Antagonism of Trichoderma longibrachiatum strains to fungicide-sensitive and -resistant strains of Venturia inaequalis

Isolates Tl 301 and Tl 304 of Trichoderma longibrachiatum were selected as efficient antagonists against fungicide (penconazole and carbendazim)-sensi tive and -resistant strains of Venturia inaequalis. The new biotypes of Tl 301 and Tl 304 with fungicide resistance were generated by chemical mutagen esis and subsequently used as parental strains for the development of multi potent strains by protoplast fusion. The fusant strain (Tlf 1) was superior in antagonistic potential along with fungicide resistance, antibiotic(s) a nd hydrolytic enzyme production. Application of Tlf I either alone or in co mbination with low doses of fungicides significantly reduced the ascospore production in apple leaves naturally infected by V. inaequalis.