Phenotypic Characterization of the First Backcross Generation Between Southern Highbush Blueberry and Vaccinium arboreum

Introgression of traits from wild Vaccinium arboreum into Vaccinium corymbosum germplasm has been a goal of the University of Florida blueberry breeding program for over two decades. Two strategies have been used to further this goal: hybridization with diploid species from section Cyanococcus that produce unreduced gametes to create a bridge for crossing tetraploid highbush blueberry, and generation of tetraploid V. arboreum plants by colchicine treatment for use in crossing directly with tetraploid highbush blueberry.  The cultivar Meadowlark was a result of the first methodology; however, seedling recovery rate using this strategy was low because of low rates of unreduced gamete formation. Hybridization of tetraploid V. arboreum with highbush blueberry was first reported by Lyrene in 2011, and nearly 4,000 backcross seedlings between these hybrids and additional highbush blueberry parents have been made. Two backcross half-sibling populations were selected for further analyses. Population A resulted from a cross between ‘Southern Belle’ and FL 08-467 (V. corymbosum x V. arboreum hybrid), and population B from the cross ‘Abundance’ x FL 08-467. The objective of this research was to study the introgression of vegetative and reproductive traits from V. arboreum into cultivated V. corymbosum germplasm. In both populations, anther awns were present on all individuals that have had flowers, a trait characteristic in V. arboreum and other species within section Batodendron. After two years, survival was dramatically different between the sibling populations, with a survival rate of 80 and 39 percent in population A and B, respectively. In general, the means for vegetative and reproductive traits measured in both backcross populations were less than the recurrent V. corymbosum parent.  For example, the average unpruned height of 72 cm and 70 cm for population A and B, respectively, while the southern highbush parent of population A and B averaged 92 cm (‘Southern Belle’) and 157 cm (‘Abundance’). Two years after planting, 85 and 58 percent of the surviving individuals in populations A and B had flowers. Pollen germination assays indicated a general increase in pollen viability compared to FL 08-467 (27%), with a mean pollen germination rate of 68 percent for both populations A and B.  Fruit maturity for all individuals in both populations was earlier than FL 08-467, and the majority of individuals in both populations reached 50 percent fruit maturity earlier than the V. corymbosum recurrent parent.