In vitro tetraploid induction of the blackcurrant (Ribes nigrum L.) and preliminary phenotypic observations

The aim of this study was to develop an in vitro polyploidisation method for the breeding of new improved cultivars of blackcurrant (Ribes nigrum L.). The Polish blackcurrant cultivars `Gofert' and Tolares' were used for the experiments. For polyploidisation, shoot explants were incubated for six days in the dark on a modified Murashige and Skoog medium supplemented with 4.5 mu M 6-benzylaminopurine (BAP), 0.3 mu M gibberellic acid (GA(3)) and 0.5 mu M indole-3-acetic acid (IAA), containing one of the following antimitotic agents: colchicine, trifluralin, oryzalin or amiprophos methyl. The strongest phytotoxic effects of antimitotic agents were observed for trifluralin (all the explants died). Tetraploids were obtained for both cultivars: 21 for 'Gofert' and 12 for 'Polares', respectively. The higher efficiencies of tetraploid induction were recorded with oryzalin (5 mg L-1), 26.3% and 28.6% for 'Gofert' and 'Polares', respectively; 25.9% with colchicine (125 mgL(-1)) for 'Polares' and 9.3% with amiprophos methyl (5 mgL(-1)) for 'Gofert'. In addition, only six (2.4%) homogeneous 'Gofert' tetraploids were selected directly. Instead, the high percentage (30.1%) of mixoploids was detected in this cultivar. All mixoploid shoots were subcultured twice. An additional 15 homogeneous tetraploids were selected based on the flow cytometry analysis from the mixoploid shoot cultures, but only from among those with a predominance of the tetraploid genotype. The polyploidisation efficiency was on average 8.4% for 'Gofert` and 9.2% for Polares'. In vitro growth and shoot multiplication of newly obtained tetraploids were very poor in the presence of BAP. Therefore, in order to obtain tetraploid shoots capable of rooting, shoot multiplication was optimized by application of 6-(3-hydroxybenzylamino)purine (meta-topolin). Replacement of BAP with meta-topolin in the medium allowed faster multiplication of the newly obtained tetraploids, which were then rooted in vitro and grown in a greenhouse. The tetraploids differed phenotypically from their diploid counterparts. Detailed measurements were done for 'Gofert' after six months of growing plants in vitro. Compared to diploid plants, tetraploids had shorter shoots, they contained fewer leaves, their leaf shape was different and chlorophyll index was higher.