SUSCEPTIBILITY TO CHILLING OF SOME CENTRAL-AFRICAN CULTIVARS OF COFFEA-ARABICA

This study was aimed at identifying cultivars of coffee plants with a low susceptibility to chilling, on the basis of laboratory measurements of various types of impairment in response to low temperature. The chilling susceptibility of nine central-African cultivars of Coffea arabica was determined using juvenile and adult potted plants. The above-ground parts were exposed for 12 h during the night to temperatures of +4°C. After rewarming, the changes in and recovery of both photosynthetic CO2 uptake and the variable fluorescence of chlorophyll-a were measured and the extent of leaf necrosis recorded. All cultivars were damaged by the chilling stress, the juvenile plants clearly being more susceptible than the adults. However, statistically significant differences were found between the individual cultivars with respect to maximal depression and speed of recovery in photosynthetic activity and extent of leaf necrosis. No clear correlation could be shown between the various parameters measured. Therefore, an index for the susceptibility to chilling was calculated from the loss in photosynthetic productivity and the extent of necrosis. The resulting appraisal of the susceptibility of cultivars with a normal growth habit was in good agreement with recordings of survival after a cold spell in coffee plantations in Chipinge, Zimbabawe (relatively resistant: K7, SL28, K33; intermediate: Mundanova; most susceptible: Agaro, Geisha). The dwarf cultivars (Caturra, Red Catuai, Catuai Yellow) suffereds relatively more damage in the laboratory experiment than in plantations, where the plants were probably exposed to less-extreme temperatures on account of their low habit of growth. © 1990.