Achievements in breeding coconut hybrids for tolerance to coconut foliar decay disease in Vanuatu, South Pacific

Coconut foliar decay (CFD) is a disease of coconut (Cocos nucifera L.) associated with infection by coconut foliar decay virus (CFDV),which is endemic in Vanuatu, South Pacific. The local cultivar 'Vanuatu Tall' (VTT) is the only cultivar that is fully tolerant to CFD, whereas introduced cultivars and hybrids are affected to different degrees. From 1967 to 2008 a conventional breeding programme was conducted with the aim of creating hybrid planting material combining tolerance to CFD with improved copra yield and high copra weight per nut. This objective was achieved by crossing the progeny of selfed trees of 'Rennell Island Tall' (RIT) cultivar, selected for their low susceptibility to CFD in field screening tests, with VTT, improved by mass selection and intercrossing. An improved VTT 9 RIT hybrid was identified with a high degree of tolerance to CFD (less than 1%of diseased trees after 11 years of exposure to high disease pressure). The annual production of the improved VTT 9 RIT hybrid ranged from21.9 to 28.6 kg of copra per tree, depending on theRIT parent, and was, on average, 34%higher than that of 'VTT Elite' an advanced cultivar obtained after four selection cycles of local VTT. However, the production of the hybrid inVanuatu involves constraints such as frequent replanting and isolation of the seed garden and CFD control for the RIT parents. The importance of conducting research on the genetic determinism and the mechanism of tolerance to CFD for better control of the disease in the event that it spreads outside Vanuatu is discussed. (Résumé d'auteur