The effect of temperature on pollen tube growth in different cherry varieties
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The study of pollen tube viability and growth had been conducted on sweet and tart cherry varieties under the variable conditions. The samples were placed into the chambers at 15 0, 20 0, 25 0 and 30 0C. Pollen tube growth was observed under the fluorescent microscope 4 hours after the pollination and than every 24 hours thereafter over the 120-hour period. Pollen tube growth in the outside field conditions were used as control. Montmorency and MC-15 were used as female varieties in all the combinations.
Very slow tube elongation and growth were observed in all self- and cross-pollinations where Montmorency was a pollen donor. The best results were obtained in combinations Montmorency X Vladimir and Montmorency X Montmore. Pollen tube penetration was completed two days after the pollination took place. Cultivars Late Duke, NY 5261 and 4X showed no germination at all. In combinations with MC-15 as a female, the following could be inferred: MC-15 self-pollinated had many vital pollen tubes traversed the style 48-72 hours after the pollination. In all cross-pollinations, there was a great variability in pollen tube elongation and behavior. They could be classified in five distinct groups.
In the first group, pollen tubes reached the ovary within the first 4 hours followed the pollination than regression appeared (Viva, NY 1625, Hedelfingen). The second group could be characterized with good pollen grain germination and tube elongation within 4 hours following the pollination and with scores of viable pollen tubes near ovary ( Ulster). In the third group, there was good germination at the beginning with a slow-down requiring 48 hours for pollen tube to reach the vicinity of the ovary (Black Tartarian, Noble). For the fourth group, the pollen tube growth progressed slowly in the first hours following the pollination, requiring 72 hours for tubes to penetrate down to the ovary (Windsor, Chinook). In the fifth group, there was extremely fast germination, growth and penetration. Within the first 4 hours of pollination, multitude of pollen tubes traversed throughout the styles with no regressing observed over the duration (120 hrs) of the experiment (Gold).
Ambiance temperature highly effected pollen tube growth. At 15 0 C in self-pollinated Montmorency, pollen tubes grew at a slower rate. Optimum growth and penetration occurred at 25 0C reaching the ovary within 24 hours following pollination. Increases in temperature caused acceleration of the pollen tube elongation rate but at the same time that was the main reason for decreased pollen tube viability. The same was true for the other varieties in the trial. The experiment revealed different but variety-specific optimum temperatures for the pollen tube growth.
Conclusions of study
Temperature effects pollen tube viability and, consequently, the fruit set.
Different varieties respond differently to the ambiance temperatures and have specific requirements when it comes to optimum temperatures for pollen tube growth, penetration and fruit set. Such response to the meteorological conditions during the bloom time and fruit set will result in the fact that certain varieties show strong self-fruitfulness under optimum conditions for pollination and pollen tube growth, whereas those same varieties will fail to set fruit under less favorable circumstances showing self-sterile behavior (such as the case in MC-15).
Our findings are in concurrence with the findings reported by the other authors (Chang, N.W., Struckmeyer, B. E., Nyeky, J., R., D. E. Kester and M.V. Bradley).
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