Wall germander is a woody subshrub in the Lamiaceae family native to the Mediterranean Basin. It bears small, light pink flowers in early summer and is commonly grown as a low hedge or groundcover in mild climates (Armitage, 1997; Brickell and Cathey, 2004). Wall germander can be propagated from cuttings without adding auxin, but rooting is more rapid and uniform with the application of 1000–3000 ppm IBA (Dirr and Heuser, 2006).
Auxins are a class of plant growth regulators that affect many plant physiological processes, including rhizogenesis. The endogenous auxin indole-3-acetic acid plays the most noteworthy role, although there are several other endogenous auxins including IBA, and many synthetic analogs with auxinic effects (Taiz et al., 2015). For many years, talc- or water-diluted IBA formulations applied to the basal end of cuttings have been used in the nursery industry to induce rhizogenesis in cuttings for plant propagation (Hartmann et al., 2011).
The application of dilute liquid auxin directly to the foliage of cuttings could reduce production costs, increase efficiency, and simplify compliance with workplace safety regulations (Blythe et al., 2004a). Workers exposed to even low concentrations of aerosolized talcum powder are legally required to wear personal protective equipment including a respirator, gloves, protective eyewear, long sleeves, and long pants (Brooker Chemical Corp., n.d.; OHP, Inc., 2010). The efficacy of foliar spray application of IBA to promote rhizogenesis has only been reported for a few species and the method has had mixed results (Blythe et al., 2002; Drahn, 2007). The method has been effective in the propagation of chrysanthemum (Chrysanthemum pacificum) and forsythia (Forsythia ×intermedia ‘Lynwood Gold’) cuttings but has been less successful with crape myrtle (Lagerstroemia indica), glossy abelia (Abelia ×grandiflora), and weeping fig (Ficus benjamina) cuttings (Blythe et al., 2003b, 2004a; Kroin, 1992). Commercial growers might consider foliar IBA rates and species efficacy proprietary information, leading to anecdotal accounts that lack data. Furthermore, suppliers of unrooted cuttings might make recommendations for foliar auxin application without providing supporting data (Yoder Brothers, 2004). At present there is no detailed research on the effects of foliar auxin application in many plant species, including wall germander or any other species in the Lamiaceae. The objective of this study was to evaluate the foliar auxin spray method for rooting wall germander cuttings.
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