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1.
Virulent Rhizoctonia spp. isolated from strawberry in Israel belonged to anastomosis groups (AG) of: binucleate Rhizoctonia (BNR) AG-A, AG-G, AG-K and AG-F, and to multinucleate Rhizoctonia (MNR) AG 4 subgroup HG-I. In addition, a soil isolate of AG 4 subgroup HG-III was also found to be virulent on strawberry. None of the Israeli isolates obtained in the present study belonged to BNR AG-I, or other MNR AGs. In the cluster analysis of rDNA-ITS sequences, all of the isolate sequences consistently clustered according to their known AGs and subgroups. One AG-F cluster included sequences of 10 strawberry isolates, while another AG-F cluster included sequences of two isolates submitted to GenBank. Additional work is needed to determine whether the isolates of these two clusters may belong to different AG-F subgroups. The current virulence bioassay used for Rhizoctonia spp. isolates on strawberry is based on inoculation of stolon-derived daughter plants with the isolates and estimation of the reduction in plant biomass, rather than on specific distinct disease severity symptoms. The duration of this test is relatively long (ca. 5 weeks or more) and the availability of daughter plants from runners is naturally limited to a certain season. Among the possible alternative methods evaluated in the present study (inoculation of fruits or seedlings developed from germinated strawberry seeds), the method based on seedlings was best. This method has a potential to replace the currently used stolon-daughter plant inoculation bioassay for testing virulence of strawberry root pathogens. This is the first report indicating that Rhizoctonia spp. isolates that belong to AG-F, AG-K, AG 4 HG-I and AG 4 HG-III are virulent to strawberry.  相似文献   

2.
Water agar, artificially infested soil and leaf sheath inoculation methods were used to assess the suitable time of application, varietal host response and persistence of Rhv7, a hypovirulent, binucleate Rhizoctonia collected from soil in the Philippines, to effectively control virulent Rhizoctonia solani AG1-IA isolate RS35 on corn. With the water agar method, prior inoculation (2 to 3 days) with the biocontrol agent is essential to achieve maximum control of the pathogen. Disease protection was increased from 23 to 70% as the pre-incubation time of Rhv7 prior to the challenge inoculation with virulent isolate was lengthened from 0 to 3 days. Disease severity and incidence of banded leaf and sheath blight (BLSB) on the three corn hybrids were also suppressed in artificially infested soil. In leaf sheath inoculation, the suppressive ability of Rhv7 against BLSB on corn persisted during lesion expansion. This suppression was expressed as slower disease progress in plants with Rhv7 than in plants without Rhv7. Early and timely brace root formation that detached infected sheaths, also aided in reducing the number of diseased plants in Rhv7-treated plots at the final observation. Mycelial growth activity of RS35 was reduced when corn plants were pre-inoculated with Rhv7 before challenge even if there was no contact detected between Rhv7 and RS35, which suggests that Rhv7 protects corn against BLSB by induced resistance. The hypovirulent, binucleate Rhizoctonia Rhv7 strain effectively controlled R. solani AG1-IA isolate RS-35 in corn. Received 30 August 1990/ Accepted in revised form 25 October 1999  相似文献   

3.
Among 153 isolates ofRhizoctonia spp. obtained from 95 soil samples collected from different fields in the USA, 42 (27.5%) isolates were hypovirulent or non-pathogenic on cabbage (tested on tap water agar plus 250 μg/ml chloramphenicol plates). Of these, 14 (33.3% of the np-R) isolates protected >60% of the cabbage seedlings againstR. solani, and the best eight isolates protected 73–95% of the cucumber seedlings. The np-R isolates RU56-8 (AG-P) and RU89-1 [AG-B(o)] induced the highest resistance against hypocotyl challenge inoculation with virulentR. solani (38.3–85.7%), whereas most of the challenged control seedlings (85–100%) collapsed. Similarly, isolates RU56-8 and RU89-1 induced the highest resistance (22.2–87.5%) against hypocotyl challenge inoculation withPythium aphanidermatum, whereas most of the challenged control seedlings collapsed (90–100%). Isolates RU56-8 and RU89-1 significantly reduced the lesion numbers and area/leaf (to 8.9–42.0% of the control) caused by challenge inoculation of the first true leaves withPseudomonas syringae pv.lachrymans. No np-R isolate could be recovered from the upper hypocotyls or from the leaves, indicating that there was no contact between the inducer and the pathogen. Root colonization with some np-R increased seedling tolerance to low soil moisture levels.  相似文献   

4.
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.  相似文献   

5.
Rhizoctonia solani AG 2-1 was recorded in Central Italy on kohlrabi plants showing root and stem rot. After artificial inoculation the fungus caused damping-off of 7-day-old seedlings and root and stem rot of 4-month-old plants developed after 15 days of incubation. This seems to be the first record ofR. solani AG 2-1 on kohlrabi.  相似文献   

6.
Bottom rot caused by Rhizoctonia solani is an increasing problem in field-grown lettuce in Germany. During the growing seasons of 1999 and 2000, 95 isolates of R. solani from lettuce plants with bottom rot symptoms were collected from eight locations. The isolates were characterised using hyphal anastomosis, pectic zymograms and morphological characteristics. Ninety-three isolates were identified as anastomosis group (AG) 1-IB, one as AG 1-IC and one as AG 2-1. Optimum hyphal growth was measured over a temperature range of 20–30 °C with an optimum at 25 °C. Aggressiveness of the AG 1-IB isolates varied from weak to strong when tested on detached lettuce leaves. The pathogenic potential of six AG 1-IB isolates was determined on 14 plant species in comparison with lettuce under conditions favourable for the fungus. Radish, broccoli, kohlrabi, spinach and millet seedlings were as severely infected as lettuce seedlings. The same isolates caused little symptoms on maize, tomato and onion. Knowledge about the host range of AGs of R. solani are important for planning an effective crop rotation as part of a control management system.  相似文献   

7.
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.  相似文献   

8.
Artificial suppression of radish damping-off disease was induced by repeated soil inoculations with Rhizoctonia solani, binucleate Rhizoctonia (BNR) and Sclerotium rolfsii in pot systems. Soils repeatedly inoculated with R. solani and BNR showed suppressive to disease caused by R. solani and S. rolfsii, while soils repeatedly inoculated with S. rolfsii were suppressive to disease caused by S. rolfsii but not by R. solani. Species of Trichoderma were consistently isolated from soils repeatedly inoculated with R. solani, BNR and S. rolfsii. These Trichoderma spp. accumulated selectively in relation to the fungal species that was repeatedly added to the soils. The ratios of the frequencies of T. viride, T. harzianum and T. hamatum were 5:2:2 and 8:5:2 in soils repeatedly inoculated with R. solani and BNR, respectively. In S. rolfsii- inoculated soils, T. koningii was predominantly isolated. T. viride, T. harzianum and T. hamatum isolates obtained from either R. solani or BNR after repeated additions to the soils suppressed radish damping-off disease caused after challenge inoculations with R. solani or S. rolfsii. Among the Trichoderma species, T. viride consistently yielded high levels of suppression. However, isolates of T. koningii obtained from S. rolfsii-infested soils suppressed disease caused by S. rolfsii but failed to suppress disease caused by R. solani. Generally, the species of Trichoderma accumulated in a selective pattern that was closely related to the species of fungal pathogen used to induce the suppressive soil.  相似文献   

9.
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.  相似文献   

10.
Resistance of sugar beet seedlings to Rhizoctonia damping-off caused by Rhizoctonia solani has not been described. A series of preliminary characterisations using a single susceptible host and four different R. solani isolates suggested the disease progression pattern was predictable. Two AG-4 isolates and a less virulent AG-2-2 isolate (W22) showed a comparable pattern of disease progression in the growth chamber where disease index values increased for the first 5–6 days, were relatively constant for the next 7–8 days, and declined thereafter. Seedlings inoculated with a highly virulent AG-2-2 isolate (R-1) under the same conditions showed similar patterns for the first 4 days post-inoculation; however disease index values continued to increase until seedling death at 13–14 days. Similar results were observed in the greenhouse, and a small expanded set of other germplasm lines were screened. One tested germplasm accession, EL51, survived seedling inoculation with R. solani AG-2-2 R-1, and its disease progress pattern was characterised. In a field seedling disease nursery artificially inoculated with R. solani AG-2-2 R-1, seedling persistence was high with EL51, but not with a susceptible hybrid. Identification of EL51 as a source of resistance to Rhizoctonia damping-off may allow investigations into the Beta vulgaris–Rhizoctonia solani pathosystem and add value in sugar beet breeding.  相似文献   

11.
To understand the distribution pattern and divergence of Rhizoctonia solani in a field over a 4-year period, R. solani AG1-IA isolates were collected from diseased tissues of several crops. Pairing tests between isolates to detect hyphal anastomosis and vegetatively compatible population (VCP) groupings were done on 2% water agar and potato dextrose agar. A single VCP of R. solani AG1-IA dominated a large upland crop field at the Institute of Plant Breeding, University of the Philippines at Los Ba?os. The VCP changed more slowly and at a lower frequency as compared to other reports. Received 27 September 1999/ Accepted in revised form 3 February 2000  相似文献   

12.
The Rhizoctonia solani species consists of multinucleate isolates that belong to anastomosis groups AG1–AG3 and differ in virulence and host affinity. R. cerealis is a binucleate species of anastomosis group AG-D which causes sharp eyespot, a common plant disease in Poland. Rhizoctonia spp. is a ubiquitous soil pathogen that poses a significant threat for global crop production due to the absence of effective crop protection products. The aim of this study was to determine the virulence of R. solani and R. cerealis isolates towards Beta vulgaris, Zea mays, Triticum spelta and T. aestivum seedlings, to confirm the presence of endopolygalacturonase genes pg1 and pg5 in the genomes of the tested isolates and to evaluate the tested isolates’ sensitivity to triazole, strobilurin, imidazole and carboxamide fungicides. All tested isolates infected B. vulgaris seedlings. but none of them were virulent against Z. mays plants. R. solani isolates AG4 PL and AG2-2IIIB PL were characterized by the highest virulence (average infestation score of 2.37 and 2.53 points on a scale of 0–3 points) against sugar beet seedlings. The prevalence of infections caused by most of the analysed isolates (in particular R. solani AG4 J—11.8, and R. cerealis RC2—0.78) was higher in spelt than in bread wheat. The virulence of the analysed isolates was not correlated with the presence of pg1 and pg5 genes. The efficacy of the tested fungicides in controlling Rhizoctonia spp. infections was estimated at 100% (propiconazole + cyproconazole), 98.8% (penthiopyrad), 95.4% (tebuconazole) and 78.3% (azoxystrobin).  相似文献   

13.
Abstrast  Three-hundred-twenty-five isolates ofRhizoctonia (215R. solani and 110 binucleateRhizoctonia) were obtained from roots and crowns of alfalfa, sainfoin and common vetch grown in Erzurum, Turkey. The isolates were assigned to five anastomosis groups (AG) ofR. solani (AG-2-1, AG-3, AG-4, AG-5, and AG-10) and two anastomosis groups of binucleateRhizoctonia (AG-I and AG-K). In pathogenicity tests on alfalfa, sainfoin and common vetch, the highest disease severities were caused by isolates of AG-4 and AG-5. Isolates of AG-10 and AG-I were not pathogenic on the three tested forage legumes, whereas isolates of AG-K on alfalfa and sainfoin, and of AG-2-1 on sainfoin, were moderately virulent. Alfalfa isolate AG-3 was moderately virulent on sainfoin. This is the first report ofR. solani AG-3, AG-5, AG-10 and binucleateRhizoctonia AG-I on alfalfa. In addition, all theR. solani and binucleateRhizoctonia groups isolated from sainfoin and common vetch were recovered from these crops for the first time in Turkey. http://www.phytoparasitica.org posting Dec. 16, 2002.  相似文献   

14.
The rDNA-ITS sequence of Rhizoctonia solani AG 1-ID was determined and compared to those of R. solani AG 1-IA, AG 1-IB, and AG 1-IC. The similarity of the isolates from each AG 1 subgroup was almost identical (99%–100%), whereas it was lower between subgroups (91%–95%) than within subgroups. Phylogenetic analysis indicated that isolates of AG 1-ID and other subgroups were separately clustered. Isolates of R. solani AG 1 were clearly separated from R. solani AG 2-1, AG 4, and binucleate Rhizoctonia AG-Bb and AG-K. These results showed that analysis of the rDNA-ITS sequence is an optimal criterion for differentiating R. solani AG 1-ID from other subgroups of R. solani AG 1.  相似文献   

15.
Basal rot is a common disease in lettuce greenhouses. A 3-year study on the diversity of pathogens associated with basal rot in Belgium was carried out. A total of 150 isolates were collected originating from 56 greenhouses. Four pathogens appeared to be involved. Rhizoctonia solani was found to be the causal agent at 23 locations, Sclerotinia spp. at 14, Botrytis cinerea at 17 and Pythium spp. at seven. The isolates of R. solani were further characterised to anastomosis groups and subgroups using morphological characteristics, pectic zymogram and PCR-RFLP. Five anastomosis groups could be distinguished: AG1-1B, AG4 HGI, AG10, AG2-1, AG2-1 Nt and AG3, with isolates of AG4 HGI and AG1-1B being the most prevalent and the most aggressive. Sclerotinia sclerotiorum was found at 13 locations, while S. minor was found at only one location. Based on ITS-sequencing Pythium isolates were assigned to three different species. At 20°C, isolates of all pathogens were able to cause lesions on detached lettuce leaves, except isolates of R. solani AG3 and AG2-1 Nt. A correlation could be found between the occurrence of the pathogens and the growing season. Botrytis cinerea was the most common pathogen in winter, whereas R. solani was most frequently isolated in summer. Sclerotinia spp. and Pythium spp. were isolated in spring, summer and autumn. The information obtained in this study will be most useful in the development of an alternative control strategy for causal agents of basal rot.  相似文献   

16.
为确定引起呼和浩特市苜蓿根腐病的病原菌种类,采用常规组织分离法对采集的疑似苜蓿根腐病病样进行病原菌分离与培养,利用形态学观察结合分子生物学方法对分离物代表菌株进行鉴定,并采用土壤接种法对代表菌株的致病性进行测定。结果表明,共分离获得6类形态学特征不同的分离物,各随机选择1株代表菌株进行鉴定,结合分子生物学鉴定结果确定呼和浩特市苜蓿根腐病病原菌有6种,分别是麦根腐平脐蠕孢菌Bipolaris sorokiniana、立枯丝核菌Rhizoctonia solani、木贼镰刀菌Fusarium equiseti、变红镰刀菌F. incarnatum、锐顶镰刀菌F. acuminatum和织球壳枯萎菌Plectosphaerella cucumerina,分别分离到1、7、14、26、7和14株菌株,占总分离菌株数的1.45%、10.14%、20.29%、37.68%、10.14%和20.29%。其中,立枯丝核菌的致病力最强,接种苜蓿幼苗发病的病情指数达82.67,其次为木贼镰刀菌、变红镰刀菌、锐顶镰刀菌、麦根腐平脐蠕孢菌和织球壳枯萎菌,病情指数分别为72.67、62.67、58.67、52....  相似文献   

17.
Fungi isolated in Brazil, from lettuce, broccoli, spinach, melon and tomato, were identified as Rhizoctonia solani. All lettuce isolates anastomosed with both AG 1-IA and IB subgroups and all isolates from broccoli, spinach, melon and tomato anastomosed with AG 4 subgroup HG-I, as well as with subgroups HG-II and HG-III. DNA sequence analyses of ribosomal internal transcribed spacers showed that isolates from lettuce were AG 1-IB, isolates from tomato and melon were AG 4 HG-I, and isolates from broccoli and spinach were AG 4 HG-III. The tomato isolates caused stem rot symptoms, the spinach, broccoli and melon isolates caused hypocotyl and root rot symptoms on the respective host plants and the lettuce isolates caused bottom rot. This is the first report on the occurrence in Brazil of R. solani AG 4 HG-I in tomato and melon, of AG 4 HG-III in broccoli and spinach and of AG 1-IB in lettuce.  相似文献   

18.
looseness-1In two observation fields, where six sites were artificially infested with Rhizoctonia solani AG 2-t, bare patches developed. These patches did not re-occur at the site of infestation in three successive years. In fields with and without artificial infestation, natural infection of tulip bulbs by Rhizoctonia spp. occurred. The spatial distribution of infected tulip bulbs was visualised in maps after kriging. The influence of sampling intensity was evaluated by stepwise reduction obtained in the observed data set of the first year. Omnidirectional semivariogram characteristics did not change when sampling intensity was reduced down to 10%. The average maximum prediction error was minimised at sampling intensities varying from 7% to 25%. Naturally occurring bare patches slowly vanished during successive cropping of flower bulbs and did not re-appear in the fourth growing season. A high frequency of isolation of R. solani AG 2-t in one field (Lisse-2) in the fourth consecutive crop did not result in bare patches in that year. It is hypothesised that a reduction in aggressiveness may account for this observation. In contrast, bulb rot due to Rhizoctonia spp. increased during the observation period. R. solani AG 5 isolates were seldom isolated before the bulbs flowered, but were the dominant isolate from bulbs at harvest. In a growth chamber experiment, it was demonstrated that AG 5 did not account for replacement of AG 2-t. However, it was demonstrated that competition may partially explain replacement of AG 2-t isolates during the growing season. At 18 °C, but not at 9 °C, an AG 4 isolate prevented AG 2-t colonising and infecting iris bulbs when both isolates were introduced together to soil. Rhizoctonia populations develop in relation to soil temperature and plant development. It is hypothesised that a temporal niche differentiation may be one of the mechanisms affecting the dynamics of rhizoctonia bare patch of tulips.  相似文献   

19.
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。  相似文献   

20.
In the last years, leafy vegetables cultivated as baby leaves have been established in the market and have attracted the interest of consumers throughout the world. During the growing seasons of 2019 and 2020, 97 isolates of Rhizoctonia solani and 112 isolates of Pythium spp. were obtained from baby leaf vegetables exhibited damping-off symptoms. Representative isolates of R. solani from each surveyed plant species were characterized using sequence analysis of the internal transcribed spacer (rDNA-ITS) region. Isolates were identified as belonging to four anastomosis groups (AGs): AG2-1, AG-IB, AG4-HGI and AG4-HGIII. AG4-HGI was the most prevalent group and phylogenetic analysis showed that the isolates were distinctly separated according to their AGs. Pathogenicity among the four AGs on 23 plant species varied considerably, from not susceptible to highly susceptible, while, in general, AGs did not exhibit host specificity. Furthermore, a total of 112 Pythium spp. isolates were obtained. The ITS region and the cytochrome oxidase II (coxII) gene were amplified, and three Pythium spp. were identified (P. ultimum, P. aphanidermatum and P. sylvaticum), which were used further for maximum-likelihood phylogenetic analysis. The pathogenicity of representative isolates was assessed in vitro and in vivo on 10 plant species. In general, all three tested Pythium spp. were virulent when used in vitro, while P. ultimum was the most virulent in vivo. This is the first comprehensive study aimed at determining the occurrence of specific R. solani AGs and Pythium spp. derived from baby leafy vegetables exhibiting damping-off symptoms in Greece.  相似文献   

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