Abstract
In response to commercial propagators’ concerns regarding potential phytotoxicity of alcohol used in root-promoting solutions of auxin for cutting propagation, three studies were conducted using stem cuttings of seven herbaceous and woody plant taxa. In study 1, cuttings received a basal quick dip in solutions prepared with indole-3-butyric acid (IBA; as water-soluble salts) at three rates (0, 1000, or 2000 ppm) in combination with isopropyl alcohol at three rates (0%, 25%, or 50%). In study 2, cuttings received a basal quick dip in solutions prepared with IBA + 1-naphthalene acetic acid from a liquid concentrate at three rates (0 + 0, 500 + 250, or 1000 + 500 ppm) in combination with isopropyl alcohol at three rates [minimum required to maintain the auxins in solution (0%, 7.5%, or 15%, respectively), 25%, or 50%]. In study 3, cuttings were treated with a 5-second, total immersion in solutions prepared with IBA (as water-soluble salts) at three rates (0, 100, or 200 ppm) in combination with isopropyl alcohol at three rates (0%, 25%, or 50%). Stem cuttings of African wormwood (
Artemisia afra
), Mammoth™ ‘Yellow Quill’ chrysanthemum (
Chrysanthemum
×
hybridum
), ‘Mary Helen’ geranium (
Pelargonium
×
hortorum
), ‘Coral’ impatiens (
Impatiens
×
hybrida
), ‘New Gold’ lantana (
Lantana camara
), weeping fig (
Ficus benjamina
), and star jasmine (
Trachelospermum jasminoides
) were used in all three studies. Cuttings of any one taxon were collected in separate batches for each study at an appropriate time of year for that taxon. All cuttings were rooted under intermittent mist in a greenhouse. Rooted and unrooted cuttings were assessed for phytotoxicity as observable stem necrosis (“stem burn”) and leaf necrosis (“leaf burn”). In study 1, the nine treatments did not cause any stem or leaf necrosis on cuttings of the seven taxa. In study 2, the nine treatments did not cause any stem or leaf necrosis on cuttings of any of the seven taxa, except for limited stem necrosis on some cuttings of ‘New Gold’ lantana. In study 3, the nine treatments did not cause any stem or leaf necrosis on cuttings of Mammoth™ ‘Yellow Quill’ chrysanthemum, ‘Coral’ impatiens, or weeping fig but caused stem and leaf necrosis on cuttings of African wormwood, ‘Mary Helen’ geranium, and ‘New Gold’ lantana. No stem or leaf necrosis was observed on cuttings of star jasmine; however, solutions containing 50% alcohol (regardless of IBA rate) increased the percentage of dead cuttings of this taxon compared with solutions containing 0% or 25% alcohol. Overall, use of alcohol-containing solutions of auxin applied with a basal quick dip resulted in no or little phytotoxicity on stem cuttings, whereas cutting response to total immersion in alcohol-containing solutions of IBA varied by taxon from no to severe phototoxicity.