Archivio Journal of Plant Pathology

Abstract:

Black coffee twig borer (BCTB), Xylosandrus compactus (Eichhoff) was recently reported as a pest of cocoa in Uganda (Kagezi et al., 2014). Females bore into primary branches and introduce an ambrosia fungus, Fusarium solani (Mart.) for feeding their brood (Ngoan et al., 1976). Infested materials wilt and die, but the cause is not fully understood. It could be due to disruption of nutrient and water movement across BCTB-damaged galleries or disease effect by F. solani (Greco and Wright, 2015). We therefore tested the pathogenicity hypothesis by isolating the fungus from mycangia of the female beetles and scrapings from BCTB-infested galleries of coffee. Isolates were identified using spore description (microconidia) as Fusarium spp. and maintained separately on potato dextrose agar (PDA) at 25°C. Spores from 7-day-old cultures designated as isolates 36, 37 and 63 were diluted to a concentration of 1.36x106 spores per ml and injected into 10 healthy coffee and cocoa seedlings per isolate. Controls were injected with distilled water. Seedlings were grown in screenhouse and observed for wilting symptoms after 30 and 90 days. At 30 days, 20, 10 and 30% of cocoa seedlings inoculated with isolate 36, 37 and 63 respectively had wilted. No more wilting of other seedlings was observed. Re-isolated fungus from wilted seedlings confirmed that Fusarium spp. causes wilting of cocoa consequent to BCTB attack. To the best of our knowledge, this is the first report of BCTB-associated Fusariun spp. causing wilting in cocoa. However, confirmation of species involved needs to be done.