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.     

Comparative colonisation by virulent versus avirulent <Emphasis Type="Italic">Pyricularia oryzae</Emphasis> on wild <Emphasis Type="Italic">Oryza australiensis</Emphasis>

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.     

Azoxystrobin and propiconazole offer significant potential for rice blast (<Emphasis Type="Italic">Pyricularia oryzae</Emphasis>) management in Australia

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.     

云南省稻瘟病菌群体的致病性分析及交配型分布

为明确云南省不同稻区稻瘟病菌Magnaporthe oryzae的毒性频率及交配型分布,利用2007—2013年分离自云南省不同稻区的112株稻瘟病菌单孢菌株,对23个持有不同抗性基因的单基因系和持有Pi57(t)的水稻渗入系IL-E1454进行致病性测定。结果表明,稻瘟病菌对不同抗病基因的毒性频率存在很大差异,分离自粳稻区的稻瘟病菌菌株对持有Piz-t、Pi5、Pi9、Pi20和Pi57(t)这5个水稻品系的毒性频率分别为14.29%、5.36%、5.51%、5.36%和0;分离自籼稻区的稻瘟病菌菌株对持有Pik-h、Piz、Pita、Piz-5、Pita-2、Pi5、Pi7和Pi9这8个水稻品系的毒性频率分别为18.25%、9.13%、9.64%、7.50%、15.72%、0、13.05%和0;分离自陆稻区的稻瘟病菌菌株菌株对持有Pik-h、Pib、Pish、Pi1、Pi5、Pi9、Pi11和Pi57(t)这8个水稻品系的毒性频率分别为6.67%、3.33%、13.79%、13.33%、7.69%、6.67%、0和3.23%;交配型测定结果显示,陆稻区菌株可交配率为100.00%,...     

Molecular and Pathotype Analysis of the Rice Blast Fungus in North Vietnam

Rice blast caused by Pyricularia oryzae is a devastating disease worldwide. In Vietnam, rice blast is especially severe in the Red River Delta in the North. The genetic diversity of 114 P. oryzae isolates collected from rice in 2001 in the Red River Delta and nine additional Vietnamese P. oryzae isolates was analysed using Amplified Fragment Length Polymorphism (AFLP). DNA similarity and cluster analysis based on 160 polymorphic AFLP markers showed twelve different AFLP genetic groups among the 123 field isolates. Isolates collected from japonica hosts clustered separately from indica host isolates with at least 60% dissimilarity with little evidence for gene flow between the two populations. In the 2001 population originating from indica hosts, three genetic groups were predominant and represented 99% of the isolates sampled. One predominant clonal lineage represented 59% of the 2001 indica host population and was found in eleven provinces in the Red River Delta of North Vietnam. Significant genotype flow could be demonstrated between the indica population south of Red river and the indica population north of Red river. There was significant linkage disequilibrium between the AFLP loci within the indica population, indicating that this is not a random mating population. Pathogenicity tests of 25 isolates selected from the 12 AFLP groups on a set of 29 differential rice lines revealed two avirulent isolates and 23 pathotypes. Different combinations of known resistance genes were found to have potential for blast resistance breeding for North Vietnam. First two authors contributed equally     

云南省水稻稻瘟病菌无毒基因AVR-Pia变异及水稻抗性基因Pia的有效性

为进一步了解田间稻瘟病菌Magnaporthe oryzae群体中AVR-Pia基因的分布及变异,利用水稻单基因系IRBLa-C水稻品种对自云南省13个市(州)采集分离得到的471株稻瘟病菌菌株进行抗性基因Pia有效性测定;利用无毒基因AVR-Pia特异性标记对471株稻瘟病菌菌株进行PCR检测和测序,并分析稻瘟病菌群体中无毒基因AVR-Pia的分布及DNA结构变异;利用有效性结果和PCR检测结果对471株菌株进行反应型划分,筛选鉴定菌株;利用鉴定菌株对云南省112份地方稻种进行Pia基因鉴定。结果表明,在471株稻瘟病菌菌株中,对含有Pia基因的水稻单基因系IRBLa-C表现为抗病和感病的菌株数分别为139株和332株,所占比例分别为29.5%和70.5%;在471株稻瘟病菌菌株中,分别有244株和227株菌株含有无毒基因AVR-Pia和不含有无毒基因AVR-Pia,所占比例分别为51.8%和48.2%,无毒基因AVR-Pia主要为完全缺失变异;在471株稻瘟病菌菌株中,A-和V+反应型菌株数分别为56株和161株,共217株,占总菌株数的46.1%,在13个市(州)稻瘟病菌群体中,A-和V+反应型菌株所占比例差异较大,其中在普洱市、红河哈尼族彝族自治州、昭通市、玉溪市4个市(州)的比例较大,分别为77.8%、57.1%、52.1%和50.0%;在112份云南省地方稻种质资源中,有20份地方稻品种含有抗性基因Pia,主要分布在9个市(州)中。表明云南省13个市(州)绝大部分水稻产区水稻Pia基因已丧抗性,含Pia基因的水稻种质在云南省分布较广。     

Site‐directed mutagenesis of the cytochrome b gene and development of diagnostic methods for identifying QoI resistance of rice blast fungus

BACKGROUND: It is possible that a single nucleotide polymorphism (SNP) (G143A mutation) in the cytochrome b gene could confer resistance to quinone outside inhibiting (QoI) fungicides (strobilurins) in rice blast fungus because this mutation caused a high level of resistance to fungicides such as azoxystrobin in Pyricularia grisea Sacc. and other fungal plant pathogens. The aim of this study was to survey Magnaporthe oryzae B Couch sp. nov. isolates in Japan for resistance to QoIs, and to try to develop molecular detection methods for QoI resistance. RESULTS: A survey on the QoI resistance among M. oryzae isolates from rice was conducted in Japan. A total of 813 single‐spore isolates of M. oryzae were tested for their sensitivity to azoxystrobin using a mycelial growth test on PDA. QoI fungicide resistance was not found among these isolates. The introduction of G143A mutation into a plasmid containing the cytochrome b gene sequence of rice blast fungus was achieved by site‐directed mutagenesis. Molecular diagnostic methods were developed for identifying QoI resistance in rice blast fungus using the plasmid construct. CONCLUSION: As the management of rice blast disease is often dependent on chemicals, the rational design of control programmes requires a proper understanding of the fungicide resistance phenomenon in field populations of the pathogen. Mutation of the cytochrome b gene of rice blast fungus would be specifically detected from diseased leaves and seeds using the molecular methods developed in this study. Copyright © 2009 Society of Chemical Industry     

Genetic distribution of the avirulence gene AVRPiz-t in Thai rice blast isolates and their pathogenicity to the broad-spectrum resistant rice variety Toride 1

Rice blast disease, caused by the filamentous fungus Pyricularia oryzae, is one of the most destructive diseases in rice worldwide. Breeding of resistant rice cultivars remains a cost-effective and environment-friendly means for controlling blast disease, but the resistance tends to break down over time because of the pathogen's rapid adaptation. In this study, AVRPiz-t gene sequences of 46 rice blast isolates were evaluated using a Southern blot analysis. The AVRPiz-t gene was present in 24 of 46 (52.2%) rice blast isolates. The pathogenicity assay showed that all blast isolates were avirulent against Japanese rice cv. Toride 1, which carries several rice blast resistance genes including Piz-t, Pii, Pi37, and Pi-ta. Screening for the Piz-t gene in Thai rice germplasm revealed that less than 20% of rice varieties harbour the Piz-t gene. Therefore, the Toride 1 rice variety could serve as an effective donor of rice blast resistance to be used in rice breeding programmes in Thailand. This study provides evidence for co-evolution between the rice blast resistance gene Piz-t and the rice blast fungal avirulence gene AVRPiz-t. Understanding this relationship will facilitate the sustainable development of breeding for rice blast resistance in the future.     

Leaf blast disease reduction by rice-phyllosphere actinomycetes producing bioactive compounds

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.     

稻梨孢菌与其他寄主梨孢菌在水稻植株上的交互作用

作者研究了1个稻梨孢菌株与4个稻以外寄主梨孢菌株在混合接种和间隔接种条件下,在水稻植株上的交互作用。结果表明:弱致病菌与强致病菌间交互作用较强,非致病菌与强致病菌间较弱。弱致病菌可明显降低强致病菌的致病性,非致病菌对强致病菌的作用,多数组合表现为减轻病害,但有少数组合表现为促进发病。弱致病菌先接种;2天后接种强致病菌,比两者混合接种具有更强烈的互作效应,病斑数减少达35.7%-38.1%。先接种菌的孢子浓度对后接种菌的致病性也有影响。     

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。     

Resistance in leaf blades assessed by counting conidia correlates with whole-plant-specific resistance in leaf sheaths in a compatible rice–Magnaporthe oryzae interaction

Resistance in the leaf blades of rice plants against a virulent race of the rice blast fungus Magnaporthe oryzae was quantitatively examined using a modified spot inoculation method. Numbers of conidia produced in the lesions were affected by plant age and paralleled the frequency of resistance infection types, which is indicative of whole-plant-specific resistance (WPSR), in the inoculated leaf sheaths of the corresponding plants. Exogenous abscisic acid treatment, which suppresses WPSR, also increased the susceptibility of the leaf blades. These results indicate a correlation between the resistance of the leaf blades and the WPSR in the leaf sheaths.     

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。     

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.     

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.     

Effects of panicle development stage and temperature on rice panicle blast infection by Magnaporthe oryzae and visualization of its infection process

Panicle blast, caused by the fungus Magnaporthe oryzae (syn. Pyricularia oryzae), directly contributes to yield loss in the field. The effects of panicle development stage and temperature on panicle blast were studied and the infection process of M. oryzae in panicles was visualized. Rice panicles at different development stages from three rice cultivars were inoculated with a conidial suspension in vitro. The rice cultivar Lijiangxintuanheigu was highly susceptible to panicle blast at 5 days postinoculation (dpi) when the pulvinus distance was 15–20 cm. Nanjing 9108 was moderately susceptible to panicle blast when the pulvinus distance was 8–10 cm, but Yliangyou 800 was resistant. The effect of temperature on panicle blast was determined under 22–35 °C temperature treatments. Inoculated panicles placed at temperatures of 28 and 30 °C showed the highest lesion grade based on lesion length at 5 dpi. The infection process of M. oryzae in rice panicles was observed by confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM). M. oryzae initially formed the appressorium to invade through the epidermis of rice panicles at 24 hours postinoculation (hpi). As the disease progressed, the invasive hyphae formed dense mycelial networks in the inner parenchyma cells at 60 hpi. Our results will contribute to the understanding of panicle development stage and temperature effects on panicle blast and improve resistance evaluation methods. Additionally, visualization of the infection process by CLSM and TEM are valuable methods to observe M. oryzae invasive hyphae inside rice panicle cells.     

侵染优质稻美香占2号的稻瘟病菌生理小种鉴定及无毒基因分析

为明确优质稻种美香占2号的抗瘟性,并为其合理布局以及与不同品种的轮换种植提供科学依据,利用7个中国鉴别品种和11个抗稻瘟病单基因系,对2013—2017年自广东省美香占2号品种上分离获得的50株稻瘟病菌Magnaporthe oryzae菌株进行生理小种鉴定和无毒基因型分析。结果显示,50株稻瘟病菌菌株被鉴定为11个生理小种,其中优势小种分别为C13、B13、B01、B05和C05;50株稻瘟病菌菌株对IRBLkh-K3(仅含Pik-h基因)、NIL-e1(仅含Pi50基因)、IRBL9-W(仅含Pi9基因)和IRBLzt-T(仅含Piz-t基因)4个抗稻瘟病单基因系表现出极低的毒性,频率分别为4%、6%、6%和8%;对IRBLz-Fu(仅含Piz基因)、IRBLkp-K60(仅含Pik-p基因)和IRBLi-F5(仅含Pii基因)3个抗稻瘟病单基因系表现出相对较高的毒性,频率分别为88%、86%和80%;自美香占2号以及其它4个主栽品种上获得的70株稻瘟病菌菌株被聚为不同类群;2003—2007年供试菌株中无毒基因AvrPi9、AvrPiz-t、AvrPi50和AvrPik-h的出现...     

海南省田间稻瘟病菌中AvrPiz-t基因位点变异

为评估在水稻育种中被广泛利用的广谱抗稻瘟病基因Piz-t的有效性,对不同年份分离自海南省陵水黎族自治县和三亚市水稻的273株田间稻瘟病菌株中的AvrPiz-t位点变异及其与菌株致病性的相关性进行系统研究。结果表明,海南省田间菌株中无毒基因AvrPiz-t位点的变异频率为0～100.00%,陵水黎族自治县菌株中的变异频率远远高于三亚市菌株。在菌株中共鉴定到3种AvrPiz-t位点变异类型,分别为基因位点完全缺失、DNA重复元件MGR583在基因位点启动子区-10 bp上游和编码区218 bp下游插入。所有AvrPiz-t位点变异的菌株对携带Piz-t抗病基因的单基因水稻系IRBL-11均表现出强的致病性。陵水黎族自治县菌株中AvrPiz-t位点的变异频率呈逐年增加趋势,2021年94株菌株中AvrPiz-t位点的变异频率为100.00%,其中51.06%的菌株变异是MGR583在启动子区-10 bp上游插入,表明DNA重复元件MGR583在AvrPiz-t位点插入是AvrPiz-t从无毒到有毒进化的重要机制之一。     

Effects of leaf blast on photosynthesis of rice 2. Canopy photosynthesis

The effect ofPyricularia oryzae, the causal organism of leaf blast in rice, on photosynthetic rate of a rice crop was determined with mobile equipment in the field. Canopy CO₂ exchanges rate (CER) was significantly reduced in plots inoculated withP. oryzae. The experimentally obtained data were used to evaluate the performance of a model for the effects of leaf blast on canopy photosynthesis. The model comprised photosynthesis and respiration routines of a mechanistic crop growth model, extended with submodels for effects of leaf blast on both processes. Canopy photosynthesis and the effect of leaf blast on CER were accurately simulated with the model.Analysis showed that the reduction in canopy photosynthesis was mainly due to an adverse effect of lesions on leaf photosynthetic rate and to shading by dead leaf are resulting from disease induced senescence. A sensitivity analysis demonstrated the importance of the vertical distribution of the disease in the canopy. This implies that disease monitoring for crop loss assessment should consider vertical disease distribution.