Biocontrol of cocoa pod diseases with mycoparasite mixtures

Five native mycoparasitic strains of Clonostachys rosea and three of Tricho derma spp. were isolated from healthy cocoa tissue or basidiocarps of Crini pellis perniciosa using a baiting technique. They were compared singly or i n combination with the commercial biocontrol agent Trichoderma virens (Soil Guard) for their potential to control three cocoa pod diseases: moniliasis, caused by Moniliophthora roreri; witches' broom, caused by C. perniciosa; and black pod, caused by Phytophthora palmivora. All isolates except Tricho derma T-1 inhibited basidiocarp formation of C. perniciosa under controlled conditions. The remaining isolates except Trichoderma T-3 reduced vegetati ve broom formation in a seedling bioassay. Clonostachys rosea G-3 and Trich oderma strains T-2 and T-3 significantly reduced symptoms caused by M. rore ri in a seedling bioassay. Host-range studies identified P. palmivora as mo st susceptible to mycoparasitism and M. roreri as most resistant; C. pernic iosa was intermediate. Different degrees of susceptibility were discovered at the pathogen strain level, especially for P. palmivora. However, broad h ost-range mycoparasites which attacked all three pathogen species were iden tified. Under field conditions, all selected treatments except a combinatio n of C. rosea G-2 + G-3 reduced moniliasis, the main disease, significantly by 14.6-24.9% as compared with optimized, cultural control alone. No signi ficant reduction of witches' broom or black pod was achieved but a combinat ion of five C. rosea strains (G-1, G-2, G-3, G-4 + G-5) performed consisten tly best against all three diseases simultaneously. Yield increased by 16.7 % and net returns by 24%. Control of moniliasis and yield were positively c orrelated to the number of mycoparasites in the inoculum. The results sugge st that simultaneous biocontrol of the three major cocoa pod diseases with mycoparasite mixtures is highly promising. Future development strategies ar e discussed. (C) 2001 Academic Press.