Résumé
Eucalyptus globulus is the second most important forest species in Chile, after Pinus radiata. The main advantages of E. globulus are its fast growth (25 m³/ha/year) and its excellent wood quality for kraft pulp production. On the negative side, its low freezing tolerance has been an obstacle for the expansion of plantations, specifically on the foothills of the Andes. The difference in the freezing resistance between clones of E. globulus has a genetic base and, therefore, it could be detected through DNA molecular markers. Fifteen clones of E. globulus, eight classified as freezing resistant and seven as freezing sensitive were analyzed using the technique of RAPD, in order to obtain molecular markers that could differentiate between freezing sensitive and resistant clones. Eighteen primers amplified reproducible bands. Three bands were only present in freezing resistant clones, two bands of 768 bp, 602 bp obtained with UBC 218 primer and one band of 248 bp obtained with UBC 237 primer. The preliminary results indicate that polymorphism can be observed with the primers employed, but it is not possible to associate the bands with the cold resistance or susceptibility in E. globulus.
Résumé
The resistance to low temperatures was assessed in seedlings of three subspecies of E. globulus (ssp globulus, ssp bicostata and ssp maidenii) of two different provenances. Lethal temperature 50 (LT50) was obtained by measuring the electrolytic conductivity, nucleation and freezing temperatures were obtained by thermal analysis and the total soluble carbohydrates concentration was determined through the phenol-sulphuric method. Results showed that the most resistant provenance corresponded to Bolaro Mountain of ssp maidenii with a LT50 lower than -9ºC. The provenance Moogora of ssp globulus, had a LT50 of -8.47ºC, which situates it, as the second most resistant to low temperatures. According to the nucleation and freezing temperatures, the results indicate that all the provenances analyzed evaded the formation of ice, except for Bolaro Mountain of ssp maidenii which was tolerant to freezing. Finally, an inverse correlation (r = -0.89) between the content of total soluble carbohydrates and the LT50 was found, indicating the cryoprotection effect of these in the resistance to low temperatures.