Effect of substrates, poly-tunnels and growing conditions on hardening of in vitro raised carnation plantlets

Micropropagated plants are very tender and delicate owing to high humidity in the culture vessels (80–100%), controlled temperatures (typically 25 ± 2°C), low light intensity and hetero- or mixo-trophic mode of propagation under which they are normally grown. Due to lack of protective mechanisms like waxy cuticle, stomatal regulation, leaf hairs, reduced differentiation of palisade cells and large intercellular spaces, they become vulnerable to dessication once exposed to the ambient conditions. The physiological and anatomical characteristics of the micropropagated plants necessitate that they should be gradually acclimatized or hardened to withstand the ambient environment. Thus, an experiment was carried out to study the effects of substrates, poly-tunnels and growing conditions on the establishment and growth of the in vitro regenerated plantlets of carnation. Seven different substrates viz., vermiculite, cocopeat, sand, soil, vermiculite + cocopeat (1:1), vermiculite + sand (1:1) and vermiculite + soil (1:1) were used as the ex vitro growing media. The plantlets were kept under poly-tunnels made of polyethelene of three grades of 200, 140 and 50 micron thickness for two weeks. The plantlets, under the polytunnels, were placed in three different conditions viz., at room temperature, in building courtyard (full shade) and under agro-shade net (75%). Out of the seven substrates, maximum plant height, number of leaves and survival percentage were recorded in the substrate vermiculite followed by cocopeat, while, among the poly-tunnels, 140 micron thickness showed better growth and survival of the plantlets. Of the three growing conditions, the building courtyard and room temperature proved to be better for hardening of the in vitro raised plantlets.