Introduction. Citrus trees in Brazil are often attacked by the blackfly, Aleurocanthus woglumi Ashby. The induction of resistance to control this pest is required to maintain the sanitary and nutritional quality of the crop. The aim of this study was to evaluate the potential of silicon in the form of potassium silicate (K 2 SiO 3 ) to modify the activity of enzymes involved in the defence of Citrus reticulata and to find any correlation between the activity of these enzymes and the development

more »

... of A. woglumi. Materials and methods. The study was conducted in a greenhouse using seedlings of C. reticulate cv. 'Dancy' in the following one-application treatments: T 1 : Infestation with A. woglumi and no K 2 SiO 3 (control, "C"); T 2 : No A. woglumi and no K 2 SiO 3 (absolute control "AC"); T 3 : 17 g L −1 K 2 SiO + A. woglumi, T 4 : 35 g L −1 K 2 SiO + A. woglumi; T 5 : 52 g L −1 K 2 SiO + A. woglumi; and T 6 : 70 g L −1 K 2 SiO + A. woglumi. To perform the enzymatic analyses, one leaf was removed separately from each mandarin seedling after 10, 30, 50, 70, and 90 days of continuous feeding of A. woglumi. The activity of peroxidase, polyphenol oxidase and phenylalanine ammonia-lyase was assessed. Results and discussion. The correlation between peroxidase activity and A. woglumi development was positive. The peroxidase and polyphenol activities indicated strong induction of plant defences against A. woglumi. The increase in peroxidase and polyphenoloxidase activity revealed the induction of synthesis of compounds for plant defence against A. woglumi, but this effect depended on the time of A. woglumi feeding and on the concentration of silicon. Conclusion. Silicon was shown to be an elicitor that potentiates the defence mechanisms of C. reticulata to A. woglumi. Keywords: Brazil / mandarin (Citrus reticulate) / blackfly (Aleurocanthus woglumi) / resistance inductor / peroxidase / polyphenol oxidase / phenylalanine ammonia-lyase Résumé -Résistance aux aleurodes noires des agrumes induite par le silicate de potassium dans les semis de mandarinier (Citrus reticulata). Introduction. Les agrumes au Brésil sont fréquemment attaqués par des aleurodes (Aleurocanthus woglumi Ashby). L'induction de résistance pour lutter contre ce ravageur est nécessaire pour maintenir la qualité sanitaire et nutritionnelle de la récolte. Le but de cette étude était d'évaluer le potentiel du silicium sous la forme de silicate de potassium (K 2 SiO 3 ) dans la modification de l'activité des enzymes impliquées dans la réaction de défense du mandarinier (Citrus reticulata), et aussi de trouver une corrélation entre l'activité de ces enzymes et le développement des aleurodes. Matériel et méthodes. L'étude a été menée en serre en utilisant des plants de mandarinier cv. Dancy. Les traitements suivants ont été appliqués : T 1