The compatibility between strains of Trichoderma harzianum (Tcomp, TH1 and TH3) and T. viride (TV1) and different active ingredients used as fungicides against seeds borne and foliar diseases of some cultures were tested under in vitro conditions. The activities of the formulations, pyraclostrobin + boscalid, cyprodinil + fludioxanil, fenhexamid and mepanipyrim were null to low on the mycelial growth of the strains tested. The compatibility percentages were low to moderate the first week, respectively 35.9, 10.0, 28.7 and 34.4% for TH3 and 59.1, 32.8, 61.9 and 84.1% for Tcomp at the recommended doses 501, 375, 750 and 400 ppm. They become high during the second week respectively 88.1, 75.4 and 100%. Seven days after incubation, the compatibility of Tcomp and TH3 was moderate (51.4%) at 200 ppm of pyrimethanil and become important after 16 days, respectively 65.0 and 78.7%. 32 days after incubation, this fungicide showed a moderate activity at the recommended dose (800 ppm), the compatibility percentages varied between 33.3 and 68.5%. After the second week, the chlorothalonil at 500 ppm showed good compatibility with Tcomp and TV1 (51.9 and 48.2%) and all the strains tested except TH1 become moderately compatible (43.5 – 72.2%) with the different concentrations after 24 days of incubation. However, thiram was able to completely inhibit mycelial growth of the Trichoderma stains during 4 weeks. No compatibility was observed between them. After one month, the Trichoderma strains produced conidia in the presence of low concentrations of chlorothalonil and in the recommended dose of fenhexamid, showing compatibility respectively ranging from 50.5 to 89.7% and 51.5 to 97.1%. The conidia production of the tested strains was inhibited at the recommended doses of the other fungicides tested. However, thiram showed good compatibility at 500 and 666.6 ppm ranging from 45.5 to 84.9%. Similary, boscalid + Pyraclostrobin at 125.5 ppm and cyprodinil + fludioxanil at 93.7 ppm were compatible respectively with TH3 and TV1 (50.6-56.1%) and TH1-TH3 (90.4-79.3%). After 24 hours of incubation, the Trichoderma conidia could germinate in the presence of different concentrations of mepanipyrim and fenhexamid showing compatibility respectively ranging from 45.0 to 98.0% and 37.5 to 97.1%. The Tcomp strain showed good ability to germinate in presence of low doses of thiram (500 ppm), chlorothalonil (375 ppm), boscalid + pyraclostrobin (125.2 ppm) and cyprodinil + fludioxonil (93.7) with respective compatibility percentages of 54.3, 54.2, 75.5 and 57.2%
