Genus Rhizoctonia Research Articles

The Genus Rhizoctonia (Cantharellales) in Russia

The Genus Rhizoctonia (Cantharellales) in Russia

Fungal Diseases in Yerba Mate: Status and Management Strategies.

Yerba mate (Ilex paraguariensis St. Hil.), with its health benefits and socioeconomic significance, plays a crucial role in Argentina and other South American countries like Brazil and Paraguay. Its cultivation in the Province of Misiones (Argentina) supports various sectors, contributes to regional development, and provides employment opportunities. However, the transition from extractive practices to monoculture, accompanied with increased demand, has led to phytosanitary challenges. Imbalanced native microbiota, disease development, and pathogen dispersion have become prevalent issues. Understanding the known pathogens associated with yerba mate plants is crucial for developing effective agricultural strategies. The primary objective of this study is to synthesise current knowledge on prevalent fungal diseases in yerba mate cultivation, as well as to provide agricultural management recommendations for effective disease control. Fungal diseases can cause significant damage to different parts of the plant, resulting in economic losses. The proximity of neighbouring plantations to yerba mate crops may contribute to the cross-contamination of pathogens, emphasizing the need for comprehensive epidemiology and accurate diagnosis. Multiple fungal genera have been reported to cause pathologies in yerba mate. Among the fungi causing foliar diseases are Ceratobasidium niltonsouzanum, Cylindrocladium spathulatum, Pseudocercospora mate, Asterina sphaerelloides, Colletotrichum gloeosporioides aff var. yerbae, and Phyllosticta sp. Caulinary diseases are caused by Alternaria sp., Phoma sp., Colletotrichum sp., and Ceratocystis fimbriata. Regarding root rot, the genera Rhizoctonia sp., Pythium sp., Fusarium sp., and Rosellinia sp. have been reported. Proper crop management practices and monitoring are essential for effective disease control. To reduce reliance on chemical compounds, the use of biocontrol agents like Trichoderma sp. has shown promise in regulating phytopathogenic fungi populations. Continued research is vital to preserve the yerba mate industry and ensure its long-term viability while minimizing environmental impact.

Characterization and report of binucleate Rhizoctonia AG‐Fb affecting soybean in Brazil

AbstractRhizoctonia root rot is a disease that can affect soybean leading to plant death usually in bare patches. Frequently, Rhizoctonia solani has been reported as the main causal agent of the disease. However, due to the great genetic diversity of the genus Rhizoctonia, there are other species that could also attack soybean plants. Thus, the objective of this study was to determine the pathogenicity and characterize an isolate of binucleate Rhizoctonia obtained from a soybean plant with symptoms of root rot cultivated in soil from southern Brazil. The isolate was identified based on the morphology and phylogenetic analysis of the internal transcribed spacer region (ITS) of the rDNA. Pathogenicity tests were then performed on seeds and roots of soybean and the optimum temperature for mycelial growth was determined. The isolate was identified as binucleate Rhizoctonia AG‐Fb and it was pathogenic to soybean seeds and roots. In the pathogenicity assay in soybean seed, the isolate reduced seed germination by 20% and caused seed rot index of 69.3. In the pathogenicity assay in soybean root, the inoculation of binucleate Rhizoctonia AG‐Fb caused 67.3 root rot severity index, and reduced the emergence speed index by 19%, seedling height by 31%, root dry mass by 25% and root volume by 43% in soybean seedlings. The optimum temperature for the mycelial growth of the isolate was 26°C. To the best of our knowledge, this is the first report of binucleate Rhizoctonia AG‐Fb associated with soybean root rot in Brazil.

Characterization of three-nucleate Rhizoctonia AG-E based on their morphology and phylogeny

The genus Rhizoctonia has been classified into two main groups according to the number of nuclei. Binucleate Rhizoctonia strains have two nuclei in each cell, whereas multinucleate Rhizoctonia fungi were observed to have a variable number of nuclei ranging from 4 to 16 in each cell. In the study, twelve Polish isolates were tested. According to ITS1-5,8S-ITS2 rDNA sequences, the isolates were classified in the AG-E. Their affiliation to AG was confirmed by anastomosis reactions with tester isolates. The number of nuclei was counted with DAPI staining under a fluorescent microscope, and the diameter of the hyphae was also measured. Not all AG-E isolates had the same number of nuclei in their cells: one group among these fungi produced cells with a diverse number of nuclei, usually 3; however, this number ranged from 2 to 4, making the average number of nuclei close to 3. It can be assumed that all isolates with three nuclei belong to this group, which may greatly facilitate the preliminary identification of trinucleate isolates of Rhizoctonia spp. belonging to AG-E. Based on these characters, we call these isolates AG-E-3n isolates. The thiamine requirement is not helpful in classifying and describing the AG-E strains.

Evaluation of Tulasnella and Ceratobasidium as Biocontrol Agents of Fusarium Wilt on Vanilla planifolia

Fusarium wilt, caused by the fungus Fusarium oxysporum f. sp. vanillae (Fov), is a disease that results in significant losses in commercial vanilla production. The genera Ceratobasidium (Ceratobasidiaceae) and Tulasnella (Tulasnellaceae), which are often reported as mutualistic symbionts in orchids, belong to the form genus Rhizoctonia, a paraphyletic group of fungi with potential for pathogen biocontrol. We assayed the antagonistic properties of the form genus Rhizoctonia from the roots of neotropical orchids: two Tulasnella spp. isolates (Bv3 and Er1) and one Ceratobasidium sp. (Er19). In a dual culture, we found that form genus Rhizoctonia isolates can generate a biocontrol effect against Fusarium through the mechanisms of antibiosis and competition for space and nutrients. On histological observations, orchid root endophytes also demonstrated potential for mutualistic symbiosis development by establishing themselves on the surface and within the root tissue of Vanilla planifolia accessions multiplied in vitro (NSF021 and NSF092). However, in plant assays, the form genus Rhizoctonia isolates did not reduce symptom expression or disease development due to infection by Fov in the host. These results contribute to the knowledge of the interactions between tropical orchids and their microbiota and demonstrate the need for multidisciplinary studies for the implementation of integrated management strategies for Fusarium disease in commercial systems.

Diversity and Aggressiveness of Rhizoctonia spp. from Nebraska on Soybean and Cross-Pathogenicity to Corn and Wheat.

Rhizoctonia and Rhizoctonia-like species of fungi that cause disease are known to have varying host ranges and aggressiveness. Accurate identification of these species causing disease is important for soybean disease management that relies upon crop rotation. The anamorphic genus Rhizoctonia contains several diverse species and anastomosis groups (AGs) including some known soybean pathogens, such as Rhizoctonia solani, whereas for others the ability to cause disease on soybean has not been well described. The present study was conducted to identify the predominant species and AG of Rhizoctonia from soybean, corn, and wheat fields that are pathogenic on soybean and characterize cross-pathogenicity to common rotational crops, corn and wheat. We surveyed for Rhizoctonia spp. in Nebraska; isolates were identified to species and AG, and aggressiveness was assessed. A total of 59 R.zeae isolates, 49 R.solani, nine binucleate Rhizoctonia, three R.circinata, and two R.oryzae isolates were collected in 2016 and 2017 from a total of 29 fields in 15 counties. The most abundant R.solani AGs were AG-4, AG-1 IB, AG-2-1, AG-3, and AG-5. R.solani AG-4 and R. zeae were found in all three regions of the state (west, central, and eastern). Some isolates that were most aggressive to soybean seedlings were cross-pathogenic on both wheat and corn. In addition, R. zeae was pathogenic on soybean when evaluated at 25°C, which is warmer than temperatures used previously, and isolates were identified that were aggressive on soybean and cross-pathogenic on both corn and wheat.

Origin of agricultural plant pathogens: Diversity and pathogenicity of Rhizoctonia fungi associated with native prairie grasses in the Sandhills of Nebraska.

The Sandhills of Nebraska is a complex ecosystem, covering 50,000 km2 in central and western Nebraska and predominantly of virgin grassland. Grasslands are the most widespread vegetation in the U.S. and once dominated regions are currently cultivated croplands, so it stands to reason that some of the current plant pathogens of cultivated crops originated from grasslands, particularly soilborne plant pathogens. The anamorphic genus Rhizoctonia includes genetically diverse organisms that are known to be necrotrophic fungal pathogens, saprophytes, mycorrhiza of orchids, and biocontrol agents. This study aimed to evaluate the diversity of Rhizoctonia spp. on four native grasses in the Sandhills of Nebraska and determine pathogenicity to native grasses and soybean. In 2016 and 2017, a total of 84 samples were collected from 11 sites in the Sandhills, located in eight counties of Nebraska. The samples included soil and symptomatic roots from the four dominant native grasses: sand bluestem, little bluestem, prairie sandreed, and needle-and-thread. Obtained were 17 Rhizoctonia-like isolates identified, including five isolates of binucleate Rhizoctonia AG-F; two isolates each from binucleate Rhizoctonia AG-B, AG-C, and AG-K, Rhizoctonia solani AGs: AG-3, and AG-4; one isolate of binucleate Rhizoctonia AG-L, and one isolate of R. zeae. Disease severity was assessed for representative isolates of each AG in a greenhouse assay using sand bluestem, needle-and-thread, and soybean; prairie sandreed and little bluestem were unable to germinate under artificial conditions. On native grasses, all but two isolates were either mildly aggressive (causing 5-21% disease severity) or aggressive (21-35% disease severity). Among those, three isolates were cross-pathogenic on soybean, with R. solani AG-4 shown to be highly aggressive (86% disease severity). Thus, it is presumed that Rhizoctonia spp. are native to the sandhills grasslands and an emerging pathogen of crops cultivated may have survived in the soil and originate from grasslands.

Evolutionary biology and interaction among the anastomosis groups of Rhizoctonia spp.

Rhizoctonia solani Kuhn and other Rhizoctonia spp. are the plant pathogenic fungi widespread in the world and in both cultivated and noncultivated soils. Rhizoctonia spp. are readily isolated from diseased plants and soils, which differ in their pathogenicity, cultural, morphological and physiological characteristics. Identification of species and intraspecific groups (ISGs) is sometimes very difficult, due to the absence of the authentic cultures, which hinders mycological and pathological studies. The genus Rhizoctonia can be identified using various techniques such as, sequence analysis of ITS regions, DNA fingerprinting and the rDNA coding sequence. The introduction of the concept of anastomosis groups (AGs) or intraspecific groups has also aided species and subspecies identification. There are 13 different anastomosis groups exists in Rhizoctonia solani of which AG 1-4 were strong pathogenic on many plants and AG 6-10 were orchid mycorrhizae. Analysis of restriction fragment length polymorphisms (RFLPs) and the sequences within ribosomal RNA genes (rDNA) among different anastomosis groups of R. solani isolates exhibited DNA base sequence homology and diverging evolutionary affinities for hyphal anastomosis. More recently, ribosomal DNA (rDNA) sequences have been used to study the genetic relationships between AG of R. solani. The ecology and epidemiology of each ISG of R. solani must be investigated in order to gain a better understanding of this important group of fungi.

Ғўза далаларида ризоктония туркумига мансуб замбуруғларни тарқалишини ўрганиш

Мақолада мамлакатимиз шароитида ғўза экинларида аниқланган замбуруғли нихол касалликлари ва уларга қарши биологик кураш чоралари муҳокама қилинади. Тақдиқотлар натижасида, ғўзада илдиз чиришининг асосий қўзғатувчиларига микроскопик замбуруғлардан Rhizoctonia solani, Thielariopsis basicola, Fuzarium spp, Pythium spp. лар киради.
 Тадқиқот маълумотлардан келиб чиқадики, ниҳол касалликлари келтирадиган зарари бўйича, охирги 3 йил учун ўртача олинганда, ҳамма касалликлардан энг юқори нобуд бўлган пахта ҳосилининг 22,6 фоизи нихол касалликлари туфайли содир бўлган. Кейинги ўринларда вертициллёз сўлиш 19,23 %, Кўсак чириши эса 19,1 % ни ҳамда энг кам фузариоз сўлиш 7.48% ни ташкил этган.
 Олинган маълумотлар асосида ғўзада илдиз чириши касалликларининг ривожланишига – тупроқ ва ҳавонинг ҳароратини паст бўлиши, уруғликни тавсия этилганидан чуқурроқ экилиши, қатқалоқ, ортиқча намлик, тупроқнинг яхши юмшатилмаганлиги, патоген замбуруғлар билан зарарланганлиги, сабаб бўлади деган хулосага келинган.

First Report of Ceratobasidium sp. Causing Root Rot of Garlic in China

Garlic (Allium sativum L.) is an important cash crop in China. In the spring of 2018, stunted and chlorotic plants in some garlic fields were observed in Jinxiang, Shandong, and Feng Counties, Jiangsu Province, in China. The growth of symptomatic plants was weaker, with affected plants showing signs of apical chlorosis, wilting, and dieback. In the aerial part of the plant, the symptoms of root rot disease resembled nutrient deficiency or drought stress. The roots were shriveled and rotted, with reduced root density. According to survey, the incidence of root rot in each garlic planting area is as high as 35 to 40%, and once the disease occurs, the commodity value of garlic will be reduced. Generally speaking, fungal diseases are among the main biotic factors affecting garlic yield, particularly those caused by species of the genera Fusarium, Phytophthora, and Pythium. In order to identify the causal agent of this disease, symptomatic plants were collected from several regions of the main garlic producing areas in China, including Jinxiang County, Jiaxiang County in Shandong Province, and Fengxian County in Jiangsu Province. The garlic variety planted is Jinxiang white garlic, which is a local garlic variety. Samples of rotten roots were washed in tap water, surface sterilized in 1.5% sodium hypochlorite for 1 min followed by 75% ethanol for 30 s, rinsed with sterilized distilled water three times, and blotted dry on sterile filter paper. Pieces of infected root tissues (2 to 3 mm) were placed on potato dextrose agar (PDA) and kept at 28°C for 7 days. After the colonies were established on PDA, the fungal strains were purified by the hyphal-tip method. Five fungal isolates with similar morphology to each other were obtained, and isolate DS54-3 was chosen for the following experiment. The fungal colony grew within 5 days on PDA containing a full culture medium. Fungal colonies were white initially and then turned brown, and septate hyphae were 3.7 to 4.3 μm in diameter and branched at right angles with a constriction at the origin of the branch point. These characteristics are typical of the genus Rhizoctonia. Binucleate cells from five isolates were observed using a lactophenol aniline blue solution stain and matched Ceratobasidium morphological descriptions (Chen et al. 1985). The morphological characteristics of isolate DS54-3 were consistent with Ceratobasidium sp. (Sneh et al. 1991). Mycelia from five isolates grown on PDA were used for DNA extraction. The rDNA-ITS region was amplified using PCR with the universal fungal primers ITS1 and ITS4 (White et al. 1990). The purified products were separately sequenced in both directions using the same primer pair (Meza-Moller et al. 2014). ITS sequence analysis (GenBank accession no. MK733974) resulted in a 100% match for one accession of Ceratobasidium sp. AG-A (MF070683.1) by BLAST in the NCBI nucleotide database. The pathogenicity of isolate DS54-3 was then tested. For each conidial suspension,12 healthy 10-day-old garlic plants (about 5 cm) were used to conduct pathogenicity tests by wound inoculation, and the garlic varieties were the same as those collected in the field. The healthy garlic plants were inoculated with 5, 10, 20, 50, and 100 ml of conidial suspension (2.95 × 10⁷ conidia/ml) by the root irrigation method. Twenty plants were inoculated with the same volume of sterile water as a control for each conidial suspension. After 20 days, the leaves of all garlic seedlings inoculated with conidial suspension gradually turned yellow, similar to the symptoms observed during natural infection. After 40 days, the root system showed typical hollow and rotten symptoms, and eventually the plants withered and died, whereas the control plants remained healthy. The same colonial fungus was reisolated, thus fulfilling Koch’s postulates. This is the first report of Ceratobasidium sp. causing root rot disease of garlic in China.

ДОМИНИРУЮЩИЙ СОСТАВ ФИТОПАТОГЕННЫХ ГРИБОВ, АССОЦИИРУЮЩИХСЯ С МИКОЗАМИ СПОРТИВНЫХ ГАЗОНОВ

Phytosanitary monitoring of diseases on football pitch in the foothills of the North Caucasus (Sochi and Essentuki), on the football pitch and golf course in the Non-Black Earth zone (Moscow and Moscow region) in 2017-2018 was carried out to determine the prevalence of phytopathogens of sports turf in different regions of Russia. Identification of pathogens was performed using traditional phytopathological methods and molecular genetic method (PCR). In spring the football pitch in the Moscow region was dominated by fungi of the genus Fusarium sp. (including Microdochium nivale) with a prevalence of up to 56%, there were pathogens of the genera Alternaria sp. (P -22%) and Cladosporium sp. (P-8-10%), Bipolaris sp. (P-14%). In Sochi in the spring dominated by fungi genera Rhizoctonia (P=58%), Fusarium (P=45%), Cladosporium (P=42%). The golf course in spring was dominated by phytopathogenic fungi of the genus Typhula (P=55%), and fungi of the genus Fusarium were the second in prevalence, which ranged from 30 to 41%. In summer fungi of the genus Rhizoctonia sp. and Alternaria sp. significantly prevailed in the pathogenic complex of grass on the football pitch of the southern region and on the Moscow football pitch - only Alternaria sp. which is more damaged by tillering nodes and leaves. At the same time, the damage to the root system of plants by Fusarium fungi remained significant. According to the results of PCR analysis it was found that among the pathogens of root rot of plants, both in the southern zone and in the Moscow region there is F. avenaceum. According to the cultural and morphological characteristics of the plants of the football pitch in Moscow has been identified F. culmorum. The composition of pathogens in spring and summer differed slightly, depending on the location and growing conditions of the turf, but Alternaria and Fusarium spp. were constantly present in the infected area. The results of monitoring can be used to develop practical recommendations for the protection of sports turf from diseases.

Conventional and real-time pcr assays for detection and identification of rhizoctonia solani AG-2-2, the causal agent of root rot of sugar beet

Soil-borne fungi belonging to the genus Rhizoctonia are considered to be among the most destructive sugar beet pathogens. Although multinucleate R. solani AG-2-2 is frequently detected as the main causal agent of root rot of sugar beet worldwide, several binucleate (AG-A, AG-E and AG-K) and multinucleate Rhizoctonia (R. solani AG-4, AG-5 and AG-8) have also been included in the disease complex. Due to their soil-borne nature and wide host range, the management of Rhizoctonia root rot of sugar beet is highly demanding. Identification of Rhizoctonia AG associated with root rot of sugar beet is the essential first step in determining a successful disease management strategy. In this paper we report a highly specific and sensitive real-time PCR protocol for detection of R. solani AG-2-2 which showed a high level of specificity after testing against 10 different anastomosis groups and subgroups, including AG-2-1 as the most closely related. Moreover, a similar conventional PCR assay showed the same specificity but proved to be at least a 100 times less sensitive. Future research will include further testing and adaptation of this protocol for direct detection and quantification of R. solani AG-2-2 in different substrates, including plant tissue and soil samples.

Impact of Irrigation Method on Root Rot and Wilt Diseases in Tomato Under Net Greenhouse in the State of Qatar.

The study involved the relationship among two irrigation methods; Subsurface Buried Diffuser (SBD) and Conventional Drip irrigation (DI) and their impact on the survival of healthy tomato plant . Tomato plant irrigated with SBD and DI methods were subjected to survey of root or shoot systems fungal diseases and infected vs. healthy Tomato plant survival incidence percentage were recorded. Surveyed tomato plant showing, root rot and wilt symptoms were subjected to isolation trails for the purpose of isolation of the causal organisms. Rhizospheric samples of different healthy and diseased plants were collected at flowering growth stage for determining the frequency occurrence of different fungi associated with the root region of healthy and infected roots of tomato plants under both irrigation methods. It was observed that the Tomato plants irrigated under DI method were more prone to fungal infection than that of SBD method. Pathogenic fungi that contributed in reducing the survival of tomato plant were high in rhizospheric soil irrigated with DI irrigation Method as compared to SBD irrigation method. The root fungal pathogens isolated from rhizospheric soil were Fusarium solani, Fusarium oxysporum, Aspergillus spp., and Pythium spp., which recorded in high frequency comparing with other microorganisms. The genus Fusarium represented in highest records followed by the genus Rhizoctonia and Pythium respectively at all assayed samples.

Aislamiento, caracterización y patogenicidad de hongos causantes de muerte descendente del nogal negro americano


 
 
 El nogal negro americano (Juglans nigra L.) es afectado por problemas fitosanitarios, destacando hongos causantes de cancros en ramas, reduciendo la producción de fruto hasta 60% del rendimiento promedio que es 1.9 t ha-1. Los objetivos de esta investigación fueron identificar los hongos asociados a cancros presentes en ramas de árboles de J. nigra con síntomas de muerte descendente y evaluar su patogenicidad. Se aislaron hongos de cancros de ramas con síntomas de muerte descendente colectadas en dos huertas del estado de Coahuila. Cuatro morfotipos de hongos fueron obtenidos y una cepa de cada uno se utilizó para su identificación morfológica a nivel de género, y mediante la secuenciación de la región ITS1 a ITS2 de los genes ribosomales (rDNA) para su identificación a nivel de especie. Las pruebas de patogenicidad se realizaron en plántulas de J. nigra de cuatro meses de edad, realizando una fisura en el tallo de 3 mm de largo e inoculando con cada especie identificada. Los hongos asociados a los cancros de J. nigra fueron identificados morfológicamente como miembros de los géneros Trichothecium, Pestalotiopsis, Alternaria y Rhizoctonia. Mediante el análisis BLAST en el GenBank de las secuencias de la región ITS1 a ITS2 fue posible determinar que las cepas se encontraron relacionadas a las especies Trichothecium roseum, Pestalotiopsis steyaertii, Alternaria alternata y a una especie binucleada no determinada de Rhizoctonia. La inoculación de las cuatro cepas a plántulas demostró que éstas son patogénicas a J. nigra.
 
 

Rhizoctonia solani AG 1-IB and AG 4 HG-I causing leaf blight and root rot in plants from the Lamiaceae family in Brazil

Rhizoctonia solani is a fungal complex represented by 14 anastomosis groups. Each group has distinct characteristics that are reflected in the management and control strategies for diseases caused by this fungus. In three distinct geographical regions, plants of the Lamiaceae family from vegetable and medicinal herb gardens were observed, with Mentha piperina, Mentha spicata and Origanum manjerona presenting symptoms of leaf blight and Ocimum basilicum, Ocimum vulgare and Rosmarinus officinalis presenting root rot symptoms. Mycelia, hymenia, basidiospores and microsclerotia were found on the stems and leaves of Mentha piperina and Mentha spicata. These are typical morphological markers of the genus Rhizoctonia. The ITS region was amplified for nine isolates and subsequently sequenced. In the phylogenetic analysis, the isolates were identified as Rhizoctonia solani belonging to AG 1-IB and AG 4 HG-I anastomosis groups. All isolates inoculated in their respective hosts caused disease symptoms resembling those typically observed in the field. This is the first report of R. solani AG 1-IB in M. spicata, M. piperina and Origanum majorana and of R. solani AG 4 HG-I in O. vulgare, R. officinalis and O. basilicum in Brazil.

Rhizoctonia solani: taxonomy, population biology and management of rhizoctonia seedling disease of soybean

Rhizoctonia solani, the most important species within the genus Rhizoctonia, is a soilborne plant pathogen with considerable diversity in cultural morphology, host range and aggressiveness. Despite its history as a destructive pathogen of economically important crops worldwide, our understanding of its taxonomic relationship with other Rhizoctonia‐like fungi, incompatibility systems, and population biology is rather limited. Among the host of diseases it has been associated with, seedling diseases inflicted on soybean are of significant importance, especially in the soybean growing regions of North America. Due to the dearth of resistant soybean genotypes, as well as the paucity of information on the mechanisms of host–pathogen interactions and other molecular aspects of pathogenicity, effective management options have mostly relied upon a combination of cultural and chemical control options. The first section of this review summarizes what is currently known about the taxonomy and systematics, population biology and molecular genetics of R. solani. The second section provides an overview of the pathology and management of rhizoctonia root and hypocotyl rot of soybean, a seedling disease of importance in North America.

MICOBIOTA ENDÓFITA DEL GÉNERO MAXILLARIA RUIZ & PAV. (ORCHIDACEAE) EN DOS RESERVAS NATURALES DEL DEPARTAMENTO DEL QUINDÍO

Anteriormente las orquídeas eran consideradas como generalistas en sus interacciones con endófitos; tras el avan- ce en el estudio de su fisiología se dio por sentado de que existe cierta variación en sus niveles de especificidad, incluso dentro de especies relacionadas filogenéticamente. Con el propósito de describir la micobiota endófita asociada al género Maxillaria en dos reservas naturales del departamento del Quindío. Se realizó un aislamiento y caracterización taxonómica de endófitos a partir de 576 fragmentos de tejido radicular provenientes de or- quídeas pertenecientes al género Maxillaria. Se obtuvieron 268 asilados clasificados en 4 géneros de hongos endófitos; caracterizados macroscópica y microscópicamente; los géneros asilados con mayor frecuencia fueron los correspondientes al género-forma Rhizoctonia, representado por los géneros Tullasnela y Ceratobasidium. Se observaron diferencias en el número de plantas colonizadas por especie vegetal y por zona de muestreo. En conclusión, a pesar de ser un trabajo basado en caracteres morfotaxonómicos, se registran morfotipos del género forma-Rhizoctonia presentes en las zonas estudiadas, además este trabajo es la primera contribución Colombiana que documenta de manera sistemática algunos aspectos de la relación hongo orquídea en el departamento del Quindío y en el género Maxillaria.

A search for the phylogenetic relationship of the ascomycete Rhizoctonia leguminicola using genetic analysis.

Rhizoctonia leguminicola, which causes fungal blackpatch disease of legumes and other plants, produces slaframine and swainsonine that are largely responsible for causing salivation, lacrimation, frequent urination, and diarrhea in grazing animals including cattle, sheep, and horses. The original identification of R. leguminicola was based only on morphological characters of the fungal mycelia in cultures because of the lack of fungal genetic markers. Recent investigations suggested that R. leguminicola does not belong to genus Rhizoctonia and is instead a member of the ascomycetes, necessitating an accurate reclassification. The objective of this study was to use both genetic and morphological characters of R. leguminicola to find taxonomic placement of this pathogen within ascomycetes. Internal transcribed spacer region (ITS) and glyceraldehyde-3-phosphate dehydrogenase (gpd) encoding gene were amplified from R. leguminicola isolates by PCR using universal primers and sequencing. Rhizoctonia leguminicola ITS and gpd sequences were aligned with other fungal sequences of close relatives, and phylogenetic trees were constructed using neighbor-joining and parsimony analyses. Rhizoctonia leguminicola isolates were clustered within a clade that contains several genera of ascomycetes belonging to the class dothideomycetes. We suggest that the fungus is misidentified in the genus Rhizoctonia and propose its reclassification in a new genus within the phylum Ascomycota.

Interactions between fungi colonizing the stem base of winter wheat

<em>In vitro</em> conditions, the interactions betecen the fungi most frequently isolated from the stem base of winter wheat were determined. These were the species from genus <em>Fusarium (F. culmorum, F. avenaceum</em> and<em> F. poae</em>) and <em>Rhizoctonia cerealis, Pseudocercosporella herpotrichoides, Alternaria alternata</em> and <em>Aureobasidium bolleyi</em>. Some saprotrophes showed stimulating effect on <em>R. cerealis, P. herpotrichoides</em> and F. poae. Certain species in combined cultures showed exceptionally favourable relationships.

First Report of Root Rot of Watermelon Caused by Ceratobasidium sp. in Sonora, Mexico.

Watermelon is one of the major crops grown in Mexico and represents 4% of the total cultivated area with fruits in this country. In 2013, Sonora State was ranked second in the production of watermelon at a national level. Fungal and oomycete diseases are among the main biotic factors affecting watermelon production, particularly those caused by species of the genera Fusarium, Phytophthora, Pythium, and Rhizoctonia. During the spring of 2013, wilting or death symptoms were confirmed in approximately 50% of ungrafted watermelon plants grown in four sampled fields along the coast of Hermosillo and Guaymas Valley in Sonora, Mexico. On both roots and stems of infected plants, localized lesions were found that were 0.2 to 2.0 cm long, reddish brown, and slightly sunken on the stem base. In some cases, the discolorations encompassed nearly 90% of the root system. One-centimeter pieces from the edge of lesions on stems and roots were superficially disinfected with 1% sodium hypochlorite, then rinsed with sterile distilled water, placed onto petri dishes containing potato dextrose agar (PDA), and incubated at 25°C for 3 days. Fungal colonies were white initially, then turned brown, and septate hyphae were 3.7 to 4.3 μm in diameter and branched at right angles with a constriction at the origin of the branch point. These characteristics are typical of the genus Rhizoctonia. Binucleate cells from five isolates were observed using a lactophenol aniline blue solution stain, according to Ceratobasidium morphological descriptions. Mycelia from five isolates grown on PDA was used for DNA extraction. The rDNA-ITS region was amplified using PCR with the universal fungal primers ITS1 and ITS4 (3). The purified products were separately sequenced in both directions using the same primer pair. The sequences obtained were 99% similar to those of Ceratobasidium sp. AG-F and AG-Fa isolates (accessions KC193238.1 on Tagetes erecta, HQ168370.1 on Musa spp., and JX913821.1 on soy-rice-weeds, respectively) from GenBank (2,4). The pathogenicity of the fungus was tested under growth chamber conditions. Sets of seven healthy watermelon seedlings of the Sugar red variety were inoculated with five isolates of Ceratobasidium. Three disks (8 mm in diameter) of mycelia grown on PDA were placed around the roots of each plantlet. The pots were maintained at 27 ± 0.1°C for 14 days with a photoperiod of 12 h. Seven uninoculated seedlings were used as a control. Initial symptoms showing water-soaked lesions developed on all inoculated seedlings within 6 to 7 days, while typical disease symptoms appeared after 10 to 14 days after inoculation. Seedlings without inoculum were free from infection. The fungus was re-isolated from the inoculated seedlings on PDA, and identified as Ceratobasidium sp., confirmed using morphological characteristics. A similar disease has been reported recently in Italy and Arizona (1); however, this report is the first description of a Ceratobasidium sp. causing root rot of watermelon in Sonora, Mexico. Agricultural areas where the study was carried represent 90% of the total area cultivated with watermelon in this state, so it is necessary to evaluate the impact of this pathogen in the crop.