Cyclic AMP Restores Appressorium Formation Inhibited by Polyamines in Magnaporthe grisea

ABSTRACT Magnaporthe grisea, the causal agent of rice blast, forms a dome-shaped melanized infection structure, an appressorium, to infect its host. Environmental cues that induce appressorium formation in this fungus include the hydrophobicity and hardness of the contact surface and chemicals produced by the host. An elevated concentration of intracellular cyclic AMP (cAMP) has been implicated in appressorium differentiation in M. grisea. Polyamines (putrescine, spermidine, and sper-mine) are involved in cell growth and differentiation in a wide range of organisms. To understand the role of polyamines in appressorium differentiation in M. grisea, intracellular polyamines were quantified, and the effects of polyamines and polyamine biosynthesis inhibitors on conidial germination and appressorium formation were tested. High levels of polyamines were detected in freshly collected spores, but the levels decreased during conidial germination. Spermidine was found to be the major component. Polyamines and polyamine biosynthesis inhibitors did not affect conidial germination, but polyamines specifically impaired appressorium formation. Furthermore, exogenous addition of cAMP restored appressorium formation inhibited by poly-amines. These results suggest that polyamines may reduce intracellular cAMP levels in M. grisea, leading to the inhibition of appressorium formation.     

水稻内生枯草芽孢杆菌对稻瘟病菌和稻恶苗病菌的抑制作用

自水稻茎和根内分离获得的枯草芽孢杆菌J215和G87菌株培养菌液和滤液对稻瘟病菌和稻恶苗病菌具有较强的抑制作用.其培养菌液(109cfu/ml)稀释2～100倍时,对稻瘟病菌和稻恶苗病菌菌丝生长抑制分别为83.6%～91.0%和60%左右;培养滤液稀释2倍时抑制率达52.4%～75.4%.细菌培养滤液处理能破坏病菌菌丝形态,使稻瘟病菌菌丝细胞膨大、细胞壁破损、原生质外渗、菌体崩溃;但对稻恶苗病菌菌丝损坏较轻,主要使菌丝细胞膨大、生长缓慢.另外,细菌培养滤液稀释10倍时对稻瘟病菌分生孢子形成和萌发的抑制分别达85%和95%以上;对稻恶苗病菌分生孢子形成和萌发的抑制率分别为90%和60%以上.     

Inhibitors of appressorium formation in Magnaporthe grisea: a new approach to control rice blast disease

Fungi were screened for the production of inhibitors of appressorium formation in germinating conidiospores of Magnaporthe grisea on inductive and non-inductive surfaces. Bioactivity-guided isolation yielded glisoprenins A, C, D and E from Gliocladium roseum and oleic acid from three fungi. The glisoprenins were active only on a hydrophobic surface, whereas oleic acid inhibited appressorium formation on a hydrophilic surface when 1,16-hexadecanediol, but not 8-(4-chlorophenylthio)adenosine-3′,5′-monophosphate, was used as inducer. The inhibition by glisoprenins could be reversed competitively by 1,2-dioctanoylglycerol but not by 1-oleoyl-2-acetyl-glycerol, both effective activators of protein kinase C in mammalian cells. Other mono-unsaturated fatty acids also inhibited appressorium formation. The corresponding methyl esters were inactive. The results agree with previous findings that at least two signal-transducing pathways are involved in appressorium formation. In addition, the differences observed between fungal signalling via PKC and the pathway used in mammalian cells could be used for the search for new and selective fungicides for rice blast disease. © 1998 Society of Chemical Industry     

水稻稻瘟病拮抗细菌的筛选与防治初探

从水稻作物根际分离筛选得到的 2 0 8个细菌菌株对稻瘟病病菌具有较强的抑制能力 ;抑菌圈直径在 2 0mm以上的有 65株。选用室内拮抗性较稳定的 8株细菌菌株经两年的田间防病试验 ,不同菌株间防效差异显著 ,其中两年防效较好的菌株是Ma 3 2 (蜡状芽孢杆菌 )和Xi 55(枯草芽孢杆菌 )。一些菌株处理种子对秧苗生长有促进作用。     

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.     

利用绿色荧光蛋白GFP研究稻瘟病菌与水稻的互作

稻瘟病菌Magnaporthe oryzae严重威胁水稻的产量与质量,明确稻瘟病菌与水稻互作过程及机理,对防治稻瘟病具有重要意义。本研究利用稻瘟病菌常用致病菌株GUY11和ZB25,构建了绿色荧光蛋白GFP的过量表达菌株,并通过荧光显微观察菌株侵染寄主水稻过程中侵染结构的形成与发育,包括孢子萌发、附着胞形成、侵染钉形成、侵染菌丝增殖、坏死斑形成及产孢。另外,通过比较过量表达菌株对稻瘟病高抗水稻和易感水稻的侵染过程,发现侵染过程的差异主要集中于侵染钉的穿透和侵染菌丝的定殖。本研究为分析稻瘟病菌对寄主水稻的定殖规律提供了一种有效工具。     

Silicon enhances the accumulation of diterpenoid phytoalexins in rice: a potential mechanism for blast resistance

ABSTRACT Although several reports underscore the importance of silicon (Si) in controlling Magnaporthe grisea on rice, no study has associated this beneficial effect with specific mechanisms of host defense responses against this fungal attack. In this study, however, we provide evidence that higher levels of momilactone phytoalexins were found in leaf extracts from plants inoculated with M. grisea and amended with silicon (Si(+)) than in leaf extracts from inoculated plants not amended with silicon (Si(-) ) or noninoculated Si(+) and Si(-) plants. On this basis, the more efficient stimulation of the terpenoid pathway in Si(+) plants and, consequently, the increase in the levels of momilactones appears to be a factor contributing to enhanced rice resistance to blast. This may explain the lower level of blast severity observed on leaves of Si(+) plants at 96 h after inoculation with M. grisea. The results of this study strongly suggest that Si plays an active role in the resistance of rice to blast rather than the formation of a physical barrier to penetration by M. grisea.     

ZJUF0986活性代谢产物对稻瘟病菌致病性的影响

通过菌丝生长速率法和悬滴法测定ZJUF0986活性代谢产物对稻瘟病菌菌丝生长、孢子萌发和附着胞形成的影响。结果表明,ZJUF0986活性代谢产物对稻瘟病菌菌丝生长的有效中浓度EC50为18.55mg/L,与对照药剂三环唑的EC50(17.30mg/L)相比无显著性差异。活性代谢产物不仅影响孢子萌发,也显著降低附着胞的形成。浓度为10mg/L的活性代谢物可完全抑制孢子萌发及附着胞的形成;浓度为1.25mg/L时则明显延缓孢子萌发及附着胞的形成,处理48h后的孢子萌发率和附着胞形成率分别为62.17%和38.46%。以浓度为1.25mg/L活性代谢产物处理的稻瘟病菌孢子悬浮液接种离体大麦叶片,病原菌孢子在大麦叶片表面能部分萌发形成附着胞,但侵染栓形成延迟,致病性明显降低。     

烯丙异噻唑刺激稻株体内超氧自由基产生与水稻抗稻瘟病的关系

 病原菌与寄生植物相互作用是个十分复杂的过程,涉及到两者很多因子的相互作用。     

水稻旱晚播“活体病株”接种法的研究及应用

作者针对水稻抗瘟育种中“旱地稻瘟病圃”易受气候生态等条件的影响,导致年际间发病的稳定性和能否发病的安全性,改进以往喷雾接种或利用病区自然诱发法,采用活体病株持续接种,和人为小气候控制等措施,完善成一套发病系数高且稳定,方法简便实用,病圃容量大,鉴定结果可靠性强的综合技术措施,在连续几年试验中鉴定筛选出一批利用价值较高的种质资源和抗病性较好的系统材料。     

晚稻稻瘟病BP神经网络分区预报

应用相关分析方法分析了浙江省19个县1988～1999年晚稻稻瘟病发病与有关环境因子的关系,筛选了8个气象因子用于晚稻稻瘟病发生程度长期预报。根据各预报因子与稻瘟病发病程度相关性,采用邻接二维图论聚类分析法,将19个点(县)划分为4个生态区。每个生态区内运用BP神经网络技术建立模型,并进行拟合和试报。1997～1999年试报验证,在划分稻瘟病生态区的基础上,应用BP神经网络模型对稻瘟病进行长期预测预报是可行的,3年试报成功率分别是78.95％、84.21％和78.95％。文中还对该方法与过去常用的预报方法的试报结果作了比较。     

Enhancement of fungicidal and insecticidal activity by reductive alkylation of chitosan

A series of N-alkyl chitosan (NAC) derivatives were synthesized using a reductive alkylation reaction to examine their fungicidal and insecticidal activity. The chemical structures were characterized by IR and (1)H NMR spectroscopy, and the degree of substitution (DS) ranged from 0.02 to 0.37. Their fungicidal activity was evaluated against the grey mould Botrytis cinerea Pers ex Fr (Leotiales: Sclerotiniaceae) and the rice leaf blast pathogen Pyricularia grisea Sacc [Teleomorph: Magnaporthe grisea (Hebert) Barr] by a radial growth bioassay. It was of interest that most of the NAC derivatives were more active against both fungi than chitosan itself. The most active derivative was N-(2,2-diphenylethyl)chitosan with EC50 values of 0.031 and 0.23 g L(-1) against B. cinerea and P. grisea respectively. In addition, some derivatives, at higher concentrations up to 1.0 g L(-1), inhibited the mycelial growth and spore formation of P. grisea. Bioassays against larvae of the cotton leafworm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) with the NAC derivatives at a rate of 5.0 g kg(-1) in artificial diet demonstrated that N-(3-phenylbutyl)chitosan was the most active compound. In addition, N-propylchitosan, N-undecanylchitosan and N-(3-phenylpropyl)chitosan derivatives strongly inhibited larval weight gain in S. littoralis, with respective reductions of 76, 66 and 65% after 4 days of feeding on treated diet.     

水稻遗传多样性田间稻瘟病菌生理小种研究

 采用7个中国稻瘟病菌鉴别品种,将来自2000年云南省石屏县水稻品种净栽和混栽田块的62个稻瘟病菌株鉴定为7群15个小种。其中,来自净栽黄壳糯田块的10个菌株被鉴定为4个种群,来自净栽汕优63田块的28个菌株鉴定为3个种群,来自汕优63/黄壳糯混栽田块的24个菌株鉴定为6个种群。本实验结果表明,混栽田块稻瘟病菌生理小种类型比净栽田块丰富,证明了水稻品种多样性种植有利于稻瘟病菌稳定化选择。     

广东水稻橙叶病发病条件及防治研究

离体条件下,植物激素ＮＡＡ和ＡＢＡ对稻瘟病菌的孢子萌芽没有影响,ＡＢＡ对菌丝生长也没有影响,ＮＡＡ对菌丝生长有一定的抑制作用。在稻株上,ＮＡＡ能减轻稻瘟病的发生,且对烯丙异噻唑有增效作用;ＡＢＡ则加重病害的发生,对烯丙异噻唑有拮抗作用。     

三环唑防治稻瘟病的应用技术及防效影响因素研究

在实验室条件下研究了三环唑防治稻瘟病的应用技术与导致药剂防效下降的因素。三环唑喷雾或浸根处理对稻瘟病都有显著防效,浸根处理优于喷雾处理;喷雾或浸根处理后5 d内表现较高防效,持效期达10 d;三环唑处理3 d后再次喷雾处理,不但可以提高防效,还可使持效期延长至15 d;在稻瘟病菌尚未侵入稻苗时用10 μg/mL三环唑喷雾处理,防效达81.3%,在稻瘟病菌完成侵入后再用三环唑处理,10 μg/mL药剂防效仅为35.6%。若水稻叶片有伤口,三环唑对稻瘟病则失去防效。药剂喷雾后1 h内降雨会导致防效显著下降, 3 h后降雨则对防效无影响。     

水稻空间诱变育种抗稻瘟病研究

粤香占和青华占2个水稻品种的种子经过高空气球搭载后,选育出株型好、分蘖力强,产量提高的空间诱变高代(6代以上)品系.为了解空间诱变品系对稻瘟病的抗性变异情况,采用36个广东省稻瘟病菌不同致病型的代表菌株分别对粤香占和青华占及其空间诱变品系进行抗谱测定.研究结果表明:①空间诱变能使水稻品种产生稻瘟病抗性变异,有的诱变品系比原种抗病,有的则比原种感病.②空间诱变产生的抗病性变异比较复杂,不同品种的抗病性变异不一样.③空间诱变引起的稻瘟病抗性变异有可能是由多个抗病基因引起的.④空间诱变可以获得抗稻瘟病的特异种质.粤香占是感病品种,本研究测定的抗谱为25%,从其空间诱变品系中,获得高抗稻瘟病的2个品系YX-8和YX-9,抗谱达到94.4%.空间诱变抗病品系的穗颈瘟鉴定试验正在进行中.     

稻瘟病拮抗菌Xi-55菌株鉴定及其发酵条件

通过对采集样品中细菌的分离获得生防菌Xi-55,经纯化培养后观察形态特征和生理生化特征,经比较鉴定,确定生防菌Xi-55为枯草芽孢杆菌。通过田间试验测定,初步确定了枯草芽孢杆菌Xi-55菌株防治稻瘟病的效果为86%。对该菌株发酵条件进行了研究,确定出最佳发酵技术参数,为微生物农药的开发提供理论依据。     

3种药剂防治水稻纹枯病、稻曲病和稻瘟病田间药效试验

采用田间药效试验方法,比较3种药剂对水稻纹枯病、稻曲病、稻瘟病的防治效果。结果表明:3种药剂对水稻纹枯病、稻曲病、稻瘟病都有一定防效。其中75%肟菌戊唑醇水分散粒剂225 g/hm2对水稻纹枯病、稻瘟病防效最好,防效分别为85.74%、85.19%;43%戊唑醇悬浮剂225 mL/hm2对稻曲病的防治效果最好,防效为88.25%。综合防治效果表明,75%肟菌戊唑醇水分散粒剂150～225 g/hm2对水稻纹枯病、稻曲病、稻瘟病的防效最好,43%戊唑醇悬浮剂225 mL/hm2对稻曲病和纹枯病防治效果较好,在实际生产上可广泛应用。     

鄂、湘、赣、滇、黔、川六省稻瘟病菌有性态的研究

作者对湖北，湖南、江西、云南、贵州和四川六省水稻栽培区１８４个稻瘟病菌Ｍａｇｎａｐｏｒｔｈｇｒｉｓｅａ Ｂａｒｒ菌株（其中３２个采自马唐草）的能育性和交配型进行了测定。结果表明：不同菌株间能育性差别很大，四川和贵州两省菌株有性态的形成率分别为５３％和５０％，而湖北的菌株全部表现不育，测得的所有可育菌株皆属交配型Ａ，杂草菌株有性态子实体形态结构与水稻菌株的十分相似。     

Ultrastructural and cytochemical aspects of silicon-mediated rice blast resistance

ABSTRACT Although exogenous application of silicon (Si) confers efficient control of rice blast, the probable hypothesis underlying this phenomenon has been confined to that of a mechanical barrier resulting from Si polymerization in planta. However, in this study, we provide the first cytological evidence that Si-mediated resistance to Magnaporthe grisea in rice correlates with specific leaf cell reaction that interfered with the development of the fungus. Accumulation of an amorphous material that stained densely with toluidine blue and reacted positively to osmium tetroxide was a typical feature of cell reaction to infection by M. grisea in samples from Si+ plants. As a result, the extent of fungal colonization was markedly reduced in samples from Si+ plants. In samples from Si- plants, M. grisea grew actively and colonized all leaf tissues. Cytochemi-cal labeling of chitin revealed no difference in the pattern of chitin localization over fungal cell walls of either Si+ or Si- plants at 96 h after inoculation, indicating limited production of chitinases by the rice plant as a mechanism of defense response. On the other hand, the occurrence of empty fungal hyphae, surrounded or trapped in amorphous material, in samples from Si+ plants suggests that phenolic-like compounds or phytoalexins played a primary role in rice defense response against infection by M. grisea. This finding brings new insights into the complex role played by Si in the nature of rice blast resistance.