Markets continue to raise the bar on requirements for fruit quality. Without question pollination plays a significant role in fruit quality in apples and pears. Understanding the process is key to making decisions about pollinizers and supplemental pollen to help maximize the quality in each orchard.
Good Pollination = Good Fruit
All five stigmas pollinated
Large, well shaped fruit with all 9-10 seeds developed
Not all stigmas pollinated
Smaller, misshapen fruit with less than 9 seeds
Flower Anatomy and Fruit Development
Apple and pear flowers have the following female reproductive parts: five stigmas, five styles and a five-celled ovary. In addition, they typically have 22 stamens, which are the male reproductive parts. Research has shown that good size and shape in apples and pears are correlated to the presence of 9-10 seeds per fruit. All five stigmas need to be pollinated to ensure that this number of seeds are formed.
Pollination vs Fertilization
Although they are distinctly separate processes, often the terms pollination and fertilization are used interchangeably. Pollination is the process of pollen transfer to the stigma. Pollination requires a source of compatible pollen and a means of transfer (e.g. honey bees or spray application). This process must occur while the stigma is receptive. Fertilization is the process in which the pollen tube grows through the style, enters the ovule and releases its sperm cells which fertilizes the embryo and endosperm. Both are critical to fruit set.
Effective Pollination Period
For successful fruit set, it is important to consider the Effective Pollination Period (EPP) or the period in which pollination must occur in order to achieve fruit set This varies with crop, cultivar and weather conditions. Typically in apples and pears EPP is approximately 2-5 days depending on variety and weather.
EPP = Length of time ovule is viable – time required for pollen tube to grow down style
For example in WA38, assuming ideal weather conditions, the stigma is receptive to pollen for up to 9 days. Ovules are also viable for about 9 days. After pollination, it takes approximately 7 days for the pollen tube to grow to the ovule and fertilize it. Using the formula above we arrive at an EPP of 2 days, meaning each flower has a window of 2 days to be pollinated after it opens. This period can be slightly different depending on variety and weather conditions, but 2 days is a good rule of thumb for apples and pears.
Timing is Critical to Pollinating High-Quality Fruit
In order to achieve full seed count each stigma would need to be pollinated in that two-day window. Furthermore, it’s important to note that apples require cross-pollination from a different compatible cultivar to set fruit, ensuring genetic diversity and fruit development. Given the 2 day EPP window this makes achieving ideal pollination a challenge. Both pollinating varieties would need to provide pollen in this window. If the King bloom are to be targeted, pollinizers should be selected accordingly. A pollinizer that blooms during the 2nd half of the commercial variety bloom may not provide enough pollen for ideal King bloom pollination. In this situation targeted pollen applications may help without creating crop load issues.