The physiological response of four commercial sugarcane genotypes to water stress was evaluated by measuring the photochemical efficiency of the photosystem II (chlorophyll a fluorescence ratio, F v /F m ), estimated chlorophyll content (SPAD unit), leaf temperature (LT) and leaf relative water content (RWC). A field trial was established in the subtropical area with well-watered and water-stressed genotypes, in completely randomized blocks with four replicates in a 4 9 2 9 3 factorial design (genotype 9 irrigation 9 evaluation date). Physiological measurements were done during a 90 day-period of formative stage of plants. The analysis of variance showed that the interaction of genotype 9 irrigation 9 evaluation date had a significant effect for three physiological markers tested, F v /F m , SPAD unit and RWC. Under non-stressed conditions, all genotypes showed similar responses for the four markers. Under water deficiency stress, two droughttolerant genotypes, HOCP01-523 and TCP89-3505 displayed higher values for F v /F m , SPAD unit and RWC, and lower values for LT, and could be classified as tolerant. It is therefore possible to use these physiological water stress associated traits as scorable marker traits for selecting drought-tolerant sugarcane genotypes in future breeding programs.

Mahanarva fimbriolata (Stål) (Hemiptera: Cercopidae) has become a key pest in the sugarcane (Saccharum officinarum) fields of center-south Brazil. Although some control technologies have shown to be efficient, the damage promoted by this spittlebug species and its interaction with sugarcane are poorly characterized. At high infestation levels the symptoms are similar to those of severe water restriction. This work was conducted to determine whether the stress promoted by spittlebug infestation can be measured in terms of free proline accumulation. The water restriction tolerance of two sugarcane genotypes was also compared. Two experiments were set up in a greenhouse and arranged in a completely randomized design in a 2 × 2 × 4 factorial, with two cultivars (SP80-1816 and RB72454), two stress levels (control and ten nymphs per plant or 50% water restriction), and four sampling dates. The water deficit caused by spittlebug nymphs sucking xylem sap does not result in proline accumulation, illustrating that there are different mechanisms to sense when the water deficit is caused by insect feeding or water potential variation in root cells. The cultivar RB72454 accumulates more free-proline, and the dry mass accumulation and stalk growth are less affected in this cultivar under water restriction. The levels of compatible solutes probably cannot be used to measure spittlebug infestation stress in sugarcane and RB72454 is more tolerant to water shortage than SP80-1816. Key words: Mahanarva fimbriolata, Saccharum spp., proline accumulation, water deficit ACÚMULO DE PROLINA EM CANA-DE-AÇÚCAR SOB ESTRESSE HÍDRICO OU SUBMETIDA AO ATAQUE DE CIGARRINHA-DAS-RAÍZESRESUMO: A cigarrinha-das-raízes Mahanarva fimbriolata (Stål) (Hemiptera: Cercopidae) tornou-se uma praga importante da cultura da cana-de-açúcar na região centro-sul do Brasil. Estratégias de controle têm sido desenvolvidas, mas os danos promovidos por essa praga e sua interação com a cana-de-açúcar ainda são pouco caracterizados. Em altos níveis de infestação da praga, os sintomas nas plantas são muito semelhantes à restrição hídrica severa. Este trabalho foi conduzido com o objetivo de determinar se o estresse promovido pela infestação de ninfas de cigarrinha-das-raízes resulta em acúmulo de prolina livre, além de comparar dois genótipos de cana-de-açúcar quanto à tolerância ao déficit hídrico. Dois experimentos foram conduzidos em delineamento inteiramente casualizado, em esquema fatorial 2 × 2 × 4 com duas cultivares (SP80-1816 e RB72454), dois níveis de estresse (controle e dez ninfas por planta ou 50% de restrição hídrica) e quatro épocas. O déficit hídrico promovido por M. fimbriolata não resultou em acúmulo de prolina, ilustrando a existência de mecanismos distintos para a percepção do estresse hídrico promovido pela praga e pela variação no potencial osmótico nas células das raízes. A cultivar RB72454 acumula maiores teores de prolina livre, e o acúmulo de massa seca e o crescimento dos colmos são menos afetados nessa cultivar sob restrição hídric...

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The increased rate of sugarcane harvest without previous burn has provided a very favorable environment to the froghopper Mahanarva fimbriolata (Stal, 1854), with high moisture and low temperature variation. Few works have studied the response of sugarcane to this pest, so little is known about resistant cultivars. Plant phenolics are widely studied compounds because of their known antiherbivore effect. This research aims to determine if the attack of M. fimbriolata nymphs stimulates the accumulation of total phenolics in sugarcane. The experiment was carried out in greenhouse and arranged in completely randomized design, in a 3 × 2 × 4 factorial with three replications. Second instar nymphs of M. fimbriolata were infested at the following rates: control, 2-4 and 4-8 nymphs per pot (first-second infestations, respectively). Pots were covered with nylon net and monitored daily to isolate the effect of leaf sucking adults. Leaf and root samples were collected and kept frozen in liquid nitrogen until analyses. Infested plants showed higher levels of phenolics in both root and leaf tissues. In roots, the cultivar SP80-1816 accumulated more phenolic compounds in response to the infestation of M. fimbriolata. On the other hand, higher levels were found in leaves and roots of control plants of SP86-42, which might be an indication of a non-preference mechanism. The increase of total phenolics in sugarcane infested with root-sucking froghopper nymphs does not seem to be useful to detect the resistance to this pest. Key words: Saccharum spp., phenolic compounds, secondary metabolism, plant-insect interaction INFESTAÇÃO DE NINFAS DE CIGARRINHAS-DAS-RAÍZES ALTERA A QUANTIDADE DE COMPOSTOS FENÓLICOS EM CANA-DE-AÇÚCARRESUMO: Com a intensificação da colheita mecanizada da cana-de-açúcar sem queima da palhada, a cigarrinha-das-raízes Mahanarva fimbriolata (Stal, 1854) tornou-se uma das principais pragas da cultura, favorecida pelas condições de umidade e baixa variação de temperatura do solo. Poucos trabalhos são dedicados ao estudo da resposta da planta ao ataque deste inseto, dificultando o conhecimento de cultivares resistentes. Os compostos fenólicos são muito estudados por sua ação anti-herbivoria. A presente pesquisa foi conduzida com o objetivo de verificar se o ataque de ninfas de M. fimbriolata induz alterações na quantidade de fenóis totais em cana-de-açúcar. O experimento foi instalado em casa de vegetação, com condições de temperatura e umidade controladas, com delineamento inteiramente casualizado em esquema fatorial 3 × 2 × 4 e três repetições. Ninfas de segundo ínstar de M. fimbriolata foram inoculadas no sistema radicular das plantas, nos níveis: controle, 2-4 e 4-8 ninfas por vaso (primeira-segunda infestação, respectivamente