Molecular Characterization of Cocoa, Mango, Banana and Yam Isolates of Botryodiplodia theobromae in Ghana

Abstract

Botryodiplodia theobromae is a virulent plant pathogen commonly found in the tropics and sub-tropics. The fungus has wide range of plant hosts and known to cause yield losses up to 80% espe-cially on cash and food crop farms. This study aimed at establishing genetic diversity of B. theo-bromae collected from four common food and cash crops grown in Ghana. A total of 25 fungal isolates were sampled from cocoa, mango, banana and yam within four geographical regions of Ghana. The isolates were developed into pure single-spore cultures on Potato Dextrose Agar (PDA). Single-spore cultures of the 25 B. theobromae isolates from the four crops were grown in V8 juice medium at 28°C on a rotary shaker for 48 hrs. Mycelia were harvested at 48 hrs of growth, washed with sterile distilled water, grounded in liquid nitrogen and the genomic DNA iso-lated. PCR products from SSR and RAPD primers were resolved on 2.5% agarose gel and the DNA bands from the 25 isolates clustered on dendrogram into 5 distinct groups of varied genetic simi-larities using NTSYS software. The study showed only two banana isolates, B(Kt) and B(Ef), shar-ing highest genetic similarity above 80%. An isolate from yam, Y(Zu), shared no genetic similarity (0%) with any of the remaining 24 fungal isolates from the four regions in Ghana. The remaining 22 isolates measured genetic similarity between 20 and 75%. The results suggest high genetic vari-ability among the B. theobromae isolates on the crops studied.

Keywords: Banana; Botryodiplodia theobromae; cocoa; genetic variability; mango; phylogeny; plant pathogen; potato dextrose agar (PDA); RAPD; SSR and yam.