Cross-Pollination Plays a Crucial Role in Optimal Yields

Cross and Self-Pollination in Blueberries

Southern highbush blueberries are generally considered to be self-fertile. That is, a plant can set fruit with itself or with another plant of the same cultivar. But are fruit set, fruit weight, and aspects of fruit quality optimal? How much do different southern highbush cultivars benefit from cross-pollination? Answers to these questions can inform planting design, such as whether to plant single-cultivar blocks or mixed blocks. If planting mixed blocks, which cultivars should be interplanted to obtain optimal yield outcomes?

 In order to successfully set fruit, blueberry flowers need to be successfully pollinated. Cross-pollination occurs when pollen is transferred between two different plants, and self-pollination occurs when pollen is transferred within the same plant or even within the same flower. Because cultivars of crop plants are generally clonal, meaning that all plants of the same cultivar are genetically identical, pollination that occurs between two plants of the same cultivar is functionally self-pollination. The quantity and quality of pollination can determine not only fruit set, but also seed set and related berry size. Additionally, in some crops, pollination success can affect fruit firmness, sugar content, nutrient content, and time to ripen. 

Research Activities

We conducted research over two years to determine how yield outcomes, including fruit set, fruit weight, and aspects of fruit quality, varied between self-pollination (pollination between plants of the same cultivar) and cross-pollination (pollination between two different cultivars). For ten common southern highbush cultivars, we hand-pollinated flowers in a greenhouse with either self-pollen or cross-pollen and tracked fruit set, time to ripen, berry weight, berry firmness, berry sugar content, and berry acid content. All cultivars were pollinated by five different cultivars, as well as self-pollinated.

Research Results

Fruit set was high, at or close to 100%, for all cultivars when self-pollinated and when cross-pollinated. This result shows that if enough pollen is received by the blueberry flower, it will generally set fruit regardless of whether it is self or cross-pollinated. However, the weight of the berry was greater when cross-pollinated for all ten cultivars tested. Increases in berry weight ranged from ~10 – 100% when cross-pollinated compared to self-pollinated (Figure 1). Additionally, time to ripen decreased for most cultivars when cross-pollinated as compared to self-pollinated; decrease in time to ripen ranged from ~5 – 30 days (Figure 2). In general, cross-pollination between any two cultivars was better than self-pollination for both berry weight and time to ripen. Berry firmness, sugar content, and acid content were variable across cultivars and did not show an overall increase or decrease with cross-pollination as compared to self-pollination. 



Research conclusions

In conclusion, our study shows that cross-pollination between different cultivars can improve berry weight and thereby yield, by up to 100%. Additionally, berries ripen faster and can thus go to market sooner, increasing profits. However, some cultivars (e.g. Avanti, Optimus, Emerald) benefitted more from cross-pollination while other cultivars (e.g. Kestrel) showed higher self-fertility. Because all cultivar combinations were generally better than self-pollination, decisions about which cultivars to plant together should be based on cultivar phenology and bloom time as well as compatibility of management. 


CREDIT:
RACHEL E. MALLINGER
& STAN CHABERT

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