ABSTRACT
Soybean stem necrosis is caused by cowpea mild mottle virus (CPMMV), transmitted by the whitefly Bemisia tabaci. CPMMV has already been recorded in all major soybean-producing areas of Brazil. The impacts caused by CPMMV to the current Brazilian soybean production are unknown, thus the main objective of this study was to evaluate the effects of CPMMV infection on the main important soybean cultivars grown in the Southern and Midwestern regions of Brazil. Although asymptomatic in some of the tested cultivars, CPMMV infection significantly reduced the plant height, the number of pods per plant and the 1,000-grain weight. In addition, estimated yield losses ranged from 174 to 638 kg ha-1, depending on the cultivar. Evidence of seed transmission of CPMMV was observed in the BMX POTÊNCIA RR cultivar. These results suggest that CPMMV could have an important role in the reduction of soybean productivity in Brazil, but symptomless infections might be hiding the actual impact of this pathogen in commercial fields and infected seeds could be the primary inoculum source of the virus in the field.
ABSTRACT
Over the past few years, the use of RNA interference (RNAi) for insect pest management has attracted considerable interest in academia and industry as a pest-specific and environment-friendly strategy for pest control. For the success of this technique, the presence of core RNAi genes and a functional silencing machinery is essential. Therefore, the aim of this study was to test whether the Neotropical brown stinkbug Euschistus heros has the main RNAi core genes and whether the supply of dsRNA could generate an efficient gene silencing response. To do this, total mRNA of all developmental stages was sequenced on an Illumina platform, followed by a de novo assembly, gene annotation and RNAi-related gene identification. Once RNAi-related genes were identified, nuclease activities in hemolymph were investigated through an ex vivo assay. To test the functionality of the siRNA machinery, E. heros adults were microinjected with ~28 ng per mg of insect of a dsRNA targeting the V-ATPase-A gene. Mortality, relative transcript levels of V-ATPase-A, and the expression of the genes involved in the siRNA machinery, Dicer-2 (DCR-2) and Argonaute 2 (AGO-2), were analyzed. Transcriptome sequencing generated more than 126 million sequenced reads, and these were annotated in approximately 80,000 contigs. The search of RNAi-related genes resulted in 47 genes involved in the three major RNAi pathways, with the absence of sid-like homologous. Although ex vivo incubation of dsRNA in E. heros hemolymph showed rapid degradation, there was 35% mortality at 4 days after treatment and a significant reduction in V-ATPase-A gene expression. These results indicated that although sid-like genes are lacking, the dsRNA uptake mechanism was very efficient. Also, 2-fold and 4-fold overexpression of DCR-2 and AGO-2, respectively, after dsRNA supply indicated the activation of the siRNA machinery. Consequently, E. heros has proven to be sensitive to RNAi upon injection of dsRNA into its hemocoel. We believe that this finding together with a publically available transcriptome and the validation of a responsive RNAi machinery provide a starting point for future field applications against one of the most important soybean pests in South America.
Subject(s)
Gene Expression Profiling/veterinary , Hemiptera/growth & development , RNA, Small Interfering/genetics , Vacuolar Proton-Translocating ATPases/genetics , Animals , Gene Expression Regulation, Developmental , Hemiptera/genetics , High-Throughput Nucleotide Sequencing/veterinary , Insect Control , Insect Proteins/genetics , Molecular Sequence Annotation , Sequence Analysis, RNA/veterinary , South AmericaABSTRACT
We applied the ddRAD genotyping-by-sequencing technique to investigate the genetic distinctiveness of Brazilian populations of the noctuid moth Spodoptera frugiperda, the fall armyworm (FAW), and the role of host-plant association as a source of genetic diversification. By strain-genotyping all field-collected individuals we found that populations collected from corn were composed primarily of corn-strain individuals, while the population collected from rice was composed almost entirely of rice-strain individuals. Outlier analyses indicated 1,184 loci putatively under selection (ca. 15% of the total) related to 194 different Gene Ontologies (GOs); the most numerous GOs were nucleotide binding, ATP binding, metal-ion binding and nucleic-acid binding. The association analyses indicated 326 loci associated with the host plant, and 216 loci associated with the individual strain, including functions related to Bacillus thuringiensis and insecticide resistance. The genetic-structure analyses indicated a moderate level of differentiation among all populations, and lower genetic structure among populations collected exclusively from corn, which suggests that the population collected from rice has a strong influence on the overall genetic structure. Populations of S. frugiperda are structured partially due to the host plant, and pairs of populations using the same host plant are more genetically similar than pairs using different hosts. Loci putatively under selection are the main factors responsible for the genetic structure of these populations, which indicates that adaptive selection on important traits, including the response to control tactics, is acting in the genetic differentiation of FAW populations in Brazil.
Subject(s)
Bacillus thuringiensis/genetics , Genetic Markers , Genetics, Population , Insecticide Resistance/genetics , Selection, Genetic , Spodoptera/genetics , Adenosine Triphosphate/chemistry , Alleles , Animals , Bayes Theorem , Brazil , Ecology , Gene Library , Gene Ontology , Genotype , Geography , Oryza/genetics , Plant Diseases/genetics , Polymorphism, Single Nucleotide , Principal Component Analysis , Protein Binding , Sequence Analysis, DNA , Transcriptome , Zea mays/geneticsABSTRACT
BACKGROUND: An understanding of the genetic basis of insect resistance to insecticides is important for the establishment of insect resistance management (IRM) strategies. In this study we evaluated the inheritance pattern of resistance to the chitin synthesis inhibitor lufenuron in Spodoptera frugiperda. RESULTS: The LC50 values (95% CI) were 0.23 µg lufenuron mL(-1) water (ppm) (0.18-0.28) for the susceptible strain (SUS) and 210.6 µg mL(-1) (175.90-258.10) for the lufenuron-resistant strain (LUF-R), based on diet-overlay bioassay. The resistance ratio was ≈ 915-fold. The LC50 values for reciprocal crosses were 4.89 µg mL(-1) (3.79-5.97) for female LUF-R and male SUS and 5.74 µg mL(-1) (4.70-6.91) for female SUS and male LUF-R, indicating that the inheritance of S. frugiperda resistance to lufenuron is an autosomal, incompletely recessive trait. Backcrosses of the progeny of reciprocal crosses with the parental LUF-R showed a polygenic effect. The estimated minimum number of independent segregations was in the 11.02 range, indicating that resistance to lufenuron is associated with multiple genes in S. frugiperda. CONCLUSIONS: Based on genetic crosses, the inheritance pattern of lufenuron resistance in S. frugiperda was autosomal, incompletely recessive and polygenic. Implications of this finding to IRM are discussed in this paper.
Subject(s)
Benzamides/pharmacology , Chitin/biosynthesis , Insecticide Resistance/genetics , Spodoptera/drug effects , Spodoptera/genetics , Animals , Female , Genes, Insect/genetics , Male , Spodoptera/metabolismABSTRACT
Em pulverizações com bicos hidráulicos, o volume de calda é um dos aspectos mais importantes para o sucesso do controle químico de pragas. O objetivo deste trabalho foi avaliar o efeito do volume de calda e inseticidas no controle de Piezodorus guildinii (Westwood), na cultura da soja. Testaram-se os volumes de calda de 50, 100 e 150l ha-1 e os inseticidas endossulfam (437,5g i.a. ha-1) e tiametoxam + lambda-cialotrina (21,15 + 15,90g i.a. ha-1). Tiametoxam + lambda-cialotrina apresentou maior efeito residual e controle de P. guildinii em relação à endossulfam. Esses inseticidas respondem da mesma forma, aumentando a eficiência de controle da praga com o aumento do volume de calda.
The spray volume is one of the most important aspects interfering on the success of pest control. The objective of this study was to evaluate the effects of spray volume on the efficiency of the insecticides in the control of Piezodorus guildinii (Westwood) in soybean crop. Were evaluated the volumes of 50, 100 and 150l ha-1 and the insecticides endosulfan (437.5g a.i. ha-1) and tiametoxan + lambda-cyhalothrin (21.15 + 15.90g a.i. ha-1). Tiametoxan + lambda-cyhalothrin had better residual and control of P. guildinii than endosulfan. Both insecticides showed the same behavior, increasing P. guildinii control with spray volume increasing.
ABSTRACT
Com o objetivo de verificar a ocorrência de insetos da parte aérea na cultura da soja convencional e geneticamente modificada resistente a glyphosate, realizou-se este trabalho durante a safra agrícola 2004/05, em Cruz Alta, RS, na área experimental da Fundação Centro de Experimentação e Pesquisa (FUNDACEP). A semeadura foi realizada no dia 26/11/2004, no delineamento experimental de blocos ao acaso com parcelas subdivididas e com quatro repetições, em esquema fatorial 2 x 3. O fator A correspondeu à cultivar "CD 214 RR" resistente a glyphosate e à "CD 201" convencional e o fator B correspondeu ao sistema de manejo das plantas daninhas (sem controle, controle mecânico e controle químico tradicional) e com um tratamento adicional (controle químico com glyphosate na cultivar "CD 214 RR"). A utilização da soja geneticamente modificada resistente a glyphosate e a aplicação do herbicida glyphosate alteraram a ocorrência de algumas espécies de insetos-praga e inimigos naturais na parte aérea da soja.
The experiment was carried out during the crop season 2004/05, in Cruz Alta, RS, Brazil at Fundação Centro de Experimentação e Pesquisa (FUNDACEP) experimental area. The objective was to study the occurrence of insects in conventional and genetically modified herbicide-tolerant soybean. The seeding was done in November, 2004. The experimental design was randomized blocks and factorial scheme. The factor A was represented by the varieties 'CD 214 RR' (glyphosate-tolerant) and 'CD 201' (conventional). The factor B was composed by weed management systems, were b1- without weed control, b2- mechanical control and b3- chemical control with conventional herbicides. An additional treatment was used, where glyphosate application on 'CD 214 RR' was done. Soybean genetically modified herbicide-tolerant and glyphosate application had effects on some pests and beneficial insects in soybean.
ABSTRACT
Foram conduzidos três experimentos, em Santa Maria e em Constantina - RS, com o objetivo de determinar a população mais adequada de plantas para o tipo II de feijoeiro comum, nas condições de cultivo da safra e da safrinha em diferentes regiões climáticas, em função da ocorrência de moléstias. O delineamento experimental adotado foi o de blocos ao acaso, com cinco repetições, no esquema de parcelas divididas. Maior população de plantas apresenta rendimentos superiores ou equivalentes aos obtidos na menor população de plantas, e a ocorrência de moléstias não acarretou redução do rendimento de grãos nas populações maiores.
Three experiments were conducted in Santa Maria and Constantina - Rio Grande do Sul State - Brazil, to determine the effect of plant population on disease occurrence in common bean (type II grown) in the first and second growing season and to determine the most appropriate plant population. The experiment was established as a split-plot randomized block design with five replications. The results showed that there was no effect of plant population in disease incidence. The high plant populations provided higher or similar grain yield compared with the grain yield of the low plant populations.
ABSTRACT
A amostragem é um dos procedimentos básicos indispensáveis ao manejo integrado de pragas. Neste experimento, comparou-se a capacidade de coleta de dois métodos de amostragem da lagarta-da-soja (Anticarsia gemmatalis Hueb., 1818) e do percevejo-verde-pequeno (Piezodorus guildinii Westw., 1837) na cultura da soja semeada em três espaçamentos entre linhas (0,30; 0,40 e 0,50m). Foi utilizado o delineamento inteiramente casualizado, com dez repetições (amostragens), em esquema fatorial 2x3; utilizaram-se dois métodos de amostragem (pano-de-batida e pano-vertical) e três espaçamentos entre linhas. A população de lagarta-da-soja e de percevejo-verde-pequeno foi avaliada nos estádios V8 e R6, respectivamente. Para lagartas, os resultados indicam maior eficiência do pano-vertical em relação pano-de-batida. Nos menores espaçamentos, o pano-vertical não deixou clara sua maior capacidade de coleta de percevejos, como observado para lagartas. Estes resultados demonstram que são necessárias pesquisas visando a aprofundar a avaliação dos métodos de amostragens de pragas da soja cultivada em diferentes espaçamentos.
