Title : Development of Gibbatrianth mycoherbicide to control Trianthema portulacastrum (horse purslane), a notorious agricultural weed
Abstract:
Weeds are a problem in crop production associated with declines in crop yields and quality, as a source of allergenic pollen and as an aesthetic nuisance. Horse purslane (Trianthema portulacastrum), a member of the family Aizoaceae, is considered number one problematic agricultural weed by virtue of its infestation in various vegetable and agricultural fields. In India, it heavily infests mustard, maize, sorghum, potato, mung beans, soybean, onion, sugarcane and cotton causing heavy losses in yields. In the past 50 years, the control of agricultural and forest weeds using biocontrol agents: fungi, bacteria and viruses, has drawn increasing attention in the quest to reduce the level of dependence on chemical products for agriculture production. Phytopathogenic fungi i.e., the fungi causing disease in plants, offer a tremendous opportunity to develop as bioherbicides/mycoherbicides. The formulations of host-specific plant pathogenic microorganisms that are applied at high inoculum rates in a similar way as chemical herbicides used to control/manage weeds are called bioherbicides. In the majority of the bioherbicides, the fungal organisms are the active ingredients, therefore the term mycoherbicide has often been used interchangeably with bioherbicide. Bioherbicides have gained acceptance because they are safe, environment- friendly, prevent hazards resulting from chemical herbicides to environment, human health, animal health and soil microbiota. Currently, they have drawn increasing attention in the quest to reduce the level of dependence on herbicides to produce organic foods for human's health and longevity. The global bioherbicides market size is rapidly growing that had been valued at US $2.7 billion in 2023 is expected to hit US $7.4 billion, at a CAGR of 11.4%, during 2024-2032 (IMARC Group, 2024). Gibbatrianth is named after its host-specific fungal pathogen (Gibbago trianthemae) and the weed host Trianthema. This mycoherbicide is a liquid formulation of conidia, mycelial fragments and surfactant. The fungus G. trianthemae was isolated for the first time from Kurukshetra (India) in 1999 from this weed infesting fields of sarson (Brassica campestris). It is a hemi-biotrophic, phaeodictyoconidial hyphomycetous fungus, growing best at 25oC on simple agar media. It is characterized by non-beaked, dark, conidia having both transverse and longitudinal septa, and developing singly through porogenous development. Each conidium germinates producing several germ tubes, and a germ tube in turn produces another conidium at its tip. Studies carried out on the mode of infection, disease development, bio efficacy and host specificity revealed that germination of conidia on leaves occurs within 6 to 12 hours post spraying, causing infection within 3 to 4 days. Entry of a conidial germ tube into the leaves takes place through stomata by producing appressoria, which is a peg like structure. Defoliation starts after 20 days leading to death of the complete plant within 30 days of inoculum spraying. Once the weed is gone, the pathogen also disappears, revealing its hemi-biotrophic nature. This pathogen showed host- specificity (i.e., causing infection exclusively to its host), an important criterion for any biocontrol agent to be developed as a bioherbicide. Gibbatrianth is the first and the only mycoherbicide developed for controlling horse purslane globally. There is a huge scope for commercial exploitation of Gibbatrianth, a nonchemical herbicide, for controlling horse purslane worldwide, including India, for getting organic vegetables, free from the carcinogenic chemicals.
