February 2008. Biology and host range of the rust fungus Puccinia spegazzinii: A new classical biological control agent for the invasive, alien weed Mikania micrantha in Asia
Carol A. Ellison, Harry C. Evans, Djamila H. Djeddour and Sarah E. Thomas
CABI Europe-UK, Silwood Park, Ascot, Berkshire SL5 7TA, UK
Received 5 September 2007; accepted 10 December 2007. Available online 16 December 2007.
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 10 h of exposure to free-water on the plant surface (optimum near to 15 h). 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.
Samoa felt that Mikania was not a threat to agriculture, not as much as other introduced weeds. It was necessary to considered the problem well before introductions were made, as it was a weed that could be easily controlled by other methods. The weeds that were thought to be a problem in Samoa were Hyptis capitata and Solanum torvum.