Screening five fungal isolates as potential antagonists against Phytophthora palmivora on cocoa pod pericarp.

Abstract

Investigations were carried out on the antagonism of Penicillium digitatum, Aspergillus repens, Paecilomyces sp., Botryodiplodia theobromae and Alternaria tenuis to Phytophthora palmivora (cocoa black pod pathogen) on cocoa pod pericarp blocks (10x1x1cm). The result revealed the antagonistic activity of the tested organism when each was placed together with pathogen on either side of the cocoa pod pericarp of length 10cm long. Penicillium digitatum and Paecilomyces sp were able to check the invasion of the pathogen by colonizing the greater part of the pericarp (70% each), followed by Aspergillus repens (62%)and Alternaria tenuis (34%) . The test antagonists were unable to colonize the samples previously invaded by the pathogen and therefore unable to eliminate the pathogen that was already established. When the test antagonists were placed on sterile intact cocoa pod, only B. theobromae produced spectacular rotand loss in weight. However, when they were inoculated on sterilized cocoa pericarp of length 10cm long, the entire block was colonised with rots and loss in weight. The decay capacity was observed to be significant (P< 0.05) with loss ranging from 28% in Paecilomyces sp to 57% in B.theobromae. Lesions were produced by all when the mixture of the pathogen with each of theantagonists was tested on cocoa pod surface; the radii of lesions obtained were significantly different (P < 0.05). Alternaria tenuis produced the largest lesion (37.9%) closely followed by B. theobromae (26.0%) while Penicillium digitatum produced the least lesions (9.8%).