Utilization of fungal biocontrol agents against rice sheath blight disease provides insight into their role in plant defense responses

Biotic and abiotic factors have an effect on rice production all around the world. Diseases are regarded as major restrictions among the biotic stressors, and rice sheath blight (Rhizoctonia solani Kühn) is one of the most calamitous diseases that significantly damage the crop. Lately, biocontrol of fungal plant pathogens has appeared as an appealing approach. The present investigation was undertaken to evaluate different biocontrol agents like Talaromyces flavus, Chaetomium globosum, Pseudomonas fluorescens and Aspergillus niger against sheath blight disease. Prior to sowing, seeds were bioprimed with each isolate and sown in the nursery. After 21 days, seedlings were transplanted in-vivo and were inoculated with a virulent isolate of Rhizoctonia solani at maximum tillering stage. Observations on biochemical parameters and gene expression studies were carried out at 24, 48, 72, and 96 hpi. Enzymatic activity viz., chitinase, ?-1,3-glucanase, catalase, and PAL was observed maximum in Chaetomium globosum. PR-genes viz., IPT, BrD, HmPr, AMP, AldD, NIC and LisH showed up-regulation at 96 hpi. Chaetomium globosum had the highest yield, maximum number of tillers with least RLH% as compared to other treatments. However, results indicated biocontrol agents are helpful and they induce multitude of defence responses against R. solani in rice.

Isolation and identification of pathogen causing damping off at seedling stage of Trollius chinensis / 中国中药杂志

Trollius chinensis is a traditional Chinese medicinal material in China, the wild resource of T. chinensis are now exhausted, and commercial medicinal T. chinensis mainly depends on artificial cultivation. As one of the most severely happened diseases at the seedling period, damping off has been a serious threaten to the breeding of T. chinensis seedlings. However, no related research have been reported so far. So, the authors collected damping-off samples of T. chinensis in 2018 from seedling breeding nursery in Guyuan, Hebei province, and carried out study on taxonomic identification of the pathogen. Damping off occurs in the T. chinensis production area from mid-May to late June every year. At the beginning, brown lesions were observed on the basal stem, then the lesions circumferential expanded and constricted, and finally resulted in the fall and death of T. chinensis seedlings. Pathogenic isolate was growing rapidly on the PDA medium, well developed aerial mycelia were grey white at first, then turned brown gradually, and a great number of small dark brown sclerotia were developed in the middle and periphery of the colony. Mycelial diameter of the pathogen was about 7 to 10 μm, near right angle or acute angle branches, near branches with septa, branches and septa with constriction. After the healthy T. chinensis seedlings were inoculated by pathogenic isolate, damping-off was observed soon, and the symptom was as same as those observed in the field. Through homogenous blast, the rDNA-ITS sequence of the pathogenic isolate shown 99.49% to 99.84% homology with Rhizoctonia solani, R. solani AG-1 IC mycelium anastomosis group and Thanatephorus cucumeris, the sexual type of Rhizoctonia. Furthermore, obvious mycelial anastomosis phenomena were observed when the pathogenic isolate and R. solani AG-1 IC strain were confronting cultured. Based on the results above, the pathogenic isolate causing damping off of T. chinensis was identified as R. solani AG-1 IC mycelial anastomosis group. RESULTS:: in the present work have important significance for further research on basic biology of the pathogen and integrated control of damping off causing by it on T. chinensis.

Effectiveness of indigenous fluorescent pseudomonads in suppressing Rhizoctonia solani root rot disease and promoting plant growth in chilli seedlings

Aims@#This study aimed to isolate and evaluate the indigenous fluorescent Pseudomonas spp. with bio-control potential against Rhizoctonia solani and promoting growth in chilli seedlings. @*Methodology@#A total of 120 fluorescent bacterial were isolated from the healthy chilli rhizosphere soil from the seven major chilli cultivation localities in Terengganu, Malaysia. Only 115 Gram negative fluorescent isolates were further invitro screened for antagonistic activities against R. solani and plant growth-promoting properties. The 50 most effective fluorescent Pseudomonads antagonist against R. solani with minimum percentage inhibition of radial growth (PIRG) of 65% were selected. Hierarchical cluster analysis was further conducted with two dendrograms derived from SPSS Statistic 20 to facilitate the comparison between these 50 isolates for antagonistic and growth-promoting properties. A total of 40 fluorescent isolates within the most potential cluster were further selected and identified using 16S rRNA sequencing. Thirty four fluorescent isolates were identified as Pseudomonas spp. and six isolates as Burkholderia spp. The top 13 ranked fluorescent Pseudomonas spp. from the scoring index were evaluated for seed germination and vigor index in chilli seedlings. There was no significant difference in germination rate between fluorescent Pseudomonas inoculated with control. However, vigor index of chilli seeds pre-inoculated with fluorescent P. putida (B5C1), P. aeruginosa (B3C56) and P. putida (B5C7) were significantly increased with 4684.9, 4657.3 and 4401.0 over control (P ≤ 0.05).@*Conclusion, significance and impact of study@#These selected fluorescent isolates: P. putida (B5C1), P. aeruginosa (B3C56) and P. putida (B5C7) have the potential to be developed as biofungicide against R. solani and as growthpromoter in chilli production system.

Fructosan form Paenibacillus kribbensis PS04 enhance disease resistance against Rhizoctonia solani and tobacco mosaic virus

BACKGROUND: Rice sheath blight (caused by Rhizoctonia solani) and tobacco mosaic virus are very important plant diseases, causing a huge loss in global crop production. Paenibacillus kribbensis PS04 is a broad-spectrum biocontrol agent, used for controlling these diseases. Previously, extracellular polysaccharides (EPS) from P. kribbensis PS04 had been purified and their structure was inferred to be fructosan. This study aimed to evaluate the effects of exogenous EPS treatment on plant­pathogen interactions. RESULTS: Plant defense genes such as phenylalanine ammonia-lyase, catalase, chitinase, allene oxide synthase, and PR1a proteins were significantly induced by exogenous EPS treatment. Moreover, subsequent challenge of EPSpretreated plants with the pathogens (R. solani or tobacco mosaic virus) resulted in higher expression of defenseassociated genes. Increased activities of defense-associated enzymes, total phenols, and flavonoids were also observed in EPS pretreated plants. The contents of malondialdehyde in plants, which act as indicator of lipid peroxidation, were reduced by EPS treatment. CONCLUSIONS: This study comprehensively showed that EPS produced from P. kribbensis PS04 enhances disease resistance in plants by the activation of defense-associated genes as well as through the enhancement of activities of defense-related enzymes.

Morphological, Pathogenic and Molecular Characterisation of Rhizoctonia solani Strains Isolated from Potato

Rhizoctonia solani Kühn [teleomorph: Thanatephorus cucumeris (Frank) Donk.] is an important fungal pathogen widespread in all potato growing areas of the world that causes stem canker and black scurf of potato (Solanum tuberosum L.). The aim of this study was to find a simple and reliable technique for determining the pathogenicity of Rhizoctonia solani isolates. Sixty (60) isolates of R. solani obtained from sclerotia on potato tubers, collected from different market of Agadir and Casablanca regions (Morocco), were studied for their morphology, pathogenicity and molecular characteristics. They were morphologically characterised by the production of sclerotia and moniloïd cells, and by the mycelium growth capacity at 15, 20, 25, 30 and 35°C. This morphological characterisation leads to three groups of isolates. The first group contained P01 and P03 isolates, which were able to develop under 35°C. However, under 25°C, they did not develop sclerotia. The second group, only formed by L17.1 isolate, did not form sclerotia under 25°C and was not able to develop under 35°C. The third group, formed by several isolates, developed sclerotia under 25°C conditions and were not able to grow under 35°C. Also, a positive correlation was consistent between the production of sclerotia and moniloïd cell formation. The anastomosis reaction revealed that P01, P03, L17.1, and L4.1 isolates were identified as AG-4 and for the other isolates as AG-3. The pathogenic characterisation has shown that P01, P03, L4.1, and L17.1 isolates caused important damping off of radish, tomato, beans, zucchini, and melon. However, the other isolates showed only a minor damping off rate. Molecular characterisation confirmed the classical anastomosis grouping of the isolates into AG-3 and AG-4 Anastomosis Groups. The molecular characterisation is the most rapid and reliable technique to determine the anastomosis group of unknown isolates. The three tests including the pathogenicity, the cultural anastomosis grouping, and the molecular method helped to separate the studied isolates to two groups AG-3 and AG-4.

Isolation and Biochemical Characterisation of Endophytic Bacillus spp from Urtica dioica and Study of Their Antagonistic Effect against Phytopathogens

Endophytic bacteria have been isolated from the roots of Urtica dioica. A total of 54 endophytic bacteria were isolated from the underground parts using suitable surface sterilisation protocol. Three isolates R45a; R45b; R21a were tested for antagonism effect against Fusarium oxysporum, Colletotrichum gloeosporioides, Rhizoctonia solani, Phytophthora parasitica in dual culture method. Significant inhibitory effects on mecylial radial growth have been revealed with a percentage superior or equal to 75%. These strains were Gram-positive rods. Cultures on nutrient agar showed irregular, entirely cream coloured colonies that are strictly aerobic and capable of forming endospore. They belong probably to the genus of Bacillus spp.

In silico analysis of disease resistance and defence-related genes for a major sheath blight qShb 9-2 QTL in rice

Aims@#Sheath blight disease (Rhizoctonia solani) is an important rice disease that causes heavy yield losses in rice annually. To date, no rice variety has been found to be completely resistant to this disease. The most desirable approach for the management of sheath blight disease is to introgress genes with major and durable resistance into the rice genome. Therefore, this study aims to identify disease resistance and defence genes within qShb 9-2, a major QTL found within moderately resistant rice population via in silico analysis. @*Methodology and results@#The sequences of tightly linked markers of qShb 9-2 from GRAMENE database was used to derive the 10.24 Mbp QTL region that contains 1581 genes according to MSU Rice Genome Annotation Project database. BLAST results showed that 11.4% of these genes were transposable elements which may be involved in gene duplication. Through Blast2GO, fifty-four (2.9%) defence-related genes were annotated within this QTL and can be classified into 5 major defence mechanisms. Further, fifty (2.7%) disease resistance genes were identified in qShb 9-2 based on the presence of NB-ARC, LRR-receptor kinase, Ser/Thr protein kinase and protein kinase domains. Lastly, directed acyclic graphs showing the interaction between all the disease resistance and defence-related genes were generated. @*Conclusion, significance and impact of study@#The presence of these genes indicates that qShb 9-2 region may contribute towards the defence against sheath blight disease. By deciphering the gene landscape within the QTL, it may be possible to further fine map the QTL into a smaller region for QTL pyramiding in breeding programmes. The resistance and defence genes are also a source for genetic engineering studies and a good source for marker development.

Evaluation of the fungitoxic activity of vegetal extracts on the mycelial growth of phytopathogens / Avaliação da atividade fungitóxica de extratos vegetais sobre o crescimento micelial de fitopatógenos

Although the productivity of common bean in Tocantins is economically favorable, it has been infected by various pathogens found in soil. Among the major diseases is the web blight and root rot caused by Rhizoctonia solani and collar rot caused by the fungus Sclerotium rolfsii. This study aimed to evaluate the fungitoxic activity of methanol extracts of eight plant species on the inhibition of mycelial growth of S. rolfsii and R. solani. The fungitoxic activities were carried out over the inhibition of mycelial growth by means in vitro assays. The extracts were applied in concentrations of 250, 500, 1000, 2500 e 5000 µg ml-1 in PDA culture medium. In bioassays, it was found the significant effect of plant, concentration and also their interaction on the antifungal activity of the extracts. However, some extracts showed no inhibition of mycelial growth of the pathogens studied. Among those who had higher inhibitions is the extract of Lantana trifolia, which inhibited the mycelial growth of S. rolfsii in all concentrations, being the same as 97% for the highest concentration. When the methanol extract of Piper amplum Kunth, inhibition of the highest concentration was 83% for S. rolfsii and 74% for R. solani. These results show the potential of methanolic extract of Lantana trifolia and Piper amplum Kunth in the control set of plant pathogens studied.

Apesar da produtividade do feijão comum no Tocantins ser economicamente favorável, o mesmo pode ser infectado por vários patógenos habitantes do solo, dentre as principais doenças encontra-se a mela e a podridão radicular causadas pelo fungo Rhizoctonia solani e a podridão do colo causada pelo fungo Sclerotium rolfsii. Este trabalho teve como objetivo avaliar a atividade fungitóxica dos extratos metanólicos de oito espécies vegetais sobre a inibição do crescimento micelial de Sclerotium rolfsii e Rhizoctonia solani. As atividades fungitóxicas foram realizadas perante a inibição do crescimento micelial por meio de ensaios in vitro, sendo os extratos aplicados nas concentrações de 250, 500, 1000, 2500 e 5000 µg ml-1 em meio de cultura BDA. Observou-se o efeito significativo dos fatores planta, concentração e também da interação destes sobre as atividades fungitóxicas. No entanto, alguns extratos não apresentaram inibição do crescimento micelial dos fitopatógenos estudados. Entre os que apresentaram maiores inibições encontra-se o extrato de Lantana trifolia, que inibiu o crescimento micelial do S. rolfsii em todas as concentrações, sendo o mesmo de 97% para a maior concentração. Já a concentração mais elevada do extrato metanólico de Piper amplum apresentou inibição de 83% sobre o crescimento micelial de S. rolfsii e 74% sobre o crescimento micelial de R. solani. Tais resultados evidenciam a potencialidade dos extratos metanólicos das folhas de Lantana trifolia e de Piper amplum no controle dos fitopatógenos estudados.

Control Efficacy of Streptomyces sp. A501 against Ginseng Damping-off and Its Antifungal Substance

Ginseng damping-off, caused by the fungal pathogens Rhizoctonia solani and Pythium sp., is a critical disease in ginseng seedling. In a continuing effort to find microorganisms with the potential of acting as a biocontrol agent against Rhizoctonia damping-off, we found that a Streptomyces sp. A501 showed significant antifungal activity against Rhizoctonia solani. In field experiment to test the efficacy of Streptomyces sp. A501 in controlling ginseng damping-off, the incidence of damping-off disease was meaningfully reduced when ginseng seeds were soaked in the culture broth of Streptomyces sp. A501 before sowing. To perform characterization of the antifungal compound, we isolated it from the culture broth of strain A501 through Diaion HP-20 and silica gel column chromatographies and preparative high-performance liquid chromatography. The structure of the antifungal compound was assigned as fungichromin by spectroscopic methods, mainly nuclear magnetic resonance and electrospray ionization-mass analysis.

Determination of lytic enzyme activities of indigenous Trichoderma isolates from Pakistan

Abstract This study investigated lytic enzyme activities in three indigenous Trichoderma strains namely, Trichoderma asperellum, Trichoderma harzianum and Trichoderma sp. Native Trichoderma strains and a virulent strain of Rhizoctonia solani isolated from infected bean plants were also included in the study. Enzyme activities were determined by measuring sugar reduction by dinitrosalicylic acid (DNS) method using suitable substrates. The antagonists were cultured in minimal salt medium with the following modifications: medium A (1 g of glucose), medium B (0.5 g of glucose + 0.5 g of deactivated R. solani mycelia), medium C (1.0 g of deactivated respective antagonist mycelium) and medium D (1 g of deactivated R. solani mycelia). T asperellum showed presence of higher amounts of chitinases, β-1, 3-glucanases and xylanases in extracellular protein extracts from medium D as compared to medium A. While, the higher activities of glucosidases and endoglucanses were shown in medium D extracts by T. harzianum. β-glucosidase activities were lower compared with other enzymes; however, activities of the extracts of medium D were significantly different. T. asperellum exhibited maximum inhibition (97.7%). On the other hand, Trichoderma sp. did not show any effect on mycelia growth of R. solani on crude extract.

Efecto antifúngico de cuatro mezclas de monoterpenos como alternativa para el control de Rhizoctonia solani Kün / Antifungal effect of four mixtures from monoterpenes like alternative by control of Rhizoctonia solani Kün

Rhizoctonia solani Kühn, es un patógeno de suelo, que causa enfermedades en un amplio rango de hospedantes de cultivos agrícolas. Las necesidades de reducir el uso indiscriminado de fungicidas químicos conllevan al estudio de otras alternativas menos agresivas al medio ambiente. Los monoterpenos presentes en los aceites esenciales de plantas, presentan una marcada actividad biocida y son compuestos que resultan menos perjudiciales desde el punto de vista ambiental. Se prepararon cuatro mezclas de monoterpenos (timol-entol, timolalcanfor, timol-citronelal y timol-1,8 cineol) con el objetivo de evaluar la actividad antifúngica in vitro sobre R. solani, mediante su efecto sinérgico. Se empleó el método de adición al medio de cultivo de cada una de las mezclas a concentraciones de: 0,5; 0,1; 0,05; 0,03 y 0,01 por ciento, partiendo de una solución madre al 10 por ciento en dimetilsufóxido (DMSO) al 5 por ciento. Se calcularon los porcentajes de inhibición y los resultados se analizaron estadísticamente. Se determinaron las dosis inhibitorias medias y se clasificaron la toxicidad de cada una de las mezclas en: inocua, ligera, moderada y tóxica a cada concentración. Las cuatro mezclas mostraron 100 por ciento de inhibición a las concentraciones de: 0, 5; 0, 1; 0,05 y 0,03 por ciento. A la menor concentración las mezclas de timol-mentol y timol-cineol fueron las de mayor efecto inhibitorio del crecimiento micelial de R. solani.

Rhizoctonia solani Kühn is a soil pathogen that causes diseases in a wide host range from agricultural crops. The need to reduce the indiscriminate use of chemical fungicide it has led to the study of other less aggressive environment alternatives. Monoterpenes, common components in plants essential oils, shows a maked biocide activity and are compounds less harmful from an environmental point of view. With the objective of evaluate the in vitro antifungal activity against R. solani, four binary monoterpenes mixtures (thymol-menthol, thymol-camphor, thymol-citronellal and thymol-1,8 cineol) with the objective of evaluate the in vitro antifungal activity against R. solani, four monoterpenes mixtures were prepared. The method of addition to culture media of each of the mixtures in concentrations of: 0, 5; 0, 1; 0, 05; 0, 03 and 0, 01 percent, from a stock solution to 10 percent in dimethylsulfoxide (DMSO) to 5 percent were used. The inhibition percentages were calculated and the results were statistically analyzed. Median inhibitory dose was determined and the toxicity of each mixture were classified in: harmless, light, moderate and toxic in each concentration. The four mixtures showed 100 percent of micelial growth inhibition in concentrations of 0, 5; 0, 1; 0,05 and 0,03 percent. The thymol-cineol and thymol-menthol mixtures had the higher inhibitory effect on micelial growth of R. solani at the lower concentration.

First Report of Web Blight of Rosemary (Rosmarinus officinalis) Caused by Rhizoctonia solani AG-1-IB in Korea

Herein, we report the first occurrence of web blight of rosemary caused by Rhizoctonia solani AG-1-IB in Gangneung, Gangwon Province, Korea, in August 2014. The leaf tissues of infected rosemary plants were blighted and white mycelial growth was seen on the stems. The fungus was isolated from diseased leaf tissue and cultured on potato dextrose agar for identification. The young hyphae had acute angular branching near the distal septum of the multinucleate cells and mature hyphal branches formed at an approximately 90degrees angle. This is morphologically identical to R. solani AG-1-IB, as per previous reports. rDNA-ITS sequences of the fungus were homologous to those of R. solani AG-1-IB isolates in the GenBank database with a similarity percentage of 99%, thereby confirming the identity of the causative agent of the disease. Pathogenicity of the fungus in rosemary plants was also confirmed by Koch's postulates.

Evolution of disease and potential biocontrol activity of Trichoderma SP. against Rhizoctonia solani on potato / Potencial do biocontrole por Trichoderma em relação à evolução da doença causada por Rhizoctonia solani em batata

Black scurf and stem canker disease cause by the fungal pathogen of Rhizoctonia solani and it is an economical important disease of potatoes in Bangladesh and throughout the world. This study evaluated the black scurf and stem canker disease development in potato and antagonistic activity of Trichoderma spp. against R. solani. The artificial infections were carried out using the inoculums of R. solani. The treatments (%inoculum) were: T1 (0% inoculum), T2 (5% inoculum), T3 (10% inoculum), T4 (20% inoculum), T5 (50% inoculum), and T6 (100% inoculum). The infection of stem canker and black scurf on progeny tubers increased with increase in inoculum levels. The highest disease incidence and severity was found in T6 (100% inocula). T6 showed the maximum black scurf infected tubers (russet, deformed and sclerotia). The lowest germination percentage, plant height and tuber yield were also obtained in the same treatment (100% inocula). Trichoderma spp reduced the growth of R. solani and the highest growth suppression was noted in isolate TM12. According to antagonistic activity, Trichoderma spp. reduced the growth of R. solani but was not able to stop the pathogen development. This finding showed management of this disease or R. solani invasion requires an integrated approach compared to Trichoderma single approach.

A rizoctoniose ou crosta negra causada por Rhizoctonia solani é a mais importante doença nos campos de batata em Bangladesh, bem como em várias regiões do mundo. Este trabalho avaliou o potencial do biocontrole com Trichoderma spp. e sua ação antagonista contra R. solani em batateira. Realizou-se as avaliações do potencial antagonosta usando inoculação artificial de R. solani. Os tratamentos (% de inóculo) foram: T1 (0% de inóculo), T2 (5% ), T3 (10%), T4 (20%), T5 (50%) , e T6 (100% de inóculo). A infecção de rizoctoniose na haste e crosta negra nos tubérculos aumentou proporcionalmente com o aumento do nível de inóculo. A maior incidência e severidade da doença ocorreu no tratamento 6 (100 % de inóculo), o qual apresentou maior quantidade de tubérculos infectados e deformados com escleródios em sua superfície. A menor porcentagem de germinação e produção de tubérculos também foi encontrada no tratamento 6, o qual também apresentou menor altura de planta. Trichoderma spp reduziu o crescimento de R. solani e a maior atividade de supressão do crescimento foi encontrada pelo isolado TM12. Foi detectada a atividade antagonista de Trichoderma spp. em reduzir o crescimento de R. solani, mas este não inibiu o crescimento total do patógeno. Conclui-se que o manejo da rizoctoniose da batateira por colonização de R. solani necessita táticas de manejo integrado em detrimento do uso isolado do manejo ou biocontrole com Trichoderma spp.

Role of Sclerotia, Plant Debris and Different Hosts on Survival of Rice Sheath Blight Pathogen, Rhizoctonia Solani.

The survival of sclerotia stored under different conditions revealed that when they were kept in laboratory survived fully up to 7 months. However in soil at 5 cm and 10 cm depth, it survived 100 percent up to 8 and 10 months. The pathogen was viable in the sclerotial form for 17 months in the lab conditions however; it survived for 19 months and 20 months when kept at 5 cm and 10 cm depth in soil respectively. The survival of pathogen along with plant debris stored under different conditions revealed that it survived fully up to 3 months under lab conditions. However in soil at 5 cm and 10 cm depth, it survived 100 percent up to 5 and 6 months respectively. The pathogen survived in diseased plant debris for 9 months in lab conditions. However, the pathogen survives in plant debris up to 11 months and 13 months when kept at 5 cm and 10 cm depth of soil respectively. The viability of pathogen in plant debris was lost gradually. This states sclerotia and plant debris served as source of primary inoculum. Out of fourteen plant species belonging to three families tested, the pathogen produced disease symptoms on all the tested plants and stating pathogen has wide host range.

In-Vitro Evaluation of Fungicides, Biocontrol Agents and Plant Extracts Against Rice Sheath Blight Pathogen Rhizoctonia Solani.

Of the fourteen fungicides of different groups evaluated in-vitro against Rhizoctonia solani , Metalaxyl (0.1%), Mancozeb (0.1%), Tricyclazole (0.1%), Thiophenate methyl (0.1%), Carbendizm+ Mancozeb (0.1%) were proved to be most effective in inhibiting the growth of the fungus. Among the bio-agents screened, Trichoderma viride was most effective in restricting the growth of Rhizoctonia solani followed by Penicillium notatum where as Aspergillus niger was proved least effective. Among the thirteen plant extracts evaluated garlic extract (10%) was most effective in inhibiting the growth of fungus followed by calotropis (10%). Datura leaf extract (10%) was found to be least effective in inhibiting the growth of Rhizoctonia solani.

Efeito de compostos orgânicos sobre podridões radiculares no feijoeiro comum / Effect of organic compounds on root rots of common beans

Os fungos habitantes do solo, Rhizoctonia solani e Fusarium solani f.sp. phaseoli, constituem um complexo etiológico com interação sinérgica, responsável por perdas de produtividade de até 50% em feijoeiro. A matéria orgânica de diversas origens é utilizada na agricultura visando, entre outros motivos, estimular a atividade microbiana para limitar a atividade dos fitopatógenos habitantes do solo. O presente trabalho teve como objetivo avaliar o efeito de doses de compostos orgânicos sobre podridões radiculares causadas por R. solani e F. solani f.sp. phaseoli, em feijoeiro cultivar Pérola, em condições de campo. O delineamento experimental foi de blocos casualizados, em esquema fatorial de 2 x 6. Os compostos orgânicos à base de crotalária (Crotalaria juncea) e grama batatais (Paspalum notatum), associados com cama de frango, foram aplicados no sulco de plantio nas doses de 0, 20, 40, 80, 160 e 320 kg.ha-1. As avaliações de severidade foram realizadas, utilizando-se escala de notas. A maior severidade de F. solani f.sp. phaseoli em plantas de feijoeiro foi observada sob efeito da dose de 320 kg.ha-1 de crotalária + cama de frango e 80 kg.ha-1 para o composto à base de grama batatais + cama de frango. Para R. solani, os compostos orgânicos e doses não influenciaram a severidade de R. solani. A dose de 80 kg.ha-1, independente do composto orgânico, proporcionou a melhor produtividade.

The soil inhabiting fungi, Rhizoctonia solani and Fusarium solani f.sp. phaseoli, constitute an etiological complex with synergic interaction, responsible for up to 50% losses in common beans. Organic matter of diverse sources is used in agriculture to stimulate microbial activity limiting the activity of soil inhabiting plant pathogens, among other uses. This study evaluated the effect of organic compound doses on root rots caused by R. solani and F. solani f.sp. phaseoli, in common beans, cultivar Pérola, in field conditions. The experimental design was randomized blocks, as a 2 x 6 factorial. The organic compounds of Crotalaria juncea or Paspalum notatum, associated with poultry bedding, were applied in the planting furrow at the doses de 0, 20, 40, 80, 160 or 320 kg.ha-1. Evaluations of severity were done using a rating scale. Greater severity of F. solani f.sp. phaseoli in common bean plants were observed at the dose of 320 kg.ha-1 crotalaria + poultry bedding e 80 kg.ha-1 with paspalum compound + poultry bedding. The organic compounds and doses did not affect R. solani severity. The dose of 80 kg.ha-1, regardless of the organic compound, resulted in greater yield.

Comparison of different methods for total RNA extraction from sclerotia of Rhizoctonia solani

Background Rhizoctonia solani (teleomorph: Thanatephorus cucumeris) is one of the most important pathogens of rice (Oryza sativa L.) that causes severe yield losses in all rice-growing regions. Sclerotia, formed from the aggregation of hyphae, are important structures in the life cycles of R. solani and contain a large quantity of polysaccharides, lipids, proteins and pigments. In order to extract high-quality total RNA from the sclerotia of R. solani, five methods, including E.Z.N.A.™ Fungal RNA Kit, sodium dodecyl sulfate (SDS)-sodium borate, SDS-polyvinylpyrrolidone (PVP), guanidinium thiocyanate (GTC) and modified Trizol, were compared in this study. Results The electrophoresis results showed that it failed to extract total RNA from the sclerotia using modified Trizol method, whereas it could extract total RNA from the sclerotia using other four methods. Further experiments confirmed that the total RNA extracted using SDS-sodium borate, SDS-PVP and E.Z.N.A.™ Fungal RNA Kit methods could be used for RT-PCR of the specific amplification of GAPDH gene fragments, and that extracted using GTC method did not fulfill the requirement for above-mentioned RT-PCR experiment. Conclusion It is concluded that SDS-sodium borate and SDS-PVP methods were the better ones for the extraction of high-quality total RNA that could be used for future gene cloning and expression studies, whereas E.Z.N.A.™ Fungal RNA Kit was not taken into consideration when deal with a large quantity of samples because it is expensive and relatively low yield.

Avaliação in vitro de diferentes métodos de análises de fungitoxicidade de óleos essenciais / Evaluation in vitro of different methods of analysis fungitoxicity of essential oils

Os problemas ambientais causados por fungicidas sintéticos têm elevado as buscas por métodos alternativos de controle de doenças de plantas. Objetivou-se avaliar o efeito do óleo essencial de capim citronela, sobre o fungo Rhizoctonia solani, em diferentes métodos de avaliação de fungitoxicidade in vitro. Foi utilizado delineamento inteiramente casualizado em esquema fatorial com quatro repetições, onde os fatores foram compostos por quatro métodos de avaliação da fungitoxicidade in vitro do óleo essencial (óleo essencial diluído em Tween 80 (0,5%) e incorporado ao meio de cultura BDA (batata, dextrose e ágar) ainda fundente; óleo essencial diluído em Tween 80 (0,5%) e distribuído na superfície do BDA; óleo essencial diluído em Tween 80 (0,5%) e distribuído em papel filtro fixado na superfície interna da tampa da placa de Petri; óleo essencial puro e distribuído na superfície do meio de cultura; e testemunha) e por cinco épocas de avaliação (2, 4, 6, 8 e 10 dias de incubação). Foram utilizados 0,25µL mL-1 do óleo do capim citronela em todos os tratamentos. Dos tratamentos avaliados o uso do óleo puro distribuído na superfície do meio de cultura foi mais eficiente na redução do diâmetro micelial em todas as avaliações. Neste método a taxa de crescimento micelial foi de 9, 02 mm dia-1, atingindo na última época de avaliação 79,77 mm.

Environmental problems caused by synthetic fungicides have increased the search for alternative methods of control of plant diseases. The objective was to evaluate the effect of essential oil of citronella grass, on the fungus Rhizoctonia solani, in different methods of in vitro fungitoxicity. We used a randomized design in a factorial design with four replications, where the factors were composed of four methods for assessing the in vitro fungitoxicity of the essential oil of citronella grass (essential oil diluted in Tween 80 (0.5%) and embedded in the culture medium PDA (potato dextrose agar) still melting, essential oil diluted in Tween 80 (0.5%) and distributed on the surface of the PDA; oil essential diluted in Tween 80 (0.5%) and distributed on filter paper attached to the inner surface of the lid of the Petri dish, pure essential oil and distributed on the surface of the culture medium, and control) and five evaluation periods (2, 4, 6, 8 and 10 days of incubation). Was used 0.25µL mL-1 of citronella oil in all treatments. Of the treatments evaluated the use of pure oil distributed on the surface of the culture medium was more effective in reducing the mycelial diameter in all evaluations. In this method the rate of mycelial growth was 9,02 mm day-1, reaching in last evaluation 79,77 mm.

A rare case of human mycosis by Rhizoctonia solani.

Rhizoctonia solani is a most widely recognized strong saprophyte with a great diversity of host plants. It is a first ever case of extensive human mycosis caused by Rhizoctonia solani in a 65-year-old diabetic and hypertensive farmer, with a history of head injury caused by fall of mud wall. Necrotic material collected revealed septate fungal hyphae with bacterial co-infection. Fungal culture on SDA at 25°C showed cotton wooly growth progressing to greyish-white to shiny metallic black colonies and identified on basis of septate mycelial growth without conidia, right angle branching, presence of compact hyphal forms and anastomosis between branching hyphae on LPCB mount.

Evaluación in vitro de aislamientos de Trichoderma harzianum para el control de Rhizoctonia solani, Sclerotium rolfsii y Fusarium oxysporum en plantas de tomate / In vitro evaluation of Trichoderma harzianum for control of Rhizoctonia solani, Sclerotium rolfsii, and Fusarium oxysporum in tomato plants

En este estudio se determinó la capacidad antagónica de aislamientos de T. harzianum para el control de Rhizoctonia solani, Sclerotium rolfsii y Fusarium oxysporum en raíces de plantas de tomate. Se obtuvieron 6 aislamientos de T. harzianum de 6 municipios del estado Trujillo, empleando la técnica de siembra directa de raíces en agar agua acidificada. El antagonismo se realizó en cultivos duales utilizando agar papa dextrosa, incubados a 25 ºC, bajo un diseño al azar, con 18 tratamientos conformados por cada aislamiento de T. harzianum y cada patógeno, 3 tratamientos testigos correspondientes a cada patógeno y 3 repeticiones por tratamiento, evaluándose el modo de acción e inhibición del crecimiento radial al tercer día. Todos los aislamientos de T. harzianum mostraron un rápido crecimiento sin diferencias significativas entre ellos (p>0,05), aún cuando se observó que el T121 fue más eficaz como controlador. Al comparar el crecimiento de los aislamientos de T. harzianum con el de los hongos patógenos, se obtuvieron diferencias significativas (p<0,05). Cuatro aislamientos de T. harzianum presentaron acción micoparasítica y dos de tipo antibiosis, mecanismos característicos de estas especies de biocontroladores. Todos los aislamientos de T. harzianum estudiados pueden ser utilizados para el control de patógenos de tomate.

This study determined the antagonistic capacity of T. harzianum isolates for control of Rhizoctonia solani, Sclerotium rolfsii, and Fusarium oxysporum in the roots of tomato plants. Six T. harzianum isolates were obtained from 6 municipalities of Trujillo State, using the direct inoculation of roots in acidified water agar technique. The antagonism was carried out in dual cultures using potato dextrose agar, incubated at 25 ºC, under a random design, with 18 treatments conformed for each T. harzianum isolate and each pathogen, 3 control treatments corresponding to each pathogen, and 3 repetitions per treatment, evaluating the mode of action and inhibition of radial growth at the third day. All the T. harzianum isolates showed rapid growth without significant differences among them (p>0.05), even though it was observed that T121 was more efficient as controller. When comparing the growth of the T. harzianum isolates with that of the pathogenic fungi, there were significant differences (p<0.05). Four T. harzianum isolates showed mycoparasitic action, and two antibiosis type action, which are characteristic mechanisms of these bio-controlling species. All the T. harzianum isolates studied can be used for the control of tomato pathogens.