Influence of boron foliar fertilization on plum pollen viability, germination and fruit set

Pollen viability and germination are very important components of flower fertilization and fruit setting for plum production. In a trial carried out at Latvia State Institute of Fruit Growing, during 2 years four plum cultivars were investigated: 'Sonora', 'Lase' (cultivars bred in Latvia), 'Duke of Edinburgh' (syn. 'Prince of Wales') and 'Stanley'. Spraying was done with 0.25% boric acid (H₃BO₃) foliar fertilizer. Staining with acetic carmine was used for viability test, and in vitro medium containing 15% sucrose, 1.5% agar and 0.01% boric acid - for germination capacity. Foliar fertilizing did not have significant effect on pollen viability of the cultivars. Between years the pollen viability did not differ significantly and was high (over 90%) for all cultivars, except 'Lase'. The latter showed very low pollen viability (below 10%) and no germination (zero), which is an evidence of pollen sterility. Pollen germination of cultivars 'Duke of Edinburgh' and 'Stanley' was very good (over 60%), for cultivar 'Sonora' - good (over 30%). Boron fertilization increased pollen germination and fruit set for plum cultivars studied. Pollen germination differed between years, it was significantly higher in 2015, and such differences were observed also in boron foliar fertilizer treatment. Boron sprays had significant positive effect on the fruit set of cultivar 'Sonora'.