Effects of temperatures on pollen germination and pollen tube growth in apple

: Apple cultivars in Korea have been experiencing poor fruit sets due to early spring low temperatures and global warming. Therefore, the present study aimed to investigate the effects of temperature on fruit setting and to select apple cultivars tolerant to extreme temperatures based on the temperature response of their pollen. The effect of temperature on pollen germination percentage (PGP) and on pollen tube length (PTL) was determined under laboratory conditions using the pollen of ten apple cultivars. The two parameters were evaluated using a pollen germination medium, at temperatures ranging from 5 to 45 °C, at 5 °C intervals. The temperature variations considerably affected pollen germination and tube growth in all the examined cultivars. The maximum pollen germination percentage ranged from 61.5 (“Green Ball”) to 99.9% (“Shinano Gold”) with a mean of 85.2%, whereas the maximum pollen tube length ranged from 716.5 (“Tsugaru”) to 989.8 µm (“Arisoo”) with mean of 855.1 µm. There were differences in the cardinal temperatures (T min , T opt , and T max ) of PGP and PTL between cultivars. Mean cardinal temperatures T min , T opt , and T max computed using the modified bilinear model were 4, 27.7, and 44.9 °C and 6.3, 28.6, and 43.7 °C for PGP and PTL, respectively. Our preliminary results may be used to select low-temperature and global warming-friendly apple cultivars for farmers and can also be exploited to develop temperature-tolerant apple cultivars during flowering.