|BALLINGTON, JAMES - North Carolina State University|
Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/7/2017
Publication Date: 10/6/2017
Citation: Ehlenfeldt, M.K., Ballington, J.R. 2017. Prolific triploid production in intersectional crosses of 4x Vaccinium corymbodendron Dunal (section Pyxothamnus) by 2x section Cyanococcus species. Euphytica. https://doi/org/10.1007/s10681-017-2027-9.
Interpretive Summary: Blueberries in commercial production represent three primary blueberry species, represented by lowbush, highbush, and rabbiteye blueberies. Significant use has been made of wild blueberry species, especially in the development of southern highbush varieties. V. corymbodendron, a species originally collected in alpine locations in Peru, but also found in Colombia, Venezuela, and Guyana, has features of notable value to conventional blueberry cultivation, among them, concentrated flowering and suitability for mechanical harvesting, as well as likely floral cold hardiness. Initial hybridization experiments between V. corymbodendron which has four sets of chromosome with a range of species having two sets of chromosomes found virtually all hybrids were triploids (having three sets of chromosomes). Such hybrids are rare in blueberry. The hybrids expressed very low fertility, nonetheless, several were used successfully in crosses. Understanding these crossing relationships may open new avenues for exploitation of this and other exotic species for blueberry improvement. These hybrids will be of value to blueberry breeders and to the commercial blueberry production industry.
Technical Abstract: V. 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 virtually 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 (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.