Caracterização morfométrica de populações de Pratylenchus brachyurus

Abstract

The taxonomy of the genus Pratylenchus has been studied due to the high intraspecific morphological variability. The objective of this work was to characterize morphologically the populations of P. brachyurus from different places and from soybean and corn host plants. Nine populations of P. brachyurus were obtained in the States of Paraná (PR) and Mato Grosso do Sul (MS), Brazil. The nematodes were extracted using the centrifugal flotation technique in a sucrose solution and then multiplied in carrot cylinders (10 individuals per cylinder). After 90 days of multiplication, the nematodes were extracted, and each population was morphometrically analyzed. To analyze each population, the variables were: body length, stylet length, esophagus length, tail length and higher body width. Subsequently, the designated body relations were determined: a (body length divided by the highest width), b (body length divided by esophagus length), c (body length divided by tail length) and V% (distance from the anterior end to vulva, as a percentage of total body length). The experimental design was completely randomized with 10 replicates for each measured variable, each replicate consisting of one female nematode. The morphometric variables measurements were compared to the literature (Loof, 1991) for statistical analysis. Both univariate and multivariate analysis were performed, estimating the arithmetic means (AM), standard deviations (SD) and coefficients of variation (CV%). The Scott-Knott was also performed, and the genetic variation of the populations was verified, using the hierarchical UPGMA and Tocher Optimization methods from the generalized distances of Mahalanobis. The analysis of canonical variables was carried out, aiming a better visualization of the existing dissimilarity among populations of P. brachyurus. The morphometric characterization indicated high variability and clustered the populations in four groups, where the populations that presented higher dissimilarity were from Terra Roxa – PR and Toledo 01 – PR, and those that presented lower dissimilarity were from Fátima do Sul 1 – MS and Nova Andradina – MS. The variables of body and esophagus length were the main responsible for the genetic deviation among P. brachyurus populations. There was a correlation between the variables body length, body width, esophagus length and tail length. Besides, the variability of stylet length showed correlation among body length, body width, and esophagus length. The variable V% showed no correlation with any of those ones. For studies which aim the genetic diversity in P. brachyurus populations, it is recommended that the variables tail length, c, and V% do not be considered.