In Vitro Induction and Primary Evaluation of Octoploid Plants in Saskatoon Berry (Amelanchier alnifolia Nutt.)

Polyploids of many species of horticultural plants are widely used in breeding programs since they are characterized by vigorous growth, larger organs, and greater resistance to biotic and abiotic stress. Saskatoon berry (Amelanchier alnifolia Nutt.) is in a form of diploid (2n = 2x = 34) and tetraploid. So far, no reports on induction of polyploidy in this species have been found. The aim of the study was to obtain Saskatoon berry octoploids with the use of in vitro shoot cultures. Shoots of the tetraploid of Canadian cultivars 'Martin' and 'Smoky' derived from in vitro cultures were used for induction of chromosome doubling. The shoot explants were incubated in a multiplication medium with the addition of one of the following antimitotics: colchicine, trifluralin, oryzalin or amiprophos methyl (APM) for two weeks (six days in the darkness and then eight days under a 16-h photoperiod). Then, the shoots were transferred to the multiplication medium without antimitotics and propagated in vitro by two subcultures. Octoploids were selected based on flow cytometry. Trifluralin showed the most phytotoxic effect. Six octoploids were obtained, four for 'Martin' after treatment with 250 mg L-1 of colchicine and two for 'Smoky' following the treatment with 5 mg L-1 of APM. All obtained octoploid individuals were multiplied and the level of ploidy was re-examined by flow cytometry and chromosome counting, which confirmed their octoploid genotype (2n = 8x = 136). They are probably the first octoploids of the genus Amelanchier in the world. The newly obtained octoploids were rooted in vitro, acclimatized to ex vitro conditions and grown in a greenhouse. Octoploids grew very slowly and showed a tendency to premature dormancy, which was manifested by inhibition of growth. In octoploid plants, the stomata were significantly larger and the number of stomata per 1 mm(2 )of leaf area was lower, compared to the tetraploid counterparts.