In-vitro Evaluation of Some Fungicides against Botrydiplodia theobromae: Causal Pathogen of Pineapple Dieback

Aims: Dieback is an economically important disease known to cause major losses in food and tree crops. The causal pathogen of pineapple dieback was investigated and the efficacies of some fungicides were evaluated in-vitro.

Study Design: Pineapple suckers were planted with a spacing of 0.5 m x 0.5 m and separated by 1.0 m. Leaf and soil samples were randomly collected from diseased pineapple plants and the rhizosphere of the pineapple respectively.

Place and Duration of Study: The experiment was conducted at the National Horticultural Research Institute field in 2014.

Methodology: The samples were inoculated on potato dextrose agar and pure culture of fungal pathogen responsible for pineapple dieback obtained. The efficacies of three fungicides namely: Z- force (a. i 80% Mancozeb), Forcelet (a.i 50% carbendazim), and Funguforce (63% mancozeb + 12.5% carbendazim) were tested in-vitro on mycelial growth inhibition of the causal agent.

Results: Pathogens isolated from diseased leaves were Botrydiplodia theobromae and Aspergillus nigerwhile Aspergillus niger, Aspergillus tamari, Botrydiplodia theobromae and Fusarium verticilliodes were isolated from the rhizosphere. On the infected leaf samples, B. theobromae had the highest occurrence (93.3%) while Aspergillus niger had the least occurrence (6.7%). Similar trend was observed in the soil samples where B. theobromae had the highest occurrence of 80% while A. tamari and F. verticilliodes had the least frequency of occurrence of 4%. Pathogenicity test revealed that B. theobromae was the causal pathogen of pineapple dieback. The three fungicides evaluated were able to inhibition the mycelial growth of B. theobromae.