Evaluation of an isolate of Myrothecium verrucaria from sicklepod (Senna obtusifolia) as a potential mycoherbicide agent

In greenhouse studies, Myrothecium verrucaria isolated from sicklepod (Senna obtusifolia) affected several plant species, including a number of economically important crop, ornamental, and weed species. Responses of inoculated plants to the fungus ranged from no reduction in dry weight to 100% mortality. New host responses (as indicated by mortality and/or greater than or equal to 50% reductions in dry weights of inoculated plants) included: beet (Beta vulgaris), turnip (Brassica rapa), radish (Raphanus sativus), sicklepod, coffee senna (Cassia occidentalis), hemp sesbania (Sesbania exaltata), spurred anoda (Anoda cristata), and jimsonweed (Datura stramonium). Disease development in sicklepod was influenced by inoculum and surfactant concentrations, dew temperature, dew duration, and growth stage of plants when inoculated. Inoculum concentrations of 2 x 10(7) conidia/ml plus 0.05% (w/v) surfactant resulted in approximately 95% mortality of sicklepod seedlings following a 6-h dew at 25 degrees C. Inoculum concentrations of 8 x 10(7) conidia/ml killed approximately 40% of sicklepod seedlings in the absence of dew Soybean (Glycine max) plants inoculated by foliar applications of 2 x 10(7) conidia/ml exhibited dry-weight reductions of 65-75%. However, the fungus applied as directed spray applications (8 x 10(7) conidia/ml) to mixed plantings of sicklepod and soybean seedlings, so that the soybean plants were inoculated only on the stems and lower leaves, killed 97% of the sicklepod plants after a 6-h dew period at 25 degrees C, with no dry-weight reduction in the soybean plants. Additional research is needed to assess the potential of the sicklepod isolate of M. verrucaria as a mycoherbicide agent. (C) 1997 Academic Press.