Population survey of phytonematodes in soybean crop in the Middle Plateau region in Rio Grande do Sul

The objective of this study was to determine and quantify the main phytonematodes found in soybean crops in the state of Rio Grande do Sul and to estimate the population level where they are found. Therefore, samples of soil and soybean roots were received from 154 municipalities of the Middle Plateau region  of Rio Grande do Sul, from 2014 to 2016. After receiving and registering the samples, nematodes were extracted, identified and quantified in each sample. Through these data, it was determined the absolute frequency (AF), relative frequency (RF), absolute density (AD) and relative density (DR) of each nematode genus as well as their average population level in the municipalities. The main genera found in the study were Meloidogyne (found in 7.5% of the samples), Pratylenchus (6.2%), Heterodera (4.3%), Rotylenchulus (1.6%) and Helicotylenchus (22.9%). The species Meloidogyne species was not identified, but for Pratylenchus two species were identified, P. brachyurus and P. zeae. Besides these two genera, others were found, among them Heterodera glycines, Rotylenchulus reniformis and Helicotylenchus dihystera. The most frequently found nematode was H. dihystera, and in relation to population level, Meloidogyne spp. stands out for showing the highest levels in the municipalities in the three years of evaluation