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

Abstract

Aegilops tauschii, the wild relative of wheat, has stronger seed dormancy, a major component of preharvest sprouting resistance (PHSR), than bread wheat. A diploid Ae. tauschii accession (AUS18836) and a tetraploid (Triticum turgidum L. ssp. durum var. Altar84) wheat were used to construct a synthetic wheat (Syn37). The genetic architecture of PHS was investigated in 271 BC 1 F 7 synthetic backcross lines (SBLs) derived from Syn37/2*Janz (resistant/susceptible). The SBLs were evaluated in three environments over 2 years and PHS was assessed by way of three measures: the germination index (GI), which measures grain dormancy, the whole spike assay (SI), which takes into account all spike morphology, and counted visually sprouted seeds out of 200 (VI). Grain color was measured using both Chroma Meter-and NaOH-based approaches. QTL for PHSR and grain color were mapped and their additive and epistatic effects as well as their interactions with environment were estimated by a mixed linear-model approach. Single-locus analysis following composite interval mapping revealed four QTL for GI, two QTL for SI, and four QTL for VI on chromosomes 3DL and 4AL. The locus QPhs.dpiv-3D.1 on chromosome 3DL was tightly linked to the red grain color (RGC) at a distance of 5 cM. The other locus on chromosome 3D, ''QPhs.dpiv-3D.2'' was independent of RGC locus. Two-locus analysis detected nine QTL with main effects and 18 additive 3 additive interactions for GI, SI, and VI. Two of the nine main effects QTL and two epistatic QTL showed significant interactions with environments. Both additive and epistatic effects contributed to phenotypic variance in PHSR and the identified markers are potential candidates for marker-assisted selection of favorable alleles at multiple loci. SBLs derived from Ae. tauschii proved to be a promising tool to dissect, introgress, and pyramid different PHSR genes into adapted wheat genetic backgrounds. The enhanced expression of PHS resistance in SBLs enabled us to develop white PHS-resistant wheat germplasm from the red-grained Ae. tauschii accession.

Maximizing the identification of QTL for pre-harvest sprouting resistance using seed dormancy measures in a white-grained hexaploid wheat population

“…The continuous normal and skewed distributions of the population indicated that multiple minor alleles are involved in controlling seed dormancy. This complex genetic control of dormancy is consistent with earlier studies Kulwal et al 2004;Imtiaz et al 2008;Mohan et al 2009;Fofana et al 2009). The f Positive sign in germination resistance (GR) and negative sign in germination index (GI) and in percent germination (PG) indicated that SC8021-V2 allele contributed resistance for respective trait measure-duration relative to the AC Karma allele (values given in range for respective trait measure with multiple durations) g QTL designation (favourable parental allele) different durations of germination maximized differential under some conditions, revealing a bimodal distribution that indicated, in addition to minor genes, the presence of a major gene.…”

“…Noda et al (2002) investigated another ABA responsive gene located on the long arm of chromosome 4A. QPhs.spa-4A, located in interval barc170-gwm397-wmc617a on 4A, is in a region associated with dormancy and preharvest sprouting resistance in numerous other QTL studies of hexaploid wheat (Flintham et al 2002;Torada et al 2005;Mares et al 2005;Tan et al 2006;Ogbonnaya et al 2008;Imtiaz et al 2008;Munkvold et al 2009;Rasul et al 2009;Kulwal et al 2010;Singh et al 2010Singh et al , 2012Lohwasser et al 2013). The locus was also identified in tetraploid ) and diploid (Nakamura et al 2007) wheat populations, and in an association mapping study (Kulwal et al 2012).…”

“…The genetic control of pre-harvest sprouting resistance is complex, factors responsible for resistance are dispersed on almost every wheat chromosome and complex interactions occur between QTL (Q 9 Q) and/or among environments (Q 9 Q 9 E) (Kulwal et al 2004;Imtiaz et al 2008;Kumar et al 2009;Mohan et al 2009). Also, the effects of QTL range from minor to major corresponding to a range in phenotypic expression from susceptible to resistant.…”

“…Also, the effects of QTL range from minor to major corresponding to a range in phenotypic expression from susceptible to resistant. As with DePauw and McCaig (1991) in the study of heritability, in order to deal with the complexity of pre-harvest sprouting resistance and identify associated QTL, different tests such as wetting spikes in an artificial rain simulator, threshed seed germination counts for dormancy, and alpha-amylase activity measured by falling number have been conducted (Roy et al 1999;Mares et al 2005;Imtiaz et al 2008;Rasul et al 2009). Knox et al (2012) reported GI, GR and PG measures each at 7, 14 and 21 days intervals from the start of germination across multiple environments.…”

Cloning and Characterization of a Critical Regulator for Preharvest Sprouting in Wheat

“…Preharvest sprouting (PHS) in wheat (physiologically mature grains germinating in spikes before harvest) causes significant loss in grain yield and quality, particularly in regions with prolonged wet weather during the harvest season. Direct annual losses caused by PHS approach $1 billion dollars worldwide (Black et al 2006).Resistance to PHS in wheat is a complex trait that is affected by both genotype and environment (Imtiaz et al 2008). Grain color and seed dormancy have long been regarded as two major factors affecting PHS resistance (Gfeller and Svejda 1960;Bewley 1997;Groos et al 2002).…”