Preliminary study of golden currant (Ribes aureum Pursh.) cultivar pollination, fertility and fruit set patterns

Two cultivars of five-year-old golden currant plants (‘Laila’ and ‘Uzbekistanskaya Krupnoplodnaya’) were grown in Jelgava, Latvia. Despite continually abundant flowering since the 2^nd growing season, fruit set and, therefore, berry harvests have been far from expected. Possible reasons for the poor fruit set could be the following NDASH spring frost damage, low temperatures slowing down pollen tube growth, weak activity of pollinating insects because of unfavorable weather conditions and/or weak nectar production in flowers, self- and cross-compatibility problems, etc. Preliminary results after a one-year experiment confirm complete self-sterility of ‘Uzbekistanskaya Krupnoplodnaya’ and partial self-compatibility of ‘Laila’. Moreover, ‘Laila’ produced mainly seedless berries; even after free and “assisted free” pollination most of the fruits were seedless. “Assisted free” pollination increased fruit set in both cultivars, compared to isolated and free-pollinated flowers, although fruit set for ‘Laila’ was higher than for ‘Uzbekistanskaya Krupnoplodnaya’ in all treatments. During the whole flowering time, low pollinating insect activity was observed in the plantation despite beehives besides the plantation, which may be explained by cool and/or windy weather during most of the period. Moreover, despite measured nectar levels in the flower tubes could in some cases reach as much as 5 mm, this was still too low for bees to reach, because flowers were typically 12 to 14 mm long. The experiment should be continued and extended to clarify the plant responses to different conditions and physiological mechanisms behind the processes.