PHYSIOLOGIA PLANTARUM 90' 319-326 1994 Cpynghl © Pl,y.smti,gia Ptmlarum t994 ,, , , , , ISSN (lOil <i3t7 t^ritit^d Ifl Denmark — atl nj^tils rcM'r\>i.'iJ Chilling sensitivity of the frost-tolerant potato Solanum commersonu Marilyn Griffith., Steven R. Boese and Norman P. A. Huner Griffith, M., Boese. S. R. and Huner, N. P A. 1994. Chilling sensitivity of the frost-tolerant potato Solanum commersonii. - Physiol. Plant. 90: 319-326. Frost tolerance has been reported in the shoots of v^ild, tuberiferous potato species such as Solanum commersonii when the plants are grown in either field or controlled conditions. However, these plants can survive as underground tubers and avoid un- favorable environmental conditions altogether. As such, leaf growth and photosyn- thesis at low temperature may not be required for survival of the plants. In order to determine the temperature sensitivity of .5. commersonii shoots, we examined leaf growth, development and photosynthesis in plants raised at 2O/I6°C (day/night). I2/9"C and 512^C. S. commersonii leaves grown at 5°C exhibited a marked decrease in leaf area and in total chlorophyll (Chi) content per leaf area when compared with leaves grown at 20"C. Funhemnore. leaves grown at 5°C did not exhibit the expected decrease in either water content or susceptibility to low-temperature-induced photoinhibition that normally characterizes cold acclimation in frost-tolerant plants. .Nleasurements of CO;-salurated O: evolution showed that the pholosynthetic apparatus of 5°C plants was functional, even though the efficiency of photosystem II photochemistry was reduced hy growth at 5°C. A decrease in the resolution of the M-peak in the slow transients for Chi a fluorescence in leaves grown as 12 and 5°C and in all leaves exposed to high light at 5°C indicated thai low temperature significantly affected processes on the reducing side of QA. the primary quinone electron acceptor in photosystem II. Thus S. com- mersonii exhibits the characteristics of a plant that is limited by chilling temperatures. Although 5. commersonii can tolerate light frosts, its sensitivity to chilling tem- peratures may result in shoot dieback in winter in its native habitat. The plants may avoid both chilling and freezing temperatures by overwintering as underground tubers. Key words - Chilling injury, cold tolerance, freezing resistance, frost tolerance, photoinhibilion, potato, Solanum commersonii. M. Griffith (corresponding aitthorl Dept of Biologv, Univ. of Waterloo, Waterloo, ON N2L SGI, Canada: S.R. Boese, Boyce Tlwmpson Institute. Tower Road, Ithaca, NY 14853, USA: N.P.A. Huner, Dept of Plant Sciences, Univ. of Western Ontario, London, ON N6A 5B7, Canada. . . . growth at 9°C, do not grow at 6°C and are killed imroauction ^^^ freezing at -3°C (P. Chen and Li 1976, Smith 1977, Cuitivars of the domesticated potato 5o/o«um rMi)fro.iHm Hetberington et al. 1983). These plants are unable to L. ssp. tuberoswti grow well in cool, temperate envi- acclimate to cold and do not survive freezing to -3°C ronments. The rate of shoot growth in S. tuberosum is after hardening at 2°C (P. Chen and Li 1976). highest in the temperature range of 20 to 25°C. whereas In order to increase the temperature tolerance of maximum tuber yields are produced at a lower tem- domesticated potatoes, research efforts have beeti perature range of 16 to 20°C (Smith 1977). Despite this focused on wild tuber-bearing potato species to tr\' to relatively low temperature optimum for tuber production, understand the physiological processes and genotypic domesticated potato cuitivars are sensitive to cold tem- variability involved in cold acclimation and freezing peratures. For example, the plants exhibit reduced shoot tolerance (P. Chen and Li 1976, Palta and Li 1979, H, H. Received 8 April, 1993; revised 11 October, 1993 Physiol. Planl. 90. 1994 319