Plant Growth Regulation 27: 131–136, 1999. © 1999 Kluwer Academic Publishers. Printed in the Netherlands. 131 Differences between Dianthus caryophyllus L. cultivar in in vitro growth and morphogenesis are related to their ethylene production M.A. Fal ∗ , J.P. Majada, A. Gonz´ alez & R. S´ anchez Tam´ es Lab. Fisiolog´ ıa Vegetal, Dpto. B.O.S., Universidad de Oviedo, C/ Catedr´ atico R. Ur´ ıa s/n, 33071- Oviedo, Spain ( ∗ author for correspondence) Received 7 July 1998; accepted in revised form 8 January 1999 Key words: Dianthus caryophyllus L., ethylene, gas exchange, hyperhydricity, in vitro culture, ventilation Abstract The involvement of ethylene in the vitro development of shoots from nodal segments of two cultivars of carnation (Dianthus caryophyllus L.) was studied. Shoots of cv. Barbaret Antares showed low hyperhydricity in contrast with the high levels showed by cv. Barbaret Tanga when both were cultured in airtight culture vessels. Longer shoots were produced, in both cases, when the rate of gas exchange in the culture vessel was increased by using vented closures, which also prevented hyperhydricity and increased the multiplication coefficient in cultures of Barbaret Tanga. The two cultivars produced ethylene throughout the culture period but, a higher amount was produced during the first, second and fourth weeks in culture by the cultivar more sensitive to ventilation (Barbaret Tanga). Trapping ethylene did not produce any effect on cv. Barbaret Antares but improved the quality of cv. Barbaret Tanga explants, decreasing hyperhydricity and increasing the number of shoots, the length of the main shoot and the multiplication coefficient. These effects were more marked when ethylene was trapped during the first two weeks in culture. Abbreviations: E – rate of gas exchange; MC – multiplication coefficient Introduction Ethylene production by plant tissues during in vitro culture has been associated with many different effects on development [1, 9] indicating that ethylene can stimulate or inhibit the processes considered. High production of ethylene during micropropagation of carnation (Dianthus caryophyllus L.) [7, 10, 24] has been associated with the occurrence of hyperhydricity [3]. In some cases it is not clear if ethylene is a causal factor or an independent signal accompanying hyper- hydricity [10]. However, addition of aminooxyacetic acid to the liquid culture medium of D. caryophyllus L. cv Ceris Royallete, reduced the hyperhydric aspect of the leaves [7], and the abnormal growth detected in sealed culture vessels was prevented by the presence of ethylene absorbing substances [15]. Differences between cultivars of carnation in in vitro growth and morphogenesis, in response to vent- ilation have been observed [13]. These differences could be due to the gaseous microenvironment, mainly to differences in ethylene concentration within culture vessels, or to differences between cultivars in their sensitivity to ethylene. So, the aim of this paper was to study the relationship between ethylene and the response of shoot growth and morphogenesis in two D. caryophyllus L. cultivars (Barbaret Antares and Barbaret Tanga) cultured in vitro under different ventilation conditions. Materials and methods Plant material and culture conditions Nodal segments 1 cm long with a pair of leaves, were aseptically excised from in vitro grown shoots of D. caryophyllus L. cv Barbaret Antares and cv. Barbaret Tanga and cultured on MS basal medium [17] plus