Distribution of Diplodia pinea and its genotypic diversity within asymptomatic Pinus patula trees
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Diplodia pinea (= Sphaeropsis sapinea) is an endophytic fungus and opportunistic canker pathogen of Pinus spp. The diversity of this fungus has been studied at broad geographic scales, but little is known regarding its population structure at smaller spatial scales such as within a single tree. This is despite the importance that diversity in a single tree might hold for understanding the biology of the fungus, especially the role of the endophytic or asymptomatic phase in disease development. Moreover there was not information regarding the distribution of the fungus within healthy trees and its persistence. The genotypic diversity of these isolates was investigated using microsatellite markers. Five polymorphic markers were developed and these were used together with eight previously developed markers and vegetative compatibility tests to study the genotypic diversity of D. pinea isolates. In this study, D. pinea was isolated for the first time in the well structured stems of healthy P. patula trees along with branches and cones. From a total of 44 isolates collected from five trees, 39 microsatellite haplotypes and 32 vegetative compatibility groups (VCG’s) were identified. The results indicate high genotypic diversity of D. pinea within individual asymptomatic trees which will lead to disease outbreak when trees are physiologically stressed.
KeywordsMicrosatellite markers Population diversity Vegetative compatibility groups Persistence
We acknowledge the DST/NRF Centre of Excellence in Tree Health Biotechnology (CTHB), Tree Pathology Co-operative Program (TPCP), National Research Foundation (NRF) and the International Foundation for Science, Stockholm, Sweden for financial support. We also thank Hardus Hatting, Brett Hurley and Jolanda Roux for assistance with the collection of samples and Mesfin Bogale is also acknowledged for his assistance in SSR primer design and validation.
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