Variation in Sclerotium rolfsii isolates in Japan

Characterizing genetic diversity of Sclerotium rolfsii isolates by biomapping of mycelial compatibility groupings and multilocus sequence analysis

Genetic diversity in Sclerotium rolfsii is useful for understanding its population structure, identifying different mycelial compatibility groups (MCGs), and developing targeted strategies for disease management in affected crops. In our study, a comprehensive genetic analysis was conducted on 50 isolates of S. rolfsii, collected from various geographic regions and host plants. Two specific genes, TEF1α and RPB2, were utilized to assess the genetic diversity and relationships among these isolates. Notably, out of 1225 pairings examined, only 154 exhibited a compatible reaction, while the majority displayed antagonistic reactions, resulting in the formation of a barrier zone. The isolates were grouped into 10 distinct MCGs. These MCGs were further characterized using genetic sequencing. TEF1α sequences distinguished the isolates into 17 distinct clusters, and RPB2 sequences classified them into 20 clusters. Some MCGs shared identical gene sequences within each gene, while others exhibited unique sequences. Intriguingly, when both TEF1α and RPB2 sequences were combined, all 10 MCGs were effectively differentiated, even those that appeared identical with single-gene analysis. This combined approach provided a comprehensive understanding of the genetic diversity and relationships among the S. rolfsii isolates, allowing for precise discrimination between different MCGs. The results shed light on the population structure and genetic variability within this plant pathogenic fungus, providing valuable insights for disease management and control strategies. This study highlights the significance of comprehending the varied virulence characteristics within S. rolfsii isolates, categorizing them into specific virulence groups based on disease severity index (DSI) values. The association with MCGs provides additional insights into the genetic underpinnings of virulence in this pathogen. Furthermore, the identification of geographical patterns in virulence implies the influence of region-specific factors, with potential implications for disease control and crop protection strategies.Please confirm if the author names are presented accurately and in the correct sequence (given name, middle name/initial, family name). Author 1 Given name: [G. M. Sandeep] Last name [Kumar]. Author 2 Given name: [Praveen Kumar] Last name [Singh]. Also, kindly confirm the details in the metadata are correct.I confirm that the given names are accurate and presented in the correct sequence.

Characterization of Sclerotium rolfsii causing foot rot: a severe threat of betel vine cultivation in Bangladesh

The development of the foot rot disease caused by the fungus Sclerotium rolfsii is one of the primary variables endangering betel vine production in Bangladesh. Consequently, with the ultimate objective of finding efficient preventive and control strategies for this infamous phytopathogen, the current study was undertaken for comprehensive population structure analysis, exploration of physiological features and incidence patterns of pathogenic S. rolfsii isolates. We discovered 22 S. rolfsii isolates from nine northern districts of Bangladesh. Mohanpur (51.90%), Bagmara (54.09%), and Durgapur (49.45%) upazilas in the Rajshahi district had the more severe occurrences of foot rot disease, while Chapainawabganj (18.89%) had the least number of cases. The isolates differed substantially in terms of morphology and growth rate. By employing the UPGMA algorithm to analyze the combined morphological data from 22 S. rolfsii isolates, these isolates were divided into six different groups with a 62% similarity level. Somatic incompatibility was also found in some isolates. The RAPD-4 primer confirmed 100% polymorphism among these isolates, and these genetic variations were further validated by molecular analysis. The results of the morphological and molecular analysis revealed that there was significant variation among the S. rolfsii isolates. Finally, a comprehensive characterization of S. rolfsii would allow for a suitable management strategy for betel vine's deadly foot rot disease.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03890-8.

Application of Hydrothermal Time Models to Predict Sclerotial Germination of Athelia rolfsii

Athelia rolfsii, causal agent of "southern blight" disease, is a soilborne fungal pathogen with a wide host range of more than 500 species. This study's objectives were to (i) quantify the effects of two environmental factors, temperature and soil moisture, on germination of A. rolfsii inoculum (sclerotia), which is a critical event for the onset of disease epidemics and (ii) predict the timing of sclerotial germination by applying population-based threshold-type hydrothermal time (HTT) models. We conducted in vitro germination experiments with three isolates of A. rolfsii isolated from peanuts, which were tested at five temperatures (T), ranging from 17 to 40°C, four matric potentials (Ψm) between -0.12 and -1.57 MPa, and two soil types (fine sand and loamy fine sand), using a factorial design. When Ψm was maintained between -0.12 and -0.53 MPa, T from 22 to 34°C was found to be conducive to sclerotial germination (>50%). The HTT models were fitted for a range of T (22 to 34°C) and Ψm (-0.12 to -1.57 MPa) that accounted for 84% or more of variation in the timing of sclerotial germination. The estimated base T ranged between 0 and 4.5°C and the estimated base Ψm between -2.96 and -1.52 MPa. The results suggest that the HTT modeling approach is a suitable means of predicting the timing of A. rolfsii sclerotial germination. This HTT methodology can potentially be tested to fine-tune fungicide application timing and in-season A. rolfsii management strategies. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

The soil-borne fungal pathogen Athelia rolfsii: past, present, and future concern in legumes

Legumes are ubiquitous, low-cost meals that are abundant in protein, vitamins, minerals, and calories. Several biotic constraints are to blame for the global output of legumes not meeting expectations. Fungi, in particular, are substantial restrictions that not only hinder production but also pose a serious health risk to both human and livestock consumption. Athelia rolfsii (Syn. Sclerotium rolfsii) is a dangerous pathogenic fungus that attacks most crops, causing massive yield losses. Legumes are no longer immune to this dreadful fungus, which can potentially result in a 100% yield loss. The initial disease symptoms based on the formation of brown color lesions at the point of infection and further development of mycelia, followed by yellowing and wilting of the whole plant. To tackle such situation, various strategies, i.e., management in cultural practices, disease-free plant growth, genetic changes, crop hybridization and in vitro culture techniques have been undertaken. This present review encapsulates the entire situation, from sclerotial dissemination through infection development and control in legume crops, with the goal of developing a tangible understanding of sustainable legume production improvements. Further study in this area might be led in an integrated manner as a result of this information, which could contribute to a better understanding of the processes of disease incidence, resistance mechanism, and its control, and fostering greater inventiveness in the production of legumes.

Morpho-molecular, cultural and pathological characterization of Athelia rolfsii causing southern blight disease on common bean

Common bean (Phaseolus vulgaris), is a winter legume crop in Bangladesh and is considered an important vegetable with export potential. However, the production of common bean is severely affected by a newly reported soilborne fungal pathogen, Athelia rolfsii. This study aimed to characterize this new pathogen by morphological, molecular, cultural, and pathological analyses and determine the host range. The disease incidence in the affected field ranged between 6 and 13%. Initial disease symptoms were observed as brown sunken lesions at the point of infection and development of mycelia, followed by yellowing and quick wilting of the whole plant. A total of 10 fungal isolates were recovered from the infected plant samples, which were morphologically similar and produced white to brown mycelia and numerous brown sclerotia on the PDA medium. Two of them viz. BTCBSr3 and BTCBSr4 were used for the detailed study. Based on morphology and phylogenetic analyses of the sequenced data of internal transcribed spacer (ITS) and translation elongation factor 1 alpha (EF-1α), the pathogen was identified as A. rolfsii. Mycelial growth rate (3.6 cm/day) and fresh weight (107 mg) were higher in the PDA medium, whereas the number of sclerotia production (328/plate) was higher in OMA media. The isolates could grow in a wider range of incubation temperatures (15-35 °C) and media pH (3-9). In the cross-inoculation assay, both isolates were pathogenic on tomato, brinjal, and chickpea, but not on chili, soybean, and cowpea. This study has laid a foundation for further pathological research on the fungus in aid to develop an effective management practice against the pathogen.

Sequence variation in two protein-coding genes correlates with mycelial compatibility groupings in Sclerotium rolfsii

Populations of Sclerotium rolfsii, the causal organism of Sclerotium root-rot on a wide range of hosts, can be placed into mycelial compatibility groups (MCGs). In this study, we evaluated three different molecular approaches to unequivocally identify each of 12 previously identified MCGs. These included restriction fragment length polymorphism (RFLP) patterns of the internal transcribed spacer (ITS) region of nuclear ribosomal DNA (rDNA) and sequence analysis of two protein-coding genes: translation elongation factor 1α (EF1α) and RNA polymerase II subunit two (RPB2). A collection of 238 single-sclerotial isolates representing 12 MCGs of S. rolfsii were obtained from diseased sugar beet plants from Chile, Italy, Portugal, and Spain. ITS-RFLP analysis using four restriction enzymes (AluI, HpaII, RsaI, and MboI) displayed a low degree of variability among MCGs. Only three different restriction profiles were identified among S. rolfsii isolates, with no correlation to MCG or to geographic origin. Based on nucleotide polymorphisms, the RPB2 gene was more variable among MCGs compared with the EF1α gene. Thus, 10 of 12 MCGs could be characterized utilizing the RPB2 region only, while the EF1α region resolved 7 MCGs. However, the analysis of combined partial sequences of EF1α and RPB2 genes allowed discrimination among each of the 12 MCGs. All isolates belonging to the same MCG showed identical nucleotide sequences that differed by at least in one nucleotide from a different MCG. The consistency of our results to identify the MCG of a given S. rolfsii isolate using the combined sequences of EF1α and RPB2 genes was confirmed using blind trials. Our study demonstrates that sequence variation in the protein-coding genes EF1α and RPB2 may be exploited as a diagnostic tool for MCG typing in S. rolfsii as well as to identify previously undescribed MCGs.

Mycelial compatibility groups and pathogenic diversity in Sclerotium rolfsii populations from sugar beet crops in Mediterranean-type climate regions

The population structure of Sclerotium rolfsii from autumn-sown sugar beet crops in Mediterranean-type climate regions of Chile, Italy, Portugal and Spain was determined by analyses of mycelial compatibility groups (MCGs) and pathogenicity to 11 economically important plant species. Twelve MCGs (i-xii) were identified among 459 S. rolfsii isolates. MCG iii was the most prevalent group in all countries except Italy. MCG i, the most abundant group (64·7% of isolates) was identified in Portugal and Spain. The remaining MCGs were restricted to various regions within one country (ii, vi, ix) or different countries (v), or to specific localities (iv, vii, viii, x, xi, xii). MCGs iv, vii and x each comprised one isolate. Fields extensively sampled in southern Spain were infected with one to three MCGs. Plant species differed in susceptibility to MCG tester isolates with a MCG by species interaction. Cluster analyses allowed selection into five MCG groupings and grouped plant species into species-groups 1 (broccoli, chickpea, sunflower, tomato) and 2 (cotton, pepper, sugar beet, watermelon). MCG groupings 1 (i, ix), 2 (ii, iii, vi, viii) and 5 (x, xii) were moderately virulent to species-group 1 and mildly virulent to species-group 2. MCG groupings 3 (iv, v, xi) and 4 (vii) were mildly virulent to both species-groups. Across MCG groups, species were rated highly susceptible (chickpea, sunflower), susceptible (cotton, pepper, tomato, watermelon), moderately resistant (broccoli, melon, sugar beet) and resistant (corn, wheat). Establishing the MCG population structure and virulence variability among S. rolfsii isolates should help in the management of sclerotium root rot diseases.

Overwintering of Sclerotium rolfsii and S. rolfsii var. delphinii in Different Latitudes of the United States

Previously known only from the southern United States, hosta petiole rot recently appeared in the northern United States. Sclerotium rolfsii var. delphinii is believed to be the predominant petiole rot pathogen in the northern United States, whereas S. rolfsii is most prevalent in the southern United States. In order to test the hypothesis that different tolerance to climate extremes affects the geographic distribution of these fungi, the survival of S. rolfsii and S. rolfsii var. delphinii in the northern and southeastern United States was investigated. At each of four locations, nylon screen bags containing sclerotia were placed on the surface of bare soil and at 20-cm depth. Sclerotia were recovered six times from November 2005 to July 2006 in North Dakota and Iowa, and from December 2005 to August 2006 in North Carolina and Georgia. Survival was estimated by quantifying percentage of sclerotium survival on carrot agar. Sclerotia of S. rolfsii var. delphinii survived until at least late July in all four states. In contrast, no S. rolfsii sclerotia survived until June in North Dakota or Iowa, whereas 18.5% survived until August in North Carolina and 10.3% survived in Georgia. The results suggest that inability to tolerate low temperature extremes limits the northern range of S. rolfsii.

A comparative study of the violet root rot fungi, Helicobasidium brebissonii and H. mompa, from Japan

A violet root rot fungus recently found in Japan was identified as Helicobasidium brebissonii. The fungus was compared with another violet root rot fungus, H. mompa, which is distributed throughout Japan, in terms of morphological characteristics of the basidiospores and the conidial state, sequences of rDNA ITS regions, and pathogenicity on carrot, sweet potato and apple rootstock. The two species were clearly discriminated by these features and the taxonomic status of both species is discussed.

Phylogenetic relationship of Sclerotium rolfsii (teleomorph Athelia rolfsii) and S delphinii based on ITS sequences

The phylogenetic relationships of the stem rot pathogens Sclerotium rolfsii and S. delphinii were examined, based on their rDNA ITS sequences. The ITS regions were cloned and sequenced to identify three distinct ITS types: r-1, r-2, and r-3. Two different ITS types exist within S. rolfsii and S. delphinii strains. Japanese strains and one strain of S. rolfsii from the USA contain types r-1 and r-2, whereas another strain from the USA and one from Chile have only one ITS type, r-2. S. delphinii strains have types r-1 and r-3. We discuss the implications of the common presence of ITS type r-1 for the taxonomy and evolution of this species complex.