The process of pollination is relatively simplified in peaches and nectarines in that only one ovule must be fertilized in order to set fruit as compared to hundreds of ovules in many other fruit species such as melons or papayas (McGregor 1976).
Most varieties of peaches and nectarines are self-fertile, meaning that fruit will form when a plant’s flowers are pollinated by its own pollen or pollen from another plant of the same variety.
There are, however, many varieties that are self-sterile, that is they do not set fruit unless they are cross-pollinated, meaning pollen from another variety is needed for successful fertilisation of the ovule (DAF 2005).
Whether the variety is self-fertile or self-sterile, a satisfactory fruit crop cannot be obtained if adequate numbers of pollinating insects are not working the peach or nectarine orchard at the time when the trees are in bloom (McGregor 1976).
A review of the pollination requirements of peaches and nectarines conducted by McGregor (1976) makes numerous references to research conducted in the mid-1900s describing the benefit of having honey bees in both glasshouses and open orchards.
More recent research has also acknowledged the value of honey bees and other pollinating insects in the pollination of peaches and nectarines (Mattu et al. 1994; Szabo et al. 1998; Nyeki and Szabo 1996).
Additionally, an Australian study by Langridge et al. (1977) showed the benefits of having bees within a peach orchard by comparing fruit set between caged and open trees of the cultivar ‘Crawford’. Trees open to honey bee pollination had a 290% increase in the percentage of flowers that set fruit and a 260% increase in the weight of fruit harvested as
compared to the trees that were caged to exclude bees (Table 1). There was also an evident decrease in fruit mutations in the open tree treatment (Langridge et al. 1977). Table 1 A study of pollination of dessert peaches cv ‘Crawford’ (after Langridge et al. 1977, as cited in DAF 2005)
Pollination management for peaches and nectarines in Australia:
There are a number of factors within the orchard which have a direct bearing on the pollination efficiency of honey bees:
- Tree and blossom density: Orchard layouts may be either designed to a traditional open-vase system or a high-density planting system. The open-vase system usually has a density of around 299 trees per hectare, each trained into a cone shape, with ample spacing between trees of around 7m. The high-density design, on the other hand, may have tree densities of between 919 and 1196 trees/ha and tree spacing reduced to around 3m (Day et al. 2005). The higher blossom density associated with these high-density plantings have been shown to increase yields and give better returns to the grower when prices are good. Under circumstances of higher tree and blossom density, the density and condition of hives would also need to be increased relatively to ensure optimal pollination (DAF 2005).
- Access: From a beekeeper’s point of view, all-weather truck access is highly desirable. Limited access may lead to an increased workload for the beekeeper, uneven placement of hives and thus inefficient pollination. Ensuring the beekeeper has good access will aid in placement of hives and be mutually beneficial to the grower (increased pollination efficiency) and the beekeeper (decreased labour effort).
Most cultivars are self-fertile however some require pollen from another cultivar to successfully set fruit (DAF 2005). Further, yields and fruit quality have been shown to be improved with cross-pollination regardless of whether a cultivar is self-fertile or self-sterile and fruit set can range from 22 to 84%.
Mattu et al. (1994) showed that if flowers of market sold peaches, canning peaches and nectarines were isolated from each other then the fruit sets for the three types were 20.9%, 21.7% and 15.7% respectively. However if the three types were open-pollinated, the fruit set increased to 34.2%, 34% and 26.5%; an average increase in fruit set of 63% (DAF 2005).
Density of bees:
The Department of Agriculture and Food West Australia (2005) recommends to 2hives/ha for young trees and 2.5hives/ha in older orchards (DAF 2005). An issue worth noting is that most peach and nectarine growers will need to use thinning practices in years when trees bear a crop that is too heavy, which can cause limb breakage and a reduction in fruit size and quality.
Some growers consider thinning of a heavy set of fruit to be a greater problem than pollination, however, it should be recognised that thinning the fruit after flowering is easier than getting fruit to set if the flowers are gone and fruit set is inadequate (McGregor 1976).
Most cultivars produce pollen at the same time that the stigma is receptive (McGregor 1976). Randhawa et al. (1963, cited in McGregor 1976) found that the flowers of peaches were fully closed at 6am, but most of them were open by 10am, and all were open by noon. They did not close at night; and stayed open with the stigma receptive for three days.
Attractiveness, nutritional value of pollen and nectar:
Peaches and nectarines blossom in the spring with many different attractive pink and reddish blossoms. A notable quantity of nectar is produced in peaches and nectarines, ranging from 5 to 45mg/flower with a sugar content of between 30 and 50% (DAF 2005).
The nectar is secreted at the base of the corolla and is highly attractive to honey bees and other pollinating insects (McGregor 1976). Bees do not appear to target pollen but rather pollen is transferred from flower to flower while the bee is foraging for nectar (DAF 2005).
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