Evaluation of Brassica species for resistance to Rhizoctonia solani and binucleate Rhizoctonia (Ceratobasidum spp.) under controlled environment conditions

Isolates of R. solani AG 2–1, AG 8, AG 10 and binucleate Rhizoctonia (Ceratobasidium spp.) were tested for virulence on Brassica crops in growth chamber experiments. Isolate virulence and genotype resistance were determined based on percent of seedling survival, shoot length reduction, and shoot fresh weight. Isolates had significant effects on all tested measurements, compared to the non-inoculated controls. Rhizoctonia solani AG 2–1 appears to be the most aggressive pathogen on all tested genotypes followed by R. solani AG 8, binucleate Rhizoctonia and R. solani AG 10, respectively. Genotype by isolate interaction effects were found to be significant for percent of seedling survival and shoot length reduction. None of the tested genotypes exhibited any level of resistance to R. solani AG 2–1, but three promising genotypes with moderate levels of resistance to R. solani AG 10, R. solani AG 8 and binucleate Rhizoctonia were identified. Moderate heritability (0.57) was observed for the percent of seedling survival in the resistant genotype KS4022.     

Vertical distribution of root damage caused by Rhizoctonia solani in wheat

Vertical distribution of root damage caused by Rhizoctonia solani within a rhizoctonia patch was examined on five occasions during the growing season using a soil core technique. The effect of depth on root damage was assessed by determining root growth of wheat seedlings grown in cores of undisturbed soil taken at depths 0−2−5, 2−5−5−0, 5−0−7−5 and 7−5−10 cm from both inside and outside a patch. Within the patch most of the damage occurred in the top 5 0 cm of soil with less in the next 2−5 cm and least in the 7−5−10 cm zone. Outside the patch, soil depth had little or no effect on root growth.     

张掖市番茄茎基腐病田间发病规律及防治方法研究

田间调查表明,番茄茎基腐病在张掖市发病初期为5月中、下旬,发病高峰期在6月中、下旬;移栽发病重,直播发病轻;碱潮地发病重,其次为灌漠地,沙壤地发病率最轻;平作发病重,垄作发病轻;膜面覆土发病轻,膜面不覆土发病重;中间破膜发病轻,中间不破膜发病重。根据种子、苗床处理、定植穴以及发病初期药剂灌根试验结果表明:供试的10种药剂中,以3%口恶霉.甲霜水剂400倍液移栽前灌根、45%敌磺.琥铜可湿性粉剂750倍液发病初期灌根,防效分别为65.5%、59.5%。     

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。     

Soybean root suberin and partial resistance to root rot caused by Phytophthora sojae

Phytophthora sojae is the causal agent of root and stem rot of soybean (Glycine max). Various cultivars with partial resistance to the pathogen have been developed to mitigate this damage. Herein, two contrasting genotypes, the cultivar Conrad (with strong partial resistance) and the line OX760-6 (with weak partial resistance), were compared regarding their amounts of preformed and induced suberin components, and to early events during the P. sojae infection process. To colonize the root, hyphae grew through the suberized middle lamellae between epidermal cells. This took 2 to 3 h longer in Conrad than in OX760-6, giving Conrad plants more time to establish their chemical defenses. Subsequent growth of hyphae through the endodermis was also delayed in Conrad. This cultivar had more preformed aliphatic suberin than the line OX760-6 and was induced to form more aliphatic suberin several days prior to that of OX760-6. However, the induced suberin was formed subsequent to the initial infection process. Eventually, the amount of induced suberin (measured 8 days postinoculation) was the same in both genotypes. Preformed root epidermal suberin provides a target for selection and development of new soybean cultivars with higher levels of expression of partial resistance to P. sojae.     

Integration of soil application and seed treatment formulations of Trichoderma species for management of wet root rot of mungbean caused by Rhizoctonia solani

BACKGROUND: The efficacy of seed dressing and soil application formulations from the isolates of Trichoderma viride (IARI P1; MTCC 5369), T. virens (IARI P3; MTCC 5370) and T. harzianum (IARI P4; MTCC 5371) were evaluated individually and in combination in pot and field experiments during the rainy seasons of 2005, 2006 and 2007 for the management of wet root rot (Rhizoctonia solani) and improvement in the yield of mungbean. RESULTS: A seed dressing formulation, Pusa 5SD, and soil application formulations, Pusa Biogranule 6 (PBG 6) and Pusa Biopellet 16G (PBP 16G), based on Trichoderma virens, were found to be superior to other formulations in reducing disease incidence and increasing seed germination and shoot and root lengths in mungbean. In field experiments, a combination of soil application with PBP 16G (T. virens) and seed treatment with Pusa 5SD (T. virens) + carboxin was superior to any of these formulations individually in increasing seed germination, shoot and root lengths and grain yield and reducing wet root rot incidence in mungbean. Seed treatment was more effective than soil application for all the evaluated parameters. The combined application of Pusa 5SD and carboxin was also superior to individual treatment. CONCLUSION: The efficacy of the evaluated formulations against wet root rot of mungbean proved that the integration of soil application of PBP 16G and seed treatment with Pusa 5SD + carboxin is highly effective for the management of wet root rot, increasing plant growth and grain yield of mungbean Copyright © 2011 Society of Chemical Industry     

Sheath rot and leaf blight – a new disease of Java citronella caused by Rhizoctonia solani

A new disease of Cymbopogon winterianus , characterized by symptoms of sheath rot and leaf blight, has been observed in the Tarai region of Uttar Pradesh (IN). The pathogen has been isolated and identified as Rhizoctonia solani.     

Chitinase levels in rice cultivars correlate with resistance to the sheath blight pathogen Rhizoctonia solani

Various rice cultivars were selected and screened for their reaction to sheath blight in the greenhouse. Cluster analysis of percent relative lesion height (% RLH) generated four groups of cultivars with a coefficient of similarity of 3.27. Chitinase activities were detected 24 h after inoculation of moderately resistant cvs Betichikon, Dudruchi, Khatochalani, Padi Pulut Malat, Kakua, IR72, Khakibinni. But in the susceptible cv. IR58, chitinase activity was detected only 36 h after inoculation. Western blot analysis showed that class 1 and class 2 chitinases were induced following Rhizoctonia solani infection of these cultivars. The % RLH and the number of infection cushions were negatively correlated with the level of chitinase activity. Moderately resistant rice cultivars had higher levels of chitinase activity and lower disease severity and numbers of infection cushions formed compared to IR58.     

Occurrence of foliar rot of pak choy and Chinese mustard caused by Rhizoctonia solani AG1-IB in China

During December 2003, leaf rot was frequently observed on leaves of pak choy and Chinese mustard in Xishuangbanna district of Yunnnan Province, China. Isolates of Rhizoctonia solani, consistently obtained from the diseased leaves, were identical to anastomosis group (AG)-1 IB based on cultural characteristics and analysis of the ITS-5.8s rDNA region. This is the first report of foliar rot of pak choy and Chinese mustard caused by R. solani AG-1 IB in China.     

Differences in resistance in onion cultivars to pink root rot disease in Iran

Forty-five onion (Allium cepa) cultivars were evaluated for disease resistance to the fungal pathogen Pyrenochaeta terrestris (pink root disease). Forty-three Iranian cultivars and two commercially exotic resistant cultivars (Texas Early Grano and Yellow Sweet Spanish) were grown in a glasshouse for two successive years (2003 and 2004) in Isfahan, Iran. Susceptibility of the cultivars was determined using a scale of 0–3. Six cultivars had significantly lower susceptibility of pink root compared to the exotic ones. High susceptibility tended to be associated with high mean scores (2–3), and the highly resistant cultivars had the lowest scores (0–1). In addition, the 45 examined cultivars were ranked from 1 to 45 according to their markedly differing reactions to P. terrestris, which differed markedly. Of 32 cultivars that were less resistant, 30 with an intermediate status or tolerance (1–2) differed considerably in their rank order. No pink root symptoms were seen in the early stages, but on blotter paper or wheat-straw agar some roots turned pink with no pycnidia formation, whereas on potato dextrose agar medium (PDA) with a few fresh healthy and sterile onion roots on the surface, mycelia and pycnidia were recovered. Variance and cluster analysis showed similar results among the cultivars with various levels of resistance, tolerance and susceptibility as determined by scoring scales.     

First report of white leaf rot on Chinese chives caused by Rhizoctonia solani AG-2-1

Delayed sprouting and white rot of leaf tips were found on Chinese chives in a greenhouse in Hokkaido, Japan, in the spring of 2006 and 2007. The causal fungus was identified as Rhizoctonia solani anastomosis group (AG)-2-1 and discriminated from the leaf rot pathogen R. solani AG-4 HG-I in terms of pathogenicity. Symptoms and the time of year that the disease occurs also apparently differ for the two pathogens. This is the first report of white leaf rot on Chinese chive caused by R. solani AG-2-1.     

己唑醇对水稻纹枯病的毒力测定及田间药效试验

根据水稻纹枯病菌在含己唑醇系列浓度的PDA培养基上的菌丝生长速率,计算出己唑醇对水稻纹枯病菌的毒力回归方程为:Y=4.0407+2.3632x,r=0.9971,药剂EC₅₀=2.5464mg/L,EC₉₅=12.6463mg/L,试验结果表明己唑醇对水稻纹枯病菌具有较高的生物活性。田间药效显示,5％己唑醇悬浮剂250mg/667m²药后15d防效达69.54％。     

Comparison of methods for detection of Rhizoctonia solani in soil

At a soil temperature that was favourable for the contaminatingRhizoctonia isolate, detection of the pathogen in soil by using Ko agar or fragments ofJuncus effusus stems as bait or by plating soil samples in small clumps (Ko and Hora, 1971) gave comparable results. At unfavourable soil temperature the use of Ko agar baits was most successful. Water agar to which 0.5% inulin and a selective solution developed by G.M. Tichelaar (formerly: IPO, Wageningen, personal communication) was added was the best plating medium.Samenvatting De methode van Ko en Hora (1971), waarbij uit een willekeurig genomen grondmonster, 1 g in kleine hoopjes op een selectieve bodem werd uitgeplaat, is o.a. vergeleken met een methode om de schimmel in de grond aan te tonen door gebruik te maken van stukjes loksubstraat, die drie dagen op 4 cm diepte in de grond hadden gelegen. Gedroogde stengeldelen vanJuncus effusus (pitrus) en druppeltjes van een voedingsagar ontwikkeld door Ko en Hora (1971) boden als loksubstraat toegepast de beste resultaten. Het voedingsmedium waarmee uit hoopjes grond en uit rus- en Ko-agar-lokaas de meesteRhizoctonia werd geïsoleerd, was water-agar met 0,5% inuline waaraan een oplossing met selectieve werking, ontwikkeld door G.M. Tichelaar (voorheen: IPO, Wageningen, persoonlijke mededeling), vóór het gieten van de bodem werd toegevoegd.Bij een bodemtemperatuur, die gunstig was voor hetRhizoctonia-isolaat waarmee de grond was besmet, waren de resultaten van beide soorten loksubstraat en de hoopjes grond vergelijkbaar. Bij ongunstige bodemtemperatuur werd met behulp van Ko-agar-loksubstraat de meesteRhizoctonia geïsoleerd.     

河北省小麦主栽品种对茎基腐病抗性鉴定及评价指标相关性分析

为明确河北省小麦主栽品种对假禾谷镰刀菌Fusarium pseudograminearum引起的小麦茎基腐病的抗性水平, 采用温室苗期与田间接种鉴定相结合的方法, 评价20份河北省小麦主栽品种的抗病性。结果显示, ‘衡0628’苗期表现为抗病, ‘山农22’等6个品种苗期表现为中抗, ‘冀麦585’等5个品种成株期表现为中抗, ‘石麦15’和‘藁优5766’ 2个品种在苗期和成株期均表现为中抗。抗性指标相关性分析结果显示, 苗期病情指数与茎基部组织中病原菌DNA含量有极强的相关性, 成株期病情指数与白穗率有显著相关性。本研究结果表明, ‘石麦15’和‘藁优5766’两个品种的抗性水平较高, 且抗性稳定, 可利用苗期茎基部组织中病原菌DNA含量及成株期白穗率分别作为评价小麦茎基腐病苗期及成株期抗性的指标之一。     

Methods of testing potato cultivars for resistance to soft rot of tubers caused by Erwinia carotovora subsp. atroseptica

The resistance of eight potato cultivars to tuber soft rot caused by E. carotovora subsp. atroseptica was assessed in 2 years using three different test methods. Similar cultivar resistance rankings were obtained for any one method within a year and between years for two methods (single site, infectivity titration), but not for the third (vacuum infiltration). However, the ranking of cultivars differed for the three methods. Ranking was not affected by inoculating the cortex or the more susceptible medullary tissue, or by assessing rotting in terms of infection frequency or lesion size, but it was affected by oxygen concentration during incubation. Differences among cultivars were greater when inoculated tubers were incubated anaerobically than when incubated with 5% oxygen. There was no relationship between the relative susceptibilities of cultivars to tuber soft rot in storage in January/February and those of mother tubers after planting.     

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.     

水稻品种抗纹枯病田间鉴定方法改进

田间试验表明,插大穴(基本苗30株,穴左右)诱发与常规穴(6株,穴左右)插植人工接茵秆法鉴定水稻品种对纹枯病的抗病性结果基本一致,以插大穴诱发鉴定发病更为充分,从而提出了水稻纹枯病田问新的鉴定方法,且该方法省工、节支.     

Infection processes and soft wheat response to root rot and crown rot caused by Fusarium culmorum

An isolate of the fungus Fusarium culmorum constitutively expressing green fluorescent protein was used to investigate the infection process and host response of primary seedling roots and stem base leaf sheaths of soft wheat cv. Genio. Disease progress was assessed macroscopically by visual symptoms, microscopically by confocal laser scanning microscopy (CLSM) and via gene expression analysis of fungal and wheat genes by real‐time quantitative RT‐PCR. In the roots, CLSM investigations revealed an initial intercellular and subsequent intracellular colonization by fungal hyphae. The fungus invaded the rhizodermal layer and cortex but was not seen to colonize the stele. The fungus consistently expressed TRI5 (24, 48 and 96 h post‐inoculation), indicating that trichothecenes were being synthesized throughout this phase of infection and colonization. The expression of the six host defence‐associated genes (Wheatwin 1‐2, PR1, Chitinase, PAL, WIR1 and LOX) increased early in infection and decreased during later stages. In the stem base, CLSM observations revealed the fungus sequentially penetrating though the first, second and third basal leaf sheaths. Expression of TRI5 was initiated early in the infection of each leaf sheath. The expression of the host defence‐associated genes varied over time and across leaf sheaths, and all were also expressed in leaf sheaths which had not yet been in contact with the fungus. Expression of LOX and WIR1 were particularly enhanced in the third leaf sheath.