Detection of Fusarium wilt pathogens of Psidium guajava L. in soil using culture independent PCR (ciPCR)

Fusarium oxysporum and Colletotrichum musae Associated with Wilt Disease of Coffea arabica in Coffee Gardens in Saudi Arabia

This study aimed to identify if Fusarium and Colletotrichum species are linked to coffee leaf wilt symptoms (Coffea arabica L.) gardens in Jazan region, Kingdom Saudi Arabia. The symptomatic wilted leaves and shoots were collected from Jazan Mountain Region Development Authority (JMRDA) farm in jabal Fifa. Samples of roots and leaves tissues were plated on Dox' Agar medium and incubated for one week at 24^oC. Two morphologically different fungus colonies grew on the medium. A PCR-based method was used for the molecular amplification and characterization of the fungi using a 18SrRNA specific primer. 1323 and 1501 bp PCR products were obtained by using the 1% agarose gel electrophoresis. The sequence analysis and genbank homology revealed that the present fungi were Fusarium oxysporum and Colletotrichum musae with 99 and 98% similarity, respectively. Both fungi sequences were submitted to the genebank under accession numbers OP010081 and OP010082, respectively. This is the first report of these two genera of fungi infecting the roots and leaves of coffee trees in Jazan Region of Saudi Arabia and suggests that other fungus species may play a significant role as diseases in other coffee-producing areas.

Epitypification of Fusarium oxysporum - clearing the taxonomic chaos

Fusarium oxysporum is the most economically important and commonly encountered species of Fusarium. This soil-borne fungus is known to harbour both pathogenic (plant, animal and human) and non-pathogenic strains. However, in its current concept F. oxysporum is a species complex consisting of numerous cryptic species. Identification and naming these cryptic species is complicated by multiple subspecific classification systems and the lack of living ex-type material to serve as basic reference point for phylogenetic inference. Therefore, to advance and stabilise the taxonomic position of F. oxysporum as a species and allow naming of the multiple cryptic species recognised in this species complex, an epitype is designated for F. oxysporum. Using multi-locus phylogenetic inference and subtle morphological differences with the newly established epitype of F. oxysporum as reference point, 15 cryptic taxa are resolved in this study and described as species.

Molecular detection and genotyping of Fusarium oxysporum f. sp. psidii isolates from different agro-ecological regions of India

Twenty one isolates of Fusarium oxysporum f. sp. psidii (Fop), causing a vascular wilt in guava (Psidium guajava L.), were collected from different agro-ecological regions of India. The pathogenicity test was performed in guava seedlings, where the Fop isolates were found to be highly pathogenic. All 21 isolates were confirmed as F. oxysporum f. sp. psidii by a newly developed, species-specific primer against the conserved regions of 28S rDNA and the intergenic spacer region. RAPD and PCR-RFLP were used for genotyping the isolates to determine their genetic relationships. Fifteen RAPD primers were tested, of which five primers produced prominent, polymorphic, and reproducible bands. RAPD yielded an average of 6.5 polymorphic bands per primer, with the amplified DNA fragments ranging from 200-2,000 bp in size. A dendrogram constructed from these data indicated a 22-74% level of homology. In RFLP analysis, two major bands (350 and 220 bp) were commonly present in all isolates of F. oxysporum. These findings provide new insight for rapid, specific, and sensitive disease diagnosis. However, genotyping could be useful in strain-level discrimination of isolates from different agro-ecological regions of India.