STRUCTURAL DIVERSITY OF LOG OF Eucalyptus spp . GENOTYPES .

Anatomical studies, besides being useful in the identification of the species, make it possible to generate information about the structure of the log in order to identify the relationships between the log and the technological properties of the wood. The aim of this work was to anatomically characterize the log of different genotypes of the genus Eucalyptus planted in the state of Minas Gerais – Brazil and to describe its main differences and/or similarities. Three genetically improved genotypes were evaluated, Eucalyptus urophylla x Eucalyptus grandis; Eucalyptus urophylla and Eucalyptus urophylla x Eucalyptus camaldulensis , aged whithin 6 to 7 years old. Discs of 9 trees were removed at breast height (1.30 meters from the ground). From each disk, specimens were obtained in the medulla-cambial direction with dimensions of approximately 2 cm3 to make permanent sheets, being that the anatomical characterization of the genotypes followed the recommendations of the IAWA Committee (1989). The results showed that the genotypes of Eucalyptus are very similar, however, differences were observed in the axial parenchyma and in the composition of rays.


INTRODUCTION
The anatomical studies, besides the identification of the species, make it possible to generate information about the wood structure, allowing to identify its interrelationship with the technological characteristics of the wood.Studies on the anatomy of the species of the genus Eucalyptus mainly address the fiber dimensions, which present great potential for use as raw material in the forest industry.
The genus Eucalyptus belongs to the family Myrtaceae and has more than 600 species, they develop in diverse conditions of soil and climate.It has great economic importance in the country, since it constitutes a large part of the plantations of the forest sector (RAPASSI et al., 2008).The species of this genus are widely planted in Brazil due to the rapid growth and quality of the wood, for the production of cellulose, fibre panels, firewood, charcoal and civil construction (DIAS JÚNIOR et al., 2016).Some species of the genus Eucalyptus are well studied, but there are other species of this genus in which the studies are scarcer, as well as for several hybrids (PIRRALHO et al., 2014;PRINSEN et al. 2012).
By characterizing the anatomical structure of the log, determining the dimensions of its cells and its structural variations, it is possible to predict the technological behavior of the material that is fundamental to the companies that consume this raw material.A growth in pulp production of around 13 million tons per year of Eucalyptus wood was expected in the year of 2015 in Brazil, due to the growth and creation of cellulose and paper industries in the country.With this, there is necessity of improvements in the productivity and quality of the clonal forests of Eucalyptus (ALVES et al., 2011).
Despite the great potential of species of the genus, there are specific restrictions of each species, however, these are minimized or solved with the implementation of genetic improvement programs, seeking the production of raw material of quality with characteristics appropriated to the processes and products, as well as cost reduction and production time.Brisola and Demarco (2011) observed gains in anatomical characteristics relevant to the forest industry for hybrids of Eucalyptus, making their use faster and the cost of the final product lower.
The anatomical study of different species, as well as the variation among individuals of the same species, is an important tool for decision making in the forest sector, such as genetic improvement, forestry and forest management (BALDIN et al., 2017).
Currently, due to the gaps that have arisen over time and the improvement of the genus species, directly influencing the log structure, there is a need to anatomically study the genotypes of the genus Eucalyptus.Only a constant effort can result in a greater understanding of the anatomy of wood and its evolution.The need for such an effort is better understood when there is a group with a diversity of wood-producing species and there is difficulty in distinguishing them (CARLQUIST, 2010).Thus, it is fundamental to verify the anatomical differences of the existing species within this genus so that it is possible to make a distinction between them and infer about the anatomical characteristics more favorable to the productivity and quality of the raw material for the production of cellulose pulp, paper and charcoal.
With that, the objective of this work was to describe the log of the different genotypes of the genus Eucalyptus, in order to allow the differentiation of the genotypes of this genus so homogeneous, using the anatomy of wood as a tool.

Collection and sampling area
The work was developed using wood from plantations from three companies that commercialize genotypes of the genus Eucalyptus L'Hérit, located in the state of Minas Gerais.Three trees of each genotype most used by each company, with commercial age (Table 1), were collected.From each tree was obtained a disc approximately five centimeters thick at the breast height (1.30 m from the ground).Three specimens were prepared, one near the medulla, one in the intermediate region and one near the cambium, with dimensions of 2x2x2 cm (tangential, radial and longitudinal) of the diametrical section of the sampled discs.

Microscopic description
For the anatomical characterization of the genotypes, permanent histological sheets were made.After cooking in water, samples of approximately 2 cm³ were sectioned in the transverse, tangential and radial planes by approximately 12 μm.The histological sections were clarified, stained, dehydrated in a gradual alcoholic battery of 30% to 100% and the blades were permanently mounted on Entelan® synthetic resin.
Measurements and descriptions were made according to the list of microscopic characteristics for angiosperms of the IAWA Committee (1989).The dimensions of these anatomical elements were obtained in an image analysis equipment, Olympus BX41 microscope with coupled camera, using the image analysis software.
In order to analyze the intervascular pits in scanning electron microscopy, it was necessary to reduce the sensing element to dimensions of approximately 1 cm³ and the surface (tangential) was covered by a thin layer of gold.
The results are mean values between the regions near the medulla, intermediate and near the exchange.

Anatomical description of the log
The main differences between genotypes are inserted in Table 2 and in the following descriptions.Axial parenchyma: paratraqueal vasocentric and diffracted apotracheal, rare, lozenge-shaped aliform of short fins.
Vases: predominantly solitary with proximity between them, however they do not share the same wall.Diagonal arrangement in relation to the radius and diffuse porosity.Average vessel diameter of 128.5 μm and frequency of 11 vessels/mm².Simple perforation plate, intervascular, alternate and areolated, minute to small, pits; presence of vasicentric tracheids.

Eucalyptus urophylla
Growth layer: demarcated by thickening the fiber wall.Axial parenchyma: paratraqueal vasocentric, lozenge-shaped aliform and diffracted apotracheal.Vessels:predominantly solitary with proximity between them, however they do not share the same wall, diagonal arrangement in relation to the ray and diffuse porosity, average diameter of the vessel of 109.6 μm and frequency of 14 vessels/mm².Simple perforation plate, intervascular, alternate and areolated, minute to small, pits; presence of vasicentric tracheids.

E. urophylla x E. camaldulensis
Growth layer: demarcated by decrease in vessel density and diameter.Axial parenchyma: paratraqueal vasocentric, rare, lozenge-shaped aliform, there is formation of short confluences and presence of diffuse.
Vessels: predominantly solitary with proximity between them, however they do not share the same wall, diagonal arrangement in relation to the ray and diffuse porosity, average diameter of the vessel of 112.29 μm and frequency of 15 vessels/mm².Simple perforation plate, intervascular, alternate and areolated, minute to small, pits; presence of vasicentric tracheids.

DISCUSSION
The study emphasized the differences in the qualitative characteristics, since quantitative characteristics such as fiber length, wall thickness, height and width of ray and vessel diameter and density are influenced by the climatic changes.
The main differences between the studied genotypes were rays and axial parenchyma, Pirralho et al. (2014), studying nine species of Eucalyptus, also noted that most of the anatomical differences in the species of the genus are related to the rays and axial parenchyma.
The genotypes of Eucalyptus studied in this work are very similar between each other, Angyalossy-Alfonso (1987) also observed this homogeneity when studying 21 species of the genus.However, it is possible to differentiate them because they have distinct qualitative characteristics inherited from the species.Thus, it is possible to affirm that there are differences in the anatomical constitution that allows to distinguish the evaluated genotypes even though they are similar to each other.In all species it was possible to notice the presence of vessels in diagonal arrangement, predominantly solitary and vasicentric tracheids, common characteristics to the species of Eucalyptus reported in several works (ANGYALOSSY-ALFONSO, 1987;ALZATE, 2009;BRISOLA AND DEMARCO, 2011) .
The rays of the studied genotypes are uniseriate, locally bisseriate, as observed in the studies of Alzate (2009), Brisola and Demarco (2011).Regarding the composition of the rays, Alzate (2009), analyzing clones of Eucalyptus grandis x Eucalyptus urophyla, did not notice the presence of square cells, considering the rays as homogeneous formed exclusively by procumbent cells.
Describing the secondary xylem of Eucalyptus benthamii Baldin et al. (1989) observed the presence of square cells, corroborating the one affirmed by Record and Hess (1949) that for the set of species of the family Myrtaceae there is the predominance of heterogenous rays.
Brisola and Demarco (2011) also observed vasocentric paratracheal axial parenchyma in Eucalyptus urophylla and eventually aliform in the hybrid Eucalyptus urophylla x Eucalyptus grandis.
It was observed that Eucalyptus urophylla and Eucalyptus urophylla x Eucalyptus grandis, as well as paratracheal parenchyma, also presented diffuse apotracheal parenchyma with little contrast in the transversal plane, constituting a novelty.Evangelista et al. (2010), when studying clones of Eucalyptus urophylla and Eucalyptus camaldulensis described the presence of confluent and vasicentric paratracheal parenchyma, respectively.
The Eucalyptus urophylla x Eucalyptus camaldulensis hybrid described in this study has a vasicentric axial parenchyma and a rare presence of a lozenge-shaped aliform, presenting a similarity to genotype Eucalyptus urophylla, also described in this paper and reported by Brisola and Demarco (2011).Thus, it is possible that these characteristics of Eucalyptus urophylla are dominant in relation to Eucalyptus camaldulensis, due to the presence of the aliform parenchyma with an elongated extension in both E. urophylla and in the hybrid E. urophylla x E. camaldulensis.
Libriforms fibres and non-septades were found in the genotypes and are reported in studies with species of the genus (Brisola e Demarco, 2011;Pirralho et al., 2014;Baldin et al., 2017), being the quantitative part of this anatomical character one of the principles considered to the industries of the forest sector.

CONCLUSION
• It is possible to distinguish the genotypes of Eucalyptus by the characteristics of the axial and radial parenchyma cells; • Eucalyptus urophylla x E. grandis and Eucalyptus urophylla presented heterogeneous rays with the presence of procumbent and square cells, Eucalyptus urophylla x E. camaldulensis presented a homogeneous ray, composed only of square cells; • Eucalyptus urophylla x E. grandis presented vasicentric axial parenchyma and diffuse apotracheal, Eucalyptus urophylla, vasocentric, aliform and apotracheal diffuse, and Eucalyptus urophylla x E. camaldulensis confluent vasicentric and diffuse apotraqueal.• The diagonal arrangement of vessels and the presence of vasicentric tracheids were observed in all genotypes.
E. urophylla x E. grandisGrowth layers: are demarcated by the slight decrease in vessel diameter and density, in addition to the thickening in the fiber wall.