Fatores intrínsecos às plantas de soja na expressão da resistência constitutiva e induzida a Spodoptera cosmioides (Walker, 1858) (Lpidoptera: Noctuidae)
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Data
2016-07-26
Autores
Freitas, Marcelo Mueller de [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Entre as pragas que causam prejuízos à soja, Spodoptera cosmioides assume importância devido a ineficiência dos métodos atuais para o seu controle, podendo causar reduções significativas na produção da cultura. Portanto, métodos alternativos dentro do manejo integrado de pragas como a resistência de plantas, tornam-se ferramentas fundamentais como táticas de controle a S. cosmioides. Variações em fatores intrínsecos às plantas podem afetar a expressão da resistência ao ataque de insetos e outros artrópodes. Desse modo, a determinação de metodologias específicas e mais precisas, em trabalhos visando à seleção de genótipos resistentes a um determinado inseto, são imprescindíveis para melhor demonstrar possíveis variações nos níveis de resistência entre genótipos. O presente trabalho teve como objetivo avaliar alguns fatores relacionados às plantas de soja que podem influenciar a expressão da resistência constitutiva e induzida a S. cosmioides. Na primeira parte avaliou-se a influência dos seguintes fatores na expressão da resistência constitutiva de dois genótipos resistente e suscetível a S. cosmioides em testes de preferência alimentar com e sem chance de escolha: substrato alimentar (disco foliar versus folíolo inteiro), posição foliar/idade foliar (folha mais nova da parte superior versus folha mais velha da parte inferior), e estrutura vegetal (folha versus vagem). Além disso, avaliou-se os efeitos de antibiose para S. cosmioides pela alimentação individual ou mista com folhas e vagens em teste sem chance de escolha. A segunda parte teve como objetivo investigar se alguns fatores como o genótipo (resistente e suscetível) e posição foliar (folhas da parte superior e folhas da parte inferior) influenciam na expressão da resistência induzida por injúria prévia. Também foram testados dois métodos de avaliação dos parâmetros biológicos de S. cosmioides, oferecendo discos foliares ou folíolos inteiros aos insetos nos bioensaios. Na primeira parte deste estudo, observou-se que o folíolo inteiro retirado da parte inferior das plantas proporcionou a melhor diferenciação na expressão da antixenose em genótipos de soja. Além disso, o desenvolvimento larval de S. cosmioides foi afetado em lagartas alimentadas apenas com vagem e quando alimentadas com vagem até o quarto ínstar e folíolo a partir do quarto ínstar. Na segunda parte, verificou-se que o genótipo resistente expressou resistência induzida a S. cosmioides em plantas de soja previamente injuriadas, enquanto que o genótipo suscetível não apresentou indução de resistência. Além disso, a posição foliar influenciou a expressão da resistência induzida no genótipo resistente, que foi melhor observada com o disco foliar coletado da parte superior. Espera-se que os resultados obtidos neste estudo, possam contribuir para o entendimento dos mecanismos de defesa em soja, fornecendo metodologias específicas para trabalhos futuros com resistência constitutiva e induzida, que poderão colaborar para o manejo integrado de pragas na cultura da soja.
Among the pests that cause damage to soybeans, Spodoptera cosmioides takes importance due to inefficiency of current methods for their control and may cause significant decreases in crop production. Therefore, alternative methods within the Integrated Pest Management as the Host-Plant Resistance become fundamental tools as control tactics against S. cosmioides. Variations on factors inherent to plants may affect the expression of resistance to insects and other arthropods. Thus, the determination of specific methodologies and most accurate in studies aiming at the selection of genotypes resistant to a particular insect are essential to better demonstrate possible variations in resistance levels between genotypes. This study aimed to evaluate some factors related to soybean plants that can influence the expression of constitutive and induced resistance to S. cosmioides. In the first part we evaluated the influence of the following factors on expression of constitutive resistance of two resistant and susceptible genotypes to S. cosmioides on feeding preference on choice and no-choice tests: leaf discs versus entire leaflets; upper part versus lower part of the plant; leaf versus pod. In addition, we evaluated the effects on larval development to S. cosmioides by individually or mixed food with leaves and pods in no-choice test. The second part aimed to investigate if some factors such as genotype (resistant and susceptible) and leaf position (upper part versus lower part of the plant) influence the expression of resistance induced by previous herbivory. We also tested two methods of evaluation of biological parameters of S. cosmioides offering leaf disks or entire leaflets insects in bioassays. In the first experiment, the entire leaflet removed from the lower part of the plants showed the best differentiation in the expression of antixenosis in soybean genotypes. The larval development of S. cosmioides was affected in caterpillars fed only on pod and when fed on pod to the fourth instar and leaflets from the fourth instar. In the second experiment, the resistant genotype expressed induced resistance to S. cosmioides in previously injured soybean plants, while the susceptible genotype showed no resistance induction. Furthermore, the position influenced the expression of induced resistance in the resistant genotype, which was better seen with leaf disc collected from upper part of the plant. We expect the results of this study can contribute to the understanding of the defense mechanisms of soybeans, providing specific methodologies for future works with constitutive and induced resistance, contributing to the Integrated Pest Management of soybeans.
Among the pests that cause damage to soybeans, Spodoptera cosmioides takes importance due to inefficiency of current methods for their control and may cause significant decreases in crop production. Therefore, alternative methods within the Integrated Pest Management as the Host-Plant Resistance become fundamental tools as control tactics against S. cosmioides. Variations on factors inherent to plants may affect the expression of resistance to insects and other arthropods. Thus, the determination of specific methodologies and most accurate in studies aiming at the selection of genotypes resistant to a particular insect are essential to better demonstrate possible variations in resistance levels between genotypes. This study aimed to evaluate some factors related to soybean plants that can influence the expression of constitutive and induced resistance to S. cosmioides. In the first part we evaluated the influence of the following factors on expression of constitutive resistance of two resistant and susceptible genotypes to S. cosmioides on feeding preference on choice and no-choice tests: leaf discs versus entire leaflets; upper part versus lower part of the plant; leaf versus pod. In addition, we evaluated the effects on larval development to S. cosmioides by individually or mixed food with leaves and pods in no-choice test. The second part aimed to investigate if some factors such as genotype (resistant and susceptible) and leaf position (upper part versus lower part of the plant) influence the expression of resistance induced by previous herbivory. We also tested two methods of evaluation of biological parameters of S. cosmioides offering leaf disks or entire leaflets insects in bioassays. In the first experiment, the entire leaflet removed from the lower part of the plants showed the best differentiation in the expression of antixenosis in soybean genotypes. The larval development of S. cosmioides was affected in caterpillars fed only on pod and when fed on pod to the fourth instar and leaflets from the fourth instar. In the second experiment, the resistant genotype expressed induced resistance to S. cosmioides in previously injured soybean plants, while the susceptible genotype showed no resistance induction. Furthermore, the position influenced the expression of induced resistance in the resistant genotype, which was better seen with leaf disc collected from upper part of the plant. We expect the results of this study can contribute to the understanding of the defense mechanisms of soybeans, providing specific methodologies for future works with constitutive and induced resistance, contributing to the Integrated Pest Management of soybeans.
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Palavras-chave
Antibiose, Interação inseto-planta, Lagarta das vagens, Metodologia de pesquisa, Antixenose, Antibiosis, Plant-insect interaction, Soybean pods armyworm, Research methodology, Feeding preference