COMPARISON OF BIOMASS AND VIABLE PROPAGULE MEASUREMENTS IN THE ANTAGONISM OF TRICHODERMA-HARZIANUM AGAINST PYTHIUM-ULTIMUM

A potting medium was used to demonstrate the biological control potential of Trichoderma harzianum against damping-off of lettuce (Lacluca saliva) caused by Pythium ultimum. Introduction of T. harzianum but not P. ultimum into the medium caused an immediate increase in the ATP and chitin contents followed by a rapid decline. By contrast, initial increases in ergostcrol concentration and esterase activity on fluoresccin diacetate were followed by inconsistent and extremely variable responses with duration of incubation. The colony-forming units (cfu) of Trichoderma increased on amendment and were sustained whereas the increased units of the P. ultimum-only treatment were reduced by T. harzianum. Respiration increased for 2 days after amendment and then declined. It is concluded that ATP and chitin measurements are suitable biomass markers for introduced fungal inocula and are inversely associated with cfus and esterase-activily measurements. Both types of measurement are useful in investigating disease potential and biocontrol activity. Biocontrol activity is primarily linked to a transient increase in Trichoderma biomass resulting in a sustained increase in active propagules of the antagonist. © 1990.