromosomes of the three hexaploid wheat genomes (Anderson et al 1993;Roy et al 1999;Zanetti et al 2000;Kato et al 2001;Mares and Mrva 2001;Flintham et al 2002;Groos et al 2002;Mares et al 2005;Imtiaz et al 2006;Kottearachchi et al 2006;Ogbonnaya et al 2006), underlying the complexity of PHSR. Four parameters, namely grain dormancy, wetting spikes, falling number (FN), and a-amylase have been used to evaluate and map gene(s)/QTL for PHSR (Zanetti et al 2000;Kuwal et al 2005;Mares et al 2005).…”