Oryzae Pathotype Research Articles

The ACE1 secondary metabolite gene cluster is a pathogenicity factor of wheat blast fungus

Wheat blast caused by Pyricularia oryzae pathotype Triticum is now becoming a very serious threat to global food security. Here, we report an essential pathogenicity factor of the wheat blast fungus that is recognized and may be targeted by a rice resistance gene. Map-based cloning of Pwt2 showed that its functional allele is the ACE1 secondary metabolite gene cluster of the wheat blast fungus required for its efficient penetration of wheat cell walls. ACE1 is required for the strong aggressiveness of Triticum, Eleusine, and Lolium pathotypes on their respective hosts, but not for that of Oryza and Setaria pathotypes on rice and foxtail millet, respectively. All ACE1 alleles found in wheat blast population are recognized by a rice resistance gene, Pi33, when introduced into rice blast isolates. ACE1 mutations for evading the recognition by Pi33 do not affect the aggressiveness of the rice blast fungus on rice but inevitably impair the aggressiveness of the wheat blast fungus on wheat. These results suggest that a blast resistance gene already defeated in rice may be revived as a durable resistance gene in wheat by targeting an Achilles heel of the wheat blast fungus.

Evolution of wheat blast resistance gene Rmg8 accompanied by differentiation of variants recognizing the powdery mildew fungus.

Wheat blast, a devastating disease having spread recently from South America to Asia and Africa, is caused by Pyricularia oryzae (synonym of Magnaporthe oryzae) pathotype Triticum, which first emerged in Brazil in 1985. Rmg8 and Rmg7, genes for resistance to wheat blast found in common wheat and tetraploid wheat, respectively, recognize the same avirulence gene, AVR-Rmg8. Here we show that an ancestral resistance gene, which had obtained an ability to recognize AVR-Rmg8 before the differentiation of Triticum and Aegilops, has expanded its target pathogens. Molecular cloning revealed that Rmg7 was an allele of Pm4, a gene for resistance to wheat powdery mildew on 2AL, whereas Rmg8 was its homoeologue on 2BL ineffective against wheat powdery mildew. Rmg8 variants with the ability to recognize AVR-Rmg8 were distributed not only in Triticum spp. but also in Aegilops speltoides, Aegilops umbellulata and Aegilops comosa. This result suggests that the origin of resistance gene(s) recognizing AVR-Rmg8 dates back to the time before differentiation of A, B, S, U and M genomes, that is, ~5 Myr before the emergence of its current target, the wheat blast fungus. Phylogenetic analyses suggested that, in the evolutionary process thereafter, some of their variants gained the ability to recognize the wheat powdery mildew fungus and evolved into genes controlling dual resistance to wheat powdery mildew and wheat blast.

Integrative genomic and transcriptomic analysis of Xanthomonas oryzae pv. oryzae pathotype IV, V, and IX in China reveals rice defense-responsive genes

Bacterial blight of rice is a devastating disease caused by the gram-negative bacteria Xanthomonas oryzae pv. oryzae (Xoo). Chinese Xoo strain pathotypes IV, V, and IX are the major virulent Xoo strain types in South China sequentially from the 1990s to the present. Here, we report the isolation of GD0201 and GD0202, which belong to pathotypes IV and IX, respectively, and the complete genome sequence and transcriptomic analysis of GD0201 (IV), GD1358 (V), and GD0202 (IX). We found that resistance genes xa5, Xa23, and Xa27 confer strong resistance to all three Xoo strains, indicating that they are currently good choices for resistance rice breeding. The genome analysis reveals fewer TAL and non-TAL effector coding genes in GD0202 than in the other two strains, potentially contributing to its strong virulence. Transcriptomic analysis of ZH11 inoculated with the three Xoo strains strongly suggests that three Xoo strains for better infection repress the ethylene response factor (ERF) gene family members. Furthermore, weighted gene co-expression network analysis (WGCNA) and protein-protein interaction (PPI) analysis revealed 14 hub genes potentially associated with rice response to the three Xoo strains. The expression of several hub genes was validated to be induced by all three Xoo strains, suggesting its role in bacterial blight disease response to Xoo strains. Genomic analysis of the Xoo strains belonging to pathotypes IV, V, and IX, identification of effectors and genes related to Xoo virulence in rice plants will provide insights into understanding the molecular mechanism underlying rice-Xoo interaction and the gene expression pattern in response to Xoo infection.

A Relationship Prediction Method for Magnaporthe oryzae-Rice Multi-Omics Data Based on WGCNA and Graph Autoencoder.

Magnaporthe oryzae Oryzae (MoO) pathotype is a devastating fungal pathogen of rice; however, its pathogenic mechanism remains poorly understood. The current research is primarily focused on single-omics data, which is insufficient to capture the complex cross-kingdom regulatory interactions between MoO and rice. To address this limitation, we proposed a novel method called Weighted Gene Autoencoder Multi-Omics Relationship Prediction (WGAEMRP), which combines weighted gene co-expression network analysis (WGCNA) and graph autoencoder to predict the relationship between MoO-rice multi-omics data. We applied WGAEMRP to construct a MoO-rice multi-omics heterogeneous interaction network, which identified 18 MoO small RNAs (sRNAs), 17 rice genes, 26 rice mRNAs, and 28 rice proteins among the key biomolecules. Most of the mined functional modules and enriched pathways were related to gene expression, protein composition, transportation, and metabolic processes, reflecting the infection mechanism of MoO. Compared to previous studies, WGAEMRP significantly improves the efficiency and accuracy of multi-omics data integration and analysis. This approach lays out a solid data foundation for studying the biological process of MoO infecting rice, refining the regulatory network of pathogenic markers, and providing new insights for developing disease-resistant rice varieties.

In-silico study of protein-protein interactions in wheat blast using docking and molecular dynamics simulation approach

Despite advancements in agricultural research and the introduction of modern biotechnological and farming techniques, food security remains a significant issue. Although the efforts of farmers to meet the demands of a growing population, many plant diseases caused by pathogens, through their effects on cell division and tissue growth, lead to the annual loss of countless food crops. The recently emerged wheat blast fungus Magnaporthe oryzae pathotype Triticum (MoT) poses a significant danger to worldwide wheat cultivation. The fungus is a highly varied lineage of the M. oryzae, responsible for causing rice blast disease. In spite of being a significant challenge to successful wheat production in South America since 1985, the underlying biology of the wheat blast pathogen is still not fully understood. The initial outbreak of the wheat blast in South Asia had a severe impact on wheat production, resulting in a complete loss of yield in affected fields. For the purpose of enhancing disease management, it’s vital to acquire a comprehensive comprehension of the infection biology of the fungus and its interaction with wheat plants on molecular levels. Host-pathogen protein interactions (HPIs) have the potential to reveal the pathogens’ mechanism for overcoming the host organism. The current study delves into the interactions between the host plant wheat and MoT through protein-protein interactions, molecular docking, and 100 ns molecular dynamic simulations. This research uncovers the structural and functional basis of these proteins, leading to improved plant health and production. Communicated by Ramaswamy H. Sarma

<i>In Vitro</i> Evaluation of Antibacterial Properties of Biogenically Synthesized Zinc Oxide Nanoparticles on Pathogenic Paddy Bacteria

Zinc oxide nanoparticles (ZnO-NP) were successfully synthesized from aloe vera extract and zinc sulphate as zinc precursor. Characterizations of the ZnO-NP were performed using UV–Vis spectrophotometer, XRD, FESEM and TEM analysis. The absorption peak from UV–Vis was at 380 nm while the XRD diagram displays high purity ZnO-NP. FESEM and TEM analysis showed agglomerated particles with a wide size distribution range. Polymerase chain reaction (PCR) analysis of Xanthomonas oryzae pv. oryzae (Xoo) pathotype 0.0 generated a product with the size of 230 bp similar to in silico PCR results, verifying the pathotype on molecular level. Subsequently, the antimicrobial activities of the ZnO-NP against Xoo pathotype 0.0 were assessed. Xoo (108 cfu/ml) were grown in LB broth supplemented with various concentrations of ZnO-NP. Collection of samples were done at 24 hours, 48 hours and 72 hours of incubation, grown on LB agar and observed for bacterial growth. Colony forming unit (cfu/ml) values revealed the number of viable cells decreased with high concentrations of ZnO-NP whereas minimal inhibition was observed at lower ZnO-NP concentrations. At lower bacteria cfu/ml (103 cfu/ml), it was found that at 24 hours incubation, ZnO-NP gave comparable antibacterial effects to commercial ZnO-NP and commercial non-nanoZnO after exposure for 1 hour. However, the antimicrobial effects decreased after 48 hours. It was also noted that the ZnO-NP provide better suppression of bacterial growth at lower bacterial concentration.

Ocorrência de Pyricularia oryzae Triticum em plantas do gênero Urochloa no Brasil

ABSTRACT: In this study Pyricularia spp., P. oryzae and the P. oryzae pathotype Triticum (PoT) were detected and identified in leaf segments of forage and invasive grasses located in or next to wheat fields. In 2018 and 2019, 66 samples of lesion leaf segments of Urochloa and other grasses were collected in Londrina (PR), Patos de Minas (MG), and Uberaba (MG). The detection and/or identification of the pathogens on the samples was conducted using moist chamber procedures and with the primers MoT3 and Pot2 by PCR. There were DNA amplification with the primer MoT3 (specific for PoT) for 13 (19.69%) of the samples, all of them from Urochloa. The finding that Urochloa hosts PoT at a relatively high rate raises concerns about the importance which these plants may have on the wheat blast cycle as an alternative host for the pathogen and/or source of inoculum for the disease.

Oryzae pathotype of Magnaporthe oryzae can cause typical blast disease symptoms on both leaves and spikes of wheat under a growth room condition

Blast diseases of rice and wheat are known to be caused by the specific pathotypes of Magnaporthe oryzae (syn. Pyricularia oryzae), M. oryzae Oryzae (MoO) and M. oryzae Triticum (MoT), respectively. Rice blast disease has been seen in Bangladesh from a very ancient time. However, Bangladesh’s first epidemic outbreak of wheat blast was recorded in 2016. This study aimed to investigate the cross-infection reactions of MoO and MoT in rice and wheat in a growth room condition. Artificial inoculation was done at vegetative and reproductive phases of both wheat and rice plants in a completely randomized design using virulent isolates of MoO and MoT. Artificial inoculation with MoO resulted in foliar symptoms with typical eye-shaped lesions as well as partially bleached or completely white head symptoms in both wheat and rice plants. On the other hand, MoT produced blast symptoms only on the leaves and spikes of wheat. Molecular analyses using PCR amplification (with Pot2, MoT3 and MoT6099 primers) and a recently developed rapid detection PCRD strip confirmed the presence of MoT and MoO pathotypes in the symptomatic plant samples. Our results demonstrated that MoO pathotype can infect the leaves and spikes of wheat but MoT is unable to infect rice plants under the same controlled environment in Bangladesh. This study has revealed the vulnerability of wheat to MoO pathotype and an urgent need to understand the molecular mechanism underlying host-specificity of the blast fungus M. oryzae. Our results also provided evidence for a potential wheat blast epidemic by MoO in many rice–wheat inter-cropping regions as climate change intensifies. A comprehensive study is needed to have a better understanding on the variability in virulence of MoO and MoT isolates in infecting wheat and rice under controlled environment by the inclusion of a large number of isolates and crop varieties/genotypes.

Avirulence gene based RFLP and rep-PCR distinguish the genetic variation of Xanthomonas oryzae pv. oryzae pathotypes in Bangladesh

Bacterial blight (BB) caused by X. oryzae pv. oryzae is one of the devastating diseases of rice mostly in Asia. Genomes of X. oryzae pv. oryzae is highly variable due to rearrangement of the large contents of transposable elements and dynamic changes of X. oryzae pv. oryzae population regulated efficiency of the control measures used for BB management of rice worldwide. In this study, genetic variation of X. oryzae pv. oryzae pathotypes of Bangladesh was studied using aviruelnce gene based RFLP and rep-PCR techniques aimed to formulate pathogen targeted effective control measures against BB of rice. Eight pathotypes of X. oryzae pv. oryzae field isolates were identified based on their reactions against 10 Near Isogenic Lines (NILs). Among eight pathotypes, pathotypes IV and V contained higher number of isolates which were 30.13% and 23.01% respectively while pathotype VIII revealed as minimum containing only 2.51% of total isolates. These eight pathotypes were studied for their genetic variation by RFLP using avrBs3 repeat domain as probe. The results conceded that Bangladeshi X. oryzae pv. oryzae strains seem carrying a minimum of two and maximum of nine avrBs3 family genes homologs. The resistance phenotype on IRBB7 and IRBB10 NILs also indicated presence of two major avrBs3 family genes viz. avrxa7 and avrXa10 in some pathotypes. Relationship of phylogenicity exhibited that X. oryzae pv. oryzae pathotypes assorted into two RFLP haplotypes as well as these haplotypes are largely distributed in Bangladesh. Phylogenetic analyses carried out by (REP, ERIC), rep-PCR and BOX depicted the presence of two main molecular haplotypes of X. oryzae pv. oryzae pathotypes. The relationship between pathotypes and molecular haplotypes of X. oryzae pv. oryzae in Bangladesh indicated that the same lineage possesses different pathotypes and different lineage possesses different pathotypes. The results indicated that eight different pathotypes might have originated from common inherited haplotypes with a wide genetic variation.

Assessment of potentiality of known bacterial blight resistant genes against Xanthomonas oryzae pv. oryzae pathotypes exist in Bangladesh

Bacterial blight (BB) caused by X. oryzae pv. oryzae is a destructive disease of rice and causes 30-50% losses to rice depending on the outbreak. Development BB resistant rice varieties have long been considered as one of the most effective approach to control the disease. However, the durability of host resistance is breaking down due to the change of pathotypes of X. oryzae pv. oryzae globally. Pathotypic analyses of 239 X. oryzae pv. oryzae Bangladeshi isolates on Near Isogenic Lines (NILs) containing resistance (R) gene (s) revealed the existence of eight pathotypes of X. oryzae pv. oryzae. Among eight pathotypes, pathotypes IV and V were considered as major comprising maximum number of isolates, (30.13% and 23.01%, respectively), whereas pathotype VIII considered as minor consisting only 2.51% of total isolates. Pathotype, I showed highest virulence or aggressiveness compatible with all NILs, whereas pathotype VIII exhibited lowest virulence to these NILs. Bacterial blight resistant genes viz. Xa1 (75.00%), Xa11 (62.50%) and Xa21 (50.00%) showed resistance to most of the pathotypes while Xa4 performed worst as compared to all others R-genes. In pyramid lines, IRBBB63 (Xa5+Xa7+Xa13) and IRBB57 (Xa5+Xa7 +Xa21) showed resistance reaction and IRBB61 (Xa4+Xa5+Xa7), IRBB60 (Xa4+Xa5+Xa13+Xa21), IRBB54 (Xa5+Xa21), and IRBB53 (Xa4+Xa21) showed susceptible reaction to X. oryzae pv. oryzae pathotypes. These results collectively indicated the deployment of Xa1, Xa11, Xa4, Xa5, Xa7, Xa13 and Xa21 either alone or in combination against BB would be a best choice for the development of BB resistant rice varieties in Bangladesh.

Virulence Pattern of Pyricularia oryzae Pathotypes Towards Blast Monogenic Lines

Rice blast caused by Pyricularia oryzae (P. oryzae) is one of the most serious diseases infecting rice worldwide. In the present study, virulence pattern of six P. oryzae pathotypes (P0.0, P0.2, P1.0, P3.0, P7.0 and P9.0) identified from the blast pathogen collected in Peninsular Malaysia, were evaluated using a set of 22 IRRI-bred blast resistance lines (IRBL) as well as to determine the resistance genes involved. The information on the virulence of the blast pathotypes and the resistance genes involved is important for breeding of new rice variety for durable resistance against blast disease. The IRBL was established from 22 monogenic lines, harbouring 22 resistance genes [Pia, Pib, Pii, Pit, Pi3, Pi5(t), Pish, Pi1, Pik, Pik-s, Pik-m, Pik-h, Pik-p, Pi7(t), Pi9, Piz, Piz-5, Piz-t, Pi19, Pi20(t), Pita-2, and Pita=Pi4(t)]. Based on the disease severity patterns, the tested pathotypes were avirulence towards seven IRBLs [IRBLi-F5, IRBLk-Ka, IRBLkh-K3, IRBLz-Fu, IRBLsh-S, IRBLPi7 (t) and IRBL9-W] of which these IRBLs harbouring Pii, Pik, Pik-h, Piz, Pish, Pi7(t) and Pi9 resistance genes, respectively. Therefore, the results suggested that the seven IRBLs carrying seven resistance genes [Pii, Pik, Pik-h, Piz, Pish, Pi7(t) and Pi9] would be suitable candidates of resistance genes to be incorporated in new breeding lines to combat the current blast pathotypes in the field.

The Risk of Wheat Blast in Rice-Wheat Co-Planting Regions in China: MoO Strains of Pyricularia oryzae Cause Typical Symptom and Host Reaction on Both Wheat Leaves and Spikes.

The Triticum pathotype of Magnaporthe oryzae (syn. Pyricularia oryzae) causes wheat blast, which has recently spread to Asia. To assess the potential risk of wheat blast in rice-wheat growing regions, we investigated the pathogenicity of 14 isolates of P. oryzae on 32 wheat cultivars, among which Oryzae pathotype of P. oryzae (MoO) isolates were completely avirulent on the wheat cultivars at 22°C but caused various degrees of infection 25°C. These reactions at 25°C were isolate and cultivar dependent, like race-cultivar specificity, which was also recognized at the heading stage and caused typical blast symptoms on spikes. Microscopic analyses indicated that a compatible MoO isolate produced appressoria and infection hyphae on wheat as on rice. When we compared transcriptomes in wheat-MoO interactions, the bulk of pathogen-related genes were upregulated or downregulated in compatible and incompatible patterns, but changes in gene transcription were more significant in a compatible pattern. These results indicate that temperature could influence the infection ratio of wheat with MoO, and some MoO strains could be potential pathogens that increase the risk of wheat blast outbreaks in wheat-rice growing regions with global warming. In addition, certain wheat cultivars exhibited resistance and are assumed to carry resistance-promoting genes to the MoO strains.

Identification of quantitative trait loci associated with resistance to Xanthomonas oryzae pv. oryzae pathotypes prevalent in South China

Bacterial blight (BB), which is caused by Xanthomonas oryzae pv. oryzae (Xoo), is an important rice disease responsible for significant yield losses. In the rice-growing regions of South China where BB outbreaks are common, the resistance of cultivars with BB resistance genes Xa4 and Xa21 has been lost because of rapid changes in the Xoo population structure and virulence. In this study, 421 diverse rice accessions were evaluated regarding their resistance to two Xoo strains, namely GD1358 (C5) and IV, which are prevalent pathotypes in South China and overcame the resistance of Xa4 and Xa21, respectively. Using the 4.8mio filtered SNP dataset, we conducted a genome-wide association study, which identified 13 loci associated with BB resistance, including eight new quantitative trait loci (QTL) and five QTL harboring known BB resistance genes: Xa3/Xa26, xa5, Xa35(t), Xa36(t), Xa40, Xa43(t), and xa44(t). Intriguingly, a steep peak was detected on chromosomes 5 and 11. Six QTL including three new ones, were distributed on chromosome 11, whereas a new QTL qBB5.1 and a known QTL were detected on chromosome 5. Haplotype analyses indicated that the LOC_Os05g01610 (OsPRAF2) gene within the qBB5.1 region, which encodes a PRAF protein, is associated with BB resistance. Furthermore, OsPRAF2 knockout lines generated using the CRISPR-Cpf1 system were significantly more resistant to Xoo strains than the wild-type plants. Our results provide researchers and breeders with useful information regarding QTL and gene resources, which may be relevant for developing new BB-resistant rice cultivars.

First report of blast of durum wheat in Bangladesh, caused by Magnaporthe oryzae pathotype Triticum

Durum wheat (Triticum turgidum var. durum Desf.) is an important cereal crop in many regions of the world. In March of 2018 and 2019, symptoms typical of blast were frequently observed on durum wheat plants under field conditions in Jashore, Bangladesh. The putative causal pathogen was isolated from infected wheat spike specimens onto potato dextrose agar and oatmeal agar, and was identified from mono-conidium cultures as Magnaporthe oryzae, based on morphological features. The pathotype of the fungus was identified as Triticum, based on comparative molecular analyses of ITS sequences and MoT3 specific markers. BLAST analysis revealed >99.8% similarity with M. oryzae/P. oryzae, retrieved from the NCBI Genebank. This was confirmed through amplification of the predicted products with MoT3 primers in PCR analysis. Pathogenicity was confirmed by inoculating healthy durum wheat seedling leaves and spikes with a conidium suspensions of M. oryzae isolate DuBWMRI1901.2A. The fungus produced similar symptoms on inoculated leaves and spikes as those observed in the field, and was subsequently re-isolated, fulfilling Koch’s postulates. This is the first report of blast of durum wheat caused by Magnaporthe oryzae pathotype Triticum in Bangladesh.

Rapid Detection of Wheat Blast Pathogen Magnaporthe oryzae Triticum Pathotype Using Genome-Specific Primers and Cas12a-mediated Technology

Wheat blast, caused by the fungus Magnaporthe oryzae Triticum (MoT) pathotype, is a devastating disease persistent in South America and Bangladesh. Since MoT generally fails to cause visual symptoms in wheat until the heading stage when the infection would have advanced, disease control by fungicide application solely based on the detection of visual symptoms is ineffective. To develop an accurate and sensitive method to detect MoT at the seedling and vegetative stages for disease control, we sequenced the genomes of two MoT isolates from Brazil and identified two DNA fragments, MoT-6098 and MoT-6099, that are present in the MoT genome but not in the genome of the rice-infecting Magnaporthe oryzae Oryzae (MoO) pathotype. Using polymerase chain reaction (PCR), we confirmed the specificity of the two markers in 53 MoT and MoO isolates from South America and Bangladesh. To test the efficiency of the two markers, we first established a loop-mediated isothermal amplification (LAMP) method to detect MoT at isothermal conditions, without the use of a PCR machine. Following this, we used the Cas12a protein and guide RNAs (gRNAs) to target the MoT-6098 and MoT-6099 sequences. The activated Cas12a showed indiscriminate single-stranded deoxyribonuclease (ssDNase) activity. We then combined target-dependent Cas12a ssDNase activation with recombinase polymerase amplification (RPA) and nucleic acid lateral flow immunoassay (NALFIA) to develop a method that accurately, sensitively, and cost-effectively detects MoT-specific DNA sequences in infected wheat plants. This novel technique can be easily adapted for the rapid detection of wheat blast and other important plant diseases in the field.

Genetic analysis for bacterial blight resistance in indica rice (Oryza sativa L.) cultivars

Prior information on genetics of bacterial blight (BB) resistance (R) genes is imperative for its successful utilization in trait development and breeding for new resistant varietiesin rice. This experiment was aimed to assess the genetics of BB resistance in susceptible but popular rice variety HUR-917 and IRBB 66 (isogenic lines of IR 24) which harbors five R genes. Bioassay results in the parental lines and crosses were revealed resistance and susceptible disease response in R gene(s) positive and negative lines, respectively with varying range of Xoo (Xanthomonas oryzae pv oryzae) pathotype specificity. Phenomics of F2 and Back Cross (BC) generations showed existence of non-allelic interaction (13:3) between R genes with substantial variability in disease severity. The plants carrying mono hetero-allelic R gene has exsertedModerately susceptible (MS) disease reaction with 6.42 to 8.86 disease severities, however, lines carrying 2 R gene(s) could be able to disease severity Moderate susceptible MS to Moderate Resistant MR against all pathotypes existing in the region make it valid that the doses complementarity and presence of interaction in R genes are major determinant in R expression. It was recorded that presence of two or more R genes (Xa21+xa13; Xa21+ xa13+xa5) exerted broad spectrum BB resistance, hence found more suitable to combat this disease in HUR-917.

Screening wheat genotypes for resistance to wheat blast disease in the vegetative and reproductive stages

The wheat blast disease has been considered one of the main biotic stress threats to food security in the world. The study aimed to evaluate the resistance of wheat cultivars to Pyricularia oryzae pathotype triticum isolates at the vegetative and reproductive stage and to perform screening of wheat lines. Experiments were carried out on plants at the vegetative and reproductive stage, with artificial inoculation of P. oryzae pathotype triticum isolates origin from different producing regions. Resistant cultivars at both stages have shown potential to be used as source of resistance in wheat breeding programs; there was no difference in aggressiveness among the P. oryzae pathotype triticum isolates tested. It was possible to identify wheat lines with resistance to the disease at the vegetative stage. Nine wheat lines selected as resistant to wheat blast disease may be incorporated at block-crosses in order to pyramidize genes of resistance to wheat blast in the breeding of new wheat cultivars.

A Strain of an Emerging Indian Xanthomonas oryzae pv. oryzae Pathotype Defeats the Rice Bacterial Blight Resistance Gene xa13 Without Inducing a Clade III SWEET Gene and Is Nearly Identical to a Recent Thai Isolate.

The rice bacterial blight pathogen Xanthomonas oryzae pv. oryzae (Xoo) injects transcription activator-like effectors (TALEs) that bind and activate host “susceptibility” (S) genes important for disease. Clade III SWEET genes are major S genes for bacterial blight. The resistance genes xa5, which reduces TALE activity generally, and xa13, a SWEET11 allele not recognized by the cognate TALE, have been effectively deployed. However, strains that defeat both resistance genes individually were recently reported in India and Thailand. To gain insight into the mechanism(s), we completely sequenced the genome of one such strain from each country and examined the encoded TALEs. Strikingly, the two strains are clones, sharing nearly identical TALE repertoires, including a TALE known to activate SWEET11 strongly enough to be effective even when diminished by xa5. We next investigated SWEET gene induction by the Indian strain. The Indian strain induced no clade III SWEET in plants harboring xa13, indicating a pathogen adaptation that relieves dependence on these genes for susceptibility. The findings open a door to mechanistic understanding of the role SWEET genes play in susceptibility and illustrate the importance of complete genome sequence-based monitoring of Xoo populations in developing varieties with effective disease resistance.

Screening of resistant Indonesian black rice cultivars against bacterial leaf blight

Black rice production in Indonesia constrained by the bacterial blight disease (BLB) caused by Xanthomonas oryzae pv. oryzae pathotype IV (Xoo). Breeding of BLB resistant cultivars is considered the most sustainable method for BLB disease control, both from an environmental and agricultural perspective. Indonesia has many local black rice varieties that can be used as genes resource to support breeding program producing resistant cultivars. The present research focuses on screening local Indonesian black rice cultivars for resistance against BLB and analyzing the expression of these resistance genes in black rice after inoculation with Xoo. The black rice cultivars Cempo Ireng, Pari Ireng, Melik, Pendek, and Indmira, were inoculated with Xoo while white rice cv. Conde, IRBB21, IR64, and Java14 were used as controls. We assayed the phenotypic performance of the cultivars samples after Xoo inoculation and analyzed their resistance gene expression at 24 and 96 h after Xoo inoculation semiquantitatively. The cultivar showed the best performance was selected for further analysis of the resistance genes using Real-time quantitative PCR. Cempo Ireng was indicated the most resistant cultivar against BLB disease based on the lowest disease intensity and Area Under Disease Progress Curve (AUDPC) value. Cempo Ireng expressed resistant genes xa5, Xa10, Xa21 and RPP13-like after inoculation of Xoo. The expression of xa5, Xa10, and Xa21 was up-regulated while that of RPP13-like was down-regulated in Cempo Ireng.

Asam Salisilat sebagai Penginduksi Ketahanan Tanaman Padi terhadap Penyakit Hawar Daun Bakteri

The use of salicylic acid as resistance inducers agents in several plants species was well known. Salicylic acid has been believed to play an important role in inducing resistance against some pathogen. This research was aimed to study the role and effectiveness of salicylic acid as inducers for the resistance of some rice variety against bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae. The experiment was arranged in completely randomized factorial design with three factors i.e. rice variety, salicylic acid, and pathotypes, each treatment was replicated three times. The results showed that salicylic acid could prolong the latent period of X. oryzae pv. oryzae pathotypes IV and VIII in paddy rice varieties Conde and Ciherang, induce the resistance of rice varieties as well as reducing the rate of infection of the two mentioned pathotypes. Salicylic acid was also able to induce the resistance of Conde and Ciherang varieties in order to suppress area under disease progress curve (AUDPC) of X. oryzae pv. oryzae pathotypes IV and VIII.