MICROPROPAGATION OF AMERICAN CHESTNUT - INCREASING ROOTING RATE AND PREVENTING SHOOT-TIP NECROSIS

A three-step medium sequence was developed for rooting microcuttings o f American chestnut [Castanea dentata (Marsh.) Borkh.]. First, individ ual shoots or clumps of shoots were cultivated on shoot-elongation med ium for 4-8 wk until shoots were 2-3 cm long. The medium consisted of modified Woody Plant Medium, 500 mg/l polyvinylpyrrolidone (MW 40,000) , and 0.89 mu M benzyladenine. Microcuttings were then excised, vertic ally split at the base to approximately 2 mm through the pith, dipped in 5 or 10 mM indolebutyric acid for 1 min, and cultivated on half-str ength Murashige and Skoog basal medium plus 0.2 g/l charcoal for 2 wk. During that time, roots were induced and became visible. Finally, the microcuttings were transferred back to shoot-elongation medium and cu ltivated for 3 wk, allowing growth of both roots and shoots. Using thi s protocol with 3 genotypes derived from one mature tree and two 1-yr- old seedlings, 57 to 73% rooting was obtained with less than 23% shoot -tip necrosis.