The onset of fruiting in apricot (Prunus armeniaca L.)

Apricot (Prunus armeniaca) is a species particularly prone to erratic fruit set. However, the causes of these irregular productions are not entirely understood. This may be related to the lack of information as far available in this species on reproductive biology and the onset of fruiting. In order to provide a framework where the low adaptability shown by most of the cultivars could be studied, anatomy of the pistil and pollen tube growth through the pistil structures have been explored from pollination to fertilisation. Likewise, early fruit growth and fruit drop have been characterised in two apricot cultivars, 'Moniqui' and 'Bulida'. The phase elapsing from pollination to fertilisation took place in a considerably shorter period of time than in other related species. Thus, the first pollen tubes reached the base of the style in 3-4 days, and fertilisation was completed by 7 days after pollination. Most of the flowers and fruitlets dropped within the first 4 weeks following pollination, and the biggest drop wave took place 3-4 weeks after pollination. At this time, all the unpollinated flowers remaining in the tree dropped. In spite of starting with a synchronised population of flowers at anthesis, large differences in development were recorded among flowers and fruitlets in the days following pollination and some flowers clearly outgrew others, that eventually dropped. These differences, although at a different scale, also occurred in unpollinated flowers. The continuous fruit growth and fruit drop in both pollinated and unpollinated flowers, together to the fact that a number of fertilised fruits also dropped, suggest that in addition to pollination or fertilisation, other factors may be involved in flower and fruit drop and fruit set. Results are discussed in terms of the implications of the nutritional status of the flower in fruit set.