Temperature and Genotype Influence Sweet Cherry Pollination Biology
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In the Pacific Northwest of the U.S., the commercial productivity of several sweet cherry (Prunus avium L.) varities with outstanding fruit attributes is poor, such as `Tieton', `Regina' and `Benton'. Study of the reproductive characteristics (e.g. flower number/spur and fruit set) of these cultivars has revealed that low fertilization rate (i.e., fruit set) is the main factor behind the low yields. More specifically, low fruit set in these cultivars appeared to be due to maternal factors (i.e., the pistil). This research project therefore studied the role of temperature on floral organ development and, stigma receptivity and ovule viability. Stigma receptivity was assessed by evaluating stigma surface development, pollen hydration level, germination rate and pollen tube growth in vivo. Controlled-climate chambers were programmed to mimic cold, average, or warm spring flowering conditions. In addition field trials were conducted to develop practical strategies to improve fruit set. The lengths of styles and filaments were most sensitive to temperature, being about 11% and 25% shorter in the low temperature environment compared to high temperature, respectively. Generally, pollen hydration and germination were poor under cool temperature and ovules were apt to lost viabilities by warm temperatures. Two to three days post flowering, the pollen hydration level, germination rate and fruit set reached the optimal value. Compared with productive cultivars, the primary ovules of `Tieton' and `Benton' lost viability at a faster rate (e.g., 13% viable ovules in `Tieton' vs. 77% in `Rainier' seven days post pollination). Lastly, field trials with aminoethoxyvinylglycine (AVG) (commercial product: ReTain® ) applied at prior to and during flowering revealed the potential to prolong the ovule lifespan and improve fruit set. The percent of inactive ovules of `Tieton' and `Regina' decreased by ca. 180% and 50% while fruit set increased by ca. 120% and 60% by with 499 g/acre ReTain®, respectively.