Metodologia de pesquisa, categorias e mecanismos de resistência em milho a Diabrotica speciosa (GERMAR) e Oligonychus pratensis (BANKS)
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Data
2016-07-26
Autores
Costa, Eduardo Neves
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Universidade Estadual Paulista (Unesp)
Resumo
O inseto Diabrotica speciosa (Germar) e o ácaro Oligonychus pratensis (Banks) representam uma das principais pragas da cultura do milho, no Brasil e nos EUA, respectivamente. Essas pragas são controladas principalmente via aplicação de inseticidas químicos; contudo, há alternativas para tornar o manejo dessas pragas menos impactante, como o uso de plantas resistentes. Assim, esse trabalho teve como objetivo avaliar: (1) a resistência de cultivares de milho crioulo a D. speciosa; (2) a resistência de híbridos de milho resistentes à seca ao ácaro O. pratensis; (3) os mecanismos relacionados com a resistência a essas pragas; e (4) definir, através de testes de metodologia de pesquisa, a melhor forma para a condução dos ensaios. Desse modo, o presente trabalho é constituído por quatro pesquisas. Na primeira pesquisa, foi avaliada a antibiose em 19 cultivares de milho crioulo a D. speciosa, investigando se a expressão dessa categoria de resistência estava associada com algum mecanismo morfológico (lignina, celulose, fibras, e hemicelulose) ou químico (fenóis totais). No segundo trabalho, estudou-se a tolerância em seis cultivares de milho crioulo, previamente selecionados no teste de antibiose. A tolerância foi correlacionada com alguns componentes que participam do metabolismo primário vegetal, como a clorofila, os carotenoides, a glicina betaína, e a prolina. Em um terceiro experimento, foi avaliada a oviposição de D. speciosa nas seis cultivares selecionadas, discutindo os resultados quanto ao comportamento do inseto. No quarto ensaio, estudou-se a antibiose e a tolerância a O. pratensis em híbridos de milho resistentes à seca. Nessa pesquisa, foi avaliado se marcadores moleculares associados com resistência a estresses bióticos amplificariam o DNA de plantas resistente e suscetível, e se seria visualizado polimorfismos nos padrões de banda do DNA quando examinados em gel de agarose. As cultivares de milho crioulo Pérola, Fortuna e Palha Roxa manifestaram antibiose a D. speciosa, sendo isso observado no desenvolvimento e na sobrevivência (Pérola e Fortuna), e na fertilidade (Palha Roxa) do inseto. Observou-se que as cultivares resistentes exibiram as menores perdas de lignina, celulose, fibras e hemicelulose nas raízes de milho injuriadas por larvas de D. speciosa. A cultivar Azteca, que foi a mais suscetível em teste de antibiose, se destacou como a mais tolerante ao ataque da praga, além de apresentar os maiores teores de clorofilas e carotenoides. No que diz respeito à preferência para oviposição, as fêmeas de D. speciosa ovipositaram igualmente em cultivares resistentes e suscetíveis. O ácaro O. pratensis encontrou dificuldades para se desenvolver e sobreviver no híbrido de milho resistente à seca Artesian. Seis genes relacionados com resistência a estresses bióticos foram encontrados nesse híbrido, enquanto que no híbrido Droughtgard, que foi suscetível ao ácaro, nenhum daqueles genes foi observado. Os resultados obtidos neste trabalho demonstram o potencial da resistência de plantas de milho para o controle de pragas agrícolas, fornecendo informações à respeito de alguns dos mecanismos envolvidos na resistência dos materiais estudados, contribuindo, assim, para o desenvolvimento do Manejo Integrado de Pragas
The insect Diabrotica speciosa (Germar) and the mite Oligonychus pratensis (Banks) represent one of the major maize crop pests, in Brazil and in the USA, respectively. These pests are controlled primarily through the application of chemical insecticides; however, there are alternatives to make the management of these pests less impactful, as the use of resistant plants. Thus, this work aimed: (1) to determine, through testing research methodologies, the best way to conduct the assays; to evaluate (2) the resistance of maize landraces to D. speciosa and (3) the resistance of drought resistant maize hybrids to the mite O. pratensis; and lastly, (4) to reveal the mechanisms associated with the resistance to these pests. Thereby, the present work is constituted by four researches. In the first research, the antibiosis to D. speciosa was assessed in 19 maize landraces, investigating whether the expression of this resistance category was related with some morphological (lignin, cellulose, fibers, and hemicellulose) or chemical (total phenols) mechanism. In the second work, the tolerance was studied in six maize landraces previously selected in the antibiosis test. The tolerance was correlated with some compounds which participate in the primary metabolism of plants, as the chlorophyll, the carotenoids, the glycine betaine, and the proline. In a third experiment, the oviposition of D. speciosa was assessed on the six cultivars selected, discussing the results regarding the insect behavior. In the fourth assay, the antibiosis and tolerance were assessed to O. pratensis in drought resistant maize hybrids. This research aimed also to evaluate whether molecular markers associated with resistance to biotic factors would amplify the DNA of resistant and susceptible plants, and if it would be visualized polymorphisms in the banding patterns of the DNA when examined in agarose gel. The maize landraces Pérola, Fortuna, and Palha Roxa manifested antibiosis to D. speciosa, and it was observed on the development and survival (Pérola and Fortuna), and on the fertility (Palha Roxa) of the insect. The resistant cultivars exhibited the lowest losses of lignin, cellulose, fibers, and hemicellulose in the injured maize roots by D. speciosa larvae. Interestingly, the cultivar Azteca, which was the most susceptible in the antibiosis test, stood out as the most tolerant to the pest attack, besides showing the highest amounts of chlorophyll and carotenoids. With regards to the oviposition preference, the D. speciosa females laid eggs equally on the resistant and susceptible cultivars. The mite O. pratensis found difficulties for the development and survival on the Artesian drought resistant maize hybrid. Six genes associated with resistance to biotic stresses were found in this hybrid, whereas in the susceptible hybrid, Droughtgard, no one gene was noted. The results obtained in this work displays the potential of the maize plant resistance for the control of agricultural pests, providing information as to some mechanisms involved in the resistance of the materials studied, contributing, thus, for the development of the Integrated Pest Management
The insect Diabrotica speciosa (Germar) and the mite Oligonychus pratensis (Banks) represent one of the major maize crop pests, in Brazil and in the USA, respectively. These pests are controlled primarily through the application of chemical insecticides; however, there are alternatives to make the management of these pests less impactful, as the use of resistant plants. Thus, this work aimed: (1) to determine, through testing research methodologies, the best way to conduct the assays; to evaluate (2) the resistance of maize landraces to D. speciosa and (3) the resistance of drought resistant maize hybrids to the mite O. pratensis; and lastly, (4) to reveal the mechanisms associated with the resistance to these pests. Thereby, the present work is constituted by four researches. In the first research, the antibiosis to D. speciosa was assessed in 19 maize landraces, investigating whether the expression of this resistance category was related with some morphological (lignin, cellulose, fibers, and hemicellulose) or chemical (total phenols) mechanism. In the second work, the tolerance was studied in six maize landraces previously selected in the antibiosis test. The tolerance was correlated with some compounds which participate in the primary metabolism of plants, as the chlorophyll, the carotenoids, the glycine betaine, and the proline. In a third experiment, the oviposition of D. speciosa was assessed on the six cultivars selected, discussing the results regarding the insect behavior. In the fourth assay, the antibiosis and tolerance were assessed to O. pratensis in drought resistant maize hybrids. This research aimed also to evaluate whether molecular markers associated with resistance to biotic factors would amplify the DNA of resistant and susceptible plants, and if it would be visualized polymorphisms in the banding patterns of the DNA when examined in agarose gel. The maize landraces Pérola, Fortuna, and Palha Roxa manifested antibiosis to D. speciosa, and it was observed on the development and survival (Pérola and Fortuna), and on the fertility (Palha Roxa) of the insect. The resistant cultivars exhibited the lowest losses of lignin, cellulose, fibers, and hemicellulose in the injured maize roots by D. speciosa larvae. Interestingly, the cultivar Azteca, which was the most susceptible in the antibiosis test, stood out as the most tolerant to the pest attack, besides showing the highest amounts of chlorophyll and carotenoids. With regards to the oviposition preference, the D. speciosa females laid eggs equally on the resistant and susceptible cultivars. The mite O. pratensis found difficulties for the development and survival on the Artesian drought resistant maize hybrid. Six genes associated with resistance to biotic stresses were found in this hybrid, whereas in the susceptible hybrid, Droughtgard, no one gene was noted. The results obtained in this work displays the potential of the maize plant resistance for the control of agricultural pests, providing information as to some mechanisms involved in the resistance of the materials studied, contributing, thus, for the development of the Integrated Pest Management
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Palavras-chave
Zea mays L., Antibiose, Antixenose, Tolerância, Barreiras morfológicas, Larva-alfinete, Antibiosis, Antixenosis, Tolerance, Morphological barriers, Corn rootworm