Short height and high yield per unit energy in controlled environments are essential to the success of a food production system for spaceflight. Temperature and light quality can be manipulated in controlled environments to reduce plant height and increase yield. Although the effects of temperature on height and yield are well studied at ambient CO2, temperature effects at elevated CO2 with a hydroponic root zone are not well characterized. We studied soybean yield and height under two lamp types over a broad range of temperatures. Temperature had little effect on yield or height, but lamp type had a significant effect on canopy height. This first study highlighted the importance of understanding spectral quality in controlling plant growth, especially canopy height. Numerous studies have compared lamp types and suggested that profound differences in leaf area, canopy height, yield, and total dry mass responses were due to blue light differences. Unfortunately, the most energy-efficient light sources have the least blue light. We have a poor understanding of the specific morphological and histological effects of blue light on leaves and stems. Three species, soybeans, wheat, and lettuce, were grown at five blue light fractions (0, 2, 6, 12, and 26%) and two light levels (200 and 500 μmol m-2 s-1). Phytochrome photoequilibria were constant among treatments. Blue light responses were species dependent. Wheat leaf area, dry mass, and stem length were insensitive to blue light fraction. Increasing blue light to 26% decreased soybean stem length, but leaf area was greatest at 6% blue. Lettuce leaf area, stem length, and dry mass were highly sensitive to blue light fraction between 0% and 6% under high pressure sodium lamps, but were insensitive between 6% and 26% under metal halide lamps. These results may be complicated by sensitivity to other wavelengths . The decrease in soybean stem length with increasing blue light was caused by an inhibition of cell division, while the decrease in leaf area was caused primarily by a decrease in cell expansion. Increased lettuce leaf area with increasing blue light fraction was caused by both cell division and expansion. This research indicates that lamps high in blue photons are not only energetically wasteful, but do not benefit, and in some cases reduce, plant growth. However, some blue light is necessary for controlling plant height in soybean and even required for proper growth and development in lettuce.

Pythium root rot caused by Pythium aphanidermatum, a destructive disease of sweet pepper and other hydroponic crops, is characterized by root browning (necrosis) and reduces growth of roots and shoots. Serious losses in crop productivity are common, in part for lack of adequate control measures. Severe root rot has been previously associated with episodes of high temperature, but whether this is due to high temperature effects on the host, the pathogen, or their interaction remains unclear. To clarify these relationships, and to provide a basis for predicting rapid increases in root rot, quantitative experiments were conducted to determine how episodes of high root-zone temperature are associated with root browning. Pepper plants were grown separately in hydroponic units containing aerated nutrient solution positioned in temperature-controlled water baths. The root zone temperature was 23°C except during high temperature treatments. Browning developed progressively earlier in roots that were maintained at 33°C for 9 to 144 h immediately before they were inoculated with zoospores of P. aphanidermatum, and in all instances earlier than in control plants maintained continuously at 23°C. The data demonstrated unequivocally that high root-zone temperature can predispose pepper plants to Pythium root rot. Browning also developed earlier when root inoculation with P. aphanidermatum was delayed as long as 216 h following exposure at 33°C for 72 h, indicating that predisposition of the host by high temperature episodes can persist for at least 9 days. The ability of Pseudomonas chlororaphis strain 63-28 to suppress Pythium root rot and promote plant growth was investigated in pepper plants grown in the hydroponic units and predisposed to the disease, i.e. plants were predisposed to high temperature (33°C for 72 h ending at 3 days before inoculation) or not predisposed (constant 23°C). When P. chlororaphis was applied in the nutrient solution at a final density of 107 CFU mL-1 7 days before the high temperature episode, the agent delayed root browning, re-mediated predisposition to root rot, and increased growth of plants that were and were not inoculated with P. aphanidermatum. It is concluded that high temperature predisposed pepper seedlings to root rot and that strain 63-28 has substantial potential for managing root rot regardless of predisposition by high temperature.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The aim of this study was to evaluate the performance and ingestive behavior of beef heifers grazing natural grassland managed under rotational grazing according to two rest periods in spring and summer. The treatments were two intervals between grazing 375 and 750 DD (degree days), based on thermal cumulative average for leaf expansion of native grasses belonging to two functional groups. The experimental design was randomized complete block design with two treatments and three replications. The experiment was conducted from November 2011 to April 2012. The test animals were Angus beef heifers, with an initial mean age of 12 months and initial weight 185.2 ± 17.4 kg. The ingestive behavior variables evaluated were grazing time, rumination and rest, and daily number and duration of meals, bite rate, number of stations visited per minute, number of steps between feeding stations, length of stay at the station. All variables of ingestive behavior were similar between treatments. However, grazing time and biting rate ranged between assessments. The different intervals between grazing on natural pasture did not influence the patterns of ingestive behavior of heifers. The variables of pasture mass of green leaf and stalk weight in different time periods evaluated the influence of grazing, ruminating and bite rate. Forage mass was higher in the 750 DD treatment, however, the mass of leaf blades were similar among treatments. The highest average daily gains and gains per area were observed in 375 DD treatment. In one evaluation period there was weight loss in animals of both treatments, that was attributed to a drought occurred and the lowest mass of leaf blades of the period. The average stocking density was similar between treatments. The treatment of lower defoliation interval presented greater individual gain. / O objetivo deste estudo foi avaliar o desempenho produtivo e o comportamento ingestivo de novilhas de corte em pastagem natural manejada sob pastoreio rotativo em função de dois intervalos de descanso na primavera-verão. Os tratamentos avaliados foram dois intervalos entre pastoreios 375 e 750 GD (graus-dia), baseados na soma térmica média acumulada para a expansão foliar de gramíneas nativas pertencentes a dois grupos funcionais. O delineamento utilizado foi em blocos completamente casualizados com dois tratamentos e três repetições de área. O experimento foi conduzido de novembro de 2011 a abril de 2012. Os animais testes foram novilhas de corte, da raça Angus, com idade média inicial de 12 meses e peso inicial 185,2 ± 17,4 kg. As variáveis do comportamento ingestivo avaliadas foram o tempo de pastejo, ruminação e ócio, além de número diário e duração das refeições, taxa de bocados, número de estações visitadas por minuto, número de passos entre estações alimentares, tempo de permanência na estação. Todas as variáveis do comportamento ingestivo foram semelhantes entre os tratamentos avaliados. No entanto, o tempo de pastejo e a taxa de bocados variaram entre as avaliações. Os diferentes intervalos entre pastoreios em pastagem natural não influenciou os padrões de comportamento ingestivo das novilhas. As variáveis do pasto MLFV e massa de colmos nos diferentes períodos avaliados influenciaram nos tempos de pastejo, ruminação e taxa de bocados. A massa de forragem foi superior no tratamento 750 GD, no entanto, a massa de lâminas foliares foi semelhante entre os tratamentos. Os maiores ganhos médios diários e ganhos por área foram observados no tratamento 375 GD. Em um dos períodos de avaliação houve perda de peso nos animais de ambos os tratamentos, que foi atribuído ao déficit hídrico ocorrido e a menor massa de lâminas foliares do período. As cargas médias foram semelhantes entre os tratamentos. O tratamento de menor intervalo entre desfolhas proporcionou aos animais maior ganho individual.

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