Black pod pathogens revealed
The development of a genetic finger-printing technique for identifying black pod (Phytophthora spp.) will save time and money in distinguishing between two similar forms of this devastating disease of cocoa.
The most common form of this fungal pathogen (P.palmivora) is present in most
cocoa-growing regions of the world.
Losses can be as high as 95% in very humid climates. However, a
more virulent form of the disease (P.megakarya) is also found in W.Africa. It currently
affects cocoa plantations in Cameroon, Nigeria and now much of Ghana. It is also suspected to be
present in Côte d'Ivoire. This particular species is faster moving than
P.palmivora so is more difficult to control. Rapid identification of this strain is
therefore necessary for effective disease surveillance and control.
The symptoms caused by both species are very similar and morphologically they can only be differentiated by microscopic examination. This procedure is not only time-consuming but requires specialist expertise to diagnose the differences between the two pathogens. However, a diagnostic assay, developed at the University of Wales, Aberystwyth (UK) will enable large numbers of samples to be analysed simultaneously and identified quickly and accurately, and at relatively low costs.
To identify the pathogen, a small amount of DNA is extracted from the diseased material. The distinctive banding pattern, which is generated by the assay technique, allows the genetic differences between the two species to be clearly identified. The advantage with this particular technique is that very little sample material is required.
