Abstract:
Nursery plants are often harvested, stored, and shipped bare-root for easier
and more economical handling. Some species of woody and herbaceous
perennials are less tolerant of postharvest handling than others. Desiccation
stress during the handling of bare-root plants has been identified as a major
problem contributing to poor survival and regrowth. In these studies, the effects
of cold storage, simulated postharvest handling stress, and the use of antidesiccant
treatments to improve the survival of bare-root deciduous trees and herbaceous
perennials after postharvest handling were examined.
Among the five species of deciduous seedling trees stored bare-root for up
to six months at temperatures ranging from +4 to -4C, Norway maple (Acer
platanoides L.) and European mountain ash {Soibus aucuparia L.) were most
tolerant, red oak (Quercus mbra L.) was slightly less tolerant, and paper birch
(Betula papyrifera Marsh.) and Washington hawthorn (Crataegus phaenopyrum
Medic.) were least tolerant of cold storage. Species which stored well had
developed deeper dormancy and lower xylem water potential during the winter
season than less tolerant species. The performance of all five species after
storage decreased with increasing length of storage time at all four test
temperatures. Survival and regrowth was better when plants were stored at 0, -2,
or -4C than at +4C. Desiccation of stem tissues at +4C might be one factor
causing poor performance of plants stored at this temperature. Survival, root
regrowth, and % budbreak were only slightly lower than pre-storage levels when
Norway maple, red oak, European mountain ash, and paper birch were stored at -
4C, and when Washington hawthorn was stored at -2C.
Desiccation tolerance of three bare-root deciduous hardwood species was
determined from Sept. 1990 through Apr. 1991. Among the three species tested,
red oak was most tolerant to desiccation followed by Norway maple and then
Washington hawthorn. Maximum desiccation tolerance of all three species
occurred during the January and February harvests.
The feasibility of using film-forming compounds to reduce water loss from
bare-root deciduous trees during postharvest handling was also examined. Of the
twenty compounds tested, 'Moisturin' was most effective in reducing water loss
during desiccation stress and improving survival and plant performance during reestablishment
in laboratory, greenhouse, and field studies. 'Moisturin' treated
plants lost up to 80% less water than untreated plant materials. Washington
hawthorn seedlings treated with 'Moisturin' before severe desiccating conditions
had the highest survival, lowest dieback/plant, and the highest root growth ratings.
Field-grown herbaceous perennials were harvested in late June and stored
bare-root for five weeks in cold storage with different antidesiccant treatments.
Iris sibirica and Iris ensata plants had similar rates of water loss during storage, but
I. sibirica plants died after replanting. Hosta and Hemerocallis plants
approximately 15 and 40%, respectively, less water than the Iris species during
storage. For the antidesiccant treatments, plants which were wrapped in
polyethylene or sealed in polyethylene bags lost approximately 25 and 90%,
respectively, less water than controls. Regrowth quality was significantly better for
Hemerocallis and Hosta plants which were bagged. Treatment of these plants with
'Moisturin' reduced water loss slightly, but did not improve survival. Reducing
water loss from I. sibmca plants during storage had little effect on improving
survival, indicating that problems other that desiccation stress during storage
might be more important for successful re-establishment of these plants.
Species which are more tolerant to desiccation, or which lose water at a
slower rate, were better adapted to postharvest handling. The use of a new
antidesiccant 'Moisturin' and sealing plants in polyethylene bags were effective in
reducing the rate of water loss and improving the survival of bare-root deciduous
trees and herbaceous perennials, respectively during postharvest handling.