Reproductive phenology, floral biology and breeding system of Aquiliaria crassna in tropical Australia

Abstract

Trees of the Aquilaria genus produce a fragrant resin and have had a long history of human use. In this study, the flowering and fruiting phenology of Aquilaria crassna is described, as well as the main reproductive system operating in A. crassna, growing in a cultivated environment. Sexual reproduction occurs annually, with a peak in flowering occurring during the dry season. Flowers are hermaphrodite borne on terminal branches. Flower anthesis typically occurred at night and the duration of the flowering and fruiting phases was 12.3 and 59.5 days respectively. Four simplified flower stages were identified: opening (0.2 to 1 day), open (2.3 to 3.6 days), closing (0.8 to 1.3 days) and closed-flower fall (1.4 to 7.4 days) or closed-fruit development (17 to 25 days). Stigma receptivity, determined using an esterase indicator, was recorded throughout the floweropen phase. Two simplified fruiting stages were identified: initiation (4 to 8 days) and maturation (25 to 58 days). Open pollinated flowers had a moderate to high fecundity with 14.5 to 46.7% of flowers setting seed. The A. crassna species demonstrated a mixed mating system that is primarily outcrossing. Hybridisation between A. baillonii (♂) and A. crassna (♀) was demonstrated.