Improving micropropagation performances in hydrangea spp.: Temporary immersion shoot culture and induction of morphogenetic events

Hydrangea is a very popular ornamental plant for garden decoration and recently it is also commercialised for the production of cut flower branches. Two selected ornamental genotypes H. quercifolia 'Snow Queen' (SQ)and H. heteromalla 'Snow Cap' (SC)were grown in vitro. Temporary Immersion (TIS)in liquid medium (using RITA vessels)and traditional culture in agarized medium (AM)were compared with the aim to improve plant quality and micropropagation efficiency. The media were composed by MS base medium with BA (0 or 0.25 or 0.5 mg/L). For the genotype SC, the highest multiplication rate (9.14 shoot/ explant/month)and the highest weight (1.04 g)were obtained in TIS with BA 0.25 mg/L. Furthermore, it was possible to obtain the highest explant height (3.74 cm)and the best rooting percentage in TIS in absence of growth regulators (100 percent). For the genotype SQ, a few rooting was obtained also in the presence of BA at any concentration; the number of roots/explant and root length were higher in TIS than in AM. Both rooted and non-rooted plants were acclimatized for 30 days in the glasshouse: all the plants survived and showed good quality. Experiments for callus induction (MS medium+2,4-D 2 mg/L)were attempted with leaves collected from three genotypes: H. involucrata 'Yoraku-tama' (YT), H. macrophylla 'Lemon Wave' (LW)and previously cited SQ. For SQ, several growth regulator combinations were also tested in order to estimate indirect somatic embryogenesis potential: MS medium plus NAA (1 mg/L)or 2,4-D (1, 2 and 4 mg/L); MS medium plus 2,4-D (2 mg/L)and 2-iP (0.8 mg/L); MS medium plus 2,4-D (4 mg/L)and BA (0.02 mg/L)and MS medium plus 2,4-D (0.5 mg/L)and Kin (0.5 mg/L). Trials for direct regeneration were done with MS medium plus BA (1 or 2 mg/L)or Zea (0.5 or 1 mg/L). The highest mean callus weight (9.82 g)was promoted by 1 mg/L of 2,4-D. The media containing BA (1 or 2 mg/L)or Zea (1 mg/L)induced direct shoot regeneration. The regenerants could be easily isolated from the leaf tissue and transferred to multiplication medium.