Chilling and frost tolerance in eucalypt leaves

Abstract

The largest restriction to eucalypt culture in the south of Brazil is due to cold and to the incidence of frosts. The aim of this work was to evaluate eucalypt plant tolerance to chilling and freezing. The species Eucalyptus saligna, E. camaldulensis and E. dunnii and the hybrids E. grandis x E. urophylla, E. maculata x E. sp. and E. benthamii x E. dunnii were tested. Plants with 60 cm of height were cultivated in substrate Plantmax® HT and maintained in a greenhouse. Leaf disks (1 cm of diameter) were obtained of the third and fourth leaves starting from the apex of the plants. Leaf disks were washed three times with ultra-pure water and dried in absorbent paper. Flasks containing 20 mL of ultra-pure water and 10 leaf disks were maintained at 25 ºC in dark for 18h before treatments. The tubes within leaf disks were placed in cold bath at 4°C, 2°C, 0, -2°C and -4 ºC for 1 h. Electrolytic conductivity from samples was measured before treatments (CD), after treatments (CT) and after storage at -80 oC for 24h (CF). Relative conductivity was estimated by CR = (CT - CD) /(CF - CD), which was used to obtain cell viability V(%) = (1-CR).100. The viability of the cells did not differ significantly among the temperatures; nevertheless there were significant differences among the plants. The viability of the cells of the hybrid E. maculata x E. sp. was significantly inferior (V=51%) compared to the other species, that did not differ between them, varying between 86.6 and 93.8%.