A new PCR-based marker on chromosome 4AL for resistance to pre-harvest sprouting in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Pre-harvest sprouting (PHS) is a complex trait controlled by multiple genes with strong interaction between environment and genotype that makes it difficult to select breeding materials by phenotypic assessment. One of the most important genes for pre-harvest sprouting resistance is consistently identified on the long arm of chromosome 4A. The 4AL PHS tolerance gene has therefore been targeted by Australian white-grained wheat breeders. A new robust PCR marker for the PHS QTL on wheat chromosome 4AL based on candidate genes search was developed in this study. The new marker was mapped on 4AL deletion bin 13-0.59-0.66 using 4AL deletion lines derived from Chinese Spring. This marker is located on 4AL between molecular markers Xbarc170 and Xwg622 in the doubled-haploid wheat population Cranbrook × Halberd. It was mapped between molecular markers Xbarc170 and Xgwm269 that have been previously shown to be closely linked to grain dormancy in the doubled haploid wheat population SW95-50213 × Cunningham and was co-located with Xgwm269 in population Janz × AUS1408. This marker offers an additional efficient tool for marker-assisted selection of dormancy for white-grained wheat breeding. Comparative analysis indicated that the wheat chromosome 4AL QTL for seed dormancy and PHS resistance is homologous with the barley QTL on chromosome 5HL controlling seed dormancy and PHS resistance. This marker will facilitate identification of the gene associated with the 4A QTL that controls a major component of grain dormancy and PHS resistance.     

Characterization of quantitative trait loci controlling genetic variation for preharvest sprouting in synthetic backcross-derived wheat lines

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 x 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.     

Mapping quantitative trait loci for preharvest sprouting resistance in white wheat

The premature germination of seeds before harvest, known as preharvest sprouting (PHS), is a serious problem in all wheat growing regions of the world. In order to determine genetic control of PHS resistance in white wheat from the relatively uncharacterized North American germplasm, a doubled haploid population consisting of 209 lines from a cross between the PHS resistant variety Cayuga and the PHS susceptible variety Caledonia was used for QTL mapping. A total of 16 environments were used to detect 15 different PHS QTL including a major QTL, QPhs.cnl-2B.1, that was significant in all environments tested and explained from 5 to 31% of the trait variation in a given environment. Three other QTL QPhs.cnl-2D.1, QPhs.cnl-3D.1, and QPhs.cnl-6D.1 were detected in six, four, and ten environments, respectively. The potentially related traits of heading date (HD), plant height (HT), seed dormancy (DOR), and rate of germination (ROG) were also recorded in a limited number of environments. HD was found to be significantly negatively correlated with PHS score in most environments, likely due to a major HD QTL, QHd.cnl-2B.1, found to be tightly linked to the PHS QTL QPhs.cnl-2B.1. Using greenhouse grown material no overlap was found between seed dormancy and the four most consistent PHS QTL, suggesting that greenhouse environments are not representative of field environments. This study provides valuable information for marker-assisted breeding for PHS resistance, future haplotyping studies, and research into seed dormancy.     

Comparative genetic analysis of a wheat seed dormancy QTL with rice and <Emphasis Type="Italic">Brachypodium</Emphasis> identifies candidate genes for ABA perception and calcium signaling

Wheat preharvest sprouting (PHS) occurs when seed germinates on the plant before harvest resulting in reduced grain quality. In wheat, PHS susceptibility is correlated with low levels of seed dormancy. A previous mapping of quantitative trait loci (QTL) revealed a major PHS/seed dormancy QTL, QPhs.cnl-2B.1, located on wheat chromosome 2B. A comparative genetic study with the related grass species rice (Oryza sativa L.) and Brachypodium distachyon at the homologous region to the QPhs.cnl-2B.1 interval was used to identify the candidate genes for marker development and subsequent fine mapping. Expressed sequence tags and a comparative mapping were used to design 278 primer pairs, of which 22 produced polymorphic amplicons that mapped to the group 2 chromosomes. Fourteen mapped to chromosome 2B, and ten were located in the QTL interval. A comparative analysis revealed good macrocollinearity between the PHS interval and 3 million base pair (mb) region on rice chromosomes 7 and 3, and a 2.7-mb region on Brachypodium Bd1. The comparative intervals in rice were found to contain three previously identified rice seed dormancy QTL. Further analyses of the interval in rice identified genes that are known to play a role in seed dormancy, including a homologue for the putative Arabidopsis ABA receptor ABAR/GUN5. Additional candidate genes involved in calcium signaling were identified and were placed in a functional protein association network that includes additional proteins critical for ABA signaling and germination. This study provides promising candidate genes for seed dormancy in both wheat and rice as well as excellent molecular markers for further comparative and fine mapping.     

A major QTL controlling seed dormancy and pre-harvest sprouting resistance on chromosome 4A in a Chinese wheat landrace

Wheat pre-harvest sprouting (PHS) can cause significant reduction in yield and end-use quality of wheat grains in many wheat-growing areas worldwide. To identify a quantitative trait locus (QTL) for PHS resistance in wheat, seed dormancy and sprouting of matured spikes were investigated in a population of 162 recombinant inbred lines (RILs) derived from a cross between the white PHS-resistant Chinese landrace Totoumai A and the white PHS-susceptible cultivar Siyang 936. Following screening of 1,125 SSR primers, 236 were found to be polymorphic between parents, and were used to screen the mapping population. Both seed dormancy and PHS of matured spikes were evaluated by the percentage of germinated kernels under controlled moist conditions. Twelve SSR markers associated with both PHS and seed dormancy were located on the long arm of chromosome 4A. One QTL for both seed dormancy and PHS resistance was detected on chromosome 4AL. Two SSR markers, Xbarc 170 and Xgwm 397, are 9.14 cM apart, and flanked the QTL that explained 28.3% of the phenotypic variation for seed dormancy and 30.6% for PHS resistance. This QTL most likely contributed to both long seed dormancy period and enhanced PHS resistance. Therefore, this QTL is most likely responsible for both seed dormancy and PHS resistance. The SSR markers linked to the QTL can be used for marker-assisted selection of PHS-resistant white wheat cultivars. Shi-Bin Cai and Cui-Xia Chen contributed equally to this work.     

Fine mapping of a preharvest sprouting QTL interval on chromosome 2B in white wheat

Key message

Fine mapping by recombinant backcross populations revealed that a preharvest sprouting QTL on 2B contained two QTLs linked in coupling with different effects on the phenotype.

Abstract

Wheat preharvest sprouting (PHS) occurs when grain germinates on the plant before harvest, resulting in reduced grain quality. Previous mapping of quantitative trait locus (QTL) revealed a major PHS QTL, QPhs.cnl-2B.1, located on chromosome 2B significant in 16 environments that explained from 5 to 31 % of the phenotypic variation. The objective of this project was to fine map the QPhs.cnl-2B.1 interval. Fine mapping was carried out in recombinant backcross populations (BC₁F₄ and BC₁F₅) that were developed by backcrossing selected doubled haploids to a recurrent parent and self-pollinating the BC₁F₄ and BC₁F₅ generations. In each generation, three markers in the QPhs.cnl-2B.1 interval were used to screen for recombinants. Fine mapping revealed that the QPhs.cnl-2B.1 interval contained two PHS QTLs linked in coupling. The distal PHS QTL, located between Wmc453c and Barc55, contributed 8 % of the phenotypic variation and also co-located with a major seed dormancy QTL determined by germination index. The proximal PHS QTL, between Wmc474 and CNL415-rCDPK, contributed 16 % of the variation. Several candidate genes including Mg-chelatase H subunit family protein, GTP-binding protein and calmodulin/Ca²⁺-dependent protein kinase were linked to the PHS QTL. Although many recombinant lines were identified, the lack of polymorphism for markers in the QTL interval prevented the localization of the recombination breakpoints and identification of the gene underlying the phenotype.     

Validating a novel allele of <Emphasis Type="Italic">viviparous-1</Emphasis> (<Emphasis Type="Italic">Vp-1Bf</Emphasis>) associated with high seed dormancy of Chinese wheat landrace,Wanxianbaimaizi

Pre-harvest sprouting (PHS) can easily lead to yield losses of wheat and downgrading of grain quality in wheat-growing areas where long periods of wet weather occur frequently during harvest. As a main component of PHS, seed dormancy is often evaluated by germination index (GI). Previous researches have proved allelic variations of Vp-1B to have a close relationship with dormancy of white-grained wheat. In the present study, a mapping population covering 157 recombinant inbred lines was developed from a cross of two white-grained varieties, Wanxianbaimaizi and Jing411. Wanxianbaimaizi is a strongly dormant landrace carrying a novel allele, Vp-1Bf; whereas, Jing411 is a non-dormant variety with wild allele, Vp-1Ba. Our objective was to validate the association between the novel allele and seed dormancy using the population. The results of sequences alignment indicated an insertion of 193 bp and a deletion of 109 bp were both identified in the novel allele, respectively, compared with wild allele in Jing411. Here, the deletion was first detected. As for lines possessing Vp-1Ba, the average GI value was 0.584, significantly higher than that of lines holding Vp-1Bf. Among three genotypes, Vp-1Bf allele was generally corresponded to the lowest average of GI value (0.195), and the highest dormancy; in addition, lines with heterozygous genotype often showed intermediate GI value (0.356). Of 92 RILs with Vp-1Ba, over 70 lines showed higher GI value (>0.40), and only about 7 lines had lower GI value (<0.20). On the other hand, among 60 RILs with Vp-1Bf, over 50 lines showed lower GI value (<0.40), and only about 7 lines had higher GI value (>0.60). The result of composite interval mapping revealed that a major QTL for seed dormancy was flanked by Xwmc446 and Vp1 on 3BL, which was proximal to Vp1 (7.6–8.4 cM). The locus could explain 24.6–40.7% of total phenotypic variation across three crop seasons. The above results could confirm that the novel allele had a striking association with high seed dormancy, and may be useful for improving PHS tolerance of white-grained wheat.     

A QTL located on chromosome 4A associated with dormancy in white- and red-grained wheats of diverse origin

Improved resistance to preharvest sprouting in modern bread wheat (Triticum aestivum. L.) can be achieved via the introgression of grain dormancy and would reduce both the incidence and severity of damage due to unfavourable weather at harvest. The dormancy phenotype is strongly influenced by environmental factors making selection difficult and time consuming and this trait an obvious candidate for marker assisted selection. A highly significant Quantitative Trait Locus (QTL) associated with grain dormancy and located on chromosome 4A was identified in three bread wheat genotypes, two white- and one red-grained, of diverse origin. Flanking SSR markers on either side of the putative dormancy gene were identified and validated in an additional population involving one of the dormant genotypes. Genotypes containing the 4A QTL varied in dormancy phenotype from dormant to intermediate dormant. Based on a comparison between dormant red- and white-grained genotypes, together with a white-grained mutant derived from the red-grained genotype, it is concluded that the 4A QTL is a critical component of dormancy; associated with at least an intermediate dormancy on its own and a dormant phenotype when combined with the R gene in the red-grained genotype and as yet unidentified gene(s) in the white-grained genotypes. These additional genes appeared to be different in AUS1408 and SW95-50213.     

Identifying alleles of <Emphasis Type="Italic">Viviparous-1B</Emphasis> associated with pre-harvest sprouting in micro-core collections of Chinese wheat germplasm

Wheat pre-harvest sprouting (PHS) is an undesired trait, which often reduces yield and downgrades end-use quality of grain. Viviparous-1B (Vp-1B), a regulator gene located on chromosome 3B, has previously been proved to be involved in inducing grain dormancy of wheat. In order to obtain some new or useful alleles associated with PHS tolerance of white-grained wheat, we developed a gene-specific marker (Vp1-b2) to identify allelic variations of Vp-1B using denaturing PAGE in micro-core collections of Chinese wheat and landraces. As a main component observed genetic variation for PHS, seed dormancy evaluated by germination index (GI) was determined at dough-yellow ripening stage in the present study. The results indicated that six alleles of Vp-1B, in our study, were discovered among 276 Chinese wheat varieties. Of these alleles, two variants were validated to be novel alleles and designated as Vp-1Be and Vp-1Bf, respectively. By investigating the association between allelic variations of Vp-1B and seed dormancy, we found allele of Vp-1Ba always inclined to weak seed dormancy and susceptibility to PHS. Up to 62.2% genotypes carrying the allele had high GI value with a range of 0.51–1.00, only 14.4% genotypes had low GI value under 0.30. On the contrary, other variants such as Vp-1Bb, Vp-1Bc, Vp-1Bd, Vp-1Be and Vp-1Bf mostly occurred in varieties with higher PHS tolerance, which average of GI values were 0.204, 0.227, 0.296, 0.256 and 0.186, respectively. In Chinese wheat germplasms, Vp-1Ba and Vp-1Bc showed the most widespread distribution followed by Vp-1Bb; other alleles fell into less used varieties. Our research confirmed rich allelic variation of Vp-1B occurred in micro-core collections of Chinese wheat and landraces, which may be useful for improving PHS tolerance as breeding parents.     

Novel loci and a role for nitric oxide for seed dormancy and preharvest sprouting in barley

Barley is used for food and feed, and brewing. Nondormant seeds are required for malting, but the lack of dormancy can lead to preharvest sprouting (PHS), which is also undesired. Here, we report several new loci that modulate barley seed dormancy and PHS. Using genome‐wide association mapping of 184 spring barley genotypes, we identified four new, highly significant associations on chromosomes 1H, 3H, and 5H previously not associated with barley seed dormancy or PHS. A total of 71 responsible genes were found mostly related to flowering time and hormone signalling. A homolog of the well‐known Arabidopsis Delay of Germination 1 (DOG1) gene was annotated on the barley chromosome 3H. Unexpectedly, DOG1 appears to play only a minor role in barley seed dormancy. However, the gibberellin oxidase gene HvGA20ox1 contributed to dormancy alleviation, and another seven important loci changed significantly during after‐ripening. Furthermore, nitric oxide release correlated negatively with dormancy and shared 27 associations. Origin and growth environment affected seed dormancy and PHS more than did agronomic traits. Days to anthesis and maturity were shorter when seeds were produced under drier conditions, seeds were less dormant, and PHS increased, with a heritability of 0.57–0.80. The results are expected to be useful for crop improvement.     

Identification of major loci for seed dormancy at different post-ripening stages after harvest and validation of a novel locus on chromosome 2AL in common wheat

A long-period duration of seed dormancy helps to reduce pre-harvest sprouting (PHS) damage in common wheat when a long period of rainfall or high humidity occurs. Identification of genes or loci underlying seed dormancy duration is of high importance for investigating genetic mechanism of PHS tolerance of wheat. In the present study, the germination index (GI) of different mapping populations at 5 days (GI5), 15 days (GI15), and 30 days (GI30) after harvest (DAH) was recorded during the 2011–2012, 2012–2013, 2013–2014, and 2014–2015 cropping seasons. Field sprouting (FS) values were also determined in 2012–2013 and 2014–2015 cropping seasons. Association analysis was performed in 260 wheat varieties and advanced lines differing in seed dormancy (SD) using 557 SSR and 14 gene-specific markers for PHS/SD-related genes. The result indicated that a total of 47 loci were significantly (P < 0.01) associated with SD using both the general linear model (GLM) and mixed linear model (MLM). Five major loci were consistently detected at different post-ripening stages after harvest, including four for GI5 and GI15 on chromosomes 3AS, 3BL, 5AL, and 5BL responsible for middle-duration SD, and one for GI5, GI15, and GI30 on 2AL associated with longer-duration SD. The major locus on 2AL (designated Qsd.ahau-2AL) is likely to be a novel QTL, which was linked to Xwmc658 by mapping analysis in 165 recombinant inbred lines (RILs) derived from the Jing 411 × Wanxianbaimaizi cross and 728 F₂ plants from Jimai 20 × Suiningtuotuomai. Furthermore, a CAPS marker CAPS-2AL was developed for Qsd.ahau-2AL locus and was validated using the 728 F₂ plants and 201 accessions of the Chinese mini-core collection. Our results also revealed that the TaMFT-like gene on 3AS had a more significant association with dormancy duration than the other six genes underlying SD/PHS resistance in Chinese wheat germplasm. This study provides useful information for marker-assisted selection in wheat breeding and enhances our understanding of molecular genetics of SD in wheat.     

Genetic variation of Vp1 in Sichuan wheat accessions and its association with pre-harvest sprouting response

Pre-harvest sprouting (PHS) in bread wheat is a major abiotic constraint reducing yield and influencing the production of high quality grain. In China both spring and winter wheat regions are affected by PHS. Sichuan lies in southwest China, where the most of rainfall occurs during April to September when wheat is harvested. The present investigation was conducted to identify the allelic variability of Vp1, a gene that plays a role in maintenance and induction of dormancy, among Sichuan landraces and recent cultivars with different dormancy levels and to find potential sources of PHS resistance for breeding. Sichuan landrace and cultivar wheat accessions had a wide range of dormancy levels. The average germination index (GI) of Sichuan landrace accessions was 0.232, whereas at 0.674 it was much higher for cultivars. The different dormancy levels between landraces and cultivars indicated that pre-harvest sprouting resistance might have been neglected in recent Sichuan wheat breeding programs. The average GI of white grained accessions was higher than for red grained accessions. Particular Vp-1B gene fragments were specific in landraces or cultivars and in white or red grained accessions. The results indicated that Vp-1B markers could be used to distinguish cultivars and landraces. Significant relationships between certain Vp-1B allelesand GI of Sichuan wheat accessions were shown by Spearman’s rank correlation analysis.     

QTLs for resistance to preharvest sprouting in rye (<Emphasis Type="Italic">Secale cereale</Emphasis> L.)

Grain quality of rye is often negatively affected by sprouting - a complex trait with a poorly understood genetic background and strong interaction with weather conditions. The aim of this report was to detect the main quantitative trait loci (QTLs) underlying preharvest sprouting resistance in rye, measured as a percentage of sprouted kernels after spraying spikes with water for 7 days. Simple and composite interval mapping, carried out in 3 environments on 94 F3 and F4 families of the cross between sprouting-susceptible (541) and sprouting-resistant (Ot1-3) inbred lines, revealed 5 QTLs located on chromosome arms 1RL, 2RL, 5RL, 6RL and 7RL. The significance of these QTLs was additionally proved by disruptive selection carried out on 5000 F2 plants of the 541 x Ot1-3 cross and continued to the F5 generation of recombinant inbred lines (RIL), which strongly affected allele frequencies at linked marker loci. Resistance to preharvest sprouting showed dominant inheritance except for QPhs.uas-7R.1 (recessive) and QPhs.uas-1R.1 (additive). Results of the present study suggest that introgression of 4-5 QTLs, identified in line Ot1-3, should substantially reduce sprouting risk in rye varieties.     

Barley mutants with low rates of endosperm starch synthesis have low grain dormancy and high susceptibility to preharvest sprouting

? Studies of embryo dormancy in relation to preharvest sprouting (PHS) in cereals have focused on ABA and other hormones. The relationship between these phenomena and the rate of grain filling has not been investigated. ? A collection of barley mutants impaired in starch synthesis was assessed for preharvest sprouting in the field. In subsequent glasshouse experiments, developing grains were assayed for germination index, sugars, abscisic acid (ABA) and the effects of temperature and exogenous ABA on germination. ? Mutant lines displayed greater preharvest sprouting in the field than parental lines. In the glasshouse, nondeep physiological dormancy was reduced in developing grains of five lines with mutations affecting proteins involved in endosperm starch synthesis. Inhibition of germination by exogenous ABA and elevated temperature was decreased in developing mutant grains. Sugar concentrations were high but embryo and endosperm ABA contents were unaltered. ? We reveal a direct connection between grain filling and the extent of grain dormancy. Impaired endosperm starch synthesis directly influences the acquisition of embryo dormancy, perhaps because endosperm sugar concentrations modulate the ABA responsiveness of the embryo. Thus environmental or genetic factors that reduce grain filling are likely to reduce dormancy and enhance susceptibility to PHS.     

Resistance of bread wheat (Triticum aestivum L.) to preharvest sprouting: An association analysis

A statistical analysis of the data about 1422 bread wheat accessions with estimated preharvest sprouting was carried out. Close associations of preharvest sprouting resistance with the grain color and with resistance to Fusarium head blight were revealed, as well as weak, but statistically significant, associations with the habit, awnedness, and reduced height genes Rht-B1 and Rht-D1 (insensitive to gibberellin GA3). The pedigree analysis showed that the cluster structures of the gene pools of the North American red-grained and white-grained varieties are practically identical. In both groups, varieties that are resistant to preharvest sprouting differ from susceptible ones in the percentage of the contributions of the Crimean and Mediterranean landraces. Resistance is associated with a high contribution by the Crimean landrace and susceptibility is associated with a high contribution by the Mediterranean landrace.     

Mapping QTLs for grain dormancy on wheat chromosome 3A and the group 4 chromosomes,and their combined effect

A major QTL for grain dormancy, QPhs.ocs-3A.1, derived from the highly dormant wheat Zenkoujikomugi (Zen), has been identified in a study made under a controlled environment. Further investigations were needed to dissect the precise position and expression of QPhs.ocs-3A.1 under different field conditions because the ability to detect genetic loci for grain dormancy traits is compromised by environmental effects and genotype/environment interactions. Group 4 chromosomes have also been shown to be possible sites of QTLs for grain dormancy. The objectives of this study were (1) to locate additional molecular markers in the QPhs.ocs-3A.1 region, (2) to identify QTLs on the group 4 chromosomes and (3) to elucidate their combined effects. We examined the recombinant inbred lines (RILs) from a cross between Chinese Spring (CS) and Zen over a 3-year period in one location and 1 year in a different location. In an interval mapping study QPhs.ocs-3A.1 was mapped to within the 4.6 cM region flanked by Xbarc310 and Xbcd907 at the proximal end of the short arm of chromosome 3A. QPhs.ocs-3A.1 was confirmed to be the predominant dormancy QTL since it explained a large portion (11.6–44.8%) of the phenotypic variation, and was strongly displayed under dormancy-breaking conditions or at low germination temperatures. For QPhs.ocs-4A.1, identified on the long arm of chromosome 4A, and QPhs.ocs-4B.1, on the centromeric region of the long arm of Chr 4B, the LOD peak positions and the desirable allele were consistent between the trials, while the LOD scores and contribution to the phenotypic variation varied. Transgressive segregants were observed among the 125 RILs and most of them had a combination of the three alleles conferring a higher dormancy: the Zen alleles at QPhs.ocs-3A.1 and QPhs.ocs-4A.1 and the CS allele at QPhs.ocs-4B1. This demonstrated a combined effect of the desirable alleles on accelerating grain dormancy, with their total effect being superior to that of Zen.     

Mapping QTLs for pre-harvest sprouting tolerance on chromosome 2D in a synthetic hexaploid wheat×common wheat cross

Based on segregation distortion of simple sequence repeat (SSR) molecular markers, we detected a significant quantitative trait loci (QTL) for pre-harvest sprouting (PHS) tolerance on the short arm of chromosome 2D (2DS) in the extremely susceptible population of F₂ progeny generated from the cross of PHS tolerant synthetic hexaploid wheat cultivar ‘RSP’ and PHS susceptible bread wheat cultivar ‘88–1643’. To identify the QTL of PHS tolerance, we constructed two SSR-based genetic maps of 2DS in 2004 and 2005. One putative QTL associated with PHS tolerance, designatedQphs.sau-2D, was identified within the marker intervalsXgwm261-Xgwm484 in 2004 and in the next year, nearly in the same position, between markerswmc112 andXgwm484. Confidence intervals based on the LOD-drop-off method ranged from 9 cM to 15.4 cM and almost completely overlapped with marker intervalXgwm261-Xgwm484. Flanking markers near this QTL could be assigned to the C-2DS1-0.33 chromosome bin, suggesting that the gene(s) controlling PHS tolerance is located in that chromosome region. The phenotypic variation explained by this QTL was about 25.73–27.50%. Genotyping of 48 F₆ PHS tolerant plants derived from the cross between PHS tolerant wheat cultivar ‘RSP’ and PHS susceptible bread wheat cultivar ‘MY11’ showed that the allele ofQphs.sau-2D found in the ‘RSP’ genome may prove useful for the improvement of PHS tolerance.     

Dissection of genetic components of preharvest sprouting resistance in white wheat

Preharvest sprouting (PHS) in rain-affected wheat (Triticum aestivum) is a major constraint to the production of high-quality wheat, especially in regions where white grain wheat cultivars are preferred. To characterize quantitative trait loci (QTLs) for PHS resistance and seed dormancy (SD), we evaluated 162 recombinant inbred lines developed from the cross between PHS-resistant white wheat landrace Tutoumai A and PHS-susceptible white wheat cultivar ‘Siyang 936’ for PHS resistance and SD in field and greenhouse experiments. Composite interval mapping (CIM) identified four QTLs for PHS resistance and long SD that explained up to 45 and 40.8% of the phenotypic variation in five PHS and four SD experiments, respectively. Qphs.pseru-4A.1 was detected in three of the five PHS experiments, and Qphs.pseru-5B.1, Qphs.pseru-5B.2, and Qphs.pseru-4B.1 were detected in two of the five PHS experiments, respectively. All four QTLs for PHS resistance also affected SD. Qphs.pseru-4A.1 was significant in all four SD experiments; the other three QTLs were detected only in one experiment. Additive and epistatic effects were observed for PHS resistance and SD. Besides three additive QTLs for PHS resistance and two for long SD, an additional 11 and 10 QTLs were detected with epistatic effects on PHS resistance and SD, respectively. The major genetic component of PHS resistance was SD, and other genetic factors may also contribute to PHS resistance in this population.     

Detection of loci controlling seed dormancy on group 4 chromosomes of wheat and comparative mapping with rice and barley genomes

Three quantitative trait loci (QTLs) controlling seed dormancy were detected on group 4 chromosomes of wheat (Triticum aestivum L.) using 119 doubled haploid lines (DHLs) derived from a cross between AC Domain and Haruyutaka. A major QTL, designated QPhs.ocs-4A.1, was identified within the marker interval between Xcdo795 and Xpsr115 in the proximal region of the long arm of chromosome 4A. Two minor QTLs, QPhs.ocs-4B.2 on 4B and QPhs.ocs-4D.2 on 4D, were flanked by common markers, Xbcd1431.1 and Xbcd1431.2 in the terminal region of the long arms, suggesting a homoeologous relationship. These three QTLs explained more than 80% of the total phenotypic variance in seed dormancy of DHLs grown in the field and under glasshouse conditions. The AC Domain alleles at the three QTLs contributed to increasing seed dormancy. Comparative maps across wheat, barley and rice demonstrated the possibility of a homoeologous relationship between QPhs.ocs-4A.1 and the barley gene SD4, while no significant effects of the chromosome regions of wheat and barley orthologous to rice chromosome 3 region carrying a major seed dormancy QTL were detected. Received: 5 June 2000 / Accepted: 31 August 2000