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  • Author or Editor: Otto J. Schwarz x
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Aqueous diffusates of either Salix erythroflexus (contorted willow) or Robinia pseudoacacia (black locust) were tested as a root-promoting substance on woody plants and Vigna radiata (mung bean). On 8 July 1995 water diffusates were prepared from fresh chopped terminal stems of either willow or locust (680 g) that were steeped in 4 liters of water for 24 hours. Semihardwood cuttings of Chionanthus retusus were double wounded, steeped in either willow, locust, or water for 24 hours followed by a treatment with 3.0% IBA in talc. One additional group of cuttings was treated with 3.0% IBA only. After 75 days, cuttings treated with willow diffusate and IBA produced the greatest number of roots, followed by the locust diffusate and IBA treatments. A similar test using willow diffusate and IBA on softwood cuttings of Chionanthus virginicus resulted in an 80% success rate. A modified mung bean bioassay was used to partially characterize and verify the effects of the diffusates. Diffusates were made from chopped frozen locust or willow terminal stems (10 g/300 ml H2O), stirred for 24 hours. Mung bean cuttings treated with either locust or willow diffusate (5 ml/10 ml H2O) plus 80 ppm IBA produced more roots than IBA or either diffusate alone. A dose response test showed a significant increase in rooting as concentrations increased (H2O,10%, 50%, 75%, and 100%) for both diffusates. Ethyl acetate extractions of each diffusate at pH 3.0 produced more roots than extracts at pH 7.0. A thermal stability test (20 min at 100 °C) on the diffusates showed willow maintained its root-promoting activity, while locust did not.

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Cultivars of flowering dogwood (Cornus florida L.) are commercially propagated by vegetative methods such as rooting cuttings or grafting. The results of these methods can be unpredictable. A reliable method of producing dogwoods through tissue culture would be very useful to rapidly produce many copies of important genotypes with horticulturally important characters such as resistance to diseases. One of the primary difficulties of propagating dogwoods (seedlings only) by axillary bud multiplication has been the low rooting efficiency of the microshoots. Various treatments were tried in order to enhance rooting. Eighty-three percent of microshoots harvested between 5 and 7 weeks and treated continuously with 4.9 micromolar IBA rooted after 4 weeks, whereas <20% of microshoots harvested before 5 weeks and after 7 weeks rooted after 4 weeks of continuous exposure to IBA. Differences were also observed in rooting potentials of microshoots that had reddish brown stems rooting at a higher frequency compared to those that had green stems. We hope to translate this method to the propagation of cultivars and potential new releases.

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