Breeding winter hardy grasses

Summary Perennial grasses are vital for Norwegian agricultural production. The nature and extent of winter damage on grasslands is highly dependent on climatic conditions, and determines both persistency and yield. Physical stresses such as frost and ice encasement predominate in coastal regions with an unstable winter climate, while biotic stresses such as low temperature fungi are more common in the inland regions. Development of hardening depends on plant adaptation and climatic conditions during autumn and winter. New winter-hardy cultivars should be bred for wide adaptation to winter stresses. The genetic background for the most important character, freezing tolerance, seems to be of polygenic nature with mainly additive gene action. Selection for increased freezing tolerance has been effective over generations in grasses, and in most grass species ample variation still exists to be exploited by breeding. However, in some species like perennial ryegrass, modern biotechnological methods should be used to improve freezing tolerance and winter hardiness.     

玉米新品种‘裕丰303’的商业育种问题讨论

在大田生产中,‘先玉335’等美系新品种在耐密植、抗倒伏、抗南方锈病、抗大斑病、抗高温热害等方面的能力都较弱。为了通过育种手段解决以上问题,本研究以玉米新品种‘裕丰303’为试验材料,通过对其在国家（黄淮海夏播、东华北中晚熟、西北春播）以及各省区域试验和生产试验中的产量、抗旱性、耐高温热害、耐密性、籽粒品质等品种特性进行分析。结果表明‘裕丰303’不仅具备美系新品种的优良特征特性,还具有耐旱、耐高温热害、抗倒伏、抗南方锈病等性状优势,实现并大幅度超越笔者原定的育种目标。以此为基础,讨论了今后种质扩增、改良、创新的技术路线和避免遗传脆弱性风险出现等相关商业育种问题。强调在育种实践中应高度重视耐高温热害性状和耐旱性状的选育,特别要注重通过不断提升基因型与环境互作的正向超正常表达选育具有广泛适应性的新品种。     

High yielding spring bread wheat germplasm for global irrigated and rainfed production systems

Global wheat (Triticum aestivum L.) production must increase 2% annually until 2020 to meet future demands. Breeding wheat cultivars with increased grain yield potential, enhanced water-use efficiency, heat tolerance, end-use quality, and durable resistance to important diseases and pests can contribute to meet at least half of the desired production increases. The remaining half must come through better agronomic and soil management practices and incentive policies. Analyses of the recent International Yield Trials indicate that grain yields of the best new entries were usually 10% higher than the local checks globally, as well as within a country across sites. Variation in yield across sites within a country/region underline the role of genotype × environment (GE) interaction and provides opportunities to select for stable genotypes, which is not often done. The lack of proper analysis undermines proper utilization of germplasm with high yield potential and stability in the national wheat breeding programs. Some of the best performers in irrigated areas were amongst the best in semiarid environments, reinforcing the fact that high yield potential and drought tolerance can be improved simultaneously. The best performing lines often had genotypic base of widely adapted genotypes Kauz, Attila, Baviacora, and Pastor, with genetic contributions from other parents including synthetic wheat. We recommend within country multilocation analysis of trial performance for a crop season to identify lines suiting particular or different locations within a country. The immediate feedback on GE interaction will also help in breeding lines for countries having substantial variation across locations and years.     

Breeding for adaptation to drought and heat in cowpea

Accomplishments in breeding for adaptation to drought and heat are reviewed based upon work with the indeterminate grain legume species cowpea. Plant traits and some crop management methods are examined that influence adaptation to rainfed production in the drought-prone, semiarid tropical Sahelian zone of Africa. Drought escape, drought resistance, delayed-leaf-senescence, and varietal intercrops are examined. In addition, adaptation to the heat that can detrimentally impact irrigated production in the hot, subtropical arid zone of California is evaluated. Heat tolerance during reproductive development, electrolyte leakage, membrane thermostability, some aspects of crop management including date of sowing, and chilling tolerance during emergence including the beneficial effects of a dehydrin protein are considered. Methods for breeding cowpeas with adaptation to drought and heat are described that have been effective.     

Variation in resistance to different winter stress factors within a full-sib family of perennial ryegrass

Wintering ability in the field and resistance to different winter-stress factors under controlled environmental conditions were studied in a full-sib family of perennial ryegrass (Lolium perenne L.). Significant variation in tolerance to freezing and ice encasement, resistance to pink snow mould (Microdochium nivale) and also in winter survival and spring growth were found between the different genotypes. No strong correlations were found between the resistances to the different stress factors. These results indicate that resistance to different winter-stress factors is controlled by separate genes in perennial ryegrass. A low but significant positive correlation was found between spring growth of plants in the field after the first winter and both freezing tolerance and M. nivale resistance measured in controlled environments. Cold hardening seemed to influence freezing tolerance and M. nivale resistance differently in the different genotypes, since no distinct correlation in tolerance to freezing or resistance to M. nivale was found between unhardened and hardened plants. Tolerance or resistance to most of the winter stress factors measured was positively correlated with plant size. This revised version was published online in July 2006 with corrections to the Cover Date.     

Root pulling resistance in rice: Inheritance and association with drought tolerance

Summary Avoidance of drought stress is commonly associated with root system characteristics and root development. The inheritance of root pulling resistance in rice (Oryza sativa L.) was investigated and its relationship with visual field scores for drought tolerance was studied. Transgressive segregation for high root pulling resistance was observed in 3 crosses (high x high, low x high, and intermediate x intermediate). Both dominant and additive genes control the variation. F₁ superiority for high root pulling resistance was observed and could be exploited in an F₁ hybrid breeding program. F₂ distribution curves indicated that plants highly resistant to root pulling can be obtained not only from low x high and high x high crosses, but also from intermediate x intermediate crosses. Root pulling resistance in rice has a low heritability (39 to 47%). Thus, breeding for a high root pulling resistance may best be accomplished by selection based on line means rather than individual plant selection. Field screening showed significant differences in leaf water potential among random F₃ lines. F₃ lines with higher leaf water potential had better visual scores for drought tolerance. Visual drought tolerance scores were correlated with root pulling resistance. Plants with high root pulling resistance had the ability to maintain higher leaf water potentials under severe drought stress. The usefulness of the root pulling technique in selecting drought tolerant genotypes was confirmed.     

Towards an objective evaluation of persistency of <Emphasis Type="Italic">Lolium perenne</Emphasis> swards using UAV imagery

Perennial ryegrass (Lolium perenne) is a perennial crop used in temperate regions as forage. In L. perenne breeding programs, persistency is an important trait. Poor persistency results in sward degradation and associated yield and nutritive value losses. Breeders assess persistency of accessions using visual scoring in field plots during the 2nd or 3rd growing season. This evaluation system is easy and cheap but is not free from human bias. In this study, the correlation between the scoring done by different breeders was only 0.243. As an alternative we have developed a methodology to assess persistency of L. perenne breeding materials based on vegetation indices (VIs) derived from Unmanned Aerial Vehicle (UAV) imagery. The VIs Excess green (ExG2), Green Leaf Index and Normalized green intensity (GCC) were found to provide consistent results for flights carried out under different light conditions and were validated by ground reference information. The correlation between the VIs and the percentage of ground cover extracted from on-ground imagery was 0.885. To test the implementation of the method we compared the ExG2 value based approach to selection with a visual score based selection methodology as applied by two breeders. The breeding decisions of Breeder A agreed well with decisions based on ExG2 values (74.6%), but those of Breeder B displayed a lower agreement (54.0%). In contrast, agreement between decisions based on different flights was very high (91.6%). The methodology was validated for general applicability. In summary, the results demonstrate that basing persistency selection in L. perenne breeding programs on ExG2 values from UAV imagery is likely to be more objective in comparison to the currently-used visual scoring method.     

农作物收获前黄曲霉毒素污染与控制措施

黄曲霉毒素(aflatoxin,AFT)是曲霉属真菌产生的一大类生物毒素,是危及食品安全和人类健康的主要物质之一。农产品收获前黄曲霉毒素污染是热带、亚热带地区普遍存在的问题,其中在玉米、花生、棉籽、辣椒籽和一些木本坚果及其产品中尤为严重。国内外现有研究结果表明,多种因素可影响作物收获前黄曲霉毒素污染,其中干旱和高温的综合胁迫是最主要的环境因素。作物抗性对降低毒素污染具有重要作用。综合运用分子生物学及常规育种技术改良作物品种对黄曲霉菌侵染或产毒的抗性以及对其他病虫害及干旱的抗(耐)性,是解决黄曲霉毒素污染问题的重要途径。作物生产过程中病虫害的防治和合理的田间管理是作物收获前黄曲霉毒素污染的有效防控措施。     

抗旱节水小麦分子遗传育种研究进展

干旱缺水等自然灾害会导致小麦产量年度间变幅较大,尤其在小麦主产区黄淮地区更为严重。小麦抗旱节水育种是应对干旱的重大措施。本综述对小麦抗旱节水常规育种、抗旱节水分子遗传育种相关性状QTL定位、抗旱相关功能基因克隆鉴定、转基因等方面的研究进展进行了综述。水旱亲本杂交与异地交叉选择是卓有成效的常规育种方法,通过分子标记鉴定了关于根重、根长、胚芽鞘、高水分利用效率等相关性状的大量QTL;42个抗旱相关基因被克隆并进行基因功能分析和验证,均从不同代谢通路上影响着小麦抗旱性;14个来自不同供体的抗旱相关基因被研究者导入小麦品种后,转基因小麦植株的抗旱能力均得到不同程度的提高,部分植株在产量和其它抗逆性方面也得到提高。以上研究进展为抗旱节水小麦分子设计育种提供了理论依据和发展方向。     

Evaluating different bahiagrass cytotypes for heat tolerance and leaf epicuticular wax content

Summary Bahiagrass (Paspalum notatum Flugge) is a polymorphic species indigenous to South America which has become naturalized in the southeastern U.S. The most common form in the United States is Pensacola bahiagrass,P. notatum var.saurae Parodi., which is a valuable forage. Pensacola is a sexual diploid, while most other bahiagrasses are apomictic tetraploids. Pensacola bahiagrass is considered to have greater heat tolerance (based on anin vitro heat tolerance test) than a number of otherPaspalum species, but has less leaf epicuticular wax (a drought avoidance mechanism) than other species. Both heat tolerance and leaf epicuticular wax are desirable characteristics for species grown where periodic drought occurs. We measured both characteristics over two years in a collection of 23 bahiagrass accessions, many of which had been collected in South America near the center of origin of the species. The collection included various ploidy levels. For both years, no accessions ranked statistically lower in damage in the heat tolerance test than Pensacola, although eight had significantly higher damage. Two entries in addition to Pensacola had very low damage in the heat tolerance test. Pensacola was high in leaf wax, with 16 accessions rated significantly lower in wax. The accession having the lowest wax content was a triploid, which also exhibited considerable leaf death in the field in response to drought and heat. The diploid entries tended to be higher in leaf wax than the other ploidy levels. This study has identified additional bahiagrass germplasm which may be of use in a breeding program.     

Genotypic variability among cotton cultivars for heat and drought tolerance using reproductive and physiological traits

Development of rapid and inexpensive screening tools for heat and drought stress tolerance is needed and will be helpful in cotton breeding programs and selecting cultivars for a niche environment. In this study, several pollen-based traits at optimum and high temperatures and physiological parameters measured during the boll-filling period were used to evaluate variability among the cultivars for heat and drought stresses. Principal component analysis and drought stress response index methods were used to categorize cotton cultivars into three heat and drought tolerant clusters. Based on the combined analysis, PX532211WRF has been identified as heat- and drought-tolerant, and would be expected to perform better under both heat- and drought-stressed environments. A poor correlation between reproductive and physiological indices indicates that screening breeders have to use different traits to screen cultivars for reproductive and vegetative tolerance. Identified traits could serve as valuable screening tools in cotton breeding programs aimed at developing genotypes to a changing climate. Moreover, cultivar-dependent relative scores will aid in the identification of cultivars best suited to niche environments to alleviate the influences of abiotic stresses at both vegetative and reproductive stages.     

Assessing inbreeding in perennial ryegrass (Lolium perenne) as a step towards F1 hybrid breeding

Perennial ryegrass is an important turf and forage grass in temperate regions worldwide. Limited genetic gains have been made with current breeding strategies compared with other grass crops, such as rice and maize, which benefit from Filial 1 (F1) hybrid breeding. One of the largest constraints on hybrid breeding in ryegrass is self-incompatibility preventing inbreeding, as homozygous parental lines are required to develop hybrids with maximal hybrid vigour. Obligate outcrossing in ryegrass has resulted in cultivars with high levels of heterozygosity, lacking trait uniformity across the population. A naturally occurring self-fertile (SF) locus that overcomes the self-incompatibility system has been identified in a European perennial ryegrass population. This study crossed the SF locus into an elite cultivar, producing a self-compatible population that was inbred for several generations. Genotyping-by-sequencing (GBS) was used to assess the population structure and degree of inbreeding in the self-compatible population. Phenotypic analysis indicated that increased homozygosity did not necessarily affect growth and performance. This study concludes that self-compatible ryegrass is a promising tool for hybrid breeding and agronomic improvement of perennial ryegrass.     

玉米耐旱分子育种研究进展

干旱是玉米生产的主要非生物胁迫因子之一,培育耐旱品种可以有效地保持其在干旱环境下的产量稳定性。目前,随着生物信息学数据库的不断完善及基因组学技术的发展,耐旱通用QTL的发掘以及关联分析技术在功能标记开发上的应用,新的耐旱相关转录因子／基因的克隆都为解释玉米耐旱性的复杂遗传网络和分子育种提供了新的机遇和方法。本文综述了耐旱基因组学研究进展及其在玉米耐旱分子育种上的应用。     

多年生黑麦草分子标记应用及基因组研究进展

多年生黑麦草(Lolium perenne L.)是一种重要的栽培牧草,具有多年生、植株繁茂、叶多质嫩、可消化物质产量高等特征,适宜用作饲草及草坪草,具有经济价值和生态效益。本综述总结概括了多年生黑麦草分子标记的开发与应用进展,重点介绍分子标记在多年生黑麦草遗传多样性分析、遗传连锁图谱构建、QTL定位分析中的应用情况,并简述了多年生黑麦草基因组研究进展。旨在为进一步发掘多年生黑麦草基因组结构和功能特点,选育优良黑麦草品种提供理论依据。     

中国气候变化对农作物育种策略影响探究

气候变化直接影响农作物产量,根据生产实际和气候特征,因地制宜选育农作物新品种,对保障中国粮食安全具有重要的意义。本文利用1979—2014年中国粮食主产区和西北地区气象站点数据及粮食产量数据,通过进一步的统计分析,明确粮食产量与气候变化特征。结果表明：中国东北地区、黄淮海地区、长江流域地区和西北地区年平均气温增幅均值分别为0.30℃/10 a、0.37℃/10 a、0.38℃/10 a和0.48℃/10 a,与粮食产量相关性显著;年平均气温空间上从南到北、从东到西呈降低趋势;由于热量资源分布不均导致各地区年降水量变化差异显著,但与粮食产量相关性不显著。粮食作物应以优质、高产、多抗以及适宜于机械化生产为原则,采用传统育种和现代分子生物学技术相结合的育种策略,重点提高东北地区水稻品种的耐涝性和抗倒性,黄淮海和长江流域地区水稻品种的耐高温性,西北地区晚稻品种的耐低温性,以及各地区小麦和玉米品种的耐旱性。     

Molecular characterization of genetic diversity in European germplasm of perennial ryegrass

Summary Perennial ryegrass (Lolium perenne L.) is the most important grass species for temperate grassland agriculture. The level and distribution of genetic variation in gene bank ecotype collections is still largely unknown but of great interest for the planning of breeding programs. The objectives of this study were to (i) assess the molecular diversity of Polish ecotypes of perennial ryegrass, and (ii) compare the relationship between this group and German ecotypes and European cultivars investigated previously. A total number of 166 polymorphic marker bands were detected among the 171 individual plants of the 9 Polish ecotypes. In a joint analysis with 9 Polish and 22 German ecotypes, and 22 European cultivars 172 polymorphic RAPD markers could be found. Genetic distance among the Polish ecotypes ranged from 0.31 to 0.51, while for all 53 populations a broader range was detected (0.25–0.67). An analysis of molecular variance (AMOVA) revealed a much larger variation within populations (71%) than among them (29%). The Polish ecotypes contained the highest within population variation (74%). The largest among group difference (15%) was found between the Polish ecotypes versus all other accessions. We conclude that the Polish ecotypes represent a valuable genetic resource for enlarging the genetic variation in the West European germplasm pool of perennial ryegrass.     

Breeding perennial ryegrass with better crown rust resistance

Improving rust resistance is one of the main goals in our breeding programme with perennial ryegrasses. We have studied the behaviour of our breeding material over several years in several locations under natural and artificial infection conditions. The narrow sense heritability of crown rust resistance is fairly high (0.46), providing scope for improving resistance, but this optimism is reduced by the negative correlation with yield. The most resistant material yielded 4% less than the most susceptible material. No decline in digestibility is expected when improving the disease resistance. The incidence of crown rust is very variable between years, locations and between spontaneous and artificial infections, creating constraints in selection. Observations for several years and at several locations appear to be the best way to improve rust resistance in perennial ryegrass.     

Variation in utilization efficiency and tolerance to reduced water and nitrogen supply among wild and cultivated barleys

Broad genotypic variation in the response to low soilmoisture and reduced nitrogen supply was found amongthe wild Hordeum spontaneum accessions and thelandraces and modern cultivars of H. vulgare ofdifferent geographic origin. Measurements at the endof vegetative growth in plants grown in soil culturesrevealed genotypically specific responses to the usedenvironmental factors. Cultivars and breeding linesfrom Syria and Ethiopian landraces combined bothdrought resistance and tolerance to low nitrogen. TheSyrian barleys were also distinguished by a highnitrogen utilization efficiency (NUE) under low Nnutrition. European cultivars indicated a pooradaptation to N shortage, but some of them wereresistant to soil drought. No stress resistant barleyswere found among the wild accessions and Sardinianlandraces. Genotypic differences in the relativevalues of NUE and water use efficiency were associatedwith low N-tolerance. Some Syrian selections,Ethiopian landraces and the modern German cv. Maresiwere found to be most drought resistant. Maintenanceof a relatively high photosynthetic activity of theuppermost leaves was associated with droughtresistance. As far as concerning with the vegetativegrowth phase, the modern Syrian germplasm andEthiopian landraces may be recommended as donors ofadaptative characters for local barley breeding.     

Detection of tolerance of barley cultivars to infection by powdery mildew (Erysiphe graminis f.sp. hordei)

Summary Barley genotypes representing a wide range of resistance expressions and origins, from major resistance genes in modern cultivars to field resistances in landraces, were assessed for tolerance to disease under glasshouse and field conditions. A few genotypes were picked out as showing less yield loss than would be expected from the level of mildew infection. Genotypes showing more than the expected yield loss were also found. The potential use of tolerance as a breeding character is discussed.     

Rhodes grass breeding in Kenya I. Intra-variety variation and character relationships

Summary Spaced swards of 3000 plants and a selected subpopulation of 750 plants of 3 commericial Rhodes varieties, Mbarara, Masaba and Pokot, were studied between 1969 and 1975. Intra-variety variation was large in heading date, vigour of growth, seed (PGS) yield, persistence, drought tolerance and in vitro digestibility.There were on average 6 weeks between the heading date of the first and the last 5% of the plants within a variety. Variation in heading date was largely accounted for by variation in vigour and vice versa. Vigorous plants tended to be early heading and only few plants were found to possess a combination of high vigour and late heading.Among plants equally selected for high vigour from within a variety, early-heading plants were higher in PGS yield, persistence, drought tolerance and digestibility.