Micropropagation and ex situ conservation of three rare and endemic ornamental Dianthus taxa (Caryophyllaceae)

Abstract

The conservation of numerous plant taxa of spontaneous flora which are endemic, endangered, vulnerable or rare is realized by in situ or ex situ methods. The biotechnology of in vitro cultures is an important part of these programmes. The aim of the study was the in vitro proliferation and rooting reactivity of three rare species of wild origin carnations (Dianthus genus) with limited distribution and conservation priority: the endangered and rare-restricted D. ingoldbyi (a local endemic from some regions of the Balkan peninsula, Turkey and North-East Greece), the Cretan local Greek endemic, range-restricted and endangered D. juniperinus subsp. bauhinorum, and the least concern or near threatened range-restricted Greek endemic of the Cyclades, Peloponnese and Ionian islands D. fruticosus subsp. occidentalis. In all Dianthus taxa, using shoot-tips as explants and NaClO as the sterilizing agent (2%) a 50-90% sterilization rate was reported. In D. fruticosus subsp. occidentalis (2 shoots/explant 18.78 mm long) a 100% shoot regeneration rate was registered in the presence of the combination of 0.25 mg/L BA, 0.1 mg/L IBA, and 0.1 mg/L GA3 (5 weeks), whereas D. juniperinus subsp. bauhinorum responded best (100% shoot proliferation, with 3.5 shoots, 22.38 mm long) in the presence of 0.5 mg/L BA + 0.1 mg/L NAA (4 weeks). Dianthus ingoldbyi yielded better performance i.e. 5.5 shoots/ explant 34.18 mm long but with a 28.33% hyperhydricity rate in the initial MS medium enriched with 0.25 mg/L BA, 0.1 mg/L IBA, 0.1 mg/L GA3 as well as in the PGR-free MS medium during the subsequent shoot multiplication stage (100% shoot proliferation, 3.88 shoots 62.09 mm long, absence of hyperhydricity) (5 weeks). Among the three tested auxins (IBA, NAA, IAA), NAA at 0.25 mg/L induced better rooting (100%, 9.75 roots/rooted microshoot 32.47 mm long) in D. juniperinus subsp. bauhinorum (5 weeks), whereas both D. fruticosus subsp. occidentalis (5.48 roots 20.51 mm long) and D. ingoldbyi (6.89 roots 23.93 mm long) showed the best rooting results (100%) on the MS auxin-free medium (4 weeks). After 3-4 weeks, the survival rates of the ex vitro acclimatized plants in the heated greenhouse mist in a peat: perlite (1:1 v/v) substrate were 100%, 90% and 50% for D. ingoldbyi, D. fruticosus subsp. occidentalis, and D. juniperinus subsp. bauhinorum, respectively.