Induction of flowering in longan in the Mekong delta, Vietnam

In the Mekong delta, besides some local longan cultivars (‘Long’, ‘Giong’, and ‘Xuong Com Vang’ - ‘XCV’) which are able to flower naturally in the on season, the others, e.g., ‘E-Daw’ and ‘Tieu Da Bo’ – ‘TDB’ requires induction techniques to commence flowering. The common techniques used include branch girdling, collar drenching with KClO₃, and the integration of the two mentioned methods. Floral induction techniques on longan varies depending on the season of cropping and cultivars. Leaf age at the time of application of chemical is also an important factor affecting longan flowering. The three cultivars, viz., ‘Long’, ‘TDB’ and ‘XCV’, are usually induced for flowering when leaves turn to light green (35-40 days old); meanwhile, the suitable leaf age for floral induction on ‘E-Daw’ is 40-45 days old. ‘Long’ flowers naturally or manually via branch girdling (2-3 mm width). For ‘XCV’, flowering is induced by KClO₃ collar drenching at the concentration of 24-36 g m^‑1 canopy diameter (c.d.) combined with branch girdling (2-3 mm width), The same method with different KClO₃ concentration (20-40 g m^‑1 c.d.) and girdling width (0.5-1.0 mm) was applied on ‘TDB’. On the other hand, only collar drenching of KClO₃ (40-60 g/g m^‑1 c.d.) was found enough for flowering of ‘E-Daw’.