Cooler Is Better: The Role of Temperature in the Reproductive Biology of Persian Walnut (Juglans regia L.) Studied in a Hungarian-Bred Cultivar

The aim was to determine the growth of pollen tubes throughout the transmitting tissue and the process of fertilization in open, optimal and over pollination on the 3rd, 6th and 9th day after pollination of pistillate flowers, together with apomixis. The experiment was carried out over 2 years in Lovasberény, Fejér district, Hungary, which differed in temperature conditions. The average number of pollen tubes in the locule of the ovary was significantly higher in 2017 (1.3%) than in 2019 (1%). A higher percentage of fruit set was recorded in 2017 compared to 2019. The percentage of apomictic fruits from variant of unpollination was higher in 2017 (10%) than in 2019 (3.7%). Based on these results it can be concluded that pollen tube growth and post-fertilization processes together with apomixis of cultivar ‘AK’ are better adaptable to lower temperatures. These findings may help us to move walnut production to the north or to higher altitudes, where the climate is more continental.