COMPARISON OF THE FROST RESISTANCE OF BARLEY (HORDEUM VULGARE L.) LANDRACES OF UPLAND ETHIOPIA USING ELECTROLYTE-LEAKAGE AND CHLOROPHYLL FLUORESCENCE

Abstract

Barley is the most important crop in the highlands of Ethiopia at altitudes above 2600 m, where its productivity is limited by cold stress. We studied 25 Ethiopian barley landraces in order to identify cold tolerant types and to describe characteristics and acclimation potentials of these landraces to cold stress. Barley plants were grown from seeds in a temperature-controlled greenhouse (20/15°C) for six weeks prior to investigation. Membrane leakage, assayed by electric conductivity, was investigated before and after the plants had been subjected to freeze-thaw cycles at different sub-freezing temperatures down to -10°C. The critical temperature (CT₅₀), at which the frost-induced damage was 50% of the maximal injury, ranged for most landraces between -5.6 and  -8.6°C. Maximum difference in sensitivity to frost among the various races was observed at -5.0°C. Neither the altitude of the habitat, from where the seeds had been collected, nor the maturation time of the landraces were correlated with the degree of frost tolerance of the landraces. The influence of the growth conditions on the capability of frost hardening of cold-tolerant and sensitive landraces was investigated using chlorophyll a fluorescence. Barley seedlings were grown under three different regimes: In a temperature controlled greenhouse (20/15°C, day/night), under simulated tropical alpine conditions (tropical-alpine greenhouse, 16/0°C, 12 h light period), and in a phytotrone at constant 2°C day and night. Effective quantum yield of photosynthesis was measured at several temperatures in the course of freeze-thaw cycles (+20 to -10 to +20°C). Whereas growth and the effective photosynthetic quantum yield of the plants in the phytotrone were low, cold hardening was effective as shown by the recovery of the photosynthetic quantum yield upon re-warming of the frozen plants. Effective quantum yield of the plants grown in the tropical alpine greenhouse was as high as with the control plants, but only 2 of 6 investigated landraces showed immediate recovery of the photosynthetic quantum yield after freezing. Landraces which showed the highest cold tolerance were found to acclimatize best.