Production and evaluation of a synthetic hexaploid in blueberry

One synthetic hexaploid clone (Hex-DT) was produced by placing 3-node stem cuttings of triploid blueberry clone FL 81-19 [V. corymbosum (4x) x V. elliottii (2x)] on blueberry micropropagation medium supplemented with 0.6% agar, 24.6 μM 2ip, and 0.02% colchicine. The most effective chromosome-doubling was achieved with colchicine over 6 days, for 6 h per day. Pollen stainability and pollen germination in the hexaploid Hex-DT were 42.2% and 13.0%, respectively, versus 87.9% and 50.9% in Hex-F1, a hexaploid F1 hybrid between V. ashei (6x) x FL 81-19 (3x). The number of seedlings produced per flower pollinated with V. ashei pollen in Hex-F1 was similar to the number obtained from V. ashei x V. ashei crosses, and at least twice the number produced by Hex-DT pollinated with V. ashei pollen. Observed mean numbers of univalents, bivalents, trivalents, quadrivalents, and hexavalents per PMC at metaphase I in Hex-DT were 1.29, 20.30, 2.31, 2.63, and 2.11, respectively. No univalents were observed in Hex-F 1, but the mean frequencies of bivalents, trivalents, quadrivalents, and hexavalents were 29.14, 0.87, 1.91, and 0.58, respectively. Irregularities such as chromosome lagging and unequal disjunction were observed at both anaphase I and II in Hex-DT. Anaphases I and II in Hex-F1 were normal with few irregularities. The high fertility observed in Hex-F1 suggests a high level of homology among the three species contributing to its makeup.