Einfluß eines variierten N-Angebots auf α-Amylase-Aktivität, primäre Dormanz und Auswuchsresistenz von Weichweizen (Triticum aestivum L.), Roggen (Secale cereale L.) und Triticale (X Triticosecale Wittmack)

Influence of Varying N-Fertilization Rates on α-Amylase Activity, Primary Dormancy and Resistance to Pre-Harvest Sprouting in Wheat ( Triticum aestivum L.), Rye ( Secale cereale L.) and Triticale (X Triticosecale Wittmack)
Pre-harvest sprouting, induced by unfavourable ecological conditions, can affect the grain growers success considerably. Positive correlations are reported between resistance to pre-harvest sprouting and primary dormancy. Genotypes with a short dormancy period have a high pre-harvest sprouting risk. In the case of a premature germination of caryopses in the head of grain a hydrolysis of intact starch granules caused by the endoenzyme α-amylase takes place in the endosperm.
Negative correlations between falling number and protein content are reported, however, it is unknown, if a varying N-application influences pre-harvest sprouting rates, dormancy periods and amylase activity. For this reason, both greenhouse and field trials were conducted with different N-fertilization rates and (additional in the greenhouse) a rain simulation treatment.
High amounts of α-amylase a few days post anthesis are opposed to small enzyme activities in mature kernels. Stratificating temperatures and germination inducing precipitations at the same time are inducing pre-harvest sprouting and a high α-amylase activity especially in rye and triticale. It seems as if N-deficiency reduces the possibility of pre-harvest sprouting, on the other hand high N-rates increase the enzymes' activity and promote germination processes in the kernel. Effects of N-fertilization on dormancy are not known.
In the discussion of reasons for an increase of α-amylase activity in sprouted grain caryopses, changes in the relation of the phytohormones gibberellic acid (promoter of enzyme activities) and abscisine acid are mainly presumed.     

Drought and high temperature increases preharvest sprouting tolerance in a genotype without grain dormancy

Preharvest sprouting is common in cereals, which lack grain dormancy when maturing grain is exposed to rainfall or high moisture conditions. Environmental conditions such as drought and high temperature during grain filling have a large effect on the expression of sprouting tolerance. A dormant (DM 2001) and non-dormant (Cunderdin) hard white spring wheat were exposed to drought or irrigated conditions and either low or high temperature during grain filling. Dormancy and embryo sensitivity to ABA were analysed throughout grain filling. The conclusions from this investigation were as follows; firstly DM 2001 was more dormant than Cunderdin, with a four-fold lower germination index (GI) at maturity. Secondly during grain ripening drought increased dormancy and overrides any increase in dormancy with low temperature. Finally embryo sensitivity can be induced in a non-dormant genotype to the extent where the non-dormant genotype in a hot dry environment can have the same phenotype as a dormant genotype grown in a cool wet environment. In summary drought during grain filling increases dormancy suggesting breeders need to avoid drought when screening for sprouting tolerance in order to maximise the chances of identifying genetic differences in grain dormancy and avoid any maturity by drought interactions.     

Effects of desiccation and a change in temperature on germination of immature grains of wheat (Triticum aestivum L.)

A study was made of the effects of desiccation and a change in temperature on the germination of wheat grains harvested 20 days after anthesis. When the germination test was performed immediately after harvesting, germination percentages ranged from 5.2% to 10.7%. Germination percentages increased to 48.2% to 90.3% after grain had been desiccated at 20 °C and then hydrated at 10 °C. This increase occurred even if grains had been desiccated in an atmosphere of high relative humidity. The germination percentage of non-desiccated grains depended on the germination temperature. When the pericarp and testa were removed from embryos, the germination percentage of grains incubated at 20 °C and then at 10 °C was higher than that of grains incubated at 10 °C. In general, a low germination temperature is believed to be effective in breaking dormancy of wheat grains. However, a change in temperature stimulated germination to a greater extent than a constant low temperature. The germination percentage of 5-day cycle alternating temperature was greater than that with 1-day, 2-day and 10-day cycles. Although the germination of immature wheat grains was stimulated by both high and low germination temperatures, it is likely that cycles shorter and, also, longer than a critical period induce limited germination. Loss of dormancy commonly occurs when development of wheat grains proceeds at a high temperature, with imbibition at a low temperature. However, germination ability of non-desiccated immature wheat grain was enhanced by a change in temperature during germination. This revised version was published online in August 2006 with corrections to the Cover Date.     

Temperature effects on seed germination and expression of seed dormancy in wheat

Because preharvest sprouting decreases quantity and quality of wheat grain, researchers need effective protocols to assess response to preharvest sprouting conditions. The aim of this study was to determine which temperature gives the greatest difference in seed germination and expression of seed dormancy in 10 spring wheat genotypes. The genotypes were grown in the field near Swift Current, Saskatchewan in 2000 in a randomized complete block with four replicates. Seed samples were harvested at approximately 25% moisture content (wet weight basis) and dried to 12% moisture content with minimal after-ripening. Germination was under controlled environment at temperatures of 10, 15, 20 and 30 °C in darkness. A weighted germination index (WGI) was calculated. The analysis of WGI, for each temperature, showed highly significant (p ≤ 0.01) genotype effects on germination. Most genotypes decreased in WGI (increased dormancy) as temperature was increased from 10 to 30 °C. The greatest differences in seed germination tended to be at 15 °C and 20 °C. The level of seed dormancy depended on the genotype and germination temperature. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

A study of grain dormancy and viability in spring barley

In field experiments carried out between 1989 and 1991, spring barley was sampled to observe changes in the grain viability and dormancy during grain filling. The weather during the grain filling periods of 1989 and 1990 was unusually warm and dry, and the crop in 1989 was affected by drought. Some grains were capable of germination shortly after anthesis, but were dormant. Dormancy declined with increasing maturity, but was prolonged by low temperatures and reduced by warm weather. Differences were found in the dormancy characteristics of the two cultivars tested. Apart from grains at the extremities of the ear, which were sometimes found to be small and with low viability and greater dormancy, though not significantly so, no consistent differences were found between the viability and dormancy of grains in different positions in the ear.     

The effect of water and nitrogen availability during grain filling on the timing of dormancy release in malting barley crops

Pre-harvest sprouting (PHS) causes immediate loss of seed viability, making barley (Hordeum vulgare L.) grains worthless for malting purposes. Grain dormancy release rate in barley crops is genetically and environmentally controlled. A 2 year experiment was conducted to evaluate the effect of soil nitrogen and water availability during grain filling on the dormancy release pattern (and then on the PHS susceptibility) for five malting barley commercial cultivars. Drought and well-irrigated control treatments were imposed from anthesis onwards, and contrast nitrogen fertilization treatments were applied at tillering. Nitrogen availability showed no effects on dormancy release. Drought during grain filling accelerated dormancy release with respect to well-irrigated control in 2004, but not in 2005 year. Mean temperatures during the last stages of grain filling were much higher (ca. 6°C) in 2005 than in 2004, indicating that high-dormancy loss promoting temperatures had masked drought effects on dormancy release.     

Genetic analysis of pre-harvest sprouting in a durum wheat cross

Pre-harvest sprouting of durum wheat (Triticum turgidum L. var durum) reduces commercial grade, although the actual effects on processing quality are controversial. Little is known about the genetics of the dormancy component of pre-harvest sprouting resistance in durum. We studied the segregation of dormancy in 98 recombinant inbred lines from a cross of a relatively non-dormant line, CI13102, with a moderately dormant line, Kyle. The lines and parents were grown in field tests over three years, 1996, 1997 and 1998. Spikes were collected at approximately 20% moisture and stored at −23 ∘C. Hand-threshed grain of the lines was germinated, and number of seeds germinated was counted each day. A germination resistance index was calculated to characterize dormancy. Dormancy appeared to be complexly inherited in this cross. Lines were observed that were significantly (P < 0.05) more dormant than the parents. The lines transgressive for dormancy expressed in different combinations of the three environments, indicating an environmental interaction. DNA of lines and parents was tested with simple sequence repeat primers and AFLPs that were used in quantitative trait loci (QTL) analysis of dormancy. Significant QTLs for dormancy were found, with the most notable being on chromosome 1A, where other QTLs for pre-harvest sprouting resistance have been reported in common wheat.     

The effect of germination temperature on seed dormancy in Croatian-grown winter wheats

The expression of seed dormancy related to germination temperature was studied in 25 wheat genotypes grown in the field at two locations near Zagreb and ?upanja in Croatia during 2008/2009 growing season. Germination tests were conducted at 15, 20 and 25?°C at harvest maturity (Time 1) as well as after 10?days (Time 2) and 15?months (Time 3) of seed after-ripening at room temperature, respectively. Significant (P?<?0.05) differences among locations (L), temperatures (T) and genotypes (G) as well as significant L?×?T, G?×?L, G?×?T and G?×?L?×?T interactions were observed for weighted germination index (WGI) at both Time 1 and Time 2. At Time 3 significant differences among genotypes for germination percentage were found only at the early stages of germination. The 25 wheat genotypes responded with decreasing WGI mean values (increasing dormancy) as temperature changed from 15 to 25?°C. The rate of dormancy increase with higher germination temperature varied among genotypes. Some genotypes, having similar values of WGI at 15?°C, significantly differed from each other at 25?°C and vice versa. This indicates that the range of germination temperatures included in the present study is useful when testing genotypes for their temperature-dependent dormancy potential. The number of genotypes with WGI values significantly different from the mean, as a measure of the power of germination test to detect differences in dormancy level among genotypes, as well as heritability estimates for WGIs were the highest at Time 1 for 15?°C and at Time 2 for 20?°C.     

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.     

Development of highly sprouting tolerant wheat germplasm with reduced germination at low temperature

The development of sprouting tolerant spring and winter wheat varieties that retain dormancy in cool, wet conditions is a long-term objective in Hokkaido, Japan. A highly tolerant spring dwarf line, “OS21-5”, derived from “Tordo” × “Zenkoji”, was used to develop transgressive spring, “OS38” and “OS74”; and winter, “OW77”, “OW104” and “OW93” wheats. More recently, winter lines with improved agronomic performance, though still deficient in quality and scab resistance, have been identified. In general, germination percentage of mature grain at 10 ^°C was closely related to the mean temperature experienced during the 5 days prior to maturity (dough–yellow ripening stage) and to the capacity to maintain a high amylograph paste viscosity. Dormancy at 10 ^°C appeared to be determined by a combination of genotype and variation in sensitivity to temperature during the later stages of ripening. Genotypes such as “OS38” and ‘OWl04’ were both highly tolerant to germination at 10 ^°C and insensitive to temperature during ripening. By comparison, most of the other cultivars showed a similar, intermediate sensitivity to ripening temperature, and dormancy decreased as ripening temperature increased. Dormancy of‘RL4137’ at maturity, and to a lesser extent ‘Gifukomugi’ and ‘KKI354’, was very sensitive to ripening temperature and useful levels of dormancy only developed under cool ripening temperatures, mean temperature < 18–20 ^°C.     

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.     

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.     

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.     

Effect of Heat Stress on Grain Starch Content in Diploid, Tetraploid and Hexaploid Wheat Species

Heat stress during grain development adversely affects the starch content of grain in wheat, which results in poor grain quality and yield. Identification of the sources of heat tolerance for grain starch content in wheat species is an important step towards breeding for heat‐tolerant wheat. In this study, 32 wild and cultivated genotypes belonging to diploid (probable donors of B, A and D genomes), tetraploid (BBAA and AAGG genomes) and hexaploid (BBAADD genome) wheat species were evaluated for heat stress tolerance in the field at the Indian Agricultural Research Institute (IARI), New Delhi, India (77°12′ E; 28°40′ N; 228.6 m m.s.l) on two dates, 18 November (normal sowing) and 15 January (heat stress), during 1995–96. The crop sown in January experienced mean maximum temperatures of 31.0–39.3 °C during grain development, which are considered to represent heat stress for wheat grain development. Hexaploids had the highest grain starch content and the lowest heat susceptibility index, followed by tetraploid and diploid species. The heat susceptibility index (S) for grain starch correlated significantly and positively with that of grain weight (Y = 1.259X ? 0.29, R² = 0.8902, P < 0.001) across wheat species, while the actual grain growth duration or the ‘S’ of grain growth duration did not correlate significantly with that of grain weight. Hence, a high mean grain growth rate under heat stress is a better trait for heat tolerance than long grain growth duration. Wide genetic variability for heat tolerance in grain starch content was observed among the wheat species. Hence, the grain weight and quality under heat stress can be improved by using the variability available among wheat species.     

Wheat ABA-insensitive mutants result in reduced grain dormancy

This paper describes the isolation of wheat mutants in the hard red spring Scarlet resulting in reduced sensitivity to the plant hormone abscisic acid (ABA) during seed germination. ABA induces seed dormancy during embryo maturation and inhibits the germination of mature seeds. Wheat sensitivity to ABA gradually decreases with dry after-ripening. Scarlet grain normally fails to germinate when fully dormant, shows ABA sensitive germination when partially after-ripened, and becomes ABA insensitive when after-ripened for 8?C12?months. Scarlet ABA-insensitive (ScABI) mutants were isolated based on the ability to germinate on 5???M ABA after only 3?weeks of after-ripening, a condition under which Scarlet would fail to germinate. Six independent seed-specific mutants were recovered. ScABI1, ScABI2, ScABI3 and ScABI4 are able to germinate more efficiently than Scarlet at up to 25???M ABA. The two strongest ABA insensitive lines, ScABI3 and ScABI4, both proved to be partly dominant suggesting that they result from gain-of-function mutations. The ScABI1, ScABI2, ScABI3, ScABI4, and ScABI5 mutants after-ripen more rapidly than Scarlet. Thus, ABA insensitivity is associated with decreased grain dormancy in Scarlet wheat. This suggests that ABA sensitivity is an important factor controlling grain dormancy in wheat, a trait that impacts seedling emergence and pre-harvest sprouting resistance.     

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.     

Expression of dormancy in a spring wheat cross grown in field and controlled environment conditions

Pre-harvest sprouting resistance in white-seeded wheat, Triticum aestivum L. is a genetically complex trait that varies with environmental conditions. Such variation causes difficulty in phenotypic characterization of populations to study inheritance or develop suitable DNA markers. To minimize random environmental effects, we evaluated controlled environments to measure dormancy. A population of 380 doubled haploid lines, AC Karma/SC8021V2, was evaluated in the glasshouse where the developing grains would not be exposed to moisture and greater consistency in temperature could be achieved. AC Karma is sprouting susceptible and SC8021-V2 is sprouting resistant. The population plus eight checks were seeded in early spring so the plants would reach physiological maturity under long days, requiring less supplemental light, and when the external temperature would be low enough that it would not cause difficulty in cooling the glasshouse. An alpha-lattice in a randomized complete block design with three replications was used. The blocks were arranged to minimize the environmental sources of variability in the glasshouse within each block. A sub-set of this population was tested in six field environments. Dormancy was characterized by germination of seed harvested near physiological maturity, from which a germination resistance index was calculated. The dormancy expressed in the glasshouse was significantly correlated with five of six field environments and highly significant in two of these. There was significant bidirectional transgressive segregation in both field and glasshouse environments. We are currently repeating this glasshouse experiment to confirm the results.     

Grain dormancy QTL identified in a doubled haploid barley population derived from two non-dormant parents

Grain dormancy provides protection against pre-harvest sprouting (PHS) in cereals. Composite interval mapping and association analyses were performed to identify quantitative trait loci (QTL) contributing grain dormancy in a doubled haploid (DH) barley population (ND24260?×?Flagship) consisting of 321 lines genotyped with DArT markers. Harvest-ripe grain collected from three field experiments was germinated over a 7-day period to determine a weighted germination index for each line. DH lines displaying moderate to high levels of grain dormancy were identified; however, both parental lines were non-dormant and displayed rapid germination within the first two?days of testing. Genetic analysis identified two QTL on chromosome 5H that were expressed consistently in each of the three environments. One QTL (donated by Flagship) was located close to the centromeric region of chromosome 5H (qSDFlag), accounting for up to 15% of the phenotypic variation. A second QTL with a larger effect (from ND24260) was detected on chromosome 5HL (qSDND), accounting for up to 35% of the phenotypic variation. qSDFlag and qSDND displayed an epistatic interaction and DH lines that had the highest levels of grain dormancy carried both genes. We demonstrate that qSDND in the ND24260?×?Flagship DH population is positioned proximal and independent to the well-characterised SD2 region that is associated with both high levels of dormancy and inferior malt quality. This indicates that it should be possible to develop cultivars that combine acceptable malting quality and adequate levels of grain dormancy for protection against PHS by utilizing these alternate QTL.     

The effects of cis-trans ABA on embryo germination and seed dormancy in wheat

Pre-harvest sprouting of wheat grain can cause economic losses especially in cultivars with low levels of seed dormancy. The aim of this study was to determine genotype differences in embryo sensitivity to germination in response to exogenous (+/–) cis-trans ABA treatments at different concentrations. Six white and four red seed-colored bread wheat genotypes that differed in dormancy were grown in a field near Swift Current, Saskatchewan in 2000 as a randomized complete block design with four replicates. The seed samples from this experiment were germinated in a controlled environment at 20 °C without light. The exogenous ABA treatments were 0 μM – whole seed (control), 0 μM-embryos, 25 μM – embryos and 50 μM – embryos. The ABA experiment was a factorial design with four randomized complete blocks with four ABA treatments in all combinations with the ten genotypes. A weighted (by day) germination index (WGI) was calculated for each genotype in each ABA treatment. Genotypes differed in response to ABA. The genotypes, ABA concentration and genotype by ABA concentration interaction effects were significant (p ≤ 0.05). Excised embryos showed significantly decreased dormancy in most of the experimental genotypes. The addition of exogenous ABA enhanced embryo dormancy of most genotypes. This revised version was published online in August 2006 with corrections to the Cover Date.