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Hannah Mathers, The Ohio State University, Horticulture and Crop Science |
The prime biological advantage of container stock over bare-root stock is that the root system is packaged and protected from transplant or mechanical stress. However, cultivar differences in susceptibility to winter injury (Colombo etal., 1984; Johnson and Havis, 1977) and summer injury (Ranney and Peet 1994; Jull etal., 1999) in container-produced stock have been reported (Colombo etal., 1984; Johnson and Havis, 1977). Responses of cultivars to different cultural practices could help us determine methods of predicting the factors that influence root and shoot hardiness and help reduce winter and summer root kill in container nursery production.
With increased production of container-grown nursery crops, root hardiness has become the most important factor determining winter (Johnson and Havis, 1977) and summer (Sibley etal., 1999) survival. Commercial distribution in horticultural crops is usually limited by inadequate top-growth hardiness. However, limits in the commercial range of ornamental production are becoming associated directly or indirectly with lack of root hardiness in winter and lack of heat tolerance of roots in summer. Nursery growers are very interested in knowing more about root winter hardiness and summer root heat tolerance levels, and how to reduce winter and summer root kill in container production.
Lyr and Hoffmann (1967) proposed that the hardiness of shoots is of little importance in determining the natural tree line in northern regions. They suggested that the real factor determining site tolerance for a species is soil temperature. Insufficient root activity as a consequence of low soil temperature would limit northern growth, because plants suffer from desiccation due to high transpiration and limited water uptake.
Heat stress can also be a major limiting factor in the distribution, adaptability, and productivity of wild and cultivated plants. Inhibition of growth or plant decline under supra-optimal temperatures can result from thermal effects on many physiological and developmental processes (Fitter and Hay, 1987). Net photosynthesis (Pn), in particular, is one of the most heat-sensitive processes that govern plant growth (Ranney and Peet, 1994). Heat stress has been shown to be a major limiting factor for plant production and adaptability in containers (Sibley etal., 1999). Seedlings are especially susceptible to high temperature stress (Columbo and Timmer, 1992).