Impact of Insect Pollination on Fruit Set, Fruit Size and Yield of Three Sweet Cherry Cultivars
Abstract
In the present research project, we compare three different pollination types (viz., with insects, without insects, and solely with honeybees) of three widespread sweet cherry cultivars, with the aim of conducting measurements and drawing conclusions pertaining to the impact of pollinators on fruit set, yield, and fruit quality in commercial orchards. It included a total of three treatments: Isolation with anti-insect nets (IS), Isolation with cages and Honeybee Pollination (HB), and Open Pollination (OP). Recent research focuses mostly on the role that different types of pollinator have in sweet cherry pollination; however, they do not provide measurements of final yields. The applied experimental method, was fast, simple, of low labor cost, and yielded robust and valid results based upon statistical analysis that are easily comprehensible by the sweet cherry growers. From the results of the experiment, it is evident that the absence of pollinators is a restrictive factor in fruit production, not only in cross-pollinated but also in self-fertile varieties. The value of open pollination, during which cherry flowers are visited by native pollinators and honeybees is beyond doubt. Wind is not a means of transporting pollen to sweet cherry trees. Honeybees have proved to be effective managed pollinators and thus they represent an efficient approach that can ensure increased yields and large size fruits, when colonies placed in sweet cherry orchards.
Keywords
Download Options
Introduction
Sweet cherry (Prunus avium L.)is a valuable fruit tree species of the Rosaceae family, grown worldwide for its exceptionally high-quality fresh fruit. According to their pollination mode, cultivated cherry varieties are classified into self-pollinating, partially self-pollinating and self-incompatible. The genotype (S-alleles, SS ) of a given cultivar determines whether this a bparticular variety is compatible with another so that pollination can be achieved. If the two varieties have the same S-alleles, then they are incompatible with each other, irrespective of whether they bloom at the same time [27], [32]. The range of factors that influence fruit set and quality indifferent sweet cherry cultivars have been examined and analyzed in the literature, as for example in the paper by Montiel et al. [31]. Such factors are pollen availability and viability, stigmatic receptivity, ovule longevity, pollen vectors such as bees, as well as high and low temperatures during bloom time [5], [34], [41]. Of critical importance also are susceptibility to frost, rootstock type, rate of pollen germination [1], [40] and age of flower at the time of pollen germination [41]. Inadequate insect pollination, low pollen germination, low viable pollen, low pollen tube growth, and rapid ovule senescence, have negative effects on fruit set [35].
Insect pollination of cherry flowers is a core issue as it impacts both fruit set and yields [26], [29]. Both Apis mellifera L. (Hymenoptera: Apidae) species and non-apis species are acknowledged as major crop pollinators worldwide [16]. Recent work has demonstrated that pollination services by wild bees in cherry are superior to those offered by honeybees [21]. In fact, the semi-natural habitats that support their diversity and abundance enhance cherry fruit set [12]. Solitary bees such as mason bees (Osmia cornuta) achieve high pollination rates after a single visit to cherry flowers [13]. Honeybees, on the other hand, that are bred and maintained by beekeepers in hives, have the great advantage that they can be transported overlong distances and offer their precious pollination services in a variety of places. Worldwide, the transportation of honeybee colonies to provide supplemental pollination services remains the defacto approach, for the time being [16]. Honeybees are regarded as exceptionally productive pollinators [38]; as a matter of fact, they are the most economically valuable pollinators of crop monocultures around the world, especially when other pollinators do not visit agricultural fields [26], as for example when agricultural land is cutoff from natural or semi-natural areas.
The number of honeybee hives recommended for pollination in commercial cherry orchards is 2 to 5 hives per hectare. Sweet cherry fruits drop in three waves. The first happens 2-2.5 weeks after full bloom, the second 1 week after the first, and the third 3 weeks after the second [7]. The natural formation of pedicel-fruit abscission zone varies by cultivar, and the general molecular basis for its activation is not well characterized [20]. Poor pollen quality gives rise to fruitlet abscission [33]. Several factors, such as variety/rootstock selection, type of pruning, number of fruits, leaf/fruit balance, tree vigor, water adequacy at critical times, and heat stress affect fruit size [30].
The aim of the current research paper was to examine the influence of insect pollination on fruit set, fruit size and yield of three commercial sweet cherry cultivars via afield simulation method. Joint isolation of the cross-pollinated sweet cherry cultivars under examination constitutes a method which has never been applied before in pollination experiments with insects. It is adopted for the first time in the current research paper, with the expectation that it may yield comprehensive results for both farmers and beekeepers on the usefulness of pollinators as a valuable input to sweet cherry production.
Conclusion
From the results of the present research project it can be concluded that the pollination of cherry flowers with insects is an ecosystem service, essential to both cross-and self-fertile cherry cultivars. Wind is not a means of transporting pollen to sweet cherry trees.
Honeybees are exceptionally effective managed pollinators and thus they constitute a valuable agricultural input that ensures high yields in commercial sweet cherry orchards. At the same time, the presence of other pollinators, mainly bees, is shown to be of great importance. Although in this study no records of other pollinators‘ diversity have been kept, the maintenance of a landscape suitable for nesting sites for solitary bees and bumblebees seems to support pollination services required for higher yields. Honeybees may be more numerous, but solitary bees may be more efficient. The latter still needs to be investigated, taking into account the particular varieties as well as the particular landscape composition and climatic conditions.
The applied experimental method, was fast, simple, of low labor cost, and yielded robust results that are easily comprehensible by the sweet cherry growers.
One of the disadvantages of the ―isolation‖ method is that for its application the planting schedule of the cultivars under investigation should be carried out in a manner that facilitates their joint isolation in cages, so as to avoid using blooming branches of the pollinating cultivars, but whole trees. Furthermore, big-sized isolation cages must be used so that pollination conditions simulate those prevailing in open fields.