Caracteres estruturais e dimensão fractal da folha de espécies de Arachis e sua relação com a cercosporiose

Abstract

O presente trabalho teve como objetivos quantificar caracteres estruturais do limbo foliar, em dois cultivares e quatro acessos de tres especies de Arachis, procurando relaciona-los com graus de resistencia a cercosporiose, bem como discriminar esses individuos por meio da analise da dimensao fractal. Foram amostradas porcoes do terco medio da regiao internervural do terceiro ou quarto foliolo da segunda folha contada a partir do apice, sendo as amostras infiltradas em historresina, seccionadas com 7æm de espessura e coradas com azul de toluidina. Foram tambem realizadas impressoes da epiderme, utilizandose cola de secagem instantanea. Os caracteres quantificados foram: area da seccao da regiao internervural; areas e espessuras de epiderme das faces adaxial e abaxial, parenquima, hipoderme e mesofilo; area do complexo estomatico; espessura da folha; porcentagens de epiderme das faces adaxial e abaxial, parenquima e hipoderme; numeros de tricomas, estomatos, cristais de oxalato de calcio e idioblasto de mucilagem; e comprimento do ostiolo. Para a analise da dimensao fractal, utilizou-se folhas totalmente expandidas digitalizadas em imagens monocromaticas, determinando-se o valor da dimensao fractal do sistema foliar, limbo foliar, bordo foliar e sistema de venacao, atraves do metodo gBox-Countingh. Os dados obtidos foram submetidos aos testes estatisticos multivariados de analise de agrupamento e analise de componentes principais. Verificou-se que os caracteres estruturais quantitativos do limbo foliar podem ser utilizados como indicadores de resistencia a cercosporiose, em cultivares e acessos de diferentes especies de Arachis. A analise da dimensao fractal dos caracteres morfologicos foliares e os caracteres estruturais quantitativos do limbo foliar, possibilitaram diferenciar A. hypogaea, A. magna e A. stenosperma entre si.

The present work's objectives were to quantify leaf blade structural characters in two cultivars and four accessions of three Arachis species, in an attempt to associate them with different degrees of late leafspot resistance, as well as to discriminate those individuals by fractal dimension analysis. Portions from the middle third of the interveinal region of the third or fourth leaflets, in the second leaf counted from the apex were sampled. The samples were infiltrated in Historesin, sectioned at 7-æm thickness, and stained with toluidine blue. Epidermal prints were also prepared using instant bonding glue. The following characters were quantified: cross section area of the interveinal region; area and thickness of the epidermal adaxial and abaxial surfaces, parenchyma, hypodermis, and mesophyll; stomatal complex area; leaf thickness; percentage values of the epidermal adaxial and abaxial surfaces, parenchyma, and hypodermis; number of trichomes, stomata, calcium oxalate crystals, and mucilage idioblasts; and ostiole length. Completely expanded leaves, digitized as monochromatic images, were used in the dimension fractal analysis. Values for the leaf system's fractal dimension, leaf blade, leaf margin, and venation system were determined by the Box-Counting method. The data thus obtained were submitted to Cluster Analysis and Principal Components Analysis multivariate statistical tests. It was observed that leaf blade quantitative structural characters can be used as late leafspot resistance indicators for cultivars and accessions of different Arachis species. The fractal dimension analysis of leaf morphological characters and leaf blade quantitative structural characters allowed A. hypogaea, A. magna, and A. stenosperma to be discriminated from one another.