Studies On Molecular Systematic Of Genus Phyllosticta And Phoma

Phyllosticta and Phoma are two important plant pathogenic fungal genera inSphaeropsidales, Coelomycetes, Imperfecti, which can cause a variety of plant diseasessuch as leaf spot, stem blight, fruit spot and so on. As morphological differences of the twogenera are so minute, and the criteria for classifying them so comfused, that it is usuallydifficulty to assign an unknown isolate in Phyllosticta, rather than in Phoma. In this paper,Molecular taxonomy of Phyllosticta and Phoma was studied using their related genera asreferences. The research mainly includes three parts.1. Similarities and differences ofculture and morphological characters among Phyllosticta, Phoma and their related genera.2. rDNA-ITS sequence determination and sequence homologous analysis of variousisolates of above genera.3. PCR amplification for every isolate to obtain its correspondingfingerprint by using molecular marker technique of inter-simple sequence repeat (ISSR),then based on the fingerprint analyzing the phylogeny of above genera. The purposes are:1.to categorize Phyllosticta, Phoma and their related genera on the molecular level.2. to findmorphological traits which are consistent with the group classification formed onmolecular level, so as to identify the fungi on traditional basis.3. to demonstratemolecularly that it is unreasonable to divide Phyllosticta and Phoma on the basis of theirparasitc organs on plant. The experiment results are as follows:(1) Phyllosticta and Phoma can be distinguished from each other by their colonycharacteristics and if or not producing conidia on ordinary cultural conditions.Phylogenetic trees constructed from either rDNA-ITS sequence or ISSR fingersprintanalysis are consistent and all able to show differences of Phyllosticta, Phoma and relatedtaxa. The results also showed that the molecular classification of Phyllosticta and Phomawas closely related with their cultivating characteristics.(2) It was found that homology of the ITS sequence between isolate separated fromleguminous plant stems and isolates of Phyllosticta reached to100%, whereas thehomology of the ITS sequence between isolate separated from tobacco leaves and isolatesof Phoma reached to98%. All results showed that the division of Phyllosticta and Phomahad no inevitable relation with their origins of leaves or stems.