The mycobiota associated with the weed water hyacinth Pontederia crassipes in Kolkata, India, with emphasis on biological control of the macrophyte

ABSTRACT The invasive macrophyte water hyacinth, Pontederia crassipes (Mart.) Solms (Pontederiaceae), was first introduced in India at the Acharya Jagadish Chandra Bose Indian Botanic Garden, near Kolkata in 1889 from where they spread throughout the sub-continent. An extensive systematic survey of water bodies in and around Kolkata, India, was done for the first time to assess the natural occurrence of indigenous phytopathogenic fungi of the weed between 2014 and 2019. The study brings into light several species, along with some first reports, of naturally occurring native phytopathogenic fungi and their evolutionary-related lineages. The occurrence and frequency of pathogens varied from site to site. Around 150 fungal pathogens isolated from water hyacinth were evaluated for their disease-causing potential against the weed. The isolated fungi were identified using morphological and molecular techniques. Fusarium Link followed by Alternaria Nees were the highest and most consistently isolated genera. Seven potential fungi that caused more than 90% disease in whole plant pathogenicity bioassay were subjected to host-range evaluation against 67 plant species selected based on ecological nearness or economic significance. Among these Fusarium oxysporum f. sp. lycopersici (WHK-59) was found to have a narrow host range and be effective against water hyacinth. With further studies on their impact assessment, environmental viability and tolerance, few of them, especially F. oxysporum (WHK- 26, 106) may effectively reduce population growth of water hyacinth by themselves or in conjunction with other introduced biocontrol agents, including insects and other plant pathogens.