Effects of pollen source on pollen tube dynamics and fruit set in two almond promising genotypes

In this study, a pollination experiment on almond species was conducted about the pollen tube penetration in the pistil with a fluorescence microscope and the rate of fruit formation by the controlled pollination in the orchard. These species included two new almond genotypes of KD 13 and K11-8 as pollen receptors, and two almond cultivars Tuono (self-compatible) and D5 (self-incompatible), a peach cultivar HolouYazdi, and GN15 (hybrid between almond and peach) as donor pollen sources. This experiment was conducted in an almond orchard with six-year-old trees at Kamal-Shahr Horticulture Research Station in Karaj, Iran. The results showed a significant difference among pollen sources for in vitro pollen grain germination. The pollen germination percentage ranged from 45 to 86% in the cultivars and genotypes under study. There were significant differences among crosses for the rate of pollen tube penetration in different parts of the style. KD13 × D5 (self-incompatible (with 9.6% and K11-8 × D5 (self-incompatible) with 7.63% showed the highest percentage of pollen tube penetration but KD13 × Tuono and K11-8  ×Tuono with 1% and 2.12%, respectively, had the lowest pollen tube insertion into the style. Ninety days after pollination, the crosses of KD13 × KD5 and K11-8 × D5 showed the highest percentage of fruit set (48.90 and 42.45%, respectively) as compared to other pollinizers. It was determined that the fruit formation was mainly influenced by the pollen source and therefore the source of pollen had a decisive role in the final fruit set. As a result, it is important to choose the right pollen source in the breeding programs before recommending the cultivation of new almond varieties.