Germplasm improvement for preharvest sprouting resistance in Chinese white-grained wheat: An overview of the current strategy

Most modern white-grained wheat (Triticum aestivum L.) cultivars in China lack sprouting resistance. Some white grain varieties showed lower preharvest sprouting percentage in different years. Tolerance to sprouting in most cultivars comes from the varieties, Wanxian White, Fulingxuxu White, Suiningtuotuo, and Yongchuan White. The α-amylase inhibitor gene under a wheat genetic background inhibited α-amylase activity and delayed sprouting. The falling number of six suspected sources, out of 835Chinese leading varieties since 1950', was independent of late maturityα-amylase. 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.     

Number of involved genes and heritability of clover rot (Sclerotinia trifoliorum) resistance in red clover (Trifolium pratense)

European red clover (Trifolium pratense) crops are challenged by clover rot, a devastating disease caused by Sclerotinia trifoliorum or, in some cases by S. sclerotiorum. No completely resistant cultivars are available and resistance breeding is hampered by the lack of knowledge on the number of involved resistance genes and the heritability of clover rot resistance. In this study, we estimated the number of major genes contributing to clover rot resistance by analysing 15 F₁ progeny populations from pair crosses between ramets of resistant and susceptible genotypes. Parent plants were chosen from diverse, diploid populations, including wild material, landraces and cultivars. Young progeny plants were inoculated with ascospores, evaluated phenotypically and the segregation of disease scores was studied. Our results indicated that clover rot resistance may be conferred by three major effect genes, although segregation patterns suggested that there may be numerous minor effect genes involved as well. No proof was found for a maternal inheritance of clover rot resistance. To get insight in the heritability of clover rot resistance, we applied divergent selection by our high-throughput bio-test on an experimental diploid population: the original population (70.5 %), the first generation after selection for susceptibility (79.2 %) and the first generation after selection for resistance (62.3 %) differed significantly in susceptibility (p < 0.001). The second generation after selection for resistance (60.0 %) was not more resistant than the first generation after selection for resistance. In the first generation of selection the heritability (h²) was on average 0.34. In the second generation of selection h² was 0.07. These findings have important implications for resistance breeding.     

Effect of Selection for Chip Colour on Some Economic Traits of Potatoes

The objective of this study was to investigate the effects of selection for chip colour after harvest (CH), after storage at 12. 8°C (OR), and after storage at 3°C (GO) on maturity, yield, tuber size and specific gravity. Three hybrid populations of random clones were used in this study. The parents plus seven other cultivars were also evaluated, as checks. Experiments were carried out at Benton Ridge and at Fredericton, NB, in 1991. The experimental design was an augmented block. Clones of populations were non-replicated and distributed randomly in the experiment. Check cultivars were replicated four times in a randomized complete block design. Negative responses were predicted for maturity, marketable and total yield, and tuber size (agronomic traits) and positive response for specific gravity in varying amounts for the three populations by selection for the three chip quality traits (CH, CR and CC). Therefore, selection for CH, CR and CC and the agronomic traits could not be made without some adverse effects on each other, whereas chip quality traits and specific gravity could be improved simultaneously.     

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.     

Heading date and resistance to septoria tritici blotch in wheat not genetically associated

Nineteen cultivars, with large differences in heading date, were evaluated for their response to septoria tritici blotch in two experimental setups in Njoro, Kenya. Due to the more or less constant temperatures during the growing season and the overhead irrigation applied the epidemic conditions were similar over the whole observation period for the early and late cultivars. In experiment 1 the cultivars were assessed for disease severity at the same moment irrespective of the developmental stage, while in experiment 2 the cultivars were assessed at the same developmental stage. Measured at the same time, the disease severity was highest in the early maturing cultivars and lowest in the late maturing cultivars (r = –0.78). When assessed at the same development stage the disease build up was independent of heading date (r = –0.10) but strongly dependent on resistance level. There were no indications that early heading cultivars were more susceptible than late heading cultivars. This revised version was published online in July 2006 with corrections to the Cover Date.     

中国小麦品种穗发芽抗性差异的研究

利用收获时种子发芽率和面粉降落值法，于2000—2002年2个小麦种植年度，研究了黄淮、北部、长江中下游、西南冬麦区和东北春麦区1950年以来的781个主要推广品种和新品系的穗发芽抗性。结果表明，小麦穗发芽抗性测定值在年度间极显著或显著正相关，不同年代小麦品种的穗发芽抗性差异较大。1990年以来育成品种的穗发芽抗性与20世纪80年代相近，但明显弱于50、60以及70年代。黄淮、西南和春小麦3个麦区种子发芽率低于2%的高抗品种数分别占各自麦区供试总数的1.7%、4.5%和5.7%，而长江中下游和北部2个冬麦区的种子发芽率都在10%以上；东北春麦区品种的抗性较强，种子发芽率平均为11.2%。利用等电聚焦电泳从发芽率和降落值均偏低的品种中鉴定出异源2号、蜀万24、蜀万761、陕160、孟县4号、京411、京9428、鉴26、燕大1817、农大45、衡水6404、晋麦5号、8号、鄂麦14和克辉等15个携带迟熟α-淀粉酶基因的品种，分布在5个不同麦区。对这些品种及其亲本进行SSR分子标记分析，发现有些与其亲缘关系密切的品种，却不携带迟熟α-淀粉酶基因。上述结果说明，该基因在我国五大小麦产区均有分布，但具该基因的品种数量少，占供试品种数的1.9%，通过育种程序容易选择出不携带该基因的小麦品种。     

Natural selection for grain yield in dry bean populations bred by the bulk method

Three dry bean harvests are possible in some regions of Brazil that differ significantly in temperature, rainfall and day length conditions. Thus in breeding programs, generation advance using the bulk method can be carried out in these three periods. It is questionable whether under conditions such as these the action of natural selection would contribute to an increased frequency of individuals considered superior by breeders. The present study assessed six segregating populations, for up to 17 successive generations to check the effects of natural selection during inbreeding. Six populations were generated from a partial diallel: one group consisting of two early maturity cultivars, ESAL 686 and Manteigão Fosco was crossed to a second group of three cultivars with medium maturity, Carioca MG, Milionario and Ouro. The six populations plus the five parents were assessed in experiments using a randomized complete block design, in three locations: Lavras, where in breeding started from the F₂ generation; Lambari and Patos de Minas, from the F₃ generation. A linear regression equation was fitted to the parents and hybrids mean data in each location, considering grain yield as the dependent variable (y) and generations (F₂ = 1, F₃ = 2, etc.) as the independent variable. Genetic progress was estimated from the differences between the linear regression coefficients of the hybrids (b_i)and the mean of the b coefficient of their respective parents (b_j). The (b_i-b_j) were positive in all cases, showing that natural selection acted in all the segregating populations and contributed to an average increase in grain yield of 2.5% per generation over the mean of the parents.     

Phenological Development–Yield Relationships in Dry Pea in Semiarid Mediterranean Conditions

Dry pea (Pisum sativum L.) growers in the semiarid Mediterranean region require cultivars that are both early maturing and high yielding. However, negative relationships between these two characteristics limit their simultaneous improvement. A better understanding of the relative importance of the developmental stages in determining yield would assist in pea improvement. Sixteen dry pea cultivars were grown for 2 years under semiarid Mediterranean conditions (Maru, north Jordan) in order to see if differences in growing degree days (GDD) to flowering and GDD from planting to physiological maturity exist and to study their relationships with seed yield. Seed yield was negatively correlated with GDD to maturity, but not significantly correlated with GDD to flowering. Increasing GDD to flowering resulted in higher seed yield, while increasing seed fill duration had little effect. Rapid seed fill rate was positively correlated with seed weight and negatively correlated with seed fill duration. These results indicate that Mediterranean-adapted cultivars would have preflowering periods lasting as long as possible, followed by short seedfill periods. Simultaneous selection for early maturity and a relatively long time to flowering is recommended for the development of early-maturing, high-yielding cultivars adapted to semiarid Mediterranean environments.     

Selection for <Emphasis Type="Italic">Phytophthora</Emphasis> field resistance in the F<Subscript>2</Subscript> generation of organic outdoor tomatoes

Tomatoes are the most important vegetable, globally as well as in Germany. Outdoor tomato production is seriously impaired due to increasing infections with evolving late blight (Phytophthora infestans) populations. Within organic agriculture, research is being conducted to develop regionally adapted and open pollinated cultivars of outdoor tomatoes with late blight field resistance. In the present experiment, three crosses, including wild, cocktail, and beefsteak tomatoes, were selected for field resistance against late blight in F₂ at one location per cross. The comparison of positive and negative selection in F₃ revealed the selection of single F₂ plants to be efficient in all three crosses. F₂ selection has proved to be a robust and efficient tool for breeding programs. The correlated response to selection in other traits, including yield, fruit weight, days to maturity, harvest period, and plant height, depended on the cross. It was evident that selection for desired traits combined with field resistance against late blight is promising, even in wide crosses. The most undesired attribute of wild tomatoes is the formation of shoots on leaves and in inflorescences. No correlation was observed between field resistance and shoot formation, allowing the selection of genotypes with improved field resistance and yield, but without morphological disadvantages.     

白皮小麦收获前穗发芽及品种抗性机制探讨

对４８个白皮小麦种质及２个红皮小麦种质连续３年测定结果,品种间收获前穗发芽率,籽粒发芽率及收获后种子休眠特性差异显著。穗发芽敏感性因年份和种子发育时期而异,开花后３５－４０天较敏感,品种间差异大。休眠期长短与穗发芽率间呈极显著负相关。收获后的种子α－淀粉酶活性,降落值,与穗发芽率间分别呈极显著正相关和极显著负相关。     

Characterization of preharvest sprouting resistance in Clark's Cream white winter wheat

Summary Resistance to preharvest sprouting has been observed in several white wheat (Triticum aestivum L.) genotypes, but the mode of resistance has not been determined. Studies were conducted to characterize the strong preharvest sprouting resistance in Clark's Cream genotype to facilitate breeding for the trait. Clark's Cream and five other hard red and white wheat genotypes were grown in the glasshouse and field and effects of simulated rain, embryo maturity, inhibitors in floral parts and GA, endogenous inhibitors, and ABA and GA combinations on sprouting were measured. The six genotypes differed significantly in sprouting after simulated rain, -amylase activity, and response to GA and ABA. Embryo maturity and inhibition levels in floral parts and caryopses were nearly similar for all genotypes. Clark's Cream appeared to differ most in high embryo sensitivity, which was fairly nonspecific for ABA, GA, and endogenous inhibitor, and in low -amylase production during sprouting. Breeding procedures that lead to the preharvest sprouting resistance of Clark's Cream are discussed.     

小麦穗发芽抗性机理与遗传研究

1987—1989年在人工模拟降雨室鉴定了123个小麦品种,发现不少白粒抗源;研究了13个品种的穗发芽率、籽粒发芽率、籽粒含水量、吸水速率和α-淀粉酶活性变化,认为抗穗发芽的主要机理是低α-淀粉酶活性和小的吸水速率;并用6个抗性不同品种的双列杂交,初步探讨了抗穗发芽性遗传,可能存在母体与子体抗性因子互作效应。     

Genetic analysis of flowering and maturity time in high latitude spring wheat

Due to the short growing season in the high northern latitudes, the development of early maturing spring wheat (Triticum aestivum L.) cultivars is important to avoid frost damage which can lower production and quality. We investigated earliness of flowering and maturity, and some associated agronomic traits, using a set of randomly selected high northern latitude adapted spring wheat cultivars (differing in maturity) and their F₁ and F₂ crosses made in a one-way diallel mating design. The parents, and their F₁ and F₂ crosses were evaluated under field conditions over 2 years. Anthesis and maturity times were controlled by both vernalization response and earliness per se genes, mainly acting additively. Non-additive genetic effects were more important in controlling grain fill duration, grain yield and plant height. Additive × additive epistatic effects were detected for all traits studied except time to anthesis. Segregation analyses of the F₂ populations for time to anthesis indicated the presence of different vernalization response genes. Molecular genetic analyses revealed the presence of Vrn-A1 and Vrn-B1 genes in the parental cultivars. Narrow-sense heritability was medium to high (60–86%) for anthesis and maturity times but low to medium (13–55%) for grain fill duration, plant height and grain yield. Selection for early flowering/maturity in early segregating generations would be expected to result in genetic improvement towards earliness in high latitude spring wheats. Incorporation of the vernalization responsive gene Vrn-B1 in combination with vernalization non-responsive gene Vrn-A1 into spring wheats would aid in the development of early maturing cultivars with high grain yield potential for the high latitude wheat growing regions of the northern hemisphere.     

丰抗号小麦的选育和若干性状选择的探讨

本文对抗锈、越冬、抗倒伏、熟期和籽粒灌浆等性状的选择进行了探讨.研究结果表明:①正确选配亲本对选育优良品种具有重要的意义.洛夫林10号对锈病和白粉病的抗性突出,且遗传传递力强,在灌浆和落黄等特性的传递方面表现也好.有芒红7号不仅越冬性好,遗传传递力强,而且是一个配合力较强的早熟亲本.它和特晚熟的洛夫林10号杂交后,通过各世代连续“中中选早”选出了中早熟的丰抗7号.可见,二者都是我国北部冬麦区不可多得的好亲本.②两个高杆品种杂交后,选育出了比较矮的后代——丰抗2、5号(株高80—85厘米).此试验表明,在矮化育种中可取材广泛些,除着重应用矮杆基因种质外,还可以选用一些综合性状好的中杆或高杆品种.     

Genetic variability of preharvest sprouting – the South African situation

Preharvest sprouting resistance is a major breeding criterion in many regions. Screening for preharvest sprouting tolerance is difficult owing to the low heritability of the trait and its tendency to be expressed as a quantitatively inherited character. The screening procedure used currently at the ARC-Small Grain Institute is designed to assess variation of sprouting in intact heads. Five winter wheat cultivars were crossed in a complete diallel fashion. The objectives of the study were to determine the genetic variability of sprouting resistance in the progeny of five winter wheat cultivars, including Elands, a cultivar with excellent sprouting resistance. The preharvest sprouting response and α-amylase activity of these cultivars and their ensuing progeny were compared. Elands was identified as contributing positively towards preharvest sprouting tolerance in various combinations. Elands also had the best overall combining ability for the improvement of sprouting tolerance.     

四川盆地9000kg hm~(-2)产量潜力小麦品种的花后冠层结构、生理及同化物分配特性

四川盆地小麦高产育种取得了突破性进展,但高产生理研究相对滞后。本研究以2011—2015连续5年的田间试验,比较了高产和一般产量潜力品种花后群体冠层结构、主要生理指标和同化物的转运分配特性,旨在揭示四川小麦9000 kg hm-2高产品种的生理基础。选择代表性高产潜力品种和一般产量潜力品种各3个,高产潜力品种产量平均9422 kg hm~(-2),比一般产量潜力品种高14.3%,增产原因是生物量或收获指数的提高。相比一般产量潜力品种,高产潜力品种旗叶短且宽,长宽比低于10,开花初期至灌浆中期叶基角和开角增加明显。开花至灌浆后期,高产潜力品种顶三叶的SPAD值及花后0 d和20 d的群体光合速率显著高于一般产量潜力品种,群体光合速率以10:00–12:00的差异最大。此外,高产潜力品种在开花期茎鞘生物量所占比例较高,而成熟期籽粒所占比例较一般产量潜力品种高1~4个百分点。籽粒产量与小麦形态、生理参数关系密切,与灌浆期旗叶基角(r=0.947,P0.01)和倒二叶基角(r=0.963,P0.01)呈正相关,与旗叶长宽比(r=-0.913,P0.01)和倒二叶长宽比(r=-0.911,P0.01)呈负相关;与开花期顶三叶SPAD值呈正相关,r值分别为0.75、0.90和0.82(P0.01);与成熟期穗轴干重比例呈负相关(r=-0.956,P0.01)。本研究表明,株高适中、株型紧凑,花后冠层叶绿素含量和群体光合速率较高,以及合理的物质分配,是高产潜力品种获得高产的生理基础。     

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.     

Segregation distortion for agronomic traits in doubled haploid lines of barley

Four barley doubled haploid populations were produced by anther culture from the reciprocal crosses between two six‐row barley cultivars, ‘Plaisant’ and ‘Orria’; the doubled haploid lines (DHLs) derived from each cross were subsequently assigned to weak or vigorous populations according to the weak or vigorous nature of the originating embryos. Well‐formed embryos at day 25 on the induction medium were considered vigorous, whereas embryos maturing later were considered weak. The classification of vigorous and weak was closely associated with the ratio of green to albino plantlets regenerated. A random set of 25 DHLs from each of the four populations were selected for field testing in a replicated trial. Furthermore, a second set consisting of a total of 454 unreplicated DHLs from the four populations were also field assessed for grain yield. Distortion during in vitro culture may impede regeneration of a random array of microspores from a given cross, and may bias genetic estimates of specific trait/marker association in genetic studies. However, no significant differences were detected in this study among the four populations for days to heading, height, grain yield and thousand‐kernel‐weight when measured on the replicated trial of 100 DHLs, nor for grain yield in the second collection of 454 entries. This suggests that the likelihood of producing improved agronomic pure lines is independent of the direction of crossing and, more importantly, independent of the time when embryos matured in the induction media, at least for these particular six‐row cultivars and for the anther culture method used.     

Gibberellic acid effects on germination and α-amylase activity of winter wheats

Summary Sensitivity to GA in non-Gai genome winter wheat (Triticum aestivum L.) cultivars was investigated to determine magnitude of variation of the trait, its association with other traits, and effects of geographical location of production. -Amylase enzyme activity was measured before and after treatment with gibberellic acid in 18 cultivars grown at one location and in five cultivars grown at six locations. Dye-labeled starch and agar-starch media procedures were used for the first and second experiments, respectively. -Amylase activity differed significantly among the 18 cultivars after germination in water, germination in GA, and in absolute and relative sensitivity to GA. Cultivars that reacted similarly to GA had some common ancestors in their pedigrees, and -amylase activity and sensitivity to GA were significantly negatively associated with seed weight. -Amylase activity differed between tall and semi-dwarf cultivars in the second experiment, but not in the first experiment. The magnitude of variation in -amylase activity and its relationship to preharvest sprouting susceptibility of the cultivars suggested that the trait can be modified to improve seed dormancy. Significant interactions between cultivar responses to GA and geographical location of grain production suggested that selection should be carried out in several environments.Contribution no. 81-162-j, Department of Agronomy, Kansas State University, Manhattan KS 66506, USA.