Pollinators and pollination enhancement in 'Conference' pear and 'Jonagold' apple

Within the Flemish horticulture sector, fruit production is of major importance. Nowadays the area planted with pome fruit is around 16.205 ha, with 9.340 ha of pear and 6.865 ha of apple. The pear cultivar Conference and apple cultivar Jonagold, are at the core of the Flemish fruit production and will be the main cultivars studied in this PhD. Most commercial cultivars of pear and apple produce more and/or better fruits when cross-pollinated. To ensure this, pollinizer cultivars are planted within the orchard, and pollinators such as honeybees (Apis mellifera L.) and bumblebees (Bombus spp.) are commonly introduced in apple but rather exceptionally in pear.

Recent declines in the honeybee populations worldwide, and their inadequate pollination service during adverse weather conditions urges to explore the use of other insect pollinators to fulfil and guarantee optimal fruit set. In particular for pear, there is also a problem with the limited attractiveness of pear nectar for pollinators, probably because of the relatively low sugar concentration and/or unattractive sugar composition.

The overall goal of this study is to investigate a range of specific measures, which can improve the pollination efficiency of apple and pear, and therefore may increase yield stability and fruit quality. First we will identify the pollinator community in apple and pear orchards and later on investigate the effects of diversifying this pollinator community. Increasing diversity of the pollinating species can be expected to increase fruit set and fruit set stability through either niche complementarity or through competition effects with the honey bees present. Using both observational and experimental methods we will evaluate the effects on pollination success, yield quality, yield quantity and yield stability through time. Furthermore, we will evaluate the the relationship between flower characteristics (nectar, pollen and morphology) and the visitation rate of pollinators in different apple and pear cultivars. Finally, some tests will be done on the spread of biological control organisms by pollinators against the fire blight disease (Erwinia amylovora) in apple and pear.