Morphological characteristics and germination and fertilization abilities of five pollen varieties for ‘Niitaka’ pear (Pyrus pyrifolia nakai) artificial pollination

Abstract

We quantified pollen size and form in a range of pear (Pyrus pyrifolia Nakai) varieties. Our data show that ‘Xuehuali’, ‘Yali’, ‘Chuwhangbae’, and ‘Imamuraaki’ have Polar/Equatorial (P/E) ratios between 1.87 and 1.98, belonging to the prolate type and ‘Wonwhang’ has a P/E ratio of 2.20, belonging to the perprolate type. The pollen surface patterns were all striate, clearly showing the varieties’ characteristics. With respect to the pollen germination rate, the pollen varieties showed lower rates at around 20 to 30% 2 hours after placement, whereas all showed at least an 80% germination rate 12 hours after placement. ‘Imamuraaki’ had the highest rate at 92% and also had the richest form of pollen. When the pollen was treated in a moist chamber for 3 hours, the pollen tube elongation of ‘Xuehuali’ was 0.73 ± 0.06 mm, ‘Yali’ was 0.81 ± 0.04 mm, ‘Chuwhangbae’ was 0.63 ± 0.08 mm, and ‘Imamuraaki’ was 0.94 ± 0.15 mm, showing good germination potential. ‘Wonwhang’ displayed pollen tube elongation of 1.32 ± 0.44 mm after being treated in a moist chamber for 9 hours. When used for fertilization at a pear orchard, all the varieties showed at least 90% or higher fruit-load rate and fruit weight of about 600 g. Each type of pollen from the five varieties used to artificially pollinate the ‘Niitaka’ pears had a unique surface pattern that could be used to quantify the pollen purity. Moreover, there seems to be no difference, in terms of the germination rate, pollen tube elongation, fruit-load rate, and fruit weight at harvest, between these varieties and domestic pear pollen.