Developing a Sustainable Strategy for Pollination in Tree Fruit

Pollination (and subsequently, fertilization) is a critical step determining fruit quality and productivity. Growers struggle perennially with many issues related to pollinators (i.e., bees) and pollinizers (i.e., trees as sources of compatible pollen). Currently, fertilization in tree fruit crops is variable and unpredictable, mediated by the western honeybee (Apis mellifera), a species under global decline, mainly due to the effects of colony collapse disorder. Our objective is the development of an artificial pollination system that eliminates the need for pollinators and pollenizers in commercial tree fruit production systems.  Our field trials are evaluating both supplemental pollination and replacement pollination (i.e., in the absence of pollinators and pollenizers). In 2014, several field trials investigated the potential for both pollination approaches. In ‘Tieton’ sweet cherry (Prunus avium L.), a single supplemental pollen application (120g/acre) increased fruit set significantly, by about 15%.  This improvement was due apparently to increased pollen deposition as we recorded a 225% increase in pollen grains per stigma from flowers treated versus those which were untreated. Full replacement pollination was evaluated by utilizing frames wrapped with a single layer of bee exclusion netting that were deployed to limbs prior to any flowers opening.  In ‘Bing’ sweet cherry, two pollination applications, at about 40% and 80% full bloom, were as effective as natural open pollination—whole tree yield was similar for both treatments (4.8 and 3.3 kg/tree for natural and replacement pollination, respectively). In addition, a trial with ‘Gala’ apple (Malus domestica Borkh.) revealed that artificial pollination treatment with two pollen suspension solutions improved fruit set by about 56% and 75% compared to open-pollinated control. These trials demonstrate the potential for artificial pollination systems to improve yield security and production efficiency in specialty crop production, and build resilience to pollinator decline and climate change.