Rice false smut (RFS) caused by Villosiclava virens (anamorph: Ustilaginoidea virens) has become one of the most destructive fungal diseases to decrease the yield and quality of rice grains. An albino strain LN02 was isolated from the white RFS balls collected in the Liaoning Province of China in 2019. The strain LN02 was considered as a natural albino mutant of V. virens by analyzing its phenotypes, internal transcribed spacer (ITS) conserved sequence, and biosynthesis gene clusters (BGCs) for secondary metabolites. The total assembled genome of strain LN02 was 38.81 Mb, which was comprised of seven nuclear chromosomes and one mitochondrial genome with an N50 value of 6,326,845 bp and 9339 protein-encoding genes. In addition, the genome of strain LN02 encoded 19 gene clusters for biosynthesis of secondary metabolites mainly including polyketides, terpenoids and non-ribosomal peptides (NRPs). Four sorbicillinoid metabolites were isolated from the cultures of strain LN02. It was found that the polyketide synthase (PKS)-encoding gene uspks1 for ustilaginoidin biosynthesis in strain LN02 was inactivated due to the deletion of four bases in the promoter sequence of uvpks1. The normal uvpks1 complementary mutant of strain LN02 could restore the ability to synthesize ustilaginoidins. It demonstrated that deficiency of ustilaginoidin biosynthesis is the cause of albinism for RFS albino strain LN02, and V. virens should be a non-melanin-producing fungus. This study further confirmed strain LN02 as a white phenotype mutant of V. virens. The albino strain LN02 will have a great potential in the development and application of secondary metabolites. The physiological and ecological functions of ustilaginoidins in RFS fungus are needed for further investigation.

分别应用3个稻曲病菌菌株ZJ09、XS14、XS1214,以及马铃薯蔗糖琼脂(potato sucrose agar,PSA)固体培养基、马铃薯葡萄糖琼脂(potato dextrose agar,PDA)固体培养基、TB3固体培养基和马铃薯蔗糖(potato sucrose,PS)液体培养基,进行固体或液体培养,实验结果表明补充0.250～0.500 g·L-1 L-半胱氨酸对稻曲病菌菌丝生长具有明显的抑制作用,作用强度随L-半胱氨酸浓度提高而增加.分别采集未补充L-半胱氨酸和补充0.250 g-L1 L-半胱氨酸的PSA固体培养基平板上培养6 d的两组ZJ09菌丝进行转录组测序,得到2 138个差异表达基因(differentially expressed genes,DEGs),其中985个被L-半胱氨酸上调表达,1 153个被L-半胱氨酸下调表达.针对转录组测序结果获得的6个DEGs进行了 RT-qPCR验证.GO富集结果显示,DEGs在细胞组分、分子功能和生物过程3个类别中均有富集,说明L-半胱氨酸抑制菌丝生长机制复杂.KEGG通路注释结果表明,L-半胱氨酸抑制菌丝生长可能主要与其影响内质网中蛋白质的加工有关.分析DEGs功能后还发现,L-半胱氨酸显著削弱菌丝中几丁质合酶D、细胞分裂控制蛋白6(cell division control protein,CDC6)及细胞分裂控制蛋白48(CDC48)编码基因的表达,推测可能与其对稻曲病菌菌丝生长的抑制作用有关.

为了解2019年浙江省小麦赤霉病菌的种群组成及其对杀菌剂的敏感性,调查了浙江省3个地区(杭州市萧山区、杭州市桐庐县、宁波市象山县)麦田的稻桩带菌率和小麦病穗率,利用PCR和DNA测序技术鉴定病菌的种群组成.结果显示,3月份3个地区田间稻桩的赤霉病菌子囊壳携带率为26.4％～55.4％,其释放的子囊孢子能正常萌发长出菌丝并快速形成菌落;小麦田间3月份空气中赤霉病菌游动孢子数量最多,4-5月份数量有所下降;田间小麦于4月份中旬开始出现病穗,4月下旬病穗率快速攀升;从386个分离菌株中随机选择的32个菌株均被鉴定为亚洲镰孢菌(Fusariuimi asiaticum);72个菌株被认定为多菌灵(10 mg·L-1)抗性菌株,约占分离菌株的18.65％.采用菌丝生长速率法检测16个分离菌株对杀菌药剂的敏感性,发现75％肟菌·戊唑醇水分散粒剂和30％唑醚·戊唑醇悬浮剂对分离菌株的EC50值(有效抑制中浓度)均低于5.0 mg·L-1,40％戊唑·咪鲜胺微乳剂和25％氰烯菌酯悬浮剂对分离菌株的EC50 值均低于2.0 μL·L-1,表明上述4种药剂的抑菌效果均良好;进一步对这4种杀菌药剂进行两两混配,检测对16个分离菌株的抑菌效果,发现混配方案"75％肟菌·戊唑醇水分散粒剂"+"30％唑醚·戊唑醇悬浮剂"对分离菌株的抑菌效果最强.

人工接种试验和田间多年自然发病调查发现,目前生产上应用的水稻品种均感稻曲病;但在自然条件下,不同水稻品种稻曲病的发生程度存在较大差异,可以人为的分为多病粒高感品种和寡病粒相对抗病的品种.为了探究水稻穗部性状与其病害抗性间的关系,本文对孕穗期不同阶段的不同水稻品种的穗部性状进行了比较分析.结果 发现表型为多病粒的高感多病粒品种与表型为寡病粒的相对抗病的品种之间在穗子大小、小花密度、穗鞘闭合程度和密封性、旗叶面积等方面均存在明显差异,寡病粒相对抗病的水稻品种穗鞘闭合程度优于高感多病粒品种.

With the aim of exploring the regulating factors and involved mechanisms for the growth of Villosiclava virens mycelia, a strain (ZJ09) of this fungus was cultured on potato sucrose agar (PSA) plates under dark and lighting (with white light from fluorescents) conditions, respectively, and the growth states of the colonies were compared. A significant inhibitory effect was observed by lighting on the growth of V. virens mycelia, which suggested that lighting condition was a regulating factor for the mycelial growth of this fungus. The mycelial samples of the fungal strain ZJ09 from the dark and lighting groups were collected and their transcriptomes were sequenced, respectively. Six hundred and ninety-five differentially expressed genes (DEGs) caused by lighting were identified, including 359 up-regulated genes and 336 down-regulated ones. Six DEGs were selected out to check by real-time quantitative polymerase chain reaction (RT-qPCR) and the expression results were consistent with those by transcriptomic sequencing. During gene ontology (GO) enrichment analysis, 491 of the 695 DEGs were enriched to the terms of biological process, cellular component and molecular function, indicating that complex mechanisms may be involved in the inhibitory effect of lighting on mycelial growth. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis results of the 695 DEGs indicated that influences on the structure and functions of ribosome, and amino acid metabolism were quite probably involved in the inhibitory effect of lighting on mycelial growth. As DEGs included a gene encoding acetyl-coenzyme A synthetase and the lighting condition significantly inhibited its expression, it was inferred that impairing the mycelial acetyl-coenzyme A synthesis ability was one of mechanisms of the inhibitory effect of lighting on mycelial growth. In contrast, as neither of the genes UvHOG1 and UvBI-1 was a DEG, the protein kinase HOG1 (high osmolarity glycerol 1) and Bax inhibitor-1 may both have nothing to do with the inhibitory effect of lighting on mycelial growth.

[目的]近40年来,稻曲病在世界各主要水稻栽培区均表现出发生规模不断扩大、严重程度不断增加的趋势,并逐渐发展成为水稻主要病害之一.前期对低温诱导初期的稻曲球进行切片,发现稻曲球内含有大量隐含菌核.本研究通过转录组高通量测序鉴定低温诱导稻曲病菌(Villosiclava virens)菌核形成的潜在调控基因,阐释菌核形成的分子机制,为揭示稻曲病发生规律及有效防治打下基础.[方法]利用高通量测序技术,对低温诱导处理的稻曲球进行转录组测序(对照组:TL911_1、TL911_2、TL911_3;低温处理组:FH1016_1、FH1016_2、FH1016_3).以稻曲病菌基因组(UV-8b)作为参考基因组进行序列比对,利用FPKM法计算基因表达量,设定参数(|log2 fold change|≥1且q-value≤0.05)筛选差异表达基因.结合基因差异表达分析、基因家族分析和富集分析(Gene Ontology/KEGG Pathway),鉴定稻曲病菌菌核形成关键基因,并利用实时荧光定量PCR (qRT-PCR)技术对其表达量进行验证.[结果]转录组测序共获得59.78 G高质量数据,其中,近93.2％的数据能够比对到稻曲病菌基因组.数据分析共鉴定到8 426个基因存在不同程度表达,占总体基因的97.13％.与对照相比,低温处理可诱导793个基因显著差异表达,分别有398和395个基因表现为上调、下调表达,随机挑选6个基因进行qRT-PCR验证,试验结果与转录组分析一致.在差异表达基因中,共注释到180个(22.7％)基因家族,其中61.67％的基因家族表现为上调表达,主要包括MFS转运蛋白、糖转运蛋白、锌指转录因子等.GO富集分析发现,差异表达基因显著富集于碳水化合物代谢、氧化还原过程、氧化还原酶活性等.KEGG分析发现,差异表达基因显著富集于次生代谢产物生物合成、淀粉蔗糖代谢、糖酵解/糖异生等代谢通路,暗示营养物质代谢和能量代谢途径相关基因表达对于低温诱导菌核形成至关重要.[结论]低温可诱导稻曲病菌菌核形成.低温使机体内部处于氧化应激状态,可通过信号转导途径放大,该过程由多个基因参与并调控多个基因家族成员,最终促使跨膜运输、细胞形态、生物合成等基因的上调表达,使得在形成菌核过程中蛋白表达活跃,达到合成细胞及物质的高峰期,进而促进菌核形成.

False smut of rice, caused by Ustilaginoidea virens, has become one of the most important diseases in rice-growing regions worldwide. The disease causes a significant yield loss and imposes health threats to humans and animals by producing mycotoxins. In this review, we update our understanding of the pathogen, including the disease cycle and infection strategies, the decoding of the U. virens genome, comparative/functional genomics, and effector biology. Whereas the decoding of the U. virens genome unveils specific adaptations of the pathogen in successfully occupying rice flowers, progresses in comparative/functional genomics and effector biology have begun to uncover the molecular mechanisms underlying U. virens virulence and pathogenicity. We highlight the identification and characterization of the produced mycotoxins and their biosynthetic pathways in U. virens.The management strategies for this disease are also discussed. The flower-specific infection strategy makes the pathogen a unique tool to unveil novel mechanisms for the interactions between nonobligate biotrophic pathogens and their hosts.

近年来再生稻一直被作为一种可节支增收的种植方式进行推广,在武义县发现再生稻生育期偏迟,稻曲病等问题比较突出.为此,进行了再生稻主要生育期稻曲病菌厚垣孢子的检测,稻曲病初侵染源数量充分,使用杀菌剂防治是一个必要措施.另外,再生稻一旦发病,容易形成大量的菌核,为来年水稻生产埋下隐患.

SummaryRice false smut has emerged as a serious grain disease in rice production worldwide. The disease is characterized by the transformation of individual rice florets into false smut balls, which is caused by the fungal pathogen Ustilaginoidea virens. To date, little is known about the host factors required for false smut ball formation by U. virens. In this study, we identified histological determinants for the formation of false smut balls by inoculating U. virens into rice floral mutants defective with respect to individual floral parts. The results showed that U. virens could form mature false smut balls in rice floral mutants with defective pistils, but failed to develop false smut balls in the superwoman mutant lacking stamens, identifying that U. virens requires rice stamens to complete its infection cycle. Comparative transcriptome analysis indicated a list of candidate host genes that may facilitate nutrient acquisition by U. virens from the rice stamens, such as SWEET11, SWEET14 and SUT5, and genes involved in the biosynthesis of trehalose and raffinose family sugars. These data pinpoint rice stamens as the key target organ of U. virens infection and provide a valuable starting point for dissecting the molecular mechanism of false smut ball formation.

稻曲病又称伪黑穗病、绿黑穗病、谷花病、青粉病.该病只发生于穗部,为害谷粒.受害谷粒内形成菌丝块,膨大后内外颖裂开,露出淡黄色块状物,后包于内外颖两侧,呈黑绿色.初时外包一层薄膜,破裂后散生墨绿色粉末(即病菌的厚垣孢子).有的两侧生黑色扁平菌核,风吹雨打后易脱落.近三四十年来,我国稻曲病的发生范围和规模呈不断上升趋势,目前,稻曲病已成为水稻的重要病害之一,特别是在长江中下游地区,已成为水稻的主要病害.稻曲病综合的防治技术主要从以下几方面入手.

稻曲病菌在水稻孕穗期侵染水稻小花,在水稻灌浆后期只在个别稻曲球上形成菌核.因此,稻曲病菌菌核分化与发育基因功能研究的相关试验难度较高.为了探究稻曲病菌在人工培养基上能否形成菌核,本文利用低温或杀菌剂环境对稻曲病菌进行了筛选.结果发现,在81个菌株中有13个在人工培养基上形成拟菌核组织,且它们可在低温处理时稳定地产生拟菌核组织.这些拟菌核组织在结构上与菌核类似,但体积较小且组织较为疏松,无法像菌核一样越冬和完成有性生殖.

In recent years, false smut disease of rice has been one of the most important diseases of cultivated rice in China. Ustilaginoidea virens is an ascomycete fungal pathogen that causes false smut in rice. There is always controversy about whether the pathogen can infect the rice root and cause the occurrence of false smut, mainly due to lack direct cytological evidence. In our study, we observed the cytological structure of rice root invaded by U. virens. The results showed that U. virens could attach to the surface of young roots and penetrate into the intercellular space of the root epidermis. The cellulose microfibrils in root epidermal cell wall are very loose and soft, and their structural features are similar to filaments of rice. After the fungus infected the roots, a large number of fungal secretions were accumulated outside of the cell walls. At 40 days, the fungus began to degrade, but pathogens still had not infected the sclerenchyma, in which the cells are arranged densely and the cell walls are thicker. U. virens could not cross the sclerenchyma layer into the endodermis and phloem of the root. To some extent, the U. virens infection affected the leaf and root growth of the rice. After inoculation, there was no fungal mycelium found in transverse sections of the rice young stem. These results suggested that root colonization of U. virens does not lead to systemic invasion in rice.

Rice false smut is heavily and increasingly occurring in subtropical zones in China in the past decades. The pathogen of the disease, Ustilaginoidea virens, can produce both chlamydospores and sclerotia, and the sclerotia seem to form frequently in temperate or high-altitude regions in China. Which of these structures play a dominant role in the pathogen’s life cycle in subtropical zones remains unclear. Here we found that Ustilaginoidea virens could produce a great number of sclerotia in subtropical zones and the maximal number of sclerotia could reach to 2.25 million per hectare. In the year with relatively low autumn temperatures, the disease severity and sclerotia numbers of U. virens increased significantly. Although there was a few sclerotia in subtropical zones capable of overwintering successfully, one individual sclerotium could produce large numbers of ascospores. In the rice-growing paddy field, the ascospores could be trapped in both temperate and subtropical zones in May–September, when rice was at the booting stage, the critical infection period of rice false smut. This suggested that the sclerotia of rice false smut in subtropical zone played an important role in the life cycle of Ustilaginoidea virens and acted as the primary inoculum. Experiments in the laboratory showed that mature sclerotia of rice false smut remained dormant for about 2–5 months, and that light was essential for fruiting body differentiation. As with ergot, the fruiting bodies of Ustilaginoidea virens secreted sticky droplets on the stromata that prevented the ascospores from dispersing into the air, implying that the transfer of ascospores of Ustilaginoidea virens to rice plants in paddy field needed an intermediary vector.

In the past decades,rice false smut has occurred increasingly and now become one of the major rice diseases in China from a minor disease in history.Recently extended studies on the disease have revealed some new findings on the fungal pathogenicity,its life cycle and control of the disease.The pathogen mainly infects rice stamen filaments and other flower tissues where cell walls are loose in texture,and extends intercellularly in host.The pathogen sclerotia play an important role in the disease occurrences in the mid and lower reaches of the Yangtze River and in its life cycle as the primary inoculum.Spraying fungicides at early rice booting stage now is the most effective measure for controlling the disease.Clarification of the pathogen life cycle in nature in the near future is necessary for establishing the prediction and early warning system in medium-and long-term disease control.

稻曲病菌(Villosiclava virens)可侵染水稻(Oryza sativa)引发稻曲病而导致水稻显著减产,还可产生对动物和植物都有害的毒素.目前对稻曲病菌毒素的植物毒性机理尚不清楚.本研究首先发现稻曲球水溶性粗毒素对水稻幼苗的根和叶片的生长都具有明显的抑制作用,对根的抑制作用更甚于对叶片的抑制作用.进而以稻曲球水溶性粗毒素处理水稻幼根,利用高通量测序技术进行转录组分析,得到2 665个差异表达基因(differentially expressed genes,DEGs).对DEGs进行基因本体(Gene Ontology,GO)富集分析,在细胞成分的分类(term)中,囊泡和胞外区富集的DEGs最多;在生物过程的分类中,胁迫响应和氧化还原过程富集的DEGs最多;在分子功能的分类中,氧化还原酶活性和转移酶活性富集的DEGs最多.对DEGs进行京都基因与基因组百科全书(Kyoto Encyclopedia of Genes and Genomes,KEGG)通路(Pathway)富集的结果表明,稻曲病菌毒素处理对糖代谢、氨基酸代谢和次生物质代谢有较大影响.经分析发现,DEGs中有62个植物转录因子家族,分属于7种植物转录因子,其中5种参与调控植物对生物胁迫的抗性.实验结果也表明,稻曲球粗毒素明显下调15个植物抗病蛋白编码基因的表达.上述实验结果表明,稻曲病菌毒素主要通过干扰水稻幼根呼吸作用而影响能量供应,通过干扰氨基酸代谢而影响蛋白质合成,进而抑制水稻幼根的生长.此外,本研究推测稻曲病菌在侵染水稻的过程中,可能通过分泌毒素来下调某些水稻抗病蛋白的表达,以降低水稻抵抗稻曲病菌入侵的能力,从而利于稻曲病菌在水稻组织内生存并扩展.本研究为深入探讨稻曲病菌毒素对植物产生毒性的机理提供了基础资料.

The fungus Villosiclava virens infects dominantly rice stamen filaments and some lodicules resul-ting in rice false smut.Here we examine the ultrastructures of the cell walls of various organs in rice spikelets around the anthesis to explore the specificity for infection.The inoculation was performed in rice cultivar,'Yongyou 12',a high susceptible cultivar,and the infected spikelets were sampled at 5,10,and 15 days after inoculation.The results showed that:(1)the stamen filament cells could elongate integrally for 4-6 folds,and the peripheral cells in top of lodicula could elongate significantly during flowering.(2) Microfibrils in those cell walls arranged loosely and could be clearly distinguished with transmission elec-tronic microspcope.Conversely,the cell walls in ovaries,stigmas,and anthers were compact and the mi-crofibrils could not be discerned.(3 )The pathogen could grow in different orientations in both cell gaps and cell wall middle lamella in the stamen filaments,but its extension in the lodicula was limited mainly in cell gaps.This indicates that the structure and components of middle lamella in filaments and lodicula are different.(4)Cytochemical labeling revealed that there was less cellulose and noβ-1 ,3-glucane in the cell walls of stamen filaments.These suggest that the ultrastructure and components in cell walls and middle lamella in various organs in rice spikelets are highly related to the specificity of infection by the pathogen.

Rapeseed is an oil crop with quite large growing areas in China, and also one of the main oil crops in the world. As one of the most serious diseases in rapeseed, Sclerotinia disease, caused by the fungal pathogen Sclerotinia sclerotiorum, can result in significant yield loss. At present, no rape cultivars are available that are resistant to S. sclerotiorum. Using fungicides is the main measure to control rapeseed Sclerotinia disease in China. Carbendazim, as a common fungicide, has been frequently applied to control rapeseed Sclerotinia disease for long. Increasing evidence of fungicide resistance in populations of S. sclerotiorum has been found. Therefore, new fungicides are constantly being requested to control rapeseed Sclerotinia disease. Acetolactate synthase (ALS) is the enzyme that catalyzes the first step in the branched-chain amino acid biosynthesis pathway in plants and microbes, and is the target of some herbicides. Recently, some studies have reported the development of new antibiotics to control bacterial pathogens or new fungicides to control fungal pathogens of human beings with ALS as the action target. However, there are few studies on developing new fungicides to control fungal pathogens of plants with ALS as the action target. In the present study, seven potential ALS inhibitors (chlorimuron-ethyl, bensulfuron-methyl, chlorsulfuron, sulfometuron-methyl, imazethapyr, imazaquin and sulfathiazole) were used to determine the effectiveness of controlling rapeseed Sclerotinia disease. Chlorimuron-ethyl, bensulfuron-methyl, chlorsulfuron and sulfometuron-methyl were chosen as the representatives of sulfonylurea-type ALS inhibitors. Imazethapyr and imazaquin were the representatives of imidazolinone-type ALS inhibitors, and sulfathiazole was the representative of sulfathiazole-type ALS inhibitors. The results indicated that the activity of ALS in S. sclerotiorum could not been inhibited by 1.0 mg/L imazethapyr. In contrast, the treatment with 1.0 mg/L chlorimuron-ethyl, bensulfuron-methyl, chlorsulfuron, sulfometuron-methyl, imazaquin and sulfathiazole showed more or less inhibitory effects on the ALS activity of S. sclerotiorum. Among them, imazaquin had the strongest inhibitory effect on ALS, but sulfometuron-methyl showed the weakest inhibitory effect. Imazaquin and sulfathiazole could effectively suppress the growth of S. sclerotiorum colony on potato dextrose agar plates at the concentration of 0.1 mg/L. Chlorimuron-ethyl, bensulfuron-methyl and chlorsulfuron had inhibitory effect at the concentration of 1.0 mg/L. However, sulfometuron-methyl and imazethapyr showed weak inhibitory effect on the growth of S. sclerotiorum colony even at the concentration of 50 mg/L. The half-maximal effective concentrations (EC50) of imazaquin, sulfathiazole, chlorimuron-ethyl, bensulfuron-methyl and chlorsulfuron were determined to be less than 10 mg/L, but EC50 values of sulfometuron-methyl and imazethapyr were determined to be more than 50 mg/L. All the seven potential ALS inhibitors showed inhibitory effects on the activity of ALS in rapeseed leaves at the concentration of 1.0 mg/L. The inhibitory effects of chlorimuron-ethyl, bensulfuron-methyl, chlorsulfuron, imazaquin and sulfometuron-methyl were much stronger than those of imazethapyr and sulfathiazole. The inhibitory effect of sulfathiazole was the weakest among the seven inhibitors. Significant damaging influences were observed on rapeseed seedlings by using chlorimuron-ethyl, bensulfuron-methyl, chlorsulfuron, imazaquin, sulfometuron-methyl and imazethapyr at the concentration of 1.0 mg/L, such as decreasing growth rate, dwarfing, reducing leaf size and leaf yellowing, but no significant influences were observed by treating rapeseed seedlings with sulfathiazole. The use of sulfathiazole could exert remarkable inhibitory effects against ALS activity and colony growth of S. sclerotiorum without giving rise to harmful influence on rapeseed seedlings. Thus, the effect of sulfathiazole on S. sclerotiorum infection to rapeseed was tested. The result indicated that the treatment with sulfathiazole significantly reduced the infection scale of S. sclerotiorum in rapeseed leaves. In conclusion, the present research indicated that S. sclerotiorum was sensitive to imazaquin, sulfathiazole, chlorimuron-ethyl, bensulfuron-methyl and chlorsulfuron other than sulfometuron-methyl and imazethapyr. On the other hand, rapeseed was sensitive to all the seven ALS inhibitors but imazethapyr and sulfathiazole. It is suggested that sulfathiazole treatment is an effective strategy to control rapeseed Sclerotinia disease caused by S. sclerotiorum. Therefore, this study concludes that sulfathiazole is a potential molecular structure basis for controlling rapeseed Sclerotinia disease with ALS of S. sclerotiorum as an action target.

Rice false smut, caused by the fungal pathogen Villosiclava virens, is one of the most important rice diseases in the world. Previous studies reported that the pathogen has less number of cell wall-degraded genes and attacks dominantly rice stamen filaments and extends intercellularly. To reveal why the fungus infects plant stamen filaments, inoculation test on barley was carried out with the similar protocol to rice. The experimental results showed that the fungus could penetrate quickly into barley stamen filaments and extends both intracellularly and intercellularly, usually resulting in severe damage of the stamen filament tissues. It also attacked young barley lodicules and grew intercellularly by chance. The light microscopic observations found that the epidermal and cortex cells in barley stamen filaments arranged loosely with very thick cell walls and large cell gaps. Cellulose microfibrils in barley stamen filament cell walls arranged very sparsely so that the cell walls looked like transparent. The cell walls were very soft and flexible, and often folded. However, V. virens extended dominantly in the noncellulose regions and seemed never to degrade microfibrils in barley and rice cell walls. This suggested that the unique structures of rice and barley stamen filaments should be fit for their function of elongation in anthesis, and also endow with the susceptibility to the fungus, V. virens.

菌核是稻曲病菌天然的越冬菌源和来年病害发生的重要初侵染源,控制田间菌核越冬数量能够从源头上遏制和减轻稻曲病的发生.为此,本研究对来自稻田土壤、菌核表面、以及青海高原的能够降解菌核的真菌进行了筛选,得到了6个有较好降解作用的生防菌株.在实验室条件下它们能够在30～70 d内彻底降解稻曲病菌菌核.真菌形态特征和rDNA-ITS序列分析表明,这些菌株分别为淡色生赤壳菌Bionectria ochroleuca、粘鞭霉Gliomastix polychroma、烟曲霉spergillus fumigatus、草酸青霉Penicillium oxalicum、粉红粘帚霉Gliocladium spp.和疣孢漆斑菌Myrothecium verrucaria.进一步超微结构观察发现,不同生防菌对菌核的降解机制可分为以重寄生作用和直接降解为主2种基本模式.春季田间撒施试验表明,其中2种生防菌的防治效果可达33.9％和46.8％.

The sclerotia of Villosiclava virens were found commonly in high altitude and the temperate regions, where the temperatures are relatively low in rice filling stage. To make sure if low temperature induce the sclerotial formation in V. virens, the inoculated rice panicles in laboratory and the diseased rice panicles cut from paddy fields were treated under different temperatures. The results showed that 3 days of night temperature at 15°C were enough to induce the sclerotial formation. The low temperature was much more effective for young balls with intact membranes. After appearance of chlamydospores on the ball surfaces, the sclerotium could not differentiate anymore. The sclerotia began to differentiate below the chlamydospore layer and gradually grew onto the ball surfaces. This suggests that low temperature in the early development stage of false smut balls is an important factor to induce the sclerotial differentiation, and rice cultivars with long growth periods are able to produce more sclerotium-bearing balls, which will produce mass of spores in paddy field in the coming year.