Genetic diversity in soybean genotypes with resistance to Heterodera glycines

The purpose of this study was to analyze the genetic diversity among soybean genotypes inoculated with Heteroderaglycines race 3. The experiments were conducted in a greenhouse. In two performance tests of morphological characteristics andresistance to the pathogen, 27 soybean genotypes were assessed. The coefficient of genotypic determination was estimated by themethod of analysis of variance and the genetic diversity analyzed based on dendrograms and optimization method. The estimatedcoefficients of determination indicated a predominantly genetic origin of the genotypic differences in the traits. The genetic variabilitywas maintained in the superior genotypes, which can be used in breeding programs for resistance to soybean cyst nematod

Longidorids from Minas Gerais State, Brazil, with focus on the morphometric variability of Xiphinema krugi (Nematoda: Longidoridae) populations

The occurrence and distribution of Longidorid nematodes in the state of Minas Gerais, Brazil, were assessed in 126 soil samples collected at different habitats in 12 municipalities across the state. The nematodes were extracted from 1 kg of soil and morphometric measures and identification of species were conducted using a light microscope with the aid of a camera lucida. Eight species of Xiphinema were identified (X. brasiliense, X. diffusum, X. elongatum, X. ensiculiferum, X. krugi, X. variegatum, X. setariae/vulgare complex and X. surinamense) and also two species of Xiphidorus (Xiphidorus amazonensis and an undescribed Xiphidorus species). Xiphinema diffusum, X. variegatum, X. ensiculiferum and Xiphidorus amazonensis constitute new reports for Minas Gerais. Populations of X. krugi, X. elongatum and X. ensiculiferum showed variation in morphometric measures and a principal component analysis separated X. krugi nematodes in two groups

Effects of silicon on the penetration and reproduction events of Meloidogyne exigua on coffee roots

Considering that the root-knot nematode Meloidogyne exigua has caused great yield losses to coffee production in Brazil, this study aimed to determine whether the penetration and the reproduction events of this nematode on the roots of plants from two coffee cultivars with different levels of basal resistance to this nematode could be affected by silicon (Si). Coffee plants from the cultivars Catuaí and IAPAR 59, which are susceptible and resistant, respectively, to M. exigua, were grown in pots containing Si-deficient soil that was amended with either calcium silicate (+Si) or calcium carbonate (–Si). The Si concentration on the root tissue significantly increased by 159 and 97% for the +Si plants from the cultivars Catuaí and IAPAR 59, respectively, compared to the –Si plants of these cultivars. The population of M. exigua, the number of galls and the number of eggs were significantly reduced on the roots of the +Si plants of the cultivars Catuaí and IAPAR 59 compared to the –Si plants of these cultivars. It was concluded that the development and reproduction events of M. exigua were negatively impacted on the roots of coffee plants supplied with Si