Phytophthora black pod disease in Ekiti state of Nigeria: Species differentation and pathogenic variation

E. D. Fagbohun*, C. R. Falegan And J. A. Arowolo

Department of Microbiology, University of Ado Ekiti, P.m.b. 5363, Ado-Ekiti Nigeria.    

ABSTRACT: Incidence and pathogenic variation among Phytopthora species was studied in some selected cocoa plantations in Ekiti State of Nigeria. Infected cocoa pods were collected from five selected plantations each at Ilu-Omoba, Aisegba, Ikere, Ijero, Ise/Emure and Aramoko and brought to the laboratory. Identification of fungal isolates were based on colony morphology, slide culture and pathogenicity tests. Isolates from Ilu-Omoba, Aisegba, Ikere-Ekiti and Ise/Emure produced white cotton-wool like colonies on potato dextrose agar, with spherical sporangia and narrow pedicel. Two isolates were obtained from Ise/Emure. These show characteristics similar to those obtained from Ilu-Omoba, Aisegba, Ikere-Ekiti axis and Aramoko axis. Isolates from Aramoko-Ekiti and Ijero produced sparse aerial mycelium with stellate appearance, and broad sporangia pedicel. All the isolate however produced chlamydospores. Healthy cocoa pods inoculated with isolates showed the characteristic Phytophthora pod rot symptoms of water soaked lesions, which gradually increases in size and turned black. Pathogenic variations were observed with the two groups of isolates. Isolates from Ilu-Omoba, Aisegba, Ikere-Ekiti and Ise/Emure were more virulent than those from Aramoko and Ijero. The colony morphology, cultural characteristic and pathogenicity tests observed show that the two groups of isolates belong to Phytophthora megakarya and P. palmivora. P. megakarya was more prevalent in Ilu-Omoba, Aisegba, Ikere, and Ise/Emure while P. palmivora was limited to Aramoko and Ijero-Ekiti. The same fungus P. megakarya was also more virulent than P.palmivora.

KEYWORDS: Incidence; Pathogenic variations; Phytophthora species; Cocoa plantations

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