RESUMO

It is well known that herbivore-induced plant defenses alter host plant quality and can affect the behavior and performance of later arriving herbivores. Effects of sequential attacks by herbivores that either suppress or induce plant defenses are less well studied. We sequentially infested leaves of tomato plants with a strain of the phytophagous spider mite Tetranychus urticae that induces plant defenses and the closely related Tetranychus evansi, which suppresses plant defenses. Plant quality was quantified through oviposition of both spider mite species and by measuring proteinase inhibitor activity using plant material that had been sequentially attacked by both herbivore species. Spider-mite oviposition data show that T. evansi could suppress an earlier induction of plant defenses by T. urticae, and T. urticae could induce defenses in plants previously attacked by T. evansi in 1 day. Longer attacks by the second species did not result in further changes in oviposition. Proteinase inhibitor activity levels showed that T. evansi suppressed the high activity levels induced by T. urticae to constitutive levels in 1 day, and further suppressed activity to levels similar to those in plants attacked by T. evansi alone. Attacks by T. urticae induced proteinase inhibitor activity in plants previously attacked by T. evansi, eventually to similar levels as induced by T. urticae alone. Hence, plant quality and plant defenses were significantly affected by sequential attacks and the order of attack does not affect subsequent performance, but does affect proteinase inhibitor activity levels. Based on our results, we discuss the evolution of suppression of plant defenses.

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We tested the sulfur-modulated plant resistance hypothesis using potted cabbage (Brassica oleracea var. capitata) plants that were grown without and with increasing levels of sulfur fertilization. Changes in plant chemical traits were assessed and developmental performance of Plutella xylostella, a highly host-specific leaf-chewing insect, was followed. Leaf sulfur concentration gradually increased with growing addition of sulfur in soil; however, there was a generalized saturation response curve, with a plateau phase, for improvements in total leaf nitrogen, defense glucosinolates and insect performance. Plutella xylostella performed better in sulfur-fertilized cabbage probably because of the higher level of nitrogen, despite of the higher content of glucosinolates, which are toxic for many non-specialized insects. Despite the importance of sulfur in plant nutrition and production, especially for Brassica crops, our results showed that sulfur fertilization could decrease plant resistance against insects with high feeding specialization.

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Browsing damage by native ungulates is often to be considered one of the reasons of regeneration failure in Nothofagus pumilio silvicultural systems. Fencing and hunting in forests at regeneration phase have been proposed to mitigate browsing effects. This study aims to determine effectiveness of these control methods in harvested forests, evaluating browsing damage over regeneration, as well as climate-related constraints (freezing or desiccation). Forest structure and regeneration plots were established in two exclosures against native ungulates (Lama guanicoe) by wire fences in the Chilean portion of Tierra del Fuego island, where tree regeneration density, growth, abiotic damage and quality (multi-stems and base/stem deformation) were assessed. Exclosures did not influence regeneration density (at the initial stage with < 1.3 m high, and at the advanced stage with >1.3 m high). However, sapling height at 10-years old was significantly lower outside (40-50 cm high) than inside exclosures (80-100 cm), and also increased their annual height growth, probably as a hunting effect. Likewise, quality was better inside exclosures. Alongside browsing, abiotic conditions negatively influenced sapling quality in the regeneration phase (20%-28% of all seedlings), but greatly to taller plants (as those from inside exclosure). This highlights the importance of considering climatic factors when analysing browsing effects. For best results, control of guanaco in recently harvested areas by fencing should be applied in combination with a reduction of guanaco density through continuous hunting. The benefits of mitigation actions (fencing and hunting) on regeneration growth may shorten the regeneration phase period in shelterwood cutting forests (30-50% less time), but incremental costs must be analysed in the framework of management planning by means of long-term studies.

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A gérbera é uma espécie ornamental perene, herbácea e pertencente à família Asteraceae. O seu cultivo, assim como todo o mercado de flores e plantas ornamentais, está hoje em plena fase de expansão. O objetivo deste trabalho foi avaliar características de crescimento e qualidade em gérbera de vaso, cultivar Red, em função de fontes e doses de potássio. O experimento foi conduzido em casa de vegetação, na UNESP/Botucatu. O delineamento experimental adotado foi em blocos casualizados, empregando o esquema fatorial 2x5, sendo duas fontes de potássio (silicato e cloreto) e cinco doses (0, 50, 100, 150 e 200 mg . L-1 4 repetições e 5 plantas por parcela. Semanalmente, durante todo o período experimental, foram feitas avaliações do número de folhas (NF) e do diâmetro da parte aérea da planta (DP). Ao final do ciclo vegetativo e do ciclo reprodutivo, aos 40 e 60 dias após a aclimatização (DAA), respectivamente, foram determinadas a área foliar (AF), a massa (seca das folhas (MSF), a massa seca da inflorescência (MSI) e a massa seca total (MST). No ponto de comercialização que é caracterizado pela abertura dos estames, quando a inflorescência apresentou no mínimo dois círculos destes abertos, com liberação de pólen, foram determinados o número de inflorescência (NI), o diâmetro de inflorescência (DI), a altura de haste (AH), o diâmetro de haste (DH) e a altura de planta (AP). Independentemente das doses, o silicato de potássio promoveu maior diâmetro de planta, maior área foliar, maior MSF, MST e maior altura de haste, características essas que favorecem a venda dos vasos de gérbera.

The Gerbera is an ornamental perennial herb, belonging to the Asteraceae family. Its cultivation, as well as the entire market for flowers and ornamental plants, is now in full expansion phase. The objective of this study was to evaluate the growth and quality Potted gerbera cultivar Red, according to sources and doses of potassium. The experiment was conducted in a greenhouse at UNESP / Botucatu. The experimental design was randomized blocks, using a 2x5 factorial arrangement, with two sources (potassium silicate and chloride) and five doses (0, 50, 100, 150 and 200 mg. L-1) 4 replications and 5 plants per plot . Weekly throughout the experimental period, assessments were made of the number of leaves (NL) and the diameter of the plant canopy (DP). at the end of the season and the reproductive cycle, at 42 and 60 days after acclimatization (DAA), respectively, were determined by leaf area (LA), mass (dry leaves (MSF), the dry mass of inflorescence (MSI) and total dry matter (TDM). at the point of marketing is that of open stamens, when the inflorescence had at least two rounds of open, releasing pollen, we determined the number of inflorescences (NI), the diameter of inflorescence (DI), the stem height (AH), the shank diameter (DH ) and plant height (PH). Regardless of the doses, potassium silicate promoted greater diameter, leaf area, greater MSF, MST and increased stem height, characteristics that favor the sale of potted gerbera.

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Seasonal variation in plant quality may be intense enough to generate predictable patterns in insect herbivore populations. In order to explain seasonal oscillations in neotropical populations of the diamondback moth Plutella xylostella (L.), we tested the following: (1) if nutritional quality of cabbage (Brassica oleraceae var. capitata), a primary host plant of diamondback moth, adversely affects the performance of this insect in late spring and early summer, when populations decline and go extinct, and (2) if nutritional features of cabbage change with the seasons. We measured the performance of diamondback moth reared on leaves of cabbages grown during the four seasons of the year. Summer plants proved to be worse for the survival of the immature stages and subsequent adult fecundity, but there were no significant differences between the remaining seasons. Our results support the hypothesis that short-lived plants, grown in different seasons of the year in the tropics, have different nutritional and defensive attributes. We analyzed nutritional quality of cabbage leaves from the four seasons, but only total lipids were reduced in summer plants. Neotropical populations of diamondback moth collapse before plant quality decay in the summer. If the diamondback moth is well adapted to the seasonal deterioration of the habitat, including the reduction in the quality of host plants, it is expected that emigration happens before the mortality increases and natality decreases during the summer.

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The objective of this research was to evaluate the vegetative and reproductive behavior as well as the length of growing stage of two chrysanthemum cultivars under protected environment and submitted to different number of prunings and pot sizes. The experiment was conducted from April 30 until December 12, 2003 in a greenhouse located at the University of Santa Maria, RS, Brazil. Three pot sizes were used: 11, 15 and 20. The variance analysis for plant height and stem diameter was conducted under a bifactorial scheme: number of prunings (1ª up to 31ª week), for each combination of cultivar and pot size. Regarding the inflorescence production, they were considered as treatments the numbers of prunings for each pot size and chrysanthemum cultivar. The means were compared using the Tukey Test (a=5%). Plant height, stem diameter and number of inflorescences increased as the number of prunings and pot size increased, however, stem diameter decreased on both cultivars. The cultivar Veria Dark was less responsive than cultivar Papiro. In order to produce good quality plants, there is a necessity to increase the number of prunings as pot size increases. To cultivate would see them Dark and Papiro had presented good performance in the region of Santa Maria, RS, mainly with the use of four lappings of the tops of corn for the vases number 11 and five for the vases number 15 and 20, being the cycle of culture of 21 weeks in the vase number 11 and 25 weeks, in the vase number 15 and 20.

O objetivo deste trabalho foi avaliar o comportamento vegetativo e reprodutivo e a duração do ciclo de duas cultivares de crisântemo multiflora, em ambiente protegido, quando submetidos a diferentes números de despontes e tamanhos de vasos. O experimento foi conduzido no período de 30 de abril a 12 de dezembro de 2003, em casa-de-vegetação do Departamento de Fitotecnia da UFSM, Santa Maria, RS, Brasil. As duas cultivares foram conduzidas em três tamanhos de vasos: número 11, 15 e 20. A análise de variância dos dados de altura e diâmetro das plantas foi realizada em esquema bifatorial: número de despontes (de dois a sete, conforme o tamanho do vaso) versus semana após transplante (1ª até a 31ª semana), para cada combinação de cultivar e tamanho de vaso. Para a análise da produção de inflorescências, consideraram-se como tratamentos os números de despontes aplicados em cada tamanho de vaso e cultivar, e as médias foram comparadas pelo Teste de Tukey (a=5%). A altura, o diâmetro das plantas e o número de inflorescências aumentam à medida que são aplicados mais despontes e cultivadas em vasos maiores, porém o diâmetro das inflorescências é reduzido, em ambas as cultivares. A cultivar "Veria Dark" apresenta menor capacidade de brotação em relação a "Papiro". O aumento do tamanho do vaso determina a necessidade de aumentar o número de despontes para a produção de plantas de qualidade. As cultivares "Veria Dark" e "Papiro" apresentaram bom desempenho na região de Santa Maria, RS, principalmente, com o emprego de quatro despontes para os vasos número 11 e cinco para os vasos número 15 e 20, sendo o ciclo de cultivo de 21 SAT nos vasos número 11 e 25 SAT nos vasos 15 e 20.

RESUMO

The objective of this research was to evaluate the vegetative and reproductive behavior as well as the length of growing stage of two chrysanthemum cultivars under protected environment and submitted to different number of prunings and pot sizes. The experiment was conducted from April 30 until December 12, 2003 in a greenhouse located at the University of Santa Maria, RS, Brazil. Three pot sizes were used: 11, 15 and 20. The variance analysis for plant height and stem diameter was conducted under a bifactorial scheme: number of prunings (1ª up to 31ª week), for each combination of cultivar and pot size. Regarding the inflorescence production, they were considered as treatments the numbers of prunings for each pot size and chrysanthemum cultivar. The means were compared using the Tukey Test (a=5%). Plant height, stem diameter and number of inflorescences increased as the number of prunings and pot size increased, however, stem diameter decreased on both cultivars. The cultivar Veria Dark was less responsive than cultivar Papiro. In order to produce good quality plants, there is a necessity to increase the number of prunings as pot size increases. To cultivate would see them Dark and Papiro had presented good performance in the region of Santa Maria, RS, mainly with the use of four lappings of the tops of corn for the vases number 11 and five for the vases number 15 and 20, being the cycle of culture of 21 weeks in the vase number 11 and 25 weeks, in the vase number 15 and 20.

O objetivo deste trabalho foi avaliar o comportamento vegetativo e reprodutivo e a duração do ciclo de duas cultivares de crisântemo multiflora, em ambiente protegido, quando submetidos a diferentes números de despontes e tamanhos de vasos. O experimento foi conduzido no período de 30 de abril a 12 de dezembro de 2003, em casa-de-vegetação do Departamento de Fitotecnia da UFSM, Santa Maria, RS, Brasil. As duas cultivares foram conduzidas em três tamanhos de vasos: número 11, 15 e 20. A análise de variância dos dados de altura e diâmetro das plantas foi realizada em esquema bifatorial: número de despontes (de dois a sete, conforme o tamanho do vaso) versus semana após transplante (1ª até a 31ª semana), para cada combinação de cultivar e tamanho de vaso. Para a análise da produção de inflorescências, consideraram-se como tratamentos os números de despontes aplicados em cada tamanho de vaso e cultivar, e as médias foram comparadas pelo Teste de Tukey (a=5%). A altura, o diâmetro das plantas e o número de inflorescências aumentam à medida que são aplicados mais despontes e cultivadas em vasos maiores, porém o diâmetro das inflorescências é reduzido, em ambas as cultivares. A cultivar "Veria Dark" apresenta menor capacidade de brotação em relação a "Papiro". O aumento do tamanho do vaso determina a necessidade de aumentar o número de despontes para a produção de plantas de qualidade. As cultivares "Veria Dark" e "Papiro" apresentaram bom desempenho na região de Santa Maria, RS, principalmente, com o emprego de quatro despontes para os vasos número 11 e cinco para os vasos número 15 e 20, sendo o ciclo de cultivo de 21 SAT nos vasos número 11 e 25 SAT nos vasos 15 e 20.