Solani AG Research Articles

The role of biological and chemical inducers in activating bean defense responses against Rhizoctonia solani

Rhizoctonia root rot is an important bean disease that causes significant yield losses. Increasing the levels of plant resistance using biological and chemical inducers is a sustainable strategy for plant disease management. In this study, the efficiency of thiamine, riboflavin, pyridoxine, folic acid, menadione, quercetin, naringenin, humic acid, fulvic acid, boric acid, zinc sulfate, manganese sulfate, Piriformospora indica and binucleate Rhizoctonia were evaluated to improve bean resistance to root rot pathogen Rhizoctonia solani AG-4 HGII. Under laboratory conditions, effect of various biological agents and chemical compounds on mycelial growth of the pathogen was evaluated. Results showed that applying boric acid, zinc sulfate and manganese sulfate at 1000 and 2000 mg L−1 concentrations and menadione at 2000, 5000, 10000 and 20000 μM completely inhibited the pathogen growth and 10000 and 20000 μM concentrations of thiamine reduced linear growth of R. solani. Under greenhouse conditions, application of the inducers significantly reduced the disease progress on treated plants compared to the non-treated plants. The highest level of disease reduction was observed using zinc sulfate and thiamine applied at 3 days before the pathogen inoculation, and also by using P. indica 14 days before inoculation with the pathogen. Thiamine, zinc sulfate and P. indica significantly reduced the disease index and improved plant growth parameters compared to the controls. Induction of resistance against R. solani by individual and combined treatments using thiamine, zinc sulfate and P. indica was associated with increased activity of various antioxidants and increased levels of membrane stability index (MSI), relative water content (RWC), lignin accumulation and total soluble phenolics in bean seedlings. Our findings revealed a practical possibility of inducing resistance and protection of bean plants against Rhizoctonia root rot with the help of biological and chemical resistance inducers.

Molecular, physiological and infection behaviour studies of Rhizoctonia solani causing the Rice Sheath Blight disease

Rhizoctonia solani is the causal agent of rice sheath blight, which is one of the most serious diseases of rice worldwide. In this study, seventeen Egyptian isolates of sheath blight pathogen, R. solani AG1 IA, were identified using morphological and molecular characterization by the internal transcribed spacer (ITS) sequences. Extracellular enzymes were assessed in in vitro and in infected rice samples. Also, pathogenicity tests for all isolates were done on two rice cultivars under greenhouse conditions. Growth behavior by RS13 isolate was studied using two rice cultivar Sakha 101 (Japonica type) and Egyptian Yasmine (Indica type). The obtained results exhibited a wide range of variability in the morphological and virulence characteristics of isolates. Two isolates RS10 and RS13 (AB5) were sequenced and found aligned with Egyptian and Chinese isolates. RS13 and RS10 isolates exhibit the highest production of cellulase, pectinase and amylase enzymes in plate culture (in vitro). While, on the plant sample tissue cellulase and pectin methylesterase (PME) activity enzymes are relating to development of rice sheath blight disease. Under the artificial condition, SK 101 rice proved the most susceptible to infection with sheath blight pathogen compare with E. Yasmine. The hyphae growth on SK101 cultivar was more than in the E. Yasmine cultivar. Furthermore, we examined the morphological developments of hyphae and sclerotial on both cultivars using light and scanning electron microscopy (SEM). It was observed that the fungal pathogen could intercept host surface structures for improving cell penetration and anchorage.

A Novel, Small Cysteine-Rich Effector, RsSCR10 in Rhizoctonia solani Is Sufficient to Trigger Plant Cell Death.

The necrotrophic phytopathogen Rhizoctonia solani (R. solani) is a fungus that causes disease in a wide range of plant species. Fungal genomes encode abundant, small cysteine-rich (SCR) secreted proteins, and the probable importance of these to pathogenesis has been highlighted in various pathogens. However, there are currently no reports of an R. solani SCR-secreted protein with evidential elicitor activity. In this study, the molecular function of 10 SCR-secreted protein genes from R. solani was explored by agroinfiltration into Nicotiana benthamiana (N. benthamiana) leaves, and a novel SCR protein RsSCR10 was identified that triggered cell death and oxidative burst in tobacco. RsSCR10 comprises 84 amino acids, including a signal peptide (SP) of 19 amino acids that is necessary for RsSCR10 to induce tobacco cell death. Elicitation of cell death by RsSCR10 was dependent on Hsp90 but not on RAR1, proving its effector activity. Two cysteine residues have important effects on the function of RsSCR10 in inducing cell death. Furthermore, RsSCR10 showed cross-interaction with five rice molecules, and the inferred functions of these rice proteins suggest they are instrumental in how the host copes with adversity. Overall, this study demonstrates that RsSCR10 is a potential effector that has a critical role in R. solani AG1 IA-host interactions.

Exploring Two Streptomyces Species to Control Rhizoctonia solani in Tomato

Streptomyces species are effective biocontrol agents toward many plant pathogens. These microorganisms are well known for producing secondary metabolites, promoting plant growth and inducing plant defense mechanisms. In this study, the ability of tomato root-colonizing Streptomyces strains to trigger the resistance against Rhizoctonia solani (J.G. Kühn) AG4 was investigated. For this goal, we evaluated the pattern of LOXB and PAL1 genes expression changes upon pathogen inoculation in primed tomato plants. The results revealed that Streptomyces globisporous (Krasil’nikov) strain F8 and S. praecox (Millard and Burr) strain R7 were able to enhance the expression of lipoxygenase and phenylalanine ammonia lyase in tomato plants. This finding suggests that Streptomyces strains F8 and R7 may trigger jasmonic acid and phenyl propanoid signaling pathways in plants, therefore, resulting an induced defense status in tomatoes against R. solani. Biochemical characterization of these Streptomyces strains showed that they were strong producers of siderophores. S. praecox strain R7 produced siderophores of hyderoxamate and catechol types and S. globisporous strain F8 produced a phenolic siderophore. Moreover, they also produced protease while only the S. praecox strain R7 was able to produce amylase. Taken together, these results indicate that S. globisporous strain F8 and S. praecox strain R7 promote plant growth and reduces disease and hence are suitable for future in depth and field studies with the aim to attain appropriate biocontrol agents to protect tomatoes against R. solani.

Isolation and identification of pathogen causing damping off at seedling stage of Trollius chinensis

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.

Inhibitory effect of cinnamon ( Cinnamomum tamala (Buch.-Ham.) T.Nees & Eberm.) essential oil and its aldehyde constituents on growth and spore germination of phytopathogenic fungi

Plant pathogens lead to severe damage of the agricultural crops, worldwide. The disease management is currently being done by the synthetic chemicals. In the present report, Cinnamomum tamala (Buch.-Ham.) T. Nees & Eberm. oil was analyzed by gas chromatography-FID and GC/MS, which revealed (E)-cinnamaldehyde (40.6%), (E)-cinnamyl acetate (19.6%), linalool (10.2%) and benzaldehyde (3.6%) as marker constituents. Contact, volatile and spore germination inhibition assays were performed to determine the antifungal activities of Cinnamomum tamala (Buch.-Ham.) T.Nees & Eberm. against Rhizoctonia solani AG 4, Choanephora cucurbitarum and Bipolaris australiensis. C. tamala oil 500-560 ppm showed complete fungal growth inhibition in poison food technique over concentration range of. Solid-phase microextraction analysis of drop diffusion assay revealed the presence of benzaldehyde in headspace of Petri-plate, and found to be one of the strongest antifungal compounds against tested phytopathogens. Similarly, an oil concentration of 500 ppm inhibits spore germination. Therefore, products containing such compositions can be used for the plant diseases management.

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.

Damping-off of Coastal Hogfennel Caused by Rhizoctonia solani AG-4

Damping-off symptoms were frequently observed on young plants of coastal hogfennel (Peucedanum japonicum) grown in a farmer’s vinyl greenhouse located in Goseong, Gangwon Province, Korea during a disease survey in June 2019. Incidence of the diseased plants was 50-70% in the vinyl greenhouse investigated during the disease survey. Eight isolates of Rhizoctonia sp. were obtained from the diseased plants. All the isolates were identified as Rhizoctonia solani AG-4 based on the morphological characteristics and anastomosis test. Three isolates of R. solani AG-4 were tested for pathogenicity on coastal hogfennel by artificial inoculation. All the tested isolates induced damping-off symptoms on the inoculated plants. The symptoms were similar to those observed in the farmer’s vinyl greenhouse investigated. This is the first report of R. solani AG-4 causing damping-off in coastal hogfennel.

Transcriptional Changes in Potato Sprouts upon Interaction with Rhizoctonia solani Indicate Pathogen-Induced Interference in the Defence Pathways of Potato.

Rhizoctonia solani is the causer of black scurf disease on potatoes and is responsible for high economical losses in global agriculture. In order to increase the limited knowledge of the plants’ molecular response to this pathogen, we inoculated potatoes with R. solani AG3-PT isolate Ben3 and carried out RNA sequencing with total RNA extracted from potato sprouts at three and eight days post inoculation (dpi). In this dual RNA-sequencing experiment, the necrotrophic lifestyle of R. solani AG3-PT during early phases of interaction with its host has already been characterised. Here the potato plants’ comprehensive transcriptional response to inoculation with R. solani AG3 was evaluated for the first time based on significantly different expressed plant genes extracted with DESeq analysis. Overall, 1640 genes were differentially expressed, comparing control (−Rs) and with R. solani AG3-PT isolate Ben3 inoculated plants (+Rs). Genes involved in the production of anti-fungal proteins and secondary metabolites with antifungal properties were significantly up regulated upon inoculation with R. solani. Gene ontology (GO) terms involved in the regulation of hormone levels (i.e., ethylene (ET) and jasmonic acid (JA) at 3 dpi and salicylic acid (SA) and JA response pathways at 8 dpi) were significantly enriched. Contrastingly, the GO term “response to abiotic stimulus” was down regulated at both time points analysed. These results may support future breeding efforts toward the development of cultivars with higher resistance level to black scurf disease or the development of new control strategies.

Effects of Inoculum Density and Cultivar Susceptibility on Rhizoctonia Damping-Off and Crown and Root Rot in Sugar Beet.

Damping-off and crown and root rot of sugar beet caused by Rhizoctonia solani anastomosis group 2-2 (AG 2-2) are important soilborne diseases in Minnesota and North Dakota. Management involves an integrated approach, including crop rotation, use of resistant cultivars, and timely fungicide application. Our objectives were to evaluate the role of inoculum density and cultivar susceptibility on the onset and development of Rhizoctonia diseases and on yield and quality in sugar beet. Three cultivars varying in susceptibility were sown in field plots inoculated with 0, 20, 40, or 60 kg/ha of R. solani AG 2-2 IIIB infested barley during 2013 and 2015. In both years, there was a significant linear effect of inoculum density with decreasing area under the stand establishment curve (AUSEC), root yield, and sucrose quality as inoculum density increased. Cultivar susceptibility significantly affected AUSEC as well as sucrose quality in both years and root yield in 2013. In both years, there was an inoculum density by cultivar interaction on disease ratings, with the partially resistant cultivar resulting in lower ratings than the moderate and susceptible cultivars, especially as inoculum density increased. These results have implications for cultivar selection and for use and timing of postemergence fungicide application based on field history of inoculum pressure.

Genome Sequence of Rhizoctonia solani Anastomosis Group 4 Strain Rhs4ca, a Widespread Pathomycete in Field Crops.

Rhizoctonia solani is an important soil-borne fungal pathogen that causes serious diseases on many agricultural crops and vegetables. Here, we report a complete genome assembly of R. solani AG4 (assembly: 45.47 Mb; contig N50: 1.56 Mb), using a combination of Illumina paired-end and PacBio long-read sequencing data. A total of 267 noncoding RNAs and 11,592 genes were predicted, including 109 genes associated with carbohydrate-active enzymes and 2,488 genes involved in host-pathogen interactions. The complete genome of R. solani AG4 represents a valuable base for studying interactions between host plants and pathogenic fungi and to search for potential antimicrobial targets.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Penicillium pinophilum has the Potential to Reduce Damping-off Caused by Rhizoctonia solani in Sugar Beet

Rhizoctonia solani is an economically important pathogen of sugar beet (Beta vulgaris L.) causing seedling damping-off, and root and crown rot. Cultural practices, partially resistant cultivars, and fungicides are among the methods most used to manage R. solani. Penicillium pinophilum, a potential biocontrol agent for Rhizoctonia damping-off, was isolated from sugar beet. Our objective was to evaluate the biocontrol potential of P. pinophilum against R. solani AG 2–2 under laboratory and greenhouse conditions. In vitro co-culture of both fungi showed that R. solani growth was inhibited by P. pinophilum. A greenhouse inoculation study was done using sclerotia of R. solani and a conidia suspension of P. pinophilum to evaluate the response of a Rhizoctonia susceptible cultivar. Treatments included R. solani sclerotia, P. pinophilum conidia suspension, a combination of R. solani sclerotia with P. pinophilum conidia suspension, and a mock inoculation with water (control). One 2-cm deep furrow was made in the middle of peat filled trays into which 10 seeds were planted. Each treatment was applied adjacent to each seed and covered with peat. There were four replicates per treatment arranged in a completely randomized design. The sole sclerotia treatment caused 75% damping-off and severe root rot on surviving plants whereas the combination of sclerotia with P. pinophilum conidia suspension reduced damping-off by 50%. No damping-off incidences were observed with the P. pinophilum conidia suspension or the mock-inoculated control. It was concluded that P. pinophilum has the potential to reduce damping-off caused by R. solani but use of the most appropriate P. pinophilum concentration and its mitigation mechanisms need further studies.

First Report of Damping-Off of Ovate-Leaf Atractylodes Caused by Rhizoctonia solani AG-5 in South Korea

In May to July 2019, ovate-leaf atractylodes seedling and plant with Damping-off symptoms were observed in farmer field at Sangju and Mungyeong, Korea. Seven fungal isolates have been retrieved from diseased root tissue and identified as Rhizoctonia solani AG-5 based on morphological and molecular characteristics. To the best of our knowledge, this is the first report on damping-off of ovate-leaf atractylodes caused by R. solani AG-5 in South Korea.

Improving evaluation of potato resistance to Rhizoctonia solani infection by optimizing inoculum-based method combined with toxin-based assay

Rhizoctonia solani causes stem canker and significantly impacts potato production. Conventional assay to evaluate potato resistance using R. solani inoculum is time consuming. To establish an effective and fast assay, 20 potato cultivars/lines were examined using both R. solani AG2-1 as an inoculum and its derived toxin (RS toxin). In field trials of 2009 and 2010, wheat-bran-mediated inoculum of R. solani AG2-1 was incorporated at either 0, 2, 3, 4 or 5 g per seed piece in the soil before sowing in the furrow. Stem canker was evaluated sixty-five days after planting. Inoculation at 2, 3, or 4 g R. solani AG2-1 well distinguished resistance of potato cultivars/lines. For a quick assay of resistance screening, a toxin-based method was established by treating potato seedlings with RS toxin of R. solani AG2-1. RS toxin was prepared by heating R. solani AG2-1 culture. Potato seedlings were obtained through tissue culture and grown in Murashige and Skoog medium. Seedlings at the stage of 12 cm in height were transferred into agar amended with RS toxin and incubated for eight days. The level of inhibition caused by RS toxin was positively correlated with toxin concentration. By evaluating various potato cultivars/liens that have different sensitivities to toxin, the inhibition was from 33% to 100% on potato stems sections and from 32% to 148% on seedlings. The toxin-based evaluation was highly correlated with field data using pathogen inoculum (r = 0.731, P < 0.01). Inoculation with wheat bran-mediated R. solani AG2-1 of 2, 3 or 4 g per seed piece was effective in field evaluations. The toxin-based assay improved the efficiency of disease resistance evaluation. Both assays showed that none of the 20 potato cultivars/liens was completely resistant to R. solani AG2-1. However, cultivar ‘Desiree’ had the lowest level of disease, whereas ‘Atlantic’, ‘Favorita’, and ‘Shepody’ were the most susceptible cultivars.

Changes in Bacterial Community Structure and Enriched Functional Bacteria Associated With Turfgrass Monoculture.

There is increasing attention being paid to utilizing microbial communities to improve plant health while reducing management inputs. Thus, the objectives of this research were to assess changes in the rhizosphere bacterial community structure associated with long-term turfgrass monoculture and to demonstrate the feasibility of using functional bacteria as beneficial biocontrol agents. Large patch disease, caused by the fungal pathogen Rhizoctonia solani AG2-2, is a significant threat to turfgrass cultivation. Rhizosphere samples were collected from 2-, 13- and 25-year turfgrass (Zoysia japonica) monocultures. The 13-year monoculture field had a higher pathogen population density than both the 2- and 25-year monoculture fields. Analyses of the rhizosphere bacterial communities revealed that Streptomyces was dominant in the 2-year field and Burkholderia was enriched in the 25-year field. Based on the culturable rhizosphere bacteria, Streptomyces neyagawaensis J6 and Burkholderia vietnamiensis J10 were obtained from the 2- and 25-year fields, respectively. Application of S. neyagawaensis J6 and B. vietnamiensis J10 led to excellent inhibition of large patch disease as well as enhanced tolerance against drought and temperature stresses. The results showed that the selected bacteria could be developed as biocontrol and abiotic stress tolerance agents for turfgrass cultivation.

Rhizoctonia solani AG2-1 causing root rot of wasabi (Eutrema japonica) in the UK.

In 2014, glasshouse-grown wasabi (Eutrema japonica) grown in a compost based media displayed symptoms of poor growth and wilting. Visual assessment of the roots showed that 25% of the symptomatic plants sampled had raised black lesions on the roots affecting between 5 and 20% of the total root area. To isolate the causal agent, affected material (approximately 5 mm3) was surface disinfested in sodium hypochlorite (2%) for 30 s, rinsed twice in sterile water and plated on to water agar medium amended with penicillin G (0.2 g/liter) and streptomycin sulfate (0.8 g/liter). Plates were incubated at 20ºC until fungal colonies were visible. After three days, colonies of Rhizoctonia solani were identified based on the presence of septate hyphae with right-angle branching, a pure culture was obtained through hyphal tip transfer onto a new plate of PDA. DNA was extracted from a 7-day old plate of the isolate (WAS1) as described previously (Woodhall et al., 2013). The AG of WAS1 was determined as AG2-1 using a subgroup specific real-time PCR assay (Budge et al., 2009b) and confirmed by DNA sequencing as described previously (Lekuona Gomez et al., 2015). The sequence was 100% identical (587/587bp) to a previously identified AG2-1 isolate 1971 (GenBank accession FJ435126) (Budge et al., (2009a). Pathogenicity of the isolate was confirmed by inoculating three healthy one-year-old wasabi plants grown in loam based compost (John Innes No.3) each with four 5 mm fully colonised PDA plugs of isolate WAS1 placed at approx. 40 mm depth in the soil. Four sterile PDA plugs were place in each of three control plants. All six plants were placed in a greenhouse at 21°C, 18h:6h light: dark and watered as required. After 21 days, multiple black root lesions typically 3-5mm in length were observed on the roots of all inoculated plants. No lesions were observed on the control plants. From three lesions per plant, isolations were attempted as described above. Rhizoctonia solani was recovered from all isolations and the resulting cultures all tested positive for AG2-1 using the real-time PCR assay. Isolations were attempted from the roots of healthy control plants but Rhizoctonia was not recovered. Here we demonstrate that R. solani AG2-1 is associated with root necrosis of Eutrema japonica. Rhizoctonia solani AG2-1 has been reported previously in various Brassica crops in the UK (Budge et al., 2009a) and on Matthiola incana (Lekuona Gómez et al., 2015). It has also been reported causing disease in potatoes and as widely present in UK field soils (Woodhall et al., 2013). Although R. solani AG1 and AG4 of R. solani have been reported to infect Eutrema japonica in Japan (Takeuchi et al., 2003; 2008), this is the first finding that identifies AG2-1 as the causal agent. The potential presence of AG2-1 in soil and/or as plant debris should be considered prior to planting susceptible hosts.

Potential for suppression of Rhizoctonia root rot is influenced by nutrient (N and P) and carbon inputs in a highly calcareous coarse-textured topsoil

Bioassays were undertaken in a controlled environment to assess whether the potential for suppression of Rhizoctonia root rot of wheat, in a highly calcareous topsoil, was positively influenced by nutrient (nitrogen (N) or phosphorus (P)) addition and whether any disease suppression response to augmented nutrition was affected by the addition of carbon (C), either as a readily available C source (sucrose) or as wheat stubble. The soil was P deficient, which limited plant growth, populations of putatively beneficial soil microorganisms, and microbial activity and diversity. This ultimately reduced potential for suppression of Rhizoctonia solani AG8. Addition of fertiliser P to the soil increased R. solani AG8 DNA and percent root infection but not the effectiveness of the pathogen. A positive effect of P fertiliser on plant growth partially compensated for the negative effect of increased root infection. Addition of P increased DNA for Microbacterium spp. where labile C had been added and in the presence of plant roots. Stubble addition alone, after 6 weeks of incubation, increased DNA for Pantoea agglomerans, Trichoderma A and Microbacterium spp. although differences in microbial activity and diversity between stubble treatments were only detected after the bioassay had commenced and P was added. Fertiliser P addition to stubble-amended soil resulted in less Rhizoctonia infection compared with that in soil without P or stubble addition. Effectiveness of R. solani AG8 was decreased by 50% with stubble amendment. The application of N alone did not have a marked effect on plant growth or potential for suppression of Rhizoctonia root disease. Agronomic management practices that affect quantity and lability of C input to soil, when combined with strategic P fertiliser decisions, are likely to improve the potential for development of suppression of Rhizoctonia root rot disease in cereal crops on alkaline and highly calcareous soils.

First occurrence of dsRNA in Rhizoctonia solani AG2-2 LP from turfgrass Zoysia japonica in Brazil / Primeiro relato de RNA dupla fita em Rhizoctonia solani AG2-2 LP, patógeno de Zoysia japônica no Brasil

Rhizoctonia solani , a complex species comprising groups and sub-groups of somatic compatibility (anastomosis groups – AG), is a cosmopolitan pathogenic fungus that causes important diseases in a wild range of plants. One example is R. solani AG2-2 LP, the causal agent of large patch disease of C4 grasses, primarily zoysiagrass. The occurrence of this pathogen in Brazil causes a severe disease that is difficult to control. Mycoviruses, viruses that replicate in fungi, are ubiquitous. Since their first report in the 1960s, they have been searched for in many classes of fungi with the purpose of finding new tools to manage diseases, improve crops and address the challenges of climate change. The genome of mycoviruses mostly consists of double-stranded RNA (dsRNA) and they may or may not induce symptoms in their host. dsRNAs have already been reported in species of Rhizoctonia, in some cases reducing virulence . We searched for dsRNAs in 12 Brazilian isolates of R. solani AG 2-2 LP, a pathogen of zoysiagrass. All isolates showed dsRNAs were present in a similar profile to each other, irrespective of the virulence of those isolates on zoysiagrass. Among the isolates the number of dsRNA segments ranged from three to eight, with different sizes, never smaller than 2 kb and with segments greater than 10 Kb in all isolates. Detection of dsRNA in all R. solani isolates may be indicative of mycoviruses being a frequent presence in these fungi.

Antagonistic potential and molecular characterization of Trichoderma asperellum against Rhizoctonia solani AG-3 causing black scurf of potato

Rhizoctonia solani Kuhn (AG-3) is a soil borne pathogen present ubiquitously and causes black scurf of potato worldwide. Considering the importance of the disease, the present study was first carried in vitro and then under field condition using three isolates each of Trichoderma spp. (T1, T2 and T3) and Pseudomonas fluorescens (P1, P2 and P3) to assess the use of these antagonists against the black scurf pathogen. Study revealed that Trichoderma isolate T1 showed 58.25% percent mycelial growth inhibition of R. solani as compared to bacterial antagonist in vitro and 87.98%, 84.41% reduction in disease severity in vivo and in greenhouse, respectively. Specific results for fingerprinting of the most effective antagonist isolate T1 were obtained by using 15 primers of SSR and 2 primers of ITS (ITS1 and ITS4). The molecular identification of most effective Trichoderma isolate (T1) revealed it as Trichoderma asperellum.

Population dynamics of Rhizoctonia, Oculimacula, and Microdochium species in soil, roots, and stems of English wheat crops

AbstractThis study aimed to elucidate the population dynamics of Rhizoctonia, Oculimacula, and Microdochium species, causing the stem base disease complex of sharp eyespot, eyespot, and brown foot rot in cereals. Pathogen DNA in soil, roots, and stem fractions, and disease expression were quantified in 102 English wheat fields in two seasons. Weather data for each site was collected to determine patterns that correlate with assessed diseases. Oculimacula spp. (66%) and R. solani AG 2‐1 (63%) were most frequently detected in soil, followed by R. cerealis (54%) and Microdochium spp. (33%). Oculimacula spp. (89%) and R. cerealis (56%) predominated on roots and soil but were not associated with root rot symptoms, suggesting that these species used soil and roots for survival and as inoculum source. M. nivale was more frequently detected than M. majus on stems up to GS 21–30 and co‐occurred on plant samples with O. acuformis. O. yallundae had higher DNA concentration than O. acuformis at the lower 5 cm basal region at GS 37–45. R. cerealis predominated in the upper 15 cm above the base beyond stem extension. Brown foot rot by Microdochium spp. was favoured by cool and wet autumns/winters and dominated in English wheat. Eyespot and sharp eyespot disease index by Oculimacula spp. and R. cerealis, respectively, correlated with wet/humid springs and summers. Results suggested that stem base pathogens generally coexisted; however, their abundance in time and space was influenced by favourable weather patterns and host development, with niche differentiation after stem extension.