First Report of Vaccinium arboreum Hybrids with Cultivated Highbush Blueberry

Over several years, we obtained no hybrids after pollinating thousands of flowers of cultivated tetraploid highbush blueberry ( Vaccinium corymbosum L. hybrids, section Cyanococcus ) with pollen from diploid V. arboreum Marshall (section Batodendron , sparkleberry), a drought-tolerant blueberry relative native in the southeastern United States. In an effort to produce tetraploid V. arboreum that could be crossed with highbush blueberry, more than 30,000 seeds were soaked in aqueous colchicine (0.1% to 0.2%) for 24 h or more. The seeds were germinated, and putative tetraploid plants (selected based on morphological characteristics) were grown long enough to obtain pollen for microscopic examination. Twelve selected seedlings that produced unusually large pollen tetrads were used as pollen parents in crosses with more than 40 different tetraploid highbush cultivars and advanced selections. Eighty-six crosses, in which a total of 17,968 flowers were pollinated, gave 1,569 plants that were verified as hybrids after one growing season in the field. Hybrids varied from very weak to quite vigorous, some equaling highbush cultivars in vigor. A few vigorous hybrids were male-sterile, but most had at least some pollen fertility. Of the most vigorous F 1 hybrids, 12 of the most fertile, based on the amount of pollen shed and on the microscopic appearance of the pollen, were backcrossed to highbush cultivars, and 3919 backcross seedlings were obtained. These varied widely in vigor but averaged higher in vigor than their F 1 interspecific hybrid parents.