Virus Diseases of Cacao in West Africa Viii. The Search for Virus‐resistant Cacao

The methods used and the results of 10 years' search for cacao resistant to swollen‐shoot disease are described. Selection among the trees surviving in farms devastated by this virus disease led to the discovery of mild virus strains which can protect trees against virulent strains. When tested by graft inoculation with virulent virus, none of the selections showed any immunity or resistance save that conferred by previous mild‐strain infection. A low degree of tolerance was found in some selections. Local selections and a range of new introductions were tested by mealybug infection, and only types from the Upper Amazon region of Ecuador were consistently resistant to infection. This genetical resistance seems to be strongest in cacao from the Nanay peninsula, near Iquitos.