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SummaryThe effect of spore concentration on spore germination and germtube growth of Trichoderma hamatum on water agar and on potato dextrose agar (PDA) was studied. Increasing inoculum size up to 109 spores/plate on PDA and up to l07 spores/plate on water agar shortened the incubation period required for germtubes emergence and increased germination rate. However, on water agar germination was inhibited at l08 and was completely arrested at 109 spores/plate. Inhibition in germination of l07 spores/plate was observed on water agar when the plates were preincubated with 109 spores/plate for 5 h or more. Addition of glucose and ammoniurr nitrate to the water agar medium allowed only 25% of the spores to germinate at 109 as compared to 78% at 107 spores/plate after 8 h of incubation. Addition of polysaccharides to the C + N supplemented medium, significantly increased germination up to 84% as compared to 100% on PDA, after 8 h of incubation. Germlings of Trichoderma hamatum phialospores exhibited positive autotropism and anastamosis on both media. The phenomenon was positively related to inoculum size, being most pronounced at l07 spores/plate.