Stem rot caused by Sclerotium rolfsii is a very important soil-borne disease of peanut. S. rolfsii is a necrotrophic plant pathogenic fungus with an extensive host range and worldwide distribution. It can infect peanut stems, roots, pegs and pods, leading to varied yield losses. S. rolfsii strains GP3 and ZY collected from peanut in different provinces of China exhibited a significant difference in aggressiveness on peanut plants by artificial inoculation test. In this study, de-novo genome sequencing of these two distinct strains was performed aiming to reveal the genomic basis of difference in aggressiveness. Scleotium rolfsii strains GP3 and ZY, with weak and high aggressiveness on peanut plants, exhibited similar growth rate and oxalic acid production in laboratory. The genomes of S. rolfsii strains GP3 and ZY were sequenced by Pacbio long read technology and exhibited 70.51 Mb and 70.61 Mb, with contigs of 27 and 23, and encoded 17,097 and 16,743 gene models, respectively. Comparative genomic analysis revealed that the pathogenicity-related gene repertoires, which might be associated with aggressiveness, differed between GP3 and ZY. There were 58 and 45 unique pathogen-host interaction (PHI) genes in GP3 and ZY, respectively. The ZY strain had more carbohydrate-active enzymes (CAZymes) in its secretome than GP3, especially in the glycoside hydrolase family (GH), the carbohydrate esterase family (CBM), and the polysaccharide lyase family (PL). GP3 and ZY also had different effector candidates and putative secondary metabolite synthetic gene clusters. These results indicated that differences in PHI, secreted CAZymes, effectors and secondary metabolites may play important roles in aggressive difference between these two strains. The data provided a further understanding of the S. rolfsii genome. Genomic comparison provided clues to the difference in aggressiveness of S. rolfsii strains.

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Genome sequencing and comparative genomic analysis of highly and weakly aggressive strains of Sclerotium rolfsii, the causal agent of peanut stem rot.

Athelia rolfsii is a globally dispersed pathogenic fungus, causing white root rot disease in many crops and horticultural plants. In this study, 90 isolates were collected from three provinces of Guilan, Mazandaran and Golestan in northern Iran. Eighteen isolates were selected for sequence analyses based on their host, sampling sites and Mycelial Compatibility Groups (MCG). Translation elongation factor 1-α(tef1-α), β-tubulin (tub2) genes and rDNA large subunit (LSU) were partially amplified and sequenced in order to conduct phylogenetic analyses. Approximately, all Iranian isolates clustered together in both tef1-α and LSU phylogenetic trees. However, after deletion of ambiguous sites, no variations were observed in tub2 sequences. ISSR and SCoT were also used to investigate the genetic structure of the population. Results of the molecular variance analysis (AMOVA) showed that 70 and 30% of the observed variance corresponded to the difference between and within the populations, respectively. According to these findings, we suggest that mating between populations would be less likely and thus, gene flow is restricted.

https://mij.areeo.ac.ir/article_124012_d4d52d37d17223b57922f0b41d34663c.pdf

Population genetics and gene sequence analysis of Athelia rolfsii collected from Northern Iran

Chickpea (Cicer arietinum L.; 2n=14) is a major legume of the world. It is an annual crop and had the capability to fix atmospheric nitrogen in the soil. It is a crop of subsistence farming and completes its life cycle within 90 days and provides economic benefits to the farming community. The desi and kabuli types are highly cultivated in India and the yields of these genotypes are highly fluctuating over the years. The reason for yield fluctuations is mainly due to the various biotic and abiotic stresses. Among the biotic stresses, diseases caused by the pathogens affecting root like wilts and root rots are of special significance as they affect the crop stand in the initial stages of crop growth and reduce the yield. Sclerotium rolfsii is one of the major pathogen of soil borne nature and International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 9 Number 9 (2020) Journal homepage: http://www.ijcmas.com

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Morphological Characterization of Kurnool Strains of Chickpea Collar Rot Casual Agent Sclerotium rolfsii Sacc.

Athelia rolfsii is a globally distributed soil-borne fungal pathogen causing root rot disease in many crops. In order to study the genetic diversity of this fungus, 90 isolates were collected and isolated from Guilan, Mazandaran and Golestan provinces (North of Iran). Genetic diversity of these isolates was investigated using Mycelial Compatibility Groups tests (MCG) and ISSR and SCoT markers. In this study, nine MCG groups were identified. The MCG3 group (with 36 members) was the most frequent in terms of the number of isolates and the most diverse group in terms of host domain (due to infection of eight host species). This group (MCG3) was also the only group that isolated from specimens in all three provinces. The dendrogram derived from cluster analysis of ISSR primers divided the isolates into four groups at a similarity level of 57%. The dendrogram obtained from cluster analysis of SCoT primers placed the isolates in a similarity level of 59% in three groups. Based on the results of both markers, Golestan isolates (except two isolates) were separated from Guilan and Mazandaran isolates. However, the presence of these two isolates in a separate cluster along with the isolates of Guilan and Mazandaran provinces was consistent with the results of MCG grouping. The results of this study showed that, these two types of markers are useful to differentiate isolates based on geographic regions.

https://rostaniha.areeo.ac.ir/article_121723_94c80c677df4bb45b5e2c178536ad671.pdf

Genetic diversity of Athelia rolfsii populations in the north of Iran

Groundnut stem rot, caused by Sclerotium rolfsii, is a serious soil-borne disease. During the 2018–2019 calendar year, we aimed to characterize fungal samples that cause stem rot in groundnuts from five groundnut-growing districts of Karnataka, India. Two locations were chosen in each district, and ten fields were considered at every location. A total of 100 fields were recorded for symptoms and occurrence. Yellowing of leaves, lack of vigor, poor root growth, rotting at the stem area, and early mortality were all noticed during the survey. White, dense, fluffy, aerial, cotton-like mycelium and the growth of deep brown spherical or round sclerotia bodies were also observed around the stem and root region. In the investigated area, disease incidence ranged from 10.71 to 18.50%. Ten diseased samples were collected, each representing one site, and the pathogen was isolated and labeled as an individual isolate. To determine pathogenicity, ten isolates were inoculated on three groundnut varieties: TMV-2, GKVK-5, and GKVK-27, all of which colonized successfully. The fungal isolates had cultural and physical traits that were similar to S. rolfsii. Concatenated sequence comparisons of all ten isolates' ITS and LSU regions revealed that the current isolates have a maximum nucleotide identity of 90.10–98.80% with other known S. rolfsii isolates retrieved from the NCBI database. Similarly, the nucleotide identity of SSU ranged from 96.8 to 97.8%. Phylogenetic analysis also confirmed this, with all ten samples clustering closely with S. rolfsii isolates reported earlier.

Morphological and molecular characterization of Sclerotium rolfsii associated with stem rot disease of groundnut (Arachis hypogaea L.)

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K. Eraivan Arutkani Aiyanathan

Papers

Virulence and genetic diversity of Sclerotium rolfsii Sacc., infecting groundnut using nuclear (RAPD & ISSR) markers