Induction of sporulation of cercosporoid pathogens of moth vine (Araujia hortorum)

Abstract

The South American vine Araujia hortorum (Apocynaceae) is now considered an invasive species in many countries. In New Zealand it has been targeted for biological control. In its native range in Argentina it is frequently affected by cercosporoid fungi but little is known about the diseases they cause. These pathogens produce no, or scarce, conidia on common artificial media thus hindering certain experimental studies such as pathogenicity and host range tests. We developed a technique to obtain abundant sporulation of two cercosporoid species isolated from diseased leaves of this host. Sporulation was studied and compared on several artificial culture media after different incubation periods. The best results were obtained on a medium prepared with a decoction of the leaves of the host and the addition of CaCO3, after an incubation period of eight days at 25°C for Cercospora sp. and after five days at 20°C for Pseudocercospora fumosa. It is expected the new medium may prove useful for other cercosporoid pathogens as well, at least for those affecting related hosts in the Apocynaceae.