Maize leaf development under climate change scenarios

The objective of this work was to simulate maize leaf development in climate change scenarios at Santa Maria, RS, Brazil, considering symmetric and asymmetric increases in air temperature. The model of Wang & Engel for leaf appearance rate (LAR), with genotype-specific coefficients for the maize variety BRS Missões, was used to simulate tip and expanded leaf accumulated number from emergence to flag leaf appearance and expansion, for nine emergence dates from August 15 to April 15. LAR model was run for each emergence date in 100-year climate scenarios: current climate, and +1, +2, +3, +4 and +5°C increase in mean air temperature, with symmetric and asymmetric increase in daily minimum and maximum air temperature. Maize crop failure due to frost decreased in elevated temperature scenarios, in the very early and very late emergence dates, indicating a lengthening in the maize growing season in warmer climates. The leaf development period in maize was shorter in elevated temperature scenarios, with greater shortening in asymmetric temperature increases, indicating that warmer nights accelerate vegetative development in maize.

Intercepted solar radiation by maize crops subjected to different tillage systems and water availability levels

The objective of this work was to evaluate changes in the photosynthetic photon flux density (PPFD) interception efficiency and PPFD extinction coefficient for maize crop subjected to different soil tillage systems and water availability levels. Crops were subjected to no-tillage and conventional tillage systems combined with full irrigation and non-irrigation treatments. Continuous measurements of transmitted PPFD on the soil surface and incoming PPFD over the canopy were taken throughout the crop cycle. Leaf area index and soil water potential were also measured during the whole period. Considering a mean value over the maize cycle, intercepted PPFD was higher in the conventional tillage than in the no-tillage system. During the initial stages of plants, intercepted PPFD in the conventional tillage was double the PPFD interception in the no-tillage treatment. However, those differences were reduced up to the maximum leaf area index, close to tasseling stage. The lowest interception of PPFD occurred in the conventional tillage during the reproductive period, as leaf senescence progressed. Over the entire crop cycle, the interception of PPFD by the non-irrigated plants was about 20% lower than by the irrigated plants. The no-tillage system reduced the extinction coefficient for PPFD, which may have allowed a higher penetration of solar radiation into the canopy

Trichogramma pretiosum attraction due to the Elasmopalpus lignosellus damage in maize

The objective of this work was to evaluate if corn plants damaged by the lesser cornstalk borer (Elasmopalpus lignosellus) larvae release volatile organic compounds capable of attracting the egg parasitoid Trichogramma pretiosum. The treatments consisted of plants subjected to harm caused by E. lignosellus larvae, plants subjected to mechanical damage, and undamaged plants. The parasitoid was more attracted by the volatiles released by the insect damaged plants than to those released by undamaged corn plants, after 24 and 72 hours. The volatiles (Z)-3-hexenyl acetate, β-pinene, β-myrcene, (E)-4,8-dimethylnona-1,3,7-triene, and benzothiazole were released in significantly larger quantities by damaged plants. Volatiles released by corn plants damaged by E. lignosellus larvae may act as an indirect defense, attracting by T. pretiosum.

'Tommy Atkins' mango trees subjected to high density planting in subhumid tropical climate in northeastern Brazil

The objective of this work was to evaluate the effects of high density planting on 'Tommy Atkins' mango trees cultivated in subhumid warm tropical climate in northeastern Brazil. Treatments consisted of five spacial arrangements of plants (8x5 m, 7x4 m, 6x3 m, 5x2 m and 4x2 m), which resulted in the following plant densities: 250 (control), 357, 555, 1,000 and 1,250 plants per hectare. Plant vegetative and reproductive variables, besides fruit quality parameters, were evaluated at seven and eight years after transplantation to the field. In general, high density planting caused reduction in vegetative and reproductive variables of individual mango trees, but had little influence on fruit quality. Above 555 plants per hectare, a significant decrease was observed in mango tree growth. Furthermore, there were decreases in the percentage of flowering, fruit yield per plant and per area. However, planting density up to 357 plants per hectare, in spite of decreasing plant growth and fruit yield per tree, increases fruit yield per area in 30% in comparison to the control.

Effect of thinning on stem form and wood characteristics of teak (Tectona grandis) in a humid tropical site in Costa Rica

Abstract

Potasssium chloride as a nutrient seed primer to enhance salt‑tolerance in maize

The objective of this work was to determine if KCl could be a useful nutrient primer for safe seed germination in maize crop under salt stress conditions. Seed priming was done using 50 mmol L‑1 of muriate of potash, and germination and seedling growth were evaluated after salt stress with NaCl up to 50 mmol L‑1. Another set of seeds was tested under the same salt stress conditions without priming. Under salinity stress, germination percentage, germination rate index, germination coefficient, and seedling vigor indexes were higher in primed seeds. In unprimed seeds, mean germination time increased, while the germination rate index and the fresh and dry matter mass decreased more sharply with salinity stress. The Na/K ratio was higher in unprimed seeds.

Superação de dormência de sementes como estratégia para restauração florestal de pastagem tropical

O objetivo deste trabalho foi avaliar a influência de tratamentos de superação da dormência de sementes sobre a taxa e o tempo de emergência de espécies arbóreas de Fabaceae, e sobre seu estabelecimento, quando reintroduzidas em pastagem, no Cerrado. Foram realizados experimentos em casa de vegetação e em campo (pastagem de Urochloa brizantha), com as espécies Mimosa caesalpiniifolia, Peltophorum dubium, Pterogyne nitens, Dimorphandra mollis, Copaifera langsdorffii e Hymenaea stigonocarpa, submetidas ou não aos seguintes tratamentos de superação de dormência: D. mollis e H. stigonocarpa, escarificação mecânica; C. langsdorffii e M. caesalpiniifolia, escarificação química com H2SO4; P. nitens, punção do tegumento; e P. dubium, imersão em água a 80ºC. O estabelecimento em campo foi monitorado por 21 meses. A superação de dormência promoveu, em casa de vegetação, maior emergência de quatro das seis espécies avaliadas, e, no campo, de cinco espécies. Além disso, reduziu o tempo de emergência das espécies e aumentou o recrutamento de M. caesalpiniifolia, P. nitens, D. mollis e H. stigonocarpa, aos 127 dias, e de H. stigonocarpa aos 659 dias. Os tratamentos de superação de dormência podem aumentar a eficiência da semeadura direta, em projetos de restauração de áreas degradadas no Cerrado, ao promover maior emergência das sementes e o estabelecimento das plantas.

Yield and mineral nutrition of soybean, maize, and Congo signal grass as affected by limestone and slag

The objective of this work was to evaluate the efficiency of superficial application of limestone and slag, and their effects on soil chemical attributes and on yield and mineral nutrition of soybean, maize, and Congo signal grass (Urochloa ruziziensis). The experiment was carried out in a Rhodic Hapludox under no tillage system. The treatments consisted of the use of limestone or slag (silicates of calcium and magnesium) to correct soil acidity, and of a control treatment without the use of soil correctives. Rates were calculated in order to raise soil base saturation up to 70%. Soybean was sown in November 2006 and maize in December 2007. Congo signal grass was sown right after the harvests of soybean and maize, and it was cropped during the off-seasons. Soil chemical attributes were evaluated at 6, 12, and 18 months after the application of the corrective materials. Slag is an efficient source for soil acidity correction, being able to raise the exchangeable base levels in the soil profile faster than lime. Both limestone and slag increase dry matter yield of Congo signal grass, and grain yield of soybean and maize. Slag is more effective in improving maize grain yield.

Protein contamination on Klason lignin contents in tropical grasses and legumes

The objective of this work was to evaluate the extent of protein contamination on Klason lignin (KL) in tropical grasses and legumes, and to propose an equation to estimate the protein-free content of Klason lignin (KLp). Five grass (30 samples) and 12 legume species (31 samples) were evaluated. Legumes had higher KL contents. Protein contamination was significant in both grasses and legumes, but greater in legume samples. The model to predict KLp was based on KL and crude protein (CP) contents, as follows: KLp = 0.8807KL - 0.0938KL x D - 0.00338CP (R2=0.935), in which D=0, for grasses, and D=1 for legumes.

Plutonium and americium isotopes as alternative chronostratigraphic markers in tropical regions: An application in the Havana Bay (Cuba)

The low 137Cs activity observed in marine sediments of tropical regions often precludes its use as chronostratigraphic marker. Here we present a study on the use of Pu and Am radioisotopes as alternative markers to constrain the 210Pb ages in a sediment core of the Havana Bay (Cuba). Mean activity ratios of 238Pu/239,240Pu, 241Am/239,240Pu and 241Pu/239,240Pu indicated that the nuclear weapon tests fallout is the main source of the anthropogenic radionuclides. While the inventory of 137Cs in the sediments is lower than the expected fallout inventory, 239,240Pu accumulates in the sediments with inventories higher than the expected fallout inventory. The high fluxes of 239,240Pu are nevertheless corroborated here through use of 210Pb, and confirm that focusing of solid particles is of great importance in the investigated site. 239,240Pu showed to be a useful time tracer in marine sites where the 137Cs signal is very low.

PRODUÇÃO DE MUDAS DE VIDEIRA 'RUBI' PELO MÉTODO DE ENXERTIA DE MESA EM ESTACAS HERBÁCEAS DOS PORTA-ENXERTOS IAC 313 'TROPICAL' E IAC 766 'CAMPINAS'

Com o objetivo de estudar o método de enxertia de mesa em estacas herbáceas para a obtenção de mudas de videira, experimentos foram desenvolvidos em câmara de nebulização, localizada no ripado do Departamento de Produção Vegetal da Faculdade de Ciências Agrárias e Veterinárias da UNESP, no período de novembro de 1997 a dezembro de 1999. Foram utilizadas estacas herbáceas dos porta-enxertos IAC 313 'Tropical' e IAC 766 'Campinas' e borbulhas e garfos da cultivar Rubi. Foram testados os métodos de enxertia de garfagem em fenda cheia e de borbulhia em placa, em estacas herbáceas sem raízes e enraizadas, o tipo de proteção do enxerto, o tamanho das estacas e o recipiente de enraizamento. Foram avaliados o enraizamento e o pegamento de enxertos. O método de enxertia de mesa com garfagem e com proteção do enxerto com saco plástico apresentou maior pegamento de enxerto aos 30 (45,25%) e 60 dias (66,20%) após a enxertia. O tamanho da estaca não afetou o pegamento dos enxertos. Contudo, em todos os experimentos, o índice de sobrevivência dos enxertos foi muito baixo ou nulo. Estacas sem enxertia proporcionaram maior porcentagem de enraizamento (65,62%) em relação às estacas enxertadas. O método de enxertia de mesa em estacas herbáceas dos porta-enxertos IAC 313 'Tropical' e IAC 766 'Campinas' não foi eficiente para a formação de mudas de videira.

'Tropical': uma nova seleção de tangerina 'Sunki'

Situado no município de Cruz das Almas, Recôncavo Baiano, o Programa de Melhoramento Genético de Citros da Embrapa Mandioca e Fruticultura possui ações dirigidas ao desenvolvimento de novos porta-enxertos, adaptados a condições de cultivo tropicais, compreendendo: hibridações controladas, visando à exploração da ampla variabilidade genética existente em Citrus e gêneros afins; introdução de novas variedades a partir de várias regiões do País e do exterior; seleção de clones nucelares, relacionados a porta-enxertos tradicionais, porém possuidores de características de interesse agronômico que os distinguem de seus padrões varietais. O presente trabalho refere-se a estudos pertinentes a esta última linha de pesquisa, baseados em avaliações dirigidas a 20 seleções de tangerina 'Sunki', tendo como objetivo principal a identificação de indivíduos que se destacam pela produção de frutos com um número médio de sementes superior ao comumente verificado nesse porta-enxerto. As análises realizadas compreenderam os seguintes caracteres: número médio de sementes por fruto, número médio de embriões por semente, intervalo de variação do número de embriões por semente, porcentagem de poliembrionia e tamanho de embrião. Os resultados obtidos permitem indicar a seleção 'Sunki Tropical' como alternativa de uso em programas de diversificação de porta-enxertos nas condições em que esta tangerina apresenta boa adaptação, principalmente em função de seu elevado número médio de sementes por fruto (18,7) e previsível uniformidade de seedlings, esta decorrente de sua elevada porcentagem de poliembrionia, próxima a 100%.

Caracterização e identificação das cultivares de pessegueiro Tropical e Douradão através de marcadores RAPD

Foi realizada a caracterização genética das cultivares de pêssego Tropical e Douradão pelo método RAPD, em comparação com 'Dourado-1', 'Tutu', 'Maravilha', 'Rubro-sol', 'Flordaprince', 'Aurora-1' e 'Talismã' do Banco Ativo de Germoplasma de Frutas de Caroço do IAC, mantido no Núcleo de Agronomia de Capão Bonito, utilizando DNA extraído de folhas jovens. Foram obtidos 31 marcadores genéticos a partir dos primers altamente polimórficos OPAD10, OPAE04, OPAE07, OPAE09, OPAE11, OPAJ04 e OPAJ06, selecionados de 96 primers avaliados. Os marcadores RAPD utilizados indicaram eficientemente o grau de parentesco entre cultivares, exceto em cultivares originadas de polinização livre. Verificou-se que, mesmo entre as cultivares irmãs como 'Tutu' e 'Talismã', encontrou-se certa distância genética (0,29), mostrando que por RAPD é possível caracterizar-se germoplasma aparentado. 'Tropical' e 'Douradão' foram bem caracterizados em relação aos parentais e demais cultivares, com as distâncias genéticas variando de 0,26 a 0,89.

Pineapple yield and fruit quality effected by NPK fertilization in a tropical soil

There is a lack of information about fertilization of pineapple grown in the State of São Paulo, Brazil. So a field experiment with pineapple 'Smooth Cayenne' was carried out to study the effects of NPK rates on yield and fruit quality. The trial was located on an Alfisol in the central part of the State of São Paulo (Agudos county). The experimental design was an incomplete NPK factorial, with 32 treatments set up in two blocks. The P was applied only at planting, at the rates of 0; 80; 160 and 320 kg/ha of P2 0(5), as superphosphate. The N and K2O rates were 0; 175; 350, and 700 kg/ha, applied as urea and potassium chloride, respectively, divided in four applications during the growth period. Response functions were adjusted to yield or to fruit characteristics in order to estimate the nutrient rates required to reach maximum values. The results showed quadratic effects of N and K on yield and a maximum of 72 t/ha of fresh fruit was attained with rates of 498 and 394 kg/ha, respectively of N and K2O. In order to reach the maximum fruit size, and to improve the percentage of first class fruit (mass greater than 2.6 kg), were necessary rates of N and K respectively 11 and 43 % higher than those for maximum yield. No effect of P rates was observed on pineapple plant growth, despite the low availability of this nutrient in the soil. The effect of N rates was negative on total soluble solids and total acidity while the opposite occurred with K, which increased also the content of vitamin C. High yield and fruit size were closely related to N and K concentrations in the leaves.