Genotypic and Pathotypic Diversity in Xanthomonas oryzae pv. oryzae in Nepal

ABSTRACT Among the 171 strains of Xanthomonas oryzae pv. oryzae (the bacterial blight pathogen of rice) collected from eight rice-producing zones in Nepal, 31 molecular haplotypes were distinguished using two polymerase chain reaction-based assays. Six common haplotypes represented nearly 63% of the strains, and some haplotypes were geographically dispersed. Multiple correspondence analysis divided the collection into five putative genetic lineages. Lineages 1, 2, and 4 were the most frequently detected and occurred in diverse geographic populations. Twenty-six pathotypes (virulence phenotypes) of X. oryzae pv. oryzae were identified using 11 near-iso-genic rice lines, each containing a single gene for resistance. The 26 pathotypes grouped into five clusters, and cluster 1 contained wide virulence spectrum strains from all geographic populations. Although molecular variation was greatest between strains of different virulence phenotypes, some variation was observed among strains with identical virulence. There was a weak correlation (r = 0.52) between molecular haplotypes and virulence phenotypes. There are two major groups of X. oryzae pv. oryzae in Nepal. One group consists of strains with high molecular polymorphism and many pathotypes that are either virulent to the 11 major resistance genes or avirulent only to Xa21. Strains in the second group have low molecular polymorphism and are avirulent to Xa4, xa5, Xa7, and Xa21.     

Genetic Diversity of Xanthomonas oryzae pv. oryzae Strains from Sri Lanka

ABSTRACT Sixty strains of Xanthomonas oryzae pv. oryzae, collected from 29 locations in Sri Lanka in 1995, were analyzed by restriction fragment length polymorphism using either polymerase chain reaction-amplified 16S and 23S rDNA or the repetitive DNA element IS1112 from X. oryzae pv. oryzae as hybridization probes. Two different ribogroups were observed in the Sri Lankan strains using rDNA probes, whereas five clusters were identified by the IS1112 probe. Bootstrap analysis revealed that the five clusters defined by IS1112 were relatively robust. Our results suggest that the Sri Lankan strains are phylogenetically composed of five different groups. Each cluster was partially associated with climatic conditions (intermediate zone and wet zone) and was related to groups based on ribotyping. Based on virulence analysis using 12 rice cultivars, each containing a single resistance gene, 14 pathotypes were identified among the Sri Lankan strains. All strains were virulent to resistance genes Xa1, Xa2, Xa4, Xa10, Xa11, and Xa14. Only one strain (pathotype 1) was virulent to all major resistance genes including Xa21, while strains of the other pathotypes were all avirulent to Xa21. A partial relationship was found between the determined phylogenetic groups using the IS1112 probe and pathotypes for all but two clusters. The results of this study will facilitate the further understanding of the population structure of X. oryzae pv. oryzae in Sri Lanka.     

Inheritance of resistance to bacterial blight in 21 cultivars of rice

ABSTRACT Genetic analysis for resistance to bacterial blight (Xanthomonas oryzae pv. oryzae) of 21 rice (Oryza sativa L.) cultivars was carried out. These cultivars were divided into two groups based on their reactions to Philippine races of bacterial blight. Cultivars of group 1 were resistant to race 1 and those of group 2 were susceptible to race 1 but resistant to race 2. All the cultivars were crossed with TN1, which is susceptible to all the Philippine races of X. oryzae pv. oryzae. F(1) and F(2) populations of hybrids of group 1 cultivars were evaluated using race 1 and F(1) and F(2) populations of hybrids of group 2 cultivars were evaluated using race 2. All the cultivars showed monogenic inheritance of resistance. Allelic relationships of the genes were investigated by crossing these cultivars with different testers having single genes for resistance. Three cultivars have Xa4, another three have xa5, one has xa8, two have Xa3, eight have Xa10, and one has Xa4 as well as Xa10. Three cultivars have new, as yet undescribed, genes. Nep Bha Bong To has a new recessive gene for moderate resistance to races 1, 2, and 3 and resistance to race 5. This gene is designated xa26(t). Arai Raj has a dominant gene for resistance to race 2 which segregates independently of Xa10. This gene is designated as Xa27(t). Lota Sail has a recessive gene for resistance to race 2 which segregates independently of Xa10. This gene is designated as xa28(t).     

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.     

Gene-for-gene relationships between rice and diverse avrBs3/pthA avirulence genes in Xanthomonas oryzae pv. oryzae

The interactions between Xanthomonas oryzae pv. oryzae (Xoo) and rice are controlled in a gene-for-gene manner. In this study, a 359 bp DNA fragment of the avrXa3 gene containing three nuclear localization signal (NLS) motifs present in all members of the avrBs3/pthA family was used as a probe to screen a genomic library of the JXOIII strain of Xoo. The results demonstrated that diverse members of the family exist in the pathogen genome. The avrBs3/pthA genes occurred at isolated individual portions or in clusters. The positive avr gene clones were transferred into the virulent recipient PXO99^A. Pathogenicity tests in near isogenic lines of rice confirmed that four resistance (R) genes ( Xa2 , Xa3 , xa5 and xa8 ) matched the four avr genes ( avrXa2 , avrXa3 , avrxa5 and avrxa8 ) in the genome of Xoo strain JXOIII. The avrBs3/PthA -like gene (1·7 kb) present in cosmid p54, may specifically interact with the Xa3 gene present in IRBB3, and is designated avr/pthA3 . Sequencing indicated that there are only 1·5 copies of the 102 bp repeat unit in avr/pthA3 . Alignment of the twelfth and thirteenth amino acids in the repetitive units encoded by this gene with those in other representatives of the AvrBs3 family revealed a unique repeat arrangement which might contribute to variation in the avirulence genes in Xoo. The parental rice line IR24 was found to contain several R genes for resistance to Xoo bacterial blight.     

Antagonistic Interactions Between Strains of Xanthomonas oryzae pv. oryzae

ABSTRACT The ability of some phytopathogenic bacterial strains to inhibit the growth of others in mixed infections has been well documented. Here we report that such antagonistic interactions occur between several wild-type strains of the rice bacterial blight pathogen Xanthomonas oryzae pv. oryzae. In mixed inoculations, a wild-type Philippine strain was found to inhibit the growth of a wild-type Korean strain. Furthermore, a nonpathogenic mutant of the Philippine strain maintained these antagonistic properties. Growth curve analysis indicated that both the wild-type Philippine strain and its nonpathogenic mutant inhibited the growth of the Korean strain 2 days after infection and prior to the onset of disease symptoms. When mixed with the nonpathogenic mutant, 10 out of 18 diverse wild-type X. oryzae pv. oryzae strains did not cause disease. Conversely, three of the strains that were not affected by the nonpathogenic mutant were found to inhibit the growth of both the wild-type and mutant Philippine strains, indicating that antagonism is widespread and strain specific. The observed growth inhibition occurred only in planta and did not correlate with bacteriocin activity in vitro. Antagonistic interactions also were found to affect resistance (R) gene-mediated resistance. The R gene Xa21 was capable of protecting rice plants coinoculated with nonantagonistic virulent and avirulent strains; however, when avirulent strains were coinoculated with virulent antagonistic strains, disease ensued. Taken together, these results indicate that X. oryzae pv. oryzae has evolved strategies to compete with rival strains in a fashion that allows virulent strains to evade R gene-mediated protection even when avirulent strains are present in the inoculum.     

Xa21转基因水稻对白叶枯病的抗性及其遗传

 采用包括与Xa21基因相对应的白叶枯病鉴别小种P6在内的12个国际鉴别小种和我国7个病原型,对通过农杆菌介导的8个不同遗传背景的Xa21转基因品系,及其不同世代的植株,进行接种和抗性分析。结果表明:Xa21在不同的遗传背景下呈现显性,并且在转基因后代中可以稳定遗传,且保留其广谱抗性。在不同的遗传背景下,Xa21的抗性表达略有差异。     

Distribution of Xanthomonas oryzae pv. oryzae Strains Virulent to Xa21 in Korea

ABSTRACT Strains of Xanthomonas oryzae pv. oryzae that are virulent to rice lines carrying the Xa21 resistance gene were widely distributed in Korea. A total of 105 strains collected during 1987 to 1996 in Korea was characterized by pathogenicity tests and restriction fragment length polymorphism analysis of the XorII methyltransferase (xorIIM) and avrXa10 genes. Although the lesion lengths on rice line IRBB21, which carries Xa21, decreased as plant age increased, resistance and susceptibility of the plants to 31 strains were clearly differentiated at the seedling (14, 21, and 28 days old), maximum tillering, and flag leaf stages. The resistance or susceptibility of seedlings was correlated with bacterial populations within an inoculated leaf. There was a significant change in the population structure of X. oryzae pv. oryzae with regard to virulence to Xa21 over the last 10 years; this change in population was confirmed by genome analysis. Lineage I, which is avirulent to Xa21 and does not have a genomic xorIIM homolog, was the predominant lineage found between 1987 and 1989, while lineage II, which is virulent to Xa21 and contains the xorIIM homolog, was predominant in strains collected between 1994 and 1995. Our results demonstrate that introduction of Xa21 into commercial rice should be based on the regional structure of X. oryzae pv. oryzae populations and suggest that Xa21 will not be useful in Korea.     

水稻白叶枯病菌单细胞系毒力分化研究

 以稀释倒平板法从0型菌086和IV型菌967-4和9620中分离到59个单细胞系;在12个近等基因系品种上,086和其单细胞系表现为弱毒力,2个IV型菌及其单细胞系能克服抗病基因Xa-1、2、3、8、10、11、14的抗性,不能克服Xa-21、4、5、7、13的抗性;带主效抗病基因的品种Asominori、XM5、M41、XM6和丰锦能把3个母株的59个单细胞系区分为12种数量差异或质量差异的不同致病型;将此5品种与近等基因系配合,适合作为病菌致病基因变异频度监测的寄主;采用"段叶沙培,切口取菌胶"法分离病菌,在中国致病型鉴定品种上划分的致病型,是田间病菌群体毒力结构的表型反应。     

水稻白叶枯病抗性基因在不同载体品种上及杂种F_1的抗性研究

本研究测试了八个水稻白叶枯病抗性基因Xa3、Xa4、xa5、Xa7、Xa10、Xa11、Xa14和Xa23在相应载体品种上对华南白叶枯病优势致病菌系Ⅳ型菌和强毒菌系Ⅴ型菌的抗性反应;分析了Xa4、xa5、Xa7和Xa23抗病基因与不同感病品种杂交组合F_1的抗性表达模式以及显性抗病基因Xa7和Xa23在杂交水稻上的利用价值。结果表明:大部分抗性基因在不同载体品种上抗性表达一致,但也有少数基因在不同载体品种上抗性表现不一,甚至截然相反,说明不同遗传背景对抗性表达有影响,而这种影响因不同抗性基因而异。隐性抗病基因xa5(IRBB5)和显性抗病基因Xa23(CBB23)与感病亲本组合的F_1代分别表现感病和抗病,符合隐性基因或显性基因的抗性表达模式;而2个显性抗病基因Xa4(IRBB4))和Xa7(IRBB7)与感病亲本组合的F_1代,有部分组合的F_1代表现抗病,符合显性基因的抗性表达模式,有部分组合的F_1代表现感病,不符合显性基因的抗性表达模式。在杂交水稻上的利用价值方面,Xa7与2个不育系组合的F_1代均表现高感,不宜在杂交水稻上利用;Xa23(CBB23)与4个感病亲本,无论是不育系还是常规稻组合的4个F_1代全部表现抗病,抗性在F_1充分表达,在杂交水稻上有重要的利用价值。     

DNA typing and virulence determination of Xanthomonas oryzae pv. oryzae population for the management of bacterial leaf blight of rice in Udham Singh Nagar,India

Bacterial leaf blight caused (BLB) by Xanthomonas oryzae pv. oryzae (Xoo) is the most serious biotic constraint of rice in Udham Singh Nagar (U.S. Nagar), India. We have experienced severe BLB outbreaks, causing total crop failure during 2007–2010. The severity of losses incurred due to BLB in U.S. Nagar necessitates the development of an ecology-conscious, effective and durable management strategy. Our interests here were focused to obtain information on the haplotypic and pathogenic variability of Xoo to develop effective breeding strategy for BLB resistance. Our results indicate that the currently existing population of Xoo in U.S. Nagar is highly virulent and genetically diverse. Twenty one haplotypes were detected among a collection of 193 strains by each of the PCR technique used i.e. rep-PCR and IS-PCR. The high value of total haplotypic diversity (H_T ⁼0.79) reflected the genetic heterogeneity of Xoo population infecting popular varieties. Strains responsible for severe BLB outbreaks were grouped into eight distinct lineages with significant bootstrap values (p?>?75). Virulence assay revealed the presence of 11 pathotypes. The interaction of lines with strains was found significant (p?<?0.01) confirming the pathogenic specialization of Xoo in U.S. Nagar. Most of the single major resistance genes used in rice breeding program at International Rice research Institute (IRRI) was defeated by Xoo strains, at the same time; effectiveness of Xa21 to all the pathotypes is encouraging. The potential of Xa21 alone or in combination with xa13 and xa5 could be exploited for pyramiding into well-adapted rice cultivars for the effective management of the pathogen in this region. This is the first report on the population structure of Xoo in U.S. Nagar, India.     

云南疣粒野生稻抗白叶枯病鉴定及叶片组织学观察

 本研究采用水稻白叶枯病菌强致病性代表菌株,评价了云南省自然分布的疣粒野生稻代表生态居群18份材料的抗病性,观察叶片组织学结构,初步分析了疣粒野生稻的抗性基因。结果表明,16份材料表现中抗、高抗甚至免疫;9份材料对4个菌株的抗性有一定差异;同时发现云南地方代表菌株X1和CN9404的致病性比C1和BD8438强。叶片组织学结构表明,高抗材料与感病的栽培稻米泉黑芒都无蜡质层,二者的叶肉组织、薄壁细胞和表皮细胞相同,表皮毛、维管束、厚壁组织等的差异也不明显,不足以引起抗病性差异。疣粒野生稻高抗或免疫白叶枯病并非借助其特殊叶片结构的物理作用,而主要是抗病基因的作用。参试疣粒野生稻中没有与Xa1、Xa21同源的基因,加之独立进化,推断其具有新的优异抗白叶枯病基因,值得深入研究和发掘利用。     

Influence of rice development on the function of bacterial blight resistance genes

Disease resistance genes most commonly used in breeding programs are single, dominant genes with relative effectiveness that is sometimes influenced by plant developmental stage. Knowing the developmental stages at which a resistance gene is functional is important for disease management. In rice, resistance at the seedling stage is crucial, because wounding during transplanting increases the potential for bacterial blight disease, and not all bacterial blight resistance genes are effective at the seedling stage. Effectiveness of the bacterial blight resistance genes Xa4, xa5, and Xa7, all in a common genetic background, was evaluated at different developmental stages by measuring lesion length and bacterial numbers after inoculation with the bacterial pathogen, Xanthomonas oryzae pv. oryzae. The Xa4 and xa5 genes controlled disease at all growth stages. In contrast, Xa7 was not fully functional in very young seedlings, but was completely effective by 21 days after sowing (das). The effects of plant developmental stage on interactions of the Xa7 gene with X. oryzae pv. oryzae strains carrying different mutant avrXa7 alleles were also tested. If a partial or fully functional avrXa7 allele was present, Xa7 resistance was effective at all growth stages tested after the transplant stage (>21 das).     

水稻白叶枯病菌北方菌株的分子鉴别和致病型分析

为了阐明水稻白叶枯病菌(Xanthomonas oryzaepv.oryzae,Xoo)北方菌株的毒性组成,对2008年和2009年从辽宁、吉林、河北、山东稻区采集的103个菌株进行了PCR分子鉴定,并利用一套水稻抗白叶枯病近等基因系作为鉴别品种,进行了致病性测定。结果表明,用3种不同引物对测定菌株基因组进行PCR扩增,均可以鉴别出与Xoo代表菌株完全一致、而与水稻条斑病菌明显不同的特异性扩增片段带型。6个水稻鉴别品种对测定菌株的感病反应明显不同,抗病性强弱依次为IRBB5IRBB13IRBB3IRBB14IRBB2IRBB24。103个菌株对6个水稻鉴别品种表现出毒力多样性,92个菌株(89.32%)表现与9个标准小种(R1~R9)代表菌株相同的致病型,其中36个R5和R8菌株为优势菌株,9个菌株为对6个水稻品种都致病的R9强毒力菌株;此外,新发现了其余11个菌株(10.68%)具有7种新的致病型(R10~R16)。     

水稻品种(组合)抗白叶枯病基因初探

 用菲律宾6个白叶枯病菌系(小种),将95个水稻品种(品系)划分为5个品种类群,为今后开展品种抗病性的基因分析提供了必要的条件。通过测试,提出舟松62、二九丰(早籼) 城特232、T₈₅₂₈、H₁₀₁、6003、T₈₈₅₀₆、T₈₈₅₁₇、R₈₉₅、绍糯₈₈₄₃、丙₈₈₁₅₁、台₂₀₂、T₈₈₅₂₂(晚粳)等13个具有广谱抗性的品种(系),可作杂交亲本利用。     

The dynamics of homologous and heterologous interactions between rice and strains of Xanthomonas campestris

Lesion development, bacterial multiplication and spread were measured in leaves of cultivars of rice containing different Xa (resistance) genes, following inoculation with different races of the bacterial leaf blight pathogen. Xanthomonas campestris pv. oryzae. Both compatible and incompatible races possessed the ability to colonize rice plants. The difference between compatible and incompatible host pathogen combinations appeared to be mainly in symptom production since multiplication rates and spread were very similar until after the onset of symptoms. No form of HR (hypersensitive response) was observed. The ability of incompatible races to modify host reaction in dual-inoculation was dependent on the genotype of the host plant. The heterologous non-pathogen of rice X. campestris pv. campestris produced few symptoms, failed either to multiply or spread within rice leaves and was unable to induce any marked cross-protection against homologous pv. oryzae strains in dual-inoculation experiments.     

云南高海拔粳稻区白叶枯病菌致病型的鉴定

水稻白叶枯病是危害水稻的重要细菌性病害之一,病原为稻生黄单胞菌水稻致病变种Xanthomonas oryzae pv.oryzae (Xoo).近10年来云南省水稻白叶枯病的危害向高海拔粳稻区扩散,在海拔2200m的剑川县,白叶枯病已成为最严重的水稻病害[1-2].开展高海拔粳稻区白叶枯病菌致病型的鉴定、分布和分化研究,对云南高海拔粳稻区稻作生产具有指导意义.     

水稻对白叶枯病强毒菌系Ⅴ型菌的抗性研究

作者报道了水稻对广东白叶枯病强毒菌系Ⅴ型菌抗性研究与抗源筛选评价结果。从1076份国内外水稻种质资源中筛选出29份抗病材料,占2.70％。其中IRBB7等5份具有广谱、高抗兼较好农艺性状。由日本和国际水稻所鉴定的14个抗性基因中Xa-3、xa-5、Xa-7、xa-13等抗Ⅴ型菌。抗Ⅴ型菌材料多数兼抗其它菌型,但亦有一些不抗Ⅳ型菌,表明菌型与品种间有强烈互作效应。水稻对Ⅴ型菌抗性与其类型有关,梗稻与籼稻、糯稻与粘稻、国外稻与国内稻比较,抗病率均以前者为高。     

Identification and fine-mapping of Xa33, a novel gene for resistance to Xanthomonas oryzae pv. oryzae

Broadening of the genetic base for identification and transfer of genes for resistance to insect pests and diseases from wild relatives of rice is an important strategy in resistance breeding programs across the world. An accession of Oryza nivara, International Rice Germplasm Collection (IRGC) accession number 105710, was identified to exhibit high level and broad-spectrum resistance to Xanthomonas oryzae pv. oryzae. In order to study the genetics of resistance and to tag and map the resistance gene or genes present in IRGC 105710, it was crossed with the bacterial blight (BB)-susceptible varieties 'TN1' and 'Samba Mahsuri' (SM) and then backcrossed to generate backcross mapping populations. Analysis of these populations and their progeny testing revealed that a single dominant gene controls resistance in IRGC 105710. The BC(1)F(2) population derived from the cross IRGC 105710/TN1//TN1 was screened with a set of 72 polymorphic simple-sequence repeat (SSR) markers distributed across the rice genome and the resistance gene was coarse mapped on chromosome 7 between the SSR markers RM5711 and RM6728 at a genetic distance of 17.0 and 19.3 centimorgans (cM), respectively. After analysis involving 49 SSR markers located between the genomic interval spanned by RM5711 and RM6728, and BC(2)F(2) population consisting of 2,011 individuals derived from the cross IRGC 105710/TN1//TN1, the gene was fine mapped between two SSR markers (RMWR7.1 and RMWR7.6) located at a genetic distance of 0.9 and 1.2 cM, respectively, from the gene and flanking it. The linkage distances were validated in a BC(1)F(2) mapping population derived from the cross IRGC 105710/SM//2 × SM. The BB resistance gene present in the O. nivara accession was identified to be novel based on its unique map location on chromosome 7 and wider spectrum of BB resistance; this gene has been named Xa33. The genomic region between the two closely flanking SSR markers was in silico analyzed for putatively expressed candidate genes. In total, eight genes were identified in the region and a putative gene encoding serinethreonine kinase appears to be a candidate for the Xa33 gene.