Leaf Blight Of Rice Research Articles

Marker-Assisted Selection of Xa21 Conferring Resistance to Bacterial Leaf Blight in indica Rice Cultivar LT2

Bacterial leaf blight of rice (BLB), caused by Xanthomonas oryzae pv. oryzae, is one of the most destructive diseases in Asian rice fields. A high-quality rice variety, LT2, was used as the recipient parent. IRBB21, which carries the Xa21 gene, was used as the donor parent. The resistance gene Xa21 was introduced into LT2 by marker-assisted backcrossing. Three Xoo races were used to inoculate the improved lines following the clipping method. Eleven BC3F3 lines carrying Xa21 were obtained based on molecular markers and agronomic performance. The 11 lines were then inoculated with the three Xoo races. All the 11 improved lines showed better resistance to BLB than the recipient parent LT2. Based on the level of resistance to BLB and their agronomic performance, five lines (BC3F3 5.1.5.1, BC3F3 5.1.5.12, BC3F3 8.5.6.44, BC3F3 9.5.4.1 and BC3F3 9.5.4.23) were selected as the most promising for commercial release. These improved lines could contribute to rice production in terms of food security.

Hiệu quả giảm bệnh và cơ chế kích kháng liên quan đến enzyme phenylalanine ammonia-lyase và polyphenol oxidase đối với bệnh cháy bìa lá lúa khi phun qua lá với dịch trích lá sống đời

Bacterial leaf blight of rice caused by Xanthomonas oryzae pv. oryzae (Xoo) is a destructive disease which constrains the production of this staple crop in many rice-cultivation regions. This study aims at testing for the disease-reducing effects and demonstrating the involvement of induced resistance in the observed effects of an aqueous leaf extract of Kalanchoe pinnata (life plant) using foliar spraying. A total of six concentrations (1, 2, 3, 4, 5 and 10% [w/v]) of the plant extract were sprayed at 14 or 7 days before inoculation. Under greenhouse conditions, 1% at 14 days before inoculation was the lowest concentration at which the extract showed the disease-reducing effects similar to those of the chemical control at all assessment time points (7, 14, and 21 days after inoculation). Induction of systemic resistance was shown by the increased accumulation of the two enzymes phenylalanine ammonia-lyase and polyphenol oxidase following foliar spraying with the K. pinnata extract and challenge inoculation with Xoo.

Effect of compost tea, streptomycin and cupravit in controlling bacterial leaf blight of rice

Compost tea, streptomycin and cupravit were evaluated against the Bacterial Leaf Blight diseases of rice cv. BR11 in two management approaches (preventive and curative) under field condition. The selected cultivar BR11 was cultivated in the field laboratory of the Department of Plant Pathology, Bangladesh Agricultural University, Mymensingh, Bangladesh during the period from July to December 2012. The field experiment was carried out with seven treatments in Randomized Complete Block Design (RCBD) and each was replicated thrice. The treatments were T0 = Control, T1= Compost tea as foliar spray 2 times (preventive) @ 1:5 w/v, T2= Compost tea as foliar spray 2 times (Curative) @ 1:5 w/v, T3 = Streptomycin as foliar spray 2 times (preventive) @1gm/10 L, T4 = Streptomycin as foliar spray 2 times (Curative) @ 1gm/10 L, T5 = Cupravit as foliar spray 2 times (preventive) @ 0.2%, T6 = Cupravit as foliar spray 2 times (Curative) @ 0.2%. Cupravit as foliar spray 2 times (Curative) @ 0.2% showed marked effect in reducing Bacterial Leaf Blight diseases of BR11 rice as well as enhancing yield and yield contributing characters. The effect of compost tea also produced similar effects on disease and yield of rice over control. Among the application options of different treatment, curative application provided better results than preventive under field condition.Bangladesh J. Agril. Res. 42(3): 447-456, September 2017

Biocontrol of Bacterial Leaf Blight of Rice and Profiling of Secondary Metabolites Produced by Rhizospheric Pseudomonas aeruginosa BRp3.

Xanthomonas oryzae pv. oryzae (Xoo) is widely prevalent and causes Bacterial Leaf Blight (BLB) in Basmati rice grown in different areas of Pakistan. There is a need to use environmentally safe approaches to overcome the loss of grain yield in rice due to this disease. The present study aimed to develop inocula, based on native antagonistic bacteria for biocontrol of BLB and to increase the yield of Super Basmati rice variety. Out of 512 bacteria isolated from the rice rhizosphere and screened for plant growth promoting determinants, the isolate BRp3 was found to be the best as it solubilized 97 μg/ mL phosphorus, produced 30 μg/mL phytohormone indole acetic acid and 15 mg/ L siderophores in vitro. The isolate BRp3 was found to be a Pseudomonas aeruginosa based on 16S rRNA gene sequencing (accession no. HQ840693). This bacterium showed antagonism in vitro against different phytopathogens including Xoo and Fusarium spp. Strain BRp3 showed consistent pathogen suppression of different strains of BLB pathogen in rice. Mass spectrometric analysis detected the production of siderophores (1-hydroxy-phenazine, pyocyanin, and pyochellin), rhamnolipids and a series of already characterized 4-hydroxy-2-alkylquinolines (HAQs) as well as novel 2,3,4-trihydroxy-2-alkylquinolines and 1,2,3,4-tetrahydroxy-2-alkylquinolines in crude extract of BRp3. These secondary metabolites might be responsible for the profound antibacterial activity of BRp3 against Xoo pathogen. Another contributing factor toward the suppression of the pathogen was the induction of defense related enzymes in the rice plant by the inoculated strain BRp3. When used as an inoculant in a field trial, this strain enhanced the grain and straw yields by 51 and 55%, respectively, over non-inoculated control. Confocal Laser Scanning Microscopy (CLSM) used in combination with immunofluorescence marker confirmed P. aeruginosa BRp3 in the rice rhizosphere under sterilized as well as field conditions. The results provide evidence that novel secondary metabolites produced by BRp3 may contribute to its activity as a biological control agent against Xoo and its potential to promote the growth and yield of Super Basmati rice.

A Transcription Activator-Like Effector Tal7 of Xanthomonas oryzae pv. oryzicola Activates Rice Gene Os09g29100 to Suppress Rice Immunity

Xanthomonas oryzae pv. oryzicola (Xoc) and X. oryzae pv. oryzae (Xoo) cause bacterial leaf streak (BLS) and bacterial leaf blight (BLB) in rice, respectively. Unlike Xoo, endogenous avirulence-resistance (avr-R) gene interactions have not been identified in the Xoc-rice pathosystem; however, both pathogens possess transcription activator-like effectors (TALEs) that are known to modulate R or S genes in rice. The transfer of individual tal genes from Xoc RS105 (hypervirulent) into Xoc YNB0-17 (hypovirulent) led to the identification of tal7, which suppressed avrXa7-Xa7 mediated defense in rice containing an Xa7 R gene. Mobility shift and microscale thermophoresis assays showed that Tal7 bound two EBE sites in the promoters of two rice genes, Os09g29100 and Os12g42970, which encode predicted Cyclin-D4-1 and GATA zinc finger family protein, respectively. Assays using designer TALEs and a TALE-free strain of Xoo revealed that Os09g29100 was the biologically relevant target of Tal7. Tal7 activates the expression of rice gene Os09g29100 that suppresses avrXa7-Xa7 mediated defense in Rice. TALEN editing of the Tal7-binding site in the Os09g29100 gene promoter further enhanced resistance to the pathogen Xoc RS105. The suppression of effector-trigger immunity (ETI) is a phenomenon that may contribute to the scarcity of BLS resistant cultivars.

Bronopol (2-Bromo-2-Nitropropane-1, 3-Diol), A Chlorine Based Chemical Compound for the Management of Bacterial Leaf Blight of Rice

Bronopol (2-Bromo-2-Nitropropane-1, 3-Diol), A Chlorine Based Chemical Compound for the Management of Bacterial Leaf Blight of Rice

Marker assisted selection for bacterial leaf blight resistance in segregating populations of Karma Mahsuri

Marker Assisted Selection for Bacterial Leaf Blight resistance in Segregating Populations of Karma Mahsuri Bacterial leaf blight (BLB) of rice is caused by Xanthomonas oryzae pv. oryzae (Xoo), this is a major disease of rice in several countries. The present investigation was undertaken with the objective to develop high yielding rice varieties possessing broad spectrum durable resistance by transferring bacterial leaf blight (BLB) resistant genes viz., xa5 xa13 and Xa21 from a donor IRBB59 and a popular high yielding rice variety i.e., Karma Mahsuri, susceptible to BLB and were selected as parents. The presence of target genes by using gene linked primers viz., xa5R, xa5S, xa13 promoter and Xa21F/R was done. Segregating population was advanced to BC2 F3 generation and foreground selection was done using gene linked markers. Genetic analysis in BC2 F3 populations confirmed the presence of genes (xa5, xa13 & Xa21) governing BLB resistance in 22 lines. p>

Comparative Efficacy of Different Chemical Treatments for Paddy Blast, Brown Leaf Spot and Bacterial Leaf Blight Diseases in Rice (Oryza Sativa L.)

Paddy blast, brown leaf spot and bacterial leaf blight of rice are the most devastating diseases of rice worldwide causing serious threats to food security. For the purpose field trials were conducted for the evaluation of different available fungicides at Rice Research Institute, Kala Shah Kaku during season of 2016. Application of different fungicide to control the disease and their effect on paddy yield under field condition were studied. The results showed that fungicide application not only controlled the disease but also improved the paddy yield as compared to control. In this study, Amistar Top 325 SC performed best to control the Paddy blast that leaf to high yield. In the case of Brown leaf spot, application of Switch DF 80 WG revealed the lowest incidence of disease along with highest protection value. Similarly, Nativo was most effective to control the Bacterial Leaf Blight incidence. Conclusively, these chemical can be used to control the studied bacterial and fungal diseases for high paddy yield.

First report of Sphingomonas sp. causing bacterial leaf blight of rice in Benin, Burkina Faso, The Gambia, Ivory Coast, Mali, Nigeria, Tanzania and Togo

Surveys of rice growing areas were conducted from 2011 to 2015 with the aim of assessing the importance of bacterial diseases in Benin, Burkina Faso, The Gambia, Ghana, Ivory Coast, Mali, Niger, Nigeria, Senegal, Tanzania and Togo. Between …

First Report of a New Bacterial Leaf Blight of Rice Caused by Pantoea ananatis and Pantoea stewartii in Benin

First Report of a New Bacterial Leaf Blight of Rice Caused by <i>Pantoea ananatis</i> and <i>Pantoea stewartii</i> in Benin

First Report of a New Bacterial Leaf Blight of Rice Caused by Pantoea ananatis and Pantoea stewartii in Togo

First Report of a New Bacterial Leaf Blight of Rice Caused by <i>Pantoea ananatis</i> and <i>Pantoea stewartii</i> in Togo

Interactive Effect of Different Nitrogen and Potash Levels on the Incidence of Bacterial Leaf Blight of Rice (&amp;lt;i&amp;gt;Oryza sativa L.&amp;lt;/i&amp;gt;)

An experiment was conducted at Rice Research Institute, Kala Shah Kaku in 2010 during kharif season to study the influence of nitrogen (N) and potash (K) on severity of Bacterial leaf blight (BLB) of rice (Oryza sativa L.) aimed at improving productivity. The experiment was laid out in randomized complete block design with factorial arrangement with three replications. Treatments comprised of: 0 kg N ha-1, 75 kg N ha-1, 100 kg N ha-1, 125 kg N ha-1 and 0 kg K ha-1, 50 kg K ha-1, 75 kg K ha-1, 100 kg K ha-1. Data on disease severity and paddy yield were recorded using standard procedures. Paddy yield was affected significantly by various combinations of N & K. In case of bacterial leaf blight, minimum diseased incidence percentage was observed when nitrogen alone was applied @ 75 kg·ha-1 in contrast to fertilizer applied @ 125 kg N ha-1 + 50 kg K ha-1 which showed maximum diseased incidence percentage. Maximum paddy yield (4.32 t·ha-1 ) was recorded when rice was fertilized @ 75 kg N ha-1 + 100 kg K ha-1 as compared to sole fertilization of 75 kg K ha-1 that produced minimum paddy yield (2.40 t·ha-1). Maximum gross income, net returns and benefit cost ratio were obtained where rice crop was fertilized @ 75 kg N ha-1 and 100 kg K ha-1.

A thiadiazole reduces the virulence of Xanthomonas oryzae pv. oryzae by inhibiting the histidine utilization pathway and quorum sensing.

Thiazole, isothiazole, thiadiazole and their derivatives are widely thought to induce host defences against plant pathogens. In this article, we report that bismerthiazol, a thiadiazole molecule, reduces disease by inhibiting the histidine utilization (Hut) pathway and quorum sensing (QS). Bismerthiazol provides excellent control of bacterial rice leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo), but does not greatly inhibit Xoo growth in vitro. According to RNA-sequencing analysis, the transcription of the Hut pathway genes of Xoo ZJ173 was inhibited after 4.5 and 9.0 h of bismerthiazol treatment. Functional studies of hutG and hutU indicated that the Hut pathway had little effect on the growth and bismerthiazol sensitivity of Xoo in vitro, but significantly reduced the aggregation of Xoo cells. Deletion mutants of hutG or hutU were more motile, produced less biofilm and were less virulent than the wild-type, indicating that the Hut pathway is involved in QS and contributes to virulence. The overexpression of the hutG-U operons in ZJ173 reduced Xoo control by bismerthiazol. Bismerthiazol did not inhibit the transcription of Hut pathway genes, QS or virulence of the bismerthiazol-resistant strain 2-1-1. The results indicate that bismerthiazol reduces Xoo virulence by inhibiting the Hut pathway and QS.

Long-term effect of niclosamide on inhibition of bacterial leaf blight in rice

AbstractBacterial leaf blight is one of the major diseases in rice and affects yields. Thus, various methods have been applied to protect rice from this disease. Here, we show systemic translocation of the human drug niclosamide (5-chloro-N-(2-chloro-4-nitrophenyl)- 2-hydroxybenzamide) in rice and its long-term effect on prevention of rice leaf blight. The development of Xanthomonas oryzae pv. oryzae-induced rice leaf blight was effectively inhibited in untreated systemic leaves as in niclosamide-treated leaves, although its effect gradually decreased in a time-dependent manner. Time-course examination after niclosamide treatment showed that the niclosamide level was highest after 3 h in non-treated distal leaves, suggesting fast systemic movement of niclosamide from the treated local site to untreated distal regions. Our data indicate that niclosamide controls rice leaf blight by its rapid systemic movement and that its effect is maintained for a long time.

PATHOTYPE PROFILE OF Xanthomonas oryzae pv. oryzae ISOLATES FROM THE RICE ECOSYSTEM IN JAVA

At present, bacterial leaf blight of rice caused by Xanthomonas oryzae pv. oryzae is highly damaging to rice production in Indonesia as most of the existing commercial rice varieties are susceptible to the existing pathotypes of the bacteria. To solve such problems, varietal rotation should be based on information on the existence and dominance of local pathotypes in a particular rice ecosystem. To obtain this information, a total of 117 isolates of X. oryzae pv. oryzae, collected from West Java, Central Java, and Yogyakarta, were evaluated for their pathotype variation on five differential rice varieties during the dry season of 2000. When disease severity was &amp;lt; 10%, the reaction was classified as resistant (R) and when &amp;gt; 11%, was susceptible (S). The data indicated that 3.42% of the isolates were pathotype III, 12.82% were pathotype IV, and 83.76% were pathotype VIII. In West Java, the bacterial pathotypes III, IV, and VIII were 4.94%, 14.81%, and 80.25%, respectively. In low elevation areas, 4.94%, 9.88%, and 45.68% were pathotypes III, IV, and VIII, respectively and in medium areas, 4.94% were pathotypes IV and 34.57% were pathotype VIII. In Central Java, no pathotype III was found, while pathotypes IV and VIII were as much as 4.52% and 90.48%, respectively. In low elevation areas, no pathotypes III was recovered, and a total of 9.53% and 76.19% were identified as pathotypes IV and VIII, respectively, and in medium areas only pathotype VIII (14.29%) was identified. In Yogyakarta, pathotypes IV and VIII were found. In low elevation areas, 6.67% and 93.33% were pathotypes IV and VIII, respectively and in medium areas, 14.29% and 85.71% were pathotypes IV and VIII, respectively. The data indicated that variation in pathotype composition over different locations was obvious and locally specific resistant varieties to the disease are needed in the management of this important bacterial disease in rice.

PATHOTYPE PROFILE OF Xanthomonas oryzae pv. oryzae ISOLATES FROM THE RICE ECOSYSTEM IN JAVA

At present, bacterial leaf blight of rice caused by Xanthomonas oryzae pv. oryzae is highly damaging to rice production in Indonesia as most of the existing commercial rice varieties are susceptible to the existing pathotypes of the bacteria. To solve such problems, varietal rotation should be based on information on the existence and dominance of local pathotypes in a particular rice ecosystem. To obtain this information, a total of 117 isolates of X. oryzae pv. oryzae, collected from West Java, Central Java, and Yogyakarta, were evaluated for their pathotype variation on five differential rice varieties during the dry season of 2000. When disease severity was &amp;lt; 10%, the reaction was classified as resistant (R) and when &amp;gt; 11%, was susceptible (S). The data indicated that 3.42% of the isolates were pathotype III, 12.82% were pathotype IV, and 83.76% were pathotype VIII. In West Java, the bacterial pathotypes III, IV, and VIII were 4.94%, 14.81%, and 80.25%, respectively. In low elevation areas, 4.94%, 9.88%, and 45.68% were pathotypes III, IV, and VIII, respectively and in medium areas, 4.94% were pathotypes IV and 34.57% were pathotype VIII. In Central Java, no pathotype III was found, while pathotypes IV and VIII were as much as 4.52% and 90.48%, respectively. In low elevation areas, no pathotypes III was recovered, and a total of 9.53% and 76.19% were identified as pathotypes IV and VIII, respectively, and in medium areas only pathotype VIII (14.29%) was identified. In Yogyakarta, pathotypes IV and VIII were found. In low elevation areas, 6.67% and 93.33% were pathotypes IV and VIII, respectively and in medium areas, 14.29% and 85.71% were pathotypes IV and VIII, respectively. The data indicated that variation in pathotype composition over different locations was obvious and locally specific resistant varieties to the disease are needed in the management of this important bacterial disease in rice.

水稲白葉枯病圃場抵抗性に関する研究 : 第 1 報圃場抵抗性の判定方法

水稲白葉枯病圃場抵抗性に関する研究 : 第 1 報圃場抵抗性の判定方法

Plant Growth Promotion and Suppression of Bacterial Leaf Blight in Rice by Inoculated Bacteria

The present study was conducted to evaluate the potential of rice rhizosphere associated antagonistic bacteria for growth promotion and disease suppression of bacterial leaf blight (BLB). A total of 811 rhizospheric bacteria were isolated and screened against 3 prevalent strains of BLB pathogen Xanthomonas oryzae pv. oryzae (Xoo) of which five antagonistic bacteria, i.e., Pseudomonas spp. E227, E233, Rh323, Serratia sp. Rh269 and Bacillus sp. Rh219 showed antagonistic potential (zone of inhibition 1–19 mm). Production of siderophores was found to be the common biocontrol determinant and all the strains solubilized inorganic phosphate (82–116 μg mL-1) and produced indole acetic acid (0.48–1.85 mg L-1) in vitro. All antagonistic bacteria were non-pathogenic to rice, and their co-inoculation significantly improved plant health in terms of reduced diseased leaf area (80%), improved shoot length (31%), root length (41%) and plant dry weight (60%) as compared to infected control plants. Furthermore, under pathogen pressure, bacterial inoculation resulted in increased activity of defense related enzymes including phenylalanine ammonia-lyase and polyphenol oxidase, along with 86% increase in peroxidase and 53% increase in catalase enzyme activities in plants inoculated with Pseudomonas sp. Rh323 as well as co-inoculated plants. Bacterial strains showed good colonization potential in the rice rhizosphere up to 21 days after seed inoculation. Application of bacterial consortia in the field resulted in an increase of 31% in grain yield and 10% in straw yield over non-inoculated plots. Although, yield increase was statistically non-significant but was accomplished with overall saving of 20% chemical fertilizers. The study showed that Pseudomonas sp. Rh323 can be used to develop dual-purpose inoculum which can serve not only to suppress BLB but also to promote plant growth in rice.

A Xanthomonas oryzae pv. oryzae effector, XopR, associates with receptor-like cytoplasmic kinases and suppresses PAMP-triggered stomatal closure.

Receptor-like kinases (RLKs) play important roles in plant immunity signaling; thus, many are hijacked by pathogen effectors to promote successful pathogenesis. Xanthomonas oryzae pv. oryzae (Xoo) is the causal agent of rice leaf blight disease. The strain PXO99A has 18 non-TAL (transcription activation-like) effectors; however, their mechanisms of action and host target proteins remain largely unknown. Although the effector XopR from the Xoo strain MAFF311018 was shown to suppress PAMP-triggered immune responses in Arabidopsis, its target has not yet been identified. Here, we show that PXO99A XopR interacts with BIK1 at the plasma membrane. BIK1 is a receptor-like cytoplasmic kinase (RLCK) belonging to the RLK family of proteins and mediates PAMP-triggered stomatal immunity. In turn, BIK1 phosphorylates XopR. Furthermore, XopR suppresses PAMP-triggered stomatal closure in transgenic Arabidopsis expressing XopR. In addition, XopR is able to associate with RLCKs other than BIK1. These results suggest that XopR likely suppresses plant immunity by targeting BIK1 and other RLCKs.

First Report of a New and Highly Virulent Race of Xanthomonas oryzae pv. oryzae, the Causal Agent of Bacterial Leaf Blight of Rice in Guangxi Province, China

HomePlant DiseaseVol. 100, No. 7First Report of a New and Highly Virulent Race of Xanthomonas oryzae pv. oryzae, the Causal Agent of Bacterial Leaf Blight of Rice in Guangxi Province, China PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of a New and Highly Virulent Race of Xanthomonas oryzae pv. oryzae, the Causal Agent of Bacterial Leaf Blight of Rice in Guangxi Province, ChinaX. L. Chen, Q. Yan, R. F. Li, K. H. Li, and L. J. GaoX. L. ChenSearch for more papers by this author, Q. YanSearch for more papers by this author, R. F. LiSearch for more papers by this author, K. H. LiSearch for more papers by this author, and L. J. GaoSearch for more papers by this authorAffiliationsAuthors and Affiliations X. L. Chen Q. Yan R. F. Li K. H. Li L. J. Gao , Institute of Plant Protection, Guangxi Academy of Agricultural Sciences, Guangxi Key Laboratory of Biology for Crop Diseases and Insect Pests, Nanning, Guangxi, 530007, China. Published Online:13 Apr 2016https://doi.org/10.1094/PDIS-12-15-1400-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat Bacterial leaf blight (BLB), caused by Xanthomonas oryzae pv. oryzae, is one of the most widely distributed and devastating diseases of rice (Oryza sativa) in Asia. BLB can cause yield losses ranging from 20 to 30% and as high as 50% (Mew 1987). Typical BLB symptoms, including tannish gray or white lesions along the veins, were observed in the rice fields in Guangxi, China, in October 2013. Fifteen rice leaves with such symptoms were collected from the infected rice fields. These leaves were cut into approximately 1-cm pieces and homogenized in 9 ml of sterile water by grinding after 1% sodium hypochlorite solution treatment. Diluted homogenates were plated on peptone sucrose agar (PSA) and incubated at 28°C for 3 to 4 days. The nonflat, mucous colonies with yellow, round and smooth margins that developed on the plates were selected for further analysis (Dye et al. 1980). A multiplex polymerase chain reaction assay was performed to distinguish X. oryzae pv. oryzae from other X. oryzae pathovars using genomic DNA of the isolates as template with the primers and cycling conditions as described previously (Lang et al. 2010). Three of the isolates were used to conduct pathogenicity assays on differential rice varieties IR26, Java 14, Nanjing 15, Tetep, and Jingang 30 (Fang et al. 1990). The seeds were sown in plastic trays (50 × 40 × 15 cm) in the greenhouse under a 12-h photocycle at 25 to 28°C, and 30-day-old seedlings were transplanted with row spacing of 25 × 20 cm. Plants were clip-inoculated with a bacterial suspension of 3 × 108 CFU/ml at the booting stage and maintained at 100% humidity for 24 h. Thirty leaves were inoculated with each isolate or with sterilized water (as control). Disease severity was scored 20 days after inoculation by visual assessment of the percentage of the leaf area covered by lesions. Leaves with lesion area <25% and >25% were classified as resistant (R), and susceptible (S), respectively (Fang et al. 1990). The result showed that all the isolates were highly virulent on all the tested rice lines, but no symptoms were observed on water-treated leaves. Colonies recovered on PSA plate from inoculated leaves were identical to field isolates and confirmed by morphology together with PCR, which fulfilled Koch’s postulates. Furthermore, pathogenicity assays using these isolates were performed on several near-isogenic lines (NILs), including IRBB4 (Xa4), IRBB5 (xa5), IRBB7 (Xa7), IRBB13 (xa13), IRBB14 (Xa14), IRBB21 (Xa21), and CBB23 (Xa23). Consequently, all the isolates displayed SRRSRSS on the NILs in contrast to SSSSSRR for the Philippine strain PXO99A. The assays were repeated three times with similar results. Previous studies revealed that CBB23 derived from a cross between a wild rice Oryza rifipogon accession (RBB16) and a susceptible indica rice variety Jingang 30 conferred high resistance to all naturally occurring X. oryzae pv. oryae races tested (Wang et al. 2014). Nevertheless, our research proved that our isolates were highly virulent on many rice lines, including CBB23. To our knowledge, this is the first report of a new and highly virulent race of X. oryzae pv. oryae causing BLB of rice in Guangxi province, China, where it could potentially be destructive under conducive conditions.