Tomato partial resistance to Rhizoctonia solani involves antioxidative defense mechanisms

The resistance interactions of four tomato cultivars to five Rhizoctonia solani isolates, causing foot rot, were investigated. Priming H₂O₂ accumulation, peroxidase and ascorbate peroxidase activity was observed in CH Falat, as a partially resistant cultivar. Maximum peroxidase activity in CH Falat was observed at 24 h post inoculation (hpi) which was earlier than maximum phenolics accumulation at 72 hpi. In addition, application of peroxidase inhibitor reduced phenolics level. Therefore, peroxidase might be involved in phenolics production, as an effective resistance mechanism in our pathosystem.     

Infection of potato by Rhizoctonia solani: effect of anastomosis group

Glasshouse and field experiments showed that the pathogenicity and disease type on potato varied between different anastomosis groups (AGs) of Rhizoctonia solani. For example, severe stem and stolon disease developed in plants inoculated with a single isolate of AG3PT and AG5. Severe root disease was observed with single isolates of AG8 and to a lesser extent AG3PT, but rarely with single isolates of the other AGs tested. In both field and glasshouse experiments the AG2‐1 isolate (X81) produced only small lesions (<5 mm). However, this was not representative of two other AG2‐1 isolates. When AG2‐1 isolates of the three different rDNA IGS1 types were tested in a glasshouse trial, one caused more severe stem and stolon infection than AG3PT. In the field experiment, the yield of tubers, by weight, was significantly less (P < 0·05) in all inoculated plants than for uninoculated (control) plants. Yield losses were greatest and tuber numbers smallest in plots inoculated with an AG8 isolate, suggesting that root infection is important in determining quantitative yield loss. The incidence of black scurf was greatest in the progeny tubers in plots inoculated with AG3PT (83·9%), whereas only very small amounts of black scurf developed on tubers from plants infected with AG2‐1 (510 bp) or AG5 isolates. This is supported by laboratory tests, where isolates of AG3PT produced significantly more sclerotia on potato dextrose agar than isolates of AGs 2‐1, 4, 5 and 8.     

Infection of potato and wheat by isolates of Rhizoctonia solani and R. cerealis

Isolates of Rhizoctonia were obtained from potato crops with stem canker or black scurf and from cereal crops with sharp eyespot. Those with many nuclei per cell, wide cells, darkening colonies and fast growth were assigned to R. solani ; those with two nuclei per cell, narrow cells, pale colonies and slow growth were assigned to R. cerealis . Only R. solani was obtained from potatoes and only R. cerealis from cereals. On young plants in the glasshouse, the isolates of R. solani infected potato substantially but not wheat; R. cerealis infected wheat substantially and potato slightly. This host preference was shown at temperatures between 10 and 25°C in growth rooms. R. solani on potato caused more disease with increasing temperature; no trend with temperature was observed for R. cerealis on wheat.     

Induction of systemic resistance by a hypovirulent Rhizoctonia solani isolate in tomato

A polynucleate Rhizoctonia isolate (R3) was analysed for virulence, growth characteristics, enzyme production and presence of dsRNAs. Taxonomic position was assessed morphologically and by anastomosis group (AG) testing and ITS sequence analysis. Results indicated that R3 is a hypovirulent R. solani AG 4. Mechanisms underlying biocontrol towards virulent R. solani and Botrytis cinerea were investigated and plant-mediated resistance was followed using biochemical markers of defence (PR1, laminarinase, chitinase). Control apparently relies on spatial and nutrient competition in soil, and on systemic induced resistance. This is the first report on induction of systemic resistance and of defence markers by a hypovirulent strain of R. solani.     

宁夏马铃薯主栽品种对黑痣病的抗性鉴定

为明确宁夏马铃薯主栽品种对黑痣病的抗性水平,利用田间和室内接种相结合的方法对供试马铃薯品种的抗病性进行评价。室内接种试验表明,供试的20份马铃薯材料中没有免疫及高抗品种,接种量与抗性水平呈负相关,其中‘陇薯7号’,‘黑美人’,‘青薯9号’在接种量为5~15g水平上表现为中抗。通过聚类分析,接种量为5g和10g时,以欧式距离13作为最佳聚类分割点,供试品种可分为3个类群。田间接种综合评价分析表明,不同品种间抗性存在显著差异,通过聚类分析,以欧式距离13作为最佳聚类分割点,试验品种可分为4个高感品种、11个中感品种和5个中抗品种。     

Hyperparasites of Rhizoctonia solani in Dutch potato fields

Gliocladium roseum was found to be the most common and probably the most effective mycoparasite in potato fields in the northern parts of the Netherlands. It is able to parasitize and kill living hyphae at temperatures of 12°C and higher. Sclerotia ofR. solani are often infected and killed by this fungus under suitable conditions, i.e. at temperatures of 16°C and more. Killing of sclerotia by other antagonistic organisms was also observed. It is also shown by not parasitic fungi and is caused by toxins produced by the antagonist.The development of theG. roseum population was studied during the growth of a potato crop in two soils. In both soils its initial level was very low. In both a slightly acid sandy soil and a neutral sandy loam, suppression ofR. solani can occur;G. roseum accumulated in the former mainly under continuous potato crops,Colletotrichum coccodes was the main antagonist in the latter.Samenvatting In de meeste Nederlandse aardappelakkers komen schimmels voor dieRhizoctonia solani kunnen aantasten en doden. De meest algemene, en waarschijnlijk ook de meest belangrijke, die we tot nu toe vonden, isGliocladium roseum (Tabel 1). Het is bekend, dat deze schimmel stoffen produceert die voorR. solani giftig zijn. Met behulp hiervan kanG. roseum, evenals andere antibiotisch actieve micro-organismen, ook de sclerotiën doden (Tabel 2). Voor doding doorG. roseum is de temperatuur een factor van belang. Hyfen worden nog gedood bij een temperatuur van 12°C, waarbij de sclerotiën niet meer aangetast kunnen worden. Gedurende het winterseizoen worden sclerotiën door deze schimmel naar alle waarschijnlijkheid niet gedood.De ontwikkeling van de populatie vanG. roseum en andere antagonisten vanR. solani werd gevolgd in aardappelvelden op een licht zure zandgrond en op een neutrale zware zavel. Op de zandgrond werden twee proefplekken bemonsterd: één waarop voor het vierde achtereenvolgende jaar aardappelen werden geteeld en één met een vruchtwisselingsschema van graan, bieten en aardappelen.In de zandgrond nam in het groeiseizoen de populatie vanG. roseum toe. Op de proefplek waar voor het vierde jaar achtereen aardappelen stonden werdR. solani vanaf half augustus onderdrukt, evenwel niet volledig. Ook in het vruchtwisselingsstuk breiddeG. roseum zich flink uit, doch een onderdrukking vanR. solani werd niet bereikt.In de zware zavel nam de populatie vanG. roseum niet toe. Hier werdR. solani — uit besmet pootgoed — onderdrukt doorColletotrichum coccodes (zelf een pathogeen van stolonen) en antagonistische bacteriën. De resultaten zijn vermeld in Tabel 3.De besmetting van de geoogste knollen met sclerotiën, zoals die voorkwam op de zandgrond, is in Tabel 4 vermeld. Op de zavel leverde schoon pootgoed een bijna schone oogst (2% van de knollen was zeer licht bezet met sclerotiën). Besmet pootgoed leverde een oogst met 58% schone knollen, 35% met een zeer lichte en 7% met een iets zwaardere sclerotiënbezetting. Hoewel uit 100% besmet pootgoed een veel schonere oogst werd verkregen, was eerder toch een beschadiging van het gewas opgetreden. Pas tegen het eind van het groeiseizoen werdR. solani flink onderdrukt.     

Characterization of Rhizoctonia solani from potato in Great Britain

One hundred and thirty five isolates of Rhizoctonia solani were obtained from British potato crops between 2001 and 2003. Isolates were assigned to anastomosis group (AG) using conventional PCR assays for AG2-1 or AG3 or through the observation of hyphal interactions, where appropriate. A previously published primer set was modified in this study to enhance specificity for AG3PT. Most of the isolates (92·6%) belonged to AG3PT whilst some (6·7%) belonged to AG2-1. Only one isolate recovered (0·7%) belonged to AG5. Isolates of AG2-1 were diverse, with variation in both the length of the rDNA intergenic spacer 1 (IGS1) region and the categories of hyphal interaction observed between pairings of AG2-1 isolates. No variation in the length of the rDNA IGS1 region was observed amongst the AG3 isolates collected. Tests carried out on potato stems with a sub-set of the isolates revealed a wide range of aggressiveness amongst AG2-1 isolates. Sequencing of the rDNA internal transcribed spacer (ITS) region of the AG2-1 isolates and construction of a neighbour joining tree with other AG2-1 sequences available indicated that AG2-1 isolates with the short IGS1 region were closely related. This is the first investigation which provides evidence of the relative AG composition of R. solani populations causing disease in potato crops in Great Britain.     

Suppression of Rhizoctonia solani in potato fields. 1. Occurrence

A search was made forRhizoctonia solani-suppressive soils by establishing many small experimental plots, half of which were planted withRhizoctonia-infected seed potatoes and the other half with disinfected seed stock. The sclerotium index of the harvested tubers was compared witht that of the seed potatoes. In suppressive soils, the sclerotium index of the harvest is much lower than that of the seed potatoes. None of the plots on holocene marine soils (loamy sand, sandy loam, clay loam and clay) proved to be suppressive in 1978 and 1979. Only on pleistocene, slightly acid sandy soil suppressiveness was observed. In 1978, four out of twelve plots showed suppressiveness when the plots were planted with seed potatoes produced on a sandy soil. In 1979, only two out of thirtyone plots were slightly suppressive when planted with seed potatoes produced on a young clay loam from a new polder. A higher percentage of sclerotia on tubers from sandy soils proved to be infected with antagonistic fungi (73%) than of those on tubers from marine clay or loam soils (25%). Factors that influence suppressiveness are suggested.     

Formation of sclerotia by Rhizoctonia solani on artificial media and potato tubers

Independent of the nutrient medium and the size of Petri dish, sclerotium initials ofRhizoctonia solani AG-3 appeared after a fixed period of time. The same held for the completion of maturation of the sclerotia. Deprivation or extra supply of nutrients reduced or increased, respectively, final mass of sclerotia but did not affect the moment of initiation and of maturation. Transfer of a mycelial mat from water agar to a nutrient-rich medium caused the formation of black solid sclerotia within four days all over the mat and not only around the site of inoculation as usually occurs on rich medium. Final sclerotial mass was higher on liquid medium than on agar. The results indicate that formation of these sclerotia is not associated with cessation of linear hyphal growth or with starvation. On mature tubers, sclerotia and hyphae are spread over the whole surface. On young growing tubers sclerotia are rarely found in the immediate vicinity of lenticels. This suggests a release of inhibitory factors at these sites which diminishes during tuber maturation. Volatile exudates from underground plant parts seem to further promote the sclerotium formation. On all underground plant parts, even the roots, final sclerotial mass was higher after wounding. After haulm destruction, development of black scurf was not stimulated by a short-term trigger or by roughning of tuber surface. The observations rather suggest that the stimulation results from an increased tuber exudation of stimulatory nutrients, water and stress factors and also from a reduction of as yet unknown inhibitory factors. Results indicated that in infested soils, the estimated inoculum density at the day of haulm destruction has no predictive value for black scurf development.     

甘肃省定西市马铃薯黑痣病菌菌丝融合群的鉴定及药剂筛选

马铃薯黑痣病立枯丝核菌(Rhizoctonia solani)菌丝存在遗传分化现象。从定西市马铃薯产区采集茎部和薯块病样80份进行融合群测定。结果表明,80株菌株中与标准菌株AG3融合的占总数的70.0%、与AG4-HG-Ⅱ融合的占15.0%、与AG2-1融合的占7.5%。为了有效控制马铃薯黑痣病,采用生长速率法在室内选取9种杀菌剂进行药效评价。结果表明:30%噻呋酰胺悬浮剂EC50最低,为0.015 2μg/mL;其次是40%氟胺·异菌脲悬浮剂、3%多抗霉素可湿性粉剂和250g/L嘧菌酯悬浮剂,其EC50分别为0.064 1、0.129 3和0.176 7μg/mL;EC50最大的是25.75%多抗·福美双可湿性粉剂,为2.930 4μg/mL。田间拌种,30%噻呋酰胺悬浮剂和250g/L嘧菌酯悬浮剂防效较好,达70%以上,值得在生产中推广。     

Genetic variability and pathogenicity of Rhizoctonia solani associated with black scurf of potato in New Zealand

Isolates (a total of 129) of Rhizoctonia solani were collected from black scurf on potato tubers from different potato‐growing regions in New Zealand. Sequence analysis of the nuclear ribosomal DNA internal transcribed spacer (rDNA–ITS) regions from these isolates identified three anastomosis groups (AGs), AG‐3PT, AG‐2‐1 and AG‐5. Isolates classified as AG‐3PT were widely distributed, whereas AG‐2‐1 and AG‐5 were confined to distinct locations. Sequence heterogeneity was identified in the ITS regions of 100 AG‐3PT and AG‐2‐1 isolates. Variation in the sequence and length of the rDNA–IGS1 region was also observed for selected isolates of AG‐3PT and AG‐2‐1. Phylogenetic studies found all AG‐2‐1 isolates belong to AG‐2Nt, a subset of AG‐2‐1 previously associated with solanaceous crops in other countries. AG‐2‐1 isolates were consistently more aggressive than those of AG‐3PT. Delayed emergence, severe infection on stolons, formation of aerial tubers and considerable yield losses were associated with AG‐2‐1, but they caused negligible black scurf. In contrast, AG‐3PT caused black scurf on progeny tubers but variable effects on stem emergence and stolons. Furthermore, AG‐2‐1 isolates caused severe tuber malformation, but isolates of other AGs did not. This is the first report on the AG composition, genetic variability and pathogenicity of R. solani isolates associated with black scurf of New Zealand potatoes.     

碳酸氢盐对马铃薯黑痣病菌毒力及田间防效

为明确碳酸氢盐对马铃薯黑痣病菌的毒力及田间防效,采用菌丝生长速率法,测定了碳酸氢盐对马铃薯黑痣病菌的毒力;并通过盆栽防治试验及田间防治试验,研究了碳酸氢盐对马铃薯黑痣病的防治效果。结果表明:碳酸氢铵抑制马铃薯黑痣病菌菌丝生长的有效中浓度EC50仅为0.71g/L,碳酸氢钾EC50为3.8g/L;在PSA培养基中同时加入0.79g/L碳酸氢铵、1g/L碳酸氢钾与在PSA培养基中含1.58g/L碳酸氢铵的抑菌效果一样;尿素对马铃薯黑痣病没有防治效果。碳酸氢铵与碳酸氢钾混配对该病有良好的防治作用,相对尿素最高防治效果可达到63.4%。覆膜栽培能够提高碳酸氢盐的防效和马铃薯产量。碳酸氢盐可用于田间马铃薯黑痣病的防治。     

A new quantitative real-time PCR assay for Rhizoctonia solani AG3-PT and the detection of AGs of Rhizoctonia solani associated with potato in soil and tuber samples in Great Britain

Rhizoctonia solani is an important pathogen of potatoes causing stem canker and black scurf. The fungus is a species complex comprised of 13 known anastomosis groups (AGs). AG3-PT is the anastomosis group frequently associated with disease in potatoes. A real-time PCR assay was designed to the rDNA ITS region of AG3-PT isolates to enable the pathogen to be detected directly in tuber and soil samples. The resulting assay was highly specific for AG3-PT, and did not amplify DNA from isolates from other AGs or subgroups of AG3. Using a bulk DNA extraction method capable of extracting from up to 250 g of soil, the assay could detect one individual sclerotium of AG3-PT (weighing 200 μg) in 250 g of soil. The AG3-PT assay was used, with assays for AG2-1, AG5 and AG8 to determine the prevalence of those AGs in UK potato soils and tubers. AG2-1 and AG3-PT were the predominant groups in tubers and soils, although AG3-PT was more frequently isolated from tubers, highlighting its importance as a potato pathogen. AG3-PT was also detected in more than half of the tuber samples tested suggesting the importance of seed borne inoculum.     

Anastomosis group and pathogenicity of isolates of Rhizoctonia solani from potato crops in South Australia

Isolates of Rhizoctonia collected from the stems, roots, tuber sclerotia and soil of potato crops in Virginia and Lenswood, South Australia, were identified to anastomosis groups (AG). Of the 301 multinucleate isolates of Rhizoctonia solani tested, 90% were AG-3, 7% were AG-4 and 2% were AG-5; 12 isolates were binucleate Rhizoctonia spp. This is the first report of isolates of AG-4 and AG-5 causing disease in potato crops in South Australia. All AG-3, AG-4 and AG-5 isolates tested caused rhizoctonia disease symptoms on the potato cultivar Coliban in pathogenicity trials conducted under glasshotise conditions. Both AG-3 and AG-5 isolates caused black scurf and stem cankers, although symptoms of black scurf were less severe with AG-5. AG-4 isolates produced the most severe stem and stolon cankers of all isolates tested. The pathogenicity of tuber-borne inoculum was confirmed by growing plants from sclerotia-infested tubers. AG-8 isolates from diseased barley and wheat produced severe root cankers and caused loss of feeder roots on inoculated potato plants. Results suggest that rhizoctonia disease in potato fields in South Australia is caused by a combination of different anastomosis groups and this has important implications for crop rotations.     

The occurrence of Rhizoctonia solani on subterranean parts of wild plants in potato fields

The subterranean parts of 1585 wild plants (weeds) belonging to 52 species, found in potato fields in the northern part of the Netherlands were examined for the presence ofRhizoctonia solani. The fungus could be isolated from 30 plants belonging to 12 species. Of these isolates 62% proved to be pathogenic to potato sprouts.Some species seemed more frequently colonized byR. solani than others, particularlySolanum nigrum, Elytrichia repens andMatricaria recutita. On some common weeds, viz.Chenopodium album andPoa annua, noR. solani was observed, while about 1% of allPolygonum persicaria were infected.Disease symptoms were only observed once onElytrichia repens as sharp eyespots, presumably caused byR. cerealis.The incidence ofR. Solani on weeds increased markedly towards the end of the growing season.

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Samenvatting Wortels, wortelstokken en ondergrondse stengeldelen van onkruiden voorkomend in aardappelakkers in Groningen, Friesland en Drenthe zijn onderzocht op de aanwezigheid vanRhizoctonia solani. Van 1585 planten, behorend tot 52 soorten, herbergde bijna 2%, d.w.z. 29 planten behorend tot 12 soorten,R. solani op de ondergrondse delen. Van dezeRhizoctonia-isolaten bleek 62% aardappelspruiten aan te tasten.Bepaalde onkruidsoorten bleken vaker drager te zijn vanR. solani dan andere. Dit was het geval met kweek, zwarte nachtschade en echte kamille. Op enkele algemene onkruiden als witte ganzevoet en straatgras is geenRhizoctonia waargenomen. Van het algemeen op zandgronden voorkomende perzikkruid bleek ongeveer 1%Rhizoctonia op de wortels te herbergen.Typische ziektesymptomen — scherpe oogvlekken — zijn alleen waargenomen op stengels van kweek. Het voorkomen vanR. solani op onkruiden neemt sterk toe tegen het eind van het groeiseizoen (eind augustus en september).

     

云南省马铃薯黑痣病病原菌融合群鉴定及8种药剂对其的毒力

由立枯丝核菌引起的马铃薯黑痣病是一种常见的土壤和种薯传播病害,在世界各地均有发生。本试验对分离纯化的67个丝核菌菌株进行融合群测定,结果表明:67个菌株都属于AG3融合群;对其中来自6个不同地域的11个菌株进行ITS测定,11个菌株的相似度为99%。8种药剂对马铃薯黑痣病菌的毒力测定结果表明,20%氟胺·嘧菌酯水分散粒剂50mg/L和25g/L咯菌腈悬浮种衣剂50mg/L的抑菌效果较好,室内抑菌效果可达100%。     

Suppression of Rhizoctonia solani in potato fields. II. Effect of origin and degree of infection with Rhizoctonia solani of seed potatoes on subsequent infestation and on formation of sclerotia

The seed potatoes used in these experiments had been grown in a slightly acid pleistocene sandy soil or in a marine, holocene sandy loam. They were free of sclerotia ofR. solani or lightly or moderately speckled with them. Seed potatoes from the sandy soil produced plants that suffered less fromRhizoctonia than plants from seed potatoes that had been grown on the marine sandy loam. Similarly harvested tubers had, in a non-conducive soil and in conducive soils with a (very) low inoculum density ofR. solani, fewer sclerotia when they came from seed potatoes grown in an acid sand. In each soil, the degree of infestation of the crop not only depended on the severity of infection of the seed potatoes, but also on their origin. With regard to sclerotia production on tubers, three types of soil were distinguished: suppressive, conducive with a high, and conducive with a very low inoculum density ofR. solani. The differences in infestation and in the amounts of sclerotia on tubers between the crop grown from seed potatoes from the sandy soil and that from seed potatoes from the marine sandy loam soil, is attributed to a richer load of antagonists on the former and possibly to a larger proportion of saprophyticRhizoctonia strains among their sclerotia. The antagonists seem to be inhabitants of the subterranean parts of the plant and to function independently of the soil. This implies possibilities for their use in biological control.     

Anastomosis groups and sensitivity to fungicides of Rhizoctonia solani strains isolated from potato in Russia

Journal of Plant Diseases and Protection - A survey of Rhizoctonia solani isolates from potato tubers and stems grown in European and Far Eastern regions of Russia in 2012–2020 was conducted....