Phytopathogenic Fungi and Their Active Metabolites With Bioherbicidal Potential Against the Invasive Alligator Weed, Alternanthera philoxeroides

Alligator weed (Alternanthera philoxeroides), originally from South America, is a notorious semi-aquatic invasive species in many countries, including India. Due to its amphibious nature, it not only damages the aquatic environment but is also detrimental to the terrestrial ecosystem. To seek an environmentally sound control option for alligator weed, this study focused on selecting an appropriate mycoherbicidal agent. A series of steps from field survey-based collection, isolation and selection of promising fungal strains, followed by host range determination to biocontrol potential studies against the weed were undertaken. Twenty-three phytopathogenic fungi were isolated, and among these, the fungi with the highest herbicidal activity (> 90% disease severity) were subjected to morphological and molecular characterisation and identified as Alternaria alternantherae (= Nimbya alternanthera). The fungus and its crude metabolites were tested against 76 plant species, showing a relatively narrow host range. This fungal species is being reported from West Bengal, India, for the first time. Although the fungus has been considered as a potential biocontrol tool against alligator weed in countries such as Australia, Brazil and China, long-term, detailed research for A. alternantherae and its active metabolites to be developed as bioherbicides against alligator weed remains indispensable.