OBSERVATIONS ON SOME TRICHODERMA SPP STRAINS THAT ARE SIMULTANEOUSLY ANTAGONISTIC TO PYTHIUM-ULTIMUM AND GROWTH-STIMULATING

One hundred and thirteen Trichoderma spp isolates belonging to several species aggregates (sensu Rifai) were screened. Culture filtrates from 7 of these isolates were found capable of increasing germination speed and rate of tomato and cucumber seeds in vitro; 4 isolates exhibited high antagonistic activity against Pythium ultimum in Petri dishes. At least 2 strains, AGI (T polysporum) and BR 105 (a benomyl-resistant T harzianum) showed both types of biological activity. These results were confirmed in greenhouse trials. When plants were seed in pots filled with an autoclaved mixture of peat and vermiculite, addition of BR 105 (10(7) cfU g-1) improved emergence rate (+31 and +25%), dry mass (+72 and +68%) and flower setting at 2 months (+84 and +236%) of tomatoes and cucumbers, respectively. In a P ultimum-infested substrate, emergence rates of cucumber and flower production by 2-month-old plants were increased by 138 and 183% respectively in pots treated with BR 105. Finally, pansies grown in a potting mixture in a commercial greenhouse had more flowering plants (+83%), 47 d after planting out when BR 105 had been incorporated into the substrate. However, a similar result was obtained through substrate treatment with a fungicide. Consequently, the interpretation of this kind of results should be made with care.