Drought Conditioning Influences Adventitious Rooting of Select Shrub Stem Cuttings
Lindsey Fox and Thayne Montague
Numerous chemical compounds (plant growth regulators) have been found to promote adventitious rooting on stem cuttings. However, even with plant growth regulators (PGRs) stem cuttings of many plant species are difficult to root. Cultural practices (light levels, media temperatures, air temperatures, misting, etc.) on stock plants and during rooting have also been found to influence adventitious rooting of cuttings. This research investigated the influence of drought conditioning (DC) stock plants and an auxin-based PGR on adventitious root formation of two ornamental plant species. Species selected were firebush (Hamelia patens) and Fraser photinia (Photinia × fraseri). Plants were purchased May 2002 in 3.7-liter containers and maintained under normal nursery conditions. On 15 July 2002 plants were brought into a glass greenhouse and DC irrigation treatments initiated. Treatments included: irrigation every day (no DC), irrigation every other day (medium DC), and irrigation every fourth day (high DC). Plants were subjected to DC treatments for 16 consecutive days. Following DC treatments, all plants were irrigated and left overnight. Terminal stem cuttings were taken the following day. Cuttings were 15.2 to 20.3 cm (6.0 to 8.0 inches) long and leaves were removed from the basal 8.0 cm of each cutting. Hormodin 2 (0.3% auxin talc formulation) was used as the PGR. Cutting treatments included: no DC + no PGR, no DC + PGR, medium DC + no PGR, medium DC + PGR, high DC + no PGR, and high DC + PGR. One cutting was placed into a
fiber pot and for each species, five cuttings of each treatment were placed in a fiberglass flat and each flat was replicated three times (total of 30 cuttings for each species × treatment combination). Flats were placed under intermittent mist and heating pads were used to maintain medium temperature near 32 °C (90 °F). On 22 Aug. (firebush) and 17 Oct. (Fraser photinia) cuttings were evaluated for rooting percentage, number of roots for each plant, length of longest root, and visual rating (0 = no rooting and 10 = profuse rooting). Analysis of variance suitable for a randomized complete block design was used and treatments means were separated by LSD. For firebush (considered an easy to root species), rooting percentage was greatest for all treatments except medium DC + no PGR and high DC + no PGR. Mean number of adventitious roots for each cutting was greatest for cuttings that had PGR treatments. Mean adventitious root length was greatest for cuttings with no DC + PGR and least for cuttings with medium DC + no PGR. Mean visual root ratings followed a similar trend as mean root length. Fraser photinia (considered a difficult-to-root species) mean rooting percentage was greatest for cuttings with high DC + no hormone and least for cuttings with no DC + PGR, medium DC + no PGR, and high DC + PGR. Mean number of roots for each cutting and mean root length were greatest for cuttings with medium DC + PGR. Mean visual root rating was greatest for cuttings treated with medium DC + PGR. Results indicate DC used in combination with PGRs may increase adventitious rooting of some ornamental plant species.
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