Growth Of Soybean Seedlings Research Articles

Relationships between the physiological and biochemical modifications in soybean seeds under different temperatures

The aim was to analyze the effect of the stress caused by different temperatures, for a period of 24 h, on seed germination and initial growth of soybean seedlings to relate these variables with the antioxidant defense system. For this, three seed lots were exposed for 24 h at temperatures of 15, 25, 35 and 40°C, being evaluated for germination, first germination counting (FGC), germination speed index (GSI), length, dry mass of roots and shoots and electrical conductivity (after three, six and 24 h), respiratory activity, in addition to superoxide dismutase, catalase and ascorbate peroxidase activity. The lot two presented a higher germination (96.72%), followed by the lot three (83.25%) and one (73.25%). Similarly, the FGC (71.79%) and the GSI (50.50) showed highest average in the lot two. This lot also presented higher growth, biomass accumulation and lower loss of leachates during the imbibition period and different temperatures, as well as more constant respiratory activity compared to the other lots, characterizing lot two as more vigorous, which is related to the antioxidant defense system response that, in a general way, demonstrated lower activity of the antioxidant enzymes in the seedlings shoot above 35°C. Thus, the antioxidant defense system activity has relationship with the physiological quality of the soybean seeds exposed to different temperatures.

Growth of soybean seedlings in relay strip intercropping systems in relation to light quantity and red:far-red ratio

Maize–soybean intercropping is a common system in several countries. However, different spatial patterns of maize and soybean can directly affect the light environment of soybean growth under this system through the combined effects of the altered light quality and the reduced light quanta. This work aimed to investigate the differences in the light environment of the soybean canopy in terms of the red:far-red (R/FR) ratio and the photosynthetically active radiation (PAR) as well as the different rates of soybean seedling growth under maize–soybean relay strip intercropping and soybean sole planting, to analyze the relationship between the morphological characteristics and the light environment, and to assess the relative contributions of the R/FR ratio and PAR transmittance to soybean seedling growth in intercropping conditions.Field experiments were performed in 2011–2013. The intercropping patterns involved the wide-narrow row planting of alternating maize and soybean. The light environment of the soybean canopy and the morphology of the soybean seedlings were estimated in the relay strip intercropping system by changing the distances of the maize and soybean rows as well as the number of maize vs. soybean rows per strip. These parameters of the intercropping system were compared with those of the soybean monocultures. Furthermore, the relationship between the light environment of the soybean canopy and its morphological parameters were analyzed using correlation analysis.Incident light in maize–soybean relay strip intercropping systems was partly reflected and absorbed by maize leaves. Thus, the spectral irradiance, R/FR ratio, and PAR of the soybean canopy were decreased with maize–soybean intercropping as compared to soybean monocropping. Simultaneously, the stem diameter, root length, aboveground biomass, total root biomass, and root–shoot ratio of relay intercropped soybean were reduced significantly, while its seedling height was increased. The correlation relationship between morphological parameters of soybean and the light environment (R/FR ratio and PAR transmittance) in different planting pattern were significant (P<0.05). Compared to PAR transmittance, the R/FR ratio of the relay intercropped soybean canopy was strongly correlated with morphological parameters of soybean seedling (P<0.01), and the correlation coefficients were higher than 0.88. The response of soybean seedlings to shading by maize was not solely influenced by the PAR or the R/FR ratio. It may be the summed effects of both parameters under relay strip intercropping systems. Therefore, the results reveal the physiological response mechanisms of soybean seedlings to changes in the quality and amount of light, which may support the building three-dimensional growth model of the responses of plant to light quantity and quality, and guide the identification of suitable population planting patterns in the intercropping system in the future.

Combined effects of cadmium and fluoranthene on germination, growth and photosynthesis of soybean seedlings

The single and combinational effects of cadmium (Cd) and fluoranthene (FLT) on germination, growth and photosynthesis of soybean seedlings were investigated. Exposure to 5, 10, or 15 mg Cd/L or 1, 5, or 10 mg FLT/L individually or in combination significantly decreased germination vigor (3 days) and final germination rate of soybean seeds, except at 1 and 5 mg FLT/L. The results of two-way ANOVA analysis and the Bliss independence model showed that at lower concentrations of FLT (1 mg/L), the interaction between Cd and FLT on germination was antagonistic, whereas the interaction was synergistic when the concentration of FLT was 5 or 10 mg/L and the concentration of Cd was 15 mg/L. Growth, expressed as dry weight, length of shoot and root, leaf area, and photosynthesis, expressed as net photosynthetic rate, intercellular CO2 concentration, chlorophyll contents and fluorescence of soybean seedlings were also reduced by exposure to 5 or 10 mg Cd/L or 1 or 5 mg FLT/L, singly or jointly. Significant antagonistic effects of exposure to 5 or 10 mg Cd/L or 1 or 5 mg FLT/L on shoot growth and photosynthesis were observed, whereas synergy and antagonism of Cd and FLT were both observed for root growth.

Ascending migration of endophytic Bacillus thuringiensis and assessment of benefits to different legumes of N.W. Himalayas

Out of twenty seven Gram positive and spore forming Bacilli, four Bacillus thuringiensis (Bt) were obtained from root nodules of six legumes. Three bipyramidal and one spherical crystal producing B. thuringiensis were isolated from root nodules of ricebean, lentil, gahat (Horsegram) and soybean plant. Double Intrinsic Antibiotic Resistance (IAR) markers were developed to detect/monitor the presence of B. thuringiensis in the natural environment. B. thuringiensis isolates were examined for their ability to enhance plant growth and ascending migration (from roots to aerial plant part) in four legumes in plant growth chamber at 28 °C. Seed bacterization with B. thuringiensis isolates positively influenced the percent germination and enhanced the plant growth of ricebean, soybean, gahat, and lentil seedlings. All B. thuringiensis isolates were recovered from rhizosphere, root endophytic region, stem lower, upper part and leaf after 45 days after sowing (DAS). Isolate VRB1 was able to colonized rhizosphere and endophytic regions (root, stem and leaf) of gahat, soybean and ricebean after 45DAS. Similarly, isolate VL4C and VLS72.1 were able to colonize rhizosphere and endophytic regions (root, stem and leaf) of lentil and soybean. While, isolate VLG15 was able to colonized rhizosphere and endophytic regions (root, stem and leaf) of lentil, soybean and gahat. Therefore, this study suggests that this approach may be utilized for the development of insect resistant crop strategy in sustainable agriculture.

Effects of bisphenol A on growth, photosynthesis and chlorophyll fluorescence in above-ground organs of soybean seedlings

Bisphenol A (BPA) is a representatively endocrine disruptor, which shows a highly toxic effect on life system. Its potential toxicity on plants that are the primary producers in earth’s ecosystem is not well documented. Here, the effects of BPA on the growth, photosynthesis, content of chlorophyll (Chl), initial fluorescence (F0), maximal photochemical efficiency (Fv/Fm), effective quantum yield of photosystem II (ΦPSII) and photosynthetic electron transport rate (ETR) in soybean seedlings were investigated by using gas exchange measurement system and chlorophyll fluorometer to understand the toxic effect of BPA on plants. It was found that when soybean seedlings were treated with BPA at the low concentration (1.5mgL−1), the growth indices (the plant height, fresh and dry weights of stems, fresh and dry weights of leaves, leaf area) were increased obviously compared with those of the control, which was not related with the photosynthesis, the content of Chl and the chlorophyll fluorescence. When soybean seedlings were treated with BPA at the high concentrations (7.0, 12.0, 17.2 and 50.0mgL−1), the growth indices, net photosynthetic rate, the content of chlorophyll, Fv/Fm, ΦPSII, ETR were decreased, while F0 was increased, compared with those of the control. Obviously, BPA at the high concentrations showed the toxic effect on soybean seedlings. The results from correlation analysis indicated that the inhibition in the growth of soybean seedlings treated with BPA was related to the decrease in photosynthesis because of the decrease in the content of chlorophyll and the change in chlorophyll fluorescence.

Crop Residue and Residue Management Effects on &lt;I&gt;Armadillidium vulgare&lt;/I&gt; (Isopoda: Armadillidiidae) Populations and Soybean Stand Densities

In general, Armadillidium vulgare (Latreille) are considered nonpests of soybean [Glycine max (L.) Merrill], but changes in soil conservation practices have shifted the pest status of this organism from an opportunistic to a perennial, early-season pest in parts of central Kansas. As a result, soybean producers that rotate with corn (Zea mays L.) under conservation tillage practices have resorted to removing excess corn residue by using controlled burns. In a 2-yr field study (2009-2010), we demonstrated that residue removal in burned compared with unburned plots (measured as previous crop residue weights) had minimal impact on numbers of live and dead A. vulgare, soybean seedling emergence, and isopod feeding damage over time. Specifically, removal of residue by burning did not result in higher emergence rates for soybean stands or less feeding damage by A. vulgare. In a separate study, we found that number of live A. vulgare and residue weights had no consistent relationship with seedling emergence or feeding damage. Furthermore, seedling emergence was not impacted by higher numbers ofA. vulgare in unburned plots, indicating that emergence in this study may have been influenced by factors other than A. vulgare densities. These studies demonstrate that removing residue through controlled burning did not impact seedling emergence in presence of A. vulgare and that residue and feeding damage to seedlings did not consistently relate to A. vulgare densities. Other factors that may have influenced a relationship between residue and live isopod numbers, such as variable moisture levels, are discussed.

Organ-specific proteomic analysis of drought-stressed soybean seedlings

Changes in protein levels in drought-stressed soybean seedlings were analyzed using a proteomics approach. Three-day-old soybean seedlings were subjected to drought stress or treated with 10% polyethylene glycol (PEG) as osmotic stress. After treatment, the proteins were extracted from the leaf, hypocotyl, and root and separated using two-dimensional polyacrylamide gel electrophoresis. The root was the most drought-responsive organ, with the levels of 32, 13, and 12 proteins changing in response to drought stress, PEG treatment, and both, respectively. In the leaves of PEG-treated and drought-stressed seedlings, metabolism-related proteins increased and energy production- and protein synthesis-related proteins decreased. For 3 proteins present in all organs in drought-stressed plants, mRNA was differentially regulated: heat shock protein 70 and actin isoform B were upregulated, and methionine synthase was downregulated. mRNA expression patterns reflected those of protein levels, suggesting transcriptional regulation of these proteins. Western blot analysis confirmed the increase in ascorbate peroxidase in drought-stressed plants. The downregulation of mRNA and decreased protein levels of methionine synthase in the leaves, hypocotyl, and roots of drought-stressed plants, but not in other treatments, indicated that methionine synthase is a drought response protein. These results also suggest that the decreased methionine synthase in response to drought stress can impair the soybean seedling growth.

Effect of soil crust strength under diff erent conditions of soil particles and soil organic matter on seedling emergence of soy bean in converted paddy field

Effect of soil crust strength under diff erent conditions of soil particles and soil organic matter on seedling emergence of soy bean in converted paddy field

A new method of applying a controlled soil water stress, and its effect on the growth of cotton and soybean seedlings at ambient and elevated carbon dioxide

While numerous studies have shown that elevated CO 2 can delay soil water depletion by causing partial stomatal closure, few studies have compared responses of plant growth to the same soil water deficits imposed at ambient and elevated CO 2. We applied a vacuum to ceramic cups in pots filled with soil to reduce the soil water matric potential to −0.10 MPa. This system resulted in uniform soil water content throughout the pot, and was used to maintain a constant mild stress for seven days. In cotton, the soil water stress treatment reduced stomatal conductance at both 380 and 560 μmol mol −1 CO 2, but the reduction was relatively smaller at the higher CO 2. No reduction of photosynthesis measured under the daytime growth conditions occurred at elevated CO 2 in stressed cotton plants, while photosynthesis was reduced by the stress in the lower CO 2 treatment. The soil water stress treatment reduced the leaf area and biomass of cotton at the lower, but not at the higher CO 2. In soybean, the soil water stress treatment reduced stomatal conductance, photosynthesis and growth at both CO 2 levels, but the effect of water stress was not less at elevated than ambient CO 2. In neither species nor CO 2 level did the soil water stress treatment cause a detectable change in daytime leaf water potential. In both species, the stomatal closure with the soil water stress may have resulted from the lower soil to leaf hydraulic conductivity. The failure of high CO 2 to protect soybean growth from the soil water stress might be related to the lower hydraulic conductivity of stressed soybeans grown at elevated compared with ambient CO 2.

Protective Effect of Cerium Ion Against Ultraviolet B Radiation-Induced Water Stress in Soybean Seedlings

Effects of cerium ion (Ce(III)) on water relations of soybean seedlings (Glycine max L.) under ultraviolet B radiation (UV-B, 280-320 nm) stress were investigated under laboratory conditions. UV-B radiation not only affected the contents of two osmolytes (proline, soluble sugar) in soybean seedlings, but also inhibited the transpiration in soybean seedlings by decreasing the stomatal density and conductance. The two effects caused the inhibition in the osmotic and metabolic absorption of water, which decreased the water content and the free water/bound water ratio. Obviously, UV-B radiation led to water stress, causing the decrease in the photosynthesis in soybean seedlings. The pretreatment with 20 mg L(-1) Ce(III) could alleviate UV-B-induced water stress by regulating the osmotic and metabolic absorption of water in soybean seedlings. The alleviated effect caused the increase in the photosynthesis and the growth of soybean seedlings. It is one of the protective effect mechanisms of Ce(III) against the UV-B radiation-induced damage to plants.

Combined effects of lanthanumion and acid rain on growth, photosynthesis and chloroplast ultrastructure in soybean seedlings

Rare earth elements (REEs) have been accumulated in the agricultural environment. Acid rain is a serious environmental issue. In the present work, the effects of lanthanum ion (La 3+) and acid rain on the growth, photosynthesis and chloroplast ultrastructure in soybean seedlings were investigated using the gas exchange measurements system, chlorophyll fluorometer, transmission electron microscopy and some biochemical techniques. It was found that although the growth and photosynthesis of soybean seedlings treated with the low concentration of La 3+ was improved, the growth and photosynthesis of soybean seedlings were obviously inhibited in the combined treatment with the low concentration of La 3+ and acid rain. At the same time, the chloroplast ultrastructure in the cell of soybean seedlings was destroyed. Under the combined treatment with the high concentration of La 3+ and acid rain, the chloroplast ultrastructure in the cell of soybean seedlings was seriously destroyed, and the growth and of photosynthesis were greatly decreased compared with those of the control, the single treatment with the high concentration of La 3+ and the single treatment with acid rain, respectively. The degree of decrease and destruction on chloroplast ultrastructure depended on the increases in the concentration of La 3+ and acid rain (H +). In conclusion, the combined pollution of La 3+ and acid rain obviously destroyed the chloroplast ultrastructure of cell and aggravated the harmful effect of the single La 3+ and acid rain on soybean seedlings. As a new combined pollutant, the harmful effect of REEs ions and acid rain on plant should be paid attention to.

Effects of Spring Post-planting Flooding on Early Soybean Production in Mississippi

Planting soybean in April to avoid late-summer drought is a common management practice in Mississippi. However, soybeans planted on Sharkey clay soils are often exposed to waterlogged conditions during the early spring. Experiments were conducted at the Delta Research and Extension Center (DREC) at Stoneville, MS, in 2003 and 2004 to assess the effects of induced flooding on soybean seedling emergence, stand establishment, and associated yield loss. In 2003, post-planting flood treatments of 0 (control), 24, or 48 h were applied before seedling emergence or at the V1 stage. In 2004, similar treatments were applied except the timings of treatment were 0, 36, and 72 h. Results indicated that flooding prior to seedling emergence reduced number of plants and plant height, whereas only plant stand was affected when flooding was applied at the V1 stage. Number of pods per plant and number of seeds per pod were higher for the non-flooded control compared with the 48-h to 72-h flood duration at the V1 stage, but the final seed yield was not affected in both years. The data suggest that waterlogged conditions lasting two to three days may not have significant effect on seed yield.

애기장대에서 GmNAP1의 과발현으로 인한 엽록소 함량 증가

암(dark) 상태에서 재배한 대두의 하배축 길이 생장의 분자 기작을 연구하기 위한 일환으로 암 상태에서 재배한 대두 하배축으로부터 cDNA library를 제작한 후 ESTs를 구축하였다. 이들 ESTs 중 색소체 ABC 단백질과 아미노산 서열이 매우 유사한 clone을 선발한 후 이 유전자의 전체염기서열을 결정하였다. GmNAP1 단백질은 엽록체로 향하는 transit peptide 서열이 존재한다. 빛에 의해 GmNAP1 유전자 전사가 어떻게 변화되는지 알아보기 위해 지속적인 적색광, 근적색광 그리고 암 상태에서 성장시키면서 유전자의 전사량을 확인하였다. 이 색소체 NAP1는 엽록소의 전구 물질인 protoporphytin IX를 세포질에서 엽록체로 이동시키는 기능을 한다. 대두에서 분리된 GmNAP1 유전자의 기능을 확인하기 위하여 35S 프로모터 뒤에 GmNAP1 유전자를 접합한 후 애기장대에 형질전환하였다. 형질전환 된 애기장대의 엽록소 함량은 야생형의 엽록소 함량보다 훨씬 높게 측정되었다. In the course of a research concerning the molecular mechanism of hypocotyl elongation that occurs during soybean seedling growth in darkness, we have generated a number of ESTs from a cDNA library prepared from the hypocotyls of dark-grown soybean seedlings. Comparison of the ESTs assigned a cDNA clone as a putative plastidic ATP-binding-cassette (ABC) protein homologue. The soybean GmNAP1 protein contains an N-terminal transit peptide which targets it into the chloroplast. The transcription level of the GmNAP1 gene was investigated under continuous red light, continuous far-red light, and complete darkness. The main function of this NAP1 protein is the transport of protoporphyrin IX which is the precursor of chlorophyll from the cytoplasm to the chloroplast. The GmNAP1 gene was transferred into the Arabidopsis under the CaMV 35S promoter. The chlorophyll level of this transgenic Arabidopsis plant was much higher than the chlorophyll level of the wild type Arabidopsis plant.

Molecular characterization and functional analysis of Glycine max sterol methyl transferase 2 genes involved in plant membrane sterol biosynthesis

Sterol C24 methyltransferase (SMT2) genes governing the pattern of phytosterols synthesized in higher plants have been studied in Glycine seedlings and wild-type and engineered Arabidopsis thaliana plants. The SMT2 genes of soybean (SMT2-1 and SMT2-2) previously cloned and characterized (Neelakandan et al. 2009) were shown to complement the SMT deficient cvp1 mutant Arabidopsis plants, consistent with their role in regulation of 24-alkyl sterol-controlled plant physiology. Further analysis of these genes showed that environmental cues, including dehydration, cold, and abscisic acid induced differential changes in transcript levels of the SMT2 during soybean seedling growth. Sterol analyses of transgenic Arabidopsis seeds originating in variant constructs of AtHMGR1, GmSMT1, and GmSMT2 engineered in seeds showed relevant modifications in the ratio of 24-methyl to 24-ethyl sterol in the direction of sitosterol formation. To provide insight into the structural features of the sterol gene that affects transcript regulation, the upstream promoter sequences of soybean SMT2 genes were cloned and characterized. Sequence analysis revealed several important cis-elements and transcription factor binding sites. The analysis of promoter-GUS fusions in transgenic Arabidopsis plants revealed shared and distinct expression features in different developmental stages and tissues. The data are interpreted to imply that SMT2 is an important contributor to normal plant growth and development.

Silicon effects on photosynthesis and antioxidant parameters of soybean seedlings under drought and ultraviolet-B radiation

Silicon (Si) may be involved in metabolic, physiological, and/or structural activity in higher plants exposed to abiotic and biotic stresses. This has not yet been determined due to the absence of direct evidence that it is part of the molecule of an essential plant constituent or metabolite. The aim of this study was to investigate the effect of silicon on soybean seedlings under drought and ultraviolet-B (UV-B) radiation stresses. The relative leaf water content (RWC), which was the main factor resulting in reduced growth in response to drought, increased 19.0% and 30.0% with Si application under drought and drought + UV-B stresses, respectively. Under UV-B radiation, the anthocyanin and phenol levels decreased 91.5% and 10.0% in the treatment of Si. Ultraviolet-B radiation and drought stress caused great membrane damage, as assessed by lipid peroxidation and osmolyte leakage, but Si application significantly reduced the membrane damage. Catalase (CAT), peroxidase (POD), superoxide dismutase (SOD) and hydrogen peroxide were observed under stress conditions. Proline increased primarily in drought-stressed seedlings and may be the drought-induced factor with a protective role in response to UV-B and silicon. Photosynthesis ( P N) increased following Si application by 21.0%, 18.3% and 21.5% under UV-B radiation, drought and the combination, respectively. The physiological and biochemical parameters measured indicated that the UV-B light had more adverse effects on growth of soybean seedlings than drought, but the data also showed that Si could alleviate seedling damage under these stress conditions.

The ameliorative effect of silicon on soybean seedlings grown in potassium-deficient medium

Crop yield and nutritional quality are significantly reduced when potassium (K) in soil is deficient. As a beneficial element for plants, silicon (Si) is effective in alleviating the toxic effects of mineral nutrients. However, the roles played by Si in mediating deficiency in essential mineral nutrients in general and K in particular have not been investigated. To evaluate the role of Si in K deficiency-induced inhibition of growth of soybean (Glycine max) seedlings, the effects of K deficiency on shoot and root growth, hydrogen peroxide accumulation, K contents, lipid peroxidation and activities of antioxidant enzymes in the absence and presence of 2 mM sodium silicate (Na(2)SiO(3)) were investigated. Both shoot and root biomass of soybean seedlings were markedly reduced when grown in K-deficient medium (1 mM K) compared with those grown in K-sufficient medium (5 mM). Addition of Na(2)SiO(3) significantly ameliorated the K deficiency-induced reductions in shoot and root growth. Sodium silicate enhanced K concentrations in leaf, stem and root of K-deficient seedlings by 105.4, 83.4 and 58.8 %, respectively. Hydrogen peroxide (H(2)O(2)) and malondialdehyde (MDA) contents in soybean seedlings were increased by 25 and 97 %, respectively, when exposed to K-deficient medium. These increases in accumulation of H(2)O(2) and MDA were removed by addition of Na(2)SiO(3). Addition of Na(2)SiO(3) reduced the K deficiency-induced increases in activities of superoxide dismutase, catalase and peroxidase. Application of Si to soybean seedlings grown in K-deficient medium markedly enhanced K use efficiency. Therefore, Si not only increases tolerance to nutrient toxicity, but also ameliorates symptoms associated with deficiency in essential nutrients in plants.

Genotoxicity effect of nitrobenzene on soybean (Glycine max) root tip cells

Nitrobenzene is a synthetic compound widely used in industry which can lead to environmental pollution. While the toxicity and carcinogenicity of nitrobenzene on humans and animals have been studied, less is known about its genotoxicity to plants. In this study, the genotoxic effects of nitrobenzene were investigated with growing soybean seedlings in solution culture. Compared with the control, the growth of soybean seedlings (taproot length, longest lateral root length and lateral roots number) decreased and showed statistics difference at nitrobenzene test concentration of 50 and 100mg/L. Micronucleus, chromosomal bridge and others chromosomal aberrations were observed in soybean root tip cells exposed to nitrobenzene. Frequency of chromosomal aberrations increased linearly with nitrobenzene test concentration between 5 and 50mg/L and decreased at 100mg/L which showed significant difference between control and 25mg/L or higher test concentration. Results of the present study suggest that nitrobenzene has genotoxicity on soybean root tip cells. The mechanism of genotoxicity of NB needs further study. It is concluded that high environmental levels of nitrobenzene in rivers, lakes and dam waters are hazardous to aquatic species and to irrigated plants.

Seed Treatment with Uniconazole Powder Improves Soybean Seedling Growth under Shading by Corn in Relay Strip Intercropping System

The relay strip intercropping system of wheat-corn-soybean is widely used in southwest China. However, it is hard to obtain a stable production of soybean with this system, since soybean plants grow under shading by corn; the stems are thinner and susceptible to lodging. We examined the effects of seed treatment with uniconazole powder (0, 2, 4 and 8 mg kg-1 seed) on the growth of soybean seedlings under relay strip intercropping, some morphological characteristics and yield. The seedling height, first internode length, cotyledonary node height and leaf area per plant were decreased, while the stem diameter, root dry weight, shoot dry weight, root volume, leaf greenness and root to shoot dry weight ratio were increased by uniconazole treatment. The root vigor and root active absorption area were also increased significantly by uniconazole treatment. Moreover, 2 and 4 mg kg-1 uniconazole powder treatment increased shoot dry weight, number of pods per plant, number of seeds per pod and seed yield significantly. Thus, the results suggested that seed treatment with uniconazole powder at a suitable concentration can improve soybean seedling growth, resist the lodging and also increase the seed yield under shading by corn in relay strip intercropping system.

Efeito de lodo de esgoto sobre patógenos habitantes do solo e severidade de oídio da soja

O lodo de esgoto, atendendo as exigências ambientais, apresenta potencial para disposição em solos agrícolas. Sua incorporação altera as propriedades químicas, físicas e biológicas do solo, pois é rico em macro e micronutrientes e matéria orgânica. Estas alterações podem proporcionar benefícios como aumento da disponibilidade de nutrientes às culturas, indução de supressividade a fitopatógenos habitantes do solo e de resistência às doenças da parte aérea. Por outro lado, pode influenciar negativamente o equilíbrio biológico e químico no solo, devido à presença de contaminantes. O objetivo do trabalho foi avaliar os efeitos da incorporação de lodo de esgoto ao solo sobre a severidade de oídio (Erysiphe diffusa) e na supressividade a Rhizoctonia solani e a Macrophomina phaseolina da soja (Glycine max). Para tanto, foram utilizados solos que receberam quatro aplicações (1999 a 2001) sucessivas de lodos de esgoto originários das Estações de Tratamento de Esgoto de Barueri e de Franca, SP, nas concentrações de 0, 1, 2, 4 e 8 vezes (0N a 8N) a dose de N recomendada para a cultura do milho. Os estudos com oídio foram realizados em casa de vegetação com inoculação natural em dois cultivos sucessivos de soja. Também foi estudado o efeito de substrato produzido com 0%, 2,5%, 5% 10%, 15% e 20% de lodo de Franca sobre a emergência de plântulas e sobre a severidade de oídio da soja em três e dois ciclos, respectivamente. Nos estudos com R. solani e M. phaseolina, os solos foram artificialmente infestados com os patógenos e posteriormente cultivados com soja por dois ciclos, sendo avaliado o tombamento e a severidade das doenças. A aplicação de lodo de esgoto no solo aumentou a atividade eliciadora de fitoalexinas em soja e a severidade do oídio foi inversamente proporcional às concentrações do lodo, tanto no estudo com o solo de campo, como com o substrato obtido com o lodo de Franca. A emergência das plântulas de soja, nos três cultivos, foi inversamente proporcional à concentração do lodo de Franca, sendo totalmente inibida na concentração de 20%. Nos estudos com R. solani não foram observados efeitos da aplicação do lodo da ETE de Franca sobre o tombamento e a severidade. No primeiro cultivo a resposta ao tombamento foi quadrática para o lodo Barueri, sendo que ocorreu aumento nas concentrações de 1N e 2N, e redução na concentração 4N. No segundo cultivo ocorreu aumento nos índices de tombamento de plantas em relação ao primeiro, com resposta quadrática para o lodo Barueri, mas com ponto de inflexão mínimo na concentração de 1N, sendo que para a concentração 8N o tombamento foi semelhante à testemunha. A severidade da doença no colo das plantas manteve a mesma resposta quadrática para o lodo de Barueri nos dois cultivos, com ponto de máximo na dose 4N. Para M. phaseolina a incidência da doença foi inversamente proporcional à concentração do lodo de Franca. Dessa forma, os resultados não permitem conclusão sobre a indução de supressividade à R. solani e M. phaseolina.

Efeito do tratamento de sementes com fungicidas e acibenzolar-S-methyl no controle da ferrugem asiática e crescimento de plântulas em cultivares de soja

A influência de acibenzolar-S-methyl (ASM), e fungicidas aplicados via tratamento de sementes sobre a ferrugem asiática bem como o crescimento de plântulas de soja foi avaliada em experimento conduzido em casa de vegetação em delineamento inteiramente casualizado com três repetições, utilizando as cultivares de soja 'Agiara', 'M-soy 8000' e 'M-soy 8080'. Os tratamentos foram três doses de ASM (0,05; 0,1 e 0,2 g de i.a. por kg de sementes), ASM (na dose de 0,1 g de i.a. por kg de sementes) combinado aos fungicidas flutriafol, pyraclostrobin e azoxystrobin, e a aplicação isolada destes, além de uma testemunha tratada com água. Os resultados mostraram redução da Área Abaixo da Curva de Progresso da Ferrugem (AACPF) com o aumento da dose de ASM nas três cultivares de soja. A utilização isolada do ASM em diferentes doses proporcionou uma redução da AACPF além de apresentar, na maioria dos casos, um efeito sinérgico com os fungicidas, aumentando a eficiência de controle quando comparada às aplicações isoladas. Com exceção do ASM na menor dosagem, todos os tratamentos apresentaram controle superior a 77 % comparados à testemunha. Em geral, o tratamento de sementes com ASM e fungicidas resultou numa redução da massa seca (MS) em relação à testemunha. A utilização de ASM associado a fungicidas na tentativa de atrasar a infecção da ferrugem asiática da soja nos períodos iniciais da cultura constitui-se em uma alternativa viável para redução do inóculo inicial, entretanto possíveis efeitos fitotóxicos devem ser considerados.