The use of a GUS transformant of Trichoderma harzianum, strain T3a, to study metabolic activity in the spermosphere and rhizosphere related to biocontrol of Pythium damping-off and root rot

The activity of Trichoderma harzianum in the spermosphere and rhizosphere o f different plant species was studied by use of a beta-glucuronidase (GUS) transformant (strain T3a). Hereby, direct observation of micro-habitats sup porting metabolic activity of T. harzianum is reported. Germination of coni dia and mycelial growth were not supported by exudates from healthy roots o f various ages. Instead, growth and activity of T. harzianum depended on ac cess to dead organic substrates such as seed coats, decaying roots, and wou nds, including those caused by infecting pathogens. A correlation between t he GUS activity of T. harzianum and the biomass of Pythium ultimum in infec ted roots was established. On the basis of our observations, we suggest tha t the biocontrol ability of T. harzianum involves competition with the path ogen for substrates including the seed coat, and wounded or infected root t issue.