Exotic rust fungus to manage the invasive mile-a-minute weed in India: Pre-release evaluation and status of establishment in the field

The mile-a-minute weed, Mikania micrantha, is a highly problematic and widespread invasive weed in the moist forests of the Western Ghats and in the north-eastern states in India causing significant damage to natural forests as well as to plantation crops, including tea, coffee, bamboo, coconut and teak. The microcyclic rust fungus, Puccinia spegazzinii, was identified as a potential classical biological control agent to replace the unsustainable or even hazardous conventional control methods. Following a successful risk analysis under quarantine at CABI (UK), a pathotype of the fungus (IMI 393067) from Trinidad and Tobago was imported into India. Prior to its release in the open field, the rust was further evaluated under strict quarantine conditions to ascertain the susceptibility of M. micrantha populations from three regions in India where the weed is invasive, and to confirm the safety of economically important plant species and indigenous flora. Results of host-specificity screening of 90 plant species belonging to 32 families ensured that the Trinidadian pathotype of P. spegazzinii was highly host- specific and could not infect any of the test plant species, though it was highly pathogenic to most of the target weed populations from Assam, Kerala and the Andaman and Nicobar Islands. The rust was released in Assam and Kerala but failed to establish at the time. However, due to the apparent success of this rust at controlling M. micrantha in the Pacific region, further releases in India are recommended.