Caracterização física e anatômica de folhas de acessos de bananeira com diferentes ploidias

Abstract

Chromosome duplication may be used in genetic breeding of banana cultivars for developing secondary triploids. Methods for estimating ploidy levels are needed. The objective of the present work is to evaluate DNA content, leaf thickness, anatomic characterization and leaf turgor of di, tri and tetraploid banana genotypes to later correlate with the number of chromosomes and establish a quicker method for estimating ploidy levels. The evaluation of DNA content was carried out by flow cytometry in the AA (Calcutta and NBA) diploids, AAA tripoloids (Grande Naine and Caipira) and the AAAA tetraploids (Calypso and Bucanero). Four replicates were carried out for each sample and five thousand nuclei were analyzed. The specific mass analysis was carried out using three discs taken from each of the two parts of the foliar limb in the apical, medium and basal positions of the first, second and third expanded leaves of plantlets of the AA diplois (Calcutta and Lidi), AAA triploids (Grande Naine and Williams) and AAAA tetraploids (Bucanero and Calypso), using four plants per each genotype. Fresh, dry (mg) and specific (mg cm-2) mass of the discs for the different genotypes, were evaluated. The anatomic characterization was carried out in leaf samples of the same diploid, triploid and tetraploid plants used in the previous experiment by the Ken-a-vision microscope. The evaluation of leaf turgor was carried out using the Wilmeter equipment by direct analysis of leaves and foliar discs of the different genotypes. Results regarding DNA content showed that the diploid genomes weigh less (0.96 pg); the triploid Grande Naine (1.48 pg) and Caipira (1.63 pg), intermediate weights and the tetraploids Calypso (1.90 pg) and Bucanero (2.26 pg), presented the heaviest DNAs. The specific mass obtained for the fresh mass of the foliar discs taken from the apical part of the leaf presented good relationship with the ploidy level. Therefore, the genotypes with greater ploidy level were those which presented highest fresh mass of the leaf discs. For the anatomic study, the tetraploid genotypes presented larger stomata and in less amount in comparison to the triploid and diploid genotypes. The turgor potential is related to ploidy level when directly observed in the plant using the Wiltmeter equipment in readings carried out at 6:30 a.m. Plants with higher ploidy level presented increased turgor pressure.