Physiological and cultural conditions affecting postharvest handling of bare-root nursery plants

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.