Abstract

S. L. Koranteng and R. T. Awuah

The study sought to suppress black pod lesion development on detached cocoa pods using yam rhizobacteria. Eight yam rhizobacterial isolates were initially screened on agar plates with the zone of inhibition technique against Phytophthora palmivora, causal agent of black pod disease of cocoa. All eight bacteria were antagonistic to P. palmivora, so one of the most promising isolates (isolate ESI) was further evaluated for black pod lesion suppression on detached cocoa pods. Areas on cocoa pods were treated with 50 l Nutrient Broth (NB) cultures of ESI. The treated pod areas (0.8 cm2 approximately), on partial drying (10 min after applying the ESI culture broth), were inoculated with 10 l zoospore suspensions of P. palmivora. Kocide 101, NB and cell- free culture filtrate of ESI were similarly used as protectants. Stability of the ESI-NB culture on cocoa pods during a 72 h period was also assessed. Black pod lesions developed on all pods inoculated with P. palmivora without prior treatment with ESI, its filtrate and Kocide 101. No lesions developed when the ESI-NB culture, ESI cell- free culture filtrate and Kocide 101 were used as protectants. Generally, the ESI-NB culture was stable as a protectant during the 72 h test period. The rhizobacterium was frequently recovered from inoculation points on pods treated with its NB culture, suggesting persistence of the bacterium on detached cocoa pods. These results show that the ESI-NB culture and its filtrate can be exploited as biofungicides for use against black pod disease of cocoa.