Resistance to Oculimacula yallundae and Oculimacula acuformis is conferred by Pch2 in wheat

The recent report of a differential response of wheat lines containing the Pch2 gene to infection with the eyespot pathogens Oculimacula yallundae and O. acuformis has prompted this re‐examination of the response to these fungi by the recombinant lines used to map Pch2. Homozygous recombinant substitution lines (RSL) derived from the hybridization of Chinese Spring (CS) and the CS chromosome substitution line Cappelle Desprez 7A (CS/CD7A), previously evaluated for response to glucuronidase (GUS)‐transformed O. yallundae, were evaluated for response to infection with GUS‐transformed O. acuformis. Based on visual scores and on GUS expression level, which reflects fungal colonization of seedling plants, evidence of a quantitative trait locus (QTL) conferring resistance to O. acuformis was found in two separate growth chamber experiments (logarithm of the odds, LOD, = 2·7 and 6·7 at 305 and 289 cM, respectively) that was equivalent in location to that for resistance to O. yallundae (LOD = 13·2 and 11·4 at 289 and 304 cM, respectively). These results confirm that Pch2 confers some degree of resistance against both O. yallundae and O. acuformis under these conditions.     

Fungicide resistance status in French populations of the wheat eyespot fungi Oculimacula acuformis and Oculimacula yallundae

Eyespot, caused by Oculimacula acuformis and Oculimacula yallundae, is the major foot disease of winter wheat in several European countries, including France. It can be controlled by chemical treatment between tillering and the second node stage. The fungicides used include antimicrotubule toxicants (benzimidazoles), inhibitors of sterol 14α‐demethylation (DMIs) or of succinate dehydrogenase (SDHIs), the anilinopyrimidines cyprodinil and the benzophenone metrafenone. Since the early 1980s, a long‐term survey has been set up in France to monitor changes in the sensitivity of eyespot populations to fungicides. Resistance to benzimidazoles has become generalised since the early 1990s, in spite of the withdrawal of this class of fungicides. In the DMI group, resistance to triazoles is generalised, whereas no resistance to the triazolinethione prothioconazole has yet developed. Resistance to the imidazole prochloraz evolved successively in O. acuformis and O. yallundae and is now well established. Specific resistance to cyprodinil has also been detected, but its frequency has generally remained low. Finally, since the early 2000s, a few strains of O. yallundae displaying multidrug resistance (MDR) have been detected. These strains display low levels of resistance to prothioconazole and SDHIs, such as boscalid. Knowledge of the spatiotemporal distribution in France of O. acuformis and O. yallundae field strains resistant to fungicides allows resistance management strategies for eyespot fungi in winter wheat to be proposed.© 2012 Society of Chemical Industry     

Development of Oculimacula yallundae and O. acuformis (eyespot) lesions on stems of winter wheat in relation to thermal time in the UK

Relationships between development of eyespot, caused by Oculimacula yallundae (OY) or O. acuformis (OA) on stems of winter wheat (cv. Avalon), and thermal time (°C days after sowing) were investigated in field experiments in 1985/86, 1986/87 and 1987/88 (two experiments). In all experiments, the incidence and severity of stem eyespot (uninoculated plots, OY- and OA-inoculated plots) were linearly related to accumulated thermal time after sowing. There were ca. 600–800°C days from the time of the first sample when eyespot lesions were recorded on stems to the time when maximum eyespot incidence or severity was recorded. Relationships between stem eyespot incidence or severity and thermal time differed between seasons, with more severe eyespot in 1986/87 and 1987/88 than 1985/86. Both the severity and volume of stem lesions were initially greater in OY-inoculated plots than OA-inoculated plots in spring but differences were less by harvest in all seasons. The percentage of plants with stems colonized by OY or OA over all plots (including uninoculated) showed a consistent pattern in 1986/87 and 1987/88 (two experiments), with the percentage colonized by OY greater initially and the percentage colonized by OA gradually increasing with time towards harvest.     

A controlled environment test for resistance to Soil-borne cereal mosaic virus (SBCMV) and its use to determine the mode of inheritance of resistance in wheat cv. Cadenza and for screening Triticum monococcum genotypes for sources of SBCMV resistance

Several wheat genotypes, including eight with known field responses, were evaluated for their reaction to Soil-borne cereal mosaic virus (SBCMV, genus Furovirus) by growing in naturally infested soil under controlled environment conditions. Virus antigen titres in the foliage 8–9 weeks after sowing mostly reflected the field responses, showing that growth chamber-based tests can be used to improve the speed and reliability of germplasm screening. Such tests were used to determine the mode of inheritance of the SBCMV resistance in cv. Cadenza, commonly used in UK wheat-breeding programmes. One hundred and eleven doubled haploid (DH) lines derived from an F ₁ of a cross between cvs Cadenza (resistant) and Avalon (susceptible) were evaluated. This DH population segregated for the reaction to SBCMV in a ratio of 1 : 1 (resistant : susceptible). This suggests that the SBCMV resistance is controlled by a single gene locus. As a first step towards identification of new sources of improved SBCMV resistance (e.g. immunity) as well as sources of the resistance to the virus vector, Polymyxa graminis , a set of 26 Triticum monococcum lines of diverse geographical origin was also screened. Most lines were susceptible to SBCMV, but one line of Bulgarian origin was resistant to the virus and possibly partially resistant to the virus vector.     

Oculimacula yallundae lifestyle revisited: relationships between the timing of eyespot symptom appearance, the development of the pathogen and the responses of infected partially resistant wheat plants

Possible relationships between the timing of eyespot symptom appearance, the development of Oculimacula yallundae and the responses of infected wheat plants were investigated. By comparing, for 45 days after inoculation (d.a.i.), eyespot- and mock-inoculated coleoptiles and leaf sheaths of a wheat line carrying the Pch1 partial resistance gene, this study showed that cell death, used as a criterion for symptom appearance, occurred on the first leaf sheath around 30 d.a.i. Monitoring of O. yallundae development by optical and scanning electron microscopy revealed that the fungus colonized the coleoptile within 30 d.a.i. It then attacked the first leaf sheath and underwent morphological and growth modifications. For 30 d.a.i., infected plants responded by local accumulations of H₂O₂ and callose in coleoptile epidermal cells and by up-regulation of pathogenesis-related (PR) genes. From 30 d.a.i., natural browning occurred in the first leaf sheath epidermis and the expression level of PR genes, determined by quantitative PCR, significantly increased in infected plants. These results show that the wheat/ O. yallundae interaction is characterized by two distinct phases: the asymptomatic phase and the symptomatic phase. The possibility that O. yallundae should be considered hemibiotrophic rather than necrotrophic is discussed.     

Evaluation and characterization of resistance to fusarium head blight caused by Fusarium culmorum in UK winter wheat cultivars

Fusarium head blight (FHB) resistance of 50 cultivars from the National List of winter wheat cultivars approved for sale (or were undergoing trails for approval in 2003) in the UK was compared with 21 reference cultivars from continental Europe which had previously been characterized for resistance. Only three UK National List cultivars (Soissons, Spark and Vector) had stable resistance over trial sites that was significantly greater than that of the FHB susceptible cultivar Wizard. In addition, under moderate disease pressure, 21 of the National List cultivars had levels of the trichothecene mycotoxin deoxynivalenol (DON) above the proposed European Union limit of 1·25 ppm in grain. Surveys show that levels of FHB and DON in the UK crop are currently very low, however, should disease pressure increase for any reason, then an improvement in the overall levels of FHB resistance of UK winter wheat germplasm will be required. In order to infer the origin of resistance and to identify potentially novel resistance, allele sizes of microsatellite (simple sequence repeat, SSR) markers linked to quantitative trait loci (QTL) for FHB resistance were compared between the test cultivars and known, characterized resistance sources. The major FHB resistance QTL from the Chinese cv. Sumai-3 (3BS, 5A and 6B), the Romanian cv. Fundulea F201R (1B and 5A) and the French cv. Renan (5AL) were screened with 17 SSRs. No National List cultivar had haplotypes similar to any of these QTL. However, the highly resistant German reference cultivar Petrus had an identical haplotype to cv. Fundulea F201R on 1B indicating that this cultivar has an allelic FHB resistance QTL at that location.     

Development of Oculimacula yallundae and O. acuformis (eyespot) on leaf sheaths of winter wheat in the UK in relation to thermal time

In a controlled environment (15/10°C) (day/night) container experiment on winter wheat (cv. Avalon), eyespot incidence (percentage of plants affected) and number of leaf sheaths penetrated after 6 weeks increased with inoculum concentration (10²−10⁶ conidia mL⁻¹) of Oculimacula yallundae (OY) or Oculimacula acuformis (OA), but there was no difference between the two species. In an outdoor container experiment, seedlings inoculated with OY 2 weeks after sowing had a greater incidence of eyespot than those inoculated with OA, when assessed 7 weeks after inoculation. Seedlings inoculated with OA at 10 or 20 weeks after sowing developed more severe eyespot by maturity than those inoculated with OY. In an experiment at 15/10°C with seedlings inoculated with OY + OA 2 weeks after sowing, more leaf sheaths were penetrated by OY (3·0 per plant) than OA (2·3 per plant) 6 weeks after inoculation. Field experiments with winter wheat consistently showed leaf sheath production, leaf sheath death, and number of leaf sheaths infected or penetrated by OA or OY were related linearly to thermal time (°C days) after sowing. Depending on cultivar, season and sample, a new leaf sheath was produced in 116–216°C days; a leaf sheath died in 221–350°C days; and infection of a new leaf sheath occurred in 129–389°C days. The mean number of living leaf sheaths infected differed between samples, cultivars and seasons for both OY and OA. Regression analysis of the 1985/86 data suggested that OY progressed more rapidly than OA through the leaf sheaths, and that both the pathogens progressed more rapidly than the rate of leaf sheath death, but more slowly than the rate at which leaf sheaths were produced. It also suggested that OA progressed more slowly than the rate at which leaf sheaths died in 1987/88, but OY did not.     

Defence responses in flag leaves and spikes of common wheat Triticum aestivum cultivars with contrasting levels of basal resistance to blast caused by Pyricularia oryzae

Wheat blast, caused by Pyricularia oryzae, can cause large yield losses in crops. This study aimed to investigate defence responses in flag leaves and spikes of wheat cultivars BR-18 (moderately resistant) and BRS-Guamirim (susceptible), which differ in their levels of basal resistance. In contrast to cultivar BRS-Guamirim, infected plants of cultivar BR-18 showed more pronounced increases in activities of β-1,3-glucanase and chitinase as well as higher concentrations of lignin-thioglycolic acid derivatives in the flag leaves and total soluble phenolics in the spikes. Polyphenoloxidase activity increased in both flag leaves and spikes in response to fungal infection, regardless of cultivar. Phenylalanine ammonia-lyase (PAL) activity increased in infected flag leaves of both cultivars, especially in BR-18. PAL activity was lower in spikes of infected compared to noninfected plants of both cultivars, although to a lesser extent in BR-18. Compared to BRS-Guamirim, the antioxidative system in both flag leaves and spikes of BR-18 was more efficient in removing reactive oxygen species, reducing cellular damage caused by fungal infection. The lower catalase and peroxidase activities, associated with high superoxide dismutase activity, in flag leaves and spikes of infected BR-18 culminated in a high hydrogen peroxide concentration. The increase in ascorbate peroxidase activity was higher in both flag leaves and spikes of infected plants of BR-18 than in infected BRS-Guamirim. It was concluded that wheat resistance to blast depended on the basal level of resistance of the cultivar, which was mainly associated with the activities of defence enzymes and a more effective antioxidative system.     

小麦抗条锈病一致性数量性状位点(MQTL)图谱构建

 小麦条锈病是造成小麦减产和品质劣化的最重要病害,定位小麦染色体上一致性条锈病抗性基因/位点/区段是小麦条锈病抗性分子育种的重要基础。本研究对至今分子标记和遗传定位的342个条锈病抗性基因/位点/区段进行数据搜集整理,借助Maccaferr和Andrzej的参考图谱,基于元分析技术进行Meta-QTL(MQTL)检测,共获得194个小麦抗条锈病MQTL,包括74个与严重度(Disease severity, DS)相关,46个与反应型(Infection type, IT)相关、19个与病程曲线下面积相关(Area under disease progress curve, AUDPC)、28个与DS和IT共相关、6个与DS和AUDPC共相关、15个与IT和AUDPC共相关、6个与其他条锈病抗性性状相关。这些抗条锈病一致性QTL定位于小麦21条染色体上,呈非均匀分布,且部分MQTL集中成簇。通过与已发表的正式命名抗条锈病基因比较分析,发现大多数正式命名基因定位于MQTL簇区段,说明这些MQTL簇区段很可能是控制小麦条锈病抗性热点区域。控制小麦抗条锈病一致性QTL遗传图谱的构建为小麦条锈病抗性基因精细定位及抗病育种提供了遗传信息参考依据。     

小麦抗条锈病一致性数量性状位点(MQTL)图谱构建

 小麦条锈病是造成小麦减产和品质劣化的最重要病害,定位小麦染色体上一致性条锈病抗性基因/位点/区段是小麦条锈病抗性分子育种的重要基础。本研究对至今分子标记和遗传定位的342个条锈病抗性基因/位点/区段进行数据搜集整理,借助Maccaferr和Andrzej的参考图谱,基于元分析技术进行Meta-QTL(MQTL)检测,共获得194个小麦抗条锈病MQTL,包括74个与严重度(Disease severity, DS)相关,46个与反应型(Infection type, IT)相关、19个与病程曲线下面积相关(Area under disease progress curve, AUDPC)、28个与DS和IT共相关、6个与DS和AUDPC共相关、15个与IT和AUDPC共相关、6个与其他条锈病抗性性状相关。这些抗条锈病一致性QTL定位于小麦21条染色体上,呈非均匀分布,且部分MQTL集中成簇。通过与已发表的正式命名抗条锈病基因比较分析,发现大多数正式命名基因定位于MQTL簇区段,说明这些MQTL簇区段很可能是控制小麦条锈病抗性热点区域。控制小麦抗条锈病一致性QTL遗传图谱的构建为小麦条锈病抗性基因精细定位及抗病育种提供了遗传信息参考依据。     

Genetic relationship between the adult plant resistance gene Lr12 and the complementary gene Lr31 for seedling resistance to leaf rust in common wheat

A resistant phenotype similar to that conferred in wheat by the complementary genes Lr27  +  Lr31 was produced in the progeny of intercrosses of cultivars carrying Lr27 and a line possessing Lr12 . This confirms that Lr12 is either completely linked with Lr31 or is the same gene. On the basis of these findings and that Lr31 is located on chromosome 4BS, it is concluded that Lr12 must also be located on 4BS. Adult-plant genetic tests confirm that the Australian wheat cultivar Timgalen carries Lr12 , and stocks with Lr12 alone were established from this cultivar.     

DArTseq physical mapping of QTLs linked to Karnal bunt (Tilletia indica) resistance in two historical wheat populations

Karnal bunt, a disease of wheat, durum, rye, and triticale, is subject to strict quarantine restrictions worldwide. The disease is considered a major threat to food security, due to its use as a non-tariff trade barrier by several wheat-importing countries. In this paper, we analysed seven years of phenotypic data to search for quantitative trait loci (QTLs) associated with resistance in common wheat, validated the QTLs using an independent population, and assessed the potential of genomic selection as a tool for pre-emptive breeding. The QTL study used phenotypic data collected from artificially inoculated field experiments involving two historical Karnal bunt resistance populations: WH542 × HD29 and WH542 × W485. QTL analyses detected four significant (p < 0.001) QTLs on chromosomes 1A, 3A, 4B, and 6B, which explained between 13.7% and 15.7% of the phenotypic variation. A panel of 130 cultivars was used to validate QTL effects. These were genotyped with the same DArTseq protocol, and two of the four QTLs were significantly (p < 0.001) associated with Karnal bunt resistance in the validation panel. The potential of genomic selection was investigated by comparing accuracies of a model trained with all available markers and a model based solely on validated QTL information from the biparental populations. Genomic prediction accuracy, based on the two scenarios, averaged 0.43 and 0.33, respectively, suggesting that even in situations where phenotyping is difficult due to quarantine restrictions, the prospects for pre-emptive breeding against Karnal bunt are encouraging, and resources are now available that will reduce the cost burden.     

Identification and location of Stb9, a gene for resistance to septoria tritici blotch in wheat cultivars Courtot and Tonic

This study reports the discovery of a gene for resistance to septoria tritici blotch (STB) in two spring wheat cultivars, Courtot and Tonic. The gene, named Stb9 , confers resistance to Mycosphaerella graminicola isolate IPO89011. It was mapped by quantitative trait loci (QTL) analysis using an existing map of Courtot × Chinese Spring and was located between markers Xfbb226 (3·6 cM) and XksuF1b (9 cM) on the long arm of chromosome 2B. Markers linked to Stb9 in Courtot were then shown to be linked to resistance to IPO89011 in F₃ families of Tonic × Longbow. Allelism tests in which Tonic was crossed with Courtot confirmed that Tonic has a gene for resistance to IPO89011 at or very close to the Stb9 locus. SSR markers flanking Stb9 may be used in marker-assisted selection to introgress this gene into winter cultivars or in spring wheat breeding programmes outside Europe.     

湖北省小麦品种(系)对赤霉病、条锈病、白粉病和纹枯病的抗性评价

为了解湖北省小麦品种(系)的抗病性水平,对2001年以来湖北省审定的46个小麦品种和在湖北省进行区域试验的447份小麦品系进行赤霉病、条锈病、白粉病和纹枯病等4种主要病害的抗病性评价。结果表明:1)参试品系中有1份材料对赤霉病表现高抗,未发现对纹枯病表现高抗或免疫的材料;对赤霉病和纹枯病的平均抗性评价分值分别为14.30和3.49,介于中感和高感之间;对条锈病和白粉病的平均抗性评价分值分别为13.43和8.34,介于中抗和中感之间。2)审定品种的综合抗性水平不高,对条锈病的抗性评价分值为12.47,介于中抗和中感之间,对其他3种病害的抗性介于中感和高感之间;审定品种的单产呈增加趋势,株高在不断降低,生育期相应延长,综合抗病性也在增强。3)审定品种的综合抗病性与对条锈病抗性的相关系数最高,为0.738;对纹枯病的抗性与株高呈显著正相关,与单产呈显著负相关;对赤霉病的抗性与株高无显著相关。鉴于此,湖北省需加强抗病育种力度,同时应充分做好小麦病害的防控。     

人工合成小麦新种质抗条锈性鉴定与Yr18基因检测

对97份来自CIMMYT的人工合成小麦新种质进行了主要农艺性状考察、Yr18分子检测和成株期田间抗锈性接种鉴定。结果表明:参鉴种质间主要农艺性状变异程度较大,尤其千粒重普遍偏高,有30份材料千粒重达50 g以上、占30.9%;利用csLV34标记检测到合成20和合成43携带Yr18,占2.1%;鉴选出成株期呈抗性反应的材料30份、占30.9%,高度慢条锈材料19份、占19.6%,其中合成2、5、14、60、75、76、78、82、83、84计10个合成种同时表现高抗和高度慢锈。这些大粒、抗条锈或慢条锈合成小麦种质的鉴定筛选,为选育小麦新品种提供了优异资源。     

小麦抗源武汉2号和品冬34的抗条锈性遗传分析

为明确小麦品种武汉2号和品冬34对小麦条锈菌流行小种的抗病性及抗病遗传规律,用小麦条锈菌生理小种CYR29、CYR31、CYR32、CYR33以及致病类型Su11-4、Su11-5、Su11-11、PST-Ch42在苗期接种小麦品种武汉2号和品冬34进行抗病性鉴定,并用武汉2号和品冬34分别与感病亲本铭贤169进行杂交,对F₂群体和F_2：3家系在温室进行苗期遗传分析。结果表明：武汉2号对CYR29和CYR32表现感病,对其它小种和致病型均表现抗病,且对CYR31的抗性由1对隐性基因控制;品冬34对所测试的小种和致病类型均表现高抗,且对CYR32的抗性由1对显性基因控制。     

5个持久抗条锈病小麦品种的抗性组分和遗传距离的研究

 小麦数量抗病品种Aquileja(AQ)、Libellula(LB)、Luke(LK)、Nugaines(NG)和咸农4号(XN)具有持久抗条锈病特点,本文对这5个品种的抗性组分及它们之间的遗传距离进行了研究,以铭贤169(MX)为感病对照品种。苗期室内抗性组分试验表明:LB、XN、AQ 3个品种与LK、NG 2个品种相比,前者的气孔下泡囊密度低于后者;前者的菌落长度短于后者。其中AQ和XN的吸器密度低于LK和NG而高于LB;LK和NG的气孔下泡囊密度甚至高于感病对照品种MX。田间抗性组分试验表明:5个数量抗病品种AQ、LB、LK、NG和XN的反应型(IT)、严重度(DS)、病情发展曲线下面积(AUDPC)和病斑长度(LL)值均低于感病对照品种MX;数量抗病品种AQ、LB、LK、NG、XN之间相比,AQ的IT值最高而LB最低;NG的DS和AUDPC值最高而LB最低;AQ、NG和XN的LL值高于LB和LK;AQ的病斑密度值低于NG和LK而高于XN和LB。由此可见,LK和NG没有抗侵入能力而在成株期具有抗扩展能力,LB、AQ和XN除了具有抗扩展能力外,还具有降低侵入频率能力。基于SSR DNA指纹数据的聚类分析,AQ与LB为同一类,NG与XN为同一类,LK单独为一类。由此推测,AQ或LB与其它3个数量抗病品种之间杂交的后代中可能会出现性状超亲分离,本实验室报道的AQ/NG杂交组合的结果证明了这一点。本文为进一步的抗病遗传育种工作提供了有用信息。     

茉莉酸对PR-1、PR-2、PR-5和Ta-JA2基因 表达以及小麦白粉病抗性的诱导

 为了探索小麦抗白粉病分子机理,明确茉莉酸对小麦白粉病抗性的诱导作用、对植物抗病性标志基因PR-1、PR-2、PR-5和本实验室克隆的1个新基因Ta-JA2的激活作用,以及抗病性变化与基因表达变化之间的相关性,本研究以感白粉病的小麦品种“中国春”、“濮麦9号” 和“周麦18”为材料,用茉莉酸甲酯（methyl jasmonate,MeJA）喷洒小麦幼苗叶片进行诱导,通过离体叶段培养法接种白粉菌（Blumeria graminis f. sp. tritici,Bgt）进行抗性鉴定;用实时定量PCR技术检测小麦叶片中PR-1、PR-2、PR-5和Ta-JA2基因的表达变化。结果表明MeJA处理可以显著提高“中国春”、“濮麦9号”和“周麦18”对白粉菌的抗病水平。茉莉酸处理显著激活了PR-1、PR-2、PR-5和Ta-JA2的转录。茉莉酸诱导的抗病性提高与抗病标志基因PR-1、PR-2、PR-5及Ta-JA2的表达增强呈正相关。植物激素茉莉酸是小麦抗白粉病反应的信号分子。     

茉莉酸诱导小麦抗病虫性初步研究

初步研究了茉莉酸诱导对小麦苗抗病虫能力的影响,结果显示,小麦在喷施茉莉酸后能够提高植株对麦长管蚜和小麦白粉病菌、小麦叶锈病菌的抵抗能力,可显著降低小麦白粉病、叶锈病的发病级别和病斑数量,对麦长管蚜则在体重和产仔数量上有显著的抑制作用。