Abstract

The neotropical rust fungus, Puccinia spegazzinii, was released in India in 2005 for the classical biological control of the invasive alien weed, Mikania micrantha. This paper contains data from the pest risk assessment that was undertaken prior to release. It includes studies on the life-cycle, pathotype variation, infection parameters and host-specificity testing. Inoculation studies confirmed the rust to be microcyclic and autoecious. Seven pathotypes of the rust from six countries were assessed for variation in macroscopic morphology, phenology, and disease development on M. micrantha. The results conclude that two ecotypes can be identified, and that this could be linked to potential efficacy under different climatic conditions. A pathotype of P. spegazzinii from Trinidad (IMI 3930670) was selected for detailed assessment prior to release in the Western Ghats of Kerala State, south-west India. The rust was able to infect M. micrantha at temperatures ranging from 15 to 25°C (optimum near to 18°C) and also after less than 10h of exposure to free-water on the plant surface (optimum near to 15h). More than 60 non-target plants were challenged with the rust, including 11 other Mikania species. The rust was found to be highly specific within the genus Mikania; only three species from Africa and one from Asia became infected with the rust to varying degrees. Three other species, closely-related to M. micrantha, developed chlorotic spots in response to the rust; however, the symptoms progressed no further. The anticipated field efficacy of the rust in the invasive range of the plant is discussed.

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