Genetic diversity among crabgrass weed ecotypes (Digitaria spp.) occurring in field crops in Rio Grande do Sul, Brazil

摘要

High genetic diversity is one of the main characteristics that ensures the adaptability and competitiveness of weeds in agricultural crops; therefore, knowledge of such diversity may be useful for outlining weed control strategies both more effectively and with less impact on the environment. The aim of the study was to use amplified fragment length polymorphism (AFLP) to evaluate the genetic similarity among ecotypes of crabgrass (Digitaria spp.) from areas cultivated with rice and soybeans from different agricultural regions of the State of Rio Grande do Sul (RS), Brazil. Samples were collected from crabgrass populations (Digitaria spp.) from February to March 2009, covering areas of rice and soybean production in 19 districts belonging to different regions of the RS. Three locations in each district were visited, and georeferences were determined at each of the three sampling points, resulting in 171 crabgrass accessions. Of the 171 ecotypes that were listed and classified by morphological traits, 34 were selected based on the geographic distribution criteria, and species diversity was assessed by AFLP. Genetic similarity among individuals was estimated using simple matching (SM) coefficients, and a dendrogram was constructed based on these data. The similarity among all ecotypes, including six different species, was 83%. When the species were analyzed separately, we found 86% similarity among the ecotypes of D. ciliaris and 89% among those of D. sanguinalis. Due to geographic distance, the lowest genetic similarity was found between the ecotypes D. tenata from Cachoeira do Sul and D. eriostachya from Itaqui. The ecotypes from upland areas were more similar than those from paddy fields. For D. ciliaris, the lowest genetic similarity was found between the ecotypes originating from Itaqui and Viam?o. Higher genetic similarity of D. sanguinalis ecotypes was observed between Arroio Grande and Dom Pedrito. Knowledge of the genetic diversity of weed populations is essential for the management and control of weeds.