Factors Affecting in Vitro Shoot Proliferation of French Tarragon

Abstract Optimum proliferation of French tarragon ( Artemisia dracunculus L. var. sativa) shoot tips was obtained on Murashige and Skoog salts and vitamins supplemented with 1.8 μM BA, 0.3 μM NAA, and 3% sucrose. Proliferation was maximal after 4 weeks of culture. Proliferation was increased with unpinched shoot tips placed horizontally on the medium. Significantly greater proliferation of shoot tips occurred on medium gelled with Gelrite than with washed Difco Bacto-agar. Medium was gelled with Gelrite (0.5, 1.0, 1.5, 2.0, 2.5, or 3.0 g·liter −1 ) or washed Difco Bacto-agar (2.0, 4.0, 6.0, 8.0, 10.0, or 12.0 g·liter −1 ). Increasing concentrations of both gelling agents decreased proliferation. Stock plant pretreatment (natural daylength or 24-hr supplemental light) did not increase proliferation in vitro. Container size had an effect on shoot proliferation, with shoots in 55 × 70 mm jars having significantly greater axillary shoot length than those in 25 × 150 mm culture tubes or 90 × 95 mm jars and significantly greater number of axillary shoots than those in 25 × 150 mm culture tubes. Long-term subculture of shoots on agar-gelled medium (4 g·liter −1 ) resulted in greater proliferation than those cultured on medium gelled with Gelrite (1.5 g·liter −1 ). Rooting was maximized by placing cuttings >10 mm in length, derived from shoots proliferated on agar-gelled medium, in clear plastic containers in the laboratory. A 5-sec dip of the basal portion of the cuttings in either NAA (537, 2685, or 5370 μM) or IBA (490, 2450, or 4990 μM) increased rooting percentage and root numbers. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine (BA); 1-naphthaleneacetic acid (NAA); l-H-indole-3-butyric acid (IBA).