146 J.E. FAUST, J.M. DOLE, AND R.G. LOPEZ
improved the appearance of unrooted poinsettia cuttings held for 1 or
3 weeks at 5◦C, but had the greatest effect when cuttings were held for
only 1 week. Similarly, geranium cuttings stored for 2, 4, or 6 weeks
under low-pressure storage had higher visual ratings than those stored
at ambient atmospheric pressure. It should be noted that in this study
the low-pressure-storage treatment also included passing the recirculat-
ing air through an ethylene scrubber; ethylene levels were not recorded
in the experiment and the ethylene scrubber may have played a role
in the positive results of low-pressure storage. With long-term storage,
up to 11 weeks for hibiscus ‘Moesiana’ cuttings, no ethylene was found
for either the ambient- or low-pressure storage and was eliminated as
a potential factor (Kirk et al. 1996). However, with low-pressure stor-
age, stomata remained open, resulting in desiccation. Hibiscus cuttings
could be successfully stored for only 3 weeks using low-pressure stor-
age (2 kPa), but for up to 5 weeks using ambient-pressure storage.
When plant material is placed in an enclosed environment, such as a
plastic bag, respiration produces carbon dioxide that can accumulate to
toxic levels and/or oxygen can be depleted, resulting in anaerobic con-
ditions (Leatherwood 2008). Respiration continues until the plant mate-
rial is substantially deteriorated. However, altering the composition of
the atmosphere around the product by increasing carbon dioxide and
reducing oxygen concentrations can depress respiration, production of
ethylene, and delay decomposition. Altered atmospheres can be created
either “actively,” in which the product is stored in a predetermined
mixture of oxygen and carbon dioxide, or “passively” using specialized
packaging films that affect the diffusion of gasses. For cuttings, the addi-
tional benefit of modified atmosphere storage is that reduced respiration
will maintain the amount of carbohydrates available for rooting. Using
modified atmosphere storage, New Guinea impatiens, geranium, and
poinsettia cuttings held in 1:20 oxygen:carbon dioxide (%) generated
higher concentrations of ethylene than any other treatments, which
ranged from atmospheric air (21% oxygen:0.03% carbon dioxide) to
1%:20% oxygen:carbon dioxide (1:20) for 7 d at 20◦C (Leatherwood
2008). Poinsettia and geranium cuttings stored in the 1:20 treatment
were severely damaged at the end of storage. Cuttings of all species
stored 10:10, 10:5, 5:10, 5:5 oxygen:carbon dioxide (%) generated less
ethylene compared to the atmospheric control. Cuttings stored in 10:5
performed best during propagation, with the lowest amount of leaf
yellowing or abscission.
Crawford (2013) studied passive modified-atmosphere storage and
noted that three different plastic bags with a range of oxygen perme-
ability rates had only modest effects on performance of argyranthemum