Sclerotium Rolfsii Sacc Research Articles

Exploration of the Potential of Bacillus spp. as an Antagonist and PGPR against Stem and Pod Rot of Groundnut.

Background: Stem and pod rot is an economically important soil borne disease of groundnut caused by Sclerotium rolfsii Sacc. resulting in significant yield losses across the globe. Bacillus spp. is rod-shaped and gram-positive bacterium which is predominantly found in the soil. Hence, considering the importance of the disease, the present investigation was carried out to evaluate the indigenous Bacillus spp. for plant growth promotion and to inhibit the pathogen in groundnut. Methods: Totally nineteen Bacillus spp. isolates from healthy groundnut rhizosphere and their antagonistic potential was recorded. The molecular characterization of five efficient Bacillus spp. was carried out using 16S rDNA. Later, morphological and biochemical characterization and plant growth promoting traits were recorded. Result: All nineteen isolates of Bacillus spp. showed antagonistic potential against S. rolfsii. Five Bacillus spp. isolates which showed higher inhibition of the pathogen were identified as B. subtilis, B. pacific, B. cereus, two isolates belonging to B. tropicus through molecular technique. The morphological, biochemical characters and growth promoting traits were recorded.

Field Screening for Tomato Spotted Wilt and White Mold (Stem Rot) Resistance among Peanut Genotypes

White mold (WM), stem rot, and southern blight are common names for the same soilborne peanut (Arachis hypogaea L.) disease caused by Athelia rolfsii (Curzi) C. C. Tu & Kimbr. = Sclerotium rolfsii Sacc. Tomato spotted wilt is a systemic foliar peanut disease caused by Tomato spotted wilt virus (TSWV). The objective of this study was to screen several currently available peanut genotypes (cultivars and breeding lines) for combined general field resistance to both of these diseases. Results from these field tests showed significant differences (P≤0.05) among the peanut genotypes evaluated for combined resistance to both WM and TSWV. The overall three-year (2018-20) average found that ‘Georgia-12Y’ had among the lowest percent incidence of mid-season TSWV, mid-late season TSWV+WM, late-season WM+TSWV, WM after digging, and the highest pod yield compared to other runner-type peanut cultivars. FloRun ‘331’ was found to have comparable WM resistance as Georgia-12Y, however it was also found to be susceptible to TSWV. ‘Georgia-14N’ was found to have moderate TSWV and WM resistance similar to ‘Georgia-07W’, and it also has a high-level of root-knot nematode (RKN) resistance.

Efficacy of Various Fungicides and Herbicides for the Management of Wheat Foot Rot Disease

The present research was conducted to investigate and assess the effectiveness of fungicides and herbicides in controlling the foot rot disease caused by the fungus Sclerotium rolfsii in wheat crops. Foot rot of wheat caused by Sclerotium rolfsii Sacc. has a major constraint and potential threat to successful wheat cultivation. Therefore affords were made to screen the different systemic, contact and combination of fungicides and herbicides in vitro condition against Sclerotium rolfsii. Different fungicides against S. rolfsii were tested in vitro. The efficacy of two systemic fungicides (Tricyclazole 75%W.P. & Carbendazim 50% WP); two non-systemic fungicides (Mancozeb 75%WP & Copper oxychloride 50% WP); one contact fungicides Propineb 70%WP and one combo fungicides (Metalaxyl 8%+Mancozeb 64%) were evaluated at different concentrations (50,150 and 250 ppm) on the development of S. rolfsii on Potato dextrose agar (PDA) medium using poisoned food technique. Among the six fungicides, Mancozeb was found best at all the concentrations followed by Tricyclazole at higher concentrations which inhibit the growth of S. rolfsii. Another method used for management strategy was herbicide for inhibiting the mycelial growth of S. Rolfsii. In vitro efficacy of selective herbicides viz. (Metribuzin 70% WP & Oxadiargyl 80% WP), systemic herbicide viz. (Pyrazosulfuron Ethyl 10% WP & Metsulfuron Methyl 20% WP) and one combo herbicides viz. (Bensulfuron Methyl 0.6% + Pretilachlor 6% GR) were tested at their recommended concentrations. Among them metribuzin showed 80.00 % growth inhibition, succeeded by Pyrazosulfuron ethyl (51.85%) and Bensulfuron methyl + Pretilachlor (45.92%).

Studies on Anti-Fungal Activity of Different Macro Algal Extracts against Soil Borne Pathogen Sclerotium rolfsii Sacc.

Management of soil-borne plant pathogens is one of the single greatest challenges facing modern agriculture worldwide. Seaweeds are considered as a source of bioactive compounds as they are able to produce a great variety of secondary metabolites characterized by a broad spectrum of biological activities. The seaweeds derived compounds showing broad range of biological activities such as antiviral, antibacterial and antifungal activities. The antimicrobial activity of macro algal extracts is generally analysed using various organic solvents which always present higher efficiency in extracting bioactive compounds. Among the different the solvent extracted macro algal extracts tested, methanol extracts of Sargassum wightii recorded maximum mycelial inhibition (88.22 %) and on par with aqueous extracts recorded 85.78% of mycelial inhibition @ 10% concentration compared to other macro algal extracts.. Among the fifteen macro algal extracts, maximum inhibition of mycelial growth was recorded the Sargassum wightii (Brown algae), Ulva lactuca (Green algae) and Gracilaria salicornia (red algae) at different concentrations. In this study, we have shown that Sargassum wightii has antimicrobial potential against the S. rolfsii. Methanol extract was found to be the best solvent for retention of the antimicrobial activity

First report of Athelia rolfsii (=Sclerotium rolfsii) associated with foot rot disease of Chrysanthemum morifolium in India.

Chrysanthemum morifolium L. is an important flower crop grown in different parts of Karnataka for its striking cut flowers and international market value. During a field survey (Mysore district, Karnataka, February, 2022), chrysanthemum fields were found infected with foot rot disease. The presence of white mycelial structures with sclerotia were recorded near the stem-soil interface. The disease incidence ranged 10-12% measured in an area of approximately 10 hectares. The infected plants showed quick wilt, yellowing and toppling of the entire plant. Infected plants from Doddamaragowdanahally and Rayanahally (n=15) were collected and associated fungal pathogen isolated after surface sterilization with NaOCl (1%) on potato dextrose agar (PDA) amended with chloramphenicol (50 mg/L). Fungal mycelia developed from the infected tissues were inoculated on to fresh PDA plates to obtained pure cultures for further identification. Fungal colonies with dense, aerial whitish-cottony mycelia with uniformly globoid sclerotia (0.284.2 mm) were observed after 15 days of incubation (28 ± 2°C). Sclerotia were white in the beginning and turned brown at maturity. The average number of sclerotia produced per plate ranged from 240 to >480 (n = 10). To further to confirm the identity of the isolates, two representative isolates (CmSr1 and CmSr2) was subjected to molecular identification based on ITS-rDNA sequences. Briefly, genomic DNA was isolated from 12 day old cultures using the CTAB method and ITS-rDNA was amplified using ITS1-ITS4 primers (White et al., 1990). An expected amplicon of >650 bp (ITS) was obtained and later sequenced from both the directions. The consensus sequences were analysed through nBLAST search which revealed that 100% sequence similarity with reference sequences of Athelia rolfsii (S. rolfsii) from GenBank database (MT127465, MN974137, KC292637; identity 656/656; 0 gaps). A phylogenetic tree obtained by the neighbor-joining method using MEGAX shared a common clade with the reference sequences retrieved and computed, thus confirming the identification based on sequence analysis and molecular phylogeny. The representative sequence of A. rolfsii isolates CmSr1 and CmSr2 isolates deposited in GenBank with Accession nos. ON456153 and ON456154, respectively. Based on etiology, morphological, cultural and molecular data the pathogen was identified as Athelia rolfsii (Curzi) Tu & Kimbrough (Syn: Sclerotium rolfsii Sacc.) (Mordue, 1974; Mahadevakumar et al., 2016, 2018). Plants (n=60) were inoculated with sclerotial bodies (2 sclerotia/plant) near stem soil interface under green house and covered with polythene bags (at 27 ± 2°C and 80% RH). Non-inoculated plants (n=20) served as controls. The development of foot rot disease was observed eight days after inoculation. A total of 48 plants showed the foot rot symptoms and 12 inoculated plants and control plants remained healthy. The identity of the fungus was confirmed by morphological and cultural characters after re-isolation. C. morifolium is an important flower crop in Karnataka. S. rolfsii is known to be associated with blight and collar rot of Chrysanthemum spp. from Kerala (Beena et al., 2002) but no species (host) identity provided. Therefore, to the best of our knowledge, this is the first report of foot rot disease caused by Athelia rolfsii on C. morifolium in India. Early diagnosis of this disease will help the farmers to adopt suitable management practices to avoid loss.

Evaluation of different fungicides against rice seedling rot incited by Sclerotium rolfsii Sacc.

Seedling rot disease in rice incited by Sclerotium rolfsii Sacc. in the rice nursery raised during December to January for summer rice cultivation is an emerging threat to rice cultivation in South Gujarat. In the present climate change scenario, rice crop is facing the challenges of new diseases which were otherwise not touching the economical threshold. Eight fungicides were evaluated under in vitro condition. Tebuconazole 50% + trifloxystrobin 25%, mancozeb 63%+ carbendazim 12%, azoxystrobin 18.2%+difenoconazole 11.4%SC, azoxystrobin 11.5% + mancozeb 30.0% and thiram 75 WS gave complete mycelial growth inhibition at 50 ppm concentration. Whereas azoxystrobin 23SC and tebuconazole 2% DS showed good mycelial growth inhibition ability with 83.30 and 90.74%, respectively. Most effective fungicides under in vitro were evaluated against seedling rot disease under field conditions during 2018 to 2020. Seed treatment with fungicides revealed that rice seeds treated with azoxystrobin 23SC @ 1ml /kg seed and soil application with Trichoderma harzianum (2×106 cfu/g) @ 1 g/m2 which was at par with seeds treated with azoxystrobin 23SC @ 1ml/kg seeds and azoxystrobin 18.2% + difenoconazole 11.4 %SC @ 1ml/kg seeds effectively managed seedling rot disease and given highest plant population with minimum seedling mortality, improved shoot and root length and good seedling vigor index.

Exploitation of indigenous fluorescent pseudomonads against stem and pod rot of groundnut caused by <i>Sclerotium rolfsii</i>

Stem and pod rot of groundnut is an economically important soil borne disease caused by Sclerotium rolfsii Sacc. The present study aimed to evaluate the indigenous bacterial bio control agent Pseudomonas fluorescens strains having multiple traits related to bio control and plant growth promoting activity. Healthy rhizospheric soil from groundnut field was collected from different North Karnataka districts. Nineteen strains of P. fluorescens were isolated by serial dilution technique on King’s B medium. The antagonistic potential of nineteen strains was tested against S. rolfsii by using dual culture technique. The per cent inhibition was highly variable among the nineteen strains of P. fluorescens ranging from 2.59 to 75.18 per cent. Maximum mycelial inhibition of S. rolfsii was recorded by the strain PF-2 (75.18%) followed by PF-3 (72.96%), PF-6 (69.62%) and least inhibition was recorded by PF-13 (2.59%). Five superior strains of P. fluorescens showed fluorescens under UV light, yellowish green pigmentation, rod shaped cells under microscope. Five superior strains were subjected for various biochemical tests and all the isolates were positive for biochemical characterization such as Gram staining, endospore production, catalase, starch hydrolysis, urease test, casein hydrolysis and gelatin liquefy action and negative for KOH and in dole test. Further, these strains were subjected for plant growth promoting traits such as HCN production, IAA production, siderophore production and volatile compounds production. Among these, the strainsviz., PF-2 and PF-3 were scored as strong with respect to antagonism and growth promotion. The strainsPF-6, PF-7 and PF-10 were scored as moderate with light brown colour. Among the tested strains of P. fluorescens, the isolates PF-2 and PF-3 were recorded higher production of siderophore, isolates PF-6, PF-7 and PF-10 showed moderate production of siderophore. The strain PF-2 of P. fluorescens showed highest per cent of mycelial inhibition of S. rolfsii indicating higher production of volatile compounds, followed by PF-3 and PF-6. Whereas, the least mycelial inhibition was recorded by the isolate PF-10 indicating less production of volatile compounds.

Development of EST-SSR primers and genetic diversity analysis of the southern blight pathogen Sclerotium rolfsii using transcriptome data.

Sclerotium rolfsii Sacc. is a globally dispersed pathogenic fungus that causes southern blight disease in many crops and Chinese herbal medicine. The high degree of variation and diversity in the fungi altered population genetic structure. Therefore, the important factors of variation within the pathogen population should be considered during the development of management strategies for the disease. In this study, S. rolfsii isolates from 13 hosts in 7 provinces of China were collected and analyzed to identify their morphological features and perform molecular characterization. To develop EST-SSR primers, transcriptome sequencing was performed on isolated CB1, and its SSR loci were comprehensively analyzed. In addition, we analyzed the polymorphisms among different populations based on screened EST-SSR primers. The results showed that all of these clean reads with total 36,165,475 assembled bases were clustered into 28,158 unigenes, ranged from 201 bp to 16,402 bp on the length, of which the average length was 1,284 bp. Of these, the SSR sequence appeared at an average interval of 15.43 kB, and the frequency of SSR was 0.0648 SSR/kB. Polymorphism of 9 primers was observed among 22 populations, and was verified by the Shannon's index (average = 1.414) and polymorphic information index (> 0.50). The genetic diversity analysis revealed diversity in all host populations and geographical populations. Further, molecular variance analysis (AMOVA) showed that the differences between groups were mainly related to geographical location. Based on cluster analysis, the 7 populations were roughly divided into 3 groups, and the results were highly consistent with those based on the geographical location, ultimately aligning with the results of STRUCTURE analysis. The findings build on current knowledge of the distribution of S. rolfsii in the southwest area of China, adding value to current knowledge base on the population structure and genetic diversity of S. rolfsii, specifically in the context of Chinese herbal medicine cultivation in China. Overall, our findings may provide valuable information for breeding of crops with enhanced resistance toward S. rolfsii.

First Report of Sclerotium rolfsii Causing Southern Blight on Stephania tetrandra in China.

Stephania tetrandra S. Moore is a perennial liana and is widely cultivated in southern China for traditional Chinese medicine as a diuretic, anti-inflammatory, and antirheumatic treatment (Jiang et al. 2020). In August 2021, it was observed that a severe stem rot disease affected St. tetrandra cultivated in Anfu, Jiangxi province, China (114°27'26" E, 27°22'46" N). The disease symptoms included constriction and rot at the base of the stem, and covered with a layer of white mycelia. The plants above-ground finally wilted and dried with a disease incidence ranging from 8% to 16%. Lots of dried plants formed withered patches of field. Sections (1.0~2.0 cm) from browning stem tissues were surface-disinfected with 75% ethanol for 15 s, followed by 60 s in 4% NaClO, rinsed twice in sterile water, dried on sterilized filter paper, placed on potato dextrose agar (PDA), and incubated at 26°C in the dark for 3 days. A white rhizomorphic fungal mycelium, that is similar to the mycelium of strain FJSR0 on the surface of an infected plant in the field, was isolated from the cultured tissues with 67% frequency. When incubated on PDA, white and fluffy mycelia with even margins and a slight halo formed. Mycelia-produced clamp connections were observed. Colonies grew quickly and covered the dish (diameter: 9 cm) in 5 or 6 days. After that, sclerotia were initially white, then turned yellow, and chestnut brown at maturity. Spherical and subspherical sclerotia were observed after 8 days, with each plate containing 448 to 634 sclerotia (0.8 to 1.4 mm diameter; mean = 0.94 mm; n = 50). On the basis of morphology, the pathogen was similar to Sclerotium rolfsii Sacc. [teleomorph: Athelia rolfsii (Curzi) Tu & Kimbrough] (Sun et al. 2020; Ling et al. 2021). For molecular confirmation, the internal transcribed spacer (ITS) region with approximately 680 bp was amplified from strains FJRS0 and FJRS1 using primers ITS1/ITS4 (White et al. 1990). Two distinct types (different in one SNP and one 1-bp InDel) of ITS sequences were obtained from each isolate, and all isolates contain the two types (FJSR0: ON972516, ON972517; FJSR1: ON972520, ON972518). BLAST analysis of each type found that the hits, with identities >99%, are A. rolfsii except for two Sc. delphinii sequences (GU567775.1 and MK073010.1). Phylogenetic analysis placed strains FJSR0 and FJSR1 in the same clade as Sc. rolfsii but away from Sc. delphinii based on the previous method (Sun et al. 2021). Both morphological and molecular characteristics confirmed that the strains were Sc. rolfsii. For pathogenicity tests, PDA plugs (8 mm in diameter) covered with 5-day-old fungal mycelium were inoculated at the stem bases of three healthy St. tetrandra seedings and incubated at 26℃ and relative humidity of 80%. On the fifth day, inoculated plants were wilting. The infected stem bases turned brown to black and constricted as previously observed in the field. Some leaves, infected by the mycelium expanded from the PDA plugs, developed an orange and irregular spot. Sclerotia were observed 20 days post inoculation. In contrast, the leaves and stems of non-inoculated control plants remained symptomless. Pathogenicity tests were repeated three times. The fungus was reisolated consistently from each symptomatic tissue, thus completing Koch's postulates. Although Sc. rolfsii has been previously reported to cause a southern blight symptoms on vegetables, ornamentals, grass, and medicinal and leguminous crops (Sun et al. 2020; Ling et al. 2021), this is the first report of Sc. rolfsii causing similar symptoms of southern blight on St. tetrandra in China.

Two polysaccharide elicitors trigger systemic acquired resistance to resist Sclerotium rolfsii and its transcriptional characteristic in Atractylodes macrocephala

The elicitors can trigger plants systemic acquired resistance. In contrast to the well-characterized exogenous elicitor-induced common response, little is known about how the plants have activated SAR response to pathogen challenge. Here, early transcriptional reprogramming and downstream immune outputs in SAR-activated plants against the Sclerotium rolfsii Sacc stress were investigated by comparative biochemical and transcriptomics in Atractylodes that sprayed by two polysaccharide elicitors (designated as CIP and SR). It was evident that the SAR-activated plants exhibit unique expression characteristics in response to pathogens stress, depending on the discrepancies between CIP and SR, the CIP-induced response depend on some antimicrobial proteins, but the SR depend on phytohormone genes family, in spite of both elicitors instigate common downstream immune output. Notably, some overlap genes not only occurred in SAR-activated plants but also in SAR-activated challenge plants, indicating invisible immune memory in plant. Otherwise, the SAR-activated plants share a reversed genes pattern with the SAR-activated challenge group, and they all tended to resist the susceptible plants' transcriptional reprogramming process (most positive defense genes were suppressed) via reversed genes pattern, which these up- and down-regulated in plant is analogous to “immuno-correct action” of animals’ vaccines.

Intracellular metabolomics and microRNAomics unveil new insight into the regulatory network for potential biocontrol mechanism of stress-tolerant Tricho-fusants interacting with phytopathogen Sclerotium rolfsii Sacc.

The present study employed microRNA (miRNA) sequencing and metabolome profiling of Trichoderma parental strains and fusants during normal growth and interaction with the phytopathogen Sclerotium rolfsii Sacc. In-vitro antagonism indicated that abiotic stress-tolerant Tricho-fusant FU21 was examined as a potent biocontroller with mycoparasitic action after 10 days. During interaction with the test pathogen, the most abundant uprising intracellular metabolite was recognized as l-proline, which corresponds to held-down l-alanine, associated with arginine and proline metabolism, biosynthesis of secondary metabolites, and nitrogen metabolism linked to predicted genes controlled by miRNAs viz., cel-miR-8210-3p, hsa-miR-3613-5p, and mml-miR-7174-3p. The miRNAs- mml-miR-320c and mmu-miR-6980-5p were found to be associated with phenylpropanoid biosynthesis, transcription factors, and signal transduction pathways, respectively, and were ascertained downregulated in potent FU21_IB compared withFU21_CB. The amino benzoate degradation and T cell receptor signaling pathways were regulated by miRNAs cel-miR-8210 and tca-miR-3824 as stress tolerance mechanisms of FU21. The intracellular metabolites l-proline, maleic acid, d-fructose, Myo-inositol, arabinitol, d-xylose, mannitol, and butane were significantly elevated as potential biocontrol and stress-tolerant constituents associated with miRNA regulatory pathways in potent FU21_IB. A network analysis between regulatory miRNA-predicted genes and intracellular metabolomics acknowledged possible biocontrol pathways/mechanisms in potent FU21_IB to restrain phytopathogen.

Comparative evaluation of native Trichoderma species from groundnut rhizosphere against stem rot caused by Sclerotium rolfsii Sacc.

Comparative evaluation of native Trichoderma species from groundnut rhizosphere against stem rot caused by Sclerotium rolfsii Sacc.

Exploring conserved and novel MicroRNA-like small RNAs from stress tolerant Trichoderma fusants and parental strains during interaction with fungal phytopathogen Sclerotium rolfsii Sacc.

The study investigated potential microRNA-like small RNAs (milRNAs) from multi-stress-tolerant Tricho-fusants and parental strains (P1- Trichoderma virens NBAIITvs12 and P2- Trichoderma koningii MTCC796) for antagonistic activity during interaction with phytopathogen Sclerotium rolfsii. The Trichoderma was cultured in-vitro, with and without antagonism, against the pathogen and total RNA was extracted followed by small RNA library construction and sequencing. The milRNAs were identified by mapping high-quality unique reads against a reference genome. The milRNAs were recognized higher in antagonist Trichoderma during interaction with test pathogen compared to normal growth. The novel milRNAs candidates were found to vary during interaction with the pathogen and normal growth. The gene ontology and functional analysis illustrated that a total of 5828 potential targeted genes were recognized for 93 milRNAs of potent Fu21_IB and 3053 genes for 62 milRNAs of least fusant Fu28_IL. Functional annotation of milRNA-predicted genes integrating KEGG pathways indicates new insights into regulatory mechanisms, by interfering with milRNAs, associated with signal transduction, amino sugar metabolism, benzoate degradation, amino acid metabolism, and steroid and alkaloid metabolism for potential biocontrol of stress-tolerant Tricho-fusant FU21 during interaction with S. rolfsii. The present investigation is the first report of conserved and novel milRNAs from Tricho-fusants and parental strains interacting with S. rolfsii.

First report of southern blight of Dendrobium huoshanense caused by Sclerotium rolfsii in Lu'an, China.

Dendrobium, the second largest genus of Orchidacea, are mainly distributed in Asia, Oceania and Europe (Ding et al., 2008). An emerging disease on D. huoshanense with symptoms resembling southern blight Sclerotium rolfsii Sacc. occurred during June to September from 2017 to 2020 in Huoshan, Lu'an, China. The yield and quality of D. huoshanense were seriously affected especially under greenhouse conditions in July, with a disease incidence of 42%. Early symptoms consisted of water-soaked lesions on the lower stem tissue. Then leaves turned pale green and withered, a dense white mycelial mat were formed on the lower stem along with 1- to 2-mm-diameter, white round sclerotia. Subsequently, infected stems collapsed with the whole stem yellow and withered, and with many dark brown sclerotia on withered stems. Sclerotia from 5 diseased plants were disinfected in 1% mercury bichloride for 10 s, rinsed in 75% ethanol for 30 s and then rinsed 4 times with sterile water, dried, and transferred to potato dextrose agar (PDA) with the cross section and incubated at 27 °C in darkness. Mycelia were selected from the edge of the colony and transferred to new PDA plates for purification of cultures after 3 days. Fungal colonies with white mycelia and abundant sclerotia developed after 7 days of incubation. Isolate morphological characteristics confirmed the identity as S. rolfsii (Mordue, 1974). To further confirm the identity of the causal fungus, the complete internal transcribed spacer (ITS) rDNA region, the elongation factor-1a gene (EF1a) and the large subunit (LSU) region of one representative isolate, MB-1, was amplified using the primers ITS1/ITS4 (White et al. 1990), EF1-983F/EF1-2218R (Rehner and Buckley 2005), and NL1/NL4 (O' Donnell et al. 1997), respectively. Sequences have been deposited in GenBank (Accession No. OM946593 for ITS, OL416131 for EF1a and OL373917 for LSU). There was 100% sequence identity to Athelia rolfsii (S. rolfsii) with the sequences MN610008.1 (ITS) and MW322687.1 (EF1a), and 99.84% sequence identity to MT225781.1 (LSU). Pathogenicity tests were performed by wound inoculation with culture discs of mycelia ( = 5 mm) on the stem base of 10-12 cm height plants (four stems per pot, one stem inoculated with one culture disc, four replicates). Four healthy stems of the plants served as a control. The test was conducted in an artificial climate incubator at 26±1 °C with a 16h light/8h dark photoperiod and plants were enclosed for 72 h in polyethylene bags (relative humidity = 90%). Two days post-inoculation, white mycelia developed in the wound and the leaves at the upper and lower parts of the wound began to turn yellow. Then the stem softened and turned yellow. White sclerotia were formed by the sixth day. By 12 days post-inoculation, stems were atrophied and collapsed, sclerotia were yellow brown, and most leaves showed yellow discolouration and fell off. S. rolfsii was re-isolated from infected plants. Control plants remained healthy. To our knowledge, this is the first report of S. rolfsii causing southern blight on D. huoshanense in Lu'an, China. Confirmation of the causal agent provides a basis for management of S. rolfsii in cultivated D. huoshanense.

Management of Collar Rot Disease of Chickpea (Cicer arietinum L.) caused by Sclerotium rolfsii Sacc. under Rice based Cropping System

Management of Collar Rot Disease of Chickpea (Cicer arietinum L.) caused by Sclerotium rolfsii Sacc. under Rice based Cropping System

First report of Athelia rolfsii (= Sclerotium rolfsii) causing southern blight on Pachyrhizus erosus in Mexico.

Pachyrhizus erosus, commonly named jicama, is native to Mexico and is cultivated for its tuberous roots which are edible. In November 2021, field sampling was carried out in municipality of Huaquechula (18.748640N, 98.550817W, 1,580 m above sea level), state of Puebla, México. The disease had an incidence between 20 and 30% in approximately 10 ha. Infected plants showed wilting, yellowing foliage, rotting with white mycelium, abundant sclerotia were observed in the roots and tuber. Tuber splits transversely over time. Twenty plants with symptoms of disease were carried out to isolate the fungus. The sclerotia found in the tubers were disinfected with 3% NaOCl, rinsed twice with sterile distilled water, and excess moisture was removed and, transferred on Potato Dextrose Agar (PDA) culture medium and incubated at 28°C. Mycelial fragments from symptomatic tubers, were plated directly to PDA. Twenty representative isolates were obtained by hyphal-tip method, one for each diseased plant sampled (10 isolates from sclerotia and the other 10 from fragments of mycelium). After 10 days, colonies showed fast-growing, dense, cottony-white aerial mycelium, forming globoid to irregular sclerotia, measuring 1.0-1.7 mm in diameter (mean = 1.42 mm; n=100). The number of sclerotia produced per Petri dish ranged from 54 to 542 (mean = 274, n = 50). These sclerotia were initially white and gradually turned brown. Microscopic examination showed septate hyphae with some cells having clamp connections. Based on morphological characteristics, the fungal isolates were identified as Athelia rolfsii (Curzi) CC Tu & Kimbr (Syn: Sclerotium rolfsii Sacc) (Mordue 1974). For molecular identification, a representative isolate (Sr.1), the ITS region was amplified (650 bp) using primers ITS1/ITS4 (White et al. 1990). The obtained sequence (GenBank: ON206899) was subjected to BLAST analysis, where it had 100% identity with A. rolfsii isolates (GenBank: MG836252 and MH517363). Phylogenetic analysis with the neighbor-joining method in MEGAX, grouped the Sr.1 isolate into a common clade with different A. rolfsii isolates. Pathogenicity was confirmed by inoculating 20 tubers detached from healthy P. erosus variety "Criolla de Morelos", into which a portion of mycelium from the Sr.1 isolate was inserted with a sterile wooden stick at one point per tuber. In five tubers, only a sterile wooden stick was inserted as negative controls. The tubers were placed under laboratory conditions with relative humidity close to 100% and a temperature of 28°C. Symptoms like those observed in the field were observed after five days. Control tubers showed no symptoms. Additional pathogenicity tests were performed on 50 plants of 100-day-old P. erosus of the variety "Criolla de Morelos", grown in pots with sterile soil. Ten sclerotia of 10 days old were deposited at the base of the stem, 10 mm below the soil surface; as control treatment only, sterile distilled water was deposited on 20 plants. The plants were placed in a greenhouse (Center for Technological Innovation in Protected Agriculture of the Popular Autonomous University of the State of Puebla), at 28 ± 1°C and 90% of temperature and relative humidity, respectively. After 15 days, all inoculated plants showed symptoms similar to those observed in the field. Control plants showed no symptoms. A. rolfsii was re-isolated from inoculated tubers and stem, fulfilling Koch's postulates. Previously, A. rolfsii was reported in Mexico, causing southern blight on sesame (Hernández-Morales et al. 2018). To our knowledge, this is the first report of Athelia rolfsii causing southern blight on P. erosus in Mexico (Farr and Rossman 2022). This research is important to design management strategies and prevent its spread to other P. erosus-producing areas.

Efficacy of Trichoderma isolates against Sclerotium rolfsii causing collar rot of lentil

Lentil collar rot disease caused by Sclerotium rolfsii Sacc. is an important disease causing significant yield loss in Nepal. Seven Trichoderma spp. isolates collected from different regions of Nepal were tested for their capacity to inhibit mycelial growth of Sclerotium rolfsii in in-vitro condition. Experiment was conducted in Completely Randomized Design with four replications in the plant pathology laboratory of Grain Legumes Research Program, Khajura, Banke during 2020. Dual culture method was performed to assess the efficacy of Trichoderma isolates. Trichoderma spp. isolates inhibited mycelial growth of S. rolfsii to various degrees ranging from 48.33-72.47% after 120 hours of inoculation. Maximum colony inhibition of S. rolfsii (72.47%) was obtained by Kapilvastu isolate followed by Nepalgunj isolate (67.72%). Minimum colony inhibition of S. rolfsii (48.33%) was obtained by Mangalpur, Chitwan isolate followed by Rampur, Chitwan isolate (49.33%). Among seven Trichoderma isolates, two isolates (Kapilbastu and Nepalgunj) showed good antagonistic activity against S. rolfsii and were also highly competitive in in-vitro condition. These isolates would therefore be useful in biological disease management.

The antagonistic potential of peanut endophytic bacteria against Sclerotium rolfsii causing stem rot

Peanut stem rot caused by Sclerotium rolfsii Sacc. is the most common disease of peanut worldwide and has become increasingly serious in recent years. This study is aimed at obtaining peanut endophytic bacteria with high antagonistic/protective effects against peanut stem rot. In total, 45 bacterial strains were isolated from healthy peanut plants from a severely impacted area. Of these, 6 exhibited antagonistic activity against S. rolfsii, including F-1 and R-11 with the most robust activity with an inhibition zone width of 20.25 and 15.49 mm, respectively. These two were identified as Bacillus sp. and Burkholderia sp., respectively, based on morphological, physiological, and biochemical characteristics and 16S rDNA sequencing. To the best of our knowledge, this is the first study to report the Burkholderia sp. antagonistic effect on S. rolfsii as a biological control agent for peanut stem rot. Their culture filtrates potently inhibited the hyphal growth, sclerotial formation, and germination of S. rolfsii. Also, the strain-produced volatile compounds inhibited the fungal growth. Pot experiments showed that F-1 and R-11 significantly reduced the peanut stem rot disease with the efficacy of 77.13 and 64.78%, respectively, which was significantly higher compared with carbendazim medicament (35.22%; P < 0.05). Meanwhile, F-1 and R-11 improved the activity of plant defense enzymes such as phenylalaninase (PAL), polyphenol oxidase (PPO), and peroxidase (POD) enhancing the systemic resistance of the peanut plants. This study demonstrated that Bacillus sp. F-1 and Burkholderia sp. R-11, with a strong antagonistic effect on S. rolfsii, can be potential biocontrol agents for peanut stem rot.

Effect of Trichoderma isolates on Sclerotium rolfsii Sacc.

Sclerotium rolfsii Sacc. is one of the most important plant pathogens commonly causing root rot, stem rot, wilt and foot rot in various crop species. A wide range of host, profuse mycelial growth, and ability to produce persistent sclerotia makes them difficult to control. Biological control using Trichoderma could provide a sustainable tool for the management of diseases caused by S. rolfsii. One hundred four Trichoderma isolates were evaluated against S. rolfsii in vitro by dual culture. Of them, 30 Trichoderma isolates found effective were selected to study parasitization of sclerotia of S. rolfsii in vitro. Similarly, four Trichoderma isolates found effective in vitro were used to study their ability to parasitize sclerotia of the pathogen in soil. Trichoderma isolates varied significantly (p&lt;0.001) for both the inhibition percentage and biocontrol index. However, they showed a differential effect as Trichoderma isolate T73, Forest soil had highest inhibition (96.96%), while Trichoderma isolate T49, Bhaktapur showed the highest bio-control index (99) against S. rolfsii. Trichoderma isolates T49, Bhaktapur and T87, Forest soil showed promising results in controlling S. rolfsii in vitro. Both isolates were also able to parasitize and reduce the germination of sclerotia in the soil. The present study demonstrated that selected Trichoderma had potential in controlling Sclerotium rolfsii.

Antagonist activities of native rhizosphere micro-flora against groundnut stem rot pathogen, Sclerotium rolfsii Sacc.

BackgroundStem rot caused by Sclerotium rolfsii Sacc. is a major nuisance in groundnut production, causing substantial yield losses in almost all groundnut-growing areas around the world. Biological control is regarded as a sustainable choice over the currently popular management strategy i.e., chemical control, as later has a negative influence on the environment. The present study evaluated the antagonistic effect of native rhizosphere micro-flora against groundnut stem rot pathogen S. rolfsii.ResultsA total of 111 bacterial isolates and 9 Trichoderma isolates isolated from groundnut rhizosphere soil were evaluated for their antagonist activity against S. rolfsii in vitro. Eight isolates (seven bacterial and one Trichoderma) were chosen as prospective biocontrol candidates based on the findings of the dual culture assay. Molecular characterization of these isolates by 16S rDNA and ITS rDNA sequencing confirmed the identity of bacterial isolates as Bacillus spp. (six B. subtilis and one B. amyloliquefaciens) and fungal isolate as Trichoderma asperellum. Also, the selected seven bacterial isolates recorded favourable results for antagonism-promoting biochemical traits.ConclusionThe results of the current study suggested that the native groundnut rhizosphere micro-flora can be exploited for biological control of groundnut stem rot pathogen S. rolfsii. Further research may enable the use of the isolated rhizosphere biocontrol agents as single organisms or in a consortium for sustainable management of the groundnut stem rot pathogen.