Abstract

Experiments were conducted to appreciate the resistance level of cocoa seedlings aged three months from combinations of fertilizers against Phytophthora megakarya based on artificial leaf disk inoculation test. The two cocoa varieties involved were: Tafo 79/501 (V1) and SNK 13 (V2). For each variety, 11 treatments with three replicates were used on 33 randomly-selected plants. These include Arbuscular Mycorrhizal Fungi (M), Trichoderma asperellum strain PR11 (T), Organic Fertilizer Gro-wild (O), Chemical fertilizers (NPK), the following combinations (TO), (MT), (MO), (MOT), (MOTNPK) as well as a negative control made by original substrate only (T-) and sterile control with sterilized substrate (TS). Results show that the resistance level of cocoa seedlings in nursery to P. megakarya varied with the cocoa variety and for a given variety with the fertilizer. Fertilizers were classified into four categories according to the variation of the infection severity index from 0 (V1MOT) to 4.72 (V1TS) and from 1.27 (V2MOT) to 4.86 (V2T-). The most efficient treatment for both V1 and V2 was MOT that allowed a dualistic action between Arbuscular Mycorrhizal Fungi and T. asperellum in the presence of organic fertilizer Gro-Wild.

Key words: Cocoa, Phytophthora megakarya, leaf disk, infection severity index, resistance.