Biocontrol of five invasive weeds of Meghalaya - a case study.
The state of Meghalaya, in North East India is endowed with a dense cover of natural forest. A vast majority of the forests are owned by communities who traditionally practice shifting cultivation. This has resulted in significant reduction of the original forest area leading to a drastic change in the floristic composition of the state. This is evident by the ubiquitous presence of various invasive weeds such as Mikania micrantha, Chromolaena odorata, Ageratum conyzoides, Spilanthes paniculata and Spermacoce hispida. A survey for natural fungal enemies against these weeds was carried out in the state with the objective of identifying potential biocontrol agents. A total of six pathogenic fungi were isolated from infected leaves of these target weeds. Of these, two fungi isolated from leaf spot and leaf necrosis disease of Mikania micrantha were identified as Gliocladium roseum and Phomopsis sp., respectively. The fungus isolated from S. paniculata, C. odorata, and A. conyzoides was Fusarium solani and from Spermococe hispida it was F. acuminatum. Pathogenicity test carried out on target weeds and agricultural crops grown in Meghalaya (Maize, Chilli, Tomato, Rice and Ginger) showed that all the isolated fungi were found infecting the weeds from which they were isolated and also maize and tomato. They were found non non pathogenic to seedlings of some economically important tree species of Meghalaya, viz., Pinus kesiya, Magnolia champaca, Alnus nepalensis, Chukrasia tabularis, Exbucklandia populnea and Castanopsis indica. Hence, these fungi can be tested in field condition on pilot scale, in forest areas but not in agricultural areas where maize or tomato is grown.