Cocoa quarantine: measures to prevent the spread of vascular‐streak dieback in planting material

Abstract

Isolation of clonal cocoa material in screened shade houses for 6 months allows adequate opportunity for detecting vascular‐streak dieback caused by Oncobasidium theobromae and in Papua New Guinea a further period of 6 months in intermediate quarantine on an isolated island has been replaced by a similar period in screened houses at a quarantine station in the importing locality. Microscopic examination of transverse sections of budwood sticks and pod stalks provides a further very thorough precaution against disease transmission because hyphae of the pathogen are large and easily detected. Hyphae were found within the stalks and placentae of pods from diseased branches but seeds from these germinated normally and there was no evidence of seed transmission. Dipping rubbed seeds in 1 g/l propiconazole plus 5 g/l metalaxyl caused a small but statistically significant reduction in seedling stem height. However, root length and percentage germination were not affected and this prophylactic seed treatment may be useful in situations where quarantine authorities require additional precautions.