Host specificity of Puccinia spegazzinii (Pucciniales: pucciniaceae), a biological control agent for Mikania micrantha (Asteraceae) in Australia

The biology and host specificity of the rust fungus Puccinia spegazzinii, a biological control agent for Mikania micrantha, was studied in a quarantine laboratory in Brisbane, Australia. Nineteen plant species, all from the family Asteraceae were inoculated during host specificity trials. Spore formation occurred only on M. micrantha and no other plant was infected. The first signs of infection (white spots on leaves, petioles and stems) occurred 7 days after exposure to inoculum, becoming yellow by day 11. Mature pustules containing teliospores had developed by 20 days. Results obtained here support testing in other countries showing that P. spegazzinii is host specific to M. micrantha and no that other plant in Australia would be at risk if it were to be released in the environment. Recommendations on assessing pathogens to improve trials were proposed. Counting infected plants, plant parts and pustules formed can demonstrate that all test plants would have been adequately exposed to inoculum and thus increase the confidence in host specificity of pathogens in weed biological control.