Morphological, Pathogenic, and Molecular Characterization of Phytophthora palmivora Isolates Causing Black Pod Disease on Cocoa in Peninsular Malaysia

Abstract

Black pod caused by Phytophthora palmivora causes major losses on cocoa (Theobroma cacao) in Malaysia and worldwide. In this study, morphological and molecular characterization as well as pathogenicity of 14 isolates of P. palmivora, obtained from main cocoa producing states of Peninsular Malaysia including Pe- rak and Pahang, were determined. In general, the results indicated that P. palmi- vora isolates were divided into two groups based on their geographical origins of the isolates. According to morphological characteristics, although some overlap was observed among the isolates obtained from the two states, isolates from Pa- hang grew faster on different agar media, and various shapes of sporangia includ- ing, globose, limoniform, ovoid and sporangia with two papilla were recorded for these isolates. Pathogenicity tests indicated that the isolates obtained from Pahang are more aggressive compared to the isolates from Perak. Phylogenetic analysis of a combined dataset of the ITS, EF-1α, and COX1 indicated that all 14 isolates belonged to P. palmivora with no difference among the isolates. These results suggest that morphological and pathogenic diversity of Malaysian isolates of P. palmivora is related to their geographical origins.