Population Genetic Structure of Rhizoctonia oryzae-sativae from Rice in Latin America and Its Adaptive Potential to Emerge as a Pathogen on Urochloa Pastures.

The fungus Rhizoctonia oryzae-sativae is an important pathogen that causes the aggregated sheath spot disease on rice. In this study, we investigated the genetic structure of rice-adapted populations of R. oryzae-sativae sampled from traditional rice-cropping areas from the Paraíba Valley, São Paulo, Brazil, and from Meta, in the Colombian Llanos, in South America. We used five microsatellite loci to measure population differentiation and infer the pathogen's reproductive system. Gene flow was detected among the three populations of R. oryzae-sativae from lowland rice in Brazil and Colombia. In contrast, a lack of gene flow was observed between the lowland and the upland rice populations of the pathogen. Evidence of sexual reproduction including low clonality, Hardy-Weinberg equilibrium within loci and gametic equilibrium between loci, indicated the predominance of a mixed reproductive system in all populations. In addition, we assessed the adaptive potential of the Brazilian populations of R. oryzae-sativae to emerge as a pathogen to Urochloa spp. (signalgrass) based on greenhouse aggressiveness assays. The Brazilian populations of R. oryzae-sativae were probably only incipiently adapted as a pathogen to Urochloa spp. Comparison between RST and QST showed the predominance of diversifying selection in the divergence between the two populations of R. oryzae-sativae from Brazil.

Effect of seed treatment with insecticides on the control of Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) in soybean / Efeito do tratamento de sementes com inseticidas no controle de Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) na cultura da soja

Fall armyworm is one of the main insect pests in Brazil. Thus, the present work aimed to evaluate the seed treatment effect on the control of Spodoptera frugiperda in initial infestations of soybean crops. The experimental design was completely randomized with four replicates of six insecticide treatments applied through seed treatment: imidacloprid plus thiodicarb at the dose of 52.5 plus 105 g a.i. (active ingredient) 100 kg-1 of seed (Cropstar® 0.350 L 100 kg-1 of seed); thiamethoxam at 105 g a.i. 100 kg-1 of seed (Cruiser 350 FS® 0.3 L 100 kg-1 of seed); chlorantraniliprole at 62.5 g a.i. 100 kg-1 of seed (Dermacor® 0.1 L 100 kg-1 of seed); cyantraniliprole at 120 g a.i. 100 kg-1 of seed (Fortenza 600 FS® 0.2 L 100 kg-1 of seed); fipronil plus pyraclostrobin and thiophanate-methyl 50 + 5 + 45 g a.i. 100 kg-1 of seed (Standak Top® 0.2 L 100 kg-1 of seed), and a control treatment. The experiment was carried out in a greenhouse. Diamide insecticides (chlorantraniliprole and cyantraniliprole) presented the best results among all treatments, with lower consumption of the treated leaves by the caterpillars and greater control efficacy of this insect. We verified that seed treatment is a viable alternative for controlling S. frugiperda at the beginning of crop development, when the caterpillar presents the behavior of cutting the seedlings and/or the consumption of leaf area, causing a reduction in the plant population and a consequent yield loss.(AU)

A lagarta-do-cartucho é um dos principais insetos-praga no Brasil. Assim, o presente trabalho teve por objetivo avaliar o efeito do tratamento de sementes no controle de Spodoptera frugiperda nas infestações iniciais da cultura da soja. O delineamento experimental foi inteiramente casualizado, com quatro amostras replicadas de seis tratamentos inseticidas aplicados via tratamento de sementes: imidacloprida mais tiodicarbe na dose de 52,5 mais 105 g i.a. (ingrediente ativo) 100 kg-1 de sementes (Cropstar® 0,350 L 100 kg-1 de sementes); tiametoxam a 105 g i.a. 100 kg-1 de sementes (Cruiser 350 FS® 0,3 L 100 kg-1 de sementes); clorantraniliprole a 62,5 g i.a. 100 kg-1 de sementes (Dermacor® 0,1 L 100 kg-1 de sementes); ciantraniliprole a 120 g i.a. 100 kg-1 de sementes (Fortenza 600 FS® 0,2 L 100 kg-1 de sementes); fipronil mais piraclostrobina e tio-fanato-metílico 50 + 5 + 45 g i.a. 100 kg-1 de sementes (Standak Top® 0,2 L 100 kg-1 de sementes) e um tratamento controle. O experimento foi conduzido em uma vegetação. Dentre todos os tratamentos, os inseticidas do grupo químico das diamidas (clorantraniliprole e ciantraniliprole) apresentaram os melhores resultados, com consumo inferior pelas lagartas das folhas tratadas e maior eficiência de controle deste inseto. Foi constatado que o tratamento de sementes é uma alternativa viável para o controle de S. frugiperda no início do desenvolvimento da cultura, quando a lagarta apresenta o comportamento de cortar as plântulas e/ou consumir área foliar, ocasionando uma redução da população de plantas e uma consequente perda de produtividade.(AU)