Ditylenchus drepanocercus (Nematoda), a potential biological control agent for Miconia calvescens (Melastomataceae): host-specificity and epidemiology

Miconia calvescens (velvet tree; miconia) is a devastating invasive weed in Hawaii and French Polynesia. As part of a program aimed at biological control of miconia, pathogens attacking it in its native range were studied. Ditylenchus drepanocercus, the aetiological agent of angular leaf-spot of miconia was selected for further evaluation of its biological control potential. Natural disease intensity was evaluated during 1 year at two sites, Viçosa and Dionísio, in the state of Minas Gerais, Brazil. At both sites, the disease incidence did not correlate with any of the climatic factors that were evaluated. At Dionísio, disease severity correlated positively with relative humidity and temperature. In a field-conducted host-range survey, D. drepanocercus was found only on Miconia prasina and Miconia calvescens. This method is an alternative for host-range evaluation of biocontrol candidates under laboratory or greenhouse conditions and its limitations and advantages are discussed. An ad hoc observation was made of D. drepanocercus attacking Miconia phanerostila indicating that the neotropical populations of the nematode have a host-range limited to some species of Miconia. These observations, together with the probable adaptation of the nematode to habitats in Hawaii and French Polynesia, suggest that this pathogen deserves further study as a classical biocontrol agent for M. calvescens.