Diverse sources of infection and cryptic recombination revealed in South African Diplodia pinea populations

This study considers the population diversity and structure of Diplodia pinea in South Africa at different spatial scales from single trees to plantations, as well as comparing infections on healthy and diseased trees. A total of 236 isolates were characterized using 13 microsatellite markers. Analysis of these markers confirmed previous results that D. pinea has a high level of gene and genotypic diversity in South Africa, with the latter values ranging from 6% to 68% for the different plantations. The data also reflect a fungus with randomly associated alleles in populations at local plantation scales and for the population as a whole. These results suggest that recombination is occurring in D. pinea and that it most likely has a cryptic sexual state. The study also reveals the sources of endophytic infection and stress related disease out-breaks as diverse infections that have occurred over a long time period. In contrast, wound-associated die-back appears to be caused by clones of the pathogen occurring in narrow time frames.