Involvement of OsNPR1/NH1 in rice basal resistance to blast fungus Magnaporthe oryzae

Rice blast disease, caused by the fungus Magnaporthe oryzae, is a major threat to worldwide rice production. Plant basal resistance is activated by virulent pathogens in susceptible host plants. OsNPR1/NH1, a rice homolog of NPR1 that is the key regulator of systemic acquired resistance in Arabidopsis thaliana, was shown to be involved in the resistance of rice to bacterial blight disease caused by Xanthomonas oryzae pv. oryzae and benzothiadiazole (BTH)-induced blast resistance. However, the role of OsNPR1/NH1 in rice basal resistance to blast fungus M. oryzae remains uncertain. In this study, the OsNPR1 gene was isolated and identified from rice cultivar Gui99. Transgenic Gui99 rice plants harbouring OsNPR1-RNAi were generated, and the OsNPR1-RNAi plants were significantly more susceptible to M. oryzae infection. Northern hybridization analysis showed that the expression of pathogenesis-related (PR) genes, such as PR-1a, PBZ1, CHI, GLU, and PAL, was significantly suppressed in the OsNPR1-RNAi plants. Consistently, overexpression of OsNPR1 in rice cultivars Gui99 and TP309 conferred significantly enhanced resistance to M. oryzae and increased expression of the above-mentioned PR genes. These results revealed that OsNPR1 is involved in rice basal resistance to the blast pathogen M. oryzae, thus providing new insights into the role of OsNPR1 in rice disease resistance.     

茉莉酸甲酯对水稻白叶枯病的诱导抗性及相关防御酶活性的影响

为探索茉莉酸甲酯(methyl jasmonate,MeJA)诱导水稻抗白叶枯病的效应,采用MeJA喷雾处理剪叶接种法,测定MeJA对水稻幼苗的白叶枯病病情指数、白叶枯病病菌Xanthomonas oryzae pv.oryzae的抑菌效果及对叶片过氧化物酶(peroridase,POD)、过氧化氢酶(catalase,CAT)、超氧化物歧化酶(superoxide dismutase,SOD)、多酚氧化酶(polyphenol oxidase,PPO)和苯丙氨酸解氨酶(phenylalnaine ammonialyase,PAL)等相关防御酶活性的影响.0.05 ～ 2.0 mmol/L的MeJA能降低水稻幼苗白叶枯病的病情指数,但对水稻白叶枯病菌无直接抑菌活性;0.1 mmol/L MeJA的诱导效果最好,处理48h后,感病品种温229和抗病品种嘉早312的诱导效果分别为73.18％和70.43％;0.05 ～2.0mmol/L的MeJA处理水稻叶片中POD、CAT、SOD、PPO和PAL活性呈上升趋势.研究表明MeJA能诱导水稻幼苗对白叶枯病的抗性,且诱导抗性的产生与MeJA提高水稻相关防御酶的活性有关.     

Races of <Emphasis Type="Italic">Magnaporthe oryzae</Emphasis> in Australia and genes with resistance to these races revealed through host resistance screening in monogenic lines of <Emphasis Type="Italic">Oryza sativa</Emphasis>

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.     

Elicitor(s) production is involved in red-light-induced resistance during spore germination of <Emphasis Type="Italic">Bipolaris oryzae</Emphasis> in the presence of host tissues

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.     

Antifungal activity of a novel compound purified from the culture filtrate of <Emphasis Type="Italic">Biscogniauxia</Emphasis> sp. O821 against the rice blast fungus <Emphasis Type="Italic">Magnaporthe oryzae</Emphasis>

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.     

Rice <Emphasis Type="Italic">terpene synthase 18</Emphasis> (<Emphasis Type="Italic">OsTPS18</Emphasis>) encodes a sesquiterpene synthase that produces an antibacterial (<Emphasis Type="Italic">E</Emphasis>)-nerolidol against a bacterial pathogen of rice

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.     

Identification of blast resistance genes in 358 rice germplasms (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) using functional molecular markers

Rice blast, caused by the fungus Magnaporthe oryzae, is one of the most devastating diseases of rice (Oryza sativa L.), and neck blast is the most destructive phase of this disease. Although neck blast causes tremendous yield loss, little is known about the molecular mechanisms underlying the neck blast resistance. To address this issue, we collected 358 rice varieties from different ecotypes in China and assessed them for the neck blast resistance under natural conditions favoring disease development in Jining, Shandong Province. Our results showed that 124 (34.6%) and 234 (65.4%) varieties were resistant and susceptible to M. oryzae under natural field conditions, respectively. Among the 358 rice varieties that were screened for the presence of 13 major blast resistance (R) genes against M. oryzae by using functional markers, 259 varieties contained one to seven R genes. In addition, the relationship between the presence of R genes and the disease reactions was also investigated by integrative analysis of phenotyping and genotyping based on functional markers. Our results showed that the rice blast resistance gene Pi2 was significantly correlated with neck blast resistance. Furthermore, any of the 13 major blast R genes was absent from 32 rice varieties exhibited obvious neck blast resistance, which would be the potential materials for identifying novel neck blast R genes. Taken together, our findings provide insight into the distribution of the 13 major blast R genes in the tested Chinese rice germplasm resources, which will serve as a basis for developing rice blast resistant. Furthermore, 32 rice varieties exhibited neck blast resistance, but they did not harbor any of the 13 major blast R genes. In the future, these varieties may be used to identify novel neck blast R genes.     

黑龙江省水稻种质抗瘟性及稻瘟病菌致病性分析

为明确黑龙江省水稻种质抗性及稻瘟病菌的致病性,以黑龙江省8个水稻品种、24个单基因系作为供试材料,120株稻瘟病菌株作为接种体,采用喷雾接种法测定了各供试水稻的抗瘟性及稻瘟病菌的致病性。结果表明,水稻品种对2010年和2011年菌株的抗性频率分别在31.67%~68.33%和21.67%~55.00%之间,2010年最好的抗性品种为松粳12,2011年最好的抗性品种为五优稻4和东农425;松粳12东农425组合联合抗病性最好。水稻单基因系对2010年和2011年菌株的抗性频率分别在10.00%~90.00%和5.00%~86.67%之间,抗性最好的单基因系分别为IRBLzt-T(Pi-zt)和IRBLz5-CA(Pi-z5);松粳12、东农425和龙粳22的基因聚合效果最好。2010年和2011年菌株对抗瘟基因群的致病率分别在8.33%~95.83%和25.00%~95.83%之间;无毒基因总出现频率分别为461和412次。研究表明,水稻种质抗性受菌株致病性影响较大,但高抗种质相对稳定,基因聚合方式更适宜当地品种抗性改良。     

水直播条件下黑龙江省不同稻区稻瘟病菌致病性分析

为明确水直播条件下黑龙江省不同稻区稻瘟病菌Magnaporthe oryzae的致病性分化情况,以24个抗瘟单基因系品种为寄主,来源于2017—2018年黑龙江省水直播稻田的242株稻瘟病菌菌株为接种体,采用离体划伤方法接种,记录病斑反应型,计算有效致病菌株率和抗性频率,并进行聚类分析。结果显示,在水直播条件下,2017年,黑龙江省南部和中东部稻区稻瘟病菌菌株对抗瘟单基因系品种的有效致病菌株率介于8.33%~95.83%和20.83%~95.83%之间,无毒基因出现频率分别为575次和622次;2018年,南部和中东部稻区稻瘟病菌菌株对鉴别体系的有效致病菌株率介于29.17%~95.83%和20.83%~91.67%之间,无毒基因出现频率分别为536次和571次。2017年,黑龙江省南部和中东部稻区稻瘟病菌菌株的致病性相似系数介于0.15~1.00和0.14~1.00之间,以致病性相似系数0.40为阈值,可将菌株分别划分为5个类群和6个类群;2018年,南部和中东部稻区菌株的致病性相似系数介于0.15~0.93和0.26~1.00之间,以致病性相似系数0.40为阈值,可将菌株分别划分为5个类群和4个类群。2017年,抗瘟单基因系品种对黑龙江省南部和中东部稻区稻瘟病菌菌株的抗性频率介于11.29%~88.71%和10.77%~86.15%之间,其中抗瘟单基因系品种IRBL9-W（Pi-9）和IRBLz5-CA（Pi-z5）抗性表现最好;2018年,抗瘟单基因系品种对南部和中东部稻区菌株的抗性频率介于10.34%~82.67%和15.79%~85.96%之间,其中抗瘟单基因系品种IRBL9-W（Pi-9）和IRBLz5-CA（Pi-z5）抗性表现最好。表明水直播条件下黑龙江省稻瘟病菌致病性分化剧烈,稻瘟病菌整体致病力较强,但仍有部分水稻种质抗性较好且相对稳定,基因聚合后抗性会得到进一步提升。     

江苏省水稻品种对水稻细菌性条斑病抗性鉴定及评价

为明确江苏省水稻条斑病菌致病力分化状况和不同类型水稻品种对条斑病抗感特性,在孕穗期采用针刺接种法对徐淮稻区2007—2009年采集分离获得的45株条斑病菌进行致病力测定,根据病原菌在6个水稻鉴别品种IRBB4、IRBB5、IRBB14、IRBB21、IR24和金刚30上的抗感反应划分致病型,从中选择具有代表性的3种不同致病型条斑病菌,并鉴定了240个不同类型的水稻品种对条斑病的抗感性。根据菌株在鉴别品种上的抗感反应将供试菌株划分为8个致病型,其中优势致病型为C3致病型,所占比例为35.5%;大多数菌株与鉴别品种间表现出弱互作关系,少数菌株表现出强互作关系。粳稻品种对条斑病的抗性明显高于籼稻,但常规粳稻和杂交粳稻对强致病力菌抗性比例仅为59.8%和37.5%。表明水稻细菌性条斑病流行仍具有潜在的威胁。     

Investigation of rice blast development in susceptible and resistant rice cultivars using a gfp‐expressing Magnaporthe oryzae isolate

In this study, an isolate of Magnaporthe oryzae expressing the green fluorescent protein gene (gfp) was used to monitor early events in the interaction of M. oryzae with resistant rice cultivars harbouring a blast resistance (R) gene. In the resistant cultivars Saber and TeQing (Pib gene), M. oryzae spores germinated normally on the leaf surface but produced morphologically abnormal germ tubes. Germling growth and development were markedly and adversely affected in leaves of these resistant cultivars. Penetration of host cells was never seen, supporting the idea that disruption of germling development on the leaf surface might be one of the resistance mechanisms associated with Pib function. Thus, this particular R gene appeared to function in the absence of host penetration by the fungal pathogen. Confocal laser scanning microscopy of M. oryzae‐infected susceptible rice cultivars showed the dimorphic growth pattern that is typically observed during the biotrophic and necrotrophic stages of leaf colonization in susceptible cultivars. The suitability of the gfp‐expressing M. oryzae isolate for further research on R‐gene function and identification of resistant genotypes in rice germplasm collections is discussed.     

Green-odour compounds have antifungal activity against the rice blast fungus <Emphasis Type="Italic">Magnaporthe oryzae</Emphasis>

Four green-odour compounds—trans-2-hexenal, cis-3-hexenol, n-hexanal, and cis-3-hexenal—were applied (0.85 μg ml⁻¹ as vapour) to rice plants in laboratory conditions to observe their biological activity against the phytopathogenic fungus Maganporthe oryzae, which causes rice blast disease worldwide. Two compounds, trans-2-hexenal and cis-3-hexenal, showed remarkable disease suppression efficacy (99.7% and 100% suppression, respectively), while n-hexanal had moderate (86.5%) and cis-3-hexenol had weak (20.8%) disease-suppressing effects. Pre-application and post-application of trans-2-hexenal or cis-3-hexenal had slight effects on blast incidence, suggesting that these compounds had direct effects to suppress M. oryzae infection. In fact, trans-2-hexenal and cis-3-hexenal exhibited a growth suppression effect on M. oryzae. Interestingly, these two compounds inhibited appressorium formation at lower concentrations than the growth suppression. Studies on the hypersensitive response (HR)-like reaction and plant β-1,3-glucanase activity in rice plant confirmed that induced resistance was not the major factor involved in the disease suppression mechanism. Results of this study conclusively showed that trans-2-hexenal and cis-3-hexenal possess potent inhibitory activities against the growth and the appressorium formation of M. oryzae and could be used as antifungal agents to significantly reduce M. oryzae infections in rice.     

Effect of plant extracts and an essential oil on the control of brown spot disease, tillering, number of panicles and yield increase in rice

The effects of essential oils (EO), cold water (CWE), hot water (HWE) and ethanol (ETHE) extracts of Callistemon citrinus L. and Cymbopogon citratus (DC) Stapf on the radial growth of Alternaria padwickii (Ganguly) M.B. Ellis and Bipolaris oryzae (Breda de Haan) Shoemaker, the control of brown spot disease, the tillering, the number of panicles and the yield increase in rice were evaluated under laboratory and field conditions. In vitro, the growth of both fungi was completely inhibited by the EO of C. citrinus and C. citratus at 4,520 μg/ml and 452 μg/ml, respectively. For solvent extracts, the ETHE of C. citrinus was the most active and inhibited 80–85 % of the fungal growth followed by the CWE of C. citratus with 77 % and 36 % diameter reduction against B. oryzae and A. padwickii, respectively at 10 000 μg/ml. Under laboratory conditions, seed treatment with the EO of C. citrinus reduced the incidence of B. oryzae in seeds by 85–100 % compared to the non-treated controls. Similarly, the seed treatment increased the germination of an irrigated rice cultivar by 10.6 %, whereas the percentage of germinated seeds of upland rice was not significantly affected. The highest germination (85–94 %) was found in the non-treated and treated samples with a low incidence (0–4 %) of B. oryzae. Under field conditions, the combined use of the essential oil of C. citrinus as a seed treatment and spraying the plants with 2 % ethanol followed by 2 % (w/v) aqueous extracts of C. citrinus or C. citratus increased the emergence, tillering, panicles/plant and the grain yield by 25–55 % of the irrigated rice. In addition, the brown spot severity was reduced by 36–42 %. For the upland rice, the treatments led to similar results with the grain yield increase of 54–137 % and 20–80 % reduction in the brown spot severity. From our results, we concluded that the EO and solvent extracts of C. citrinus and C. citratus have potential as control agents against brown spot and other seed-borne fungal diseases in rice under both conventional and organic farming.     

Generation and characterisation of Tn5-tagged <Emphasis Type="Italic">Xanthomonas oryzae</Emphasis> pv. <Emphasis Type="Italic">oryzae</Emphasis> mutants that overcome <Emphasis Type="Italic">Xa23</Emphasis>-mediated resistance to bacterial blight of rice

Xanthomonas oryzae pv. oryzae causes bacterial blight of rice. Xa23, a bacterial blight resistance gene identified originally in wild rice, Oryza rufipogon, is dominant and resistant to all X. oryzae pv. oryzae field isolates tested. The corresponding avirulence gene avrXa23 is unknown. Here we report the generation of a random insertion mutant library of X. oryzae pv. oryzae strain PXO99 using a Tn5-derived transposon tagging system, and identification of mutant strains that are virulent on CBB23, a near-isogenic rice line containing Xa23. A total of 24,192 Tn5 inserted clones was screened on CBB23 by leaf-cutting inoculation and at least eight of them caused lesions on CBB23 comparable to those on JG30, the susceptible recurrent parent of CBB23. Polymerase chain reaction and Southern blot analysis showed that all the eight mutants, designated as P99M1, P99M2, P99M3, P99M4, P99M5, P99M6, P99M7 and P99M8, have a single Tn5-insertion in their genomes. The flanking DNA sequences of the Tn5-insertion sites were isolated by PCR-walking and sequenced. Bioinformatic analysis of the flanking sequences, by aligning them with the whole genome sequences of X. oryzae pv. oryzae strains PXO99, KACC10331 and MAFF311018 through NCBI, revealed that the Tn5-insertions disrupted genes that encode TAL effector AvrBs3/PthA, ISXo1 transposase, Type II secretion system protein-like protein or outer membrane protein, glycogen synthase, cytochrome C5 and conserved hypothetical protein. Further identification of these mutants will facilitate the molecular cloning of avirulence gene avrXa23. The authors C.-L. Wang, A.-B. Xu contributed equally to this work; Y. Gao and Y.-L. Fan contributed equally to this work.     

Antifungal activity of <Emphasis Type="Italic">Biscogniauxia</Emphasis> sp. culture filtrates against the rice pathogen <Emphasis Type="Italic">Magnaporthe oryzae</Emphasis>

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.     

Role of earhead bug (leptocorisa acuta) feeding on sheath rot disease caused bysarocladium oryzae inoryza sativa in India

A study was conducted to determine the role of the earhead bug (Leptocorisa acuta Thumb. [Heteroptera: Alydidae]) in the manifestation of sheath rot disease caused bySarocladium oryzae (Sawada) W. Gams & D. Hawksw. [syn.Acrocylindrium oryzae (Sawada)], with the aim of formulating effective control measures against the disease. In greenhouse studies, rice plants (Oryza sativa, cv. IR 20) exhibited typical sheath rot within 12 days whenS. oryzae spore suspensions (5 x 10⁷ conidia/ml) were sprayed on earhead bug-infested plants (5 bugs/tiller). In a comparison of various inoculation methods, swabbing a spore suspension (using a camel?s hair brash) on the sheath surface of earhead bug-infested plants, and inserting a single-grain culture inside the sheath of infested plants, produced the greatest disease severity within 18 days of inoculation. The results demonstrated (a) the role of the earhead bug in sheath rot disease manifestation and (b) that rice genotypes can be screened effectively and rapidly in the greenhouse for resistance to the disease, using the described inoculation techniques.     

Expression profiling of rice genes in early defense responses to blast and bacterial blight pathogens using cDNA microarray

In order to understand the defense machinery in the model cereal crop rice, we performed a large-scale analysis of rice gene expression in response to rice blast Magnaporthe grisea (M. grisea) or Magnaporthe oryzae and bacterial blight Xanthomonas oryzae pv. oryzae (Xoo) during the early incompatible and compatible interactions. Using a gene chip containing 10 254 rice cDNAs representing 9240 unique genes, we identified 794 and 612 genes differentially expressed in the incompatible and compatible rice–M. grisea interactions, respectively, with 274 genes co-regulated during both interactions. In the rice–Xoo pathosystem, 454 and 498 differentially expressed genes were identified in the incompatible and compatible interactions, respectively, including 237 co-regulated genes in the both interactions. By clustering differentially regulated genes from all these interactions, we identified 29 co-regulated genes in the all four interactions, and 86 and 74 co-regulated genes in the two incompatible and two compatible interactions, respectively. These differentially expressed genes could be classified into three categories, including M. grisea- and Xoo-regulated, M. grisea-specific, and Xoo-specific. The expression patterns of representative defense-related genes were further confirmed by RT-PCR. The large-scale expression data from our microarray analysis indicated the existence of distinctive as well as shared defense pathways between the rice–M. grisea and rice–Xoo interactions.     

Mining of rice blast resistance gene Pi54 shows effect of single nucleotide polymorphisms on phenotypic expression of the alleles

The rice blast resistance gene Pi54 (formerly Pi-k ^h ) isolated from indica rice line Tetep confers broad spectrum resistance to different strains of Magnaporthe oryzae in India. In this study, we performed PCR based allele mining for blast resistance gene Pi54 from six cultivated rice lines and eight wild rice species to understand its structural variation and its impact on the phenotypes. Sequence analysis indicates presence of more variation between cultivated and wild species (35–90 %) than variation found among cultivated species (1–20 %). Structural analysis of alleles showed presence of variable number of Open Reading Frames (0–2) principally having point mutations in the leucine rich repeats (LRR) regions. The Ka/Ks ratio of LRR region was >1, which shows the effect of selection pressure at this domain. The Pi54 alleles have 142 polymorphic sites with average nucleotide diversity of 0.04522. The K_a/K_s ratio of coding region ranged from 0 to >1 and Tajima’s D test showed negative as well as Darwinian selection within the alleles, which corresponded well with their phenotypic reaction to M. oryzae. The results obtained in this study shows divergent nature of Pi54 allele in wild species and land races of rice. The resistance alleles identified in this study can be used in effective management of rice blast disease through gene pyramiding.     

冈优725对四个稻瘟病菌生理小种毒素的响应

为了明确稻瘟病菌对杂交水稻的毒害机制,采用稻瘟病菌粗毒素浇灌水稻植株,探讨4个稻瘟病菌生理小种的粗毒素对冈优725各器官物质积累、转运及产量的影响规律。结果显示:4个稻瘟病菌生理小种毒素均不同程度地抑制了冈优725干物质积累并引起大幅减产,根部干物质积累量、地上部干物质积累量、有效输出率、有效转化率平均下降34.57%、21.48%、31.34%、40.90%;穗粒数、结实率、千粒重和产量平均降低17.24%、12.84%、5.65%和10.83%;生理小种间毒力差异显著,其中ZA10毒素的毒性最强;孕穗期是冈优725对稻瘟病菌毒素最敏感的时期。