Microscopic aspects of silicon-mediated rice resistance to leaf scald

This study investigated the effect of silicon (Si) on the potentiation of rice resistance against leaf scald at the microscopic level. Rice plants (‘Primavera’) were grown in a nutrient solution containing 0 (−Si) or 2 mM (+Si) Si. The foliar Si concentration of the +Si plants (3.6 dag/kg) increased in comparison with the −Si plants (0.3 dag/kg). An X-ray microanalysis revealed that the leaf tissue of +Si plants infected with Microdochium oryzae had higher peaks and deposition of insoluble Si than that of −Si plants. The high foliar Si concentration for the +Si plants reduced the expansion of leaf scald lesions. Scanning electron microscopy revealed that fungal hyphae and appressorium-like structures of M. oryzae were more abundant in the leaf surface of −Si plants relative to +Si plants. At both histopathological and ultrastructural levels, fungal hyphae grew abundantly into the leaf tissue of −Si plants. By contrast, rice cell walls were rarely degraded and fungal hyphae were often surrounded by amorphous granular material in the leaf tissue of +Si plants. Conidiophores emerged from stomata 36 h after fungal penetration, and conidia were noticed inside the leaf tissue of the −Si plants in great abundance. The collective results of the present study showed a high concentration and deposition of Si and a considerable deposition of phenolic-like compounds in the leaf tissue of +Si plants. These results indicate that the potentiation of the phenylpropanoid pathway in these plants supplied with Si was favorable for the increase in rice resistance to leaf scald

Infection process of Phakopsora gossypii in cotton leaves

Tropical rust caused by the biotrophic fungus Phakopsora gossypii is an emerging disease in cotton that has caused significant yield losses of crop/cotton cultivated in Brazil. Considering the current importance of tropical rust and the need to obtain additional basic information about its causal agent to better control this disease, the present study aimed to determine the infection process of P. gossypii in cotton leaves using scanning electron microscopy (SEM). Thirty-day-old plants were inoculated with a suspension of P. gossypii uredospores, and leaf fragments were collected 42 h after inoculation (hai) as well as 20, 25 and 35 days after inoculation (dai) for SEM observations. By 42 hai, the uredospores of P. gossypii had germinated and produced a germ tube and an appressorium that may directly penetrate the leaf cuticle. At 20 dai, closed uredia containing uredospores were observed on the abaxial leaf surface. At 25 dai, the uredia started to open and became fully open by 35 dai and contained many uredospores. By 25 dai, fungal hyphae were growing abundantly in the mesophyll next to the uredia that formed in the leaf fragments with total or partial removal of the epidermis. The results of the present study provide novel information regarding the infection process of P. gossypii in cotton leaves, which might be useful for the development of new and more effective strategies for tropical rust control

Influência de semeaduras sucessivas de feijoeiro na severidade da mancha-angular e ferrugem e perdas na produção

Angular leaf spot (Phaeoisariopsis griseola) and rust (Uromyces appendiculatus) are some of the most damaging bean diseases in the region of Triângulo Mineiro, State of Minas Gerais, Brazil. The experiments were conducted under field conditions during the 1994 dry season (under sprinkler irrigation) and 1994/95 rainy season, with three bean planting dates in each season. The purpose of this study was to determine the influence of these sequential plantings on the severity of angular leaf spot and rust in field beans, as well as the yield reduction caused by these diseases. The severity of angular leaf spot and rust increased significantly from the first to the third planting time and reached the highest severity in the third. Previous bean cultivation were the source of inoculum for the subsequent plantings. Fungicide applications were efficient in controlling both diseases. Bean grain yield was significantly higher when fungicide was used compared to the untreated control. Angular leaf spot showed the highest severity in both dry and rainy season. The rust, only in the 1994 in the dry season. The seasons showed climatic conditions (temperature and relative humidity) more favorable for diseases evolution, resulting in increase of severity. A negative and highly significant correlation was observed between the severity of angular leaf spot and rust with the grain yield in the two seasons.A mancha-angular (Phaeoisariopsis griseola) e a ferrugem (Uromyces appendiculatus) são algumas das mais prejudiciais doenças do feijoeiro na região do Triângulo Mineiro, Minas Gerais. O objetivo deste estudo foi determinar a influência das semeaduras sucessivas na severidade da mancha-angular e da ferrugem, bem como as perdas na produção em decorrência dessas doenças. Os experimentos foram conduzidos em condições de campo, nas safras outono-inverno (1994) e das águas (1994/95), cada uma com três semeaduras sucessivas de feijão. A severidade da mancha-angular e da ferrugem aumentou significativamente da primeira para a terceira semeadura, atingindo nível mais elevado na última. As semeaduras anteriores foram a fonte de inóculo para os cultivos subseqüentes. Aplicações de fungicida foram eficientes no controle das doenças, permitindo um aumento significativo da produção de grãos, quando comparado com o controle. A mancha-angular apresentou maior incidência no outono-inverno e nas águas, e a ferrugem, apenas no outono-inverno. Nessas safras as condições climáticas (temperatura e umidade relativa) favoreceram a evolução das doenças, resultando num aumento da severidade. Houve uma correlação negativa e altamente significativa entre a severidade da mancha-angular e da ferrugem com a produção de grãos nas duas safras

Silicon and manganese on rice resistance to blast

Blast, caused by the fungus Pyricularia oryzae, is the most important fungal disease of rice. The effect of silicon (Si) and manganese (Mn), and their interaction, on rice resistance to blast was investigated. Rice plants (cultivar "Metica 1") were grown in hydroponic solution with 0 or 2 mmol L-1 of Si and with 0.5, 2.5, and 10 mmol L-1 of Mn. Sixty-day-old plants were inoculated with a conidial suspension of P. oryzae and the incubation period (IP), the number of lesions (NL) per cm2 of leaf area, the lesion size (LS), and blast severity were evaluated. Blast severity was scored at 48, 72, 96, and 144 hours after inoculation and data were used to obtain the area under blast progress curve (AUBPC). Silicon concentration was significantly higher in leaf tissues of plants supplied with this element than on its absence, regardless of Mn rates. There was no significant difference in Si concentration among the Mn rates for both - Si and +Si treatments. The Mn concentration was significantly higher in the tissues of plants from the - Si treatment as compared to plants of the +Si treatment, but only at the rate of 10 mmol L-1 of Mn. There was a significant increase in Mn concentration as the rates of this micronutrient increased from 0.5 to 10 mmol L-1 regardless of the Si treatments. The IP significantly increased in the +Si treatment. The Mn rates had no effect on the IP regardless of the Si treatments. The NL was significantly lower in the presence of Si regardless of the Mn rates. The Mn rates had no effect on NL regardless of the Si treatments. The addition of Si to the nutrient solution significantly reduced both LS and AUBPC regardless of Mn rates. However, in the absence of Si, the values for LS and AUBPC were significantly lower at the Mn rate of 10 µmol L-1 as compared to the rate of 0.5 µmol L-1. Overall, the results from this study showed the potential of Si to decrease blast development on rice regardless of the foliar concentration of Mn.A brusone, causada pelo fungo Pyricularia oryzae, é a doença fúngica mais importante do arroz. O efeito do silício (Si), do manganês (Mn) e da interação deles na resistência do arroz à brusone foi investigado. Plantas de arroz da cultivar Metica 1 foram cultivadas em solução nutritiva contendo 0 ou 2 mmol L-1 de Si e 0,5, 2,5 e 10 mmol L-1 de Mn. Aos 60 dias, as plantas foram submetidas à inoculação com uma suspensão de conídios de P. oryzae e foram avaliados o período de incubação (PI), o número de lesões (NL) por cm2 de área foliar, o tamanho de lesão (TL) e a severidade da brusone. A severidade da brusone foi avaliada às 48, 72, 96 e 144 horas após a inoculação e os dados foram usados para calcular a área abaixo da curva do progresso da brusone (AACPB). A concentração foliar de Si foi maior nas plantas supridas com Si. A concentração de Mn na solução nutritiva não interferiu na concentração de Si nas folhas das plantas de arroz. Houve aumento na concentração foliar de Mn à medida que a concentração desse micronutriente na solução nutritiva aumentou, independentemente da presença do Si. A presença de Si na solução nutritiva reduziu a concentração de Mn nas plantas cultivadas na dose de 10 mmol L-1 de Mn. O fornecimento de Si aumentou PI e reduziu o NL, o Tl e a AACPB. As doses de Mn não tiveram efeito no PI e no NL, independentemente da presença ou não do Si. Na ausência de Si, os valores do TL e da AACPB foram significativamente menores para a dose de 10 µmol L-1 de Mn em comparação com a dose de 0,5 µmol L-1 de Mn. Os resultados deste estudo reforçam o potencial do Si em reduzir o progresso da brusone em arroz independentemente da concentração foliar de Mn

PHOTOSYNTHETIC RESPONSE OF TWO MANGO CULTIVARS SUBMITTED TO SALT STRESS AND INFECTED WITH CERATOCYSTIS FIMBRIATA

This study aimed to investigate the alterations on the photosynthetic performance of mango plants from cultivars Tommy Atkins and Ubá when exposed to salt stresss and infected with Ceratocystis fimbriata. Plants from these two cutivars were grown in plastic pots receiving nutrient solution with 0 and 90 mM NaCl for 50 days. At 42 days after fungal inoculation, the leaf gas exchange parameters net CO2 assimilation rate [A], stomatal conductance to water vapor [gs], internal CO2 concentration [Ci], and transpiration rate [E] as well as the lesion length, the upward and the downward relative lesion length and the radial fungal colonization were evaluated. Based on the disease variables evaluated, plants from cultivar Ubá were more resistant to infection by C. fimbriata in comparison to plants from cultivar Tommy Atkins. Lower values of A were obtained for plants from cultivar Tommy Atkins submitted to salt stress and infeted with C. fimbriata resulting, therefore, in reduced values of gs and E. In general, plants from cultivar Tommy Atkins were more affected at the photosynthetic level in comparison to plants from cultivar Ubá under salt stress and infected with C. fimbriata. Under salt stress, stomatal closure reduced the Ci values especially on plants from cultivar Tommy Atkins. Plants from cultivar Tommy Atkins were more susceptible to infection by C. fimbriata even when exposed to salt stress

Severidade da podridão-radicular de Rhizoctonia do feijoeiro influenciada pela calagem, e pelas fontes e doses de nitrogênio

The objective of this study was to determine the effects of liming, nitrogen sources and rates on the severity of Rhizoctonia root rot (RRR) in beans under controlled conditions. In the first experiment, the soil was amended with 0, 1.75, 2.25, 2.75, 3.25 and 3.75 g of dolomitic lime per kilogram of soil. In the second experiment, the soil was fertilized with 0, 11, 16, 21, 26 and 31 mg N kg-1 of soil, using ammonium sulfate and sodium nitrate as N sources. For the second experiment, soil acidity was adjusted by applying 1.75 g of dolomitic lime per kilogram of soil. Both experiments were arranged in a completely randomized design, with five replications. Soil was infested before sowing with 16 g of rice grains infested by Rhizoctonia solani per kilogram of soil. Twenty-five days after seed germination, the severity of RRR was evaluated based on lesion development on the hypocotyls, by using a scale ranging from 0 to 5. Data obtained were used to calculate the disease index (DI, %). Linear equations significantly described liming and N source-severity of RRR relationships. Liming increased DI by 32% over the control. After liming, application of ammonium sulfate reduced DI by 22%, while sodium nitrate increased DI by 18%, over the control.Avaliou-se o efeito da calagem e de doses e fontes de N na severidade da podridão-radicular de Rhizoctonia (PRR) em feijoeiro em condições controladas. No primeiro ensaio, utilizaram-se as doses de 0, 1,75, 2,25, 2,75, 3,25 e 3,75 g de calcário dolomítico por quilograma de solo. No segundo ensaio, os tratamentos constituíram um fatorial 2x6, ou seja: duas fontes de N (sulfato de amônio e nitrato de sódio) e seis doses de N (0, 11, 16, 21, 26 e 31 mg kg-1 de solo). A acidez do material de solo usado no segundo ensaio foi corrigida com 1,75 g de calcário por quilograma de solo. Foram colocados 16 g de grãos de arroz infestados por R. solani em cada vaso com 1 kg de material de solo. Utilizou-se, em ambos os ensaios, o delineamento inteiramente casualizado, com cinco repetições. A severidade da PRR foi avaliada 25 dias após a emergência das plantas, atribuindo-se nota para cada planta de acordo com o tamanho das lesões formadas no hipocótilo. Os dados obtidos foram usados para calcular o índice de doença (ID, %). Foram obtidas equações lineares significativas que permitiram descrever as relações entre a calagem e fontes de N com a severidade da PRR. Houve um acréscimo de 32% no ID, em virtude das doses crescentes de calcário. Após a calagem, a aplicação de sulfato de amônio reduziu em 22% o ID, enquanto o nitrato de sódio o aumentou em 18%, com relação ao controle

Flutuação populacional da mosca-branca e a incidência de mosaico dourado em feijoeiro

Bean golden mosaic (BGMV) is an economically pernicious disease in Latin America, especially in Brazil. With the objective of studying the fluctuation of the vector population and its relation to the variation of bean golden mosaic incidence and to the climatic conditions (temperature and rain), this research was carried out from 1994 to 1995. Early in September, the whitefly population sizes were small, but increased steadily up to February, when the bean golden mosaic incidence was also at high levels. In March, even with high vector populations moving from soybean fields, there was no increase in this disease incidence, which indicated that a greater proportion of the flies were not virulent. The decrease in vector population was related to low temperatures, specially to the minimum temperatures in April; nevertheless, the bean golden mosaic incidence was constant. It was concluded that small whitefly populations may be sufficient to promote BGMV epidemics, given that the number of virulent whiteflies rise due to successive bean plantings in time and to the presence of the virus/vector hosts.O mosaico dourado do feijoeiro (BGMV) é uma doença de implicância econômica na América Latina, especialmente no Brasil. Com o objetivo de estudar a flutuação populacional da mosca-branca, associando-a com a incidência de mosaico dourado e com as condições climáticas, conduziu-se um experimento entre 1994 e 1995. O delineamento experimental utilizado foi o de blocos ao acaso, com quatro repetições, num esquema de parcelas subdivididas. As parcelas corresponderam aos 12 meses de semeadura (de setembro a agosto) e as subparcelas às cinco cultivares de feijão. No início de setembro, a população desse inseto foi menor, mas crescente até fevereiro, juntamente com a incidência de mosaico dourado. Em março, mesmo com uma alta população da mosca-branca, oriunda da soja, não ocorreu aumento na incidência da virose, pressupondo que pequena parte daquelas moscas eram realmente portadoras de vírus. A queda da população do vetor do BGMV acompanhou a diminuição das temperaturas, principalmente as mínimas, a partir de abril; mas os índices de infecção foram constantes. Conclui-se que pequenas populações desse inseto podem causar epidemias de mosaico dourado, desde que o número de moscas-brancas virulíferas aumente, garantido pelo plantio escalonado e pela presença de hospedeiras do vírus e/ou do próprio vetor

Efeito do silicato de cálcio e da autoclavagem na supressividade e na conducividade de dois solos à Rhizoctonia solani

The effect of calcium silicate slag and soil sterilization on the natural suppressiveness of a Typic Acrustox (clay Dark Red Latosol – LEa) and the natural conduciveness of an Oxic Haplustoll (TRe) to Rhizoctonia solani were studied under greenhouse conditions. The experimental design was a three-replicate completely randomized one, with 2 x 3 x 2 factorial combination of the following treatments: two soil kinds (LEa and TRe, collected at 0-20 cm layer); three treatments with and without soil sterilization, calcium silicate slag and nontreated control; and uninfested and infested with R. solani. Each soil material was infested previously with 800 mg of the inoculum per kg soil. Application of silicate was done mixing 0,63 g of this product with 1 kg each soil material and incubated for 30 days. The application of silicate increased the exchangeable Ca2+ and bases amount in both soils. The decrease in the aluminum saturation level from 70 to 19% and the increase in base saturation from 9 to 21% altered significantly the natural suppressiveness of LEa to R. solani. Application of silicate to the TRe had no effect on its conduciveness, for its natural eutrophic character, which is benefic to R. solani development. Sterilization by autoclavation did not influence disease development on bean by R. solani. This suggests that possibly other abiotic factors were responsible for either suppressiveness or conduciveness of these soils.Objetivou-se verificar o efeito da aplicação de silicato de cálcio e da esterilização na supressividade natural de um Latossolo Vermelho-Escuro (LEa) álico textura muito argilosa e na conducividade natural de uma Terra Roxa Estruturada eutrófica (TRe) ao fungo Rhizoctonia solani, em condições de casa de vegetação. Utilizou-se o delineamento inteiramente casualizado em esquema fatorial 2 x 3 x 2. Os fatores foram: duas classes de solo (LEa e TRe - 0-20 cm); três tratamentos (esterilização ou não por autoclavagem, aplicação de silicato e testemunha) e infestação ou não com R. solani, com três repetições e 16 plântulas de feijoeiro por parcela. A aplicação de silicato foi feita incorporando 0,63 g do produto em 1 kg de cada material de solo, seguido de incubação por 30 dias. Para promover a infestação artificial, foram colocados 800 mg de inóculo em 1 kg de cada material de solo. O silicato de cálcio aumentou os teores de Ca trocável e a soma de bases nos dois solos. Um decréscimo na saturação por Al de 70 para 19% e um aumento na saturação por bases de 9 para 21% alteraram significativamente a supressividade natural do LEa à R. solani. Com relação à TRe, a aplicação de silicato não teve nenhum efeito na sua conducividade, dado ao seu natural caráter eutrófico, o qual já é favorável ao desenvolvimento deste fungo. A esterilização não influiu no desenvolvimento de R. solani, o que sugere que os fatores abióticos foram os responsáveis pela supressividade ou conducividade desses solos

Oltre il senso comune. Il concetto di pluralit\ue0 in Hannah Arendt, tra estetica e politica

O trabalho foi desenvolvido na fazenda Jordão (município de Araguari, MG), na época do verão (período das águas), com o objetivo de verificar o desempenho agronômico de genótipos de tomateiro tipo Santa Cruz. Utilizou-se o delineamento experimental blocos casualizados, com 16 tratamentos (genótipos) e quatro repetições. A parcela experimental foi constituída por duas fileiras com 12 plantas cada, no espaçamento de 1,00 m entre linhas e 0,55 m entre plantas (1 planta/cova). Efetuaram-se 17 colheitas, sendo a primeira aos 69 dias após o transplante. Vários genótipos apresentaram um bom desempenho agronômico, principalmente Saladinha, Débora Plus, SM-16 e Atlas, podendo ser cultivados no período de verão. Apenas Saladinha e Atlas ultrapassaram 140 g de peso médio, destacando-se também em frutos do tipo extra AA. Observou-se uma correlação significativa e negativa com r = -0,52 e -0,54 na primeira avaliação, e r = -0,55 e -0,45 na segunda avaliação para a produção total e produção comercial, respectivamente, em relação à incidência de geminivírus nos diferentes genótipos. Os híbridos Saladinha e SM-16 apresentaram o menor número de plantas viróticas, enquanto Santa Clara Importada, Santa Clara, Jumbo AG-592 e IAC Santa Clara, apresentaram o maior número.A field experiment was carried out in the Jordão farm in Araguari, MG, Brazil, during the summer season, to evaluate the agronomic potential of genotypes (Santa Cruz type) of tomato. A randomized block design was used with 16 treatments (genotypes) and four replicates. The experimental plot was made up of two lines (1.00 m between lines and 0.55 m between plants) with 12 plants each (1 plant/pit). Seventeen harvests were made, starting 69 days after transplanting. Several genotypes as Saladinha, Débora Plus, SM-16 and Atlas had a good agronomic performance, being recommended to be cultivated in the region, in the summer season. Classified as AA type, the Saladinha and Atlas showed an average of 140 g/fruit. During the experiment a negative correlation, r = -0.52 and -0.54, could be observed, in the first evaluation, and correlation r = -0.55 and -0.45 in the second evaluation between total production, and commercial production in relation to geminivirus infection, respectively, for the different genotypes. The Saladinha e SM-16 hybrids showed the lowest number of infected plants, while Santa Clara Imported, Santa Clara, Jumbo AG-592 and IAC Santa Clara showed the highest number

Produtos alternativos para o controlo de doenças das plantas

Os fosfitos e os silicatos, embora considerados nutrientes minerais das plantas, podem também funcionar como produtos alternativos no controlo de doenças em diferentes culturas. Estes minerais inorgânicos podem atuar diretamente contra os microrganismos patogénicos e/ou induzir as respostas de defesa das plantasinfo:eu-repo/semantics/publishedVersio