QTL mapping of the domestication traits pre-harvest sprouting and dormancy in wheat (<Emphasis Type="BoldItalic">Triticum aestivum L.</Emphasis>)

A set of 75 recombinant inbred lines (RILs) of the ITMI mapping population was grown under field conditions in Gatersleben. The lines were evaluated for the domestication traits pre-harvest sprouting and dormancy (germinability). Main QTLs could be localized for pre-harvest sprouting on chromosome 4AL and dormancy on chromosome 3AL. In addition, 85 Triticum aestivum cv. “Chinese Spring”-Aegilops tauschii introgression lines grown under greenhouse conditions were researched. No QTL could be found for pre-harvest sprouting but a major QTL could be detected for dormancy on chromosome 6DL.     

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

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 white-grained 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 Zen-allele 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.     

Enhancing the identification of genetic loci and transgressive segregants for preharvest sprouting resistance in a durum wheat population

Preharvest sprouting reduces grain quality and lowers grade. Characterization of preharvest sprouting resistance is important in selection in breeding for transgressive segregation and understanding the genetics of the trait for identifying QTL. Methods of measuring dormancy and other factors contributing to preharvest sprouting resistance are varied. The objective of this study was to demonstrate the requirement of multiple methods of measurement over multiple durations of germination to maximize understanding of transgressive segregation and QTL for preharvest sprouting resistance within a segregating durum wheat population grown in multiple environments. Ninety-eight durum wheat (Triticum turgidum L. var. durum) recombinant inbred lines (RIL) from a cross of a minimally dormant line, Sentry, by a moderately dormant line, Kyle, and controls were grown in replicated field tests in 1996, 1997 and 1998 and in a growth chamber trial in 1998. Preharvest sprouting was measured from intact spikes as sprouting index or from hand threshed grain as germination index (GI), germination resistance (GR), and percent germination (PG). The threshed grain measures were evaluated using counts at 7, 14 and 21 days intervals from the start of germination. Correlations performed on the measure type and duration using lines within the RIL population showed some discontinuity across environments, type of measure and duration of measure, with counts at extended intervals for PG producing the lowest correlations. The number of transgressive segregant lines varied with environment, duration and type of measure. Different QTL were identified by different types of measures and duration of counts. GI calculated for 7, 14 and 21 days germination count intervals and GR calculated for 21 days identified a highly significant QTL on chromosome1A (QPhsd.spa.-1A.1). GR calculated for 7 days identified a highly significant QTL on 2A (QPhsd.spa.-2A.1) in two different environments, and GI calculated for 21 days and PG at 7 days identified the same highly significant QTL on chromosome 7B (QPhsd.spa.-7B.1). The results indicated that multiple measures and durations of measure intervals must be applied to results collected across different environments to maximize the identification of QTL and transgressive segregants of the population segregating for preharvest sprouting resistance.     

Breeding of white-grained wheats for Japan

The possibility of breeding white-grained wheats tolerant to pre-harvest sprouting under Japanese humid weather conditions is discussed. New genetic dormancy sources, such as, AUS1408, 8019R1 and RyuuMai7, were evaluated for seed dormancy in different weather conditions. Some white-grained dormant wheats showed a strong dormancy similar to that of red-grained dormant wheats in a greenhouse trial, in the field their dormancy expression was much less than the red wheats. Three populations involving crosses with these new sources for winter wheat breeding were examined under repeated selection for seed dormancy. Some dormant white-grained lines, as judged under glasshouse conditions, were developed. Again the level of dormancy in these lines was not sufficient compared to red dormant varieties in field trial. In order to develop truly superior dormant white-grained materials, one population involving crosses with two dormant varieties, AUS1408 and 8019R1, was examined under repeated selection. From these materials we succeeded in breeding lines that had not only a good dormancy but also showed adaptation to Japanese weather conditions, including earliness, scab resistance and good seed appearance. However again the dormancy of these lines in field trial was not sufficient compared to that of red wheats and there was not a clear difference for seed dormancy between breeding lines and their parents. We conclude therefore that more work involving the use of new genetic sources or new breeding techniques, will be necessary for breeding advanced lines that maintain a sufficient tolerance to PHS in humid Japanese weather condition. This revised version was published online in August 2006 with corrections to the Cover Date.     

Development of winter wheat with excellent resistance to pre-harvest sprouting and rain damage

Pre-harvest sprouting and high alpha-amylase activity are the most serious problems for the wheat production in Hokkaido, the northern most part of Japan. It has become more frequent for wheats to be exposed to continuous rain for several days in harvest time. In addition, low temperature below 15 ^°C, combined with rainfall, accelerates the damage of pre-harvest sprouting. Therefore, we started a breeding program in 1998 to develop wheat varieties with excellent resistant to sprouting damage in Hokkaido.Selection and evaluation of pre-harvest sprouting of resistant lines were conducted by two tests. One test was artificial rain treatment of intact spikes and the other was a germination test of hand-threshed grains at 10, 15 and 20 ^°C. The spikes of each line and variety were collected at physiological maturity and at one week after the first sampling date. Falling number was also measured.We have succeeded in breeding a deeply dormant breeding line, Kitakei 1802, from 1,923 doubled haploid lines raised by anther culture from the cross between Kitakei 1616 and Nishikazekomugi. Kitakei 1802 hardly sprouted through 10 days” continuous rainfall treatment at low temperature (15 ^°C) and maintained high falling number (> 300 s) in 2002 and 2003.     

Relationship between sprouting in wheat and embryo response to endogenous inhibition

Summary Seed dormancy in wheat (Triticum aestivum L. em Thell) is important for minimizing pre-harvest sprouting. To facilitate breeding cultivars that tolerate pre-harvest sprouting conditions, we assessed mode and magnitude of variation of seed dormancy among genotypes and investigated involvement of endogenous water-soluble inhibitor(s) in seed germination. Embryo bio-assays established that water-soluble inhibitor was ubiquitous among the wheat cultivars studied and did not diminish in quantity during after-ripening. Germination response of embryos was decreased by endogenous inhibitor, but the effect markedly declined as embryos aged at room temperature. Variation in dormancy among cultivars was primarily caused by differential response of their embryos to endogenous inhibitor. Gibberellic acid counteracted the initial inhibitory effect of endogenous inhibitor on germination but not the subsequent inhibitory effect on seedling growth. We concluded that pre-harvest sprouting resistance involves multiple factors, particularly embryo receptivity to endogenous inhibitor, and that variation in inhibitor quantity is not solely responsible for genotypic differences in susceptibility to pre-harvest sprouting. The possibility of additional approaches to breeding for pre-harvest sprouting resistance is indicated.Contribution no. 81-389-j, Department of Agronomy, Kansas State University, Manhattan, KS 66506, U.S.A.     

Novel resistance to pre-harvest sprouting in Australian wheat from the wild relative Triticum tauschii

The diploid D-genome progenitor of hexaploid wheat, Triticum tauschii (Coss.) Schmahl., was screened to identify mechanisms for resistance to pre-harvest sprouting. A number of promising mechanisms were identified, and transferred to hexaploid wheat via wide-hybridisation. One identified mechanism, an inhibitory phenolic compound present in the bracts surrounding the grain, has been shown to function effectively in synthetic hexaploid wheats. A number of seed-borne dormancy mechanisms were also identified. Expression of embryo dormancy in synthetic hexaploid wheats was demonstrated when compared with non-dormant hexaploid wheat. Effects of the seed coat on dormancy were also studied, with the seed coat of synthetic hexaploids accelerating rather than inhibiting germination. Embryo dormancy was also demonstrated in two `direct-cross' hybrids. The results suggest that a combination of the described mechanisms may produce white wheats with resistance to pre-harvest sprouting adequate for most Australian climatic conditions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Identification of genomic regions associated with seed dormancy in white-grained wheat

Pre-harvest sprouting (PHS) in developing wheat (Triticum aestivum L.) spikes is stimulated by cool and wet weather and leads to a decline in grain quality. A low level of harvest-time seed dormancy is a major factor for PHS, which generally is a larger problem in white-grained as compared to red-grained wheat. We have in this study analyzed seed dormancy levels at the 92nd Zadok growth stage of spike development in a doubled-haploid (DH) white wheat population and associated variation for the trait with regions on the wheat genome. The phenotypic data was generated by growing the parent lines Argent (non-dormant) and W98616 (dormant) and 151 lines of the DH population in the field during 2002 and 2003, at two locations each year, followed by assessment of harvest-time seed dormancy by germination tests. A genetic map of 2681 cM was constructed for the population upon genotyping 90 DH lines using 361 SSR, 292 AFLP, 252 DArT and 10 EST markers. Single marker analysis of the 90 genotyped lines associated regions on chromosomes 1A, 2B, 3A, 4A, 5B, 6B, and 7A with seed dormancy in at least two out of the four trials. All seven putative quantitative trait loci (QTLs) were contributed by alleles of the dormant parent, W98616. The strongest QTLs positioned on chromosomes 1A, 3A, 4A and 7A were confirmed by interval mapping and markers at these loci have potential use in marker-assisted selection of PHS resistant white-grained wheat.     

Dormancy breaking procedures and the breeding of white-grained wheat with resistance to pre-harvest sprouting

Summary Gibberellic acid, cold (4°C) and a combination of these two treatments were tested for use in breaking dormancy in 27 lines of white-grained wheat with varying levels of resistance to pre-harvest sprouting. Germination increased in all lines treated with gibberellic acid. Dormancy could be broken with 1 M gibberellic acid. Response to cold varied. A combination of gibberellic acid and cold treatment was the most effective. This technique has been found useful in treating seed in a breeding program aimed at producing wheats with resistance to pre-harvest sprouting.     

Mapping quantitative trait loci controlling pre-harvest sprouting resistance in a red × white seeded spring wheat cross

Hard white wheat (Triticum aestivum L.) is a value-added product because of its processing advantages over red wheat; however, white wheat tends to be more susceptible to pre-harvest sprouting (PHS). To identify quantitative trait loci (QTLs) associated with PHS tolerance, we developed a doubled haploid (DH) mapping population from the cross AC Domain (red seeded) × White-RL4137 (white seeded). A genetic map was constructed using microsatellite markers located on chromosome groups 3, 4, 5 and 6. A population of 174 DH lines was characterized for important aspects of PHS including sprouting index, germination index, Hagberg falling number and seed coat colour. A total of 11 QTLs were identified on group 3 chromosomes and on chromosome 5D. Seven QTLs associated with the PHS traits were found to be co-incident with seed coat colour on chromosomes 3A, 3B and 3D. The 5D PHS QTL was notable because it is independent of seed coat colour.     

四川省小麦品种(系)穗发芽抗性评价

穗发芽严重影响小麦产量和品质,受到生长环境、种皮颜色和遗传基因的共同控制。由于四川地区在小麦收获季节容易出现高温高湿的气候条件,是小麦穗发芽的常发和重发区。依据材料的穗发芽抗性,有目的性地配制杂交组合选育抗性品种是控制小麦穗发芽的重要策略,而系统鉴定分析各优良品种及品系的穗发芽抗性是亲本选配的重要依据。本研究调查分析了242份2000年来四川省审定小麦品种及即将成为未来几年新品种的2017—2018 年四川省区试品系的田间穗发芽情况,发现分别有23(9.5%)和67 (27.7%)份材料具有强（穗发芽率低于5%）和高（穗发芽率介于5%~15%）的穗发芽抗性。这为穗发芽抗性育种亲本的选择提供了参考;并且发现穗发芽抗性在不同类型材料中存在差异：2000 年来审定品种＜区试普通小麦品系＜区试早播早熟小麦品系＜区试特殊用途小麦品系,穗发芽抗性在未来几年品种中将有所增强;种皮颜色对穗发芽抗性具有强烈影响,随着种皮颜色加深,穗发芽抗性越强,但仍发现3 份（‘川育26’、‘川辐9 号’、‘川辐17 号’）白皮小麦材料具有强的穗发芽抗性,为白皮小麦抗穗发芽育种提供参考。其次发现在四川环境下,早播可能会提高小麦品种的穗发芽抗性。     

Cereal comparative genetics and preharvest sprouting

Most genes in hexaploid bread wheat are triplicated. Knowledge of the relationships between the three genomes then allows us to build consensus maps of loci controlling any trait. In this paper we show such a map of some of the major genes and QTL effects that have been reported to be associated with pre-harvest sprouting. The result highlights regions of the genome that have featured in several studies and possible links between QTL and major genes. The same analysis can be extended to other economic grass crop species, where the comparative genome relationships are known in some detail. In this way, loci related to preharvest sprouting in wheat have been compared with some major genes affecting dormancy in maize and dormancy related QTLs in rice. This alignment identifies some candidate loci from maize and some regions of the rice genome that may relate to important wheat QTLs. In turn this approach will open up application of the emerging rice genomic DNA sequence to wheat pre-harvest sprouting research. This revised version was published online in August 2006 with corrections to the Cover Date.     

关于水稻穗芽的生理学研究

利用重组自交系籼稻中-156/谷梅2号304份株系为材料，在田间条件下营造高温、高湿的小气候，以“穗穗芽率”及“粒穗芽率”为指标，筛选易发生穗芽与不易发生穗芽的极端材料，比较研究重组自交系亲本与各供试株系籽粒在穗芽发生期间的生理差异。结果表明，该重组自交系母本谷梅2号比父本中-156易穗芽，在正常成熟过程中籽粒内源GA₁含量水平高于中-156，ABA含量水平低于中-156；谷梅2号籽粒淀粉酶活性也高于中-156。花后15 d至完熟的籽粒灌浆期如遇高温、高湿条件，谷梅2号及易穗芽的株系籽粒内源GA1随雨日渐增，增幅高于中-156及不易穗芽的株系，同时其淀粉酶活性回升，在正常成熟过程中花后15 d后籽粒中淀粉酶活性与日渐降，但其幅度远高于父本中-156及不易穗芽的株系，这种变化可能是易穗芽的亲本与株系对高温、高湿敏感诱发穗上发芽的主要生理基础。     

Screening for grain dormancy in segregating generations of dormant × non-dormant crosses in white-grained wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Pre-harvest sprouting (PHS) in wheat (Triticum aestivum L.) is a significant problem. Introgression of genes controlling grain dormancy into white-grained bread wheat is one means of improving resistance to PHS. In this study seven dormant (containing the SW95-50213 and AUS1408 sources) × non-dormant crosses were produced to investigate the effectiveness of selection for grain dormancy in early segregating generations. Each generation (F₁–F₄) was grown in a temperature controlled glasshouse with an extended photoperiod (i.e. continuous light). F₂ and F₃ generations were subject to selection. Five hundred harvest-ripe grains were tested for germination over a 14 day period, and the 100 most dormant grains were retained and grown-on to produce the next generation within each cross. The response to selection was assessed through analysis of the time to 50% germination (G₅₀) in the F₂, F₃ and F₄ generations. In addition, changes in marker class frequencies for two SSR markers (barc170 and gpw2279) flanking a known quantitative trait locus (QTL) for grain dormancy on chromosome 4A were assessed in DNA from F₂ plants selected from early germinating (non-dormant) and late germinating (dormant) phenotypic extremes within each cross. Selection for grain dormancy in the F₂ and F₃ generations effectively recovered the dormant phenotype in all seven crosses, i.e. the F₄ generation was not significantly different from the dormant parent. Further, selection based on individual F₂ grains changed marker class frequencies for the 4A dormancy QTL; in most cases eliminating the marker class homozygous for the non-dormant alleles. Application of this screening method will enable breeders to better select for grain dormancy and may lead to development of new cultivars offering effective resistance to PHS in the near future.     

Detection of QTLs for traits associated with pre-harvest sprouting resistance in bread wheat (Triticum aestivum L.)

Pre-harvest sprouting (PHS) is one of the serious problems for wheat production, especially in rainy regions. Although seed dormancy is the most critical trait for PHS resistance, the control of heading time should also be considered to prevent seed maturation during unfavorable conditions. In addition, awning is known to enhance water absorption by the spike, causing PHS. In this study, we conducted QTL analysis for three PHS resistant related traits, seed dormancy, heading time and awn length, by using recombinant inbred lines from ‘Zenkouji-komugi’ (high PHS resistance) × ‘Chinese Spring’ (weak PHS resistance). QTLs for seed dormancy were detected on chromosomes 1B (QDor-1B) and 4A (QDor-4A), in addition to a QTL on chromosome 3A, which was recently cloned as TaMFT-3A. In addition, the accumulation of the QTLs and their epistatic interactions contributed significantly to a higher level of dormancy. QDor-4A is co-located with the Hooded locus for awn development. Furthermore, an effective QTL, which confers early heading by the Zenkouji-komugi allele, was detected on the short arm of chromosome 7B, where the Vrn-B3 locus is located. Understanding the genetic architecture of traits associated with PHS resistance will facilitate the marker assisted selection to breed new varieties with higher PHS resistance.     

Grain dormancy in fixed lines of white-grained wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) grown under controlled environmental conditions

Pre-harvest sprouting (PHS) in wheat (Triticum aestivum L.) can be a significant problem, causing deleterious effects on grain quality. However, the adverse impacts of PHS can be reduced by introgressing genes controlling grain dormancy into white-grained bread wheat. Screening for grain dormancy typically involves germination testing of harvest-ripe grain grown in a glasshouse or field. However, the more uniform environmental conditions provided by temperature controlled glasshouses (i.e. controlled environmental conditions—CEC) may provide significant benefits for the assessment of grain dormancy. In this study, the dormancy phenotype of grain grown under CEC incorporating an extended photoperiod, was compared with 2 years of data from field grown material. Four dormant double haploid lines (derived from SW95-50213 and AUS1408) and two locally adapted non-dormant cultivars EGA Gregory and EGA Wills were compared in three replicated experiments grown under CEC (22 ± 3°C and 24 h photoperiod). The germination response of harvest-ripe grain was examined to assess the expression of grain dormancy. Two measures of germination, the predicted time to 50% germination (G ₅₀) and a weighted germination index, both clearly differentiated dormant and non-dormant lines grown under CEC. In addition, levels of grain dormancy were similar to field-grown plants. These results demonstrated that CEC with an extended photoperiod can be used for rapid and reliable characterisation of grain dormancy in fixed lines of bread wheat.     

Quantitative trait loci influencing grain protein content in tetraploid wheats

Seed storage protein content of durum wheat (Triticum turgidum var. durum) has an important effect on nutritional value and pasta-making characteristics. The objective of this study was to determine by association with genetic markers the number, chromosomal location, and magnitude of effect of quantitative trait loci (QTLs) controlling protein concentration in kernels. A set of 65 recombinant inbred lines (RIs) was developed by single seed descent from a cross between cultivated durum wheat cv. ‘Messapia’ (low protein content) and accession MG4343 of the wild tetraploid wheat var. dicoccoides (high protein content). This population was characterized for eight morphological, six storage protein, one isozyme and 124 RFLP loci. Field trials were conducted in one location in 1993 and two locations in 1994. QTLs were mapped by regression analysis on each marker locus for each location and for the average across environments. A total of six putative QTLs were located on chromosome arms 4BS, SAL, 6AS, 6BS and 7BS. The number and size of QTLs detected varied across environments. The marker with the highest r² value per QTL in each environment and across environments was chosen for a multiple linear regression analysis, which explained 49.2- 56.4% of the phenotypic variation for protein content. Only some of the markers were found to be negatively associated with plant grain yield and/or seed weight in one or two of the environments.     

Resistance to Septoria tritici in Hordeum chilense×Triticum spp. Amphiploids

The reaction of tritordeum and its Hordeum chilense and Triticum spp. parents to Septoria tritici was studied in field and seedling experiments. All H. chilense lines were highly resistant to all the isolates and did not allow pycnidia development. The ‘durum wheat isolate’ developed pycnidia only on durum wheats. The ‘breed wheat isolate’ was very virulent on bread wheat but also on the wild tetra-ploid wheats. The other two isolates were compatible with durum and bread wheat. All hexaploid tritordeums were highly resistant both in the field and the seedling experiments. Some octoploid tritordeums allowed pycnidial development, but at much lower levels than their wheat parent. Resistance in tritordeum was not associated with plant stature and only in octoploid tritordeum was association of resistance with late maturity detected.     

Seed development-related expression of ARGONAUTE4_9 class of genes in barley: possible role in seed dormancy

Resistance to pre-harvest sprouting is an important breeding objective for cereal crops like barley and wheat. Seed dormancy, which determines the resistance or susceptibility to pre-harvest sprouting (PHS), is a complex trait. It is largely controlled by the antagonistic action of the plant hormones abscisic acid and gibberellic acid, but also has a large component of genotype?×?environment interaction. Recent studies have revealed a role for epigenetic changes through histone modification in controlling seed dormancy. However, the role of DNA methylation in seed development and dormancy is not known. In this study, we explored the role of ARGONAUTE4_9 class genes of the DNA methylation pathway in seed development and dormancy in barley. Our results show that the two AGO4_9 class genes in barley, i.e. AGO1002 and AGO1003, are preferentially expressed in ovaries at meiosis and in embryos 25?days after pollination (DAP). The expression of AGO1003 is two to fivefold higher than that of AGO1002 in these tissues, demonstrating differential expression of these genes. We also analysed the expression of AGO1003 in embryos of PHS-resistant and -susceptible varieties at 25?DAP and found a significant variation in the expression of this gene in seeds of dormant and non-dormant lines. The observed expression pattern of AGO1002 and AGO1003 suggests a possible role in sporogenesis and post-fertilization seed development. Indirectly these results imply a potential role of DNA methylation in seed development and seed dormancy.     

On the problem of pre-harvest sprouting of wheat

Summary The problem of pre-harvest sprouting in wheat is very intricate. New concepts in breeding for resistance to pre-harvest sprouting regard many components such as -amylase production potential, response to gibberellic acid and inhibition in the bracts as important as dormancy. In the research work carried out at The University of Sydney's Plant Breeding Institute, we found varietal differences for each of these components. We also developed criteria for screening breeding material for these components. The implications of our findings in planning efficient breeding programmes to evolve varieties with multiple resistance to pre-harvest sprouting have been discussed briefly.