COMPARISON OF ISOLATES OF Phytophthora colocasiae Raciborski FROM DIVERSE ALTITUDES AND APPRAISAL OF PLANT EXTRACTS FOR ITS MANAGEMENT IN VITRO

Abstract

Leaf blight disease caused by Phytophthora colocasiae Raciborski is a serious constraint to taro production. This study was carried out to characterize the isolates of P. colocasiae from Makurdi, Nigeria and Befang, Cameroon; and evaluate the potential of aqueous leaf extracts of Eucalyptus, neem and mahogany at 0, 50 and 100% concentrations for management of the pathogen. A synthetic fungicide (Mancozeb) was included as a check. The isolate from Befang had more radial growth than that from Makurdi. The colonies of both isolates were translucent and low on corn meal agar (CMA) but opaque and high on acetate differential agar enriched with dextrose (ADAD). The texture of the Befang isolate was filamentous on CMA but hard and grainy on ADAD; the Makurdi isolate was filamentous on both media. Mancozeb and all the plant extracts inhibited the growth of the pathogen significantly (P≤0.05). Among the extracts, Eucalyptus at 100% concentration was the most potent (94.4-100.0% inhibition) and it was comparable to Mancozeb (100% inhibition); mahogany at 50% was the least potent (<20%). Both concentrations of neem gave similar levels of growth inhibition (mean=50.0–64.6%) throughout. Other inhibitory levels were 32.0–57.3% for Eucalyptus at 50% and 24.0–53.9% for mahogany at 100%. These results indicated that ADAD and CMA were appropriate culture media for the fungus. The extracts of Eucalyptus, neem and mahogany had fungicidal activity against P. colocasiae; therefore they should be incorporated into management programmes for the pathogen.