Prolific triploid production in intersectional crosses of 4x Vaccinium corymbodendron Dunal (section Pyxothamnus) by 2x section Cyanococcus species

Abstract

Vaccinium corymbodendron (section Pyxothamnus) is a tetraploid species native to high-altitude locations in Peru, Colombia, and Venezuela, and is of considerable interest because it flowers at times when nighttime temperatures drop below freezing. It also is notable for its profuse, concentrated flowering, and monopodial plant structure both of which may be useful in breeding for mechanical harvest. Initial hybridization experiments of 4x V. corymbodendron with a range of 2x species from section Cyanococcus found all hybrids were triploids. 4x × 2x crosses in conventional Vaccinium germplasm typically result in an almost absolute block of triploid offspring. The triploids expressed very low fertility as both males and females, nonetheless, several were used successfully in crosses. A single hybrid from 4x V. corymbodendron × 2x V. vitis-idaea L. (lingonberry, section Vitis-idaea) 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 and other tertiary gene pool germplasm.