An in vitro microplant bioassay using clonal white ash to test for tall fescue allelopathy

Abstract

Axillary shoots from three selected white ash (Fraxinus americana L.) clones were harvested from in vitro shoot cultures. Roots were initiated by pulsing excised shoots for eight days in the dark in MS medium supplemented with 2% sucrose, 0.7% agar, 5 μM NAA, and 1 μM IBA. Pulsed shoots were transferred to a root elongation medium consisting of 25% MS macrosalts, full-strength microsalts and organics, 1% sucrose, 0.7% agar and no auxins. When roots were visible (6–10 days after transfer to root elongation medium), microplants were transferred to vessels containing the same minimal medium and tall fescue (Festuca elatior var. arundinacea (Schreb.) Wimm.) leaf extracts, leaf leachates, or soil leachates from plant boxes with and without tall fescue sod. After four weeks in vitro, primary adventitious and secondary root growth was reduced by extracts obtained from 5 and 10 g ground leaves per 100 ml of medium. Leachates obtained from 5 g soaked leaves per 100 ml of medium stimulated primary root growth. Soil leachates from bare soil also stimulated primary root growth. Variation was observed among the clones for root growth when plantlets were grown in extracts or leachates from tall fescue.