Variability in the Rate of Cold Acclimation and Deacclimation among Tuber-bearing Solanum (Potato) Species

Two major components of frost resistance are freezing tolerance in the nonacclimated state (growing in normal condition) and capacity to cold acclimate (increase in freezing tolerance upon exposure to chilling temperatures). In addition to these two major components, numerous factors contribute to frost survival. Although the rate of cold acclimation and deacclimation have been recognized as important factors contributing to frost survival, very little information about them is available. Our objective was to determine if there is variability in the rate of cold acclimation and deacclimation among tuber-bearing wild potato species: S. acaule Bitter, S. commersonii Dunal, S. megistacrolobum Bitter, S. multidissectum Hawkes, S. polytrichon Rydb., S. sanctae-rosae Hawkes, and S. megistacrolobum subsp. toralapanum (Cárdenas & Hawkes) Giannattasio&Spooner. Relative freezing tolerance of these species was measured after 0, 3, 6, 9 and 12 days of cold acclimation and after 12 and 24 hours deacclimation. Our results showed there were differences in the rates of cold acclimation and deacclimation among these species. With respect to the rate of acclimation we found these species can be divided into four groups: (i) early; (ii) late acclimators; (iii) progressive acclimators, and (iv) nonacclimators. Likewise, a wide range of cold deacclimation behavior was found. Some species showed as low a loss of 20% of their freezing tolerance, others showed as much as >60% loss after 12 hours of deacclimation. Significant deacclimation was observed in all cold acclimating species after 1 day. These results demonstrate that the rates of cold acclimation and deacclimation were not necessarily related to the cold acclimation capacity of a species. Rapid acclimation in response to low temperatures preceding a frost episode and slow deacclimation in response to unseasonably warm daytime temperatures could be advantageous for plants to survive frost events. Thus, in addition to nonacclimated freezing tolerance and acclimation capacity, it would be very desirable to be able to select for rapid acclimation and slow deacclimation abilities. Results demonstrate that variability for these two traits exists in Solanum L. (potato) species. Two major components of freezing stress resistance are freezing tolerance in the nonacclimated state (normal growing condition) and capacity to cold acclimate (increase in freezing tolerance upon exposure to chilling temperatures) among annual and perennial plant species (Levitt, 1966; Li and Palta, 1978; Palta and Simon, 1993; Sakai and Larcher, 1987; Teutonico et al., 1995). Solanum species vary greatly in both nonacclimated freezing tolerance and cold acclimation capacity (Chen and Li, 1980; Li and Palta, 1978; Palta and Li, 1979; Vega and Bamberg, 1995). Stone et al. (1993) demonstrated that nonacclimated freezing tolerance and the ability to cold acclimate are under independent genetic control in potato. This has now been confirmed in other plants (Arora et al., 1998; Teutonico et al., 1993; 1995). In addition to these two components of freezing stress resistance, many other environmental and plant factors contribute to survival of a plant from a frost episode. Environmental factors such as lowest temperature reached, freezing (cooling) rate, duration of freezing temperatures, ice nucleation temperature, thawing rate and postthaw conditions should be considered. Two important plant factors are hardening status of the plant and plant health and age (Palta and Weiss, 1993). Likewise, the rate of cold acclimation and deacclimation have been recognized as important factors that contribute to frost and winter survival (Palta, 1994; Palta et al., 1997; Pellet, 1997). While nonacclimated freezing tolerance and the acclimation capacity of several plant species have been investigated and in some cases used in genetic and breeding studies (Chen and Li, 1980; Chen et al., 1999a; 1999b; Palta and Simon, 1993; Stone et Received for publication 5 Mar. 1999. Accepted for publication 4 Nov. 1999. The authors thank the Inter-Regional Potato Introduction Station for providing seeds, and colleagues at the Stress Physiology Laboratory, Department of Horticulture and Biotron, Univ. of Wisconsin, for cooperation regarding this work. Support was provided by a USDA/NRI grant 93-37100-8924 to J.P.P. and J.B.B. and by the College of Agriculture and Life Sciences, University of Wisconsin, Madison, Hatch Grant 142C737 to J.P.P. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. Research assistant. Campbell-Bascom professor of horticulture; to whom reprint requests should be addressed. Geneticist. Freezing temperatures cause major yield losses in potato (Solanum tuberosum L.) production in many parts of the world (Estrada, 1978; Li and Palta, 1978; Midmore, 1992; Plaisted and Hoopes, 1989). While in the temperate regions of North America the growing season is limited by frost damage during spring and fall, in the Andean highlands of South America frost can damage the potato crop at any time during the growing season. Unfortunately, only limited success has been achieved by using traditional plant breeding methods for improvement of freezing stress resistance in crop plants (Estrada, 1978; Marshall, 1982; Midmore, 1992; Palta, 1991; Palta and Simon, 1993; Ross and Rowe, 1969; Stushnoff et al., 1984). One of the main reasons is probably because frost and winter survival have been recognized as complex traits, in which many factors may interact (Palta, 1991; Palta and Simon, 1993; Palta and Weiss, 1993; Stushnoff et al., 1984; Teutonico et al., 1993).