Cross-pollination increases the number of drupelets in the fruits of red raspberry (Rubus idaeus L.)

The study was conducted in 2014 at the Research Institute of Horticulture in Skierniewice, Poland. Its aim was to assess the effects of self-pollination (self-fertilization) and cross-pollination (cross-fertilization) on the size of the fruit of ten red raspberry cultivars, determined as the number of drupelets in one fruit. The investigated cultivars were: 'Canby', 'Glen Ample', 'Laszka', 'Polana', 'Polka', 'Radziejowa', 'Schöneman', 'Veten' and 'Willamette'. They were self- and controlled cross-pollinated in a greenhouse in the spring of 2014. The pollination program was based on a half-diallel mating design (Griffing's method II) among these cultivars, producing 55 hybrid families (45 from controlled cross-pollination and 10 from self-pollination of maternal cultivars), which allowed to study the influence of the pollen cultivar on the number of drupelets in a single raspberry fruit. The study revealed an overwhelming advantage of cross-pollination over self-pollination. The average number of drupelets in the fruits from cross-pollinated flowers ranged from 48.3 in 'Glen Ample' (76.9% more drupelets than in self-pollinated 'Glen Ample') to 92.9 in 'Radziejowa' (96.8% more drupelets than in self-pollinated 'Radziejowa').