S04 - Session P1 - New Tools II - Extending the genetic variability of the sweet cherry (Prunus avium L.) by in vitro polyploidization

Authors: Aleksandra Trzewik *, Danuta Kucharska, Ma322gorzata Podwyszy324ska, Monika Marat

The sour cherry ( Prunus cerasus ) and the sweet cherry ( Prunus avium ) are important species of fruit plants. Hybrids of sour cherries and sweet cherries produce very tasty fruits. The sweet cherry is a diploid (2n = 2x = 16) and sour cherry is a tetraploid (2n = 4x = 32). Their natural hybrids are triploids. Such genotypes, however, are characterized by the low fertility and productivity. To obtain fertile tetraploid hybrids, it is necessary to double the number of chromosomes in the sweet cherry cultivars selected for crossing with sour cherry. The aim of the study was to develop a polyploidization method for sweet cherries. The in vitro shoot cultures of 'Merton Premier' and 'Liliana' sweet cherry cultivars were used for the study. Shoots were multiplied on standard propagation medium containing MS salts, 0.8 mg L -1 BAP, 1 mg L -1 GA 3 and 0.01 mg L -1 IBA. In order to induce chromosome doubling, the shoots were treated with antimitotic agents such as colchicine, trifluralin, oryzalin, and amiprophos methyl (APM) by incubation on the antimitotic containing media for four weeks (two weeks in the dark then in the 16-h light). Phytotoxicity of the antimitotics was assessed four weeks after treatments. Then the shoots were subcultured every four weeks on standard multiplication medium. Eight weeks after antimitotic treatments, the leaf samples were collected from regenerants and analysed by flow cytometry (FCM). The antimitotics did not have a strong phytotoxic effect on the in vitro shoot cultures of sweet cherries. In all polyploidization treatments, some shoots survived and undertook multiplication. A total of 398 shoots were tested by FCM. Two homogeneous tetraploids and 113 mixoploids were detected. From the mixoploids that were characterised, based on FCM analysis, by a higher proportion of tetraploid genome, three additional homogeneous tetraploids were selected following further mixoploid shoot multiplication and FCM analysis. Finally, two and three tetraploids were obtained for 'Liliana' and 'Merton Premier', respectively, after the treatment with trifluralin (50 and 100 mg L -1 ). The shoots of tetraploids differed significantly compared to their diploid counterparts. Tetraploids were dark green in colour, they had shorted and thicker shoots, and larger leaves.