Nutritional requirements of the mycoparasitic fungus Verticillium biguttatum

Verticillium biguttatum was able to grow axenically in a synthetic liquid medium with a compound containing ammonium or amino group as nitrogen source, glucose as carbon source and biotin as growth factor. Among various carbon and nitrogen compounds tested, highest mycelial production was achieved with mannitol and with two ammonium salts and glutamine; sporulation reached highest values with galactose and glutamine. Highest yields of mycelium and conidia were obtained at pH 4.3 and 5.1, respectively. Although neutral and alkaline conditions were growth-limiting in the synthetic medium some growth ofV.biguttatum occurred on solid media at pH 7.0 and on sclerotia ofRhizoctonia solani in natural soil at pH 7.2–7.3.Samenvatting Een synthetisch vloeibaar medium met glucose als koolstofbron, een ammonium- of aminogroep bevattende verbinding als stikstofbron en biotine als groeifactor voldeed aan de voedingseisen vanVerticillium biguttatum. Van de verschillende koolstof- en stikstofbronnen leverden mannitol en twee ammoniumzouten en glutamine de hoogste opbrengsten aan mycelium; de opbrengst aan conidiën was het hoogst met galactose en glutamine. De hoogste opbrengsten aan mycelium en conidiën werden bereikt bij respectievelijk pH 4,3 en 5.1. Ofschoon neutrale en alkalische omstandigheden de groei vanV. biguttatum in het synthetische medium beperkten, werd enige groei vanV. biguttatum waargenomen op vaste voedingsbodems bij pH 7,0 en op sclerotia vanR. solani in natuurlijke grond bij pH 7,2–7,3.     

Biotrophic mycoparasitism byVerticillium biguttatum onRhizoctonia solani

Verticillium biguttatum cannot utilise cellulose or nitrate-nitrogen and it requires biotin for growth, yet it grew and sporulated abundantly onRhizoctonia solani on cellulose, obtaining at least organic carbon, nitrogen and biotin fromR. solani. Videomicroscopy of inter-hyphal interactions on films of water agar showed thatV. biguttatum behaved as a biotrophic mycoparasite. From germinating spores, it penetrated the hyphae ofR. solani and formed haustorium-like branches without killing the host cells, and the haustoria supported an external mycelial network of the mycoparasite. Later the mycoparasite sporulated, and the infected host cells died. On cellulosic substrataV. biguttatum did not reduce the growth ofR. solani, and often enhanced the rate of cellulose degradation. However,V. biguttatum drastically reduced the production of sclerotia byR. solani, often completely suppressing sclerotium production when the mycoparasite infected only a localized region of the host colony. This is ascribed to the creation of a nutrient sink by the parasite, consistent with biotrophy. On plates of cellulose agar the suppression of sclerotia was not confined to parasitized colonies but extended to adjacent colonies ofR. solani that had successfully anastomosed with the parasitized colony. There was no effect on adjacent vegetatively incompatible colonies, where attempted anastomoses caused cytoplasmic death. In comparable experiments the necrotrophic mycoparasiteGliocladium roseum had no long-distance effect on sclerotium production byR. solani.Suppression of sclerotium production may explain the reported success ofV. biguttatum in biocontrol of black scurf of potato in experimental field conditions.     

Biological destruction of conidia ofVerticillium biguttatum

Because biological control ofRhizoctonia solani in potato with conidial suspensions of the mycoparasiteVerticillium biguttatum was often less successful in sandy soils than in loamy soils, we examined soils of potato fields for the presence of organisms destructive to conidia ofV. biguttatum.Representatives of conidiophagous testate amoebae were frequently present on sclerotium disks ofR. solani infected withV. biguttatum in all soils studied and were most active under moist conditions. Conidiophagous naked amoebae were also numerous, except for two loam soils, and were not sensitive to moist conditions. Conidiophagous ciliates were found in rather low numbers and were most frequently isolated from coarsely structured soils under moist conditions. Conidiophagous flagellates were very infrequently observed.A bacterial type, parasitizing and killing conidia and hyphae ofV. biguttatum, was observed in all soils studied. It produced clusters of cocci fixed to the outside of conidia and hyphae and was most active under moist soil conditions.The possible role of protozoan predators and bacterial parasites in the biological control ofR. solani in potato withV. biguttatum applied at planting is discussed.     

寡雄腐霉GAQ1对辣椒疫病的防效及对辣椒的促生作用

为明确自主分离的生防菌株寡雄腐霉Pythium oligandrum GAQ1对辣椒疫病的生防效果及其防御机制,通过平板拮抗和盆栽防效试验测定寡雄腐霉菌株GAQ1对辣椒疫霉Phytophthora capsici菌丝的拮抗作用、对辣椒疫病的防效和对辣椒的促生效果,同时应用实时荧光定量PCR技术检测菌株GAQ1处理后辣椒抗性基因表达的变化。结果表明,寡雄腐霉菌株GAQ1的菌丝可以缠绕并吸附寄生在辣椒疫霉菌丝表面或穿入菌丝体内,使辣椒疫霉菌丝细胞死亡;菌株GAQ1发酵液处理辣椒离体叶片再接种辣椒疫霉后产生的病斑直径较对照组显著减少,离体防效为30.79%;接种菌株GAQ1菌丝球后,辣椒疫病的病情指数较对照组显著降低,盆栽防效达69.16%;经菌株GAQ1处理辣椒后可诱导相关抗性基因PR1、WRKY40、WRKY53、ACCO和GST的相对表达量出现不同程度的升高,说明菌株GAQ1可诱导辣椒植株产生不同程度的防御系统应答。菌株GAQ1对辣椒具有良好的促生效果,处理后第5周其株高、株重及根重分别较对照组提高10.11%、33.23%和24.72%,其叶片中叶绿素a、叶绿素b及类胡萝卜素的含量分...     

楚雄腮扁叶蜂虫生真菌粉红粘帚霉的鉴定及其生物学特性

为明确楚雄腮扁叶蜂Cephalcia chuxiongica病原真菌的种类,以组织分离法对自然罹病死亡的楚雄腮扁叶蜂进行虫生真菌的分离培养,根据形态学特征和rDNA ITS序列分析对所得虫生真菌进行鉴定,并对其中的高毒力菌株进行生物学特性测定。结果表明:共分离得到4属25株菌株,其中以粉红粘帚霉Clonostachys rosea出现频率最高,共分离到15株,均与GenBank中粉红粘帚霉相关菌株亲缘关系最近,ITS序列同源性达100%,属优势种。按照柯赫法则证实4个属的虫生真菌对楚雄腮扁叶蜂均有致病力,其中粉红粘帚霉致病力最强,其高毒力菌株SWFUYHL 02-01对楚雄腮扁叶蜂幼虫致死中时为10 h;蛋白胨马铃薯葡萄糖琼脂培养基最适宜该菌株生长和产孢,其次是马铃薯葡萄糖琼脂培养基;该菌的最适生长温度为25℃,光照对其菌丝生长无显著影响;在以不同种类糖为碳源的培养基上该菌株均能生长,以蔗糖为碳源的培养基上产孢量最高,显著高于以其它糖为碳源时;适宜其生长的氮源是酵母浸出粉,适宜产孢的氮源是硝酸铵和尿素,以硫酸铵和酵母浸出粉为氮源时不产孢;适宜菌丝生长和产孢的无机盐分别是MnSO_4和MgSO_4,添加CaCl_2的培养基上未见产孢;光照对粉红粘帚霉孢子萌发无显著影响。粉红粘帚霉菌株在采样点的出现频率与其生物学特性完全吻合。     

Inhibition of in vitro growth of <Emphasis Type="Italic">Rhizoctonia solani</Emphasis> by liquid residue derived from steam-treated grass clippings

The effects of liquid residue derived from grass clipping after steam-treatment on the in vitro growth of Rhizoctonia solani SN-1, AG-4 were evaluated to verify the antifungal activities of the residue. The liquid residue inhibited R. solani growth, with increasing inhibition with higher concentrations and lower pH. Test of individual organic acids (acetic, formic and propionic acids) present in the residue indicate that the inhibitory effect may be attributed to the organic acids, and the effect of the organic acids seems to depend on pH, especially at lower concentrations.     

水稻与纹枯病菌互作的分子机制研究进展

水稻纹枯病是由死体营养型真菌立枯丝核菌Rhizoctonia solani AG1-IA亚群引起的一种土传病害,在世界水稻种植区均有发生,是限制水稻高产的主要病害之一。虽然国内外学者针对纹枯病菌已开展了大量的研究工作,但由于该菌寄主范围较广、抗性水稻资源缺乏及其田间抗性鉴定的不稳定性等问题,该病害的研究仍没有取得突破性进展。挖掘自然界中存在的纹枯病抗源材料,选育抗病水稻品种是防控该病害、降低水稻产量损失,从而最大限度保障全球水稻产业可持续发展的有效手段。该文对近年来国内外关于水稻纹枯病菌与寄主的互作分子机制、抗性水稻基因资源挖掘及其抗性机制的最新研究进展进行综述,并提出下一步的重点研究方向,以期为推动水稻对纹枯病的抗性机制解析及抗纹枯病水稻育种提供参考。     

Characterization ofRhizoctonia solani isolates from potatoes in turkey and screening potato cultivars for resistance to AG-3 isolates

A total of 304Rhizoctonia solani isolates and 60 binucleateRhizoctonia-like fungi were recovered from stems and tubers of infected potato plants over a 2-yr period in northeast Turkey.R. solani isolates were identified to 11 anastomosis groups (AGs): AG-1 (0.66%), AG-2-1 (5.6%), AG-2-2 (0.99%), AG-3 (83.9%), AG-5 (4.6%), AG-6 (0.66%), AG-8 (1.32%), AG-9 (0.33%), AG-10 (1.32%), AG-12 (0.33%), and AG-13 (0.33%). In the greenhouse tests, most of the AG-3 isolates were significantly more virulent than isolates belonging to other AGs on potato cv. Batum. Isolates of other anastomosis groups differed in their virulence. Results indicated that AG-3 is an important pathogen on potatoes grown in the study area. Five of 22 commercial and local potato cultivars evaluated for their reaction toR. solani AG-3 isolates (TP-2) under greenhouse conditions were highly resistant; the remaining cultivars exhibited different levels of susceptibility to the pathogen isolate. http://www.phytoparasitica.org posting July 14, 2005.     

Characterization of Rhizoctonia Species Associated with Foliar Necrosis and Leaf Scorch of Clonally-propagated Eucalyptus in Brazil

The objective was to identify and characterize the causal agent of foliar necrosis and leaf scorch of Eucalyptus spp. in Brazil. Nineteen putative isolates of Rhizoctonia obtained from Eucalyptus plants during clonal propagation were compared with isolates from other hosts and with tester strains of anastomosis groups of Rhizoctonia solani. Features compared were morphological characteristics of anamorphs and teleomorphs, numbers of nuclei per cell in the vegetative hyphae, anastomosis of hyphae, and ability to produce necrotic lesions on cuttings and damping-off of E. grandis×E. urophylla hybrid seedlings. Rhizoctonia solani AG1 (AG1-IB like) was the most frequent causal agent isolated from Eucalyptus plants and cuttings with symptoms of leaf scorch and foliar necrosis respectively. These isolates were highly virulent on Eucalyptus cuttings and presented naturally epiphytic growth on Eucalyptus shoots. Binucleate isolates and isolates of R. solani AG4 were also virulent on cuttings and were most virulent on Eucalyptus seedlings causing pre- and post-emergence damping-off. Virulence on Eucalyptus cuttings and seedlings was not restricted to a single species or anastomosis group of Rhizoctonia.     

Investigations on the effect of haulm destruction and additional root cutting on black scurf on potato tubers

In greenhouse experiments factors which are involved in the stimulation of sclerotia formation byRhizoctonia solani Kühn on potato tubers after haulm destruction were investigated. Cutting off the shoot stimulated the production of sclerotia as much as chemical haulm destruction. This was also observed when potato tubers were grown away from the roots in a separate compartment filled with steamed perlite. Fewer sclerotia were produced when roots were cut in addition to haulm destruction compared to haulm destruction alone. Cutting off the roots alone often stimulated sclerotia production. The data indicate that sclerotia production was directly affected by the tuber and probably due to physiological changes in the tuber caused by elimination of the shoot.Samenvatting In kasproeven werd onderzocht welke factoren betrokken zijn bij de stimulering van de produktie van sclerotiën op aardappel doorRhizoctonia solani Kühn als gevolg van loofvernietiging. Afknippen van het loof stimuleerde de vorming van sclerotiën evenzeer als chemische vernietiging. Na afknippen van het loof trad de stimulering ook op bij knollen, die zich ruimtelijk gescheiden van de wortels in gestoomd vochtig perliet konden ontwikkelen. Doodspuiten plus doorsnijden van de wortels resulteerde in minder lakschurft dan doodspuiten alleen. Wanneer alleen de wortels werden doorgesneden resulteerde dat vaak in meer lakschurft. De vorming van sclerotiën wordt dus direct door de knol beïnvloed. Dit effect lijkt voort te komen uit fysiologische veranderingen in de knol.     

Biological control of Rhizoctonia solani on potatoes by antagonists. 4. Inoculation of seed tubers with Verticillium biguttatum and other antagonists in field experiments

Inoculation of seed potatoes with the mycoparasiteVerticillium biguttatum, isolate M73 (combined withGliocladium roseum in 1981, either alone or mixed with isolate M180 plus antibiotics-producing isolates ofAzotobacter chroococcum in 1982) repeatedly proved successful in reducingRhizoctonia solani on stolons and stems. In field experiments, this ultimately led to a reduced formation of sclerotia on new tubers, particularly in neutral sandy loam and clay loam soils. In 1981 inoculation with antagonists led, when compared with no inoculation, to average reductions of 22 and 42% for the harvest from clean, and 15 and 26% for the harvest from infected seed tubers grown on slightly acid sandy soils and on neutral loam soils, respectively. The harvest from clean, inoculated seed tubers had the lowest sclerotium index. In 1982 inoculation of seed tubers planted in slightly acid sandy soils gave reductions of the sclerotium index of up to 22%. In the neutral marine loam soils considerable reductions were often achieved, viz., in slightly infected loams 51–68% and in rather heavily infected ones 4–43%. Chemical disinfection of seed tubers proved effective only in loam soils that were slightly infested withR. solani. In both years inoculation of seed tubers with antagonists led to significantly lower sclerotium indices of the harvest (p=0.1% in 1981; p=5% in 1982). V. biguttatum was present more frequently and in greater densities on stems and stolons of plants from inoculated than from non-inoculated seed tubers. The latter were colonized by wildV. biguttatum strains from the soil, apparently less effective antagonists.Early in the season, the soil temperature was too low for growth ofV. biguttatum. Nevertheless, inoculation of tubers that were planted early resulted in a considerable cotrol ofR. solani.Samenvatting Het beënten van poters met de opRhizoctonia solani parasiterende schimmelVerticillium biguttatum isolaat M73 in combinatie metGliocladium roseum (1981) of metV. biguttatum M73 alleen of in combinatie met isolaat M180 plus antibiotische isolaten van de bacterieAzotobacter chroococcum (1982), bleek effectief in het terugdringen of het onderdrukken vanR. solani op stengels en stolonen en het verminderen van de aantasting.Beënting van het pootgoed leidde tot een vermindering van de sclerotium (lakschurft)-vorming op de nieuwe knollen, vooral in klei-en zavelgronden. In 1981 leidde beënting van poters tot reductie in de sclerotiumvorming van gemiddeld 22 en 42% voor de oogst uit schoon en 15 en 26% voor de oogst uit besmet pootgoed geteeld op respectievelijk zandgrond en klei- en zavelgrond.In 1982 leidde beënten van de poters uitgeplant in licht zure zandgrond tot een gemiddelde reductie van de sclerotiumindex van de oogst van 22%. In zwaar besmette zandgrond trad evenwel geen reductie op; de infectiedruk was hier te groot. In de neutrale zavel- en kleigronden, vaak ook in de zwaarder besmette percelen werden aanzienlijke reducties bereikt, in de licht besmette gemiddeld 51–68% en in de zwaarder besmette 4–43%. Ontsmetten van pootgoed bleek alleen effectief in percelen die licht metR. solani waren besmet.In beide jaren bleek beënten van pootgoed met antagonisten te resulteren in een significant lagere sclerotiumindex van de oogst (p=0,1% in 1981; p=5% in 1982). V. biguttatum was veel vaker en meer aanwezig op de ondergrondse stengeldelen en stolonen van planten uit beënt pootgoed dan op die van niet beënte poters. De laatsten werden gekoloniseerd door wilde stammen vanV. biguttatum uit de grond, die vaak minder effectieve antagonisten waren. Beënting van vroeg gepote knollen — als de temperatuur nog te laag is voor de groei vanV. biguttatum — leverde toch gunstige resultaten op.     

Contribution to the taxonomy and pathogenicity of fungicolous Verticillium species. I. Taxonomy

The genusVerticillium is divided into four sections (two new) and a residual group. The new sectionNigrescentia comprises the well-known plant-pathogenic and some other saprophytic species with dark resting structures. The new sectionAlbo-erecta is characterized by white (or yellowish) colonies and erect conidiophores and contains mainly fungicolous species. Seven (two new) species and two new varieties are described and keyed out. Three other species have known teleomorphs ofNectriopsis (one new and two new combinations). This genus had been merged withNectria by Samuels, but its retention is justified, as the original and the here described fungicolous (and myxomyceticolous) species are more suitably accomodated inNectriopsis than inHypomyces.The common causal agent of dry bubble inAgaricus bisporus, Verticillium fungicola var.fungicola, is redescribed and defined more narrowly than by Gams (1971) by its maximum growth temperature below 27°C. A similar fungus with a maximum growth temperature near 33°C, causing brown spots inA. bitorquis, is described asV. fungicola var.aleophilum. Isolates from wild agarics with a strongly reduced growth at 24°C and a maximum below 27°C, a yellowish mycelium and inconspicuous sclerotia, are described asV. fungicola var.flavidum. V. biguttatum W. Gams,sp. nov., with cylindrical biguttulate conidia, is a common soil fungus and hyperparasite ofRhizoctonia solani. Gliocladium microspermum (Sacc.) W. Gams,comb. nov., the anamorph ofNectriopsis broomeana (Tul.) W. Gams,comb. nov., which is intermediate betweenGliocladium andVerticillium, is included because of its fungicolous habit.Samenvatting Het geslachtVerticillium wordt onderverdeeld in vier secties (waaronder twee nieuwe) en een restgroep. De nieuwe sectieNigrescentia bevat onder meer de bekende ziekteverwekkende soorten met donkere ruststructuren. De nieuwe sectieAlbo-erecta wordt gekarakteriseerd door witte (of geelachtige) kolonies en rechtopstaande conidioforen en bevat hoofdzakelijk op andere fungi groeiende soorten. Zeven soorten (waaronder twee nieuwe) en twee nieuwe variëteiten worden beschreven en in een sleutel verwerkt. Drie andere soorten bezitten perfecte vormen vanNectriopsis (waaronder één nieuwe en twee nieuwe combinaties). Dit geslacht werd door Samuels metNectria samengevoegd, maar kan gehandhaafd worden en lijkt beter geschikt om de hier beschreven ascomyceten onder te brengen danHypomyces. Verticillium fungicola var.fungicola, de algemene veroorzaker van droge mollen bij de champignon (Agaricus bisporus), wordt beschreven en met zijn temperatuur-maximum beneden 27°C nauwkeuriger gedefiniëerd dan in een vroegere studie (Gams, 1971). Een vergelijkbare schimmel met een temperatuurmaximum van ongeveer 33°C, die bijA. bitorquis bruine vlekken veroorzaakt, wordt beschreven alsV. fungicola var.aleophilum. Isolaten van wilde paddestoelen met een optimum duidelijk beneden 24°C en een maximum beneden 27°C, geelachtig mycelium en onopvallende sclerotiën, worden beschreven alsV. fungicola var.flavidum. V. biguttatum W. Gams, sp. nov., met cilindrische, biguttate conidiën, is een algemene grondschimmel en hyperparasiet vanRhizoctonia solani. Gliocladium microspermum (Sacc.) W. Gams, comb. nov., de imperfecte vorm vanNectriopsis broomeana (Tul.) W. Gams, comb. nov., een tussenvorm tussenGliocladium enVerticillium, wordt opgenomen wegens zijn voorkomen op vruchtlichamen van de dennemoorder.     

Biocontrol ofRhizoctonia damping-off of cucumber by non-pathogenic binucleateRhizoctonia

Three isolates of binucleateRhizoctonia (BNR) were tested for biological control of damping-off of cucumber seedlings caused byRhizoctonia solani AG 2-2 and AG 4. BNR isolates L2 (AG Ba) and W1 and W7 (AG A) provided protection of 58 to 71% against virulent isolate C4 of AG 4 and 64 to 75% protection against virulent isolate RH 65 of AG 2-2. Varying protection was provided to the seedlings by the BNR isolates against the virulentR. solani from the two AGs depending on their combination. The BNR isolates did not vary in providing protection to the seedling when tested against virulent C4 when both isolates were inoculated using three different methods,viz. in water agar, combination of water agar and soil and using soil alone. Protection of 58 to 71 % was provided by the isolates when inoculation was done on the hypocotyl using water agar, 62.8 to 75% using the combination of water agar and soil, and 75 to 85% when inoculation of both isolates was done in soil. Pre-incubation of BNR W7 or delayed inoculation of C4 (from 0.5 day to longer duration) using the different methods provided an increased protection to the seedlings to give complete inhibition of damping-off disease. Simultaneous inoculation of both BNR W7 and C4 using the three methods failed to provide protection to the seedlings. Among the BNR isolates, BNR W7 showed plant growth promotion in terms of significant increase in plant height (P=0.01) and fresh weight (P=0.05).     

山东省玉米纹枯病菌对噻呋酰胺的敏感性及其抗性突变体的生物学性状

为明确山东省玉米纹枯病菌对噻呋酰胺的敏感性及其抗药性风险,采用菌丝生长速率法分别测定了采自山东泰安、临沂、潍坊、莱芜、日照及青岛6个地区的102株玉米纹枯病菌对噻呋酰胺的敏感性。结果表明:其EC₅₀值分布范围为0.010～0.194 μg/mL,平均EC₅₀ 值为 (0.086 ± 0.004) μg/mL,且敏感性呈连续单峰曲线分布。通过紫外诱导与药剂驯化的方法各获得5株耐药性菌株 (TA3-X2、TA17-X6、LY8-3、QD14-Y7和WF6-A2) 和1株抗性突变体 (QD2-Y4),其抗性水平在6.46～20.08倍之间,突变频率分别为0.87%和0.52%。对抗性突变体生物学性状的研究表明,紫外诱导获得的5株耐药性菌株其耐药性不能稳定遗传,而经药剂驯化获得的1株抗性突变体QD2-Y4的抗药性可稳定遗传;耐药性菌株TA3-X2的菌丝生长速率高于亲本菌株,其余菌株与亲本菌株差异不明显;5株耐药性菌株和1株抗性突变体的菌丝干重和菌核干重均低于亲本菌株;TA3-X2、WF6-A2及QD2-Y4的致病力低于亲本菌株,TA17-X6、LY8-3及QD14-Y7的致病力与亲本菌株无明显差异。交互抗性测定表明,噻呋酰胺抗性突变体与戊唑醇、丙环唑、咯菌腈、井冈霉素、苯醚甲环唑和多菌灵之间均无交互抗性,与啶酰菌胺和氟唑菌苯胺之间则存在交互抗性。研究表明,山东省6个地区的玉米纹枯病菌对噻呋酰胺比较敏感,推测噻呋酰胺可作为防治玉米纹枯病的理想候选药剂。     

土传黄瓜立枯病高效拮抗菌的筛选鉴定及其生物效应

采用平板对峙法从黄瓜根际土壤中分离出的400余株细菌菌株中筛选出16株对立枯丝核菌Rhizoctonia solani具有拮抗效果的菌株,抑菌带直径在0.81～1.93 cm之间。并从中选出3株抑菌带直径在1.6cm以上的菌株N33、N35和N43,结合形态、生理生化特性及16S rDNA序列比对分析,鉴定N33菌株为假单胞菌属Pseudomonas sp.,N35和N43菌株为芽胞杆菌属Bacillus sp.。通过在黄瓜育苗基质中添加选育的高效拮抗菌株,观测其对黄瓜苗生长的促进作用以及对立枯病的防治作用,3株菌株均具有促进黄瓜苗期生长和防治苗期立枯病的作用,其中N43菌株促生及防病效果均最显著,地上部鲜重比对照处理增加62.16%,防治效果达62%。     

Control of rice sheath blight by phyllosphere epiphytic microbial antagonists

Epiphytic microorganisms on the phyllosphere of traditional and high-yielding rice varieties were isolated from different agroecological zones of Sri Lanka and screened for theirin vitro andin vivo antagonism againstRhizoctonia solani Kühn AG-1 1A, the sheath blight pathogen of rice. Among a total of 196 bacterial and 91 fungal isolates, 12 bacterial and two fungal isolates which showed more than 50% growth inhibition ofR. solani were tested for theirin vivo antagonism. Among the 14 antagonists tested, six bacterial and one fungal isolate substantially reduced the incidence of sheath blight (by more than 82%) and severity (by more than 92%) of the rice varieties BG94-1 and IR8 grown in a pot experiment under open field conditions. Using five antagonists that showed the bestin vitro antagonism, a pot experiment was conducted to determine whether the presence of indigenous microflora on the rice sheath had any effect on the effectiveness of antagonism. Three isolates (B4, GbB5 and HMWB4) controlled sheath blight incidence and severity equally well in the presence and absence of indigenous microflora. Two isolates (BG352B1 and BG300B1) were more effective when they were introduced into the rice sheath without indigenous microflora. Among the effective antagonists determined by the pot experiment, isolates B4, B16, BG94-1B5, GbB5, HMWB4 and BG379-F2 were tested under field conditions for two consecutive growing seasons. Under field conditions, severity of rice sheath blight was significantly reduced by the application of all the tested antagonists as a spray on rice sheath at a concentration of 10⁸ cfu ml⁻¹, starting 3 days after the development of symptoms and continuing for three applications at 10-day intervals. Antagonistic performances were consistent in the two seasons under field conditions andB. megatarium A (isolate B16) andAspergillus niger (isolate BG379-F2) performed as the most effective antagonists in both seasons. When disease severity was quantified as percentage sheath area covered by the disease lesions, the respective reductions in disease severity were greater than 50% and 61% byB. megaterium A (isolate B16) andAspergillus niger (isolate BG379-F2), respectively, in both seasons. http://www.phytoparasitica.org posting Jan. 10, 2008.     

Purification of an Elicitor-Inducible Antifungal Chitinase from Suspension-Cultured Rice Cells

Suspension-cultured rice cells showed an appreciable amount of chitinase activity when the cultured cells were treated with an elicitor isolated fromRhizoctonia solani, the rice sheath blight pathogen. A fivefold increase in chitinase activity was observed 24 h after elicitor treatment. The elicitor-inducible chitinase was purified by ammonium sulfate fractionation, chitin affinity chromatography and gel filtration. Its molecular weight is 35 kDa and it has an isoelectric point of 8.3. The 35 kDa basic chitinase inhibited mycelial growth ofR. solani in vitro. Morphological changes appeared within 1 h following exposure of mycelium to the chitinase. The hyphal tip showed marked swelling and subsequently lysis was also observed.     

Anastomosis Groups, Pathogenicity and Sensitivity to Fungicides of Rhizoctonia solani Isolates Collected on Potato Crops in France

A collection of 241 isolates of Rhizoctonia solani obtained from potato plants grown in different areas in France was characterized for anastomosis grouping, symptomatology on tubers of different cultivars and sensitivity to three fungicides. Most isolates collected belonged to (anastomosis groups (AGs)) AG 3, but 2% and 4% of the isolates were AG 5 and AG 2-1. AG 3 and AG 2-1 isolates were mostly obtained from sclerotia on tubers, but all AG 5, some AG 3 and some AG 2-1 isolates were recovered from superficial tuber alterations, like deformations, corky or scabby lesions. Sclerotia were formed on tubers produced by healthy stem cuttings grown in soil artificially infested with AG 3, but not on tubers grown in soil infested with either AG 5 or AG 2-1. No variation in susceptibility to sclerotial formation was observed among five potato cultivars. In all cases, a large proportion of tubers showed superficial corky lesions, often associated with deformations. The proportion of tubers with lesions and deformations was highest in soil infested with AG 2-1 and significantly lower on cv. Samba in all treatments. All isolates were highly sensitive to flutolanil, iprodione and pencycuron, except the AG 5 isolates, moderately sensitive to pencycuron. These results show that, although AG 3 is the most common R. solani group on potato in France, AG 5 and AG 2-1 may be present. Isolates differed for pathogenicity. In vitro sensitivity to fungicides varied among AGs.     

葡萄生单轴霉重寄生菌F3的鉴定及防治效果测定

为明确从生长异常的葡萄霜霉层上分离获得的菌株F3对葡萄生单轴霉Plasmopara viticola的重寄生作用及对葡萄霜霉病的防治效果,通过光学和扫描电子显微镜观察菌株F3对葡萄生单轴霉的重寄生作用,并对菌株F3进行形态特征观察及28S rDNA序列分析,采用孢子囊萌发抑制和离体叶片点样法测定该菌株对葡萄霜霉病的防治效果。结果表明,菌株F3对葡萄生单轴霉表现出覆盖、缠绕的重寄生现象。结合形态特征与序列分析结果将该菌株最终鉴定为层生镰刀菌Fusarium proliferatum。菌株F3分生孢子悬浮液及其无菌发酵液对葡萄霜霉菌孢子囊萌发具有显著的抑制作用,抑制率分别为86.8%和83.1%;经菌株F3分生孢子悬浮液预防处理后的离体葡萄叶片发病率为10.9%,显著低于对照的发病率98.8%,防治效果达88.9%;菌株F3分生孢子悬浮液与葡萄霜霉病菌孢子囊混合后点样接种处理的叶片发病率为50.0%,也显著低于对照,防治效果为49.1%;而治疗处理的叶片发病率与对照间无显著差异。表明层生镰刀菌对葡萄生单轴霉具有重寄生作用,且对葡萄霜霉病具有较强的预防控制作用。     

Management of the yellow beet cyst nematode with crop rotation,soil fumigation and granular nematicides

A trail field was managed for six years to test effects of short crop rotations, soil fumigation and granular nematicides on the population dynamics of the yellow beet cyst nematode (Heterodera trifolii f. sp.beta) and sugar-beet yields.In the two-year rotation, the cyst nematode population before planting varied from about the tolerance level (5 eggs per millilitre of soil) to 25 eggs per millitlitre of soil, leading to losses of sugar yield. Soil fumigation with metam-sodium effectively reduced the nematode density before planting, resulting in a 15 and 25% increase in sugar yield in the first two crops, respectively, but was insufficient to protect the third sugar-beet crop from yield-reducing nematode attack. This was attributed to the wet soil at the time of application and accelerated disappearence of the chemical in the soil through biological adaptation to repeated fumigation. Oxamyl or aldicarb granular nematicides applied as a side-dressing to the rows had insufficient effect to protect the sugar-beet from yield-reducing nematode attack. An overall treatment with aldicarb rotavated into the soil, alone and in addition to soil fumigation, increased sugar yield significantly. However in the two-year rotation, yield of the third sugar-beet crop treated with soil fumigation and granular nematicide was still lower than that of the untreated second crop in the three-year rotation.In the three-year rotation, thecyst nematode population before sugar-beet varied from hardly detectable to about the tolerance level. Here sugar-beet could be protected from yield-reducing nematode attack by soil fumigation or an overall treatment with granular nematicide. In the threeyear rotation with soil fumigation an increase ofRhizoctonia crown rot was observed in the second sugar-beet crop.Samenvatting Om de effecten na te gaan van korte rotaties, grondontsmetting en nematicide granulaten op het populatieverloop van de gele bietcystenematode (Heterodera trifolii f.sp.beta) en de opbrengsten van suikerbieten werd gedurende zes jaren een proef uitgevoerd op een natuurlijk besmet perceel van de proefboerderij Vredepeel.In de tweejarige rotatie variëerde de cystenematodepopulatie vóór het bietegewas boven de schadedrempel, wat resulteerde in verlaging van de suikeropbrengst. Grondontsmetting met metam-natrium veroorzaakte een effective vermindering van de dichtheid van de nematoden vóór de bieten en een verhoging van de suikeropbrengst van respectievelijk 15 en 25% bij de eerste twee gewassen, maar was onvoldeende om het derde bietegewas te beschermen tegen een opbrengst verminderende aantasting door nematoden. Dit was een gevolg van natte bodemomstandigheden bij het injecteren en het versneld verdwijenen van het middel door biologische adaptatie van de grond na herhaalde ontsmetting. Nematicide granulaten (oxamyl of aldicarb) naast de rij toegepast hadden onvoldoende effect om de bieten te beschermen tegen een opbrengstverminderende aantasting door nematoden. Een volvelds toepassing van in de grond gefreesde aldicarb alleen en toegevoegd na grondontsmetting verhoodge de suikeropbrengst beduidend. De opbrengst van het derde suikerbietegewas in de tweejarige rotatie was echter na toepassing van grondontsmetting en nematicide granulaten nog beduidend lager dan die van het onbehandelde tweede suikerbietegewas in de driejarige rotatie.In de driejarige rotatie variëerde de cystenematodepopulatie vóór het bietegewas van nauwelijks aantoonbaar tot nabij de tolerantiegrens. Hier kon het suikerbietegewas worden beschermd tegen een eventueel opbrengst verminderende nematodenaantasting door grondontsmetting of volveldstoepassing van nematicide granulaten.