- THE FLORICULTURE VEGETATIVE CUTTING INDUSTRY 141
yellowing, and defoliation is common (Rapaka 2007b). Epinasty is
an ethylene response where the petioles turn downward, giving a
wilted appearance, but on close inspection the petioles are turgid (van
Dijk and Barendse 1991). On impatiens, epinasty is most frequently
observed when ethephon applications have occurred on the stock
plants in close proximity to the time of cutting harvest. The petioles
of the cuttings begin to bend downward during shipping or in the
propagation environment, resulting in the cuttings becoming dislodged
from the propagation media as the petioles and leaves lift the stem
upward. Leatherwood et al. (2009) noted that ethephon applications on
impatiens can continue to release ethylene after cuttings are harvested
for at least 21 d after application. Higher rates of ethephon increased
postharvest ethylene production, and rinsing of cutting with water prior
to shipping/storage reduced ethylene production by half compared
with treated and unrinsed cuttings. Decreasing storage temperature
from 25◦Cto10◦C also reduced postharvest ethylene production from
ethephon residues.
Ethylene levels increase with increasing temperature and with time
after cutting harvest for many species (Faust and Lewis 2005b; Enfield
2011). Similarly, leaf abscission increases with increasing temperature
for ethylene-sensitive species, such as lantana, poinsettia, and portu-
laca. Rapaka et al. (2008) noted that ethylene levels started out high
when measured at 24 h after cutting harvest and declined with extended
storage up to 72 h. Leatherwood et al. (2016) tested cuttings of 59 herba-
ceous taxa and found that only begonia (Begonia×hybrida), lantana,
and portulaca were sensitive to 1μL⋅L−^1 ethylene, as demonstrated by
rapid leaf abscission within 24 h of treatment. However, this work used
freshly harvested cuttings that likely had high endogenous carbohy-
drate levels, reducing the effect of the exogenous ethylene. As an exam-
ple of interaction of ethylene and carbohydrate levels, stored geranium
cuttings are sensitive to exogenous ethylene, while freshly harvested
cuttings do not appear to be affected by exogenous ethylene (Leather-
wood et al. 2016). Wang and Arteca (1995) identified three genes,GEFE-
1 ,GAC-1,andGAC-2related to 1-aminocyclopropane-1-carboxylate
synthase and oxidase that were not induced by the presence of ethylene,
butGAC-1was induced by osmotic stress. Thus, it appears that fresh
cuttings will not produce endogenous ethylene due to exogenous ethy-
lene application, but will produce endogenous ethylene if subjected to
an osmotic stress. Mutui (2005) also linked ethylene production to leaf
yellowing in geranium.
Ethylene absorbents are commercially available, including potassium
permanganate and activated charcoal. However, the efficacy of these