Fertile Hybrids between Tetraploid Highbush Blueberry Cultivars (Vaccinium section Cyanococcus) and Colchicine-induced Tetraploid Vaccinium stamineum (section Polycodium)

Open-pollinated seed of Vaccinium stamineum were collected from a dry, upland forest in northeast Florida.  Six tetraploid plants were identified by screening for large pollen tetrads after seeds and young seedlings had been treated with  colchicine.  The selected plants shed pollen abundantly. Most of their  pollen occurred in well-formed tetrads, which appeared, at 250 X, to be potentially viable.  In Spring 2013, four selected V. stamineum plants were used to pollinate emasculated flowers of 14 tetraploid highbush cultivars.  From 2700 pollinated highbush flowers, more than 1800 seedlings were  obtained.  Eight hundred seedlings were grown in a high-density field nursery for nine months. These were notably weaker than seedlings of both parent taxa growing in the same nursery, and nearly all had bronze-colored leaves rather than green.  Seventy seedlings that appeared large enough to flower were potted in December, 2014, held at 5 °C for a month, then moved to a warm greenhouse.  Forty-eight plants flowered.  Their hybridity was confirmed by three characters that are present in V. stamineum but absent in highbush blueberry: flowers that are open in the bud, anthers that extend beyond the corolla at anthesis, and presence of anther awns. Most of the 48 hybrids shed pollen abundantly, but the median  plant had only 25% of the individual pollen grains well-formed and potentially viable.  Twenty F1 plants that had enough flowers were backcrossed to highbush cultivars.  As females, 12 F1 hybrids had fruit set above 70%.  Fruit set was variable on highbush pollinated with F1 pollen, but numerous plump backcross seeds were obtained. It appears rather easy to move genes from V. stamineum into the cultivated highbush blueberry gene pool.  Traits of interest in V. stamineum include adaptation to sandy, upland soils, flower structure more amenable to honeybee pollination, berries with purple flesh color, and exotic flavors.