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.     

Pre-maturity α-amylase and incipient sprouting in UK winter wheat,with special reference to the variety Rialto

In 1998 and 1999 the UK winter wheat variety Rialto produced unexpected low Hagberg falling numbers that could not be directly linked to sprouting. It was proposed that these reductions in quality could be due to pre-maturity α-amylase activity (PMAA). The problem was not identified during the selection and commercial development stages. Our study tested the hypothesis that the variety Rialto is PMAA-susceptible. Analysis was done on 13 year-location combinations of field grown Rialto. Together, visual and chemical assessments of sprouting and iso-electric focusing of α-amylase isozymes identified several samples with significant α-amylase activity in the apparent absence of sprouting. In addition, tests with α-amylase sensitive Phadebas gel revealed distinctive PMAA discoloration patterns in 10–44% of the grain from the 13 samples, leading to the conclusion that Rialto is PMAA-susceptible. Diurnal temperature range accumulated for an 11 day period during a warm spell in early simulated grain development displayed a significant but negative correlation with the number of grains showing clear PMAA discoloration patterns on Phadebas gel. The number of clear PMAA grains correlated positively with rainfall accumulated over 11 days. These results suggest that PMAA can increase under conditions similar to those conducive to pre-harvest sprouting. It is however also possible that in some instances both PMAA and incipient sprouting could have produced similar patterns of α-amylase activity. In addition to tests with Rialto, Phadebas gel tests were therefore also done with the known high Hagberg varieties Option and Malacca, sprouted in a controlled environment. Results from the additional gel tests suggest that visual and chemical assessments of sprouting in the grain combined with Phadebas gel analysis could identify PMAA more reliably in grain sub-samples than Phadebas gel analysis alone.     

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.     

Regulation of high pI α-amylase synthesis in wheat aleurone by a gene(s) located on chromosome 6B

Synthesis of high and low pI α-amylase in germinating wheat grains and GA₃-treated de-embryonated grains of Chinese Spring (CS) and its ditelosomic derivative (CS dit 6BS) were compared and related to high pI α-amylase production in grains affected by late maturity α-amylase (LMA). In de-embryonated grains of CS dit 6BS (lacking the long arm of chromosome 6B) treated with GA₃, synthesis of high pI α-amylase isozymes controlled by Amy-1 genes on chromosomes 6A and 6D was dramatically reduced compared to Chinese Spring. The results suggest the presence of a gene(s) on the long arm of chromosome 6B, which is (are) required for GA-induced α-amylase synthesis in the aleurone. Similarly, in wheat grains affected by LMA, high pI α- Amy genes on the group 6 chromosomes are activated apparently by a single gene, tentatively located on chromosome 6B. Both genes may be part of the GA-induced amylase synthesis pathway in the aleurone. By contrast, synthesis of the high pI α-amylase isozymes in the early stages of germination of CS dit 6BS grains was very similar to CS. This contrast between GA₃-treated de-embryonated grains and germinating grains could be explained by control of α-amylase synthesis in scutellum in the early stages of germination being different to that in GA₃-treated aleurone. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inheritance in synthetic hexaploid wheat ‘RSP’ of sprouting tolerance derived from Aegilops tauschii Cosson

An artificial amphiploid ‘RSP’ (2n = 42, AABBDD) between tetraploid landrace Ailanmai (Triticum turgidum L., 2 = 28, AABB) and Aegilops tauschii (DD, 2n = 14) expressed high tolerance to preharvest sprouting which derived from Aegilops tauschii. To determine the inheritance of sprouting tolerance in ‘RSP’, it was crossed with six cultivars which vary in susceptibility to preharvest sprouting. Preharvest sprouting tolerance was assessed on F₂ plants using germination towels. Preharvest sprouting tolerance was inherited as a recessive trait which was controlled by one gene. This revised version was published online in July 2006 with corrections to the Cover Date.     

Chromosomes responsible for sensitivity of embryo to abscisic acid and dormancy in wheat

The sensitivity of the embryo to abscisic acid (ABA) has been reported toplay an important role in seed dormancy. Using ditelocentric lines of wheatcv. Chinese Spring (CS, nondormant and ABA insensitive), F₂ seedsbetween monosomic lines of CS and a wheat line Kitakei-1354 (dormant,ABA sensitive) and deletion lines of CS chromosome 4A, germinability ofseeds and embryo-half seeds incubated in water and ABA were examined. The results indicated that the long arm of chromosome 4A carried majorgene(s) for the embryo sensitivity to ABA and dormancy. Chromosome2D might be also involved in the sensitivity to ABA.     

异源细胞质对普通小麦穗发芽抗性影响的初步研究

采用种子发芽法和室内穗上发芽法,分析比较了不同异源细胞质对普通小麦及杂种F_1的穗发芽抗性的影响,结果表明:不同细胞质对穗发芽抗性表现出不同的遗传效应,在小麦抗穗发芽育种及杂种优势利用中有一定参考价值。     

Methods for characterization of preharvest sprouting resistance in a wheat breeding program

Preharvest sprouting (PHS) can be a serious problem in western Canada resulting in economically important yield and grade losses for wheat producers. Improved PHS resistance is an important breeding objective and wheat breeders require effective and reliable methods to select for PHS resistance. The objective of this study was to evaluate whether differences exist between field and artificial weathering in the evaluation of PHS resistance in breeding lines and to determine whether sprouting scores are a good estimator of PHS resistance when compared to Hagberg falling numbers. Results suggest that both field and artificial weathering can be effectively used to screen for PHS resistance in wheat breeding lines. Although in this study, field weathering resulted in greater sprouting damage than artificial weathering, the ability to control conditions may make artificial weathering the more reliable test for PHS resistance in a breeding program. Mean sprouting scores greater than 7.5 consistently identified lines with low PHS resistance; hence, sprouting scores can be used to discard the most sprouting susceptible lines. However, falling numbers appear to be more reliable to evaluate the PHS resistance of advanced lines. 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.     

贵农小麦系列穗发芽抗性研究

１９９８～１９９９年对遗农小麦系列的九个材料进行了穗发芽的抗性和α－淀粉酶的同工酶研究,结果表明九个材料的抗穗发芽性能有着显著的差异,其中以贵农１０的穗发芽率最小,经过一周的发芽率为１．０％,二周的发芽率为４．５％,对照绵阳２６的发芽率最高,第一周为６７．０％,第二周为９８．６％,而α－淀粉酶的同工酶酶谱也表现出差异,绵阳２６和丰产３号这两个穗发芽率最高材料的同工酶酶带是最强的,其他材料的酶带都比     

Breeding for salinity resistance in mulberry (<Emphasis Type="Italic">Morus</Emphasis> spp.)

Late maturity α-amylase (LMA) is a genetic defect that is fairly widely spread in bread wheat (Triticum aestivum L.) germplasm, and recently detected in durum cultivars, which can result in unacceptably high α-amylase activity (low falling number) in ripe grain. LMA has also been observed at unexpectedly high frequency and severity in synthetic hexaploid wheats derived from the interspecific hybridisation of Triticum durum (AABB) and Aegilops tauschii (DD). Since synthetic hexaploids represent an important new source of resistances/tolerances to a range of biotic and abiotic stresses for wheat breeders, there is a pressing need to understand the mechanisms involved in LMA in synthetics and develop strategies for avoiding its adverse effects on grain quality. The objectives of this study were to firstly, compare the LMA phenotype of synthetics that varied for plant height, secondly, to characterise the LMA phenotype in groups of synthetics derived from the same durum parents and finally to determine whether LMA in primary synthetics is associated with the QTL previously reported in conventional bread wheat. More than 250 synthetic hexaploids, a range of durum cultivars and a doubled haploid population derived from Worrakatta (non-LMA) × AUS29663 (high LMA synthetic) were phenotyped and genotyped with markers reported to be linked to LMA in conventional bread wheat and markers diagnostic for the semi-dwarfing gene, Rht1. More than 85% of synthetics were prone to LMA, approximately 60% ranked as very high. Genetic control of LMA in synthetic hexaploids appeared to involve QTL located on 7B, and to a lesser extent 3B, similar to bread wheats. However, the LMA phenotype of many synthetic hexaploids appeared to be more extreme than could be explained by comparisons with bread wheat even taking into account the apparent absence of Rht1 in most genotypes. Other mechanisms, possibly triggered by the interaction between the AABB and DD genomes cannot be excluded. The presence of wild type rht1 in most synthetic hexaploids and their extreme height is difficult to reconcile with the semi-dwarf, Rht1, stature of many of the durums used in the interspecific hybridisation process. Mechanisms that could explain this observation remain unclear.     

Spike-based and seed-based selection for preharvest sprouting resistance in wheat

Summary The utility of spike- and seed-based mass selection techniques for improving preharvest sprouting resistance in heterogeneous wheat (Triticum spp.) populations was evaluated. Sorting seed by size improved selection efficiency in some cases, putatively by physiological synchronization. Progeny testing, as well as changes in frequency of red-kernelled types, indicate effectiveness of both spike- and seed-based mass selection for reduced preharvest sprouting. Differential effectiveness of mass selection, in populations segregating for dormancy from different sources, is consistent with previous work on mechanisms of dormancy from these sources. These results are of value to improvement of preharvest sprouting resistance in large, heterogeneous wheat populations.     

Profiles of Trinexapac-ethyl- and ABA-induced heat-stable proteins in embryonic axes of wheat seeds

Treatment of plants with abscisic acid (ABA) can enhance resistance to environmental stresses in general and to preharvest sprouting in particular. Inhibitors of gibberellin (GA) synthesis have been reported to enhance the metabolic activity or effectiveness of ABA. Wheat seeds(Triticum aestivum L., cv. Bet Hashita) were soaked for 2 h in100 μm ABA, in 1250 ppm trinexapac-ethyl (TE, anacylcyclohexanedione-based GA synthesis inhibitor), or in a combination of the two. After drying, seeds were imbibed 24 h in water and the protein in heat-stable extracts from embryos was examined. Treatment with ABA alone increased expression of dehydrin and of a 37 kDa protein. Treatment with TE more than doubled protein concentration in the embryo and enhanced expression of dehydrin and of proteins weighing 37, 20, and15 kDa. Combined treatments of TE and ABA led to enhanced expression of dehydrin and of a 15 kDa protein. This revised version was published online in August 2006 with corrections to the Cover Date.