Breeding and Hybridization of Vaccinium corymbodendron Dunal: Unexpected Triploidy

V. corymbodendron (Section Pyxothamnus) is a tetraploid species native to high-altitude locations in Peru, Colombia, and Venezuela. This species is of considerable interest because it flowers at times when nighttime temperatures drop below freezing, and it is also notable for its profuse flowering, and monopodial plant structure. Initial hybridization experiments that crossed V. corymbodendron to a range of diploid material found that despite a strong triploid block in conventional Vaccinium germplasm, virtually all hybrids generated from V. corymbodendron x 2x species were triploids. Although the triploids expressed low fertility as both males and females, several were used successfully in crosses. A single hybrid using 2x V. vitis-idaea (lingonberry) as the male was unexpectedly found to be tetraploid and was highly fertile. These crossing results suggest V. corymbodendron either possesses no ploidy barriers to hybridization, or possesses genomic dosage factors that differ from Section Cyanococcus species. Understanding these crossing relationships may open new avenues for exploitation of this germplasm.