Evaluation of resistance of current wheat cultivars and breeding lines to stripe rust from three Gorges reservoir area

Nearly 100,000 ha in the Three Gorges Reservoir Area (TGRA) are in wheat production and the area is a junction where wheat stripe rust overwinters and causes epidemics the next spring; thus the area plays a pivotal role in wheat stripe rust epidemics in China. To better understand wheat resistance levels and the application of Yr genes in this area, 116 wheat cultivars (lines) were collected from the TGRA to investigate stripe rust resistance during the 2014–2016 cropping seasons. Seedling resistance evaluation results indicated that only nine accessions (7.8%) were immune or nearly immune to three predominant races of CYR32, CYR33 and PST-V26. In the field evaluation, 51 accessions (43.9%) showed adult-plant resistance, whereas 56 accessions (48.3%) were susceptible. The application of resistant sources focused on ineffective Yr9 (26.7%) and Yr17 (18.9%), and gradual ineffective Yr26 (34.5%), while effective Yr5, Yr10 and Yr15 were absent. Among them, 21 accessions (18.1%) were combined with two resistance genes. Both low resistance and more concentrated use of Yr genes indicated that this region faces a major risk for a wheat stripe rust epidemic. To improve the wheat resistance level in the TGRA, it is important to discover new all-stage resistance resources and diversify resistance resources for breeding.     

22份中国小麦生产主栽品种抗条锈病基因解析

为挖掘新的小麦抗条锈病基因,掌握小麦生产主栽品种的抗条锈病基因携带情况,有效防控小麦条锈病,采用抗性鉴定、基因推导分析和分子标记技术对22份小麦生产上主栽品种进行了研究,通过抗性鉴定比较22份小麦主栽品种与已知基因载体品种的抗谱。结果显示,共推测出14份供试品种携带已知抗条锈基因,8份供试品种携带未知抗条锈基因,是新的抗锈基因资源;聚类分析结果显示,供试22份小麦品种可分为2个大类6个亚类;利用SSR分子标记检测抗条锈病基因Yr1、Yr10和Yr24的携带情况发现,11份品种携带Yr1基因,2份品种携带Yr10基因,22份品种均不携带Yr24基因。部分生产主栽品种携带新的抗条锈病基因,表明小麦品种选育中避免了抗性基因单一化,并加强了未知基因的利用。     

陇南小麦条锈病的品种遗传多样性控制

为实现陇南小麦条锈病持续控制的目标,以遗传多样性为原则,组建以提高生产品种抗条锈基因丰富度、在锈菌越夏区和越冬区进行基因布局和持久抗性、慢条锈性、高温成株抗性等多种抗性利用为主要内容的控制技术体系。利用Yr10、Yr12、Yr13、Yr16、Yr26、YrC591等有效抗条锈基因的载体品种、Flinor 等持久抗性品种及中四等其它抗源材料育成一批综合性状优良、具有不同遗传背景的抗病品种和类型,其中2004年以来育成的10个品种产量性状有明显提高,在区域试验中较对照增产7.3%~28.9%。陇南小麦条锈病的控制已进入一个新阶段。     

Suppression subtractive hybridization and microarray analysis reveal differentially expressed genes in the <Emphasis Type="Italic">Lr39/41</Emphasis>-mediated wheat resistance to <Emphasis Type="Italic">Puccinia triticina</Emphasis>

Wheat leaf rust caused by Puccinia triticina (Pt) is one of the most severe fungal diseases threatening the global wheat production. The use of leaf rust resistance (Lr) genes in wheat breeding programs is the major solution to solve this issue. Wheat isogenic line carrying the Lr39/41 gene has shown a moderate to high resistance to most of the Pt pathotypes detected in China. In the present study, a typical hypersensitive response (HR) was observed using microscopy in leaves of the Lr39/41 isogenic line inoculated with the avirulent Pt pathotype THTT from 48 h-post inoculation. Two Lr39/41 resistance-associated suppression subtractive hybridization (SSH) libraries with a total of 6000 clones were established. Microarray hybridizations were performed on all obtained SSH clones using RNAs extracted from leaves of the Pt-inoculated and non-inoculated Lr39/41 isogenic lines, and leaves of the Pt-inoculated and non-inoculated Thatcher susceptible lines. Differentially expressed clones were analyzed by significance analysis of microarrays (SAM), followed by further sequencing. A total of 36 Lr39/41-resistance-related differentially expressed genes (DEGs) were identified, many of which had been previously reported to be involved in the plant defense response. The expression levels of eight selected DEGs during different stages of the Lr39/41-mediated resistance were further quantified by a qRT-PCR assay. Several pathogenesis-related (PR) and HR-related genes seem to be crucial for the Lr39/41-mediated resistance. In general, a brief profile of DEGs associated with the Lr39/41-mediated wheat resistance to Pt was drafted.     

Effect of controlled fluctuating low temperatures on survival of <Emphasis Type="Italic">Puccinia striiformis</Emphasis> f. sp. <Emphasis Type="Italic">tritici</Emphasis>

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is an important disease of wheat worldwide. Understanding the survival of Pst during the winter is critical for predicting Pst epidemics in the spring. We used a real-time quantitative PCR (qPCR) method to quantify Pst CYR32 biomass in infected wheat seedlings under several fluctuating temperature regimes (three average temperatures 0, ?5 and ?10 °C, each with two daily fluctuating amplitudes 8 and 13 °C). The survival of Pst CYR32 increased with increasing average temperature but also varied greatly with the amplitude – larger amplitude led to lower survival, particularly at 0 and ?5 °C. Nevertheless the survival at both amplitudes was still significantly greater than under the corresponding constant temperatures. There were small, albeit statistically significant, differences between the two cultivars (Xiaoyan 22, low winter-hardiness; Lantian 15, high winter-hardiness) in Pst CYR32 survival. This study indicated potential errors that could result from using daily average temperatures to predict Pst survival during the winter.     

豫鲁皖三省重要小麦品种抗条锈基因推导

 根据对26个不同毒性谱的小麦条锈菌菌系的反应,并结合品种系谱分析,研究了河南、山东和安徽3省的50个重要小麦生产品种所具有的抗条锈基因。结果表明,没有1个品种可抵抗所有供试的26个条锈菌菌系,在已知的抗条锈基因中Yr 9所占比例最大,至少存在于17个品种中,Yr 2和Yr 1次之,分别存在于10个和8个品种中,个别品种则具有Yr A、Yr 3或Yr Sel,还有些品种可能具有未知的抗条锈基因或基因组合。由于上述已知基因对目前的条锈菌优势小种基本上均不抵抗,培育和推广具有效抗条锈基因的新品种迫在眉睫。     

豫鲁皖三省重要小麦品种抗条锈基因推导

 根据对26个不同毒性谱的小麦条锈菌菌系的反应,并结合品种系谱分析,研究了河南、山东和安徽3省的50个重要小麦生产品种所具有的抗条锈基因。结果表明,没有1个品种可抵抗所有供试的26个条锈菌菌系,在已知的抗条锈基因中Yr 9所占比例最大,至少存在于17个品种中,Yr 2和Yr 1次之,分别存在于10个和8个品种中,个别品种则具有Yr A、Yr 3或Yr Sel,还有些品种可能具有未知的抗条锈基因或基因组合。由于上述已知基因对目前的条锈菌优势小种基本上均不抵抗,培育和推广具有效抗条锈基因的新品种迫在眉睫。     

A myosin passenger protein gene (<Emphasis Type="Italic">FaSmy1</Emphasis>) is an essential regulator of cell development,pathogenicity, DON biosynthesis,and resistance to the fungicide phenamacril in <Emphasis Type="Italic">Fusarium asiaticum</Emphasis>

Wheat streak mosaic virus (WSMV) and Triticum mosaic virus (TriMV) are important viruses of wheat (Triticum aestivum L.) in the Great Plains of United States. In addition to agronomic practices to prevent damage from these viruses, temperature sensitive resistance genes Wsm1, Wsm2 and Wsm3, have been identified. However, threshold temperatures for Wsm1 and Wsm3 have not been clearly defined. To better understand these two resistance genes, wheat lines C.I.15092 (Wsm1), KS96HW10–3 (Wsm1), and KS12WGGRC59 (Wsm3) were evaluated for WSMV resistance at 27, 30, 33 and 35 °C and for TriMV resistance at 18, 21, 24, 27, 30, 33 and 35 °C. The results showed that only C.I.15092 remained resistant at 30 °C for both viruses. This line also tolerated TriMV at 33 and 35 °C with less sever symptom and lower infection rates. Wheat lines KS96HW10–3 and KS12WGGRC59 hold resistance to TriMV up to 21 °C. Molecular marker results suggested that the resistance in C.I.15092 is most probably conditioned by the resistance gene Wsm1 and additional gene(s) other than Wsm2 and Wsm3.     

中国75个国审小麦品种抗条锈基因推导

为明确通过国家农作物品种审定委员会审定的75个小麦品种对条锈病抗病基因状况,根据供试品种与21个来自不同国家或地区条锈菌菌系的互作反应,与已知基因载体品种侵染型进行比较。结果显示,在已知抗条锈病基因中,Yr1、Yr2、Yr3、Yr5、Yr6、Yr7、Yr8、Yr9、Yr17、Yr27、YrA、Yr25、YrSu、YrSp、YrSk等基因以单基因或基因组合形式分布在49个小麦品种（系）中,Yr3所占比例为26.7%,Yr2为20.0%,Yr2、Yr3以基因组合形式存在的占14.7%;其次,携带Yr9的品种有12个,占16.0%;携带Yr1、YrSp的品种各10个,均占13.6%;其余推导出的抗条锈病基因比例均在10.0%以下。镇麦8号、宁麦15和生选6号感染所有菌系,推导其不含有已知抗条锈病基因。     

Korean <Emphasis Type="Italic">Brassica oleracea</Emphasis> germplasm offers a novel source of qualitative resistance to blackleg disease

Blackleg disease, caused by the hemibiotrophic fungal pathogen Leptosphaeria maculans, is one of the most devastating disease of Brassica species worldwide. To date, a total of 20 race-specific blackleg resistance (R) genes have been reported and all of those loci are located in either the A or B genomes of various Brassica species. The B. oleracea genome (CC) shares a high ancestral synteny with the A genome of B. rapa, suggesting the presence of qualitative (race specific) resistance to blackleg disease is also possible in B. oleracea germplasm. In the present study the C genome of Korean B. oleracea germplasm was screened for the presence of blackleg R genes. Thirty-two inbred cabbage lines with unknown resistance profiles, along with five control B. napus lines with well-characterised race-specific R genes, were assessed for cotyledon resistance against two L. maculans isolates with known and highly-contrasting avirulence gene (Avr) profiles. Two cabbage accessions were identified which produced a strong resistance when challenged with either isolate, demonstrating the presence of effective blackleg R genes in the cabbage C genome. Additionally, 16 microsatellite markers linked to seven different R genes of the B. napus A genome were converted into markers for their homologous regions on the B. oleracea C genome. These markers were used to screen all B. oleracea lines to assess if the novel C genome R genes were syntenous to known R gene-homologous regions of the A genome. The resistant cabbage lines offer C genome R genes for the protection of B. oleracea varieties against incursion of blackleg disease, as well as novel additional resistance sources for introgression into B. napus and B. carinata breeding material.     

78个重要小麦品种苗期抗条锈性的聚类分析

选用20个具有不同毒性谱的条锈菌菌系,对78个重要小麦品种材料进行了苗期接种鉴定,以得到的数据为基础,用类平均法对供试小麦品种的抗条锈性进行了聚类分析。鄂恩1号等19个品种被聚在一类,它们具有Yr9或与之相似的抗性;碧玛1号等10个品种被聚在一类,它们具有Yr1或与之相似的抗性;兰天5号等9个品种聚为一类,它们可抗所有供试菌系或仅对1～2个菌系感病;还有些品种被分别聚合为几小类。获知了一批具有未知抗条锈基因或基因组合的重要小麦品种的抗性特点,本结果可为小麦生产品种的合理布局与利用、抗锈育种中抗源的选用以及生产品种抗性变异预测提供重要依据。     

Conidial sporulation of <Emphasis Type="Italic">Stemphylium solani</Emphasis> under laboratory conditions and infectivity of the inoculum produced <Emphasis Type="Italic">in vitro</Emphasis>

Potato virus Y (PVY) is the type-species of the genus Potyvirus, family Potyviridae, being reported as a major tomato (Solanum lycopersicum L.) pathogen in several regions of the world. Pepper yellow mosaic virus (PepYMV) was originally described as a resistance-breaking Potato virus Y (PVY) isolate on Capsicum annuum L. cultivars, and afterwards it was also reported infecting tomatoes in Brazil. In the present work, a search for sources of resistance to both PepYMV and PVY was conducted in a collection of 119 accessions belonging to seven Solanum (section Lycopersicon) species. This germplasm was initially evaluated to PepYMV reaction by mechanical inoculation followed by symptom observations and ELISA. Potential PepYMV resistance sources were identified for the first time in S. habrochaites, S. peruvianum, S. corneliomuelleri, S. chilense, S. pimpinellifolium, and one accession derived from an interspecific cross (S. lycopersicum x S. peruvianum). A sub-group of 24 accessions with negative serology for PepYMV was also challenged with a PVY isolate, followed by serological and molecular detection with universal primers. Solanum habrochaites ‘L.03683’ and ‘L.03684’ were the only accessions found with stable resistance to both viruses. These results confirm S. habrochaites as the most important source of multiple resistance factor(s) to distinct Potyvirus species.     

Rice <Emphasis Type="Italic">OsPBL1</Emphasis> (ORYZA SATIVA ARABIDOPSIS PBS1-LIKE 1) enhanced defense of <Emphasis Type="Italic">Arabidopsis</Emphasis> against <Emphasis Type="Italic">Pseudomonas syringae</Emphasis> DC3000

The receptor-like cytoplasmic kinases (RLCK family VII) are required for plant defense against various pathogens. Previously, OsPBL1 (ORYZA SATIVA ARABIDOPSIS PBS1-LIKE 1) was isolated from rice as a potential RSV (rice stripe virus) resistant factor, but its physiological roles in plant defense are yet to be investigated. In this study, we demonstrated that OsPBL1increased defense against P. syringae in transgenic Arabidopsis. To ascertain the role of OsPBL1 gene in plant defense, OsPBL1 tagged with HA (i.e. Hemagglutinin) was overexpressed in Arabidopsis and examined for the resistance against Pseudomonas syringae pv. tomato DC3000 (i.e. Pst DC3000). At 3 dpi of Pst DC3000, transgenic Arabidopsis lines exhibited the reduced chlorotic lesion and propagation of P. syringae, compared to wild type. Elevated pathogen resistance of transgenic lines was correlated with increased H₂O₂ accumulation and callose deposition on the infected leaves. It was also revealed that expression levels of salicylic acid dependent genes such as PR1, PR2, and PR5, were induced higher in transgenic lines than wild type. Taken together, our data suggested that OsPBL1 exerted the role in defense against pathogen attacks in plant via mainly facilitating salicylic acid dependent pathway.     

Virulence profiling of <Emphasis Type="Italic">Xanthomonas oryzae</Emphasis> pv. <Emphasis Type="Italic">oryzae</Emphasis> isolates,causing bacterial blight of rice in India

Bacterial blight (BB) of rice caused by Xanthomonas oryzae pv. oryzae (Xoo), remains a major production constraint in rice cultivation especially in irrigated and rainfed lowland ecosystems in India. The pathogen is highly dynamic in nature and knowledge on pathotype composition among the Xoo population is imperative for designing a scientific resistance breeding program. In this study, four hundred isolates of Xoo collected from diverse rice growing regions of India were analyzed for their virulence and genetic composition. Virulence profiling was carried out on a set of differentials consisting of 22 near isogenic lines (NILs) of IR24 possessing different BB resistance genes and their combinations along with the checks. It was observed that different NILs possessing single BB resistance gene were susceptible to about 59–94% of the Xoo isolates except IRBB 13 (containing BB resistance gene xa13), which showed susceptibility to about 35% of the isolates. Based on the reaction of the Xoo isolates on the differentials, they were categorized into 22 pathotypes. Among the 22 pathotypes, IXoPt-1 and IXoPt-2 were least virulent and IXoPt # 18–22 were highly virulent. Pathotype IXoPt-19 which was virulent on all single BB resistance genes except xa13 constituted the major pathotype (22.5% isolates) and was widely distributed throughout India (16 states). This was followed by pathotype IXoPt-22 (17.25%) which was virulent on all the NILs possessing single BB resistance genes. Molecular analysis was carried out using two outwardly directed primers complementary to sequence of IS1112, a repetitive element of Xoo. A high level of genetic polymorphism was detected among these isolates and the isolates were grouped into 12 major clusters. The data indicated complex nature of evolution of the Xoo pathotypes and there was no strong correlation between pathotypes and genetic clusters as each genetic cluster was composed of Xoo isolates belonging to different pathotypes. The study indicated that none of the single BB resistance genes can provide broad spectrum resistance in India. However, two-gene combinations like xa5 + xa13 and different 3 or 4 genes combination like Xa4 + xa5 + xa13, Xa4 + xa13 + Xa21, xa5 + xa13 + Xa21 and Xa4 + xa5 + xa13 + Xa21 are broadly effective throughout India.     

100个小麦品种资源抗条锈性鉴定及重要抗条锈病基因的SSR检测

了解小麦品种资源对中国条锈菌生理小种的抗病性水平及其所含重要抗条锈病基因,可为合理种植和利用小麦品种提供理论依据。选用中国小麦条锈菌不同生理小种CYR17、CYR32、CYR33和V26及条锈菌混合小种分别对100个小麦品种资源进行苗期和成株期抗条锈性鉴定,并采用SSR分子标记技术检测重要抗条锈病基因Yr5、Yr10、Yr15、Yr18、Yr24和Yr26。结果表明,在苗期对4个生理小种均表现抗病性的有‘Mos311’、‘兰天15号’等30个品种;在成株期表现抗病性的有‘Yeoman’、‘兰天1号’、‘小红麦’等88个品种;苗期和成株期均抗病的有‘Mos311’、‘兰天15号’等30个品种。SSR检测发现,‘贵农22’可能含有Yr5,‘兰天23号’、‘兰天24’号、‘中梁04260’和‘中梁04335’可能含有Yr10,‘Little Joss’和‘中梁5号’可能含有Yr15,‘清农3号’、‘兰天2号’、‘中梁04335’等19个品种可能含有Yr18,检测品种可能均不含Yr24和Yr26。在鉴定中保持稳定抗病性的‘Mos311’、‘兰天15号’等8个品种在抗病品种选育中有重要应用价值。     

<Emphasis Type="Italic">Fusarium oxysporum</Emphasis> and <Emphasis Type="Italic">Fusarium avenaceum</Emphasis> associated with yield-decline of pyrethrum in Australia

Fusarium wilt, one of the destructive diseases of cucumber can be effectively controlled by using biocontrol agents such as Trichoderma harzianum. However, the mechanisms controlling T. harzianum-induced enhanced resistance remain largely unknown in cucumber plants. Here we screened the potent T. harzianum isolate TH58 that could effectively control F. oxysporum (FO). Glasshouse efficacy trials also showed that TH58 decreased disease incidence by 69.7 %. FO induced ROS over accumulation, while TH58 inoculation suppressed ROS over accumulation and improved root cell viability under F. oxysporum infection. TH58 inoculation could reverse the FO-induced cell division block and regulate the proportional distribution of nuclear DNA content through inducing 2C fraction. Moreover, the expression levels of cell cycle-related genes such as CDKA, CDKB, CycA, CycB, CycD3;1 and CycD3;2 in TH58 - pre-inoculated seedlings were up-regulated compared with those infected with FO alone. Taken together, these results suggest that T. harzianum improved plant resistance against Fusarium wilt disease via alterations in nuclear DNA content and cell cycle-related genes expression that might maintain a lower ROS accumulation and higher root cell viability in cucumber seedlings.