Wood anatomy of field grown eucalypt genotypes exhibiting differential dieback and water deficit tolerance

The wood anatomy of three commercial genotypes of eucalypt, harvested at the Suzano Pulp and Paper plantation areas, was analyzed in the search for features related to their differential tolerance to dieback and drought in field conditions. The average diameter of the vessels in the latewood, the vessel dispersion among diameter classes and theoretical hydraulic conductivity displayed significant differences among the evaluated genotypes. When these genotypes were appraised in different environmental conditions, lower precipitation was related to an increase on the volume of the vessels and of the mesomorphy index. The tolerant and the medium tolerant genotypes exhibited differences compared to the susceptible genotype, such as the average of vessels/mm(2), average diameter of vessel elements, vulnerability index, dispersion of vessel in diameter classes and theoretical hydraulic conductivity. In short, the combined and balanced effort of the set of these characteristics is thought to contribute to the resistant phenotype. This set of characteristics were poled apart based on the growth rings. The vessel element diameter, vulnerability index, vessel element distribution and the difference of the hydraulic conductivity between the earlywood and latewood best represented the variability in the samples and were used for PCA analysis. In the graph dispersion with the PCA variables, the tolerant, medium tolerant and susceptible genotypes were discriminated indicating a feasible approach for separating divergent genotypes according to tolerance to dieback. The relative importance of wood anatomy characteristics to eucalypt dieback and water stress tolerance is discussed.