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1.
Rice blast is the most serious disease threat to rice production worldwide. It is difficult to control due to the complex diversity and wide geographic distribution of the causal pathogen Magnaporthe oryzae. In Australia, rice blast occurs in northern Australia but remains exotic to the main south-eastern rice growing area; however, there is the potential for rice blast to threaten this area; in addition, rice production is currently expanding from south-eastern Australia into northern Australia, which makes rice blast a major concern and challenge to rice industry in Australia. Prior to this study, there was lack of information on the race status of M. oryzae present in Australia and on how to manage the disease through host resistance. The races of rice blast isolates collected in northern Australia was characterised based on the disease reactions of eight standard rice differentials used in an international race differential system. The following studies revealed genes conferring resistance to these races through investigating the responses of 25 monogenic rice lines with targeted resistance gene against different races. The rice blast isolates were characterised into five races: IA-1, IA-3, IA-63, IB-3 and IB-59. Genes Pi40, Piz-t, Pi9, Pi5(t) and Pi12(t) exhibited resistance to all the isolates belonging to five races. In addition, two genes showed complete resistance to multiple races, viz. Pi9 that showed complete resistance to races IA-1, IA-3, IA-63 and IB-3 and Pita2 that had complete resistance to races IA-3, IB-3 and IB-59. This study provides information about the races of M. oryzae in Australia. Genes identified conferring resistance to multiple races will not only streamline the identification via molecular markers of imported rice varieties with resistance to rice blast in Australia, but will also allow the Australian rice breeding program to develop new varieties with broad-spectrum resistance to rice blast and pyramid multi-gene resistance into Australian rice varieties.  相似文献   

2.
Rice blast is a devastating fungal disease resulting in major losses to rice crops. Owing to continuous acquisition of resistance by the causal fungus, several fungicide chemicals are no longer effective. Therefore, there is a need to identify natural components and develop new agents to control fungal pathogens. We previously demonstrated that the culture filtrate of Biscogniauxia sp. O821 inhibited infection behavior of Magnaporthe oryzae and subsequent blast lesion formation. In the present study, we isolated a new compound, (3aS,4aR,8aS,9aR)-3a-hydroxy-8a-methyl-3,5-dimethylenedecahydronaphto[2,3-b]furan-2(3H)-one (HDFO), from the culture filtrate of Biscogniauxia sp. O821 and determined its molecular weight as 248. The HDFO structure was determined by electrospray ionization-mass spectrometry and nuclear magnetic resonance spectroscopy after purification with column chromatography and high-performance liquid chromatography. The structure of this antifungal compound was similar to that of alantolactone and isoalantolactone. The growth inhibition zone against M. oryzae in presence of HDFO was observed at Rf 0.5–0.6 on a thin layer chromatography plate. HDFO inhibited conidial germination of M. oryzae in a dose-dependent manner (1–200 ppm). Furthermore, blast lesion formation was significantly suppressed by HDFO at over 5 ppm. These results suggest that HDFO from the culture filtrate of Biscogniauxia sp. O821 can protect rice from rice blast disease caused by M. oryzae. This is the first report that HDFO produced by Biscogniauxia sp. can serve as an antifungal compound against M. oryzae.  相似文献   

3.
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.  相似文献   

4.
Pyricularia oryzae (rice blast) conidial development at pre-penetration stage determines success or otherwise of infection inside the rice host plants. Studies on conidial germination and growth on the leaf surface in commercial rice (Oryza sativa) report differently, dependent upon host type and level of blast resistance. Although wild rice (O. australiensis) is known to be an alternative host of blast, the interaction between P. oryzae conidia and wild O. australiensis on its leaf surface has not been previously studied. We found significant (P?<?0.001) differences in conidial development between two blast isolates with different virulence in terms of conidial germination, germ tube growth and appressoria formation on both wild and cultivated rice. Conidial germination at 6 h post-inoculation (hpi) for the virulent isolate was significantly (P?<?0.001) delayed. Germ tubes of the avirulent isolate conidia grew significantly (P?<?0.001) faster and with significantly (P?<?0.001) longer germ tubes than from virulent conidia. Appressoria development for the virulent isolate was significantly (P?<?0.001) faster at its later growth stages of 12 and 18 hpi when approximately 100% of germ tubes formed appressoria. In contrast, formation rate of appressoria for the avirulent isolate was significantly (P?<?0.001) slower and only reached 76% of germ tubes forming appressoria. Appressoria formation on O. australiensis was significantly (P?<?0.001) greater than the formation on O. sativa for both virulent and avirulent P. oryzae at 12 hpi, a clear indication that host type influences the extent of appressoria formation.  相似文献   

5.
Rice production is currently expanding from the south-eastern regions of Australia into northern Australia where indigenous species of wild rice occur widely. A survey of fungal diseases on wild (Oryza australiensis, Oryza spp.) and cultivated rice (Oryza sativa) in North Queensland, Australia, in May 2014 revealed a diverse range of fungal genera species, including important pathogens of cultivated rice. Whilst a single isolate of Magnaporthe oryzae (causal agent of rice blast) was obtained from wild rice, Bipolaris oryzae (causal agent of brown spot) was the predominant pathogen detected under North Queensland conditions. For the first time for Australia, we report Rhizoctonia oryzae-sativae (causal agent of aggregate sheath spot) occurring on wild rice. Other pathogens detected on wild rice included Curvularia lunata, Cochliobolus intermedius, Cochliobolus geniculatus, and Fusarium equiseti present in the majority of wild rice samples. Nearby cultivated rice fields harboured additional pathogens not found in wild rice including Fusarium graminearum, Leptosphaeria spegazzinii and Cochliobolus lunatus, causing scab disease, glume blight and leaf blight, respectively. We also confirmed that Bipolaris oryzae from wild rice can infect cultivated rice. This study highlights the importance of wild rice species as alternative hosts harbouring pathogens of cultivated rice and the likely disease threats to expansion of cultivated rice into the same region(s) where wild rice is endemic.  相似文献   

6.
The rice blast fungus Pyricularia oryzae mainly overwinters in infested rice organs stored indoors, whereas it is difficult or impossible for the pathogen to overwinter outdoors. By contrast, blast pathogens infecting weed grasses must overwinter outdoors every winter to continue their life cycle. In this study, we investigated the overwintering location of P. oryzae infecting wild, green, and giant foxtails to identify the mechanism that enables them to overwinter. Recovery of P. oryzae was tested in seeds of wild foxtail collected from the soil surface from December to April over three winters. No P. oryzae was recovered from the seed samples of any wild foxtail collected at the ends of the three experimental periods in April. Recovery was also tested from blast lesions on leaves and seeds sampled from withered green foxtail in the experimental field of Saga University from November to April during two winters. In contrast to seeds on the soil surface, P. oryzae survived in lesions and seeds at the ends of the two experimental periods during April, suggesting that withered host plants could be the overwintering site of the pathogen. Rice plants are reaped and removed from paddy fields after harvesting. Thus, withered, standing plants may be available solely to blast pathogens infecting wild grasses, possibly explaining the higher winter survival frequency of weed pathogens than that of rice blast pathogens outdoors.  相似文献   

7.
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8.
Plant volatile compounds, including terpenes, are known to be involved in the rice defense system. In the present analysis of a terpene synthase, OsTPS18, in rice, we found that OsTPS18 was localized in the cytoplasm and synthesized the sesquiterpenes (E)-nerolidol and (E)-β-farnesene. The amounts of (E)-nerolidol and (E)-β-farnesene increased after jasmonic acid (JA) treatment. (E)-Nerolidol had significant antibacterial activity against Xanthomonas oryzae pv. oryzae (Xoo). These results suggest that (E)-nerolidol plays an important role in JA-induced resistance against Xoo and that it functions as an antibacterial compound in rice.  相似文献   

9.
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.  相似文献   

10.
MicroRNAs (miRNAs) play an important role in plant growth, development and responses to stresses. Rice blast is one of the most devastating diseases in rice production. However, little is known regarding the effects of miRNAs response to rice blast. Herein, by deep sequencing small RNA from the susceptible line ZhongerRuanzhan and its space-induced blast resistant mutant line H4 under normal conditions and upon Magnaporthe oryzae (M. orzyzae) infection, several known miRNAs were detected and their expression profiles were found to be negatively correlated with their targets. And, a total of 50 novel miRNAs induced by M. oryzae infection were also identified from four small RNA libraries. Moreover, 176 putative targets of 23 novel miRNAs, which are involved in the various functions, were validated by two degradome analysis. Six novel miRNAs were selected for further validation with qRT-PCR analysis and the results showed that their expression levels were associated with blast response. The knowledge obtained in this study will help us understanding the functions of miRNAs and their targets in regulating blast resistance.  相似文献   

11.
Fungicides are the preferred rice blast (Pyricularia oryzae) control option by farmers. However, no fungicides are yet registered for this purpose in Australia. Hence, it is important to test the baseline sensitivity of P. oryzae isolates collected from blast-affected regions across northern Australia, which have not yet been exposed to the fungicides, as part of a resistance management strategy. Further, it is also important to investigate and compare effect of application timing of fungicides on conidial development, including germination and germ tube growth, and penetration on susceptible rice. The EC50 of a collection of fungicide-sensitive blast isolates were within the range of 0.02–2.02 and 0.06–1.91 mg L?1 for azoxystrobin and propiconazole, respectively. Azoxystrobin was shown to have greater inhibitory effect on conidial germination than propiconazole. In addition, for pre-inoculation application, only germ tubes in the presence of external nutrients continued to grow from 24 to 48 hpi. On susceptible seedlings, both fungicides completely controlled blast disease when applied the same day as inoculation. However, for pre- or post-inoculation application of fungicide, the extent of disease control was reduced, with azoxystrobin more efficacious than propiconazole. A stimulatory effect of both fungicides at low dose was observed on certain P. oryzae isolates. This is the first study to assess the baseline sensitivity of the P. oryzae population in Australia and the first to report a stimulatory effect of low azoxystrobin concentration on growth of P. oryzae. The study highlights, for the first time, the critical role of external nutrients in promoting germ tube growth under fungicide stress conditions. Lastly, it demonstrates the high degree of efficacy of the fungicides and their potential for future rice blast management in Australia.  相似文献   

12.
An ethyl acetate extract of a culture filtrate (ECF) from an unidentified fungal isolate O821 was evaluated for antifungal activity against the rice pathogen Magnaporthe oryzae. The O821-ECF significantly inhibited spore germination, appressorium formation, and mycelial growth of M. oryzae, and its antifungal activity was heat-stable. It also significantly suppressed the number and size of blast lesions. In an analysis of the ITS sequence of this isolate, it shared similarities with species of the fungus Biscogniauxia. These results suggest that isolate O821 of the genus Biscogniauxia produces a heat-stable antifungal compound(s) in its culture filtrate.  相似文献   

13.
In the present study, the effect of red light on the infection behavior of Bipolaris oryzae on rice leaves and the effects of chemical inhibitors and spore germination fluid (SGF) of B. oryzae on red-light-induced resistance against brown spot disease were investigated. Red light irradiation and natural light did not differ significantly with respect to their effect on spore germination and appressorium formation of B. oryzae 24 h after inoculation. However, formation of infection hyphae was significantly inhibited under red light compared to that under natural light. Pretreatment with the photosynthetic inhibitor 3-(3,4-dichorophenyl)-1,1-dimethylurea (DCMU) or with the aromatic amino acid inhibitor N-(phosphonomethyl) glycine (glyphosate) for 24 h inhibited the development of resistance in rice leaves. To elucidate the elicitor(s) produced during the B. oryzae–rice plant interaction, the effect of SGF prepared in the absence (A-SGF) or presence (P-SGF) of rice leaves on red-light-induced resistance was investigated. When rice plants were pretreated with A-SGF or P-SGF for 24 h, P-SGF had elicitor activity under red light, but not under natural light or with A-SGF. These results suggest that germinating spore of B. oryzae produced an elicitor(s) under red light conditions in a host-dependent manner. In conclusion, we hypothesize that an unidentified elicitor(s) produced at an early stage of fungal infection during the B. oryzae–rice interaction contributes to the inhibition of cell death in rice leaves under red light and enhances resistance-related tryptophan and phenylpropanoid pathways.  相似文献   

14.
Magnaporthe oryzae chrysovirus 1 strain A (MoCV1-A) is associated with an impaired growth phenotype of its host fungus, Magnaporthe oryzae. In this report, we assayed the virulence and pathogenicity of MoCV1-A-infected and MoCV1-A-free M. oryzae on rice plants. MoCV1-A infection did not affect virulence-associated fungal traits, such as conidial germination and appressorium formation. However, after punch inoculation of leaves on rice plants, MoCV1-A-infected strain formed smaller lesions than the MoCV1-A-free strain did on all rice varieties tested, showing that MoCV1-A infection resulted in reduced virulence of host fungi in rice plants. In contrast, after spray inoculation of rice seedlings, in some cases, MoCV1-A-infected and MoCV1-A-free strains caused different lesion types (resistance to susceptible, or vice versa) on individual international differential rice varieties. However, we did not find any gain/loss of the fungal avirulence genes by PCR, suggesting that MoCV1-A infection can convert the pathogenicity of the host M. oryzae from avirulence to virulence, or from virulence to avirulence, depending on the rice variety. We also confirmed the correlation of these race conversion events and invasive hyphae growth of the fungi in a leaf sheath inoculation assay. These data suggested that MoCV1-A infection generally confers hypovirulence to the fungal host and could be a driving force to generate physiological diversity, including pathogenic races.  相似文献   

15.
Fungal leaf blast, caused by Pyricularia oryzae, is a devastating disease of rice plants that annually causes severe production losses worldwide and is one of the top 10 fungal diseases that threaten global food security. Thus, a reliable control strategy against this disease is essential. In this study, the antagonistic activity of indigenous phyllosphere actinomycetes was elucidated against P. oryzae in vitro and in planta to develop an efficient, effective and environmental friendly approach to protect rice plants against P. oryzae. Of 75 isolates of actinomycetes isolated from the rice phyllosphere, 18 isolates inhibited P. oryzae by >45%. According to analysis of their 16 S rRNA gene sequences, the majority of the 18 isolates belonged to Streptomyces genera; others were identified as belonging to Saccharothrix, Gordonia, or Lentzea. Isolates that potentially produced a bioactive compound(s) were identified among the 18 isolates: 17 isolates (94.44%) had a domain marker for nonribosomal peptide synthetase (NRPS) gene and 12 (66.67%) had type-I polyketide synthase (PKS) gene in their corresponding genome. Interestingly, isolates JSN1.9, SKB2.14, and SKB2.3 suppressed disease suppression by approximately 88%. To our knowledge, this is the first report on the application of rice-phyllosphere actinomycetes producing bioactive compounds to control leaf blast disease in Indonesia. Thus, these findings have escalated the potential application of phyllosphere actinomycetes as a supreme biocontrol agent against fungal leaf blast disease.  相似文献   

16.
Whole genome sequencing of a copper resistant (CuR) black rot strain of Xanthomonas campestris pv. campestris (Xcc) isolated from a broccoli plant in Trinidad revealed a unique operon for copper resistance. The cop genes of strain Xcc-BrA1 were determined to be present on a 160 to 180 kb plasmid shown to be non-conjugative with other xanthomonads. While nucleotide comparison of a putative 8.0 Kbp copLABMGF gene cluster identified in Xcc-BrA1 genome did not reveal any homologous region with other known CuR Xanthomonas strains from diverse origins, the comparison of the translated amino acid sequence indicated similarity with X. citri, X. c. pv. citrumelonis and X. vesicatoria Cop proteins. Cloning of the copLAB gene cluster from Xcc-BrA1 conferred copper resistance to other copper-sensitive xanthomonads. Although Xcc-BrA1 harbors copLAB genes with similar sizes and organization and is able to grow on Cu-amended medium as other CuR xanthomonads, the phylogenetic analysis of nucleotide sequences indicates that the cop cluster in Xcc-BrA1 is unique and distantly related to other copLAB genes from Xanthomonas and Stenotrophomonas. The origin of copper resistance genes in Xcc-BrA1 is likely a result of horizontal gene acquisition from a still unknown phylloplane cohabitant. The findings of this study have implications for the management of crop diseases caused by CuR xanthomonads. Future studies could focus on and determining the distribution, overall importance and appropriate control measures for strains harbouring these unique genes.  相似文献   

17.
The virulence spectrum of 300 isolates of Xanthomonas oryzae pv. oryzae (Xoo), representing 17 districts of Punjab, Pakistan was elucidated through inoculation on a set of six rice IRRI-differentials. The virulence level was assessed by using principal component and cluster analysis. Among six principal components (PCs), PC-1 exhibited 59.3 % of the total variance. The highly virulent isolates clusters on the positive side of the ordination away from the point of intersection of PC1 and PC2 and classifies the Xoo isolates from slow disease to the highest disease causing entities. The 300 isolates were categorized into 29 pathotypes (Pt1-29) wherein the highly virulent pathotype (Pt-1), comprises of 39 Xoo isolates were widespread in 12 districts. The majority of Xoo isolates were moderately to least virulent (21.7–43 %) and average disease progress curves confirmed the field reactions of these pathotype clusters for an efficient recognition of Xoo isolates. Interaction of the pathogen with differentials harboring different resistant genes was well investigated in the current study for future management approaches for which the surveillance of the new Xoo pathotypes may expedite the disease resistant rice breeding programme in the country.  相似文献   

18.
Plant response to one type of stress can be affected by simultaneous exposure to a second stress, for example when abiotic and biotic stresses occur together. Ten rice genotypes comprising those with bacterial blight (BB) resistance (R) genes, drought quantitative trait loci (QTLs) plus a BB R gene, and BB susceptible genotypes, were subjected to mild and moderate drought stress and plants were inoculated with two Xoo strains (PXO99 and PXO145) to simulate the challenges rice crops face under simultaneous stress of drought and BB. Plant height and dry shoot biomass were significantly reduced by drought stress treatments. The BB disease lesion lengths varied according to rice genotypes and PXO99 Xoo multiplication and spread in planta was higher compared to that of PXO145, which generally decreased under mild drought stress. Rice genotype IRBB7 (Xa7) showed less Xoo spread and a reduced Xoo multiplication under drought stress compared to the well-watered control with PXO145. In contrast, in genotypes with a different BB R gene and/or drought QTLs [IRBB4 (Xa4), IR87705–6-9-B (Xa4 + qDYT 2.2 ), IR87707–445-B-B-B (Xa4 + qDYT 2.2  + qDYT 4.1 ) and IR87707–446-B-B-B (Xa4 + qDYT 2.2  + qDYT 4.1 )], Xoo multiplication and spread in planta was higher with drought stress. This study has shown that drought stress affected rice response to the BB pathogen and the response varied according to the rice genotype. It is concluded that evaluating rice varieties under combined abiotic and biotic stresses will be the best strategy to determine biotic stress resistance durability under climate change.  相似文献   

19.
Appressorium differentiation, one of the most important steps in pathogenesis by the rice blast fungus, Pyricularia oryzae, is strongly coordinated with the cell cycle. In this study, we identified an ortholog gene of 53BP1, which encodes a signal transducer protein that participates in G2-M cell cycle checkpoint in higher eukaryotes, in the genome of P. oryzae and characterized the phenotype of deletion and overexpression mutants. Deletion mutants showed no significant deficiency in vegetative growth compared to wild-type and complemented strains, even on the media containing DNA-damaging agents. However, these null mutants had abnormal appressoria and formed more appressoria per conidium than in the wild type and were unable to penetrate the epidermis of rice leaves. eGFP-fused Mop53BP1 and qRT-PCR analyses revealed that Mop53BP1 is expressed during the first hours of appressorium formation. In addition, in overexpression mutants, Mop53BP1 localized to nuclei during all stages of appressorium maturation and penetration, and the mutants were resistant to the microtubule inhibitor benomyl, suggesting that Mop53BP1 is nuclear protein and may have some role related to microtubules.  相似文献   

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