Pragas e inimigos naturais na soja e no milho cultivados em sistemas diversificados

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of doses of fungicides and plant resistance activators on the control of Rhizoctonia foliar blight of soybean, and on Rhizoctonia solani AG1-IA in vitro development

Rhizoctonia foliar blight (RFB) of soybean [Glycine max (L.) Merrill] occurs in many tropical and subtropical regions, causing yield reductions of up to 70% and in Brazil, up to 60%. The disease is caused by Rhizoetonia solani AG1-IA and AG1-IB, and by AG2-3 in Japan. RFB occurs in the North, Northeast and Mid-west regions of Brazil. Chemical control remains the only effective method of controlling RFB, but its efficiency depends upon environmental conditions. In this study, 18 fungicides, salicylic acid (SA) and acibenzolar-s-methyl (ASM) were evaluated on R. solani AG1-IA in vitro, by mycelial growth rating and estimating effective concentration for 50% (EC 50) and 90% (EC 90) inhibition of mycelial growth, and in vivo by reduction of disease severity on soybean plants in greenhouse conditions. Mycelial growth was strongly inhibited by the fungicides pyraclostrobin + boscalid and fludioxonil. Preventive fungicide applications were the most effective. Strobilurins were more efficient both in preventive and curative applications. Best results with plant resistance activators were obtained with SA (2.5 mM) sprayed at 20 d before inoculation and with ASM (12.5 mg a.i. l(-1)) 10 d before inoculation. (c) 2005 Elsevier Ltd. All rights reserved.

Manganês no solo, sua avaliação e toxidez de manganês em soja

Two experiments were carried out in pots with a Dusky Latossol showing a 15% base saturation. In the first experiment dolomitic limestone was applied to reach 45, 60, 75 and 90% of base saturation. In the second, MnSO4 was applied in rates of 30, 60, 90 and 120 ppm,and base saturation was raised to 70%.Soybean plants cv. IAC-9 were grown up to R6, when dry matter production and manganese accumulation were evaluated. Soybean responded to liming up to 60% base saturation, as Mn availability and evantualy Mn absorption were decreased to non-toxic levels. Mn applied to a reclamed soil up to 120 ppm was not enough to cause toxicity to soybean cv IAC-9. All of the chemical extractors (Ammonium Acetate, DTA, Mehlich and H2SO4) showed modification in Mn availabity in soil but were not definitely related to Mn absorption and dry matter production.

POTASSIUM FERTILIZATION, ROOT MORPHOLOGY AND POTASSIUM ABSORPTION BY SOYBEAN

A greenhouse experiment studied the effect of potassium fertilization on soybean (Glycine max L. Merrill) root morphology and on K absorption by six soybean cultivars of different maturation groups and growth habits. The Plants were grown up to 70 days after plant emergence, in pots containing 6.0 kg of soil. In the absence of K, no significant difference in K absorption was observed among the cultivars or in root length and surface, but root mean radius was correlated to K absorption. Differences in K absorption were not associated with root characteristics in the presence of K fertilization. Physiological adjustments in K uptake, as well as K availability in the soil, were more important in soybean nutrition than were morphological adjustments in the root system. The results were not associated with plant growth habit or with maturation group.

Deficiência de Mn em soja, induzida por adubação potássica e calagem

Tanto a toxidez como a deficiência de Mn em soja (Glycine max (L.) Merrill), levam a um prejuízo na produtividade. Tem-se recomendado a calagem para superar os graves problemas de toxidez de Mn em soja, mas existem condições potenciais para ocorrer indução de deficiências de micronutrientes, inclusive o Mn. Com o objetivo de explorar esta possibilidade, a cultivar de soja Cristalina foi plantada em vasos, contendo dois Latossolos Vermelho- Escuro de textura média, na presença ou ausência de adubação potássica (50 ug/cm3), e calagem. Os resultados obtidos demonstraram que a adubação potássica pode ter como consequência uma menor absorção de Mn pela soja, e quando associada à calagem (pH 6,5) pode levar à ocorrência de deficiência induzida de Mn, que se manifesta como clorose internerval nas folhas do terço superior da planta.

Diferentes resposta de cutivares de soja e potássio

Soybean (Glycine max (L.) Merrill) is known to have a high ability as a potassium extractor, and different cultivars show different potassium requirements. An experiment was run to study the potassium nutrition of soybean as related to plant characteristics. Six soybean cultivars (FT-2, Bossier, IAC-11, IAC-17, IAC-18 and IAC-19) were grown in 6 kg pots filled with the topsoil of a Dark Red Latosol (sandy loam), either with and without K fertilization. The plants were harvested 70 days after emergence. Soybean response to potassium was not related to growth habit or group of maturation. There was a different response to K. The cultivars IAC-18 and FT-2 were less tolerant to K deficiency. Potassium deficiency in the leaves was not related to top dry matter production. With K fertilization soybean plants showed small root volume and higher ratio canopy/root. With high K in soil, all of the cultivars showed higher nodulation.

Épocas de semeadura da soja I. Efeitos na produção de grãos e nos componentes da produção

O presente trabalho foi realizado como objetivo de estudar os efeitos de épocas da semeadura na produção de grãos e nos componentes de produção de três cultivares de soja (Glycine max (L.) Merrill) de ciclos culturais distintos. Os experimentos foram desenvolvidos em campo, no município de Botucatu, Estado de São Paulo (latitude 22º 51 'S e longitude 48º 27'W.Grw.), em solo classificado como Terra Roxa Estruturada, durante os anos agrícolas de 1977/78, 1978/79 e 1979/80. As cultivares empregadas foram Paraná, Santa Rosa, UFV-1. As semeaduras, em número de seis, foram realizadas com intervalos, aproximadamente, quinzenais, com início de semeadura em outubro. Foram avaliados: a produção de sementes (kg/ha), número de vagens/planta, percentagem de vagens normais e peso de 100 sementes. As maiores produções de grãos, para as três cultivares, foram obtidas nas semeaduras realizadas na segunda quinzena de outubro e durante o mês de novembro. O número de vagens por planta e o peso de 100 grãos foram os componentes da produção que mais sofreram efeitos das épocas de semeadura.

EFFECT OF DROUGHT AND DEFOLIATION STRESS IN THE FIELD ON SOYBEAN SEED-GERMINATION AND VIGOR

Although drought and defoliation stress have been shown to reduce soybean [Glycine max (L.). Merr.] yield, little information has been published regarding their effects on soybean seed quality. Field experiments were conducted in 1986, 1987, and 1989 to evaluate the effect of drought and defoliation (1989 only) stress during soybean seed development on seed germination and vigor. Essex (MG [maturity group] V) and Union (MG III) were grown in 1986 and 1987, and Harper (MG III) and McCall (MG 00) in 1989. Moisture treatments were either well watered or drought stressed during seed development (R5 to R7). In 1989, a total defoliation treatment was also imposed at R6 as an additional stress factor. There were significant reductions in yield and yield components following drought stress in all 3 yr and following defoliation in 1989. Leaf conductance and transpiration also decreased in the drought stress treatments. There was no effect of drought stress on seed germination or seed vigor as measured by accelerated aging germination and the cold test across the four cultivars (determinate and indeterminate) and 3 yr. In 1989 slight changes in 3-d germination and conductivity occurred for some drought stress treatments. Most of this response, however, was related to increased occurrence of hard seed, which does not represent an indication of a change in vigor. Seed germination and vigor were significantly reduced for small, flat, shriveled, and underdeveloped seeds that only occurred following defoliation. These seeds represented a small portion of the seed lot that would normally be removed during conditioning. The data suggest that drought stress would have no effect on seed germination or vigor, unless the stress was severe enough to produce shriveled, flat, underdeveloped seeds.

Efeitos dos danos mecânicos e fisiológicos na colheita e beneficiamento de sementes de soja

The objective of this study was to evaluate the effect of mechanical damage and physiological events in harvesting and processing of soybean cv. Mosoy RR 8000. The samples were taken during harvest manual, mechanical harvesting and during processing (receipt, pre-cleaning, cleaning, spiral separator, classification and gravity table). The physiological and physical quality was analized through the purity, germination, vigor (first germination count, seedling dry matter, accelerated aging, electrical conductivity, tetrazolium, mechanical damages and seedling field emergence) tests. The statistical design used was a entirely randomized with nine treatments (9 sampling points) with 4 replications, being the means compared by the Tuckey test at 5% probability. In the purity and seedling field emergence were observed highly significative difference between the sampling process, also this differences were obtained the first germination count, seedling dry weight matter, accelerated aging and electrical conductivity which showed smaller results for the mechanical harvesting when compared with the manual harvesting. The germination was obtained differences at 5% for the manual harvesting in relation to the mechanical harvesting were obtained smaller results, being the main cause of reducing the soybean seed quality, when compared with the manual harvesting.

An Innovative Crop-Forage Intercrop System: Early Cycle Soybean Cultivars and Palisadegrass

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Efeito alelopático do extrato aquoso de folhas de girassol sobre a germinação de soja e picão-preto

The aim of this work was to evaluate the allelopathic effect of water extract from sunflower fresh leaves on the germination and initial development of conventional and transgenic soybean cultivars, and of the invasive hairy beggartick (Bidens pilosa L.). Experiments were carried out at Laboratory of Plant Physiology, Universidade Estadual do Oeste do Parana, in 2007. Fresh leaves from sunflower were ground in a blender at the proportion 200g/1L distilled water, resulting in crude extract (100%), in which pH was measured. Dilutions of 80%, 60%, 40% and 20% were done from the crude extract, and only distilled water was used as control. Statistical analysis (Tukey 5% probability) indicated that only the highest extract concentrations (60%, 80% and 100%) influenced the analyzed parameters for conventional and transgenic soybean. Beggartick seeds, however, had germination percentage completely inhibited when 40% water extract was applied, which indicates that sunflower straw could be used as a natural herbicide. Nevertheless, field studies must be carried out to prove such effect.

Comportamento de cultivares de soja quanto a qualidade fisiológica de sementes

This work was carried out in order to evaluate if there was a relationship between genotypes and the physiological soybean (Glycine max L.) seed quality. It was conducted during three years using seven cultivars each year. The seeds were harvested at: 1) yellow radicle or expanded pod stage, 2) yellow pod or physiological maturity (R7), 3) harvest maturity (R8), and 4) R8 + 21 days delay. Seed moisture content, standard germination, and vigor tests were performed. The germination and vigor evaluated by accelerated aging and electrical conductivity did not show physiological seed quality differences among genotypes as harvested at physiological maturity. Then, the evaluation of seed germination and vigor, when the environment is not a considered factor, is not an efficient method to show differences among soybean genotypes in terms of seed quality.

Eficiência de absorção e utilização de potãssio por plantas de soja em solução nutritiva

A greenhouse experiment was conducted in a factorial design of randomized complete blocks, with three replications, to study plantage response of soybean cultivars on efficiency: update (EAB); conversion (EC) and utilization, as well as utilization index (IU) by soybean cultivars. Four soybean cultivars (IAC 17, IAC 18, IAC 11 e FT 2) were grown in nutrient solutions with either adequate or deficient K levels (0.5 and 1.82 mmol. L-1) and harvested 20, 40 and 60 days after plant emergence (DAPE). The plants were separated in top, median and lower leaves, stems and roots, dried, ground and analyzed for K contents. Regardless of cultivar, in deficient plants K was translocated from the other organs to median leaves, in order to maintain its K contents. This behavior was particularly evident in 'IAC 11' and 'IAC 18'. Well nourished plants showed higher EAB than deficient plants. 'IAC 17' and 'IAC 18' showed higher EAB at either adequate or deficient K. levels. 'FT 2' showed highest EUK in deficient solutions at 40 DAPE (immediately before flowering), and the lowest EUK at 60 DAPE. The utilization index was helpful in determining cultivar plasticity to adapt to K deficiency. The highest plasticity was observed for 'FT 2' at 40 DAPE and for 'IAC 18' at 60 DAPE. K-deficient plants were more efficient in EC, yielding more dry matter for K uptake unit.

Ferulic acid uptake by soybean root in nutrient culture

Ferulic acid uptake by soybean root in nutrient culture was investigated by the depletion method at different concentrations, temperatures and pH. Results showed that soybean roots absorbed this compound at greater rates in the concentrations between 0.05-mM and 1.0-mM and it was concentration dependent. Ferulic acid uptake was unaffected at pH 4.5 or 6.0 but reduced at pH 7.0. At pH 6.0, uptake rates decreased significantly with increasing temperature of nutrient solution.

Carbohydrate and lipid status in soybean roots influenced by ferulic acid uptake

The objective of this research was to investigate how the allelochemical ferulic acid affects the carbohydrate and lipid contents of soybean roots cultivated in nutrient culture. The results presented revealed that ferulic acid has significant effects on carbohydrates by the increase in xylose, fructose and sucrose and decrease in glucose, after 24 h treatment of roots. Ferulic acid increased the contents of saturated and unsaturated fatty acids of the polar and non-polar lipid fractions. The results may contribute as additional data to explain allelopathic effects caused by ferulic acid.