In Vitro Shoot Proliferation of Minnesota Deciduous Azaleas

Abstract

Shoot tips of azalea ( Rhododendron spp.) accessions 620014, 800057, and 800374 multiplied rapidly when cultured on a Murashige and Skoog (MS) medium modified by reducing concentrations of NH 4 NO 3 and KNO 3 , adding (NH 4 ) 2 SO 4 (to give an : ratio of 1:1), omitting KI, and replacing Na 2 EDTA and FeSO 4 with FeNaDTPA. The organic constituents were in mg/liter: thiamine-HCl, 0.4; myo-inositol, 100; sucrose, 20,000; agar, 6,000; N 6 -(Δ 2 -isopentenyl)-adenine (2iP), 5, 10, or 20 and the pH varied from 4.0 to 6.0 with 5.0 the most effective. An average 4-to-6-fold multiplication rate for the different clones was achieved after 10 weeks culture in this medium and weekly subculturing was unnecessary and detrimental. The harvested shoots could be rooted either in a soilless medium or recultured on fresh medium. The tissue remaining after shoot harvest, when recultured on fresh medium, produced 11–34 shoots for additional harvests at 6-week intervals. Additions of 1 mg/liter indoleacetic acid (IAA) in the medium in such recultures increased the number of usable shoots and improved their quality.