Biological features of flowers influence the fertility of Lonicera spp. cultivars

Fertility experiments were carried out on a plantation of haskap berries (40 cultivars) in southern Poland. Based on the observation of phenological phases, the cultivars were divided into three groups with similar overlapping periods of full flowering: the earliest comprising 11 cultivars; the moderate-early, 17 cultivars; and the latest, 7 cultivars. The attractiveness of cultivars for pollinating insects was evaluated on the basis of flower biometric measurements. Flowers are more diverse in length than in width of the sympetalous corolla, with the pistil always being longer than the corolla, which is conducive to effective insect pollination. A pollen viability coloring test and germination capacity on agar medium were used to assess pollen quality. Despite very high pollen viability (on average, 90%), the percentage of germinating pollen was very low and ranged from 3.3 to 34.5%. Pollen yields for each cultivar were calculated based on the number of pollen grains in the flowers. The cultivars differed significantly in terms of the number of pollen grains in the flowers. The cultivar Morena was characterized by the highest number of pollen grains (45,375), while the cultivar Fialka had the lowest (2750). Microscopic observations of pollen tube overgrowth through the style of the pistil after open pollination and self-pollination allowed for calculation of the pollen germination index (PGI) used to assess the fertility of the cultivars. Self-pollinated cultivars with a PGI<2 were characterized by self-incompatibility. It was found that among the 40 cultivars studied, only the Docz Velikana cultivar exhibited PGI>2, which proves the self-fertility tendency of this cultivar.