APPLICATION OF POLYPLOIDY TO CRANBERRY BREEDING AND BIOTECHNOLOGY

Abstract

The development of polyploid cranberry (Vaccinium macrocarpon) was pursued to exploit the potential for improved fruit size and flower bud set. In addition, polyploidy may provide a method to reproductively isolate transgenic cranberry. Colchicine-induced polyploids were produced in vitro using an inverted stem technique. With a 24-hour treatment of 0.1 to 1 % colchicine, up to 100% of treated microshoots yielded at least one recovered polyploid plant. Polyploid status of the resulting plants was verified by increased stem, leaf, flower and pollen tetrad size. Colchiploids of 'Pilgrim', 'HyRed' (a recently released 'Stevens' x 'Ben Lear' selection) and an individual of mixed 'Ben Lear', 'Stevens' and 'Pilgrim' heritage yielded some fertility. First and second generation inbred and out-crossed progeny of these colchiploids are being evaluated both in the greenhouse and in the field. Initial results indicate some individuals have high levels of self-fertility with large fruit size. A parallel cross between the 'HyRed' colchiploid and a colchiploid of a bar-transformed 'Pilgrim' (tolerant to glufosinate herbicides) has produced some self-fertile progeny. Greenhouse tests have found that limited fruit and seeds can be produced when pollen from these plants was used to pollinate untransformed diploid plants. However, even if herbicide-tolerant triploid plants are produced from diploid/tetraploid crosses, previous triploids of cranberry showed no fertility when self-pollinated or pollinated with pollen from diploid plants. Verification of a lack of fertility in polyploid to diploid crosses would allow the planting of transgenic polyploid cranberry without a high risk of transfer of introduced genes to either conventional cranberry crops or native cranberry populations.