The relationship between floral structure and honeybee pollination efficiency in 'Jonathan' and 'Topred' apple cultivars

Apple (Malus domestica) has a gametophytically determined self-incompatibility (SI) system, which limits inbreeding. As a result, apple fruit-set is dependent on effective cross-pollination, which may be enhanced by honeybees (Apis mellifera) Excess pollination results in over-cropping, leading to many small fruit, regarded as of low quality. On the other hand insufficient pollination is also possible, and is manifested by low crop production. In the present work, characteristics of nectar reward and floral morphology revealed that 'Jonathan' and 'Topred' flowers had similar nectar constitutions. However, honeybee behaviour was totally different in the two cultivars. 'Jonathan' flowers attracted fewer honeybees but, due to their anther arrangement, more of the flowers were approached from the top by honeybees collecting nectar than in 'Topred'. This finding demonstrates the importance of determining the pollination efficiency to achieve optimum honeybee management, in terms of the number of honeybee colonies required for sufficient pollination and minimum fruit thinning.