Date of Award
Master of Science
Willard T. Witte
Otto J. Schwarz, Donna C. Fare, Robert M. Augé
Treatments with aqueous diffusates from Salix species and other easy-to-root plants have promoted adventitious rooting of stem cuttings. Aqueous plant diffusates from some difficult-to-root plants have been known to contain rooting inhibitors. This study investigated the use of aqueous diffusates of both contorted willow (Salix xerythroflexuosa RAG.) and black locust (Robinia pseudoacacia L.) as sources of root promoting substances and white fringetree (Chionanthus virginicus L.) as a source of an inhibitor on woody ornamental cuttings. The effects of leaching stem cuttings in water as a pretreatment was also investigated.
Aqueous diffusates of either contorted willow or black locust were tested for root promoting activity on three ornamental plants: holly (Ilex x'Nellie R. Stevens'), Chinese fringetree (Chionanthus retusus Lindl. & Paxt.) and white fringetree, and on mung bean (Vigna radiata L.) White fringetree diffusate was tested as a root inhibitor on holly.
On 8 July 1996, water diffusates were prepared from fresh chopped terminal stems of either locust or willow (680 g for each species) that were steeped in 4 liters of water for 24 hours. One hundred eighty cuttings of holly, Chinese fringetree, and white fringetree were leached in running tap water (1 liter / 15 minutes) for 24 hours. All cuttings were then double wounded. Twenty cuttings of each species were then treated with either 0.0%, 0.8%, or 3.0% IBA in talc. The remaining cuttings were divided into two groups of sixty and placed in either locust or willow diffusate for 24 hours. Within these two groups, twenty cuttings of each species were treated with either 0.0%, 0.8%, or 3.0% IBA in talc. After 61 days, holly cuttings treated with 3.0% IBA produced the greatest mean number of roots but were not significantly different from those treated with locust diffusate followed by 0.8% and 3.0% IBA. After 71 days, Chinese fringetree cuttings treated with locust diffusate followed by 3.0% ffiA produced the greatest mean number of roots but were not significantly different than locust diffusate followed by 0.8% IBA. After 75 days, only one white fringetree cutting treated with locust diffusate followed by 3.0% IBA produced roots. A similar test using willow diffusate followed by 3.0% EBA on softwood cuttings of juvenile white fringetree resulted in an 80% success rate.
A comparison of leached and non-leached cuttings of Chinese fringetree and white fringetree was made to determine their effects on rooting. On 9 July 1996, 60 cuttings of each species were double wounded; of these, 20 cuttings were treated with 3.0% IBA in talc; 20 cuttings received a 24 hour soak in locust diffusate followed by 3.0% IBA in talc; and 20 cuttings received a 24 hour soak in willow diffusate followed by 3.0% IBA in talc. These cuttings were compared to the water-leached cuttings in the previous experiment. After 71 days, non-leached cuttings treated with willow diffusate followed by 3.0% EBA produced the highest mean number of roots and were significantly different from all other treatments.
White fringetree diffusate was prepared by placing ten fresh terminal shoots basal end down in a beaker containing 200 ml of water for 24 hours. Terminal shoots were then discarded. Twenty softwood cuttings of holly were leached in water for 24 hours, double wounded and placed basal end down in the diffusate for 24 hours. Cuttings were then treated with 3.0% IBA in talc. These holly cuttings were compared to holly cuttings treated with either a water control, or locust diffusate, or willow diffusate followed by 3.0% IB A in the first experiment. After 61 days, results showed white fringetree diffusate did not inhibit rooting, and promoted more roots than willow diffusate followed by 3.0% IBA.
A 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 placed in water (10 g / 300 ml H2O), and stirred for 24 hours. Mung bean cuttings treated with either locust or willow diffusate (5 ml / 10 ml H2O ) plus 8 ppm IBA stimulated the production of roots more than IBA or either diffusate alone. A dose response test showed a significant increase in rooting as concentrations increased (0%, 3.3%, 16.7%, 25.0%, and 33.3%) for both diffusates. Ethyl acetate extracts of each diffusates at pH 3.0 produced more roots than extracts at pH 7.0. A thermal stability test (20 min. at 121C) of the diffusates showed locust and willow diffusates/extracts maintained most of their root promoting activity. Silica gel thin-layer chromatography of locust diffusate and pH 3.0 extract showed no detectable color spots when tested for indoles. Willow diffusate showed five detectable color bands, which were pink and rose in character, at Rf 0.05, 0.25, 0.35, 0.68, and 0.93. Willow extract pH 3.0 showed four similarly colored bands at Rf 0.24, 0.38, 0.54, and 0.73. These colors indicated the presence of indoles in the willow diffusate and the willow extract pH 3.0. Willow diffusate fraction four (Rf = 0.68) was the only band that produced significantly more roots than a water control in the mung bean bioassay.
Results of this thesis support the use of easy-to-root plant diffusates followed by IBA in talc to increase rooting of moderate to difficult-to-root plants such as Chinese fringetree and white fringetree. The mung bean bioassay demonstrated root promoting substances existed in both locust and willow diffusate and their pH 3.0 ethyl acetate extracts. Both locust diffusate and locust extract pH 3.0 failed to produce color spots when tested for indoles after thin layer chromatography. Both willow diffusate and willow extract pH 3.0 tested positive for four to five indoles but these were unidentified.
Arena, Mark J., "Influence of water soluble diffusates on root initiation in woody ornamental and Vigna radiata L. cuttings. " Master's Thesis, University of Tennessee, 1997.