Effects of temperature on the pollination biology of Luntai Xiaobai apricot

【Objective】The study aimed to investigate the influence of temperature on the pollination biology of Luntai Xiaobai apricot (Prunus armeniaca L.) in order to provide a theoretical foundation for determining the optimal timing for artificially assisted pollination.【Methods】The dynamic flowering of Luntai Xiaobai apricot was observed and recorded from March to April 2024. At the same time, the stigma receptivity in different times since the flowers blossomed in the field were evaluated. Subsequently, Suletan apricot was utilized to pollinate Luntai Xiaobai apricots, and the fruit setting rate wasinvestigated in the end of April. Seven different temperature treatments (10, 14, 18, 22, 28, 32, and 36 ℃) were established to identify the effect of temperature on the receptivity of the stigma. During the blooming stage of Luntai Xiaobai apricot, we collected vigorous inflorescence branches by systematically removing the already opened flowers and retaining only those about to open. The branches were cultured at the mentioned temperatures above for 120 hours. The stigma receptivity was evaluated hourly using benzidine-hydrogen peroxide during the first 6 hours after flowering. Then, the stigma receptivity was assessed at 24-hour intervals. At the same time, we also investigated the effect of different temperatures (10, 14, 18, 22, 28, 32, and 36 ℃) on the pollen viability of Suletan apricot.【Results】The overall flowering of Luntai Xiaobai apricot was fast and concentrated. It only took 10 hours for flowering from 5% to 50%, and 22 hours from 5% to 90%. Additionally, the Luntai Xiaobai apricot predominantly flowered from 10:00 to 16:00. The number of Luntai Xiaobai apricot flowers increased gradually from 10:00 to 16:00 but decreased significantly from 16:00 to 20:00. There was a significant correlation between the number of Luntai Xiaobai apricot flowers and temperature (p ＜ 0.01), and the correlation coefficient was 0.58. The stigma receptivity exhibited a "low-high-low" trend over time. Under field conditions in 2024, Luntai Xiaobai apricot displayed high stigma receptivity only within the first 2 to 3 hours after flowering. The stigma exhibited the longest duration of strong receptivity within the temperature range of 18 ℃ to 22 ℃. The lower temperatures delayed the onset of strong stigma receptivity, while excessively high temperatures shortened the period of stigma receptivity. The laboratory results also indicated that different culture temperatures affected stigma receptivity differently. At 10 ℃, stigma receptivity was weak at 0 and 1 hour post-anthesis, moderate from 2 to 120 hours, and no strong stigma receptivity was observed. At 14 ℃, strong receptivity emerged 5 hours post-anthesis. As the temperature gradually increased, the onset of strong stigma receptivity in Luntai Xiaobai apricot was further advanced. Within the temperature range of 18 ℃ to 22 ℃, strong stigma receptivity could occur as early as 3 hours post-anthesis and last until 48 hours post-anthesis. At 28 ℃, strong receptivity appeared at 2 hours post-anthesis but declined quickly. At 32 ℃ and 36 ℃, the duration of stigma receptivity was reduced, strong receptivity was absent, and stigma receptivity was lost on the day of flowering. The temperature exerted a significant impact on the pollen germination rate of Suletan apricot in vitro. The temperature range of 18 to 22 ℃ was most favorable for pollen germination, with 22 ℃ being the optimal temperature. Specifically, the pollen germination rates at 10, 14, 18, and 22 ℃ were 38.15%, 41.13%, 47.15%, and 60.54%, respectively. When the temperature exceeded 22 ℃, the pollen germination rate began to decline, decreasing to 42.95%, 42.42%, and 39.61% at 28 ℃, 32 ℃, and 36 ℃, respectively. Similarly, the effects of temperature on pollen tube elongation of Suletan apricot were extremely significant. The results showed that 22 ℃ was the most favorable temperature for pollen tube elongation. In the first hour of pollen germination, the increase in temperature was conducive to the elongation of the pollen tube. The pollen tubes at 28 ℃ and 32 ℃ were the longest, reaching 140.00 μm and 145.60 μm, respectively. After two hours, the growth of pollen tubes at 22 ℃ and 28 ℃ was the fastest, reaching 315.43 μm and 336.88 μm, respectively, which was significantly longer than those under other temperature conditions. After three and four hours of treatment, the length of the pollen tube at 22 ℃ was significantly greater than those in other treatments. The fruit setting rate of Luntai Xiaobai apricot pollinated by Suletan apricot pollen was 62.28%, which was significantly higher than that under natural pollination.【Conclusion】The overall flowering of Luntai Xiaobai apricot was fast and concentrated, and the strong stigma receptivity in the field only could maintain for only 2 to 3 hours. These characteristics would result in a very short duration for effective pollination. Suletan apricot pollen could be used aspollinater for Luntai Xiaobai apricot.