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.
Highlights
Theobroma cacao L. is one of the most important cash crops in Cameroon, and other countries in Central and West Africa (Assoumou, 1997)
Treatments are classified into four categories depending on the variation of the infection severity index of P. megakarya which determined the degree of susceptibility of different plants to the black pod disease
3a b daaddb the faculty of resistance acquired by the corresponding seedling plants; high index values determine the high susceptibility of plants to black pod disease (Table 2)
Summary
Theobroma cacao L. is one of the most important cash crops in Cameroon, and other countries in Central and West Africa (Assoumou, 1997). Since 1990, Cameroon has suffered a drastic drop in its cocoa production (Mossu, 1990) whose main causes, among others, are the rural exodus, the stopping of state subsidies to cocoa farmers, the falling price of cocoa kilogram, the aging of cocoa plantations, pests and various diseases (Tchameni et al, 2012). Phytophthora megakarya is one of the Oomycete pathogens reported on Theobroma cacao (Tchameni et al, 2012). It is the most virulent of Phytophthora species that was first reported as the causal agent of black pod disease in 1979 (Akrofi, 2015)
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