IN VITRO CULTURE OF RANUNCULUS HYBRIDS FOR EVALUATION OF FLOWERING POTTED PLANT LONGEVITY

Postproduction performance of flowering potted plants under interior conditions has become a research area of great interest. The aim of the present work was to verify whether an in vitro system could be used to select Ranunculus for the character of flower and plant longevity. In vitro cultured shoots of commercial varieties of Ranunculus hybrids (by Brea-Italy) "Grazia 404" with white flowers and "Grazia 115" with orange flowers were multiplied on agar medium (Linsmaier and Skoog, 1965) supplemented with kinetin (5 mg/l) and NAA (0.5 mg/l). Filter-sterilised aqueous solutions of 1 mM 1-aminocyclopropane-1-carboxylic acid (ACC) and 1 mM of aminooxyacetic acid (AOA) were dispensed in drops above the explants (100 μl/explant). The explants were cultured in 30 ml glass bottles (4 explants/bottle). The bottles were closed with a double layer of aluminium foil. All cultures were kept at 15°C under cool white fluorescent light (30 μmol m^-2s^-1) for 16 h d^-1. Each treatment was replicated five times and experiments were repeated at least two times. Ethylene was gaschromatographically determined in 1 ml air samples withdrawn from containers sealed for 1 h. The keeping quality of flowering potted plants of the two hybrids were evaluated according to previous experiments (Mensuali-Sodi et al., 1998).

"Grazia 404" evolved in vitro low ethylene amounts and a positive effect on root regeneration was related to ACC-induced ethylene increase while a reduction of the endogenous levels by means of AOA negatively affected lateral shoot proliferation in “Grazia 115” which showed the highest ethylene production during the culture (Fig. 1).

Differences in ethylene emanation were detected between the flowers of the two cultivars (Fig.2). Postproduction longevity of potted plants (8 and 14 days from the marketing stage to 50% of wilted flowers for “Grazia 115” and “Grazia 404” respectively) was inversely correlated with ethylene synthesis. Therefore, ethylene analysis in tissue culture proved to be a possible tool for investigating keeping quality of Ranunculus asiaticus L. which is a flower crop of increasing interest as a pot plant in Italy.