- THE FLORICULTURE VEGETATIVE CUTTING INDUSTRY 137
morning hours. Studies have demonstrated that lantana and portulaca
cuttings harvested just 2 h after sunrise have significantly longer shelf
life than cuttings harvested at sunrise (Rapaka et al. 2007a, 2007b). The
benefits of later harvest time tend to diminish as DLI accumulates dur-
ing the day. When cuttings are low in carbohydrate content, the older
leaves become quickly depleted as the carbohydrates are mobilized to
support the shoot tip and stem base, from which adventitious roots ini-
tiate. This results in leaf chlorosis in the oldest leaves of the cutting
during the first 3–4 d in propagation. In more severe situations, such as
when the postharvest environment is too warm, leaf abscission occurs
before leaf chlorosis is observed.
III. POSTHARVEST HANDLING AND PHYSIOLOGY
A. Physiological Considerations
There are four key issues in postharvest management of cuttings: tem-
perature, water, ethylene, and pathogens. While all of these issues
are important, temperature is most critical during shipping in that it
directly affects respiration rates, water loss, ethylene production, and
pathogen pressure.
- Storage Temperature and Duration.Unrooted cuttings continue to
respire after harvest, with the highest respiration rates occurring shortly
after harvest, then decreasing rapidly, leveling off by 24 h after har-
vest (Enfield 2011). Initial respiration rates and the steady-state rates
increased with increasing temperatures. Enfield (2011) calculated Q 10
values at 5◦C intervals from 10◦Cto25◦C for four species: double impa-
tiens (Impatiens walleriana), New Guinea impatiens, petunia, and poin-
settia. The Q 10 values for 10–15◦C ranged from 2.0 to 3.4 amongst
species. The Q 10 values decreased as temperature increased, so that the
values ranged from 1.3 to 2.1 at 20–25◦C.
The respiration rate needs to be kept as low as possible to extend
the storage life of a cutting while avoiding chilling or freezing injury.
Optimum storage temperature and duration varies with the species. For
chilling-sensitive species, such as New Guinea impatiens and poinset-
tia, the optimal storage temperature is 10◦C (Williams and Ruis 1995;
Ecke et al. 2004). Cold-tolerant species, such as chrysanthemum and
carnation, can be stored as low as 0–1◦C (Altstadt and Holley 1964;
Rajapakse and Kelly 1995; Rajapakse et al. 1996), although commercial
coolers are often set at 2–4.5◦C to avoid freezing damage due to poor