Self-incompatibility of raspberry cultivars assessed by SSR markers

Self-incompatibility in European red raspberry (Rubus idaeus L.) is less studied compared to other horticulturally relevant rosaceous crops, although cultivars of this species show differences in self-fertility. In this study, we genotyped progenies of 16 open pollinated raspberry cultivars with SSR markers to determine their natural propensity for self- and cross-fertilization. In further experiments, we genotyped progenies of selected cultivars from a topcross environment and studied seed set after hand pollination. A wide spectrum of cross-fertilized progeny ratio was discovered among the cultivars ranging from 5% of 'Dorman Red' progeny to 100% of 'Rumla' progeny derived by cross-fertilization. This was consistent with results obtained by hand pollination, where a significantly higher number of seed was produced in self-pollinated fruit of 'Dorman Red' and cross-pollinated fruit of 'Rumla'. The difference was particularly large in 'Rumla'; its self-pollinated fruit developed 10.95 drupelets per fruit on average, almost seven times less than its cross-pollinated fruit. The cultivar 'Rumla' showed 100% cross-fertilized progeny in a topcross environment as well, in contrast to the cultivars 'Lucana' and 'Preußen', which both had no cross-fertilized progeny. The results of this study show that there are differences in fertilization behavior between raspberry cultivars. Such information on the fertilization behavior of selected cultivars is useful in planning for cultivar selection in protected growing, where pollination is of special consideration.