Airborne Dispersal of Phytophthora palmivora, causing Black-Pod Disease of Theobroma cacao

Abstract

AT the 1951 Cocoa Conference, Mr. G. F. Bowman, chief of the American Cacao Research Centre, Turrialba¹, referred to work by Salazar² which shows that the sporangia of P. polmivora are almost certainly not airborne, except in drops of water. Contrary evidence was not apparently produced at the Conference ; therefore it is desirable to direct attention to certain observations in Nigeria which indicate that P. palmivora sporangia may be airborne and that infection apparently results thereby. In this respect, the species in question would appear to be comparable with P. infestans in temperate regions, the airborne dispersion of which has been discussed by Gregory³ and by Van der Plank⁴. It seems necessary to postulate long-distance dispersal to explain the epidemiology of black-pod disease. Observations have therefore been made to test this hypothesis, and also to determine whether free moisture is essential for take-off and dispersal of sporangia in Nigeria.