INTERACTION OF SOIL MICROFLORA WITH THE BIOHERBICIDE PHOSPHINOTHRICIN

Phosphinothricin, a microbial toxin synthesized industrially for chemi cal weed control and currently under development as a selective weed k iller in cultivation of transgenic plants engineered to resist its pre sence, is investigated for its effects on the distribution of microorg anisms in 15 agricultural and non-agricultural soils. In agricultural soils, the presence of 1 mM phosphinothricin reduced the number of fun gi isolated by about 20% and bacteria by about 40%. Under these condit ions the isolation of bacteria from boreal forest soils was also suppr essed by about 20%. Differences in herbicide resistance were confirmed when a random selection of fungi, bacteria and actinomycetes isolated in the absence of herbicide was grown with 1 mM phosphinothricin. Soi l isolates growing in the presence of 1 mM phosphinothricin exhibited a wide spectrum of tolerance to increasing herbicide concentration ove r the range of 0-50 mM phosphinothricin. Of fungal isolates, the plant pathogen Verticilium alboatrum was among the most resistant, while th e mycoparasitic species Trichoderma harzianum and T. longipilus were a mong the most sensitive to the presence of phosphinothricin.