Effect of alcohol solvents and IBA on rooting of select woody ornamental and herbaceous plants

Alcohol toxicity based on solvent has been reported to be a problem in the propagation of certain woody ornamental plants. The purposes of this study were: (1) to evaluate the phytotoxicity of several alcohol solvents; (2) to evaluate the effect of ISA levels on several varieties of woody and herbaceous plants; (3) to determine whether or not the alcohol solvents could reduce the rate of IBA oxidation in solution. Ethanol, polyethylene glycol 400, propylene glycol and isopropanol were selected as solvents for IBA. Terminal cuttings of several varieties of herbaceous and woody plants suspected to be alcohol sensitive were treated with a five-second quick-dip of the alcohol IBA solutions. After the cuttings were rooted and evaluated, no meaningful significant difference on rooting was found between the four alcohols tested, and no phytotoxicity was observed on any of the plant varieties tested. The primary influence on rooting was the concentration of IBA in the quick-dips. A mung bean hypocotyl rooting bioassay was developed to study the effect of the alcohol solvents in the reduction rate of IBA oxidation in solution. Analysis of variance showed a significant influence of IBA, solvent, and age on root number of rooted mung bean hypocotyl cuttings. All interactions of these factors other than the IBA and age interaction were significant as well. Duncan's New Multiple Range Test showed that one year old solutions of 1 and 10 ppm IBA in polyethylene glycol 400 produced significantly fewer roots per experimental unit than did freshly prepared solutions of 1 and 10 ppm IBA in PEG at the 1 percent level of significance. The results indicate that ETOH, PG and IPA reduce the oxidation rate of IBA in solution compared to PEG, and that no auxin activity is lost after one year in solution. Visual observation showed differences in color among freshly prepared and aged 1000 ppm IBA solutions in ETOH, PEG, PG and IPA. Spectro- photometric analysis was used to analyze the differences among these IBA solutions. Spectrophotometric analysis revealed a large peak at approximately 225 nm in all of the freshly prepared IBA solutions. Aged solutions of IBA in ETOH, PG and IPA produced lower peaks than the comparable freshly prepared solutions at 225 nm, whereas the aged IBA solution in PEG produced no peak whatsoever at 225 nm. The absence of a peak at 225 nm in the aged IBA solution in PEG and the lower peak for PG corresponded with the reduced rooting in the mung bean bioassay.