Virulence and genetic diversity of Phytophthora isolates associated with cocoa pod rot

Abstract

Phytophthora palmivora is an important pathogen of cocoa in the world and it has a widest host-range. High adaptability to host plants and changes in environmental conditions forms a new evolutionary strain among P. palmivora populations. The purpose of this study was to analyze the virulence and genetic diversity of the isolates associated with cocoa pod rot symptoms. The isolates (infected cocoa pods) collected from Bone, Bulukumba and Pinrang regencies were characterize morphologically and molecularly. For morphological identification, Phytophthora black pod disease was determined by hyphal growth on juice V8 agar medium and for genetical and virulent identification, pathogen was tested with primer pairs of ITS4 and ITS5 and the diversity was then analyzed with the BOXA1R primer. The Hyphae of isolates were found to have stellate pattern, ovoid sporangium, smooth globose oogonium and oospores. Of 21 isolates, 14 isolates were obtained from Bone, 6 isolates from Bulukumba and 3 isolates from Pinrang respectively and testing virulence of the isolates after reinoculated onto the pod layer shown that seventeen (17) isolates expressed a much higher virulent level and only four (4) isolates performed moderately level. DNA fragments of isolates were amplified at 900 bp and the highest genetic diversity among isolates were 67% level.