Fruiting pattern in longan, Dimocarpus longan: from pollination to aril development

Abstract

In most fleshy fruits, the edible part of the fruit is formed either by the pericarp derived from the ovary wall or by an engrossed receptacle. However, in a number of fruit tree species the edible part is the aril, an outgrowth of the ovule that envelops the seed, and there is a paucity of information on fruit development and fruiting pattern in these crops. To fill this gap, in this work, we have characterised the progamic phase, fruit development and fruit/fruitlet drop in longan, Dimocarpus longan. The progamic phase from pollination to fertilisation took just 3 days; the pollen tubes arrived to the base of the style in 1 day, reached the locule 1 day later and penetrated the ovules 3 days after pollination. Only one of the two ovules present in each longan flower fertilised. However, this did not result in rapid fruitlet growth, since a very slow fruit development occurred up to 6 weeks after flowering. Pollination was required for fruiting and unpollinated flowers dropped 9 days after anthesis. Only 7% of the female flowers produced became fruits. There was a first flower/fruitlet drop 2–4 weeks after flowering that appeared to be related to lack of fertilisation followed by a second fruitlet drop 5–6 weeks after flowering, concomitantly with the rapid growth of the embryo and the aril, that appears to be related to competition for nutrients. These results set a frameline to understand fruiting in tree species in which the edible part of the fruit is a fleshy aril.