Hybridization of Cultivated Highbush Blueberry with Vaccinium stamineum: Phenotype and Fertility of Backcross1 Populations

Abstract

Nine F1 hybrids produced by crossing seven tetraploid highbush blueberry cultivars with three tetraploid Vaccinium stamineum genotypes were backcrossed to an array of highbush blueberry cultivars to produce 2500 Backcross1 (BC1) seedlings. Thirty of the most vigorous BC1 plants were intercrossed in a greenhouse. Fertility of the BC1 plants was studied by examining their pollen at 250× and by determining the number of well-developed seeds per pollinated flower after the crosses. Percent well-formed microspores averaged 62.7% for BC1 plants compared with 30.9% for their F1 hybrid parents. Fruit set percentage was high from the BC1 intercrosses, with an average of 9.29 plump seeds per pollinated flower. The 2500 BC1 seedlings in the field were highly variable in vigor, but fewer than 10% were as vigorous as the median vigor of highbush × highbush seedlings. BC1 plants in the field averaged ≈1 month later ripening than highbush × highbush seedlings and berries averaged slightly smaller. Berry clusters were very loose compared with those of highbush. Berry flavor was highly variable from plant to plant, but the berries averaged less sweet and lower in acid than highbush berries. New flavor components not found in highbush seedlings were found in only a few BC1 seedlings. Fresh berries from BC1 plants made bright red juice when crushed in water, whereas berries from most highbush cultivars produced brown to yellow juice/water mixes. Although berry quality in the BC1 population averaged lower than in highbush seedlings, some plants had berry quality as high as typical cultivars. Because V. stamineum is highly drought-tolerant, cultivars bred using V. stamineum introgression could have improved upland adaptation.