TOLÉRANCE AU GEL ET TENEUR EN SUCRES ET EN PROLINE DU COLLET DU FRAISIER (Fragaria ananassa Duch) DURANT L’HIVER

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Abstract
A 4-yr (1983–1987) project was initiated to follow the frost tolerance of vegetative and floral buds of two strawberry cultivars, Redcoat and Bounty, grown in a field near Quebec City (Quebec, Canada), and to record changes in the sugar and proline contents of crowns during the cold season. Strawberry begins to cold harden in September and its frost tolerance (LT50) increases during the autumn, even under the snow, to reach a maximum in January and thereafter decreases to return in May to its original level of September. The vegetative buds have a LT50 similar to that of the flower buds in September and May, but in January the former attain a maximum LT50 of −18.9 °C while that of the latter is −15.1 °C showing a significant difference of 3.8 °C. Strawberry frost tolerance is largely dependent on the decrease in temperature during the autumn, showing correlation coefficients of 0.89 for the vegetative buds and 0.93 for the floral buds. The sucrose, reducing and total sugar contents increase during cold hardening to reach a maximum that coincides with maximal LT50 in January. Relations between the strawberry LT50 and the crown sugar contents are significant. The proline content of crowns varies greatly during cold hardening and dehardening, and its relation with the frost tolerance of the floral and vegetative buds is more than doubtful even if the correlation coefficients are significant.Key words: Strawberry, frost tolerance, sugars, proline, winter survival

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