Substrate colonization, strain competition, enzyme production in vitro, and biocontrol of Pythium ultimum by Trichoderma spp. isolates P1 and T3

The antagonistic Trichoderma spp. isolates P1 and T3 differed in their abil ity to colonize and to compete in sphagnum peat moss and on wood chips. In peat supplemented with straw, isolate T3 produced twice as many colony form ing units (cfu) as isolate P1. On wood chips, the two isolates formed a sim ilar number of cfu. When the two Trichoderma isolates were cultivated toget her approximately 85-90% of the cfu were from T3 on both substrates. The pr esence of Pythium ultimum in peat amended with straw did not influence the number of Trichoderma cfu formed. The two Trichoderma isolates produced dif ferent amounts of hydrolytic enzymes both in liquid cultures and in peat. S even different enzyme activities were tested. Enzyme production by T. harzi anum isolate T3 was less influenced by the type of carbon source amendment than that of isolate T. atroviride P1. Culture filtrates of isolate P1 grow n on complex carbon sources were high in endochitinase activity, whereas ce llulase and endo-1,3-beta-glucanase activities were more pronounced in filt rates of isolate T3. There was no significant difference between the two is olates in their ability to protect cucumber seedlings against P. ultimum wh ile the combination of the two fungi resulted in significantly less biocont rol than each isolate alone.