A careful choice of compatible pollinizers significantly improves the size of fruits in red raspberry (Rubus idaeus L.)

Good pollination (fertilization) of flowers is the key to high yields in most of the fruit crops grown in temperate zones. Detailed studies on influence of the pollen source on the berry size and the number of seeds in fruits of the red raspberry were conducted at the Research Institute of Horticulture in Skierniewice, Poland. Studies were carried on under controlled conditions and were based on three separate greenhouse experiments conducted in 2015-2017. In these experiments flowers of red raspberries 'Canby', 'Glen Ample', 'Laszka', 'Polana', 'Polka', 'Radziejowa', 'Schonemann' and' Willamette' were artificially pollinated (by hand) with pollen coming from either the same cultivar (self-pollination, self-fertilization) and/or with pollen collected from other cultivars (cross-pollination, cross-fertilization). It was found that cross-pollination resulted in increase of fruit size and number of seeds per fruit compared to fruits obtained from self-pollination. In majority of the cross-combinations (pollination treatments) the differences between cross-pollination and self-pollination were significant. The larger fruit size and the number of seeds per fruit from cross-pollinated flowers was depended on the particular pollinizer. The results confirm that the cross-fertilization is essential for high yield and improved mass of each berry. It is particularly important in cultivation of red raspberries under the high tunnels for early harvest, where predominantly single cultivar is grown in so called varietal monoculture. These findings suggest that selection of suitable pollinizer should be a new area of research for red raspberry production under cover for early or late crop.