Effect of Explant Origin and Medium Plant Growth Regulators on In Vitro Shoot Proliferation and Rooting of Salvia tomentosa, a Native Sage of the Northeastern Mediterranean Basin

Abstract

Salvia tomentosa is a perennial sage of the maquis vegetation, strongly aromatic, with medicinal and ornamental value. Aiming to facilitate the promotion of the species in the floriculture sector, its micropropagation was studied in terms of the effect of explant origin and medium plant growth regulators on in vitro cultures establishment, shoot proliferation and rooting. Shoot tip or single node explants excised from either in vitro grown seedlings or greenhouse plants grown from cuttings of mature plants were cultured on MS medium supplemented with 6-benzyladenine (BA) at concentrations 0.0–3.2 mg L−1 in combination with 0.0, 0.01 and 0.1 mg L−1 1-naphthaleneacetic acid (NAA). Infections were the biggest problem for establishing cultures from greenhouse plants, while explants from in vitro seedlings showed hyperhydricity, especially the nodal ones. In the multiplication stage, high BA concentrations reduced explant response to produce shoots as well as the length of shoots produced, and although they increased shoot number per responding explant, a large number of shoots were hyperhydrated especially in explants of seedling origin. In general, the highest multiplication indexes, relevant to normal shoots, were given by the hormone-free medium or one with low BA concentration, and by shoot tip explants originated from greenhouse adult plants. The highest rooting rates (70–78%) were achieved either at full or half strength hormone-free or with 0.1 mg L−1 indole-3-butyric acid (IBA) medium. Increasing IBA resulted in an increase in root number, but a decrease in rooting rate and root length. Ex vitro acclimatization was highly successful (92–96%) in peat-perlite (1:1 v/v) substrate. The micropropagation protocol developed will contribute to the promotion of S. tomentosa in the floriculture and pharmaceutical industry and will be a tool for breeding programs targeting high value products.