Determination of parameters for selection of Eucalyptus clones tolerant to drought

Climatic changes have induced the spread of aridity in many parts of the globe. Eucalyptus plantations show wide variations in productivity due to several factors, including climatic changes. Therefore, Eucalyptus genotypes that can adapt to such conditions is very welcome. Thus, an evaluation was done by comparing the physiological responses of two Eucalyptus genotypes, tolerant and drought-sensitive. They were assessed in different stages of experimental period and the rate of chlorophyll and chlorophyll fluorescence (minimal fluorescence and maximal fluorescence) were recorded. The potential photosystem II (PSII) quantum efficiency was then calculated. A decline in the rate of total chlorophyll (values below 25) and in the minimal fluorescence (values below 190) in clone sensitive due to the water stress was observed, while an increase was noted in clone tolerant to aridity. A reduction in the maximal fluorescence and photochemical efficiency was recorded in the genotype not being irrigated, with an earlier and more severe effect being verified for the sensitive genotype with values below 300 and 0.40, respectively. The variables studied confirm that clone tolerant exhibits greater drought tolerance, thus indicating that the photochemical efficiency of photosystem II is a reliable tool that enables the nondestructive choice of genotypes naturally tolerant to water scarcity conditions.  Key words: Abiotic stress, arid land plants, chlorophyll, ecophysiology, photochemical efficiency, tree drought tolerance, water deficit, water potential.