Polyploidy induction of raspberry species (<i>Rubus</i>) using colchicine and oryzalin

Raspberry (Rubus spp.) is a fruit crop used in many products across the United States. Commercial production of raspberry in North Dakota is challenging due to lack of cultivars with winter hardiness. In this study, two diploid red raspberry cultivars 'Prelude' and 'Polana' that are reported hardy in USDA hardiness zone 5 were used to induce polyploid raspberries that may have benefits of greater growth vigor, enhanced stress tolerance, larger fruit size, and higher yield. The effects of cultivar, anti-mitotic agent and its concentration, and the treatment duration on in vitro and ex vitro polyploidy induction were determined. 'Prelude' succeeded in polyploidy induction through the colchicine treatment of in vitro explants (apical and nodal buds) and ex vitro root dipping. There were three verified tetraploid 'Prelude' plants. One tetraploid plant of 'Prelude' was developed when in vitro explants were treated with 160 mM colchicine for 96 h and the other two were developed when the root system was dipped in the 10 mM colchicine for 8 h. No polyploid plants of 'Polana' were developed. Oryzalin, another anti-mitotic agent, did not succeed in polyploidy induction in this study. This study provides useful information on polyploidy induction in raspberry species, which could benefit future germplasm enhancement of raspberry and other Rubus species.