Effect of silicon in the induction of resistance to the spittlebug Mahanarva fimbriolata Stål (Hemiptera: Cercopidae) on sugarcane cultivars / Efeito do silício na indução de resistência à cigarrinha-das-raízes Mahanarva fimbriolata Stål (Hemiptera: Cercopidae) em cultivares de cana-de-açúcar

Ana Paula Korndorfer

The present work aimed to study the effect of silicon applied in different cultivars of sugarcanes in biological and behavioral aspects of the spittlebug (Mahanarva fimbriolata) and in the yield and quality of the cane. Studies were conducted in the laboratory and on the field. In laboratory the cultivars SP79-1011 and SP80-1816 (resistant to spittlebug) and SP81-3250 (susceptible) were grown in sandy or clay soil with and without silicon fertilization (800 kg·ha-1 of potassium silicate). In another experiment, the cultivars SP81-3250 and SP79-1011 were kept in pots with and without silicon addition, and were exposed to spittlebug adults throughout different periods (0, 12, 24 and 36h), and the concentration of soluble phenolic compounds in plants were quantified. In both experiments the insects were obtained from a laboratory rearing. The field experiment was conducted at Guaíra Sugarcane Mill, in Guaíra, São Paulo. Treatments consisted of 16 cultivars with and without silicon application (800 kg·ha-1 of calcium and magnesium silicate). The evaluation of spittlebug infestation (nymphs and adults) was performed fortnightly. At the time of sugarcane harvest, plants were collected to carry out the analysis of technological parameters. In the laboratory experiment, the silicon absorbed and accumulated in the plant caused an increase in nymphs mortality and, depending on variety, this element also provided an increase in the duration of the nymphal stage and decreased longevity of males and females. The SP79-1011 cultivar showed the best performance in most parameters, presenting higher silicon content in leaves and causing increased mortality of nymphs and shorter female longevity. The pre-oviposition period, fecundity and egg viability were not affected by the silicon in plants or the cultivar used. The value of soluble phenolic compounds did not differ between plants treated and not treated with silicon. After the first hours of exposure to spittlebug, the resistant cultivar not only produced a higher concentration of phenolic compounds, but when treated with silicon responded more quickly to the attack. Silicon fertilization in the field reduced the number of nymphs but did not affect the adult population and increased values of Brix% and Pol% from cane juice, and the sugarcane fiber content. Moreover, there was change in yield among cultivars with the highest values for SP84-1431 and SP80-3280.

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