Variability in Indian isolates ofSclerotium rolfsii

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.

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.

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

Introduction

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.

Methods

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.

Results

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.

Discussion

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.

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.

Identification and Characterization of Sclerotium delphinii Causing Southern Blight on Aconitum kusnezoffii in Northeast China

Aconitum kusnezoffii is a perennial medicinal plant that belongs to the Ranunculaceae family and is distributed mainly in Northeast and North China. In July 2018, a typical southern blight disease of A. kusnezoffii was observed in commercial fields of Qingyuan County, Fushun City, Liaoning Province, China. The fungus mainly infected stem base and tuberous roots of the plant by wrapping the hyphae and absorbing nutrition, resulting in tuberous root wilted or whole plant death. Morphological characteristics of colony and sclerotia of three representative strains isolated from the diseased plants differed from those of Sclerotium rolfsii isolated from A. carmichaelii. Sclerotia were large (0.8 to 5.1 mm), reddish-brown, and irregular and had pitted surfaces, and the hyphae were white, compact, or fluffy, with a growth rate ranging from 8.0 to 10.1 mm/day. Phylogenetic analysis of the internal transcribed spacer and the large subunit sequences of Akln6, Akln9, and Akln15 showed that three strains isolated from A. kusnezoffii formed a unique and well-supported clade that groups with the reference isolates of S. delphinii. Based on phylogenetic analysis and cultural and morphological characteristics, the three isolates of A. kusnezoffii were identified as S. delphinii. The optimum temperature for mycelial growth of the three tested isolates was 30°C, and sclerotia formed and matured more easily at 20°C. Light promoted the growth of mycelial, whereas dark was beneficial to the formation and maturation of sclerotia. The pathogenicity of S. delphinii showed stronger than S. rolfsii at low temperature (20°C). This is the first report of S. delphinii causing southern blight on A. kusnezoffii in China, and this finding provides a basis for disease-accurate diagnosis and the development of effective management strategies.

Fungal Guttation, a Source of Bioactive Compounds, and Its Ecological Role-A Review

Guttation is a common phenomenon in the fungal kingdom. Its occurrence and intensity depend largely on culture conditions, such as growth medium composition or incubation temperature. As filamentous fungi are a rich source of compounds, possessing various biological activities, guttation exudates could also contain bioactive substances. Among such molecules, researchers have already found numerous mycotoxins, antimicrobials, insecticides, bioherbicides, antiviral, and anticancer agents in exudate droplets. They belong to either secondary metabolites (SMs) or proteins and are secreted with different intensities. The background of guttation, in terms of its biological role, in vivo, and promoting factors, has been explored only partially. In this review, we describe the metabolites present in fungal exudates, their diversity, and bioactivities. Pointing to the significance of fungal ecology and natural products discovery, selected aspects of guttation in the fungi are discussed.

Mycelial Compatibility and Pathogenic Diversity Among Sclerotium rolfsii Isolates in the Southern United States

Sclerotium rolfsii is a soilborne fungus that causes southern blight on a wide range of plants in tropical and subtropical regions of the world. Eighty-four isolates collected from Florida, Georgia, Louisiana, South Carolina, Texas, and Virginia were paired and assigned to 23 mycelial compatibility groups (MCGs), of which 11 MCGs consisted of a single isolate. Isolates within an MCG typically originated from different hosts and different geographical areas, with the exception of MCG 11. In all, 13 of the 15 isolates in MCG 11 originated from peanut in Georgia and Florida, while the other 2 isolates originated from potato in Virginia and from the ornamental Barlaeria cristata in Florida. Significant differences in the size and number of sclerotia produced in vitro existed between isolates from peanut and other hosts. Nineteen isolates representative of the most common MCGs (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14, 15, 16, 17, and 18) were tested for pathogenicity on tomato, pepper, and peanut. All isolates were pathogenic on all hosts but virulence differed significantly among isolates. Isolates collected from peanut were the most virulent on all three hosts compared with isolates collected from tomato and pepper. 'Georgia Green' peanut was more susceptible to peanut isolates from Georgia than to the other tested isolates. Of the two tomato entries, the commercial tomato 'Tygress' was less susceptible than the previously reported resistant breeding line 5635M to many of the S. rolfsii isolates tested, with the exception of the peanut isolates collected from Georgia. These initial findings suggest that considerable variation exists among S. rolfsii isolates throughout the southern United States, with some indications of specialization for the isolates collected from peanut.

Metabolite composition and bioactivity of Rhizoctonia solani sclerotial exudates

Sclerotia are vegetative structures that play a major role in survival of fungi under adverse conditions. The sclerotia of the plant pathogen Rhizoctonia solani AG2-2 IIIB exude liquid brown droplets that were evaluated for their bioactivity and toxicity against microorganisms and plant species. Also, their metabolic composition was analyzed by integrating Fourier transform ion cyclotron resonance-mass spectrometry (FT-ICR/MS), gas chromatography-MS (GC/MS), and proton nuclear magnetic resonance ((1)H NMR) spectroscopy. The results showed that exudates are complex mixtures composed of phenolics (17.40%), carboxylic acids (12.79%), carbohydrates (6.08%), fatty acids (3.78%), and amino acids (3.47%). The presence of such metabolites contributed to their antifungal and phytotoxic activities. The biological interpretation of the results highly suggests that the exudates not only have multiple roles in fungal physiology but also are a potential bioactive source with moderate toxicity. Our findings show with certainty that the integration of different analytical platforms is a powerful approach for extracting the maximum and reliable information on the metabolic composition of complex biological samples.

Differential methods of inoculation of plant growth-promoting rhizobacteria induce synthesis of phenylalanine ammonia-lyase and phenolic compounds differentially in chickpca

Foliar spray and micro-injection of plant growth-promoting rhizobacterial species, viz. Pseudomonas fluorescens and P. aeruginosa on chickpea induced synthesis of phenylalanine ammonia-lyase (PAL) when tested against Sclerotinia sclerotiorum. Induction of PAL was also associated with increased synthesis of phenolic compounds such as tannic, gallic, caffeic, chlorogenic and cinnamic acids. Treatment with P. fluorescens was found to be more effective in inducing phenolic compounds as compared to P. aeruginosa. However, persistence of PAL activity was observed more with P. aeruginosa. Although both the inoculation methods were effective, foliar application was found to be superior to micro-injection in terms of rapid PAL activity leading to the synthesis of phenolic compounds.

Phenolic Acid Changes in Mycelia of Sclerotium rolfsii After Garlic and Onion Supplementation in a Broth Medium

High performance liquid chromatographic (HPLC) analysis of mycelia of Sclerotium rolfsii grown in broth medium supplemented with garlic (Allium sativum) and onion (Allium cepa) was carried out to estimate qualitative and quantitative changes in phenolic acids. Several phenolic acids, such as gallic, chlorogenic, ferulic, o-coumaric and cinnamic acids were detected in varied amounts in mycelia grown on such media as compared to control. Phenolic acids represents a wide range of secondary metabolite found in the cells of plants and microbes including fungi. The growth characters of S. rolfsii in various supplements also varied from thin and transparent to thick and opaque.

Induction of Sexual Stage and Colony Morphology of Some Isolates of Sclerotium rolfsii Causing Spotted Leaf Rot in Plants

Twenty-two isolates of Sclerotium rolfsii causing spotted leaf rot from Varanasi, India were grown on 6% Cyperus rotundus rhizome meal agar (CRMA) medium for the induction of athelial stage (Athelia rolfsii). Only one isolate obtained from Sphaeranthus indicus formed basidial stage on CRMA medium while the other 21 isolates did not. Basidial stage was also produced in S. indicus isolate at different concentrations (5.5, 6.0 and 6.5% w/v) of CRMA medium. Size of basidia, sterigmata and basidiospores of this isolate was measured. Basidia clavate, hyaline and measured 10~12 × 4~5 µm in size, basidiospores hyaline, unicellular, subglobose to ellipsoid produced on sterigmata and measured 3~5 × 2~4µm in size, sterigmata hyaline and measured 4~5 × 1.5~2 µm in size. The results of the present study revealed wide variation in spotted leaf rot isolates of S. rolfsii. A reddish zone around the colony of S. rolfsii isolate from Vernonia sp. was observed on CRMA medium. HPLC analysis of the zone revealed the presence of gallic and ferulic acid which were also thought to be responsible for reduced mycelial growth of the isolate on CRMA medium.