03-08-2013, 04:27 PM
The potential of mycoherbicides for weed management :
A case study with Gibbago trianthemae
ABSTRACT
The strategies for management of terrestrial weeds include preventive measures like- physical control, cultural method like crop rotation, inter cropping, soil solarization and use of chemical herbicides. Biocontrol of weed with plant pathogens (mycoherbicides) has proven to be a feasible component of modern integrated weed management system. Mycoherbicides like Devine (Phytophthora palmivora) for control of milk weed wine in citrus orchards, Collego (Colletotrichum gloeosporioides f. sp. aeschynomene) against northern jointvetch, Colletotrichum capsici for pitted morning glory, C. truncatum for fireweed, C. gloeosporioides f. sp. malvae for round-leaved mallow, C. orbiculare for Xanthium spinosum, have been commercialized. Yet the biological pesticides represent only 2.4 per cent of pesticide global market (Mortone, 2007). The local isolate of Gibbago trianthemae (ITCC 6407) was evaluated as mycoherbicide of Trinthema portulacastrum. The disease severity increased with increased inoculum density and was maximum (100 per cent) in plants inoculated with 1×106 conidia ml-1. Thirteen different formulations consisting of G. trianthemae spores, different inert carriers, oils and Tween 20, were evaluated for disease development on pot -grown plants of T. portulacastrum. The Maximum per cent disease index (PDI) and the lowest fresh and dry weight were observed with G. trianthemae spores + Kaoline + Parafine oil + Water, followed by G. trianthemae spores+ bentonite + Parafine oil + Water formulation. In microplot testing during two years, WOW formulation of G. trianthemae resulted in maximum disease (PDI), highest plant mortality and significantly lower fresh and dry plant weight as compared to uninoculated control. The possibility of production of toxin by G.trianthemae,, its involvement in pathogenesis and the extent of survival of G. trianthemae in the field and its seed transmission need to be worked out for its natural potential to spread in the weed host.