Frost tolerance induced by cold acclimation in olive (Olea europaea L.)

One-year-old potted plants of four olive cultivars (Bouteillan, Nostrale di Rigali, Frantoio and Moraiolo) were tested for frost resistance. For each cultivar non acclimated (NA) plants and cold acclimated (CA) (4degreesC for 5-12-19 days) plants were compared. Freezing stress was applied in October 1998 and March 1999 and the most evident result was the different response of the plants to cold acclimation in the two different months. In fact, in October cold acclimation did not induce any improvement in terms of frost resistance, whereas in March CA plants were always more frost resistant than NA plants. No clear differences in terms of frost resistance among the cultivars; were found. GLC analysis of sugars highlighted a sharp increase of sucrose in CA plants both in October and in March, whilst glucose and mannitol were not affected by cold acclimation. Nevertheless, there was no evidence of the effect of sucrose as cryoprotectant. A possible explanation for this different response to a freezing stress is that in March plants were already 'prehardened' compared to October.