Preservation of Phakopsora pachyrhizi uredospores

This study compared different temperatures and dormancy-reversion procedures for preservation of Phakopsora pachyrhizi uredospores. The storage temperatures tested were room temperature, 5 degrees C, -20 degrees C and -80 degrees C. Dehydrated and non-dehydrated uredospores were used, and evaluations for germination (%) and infectivity (no. of lesions/cm(2)) were made with fresh harvested spores and after 15, 29 76, 154 and 231 days of storage. The dormancy-reversion procedures evaluated were thermal shock (40 degrees C/5 min) followed or not by hydration (moist chamber,24 h). Uredospores stored at room temperature were viable only up to a month of storage, regardless of their hydration condition. Survival of uredospores increased with storage at lower temperatures. Dehydration of uredospores prior to storage increased their viability, mainly for uredospores stored at 5 degrees C, -20 degrees C and -80 degrees C. At 5 degrees C and -20 degrees C, dehydrated uredospores showed increases in viability of at least 47 and 127 days, respectively, compared to non-dehydrated spores. Uredospore germination and infectivity after storage for 231 days (7.7 months), could only be observed at -80 degrees C, for both hydration conditions. At this storage temperature, dehydrated and non-dehydrated uredospores exhibited 56 and 28% of germination at the end of the experiment, respectively. Storage at -80 degrees C also maintained uredospore infectivity, based upon levels of Infection frequency, for both hydration conditions. Among the dormancy-reversion treatments applied to spores stored at -80 degrees C, those involving hydration allowed recoveries of 85 to 92% of the initial germination.

Adhesion of uredospores of Phakopsora pachyrhizi on soybean seeds and their viability during storage

To study adhesion and viability of uredospores of the fungus Phakopsora pachyrhizi on soybean seeds during storage, suspension tests of those uredospores were carried out by washing seeds at each 30 days interval. Furthermore, germination and inoculation tests of uredospores on soybean plants were performed with uredospores collected from seeds of two soybean production areas, located in the municipalities "Chapada dos Guimarães" and "Tangará da Serra", State of Mato Grosso, Brazil. High levels of uredospores infestation were detected before storage [249.31 and 85.18 uredospores/100 seeds (U/100)] on seeds collected in both localities, respectively. After 30 days storage, these figures were 46.12 and 122.5 U/100; at 60 days were 14.62 and 26.62 U/100; and at 90 days were only 2.87 and 3,68 U/100, respectively; dropping to zero after 120 days storage. The percentage of germinated uredospores decreased with increasing storage periods and at 120 days germination percentage was nil. When uredospores were inoculated on soybean plants, rust symptoms were only observed for uredospores collected from freshly harvested seeds. Uredospores associated to soybean seed germinate until 90 days after storage, but are not viable after this time span. Infection of plants only occurs with inoculation of uredospores obtained from freshly harvested seeds.

Influência da luminosidade e da camada de cera epicuticular de superfícies de folhas de soja na infecção de Phakopsora pachyrhizi

A ferrugem asiática, causada pelo fungo Phakopsora pachyrhizi, apresenta-se como um dos mais graves problemas fitossanitários da cultura da soja no Brasil, principalmente por não existirem, até o presente momento, cultivares com níveis de resistência satisfatórios. Objetivou-se estudar a influência da luminosidade e da camada de cera das superfícies foliares na infecção de folhas de soja por P. pachyrhizi. A superfície adaxial ou abaxial de folíolos do primeiro trifólio de plantas da cultivar BRS 154, estádio fenológico V2, foi inoculada com suspensão de 10(5) urediniósporos/mL-1. As plantas foram mantidas por 24 horas em câmara úmida e temperatura de 23ºC, sob luz ou escuro, em delineamento fatorial. Posteriormente, permaneceram 14 dias em fotoperíodo de 12 horas, sendo em seguida avaliada a densidade de lesões e a severidade da doença. Em um segundo experimento, avaliou-se in vitro , no escuro e na luz, a porcentagem de germinação de urediniósporos e de formação de apressórios. As camadas de cera adaxial e abaxial dos folíolos foram analisadas quantitativamente (extrações com clorofórmio) e estruturalmente (microscopia eletrônica de varredura). A densidade de lesões e a severidade foram maiores quando se inoculou a superfície adaxial de plantas incubadas no escuro, sem interação significativa entre os fatores. A germinação dos esporos no escuro (40,7%) foi significativamente superior à germinação na luz (28,5%). O mesmo ocorreu para a formação de apressórios, no escuro (24,7%) e na luz (12,8%). A quantidade e a estrutura das ceras epicuticulares não apresentaram diferenças entre as duas superfícies.

The Infection of Soybean Leaves by Phakopsora pachyrhizi during Conditions of Discontinuous Wetness

The ability of Phakopsora pachyrhizi to cause infection under conditions of discontinuous wetness was investigated. In in vitro experiments, droplets of a uredospore suspension were deposited onto the surface of polystyrene. After an initial wetting period of either 1, 2 or 4 h, the drops were dried for different time intervals and then the wetness was restored for 11, 10 or 8 h. Germination and appressorium formation were evaluated. In in vivo experiments, soybean plants were inoculated with a uredospore suspension. Leaf wetness was interrupted for 1, 3 or 6 h after initial wetting periods of 1, 2 or 4 h. Then, the wetting was re-established for 11, 10 or 8 h, respectively. Rust severity was evaluated 14 days after inoculation. The germination of the spores and the formation of the appressoria on the soybean leaves after different periods of wetness were also quantified in vivo by scanning electron microscopy. P. pachyrhizi showed a high infective capacity during short periods of time. An interruption of wetness after 1 h caused average reductions in germination from 56 to 75% and in appressorium formation from 84 to 96%. Rust severity was lower in all of the in vivo treatments with discontinuous wetness when compared to the control plants. Rust severity was zero when the interruption of wetness occurred 4 h after the initial wetting. Wetting interruptions after 1 and 2 h reduced the average rust severity by 83 and 77%, respectively. The germination of the uredospores on the soybean leaves occurred after 2 h of wetness, with a maximum germination appearing after 4 h of wetness. Wetness interruption affected mainly the spores that had initiated the germination.

Influence of light and leaf epicuticular wax layer on Phakopsora pachyrhizi infection in soybean

Influence of light and leaf epicuticular wax layer on Phakopsora pachyrhizi infection in soybean Asian rust, caused by the fungus Phakopsora pachyrhizi, is one of the most serious phytosanitary problems of soybean in Brazil, especially because no cultivars with satisfactory resistance levels as yet exist. The objective of this study was to evaluate the influence of luminosity and of leaf epicuticular wax on the infection of soybean by P. pachyrhizi. The adaxial and abaxial leaflet surfaces of the first trifoliate leaf from cultivar BRS 154, phenological stage V2, were inoculated with a suspension of 105 uredospores/mL. The plants were kept for 24 hours in a humid chamber at temperature of 23 degrees C, in light or dark conditions, using a factorial design. Subsequently, the plants were maintained for 14 days under a 12-hour photoperiod. The disease severity and density were evaluated. For in vitro experiments, in light or dark conditions, the evaluation was done in terms of uredospore germination and appressorium formation. The wax content of adaxial and abaxial leaflets was analyzed quantitatively using chloroform extraction and ultrastructurally using scanning electron microscope. Higher density and severity were observed when the adaxial surface was inoculated, with later incubation of the plants in the dark, with no significant interaction between these factors. Spore germination in the dark (40.7%) was statistically different from spore germination in the light (28.5%). The same effect was observed with appressorium formation, in the dark (24.7%) and in the light (12.8%). The quantity and the ultrastructural aspects of epicuticular wax content did not show differences between the adaxial and abaxial surfaces; nor did they show any effect on infection by Phakopsora pachyrhizi in the soybean cultivar studied.

Influence of soybean phenological stage and leaflets age on infection by Phakopsora pachyrhizi

Influence of soybean phenological stage and leaflets age on infection by Phakopsora pachyrhizi This work was conducted to study the influence of soybean growth stage and leaf age on the infection of Phakopsora pachyrhizi, the soybean rust pathogen. Soybean plants (cv. BRS 154 and BRS 258) at the V(3), R(1) and R(5) growth stages were inoculated with a 1 x 10(5) urediniospores per mL suspension. After a period of 24 hours in dew chambers, all plants were removed from the chambers and placed under greenhouse conditions for 20 days. Mean latent period (PLM) and disease severity were estimated. The susceptibility of trifoliate leaves to soybean rust was estimated on cv. BRS 154 at the growth stage R5. Pathogen inoculation was done at the first four trifoliate leaves. Fifteen days after inoculation, leaflets of each trefoil were evaluated for disease severity, lesion mean size and infection frequency. Plants` growth stage did not influence the PLM. Cultivars BRS 154 and BRS 258 presented PLM of 8 and 9 days, respectively. There was no difference in disease severity at the growth stages V(3) and R(1), but those values were higher than at the R(5) growth stage, 8 days after inoculation. The oldest trefoil showed the highest disease values.

Adjuvant concentrations and uredospore densities on Phakopsora pachyrhizi infection efficiency in soybean

Experiments were carried out in a growth chamber to evaluate the effect of spreader and uredospore concentrations on the efficiency of infection by Phakopsora pachyrhizi, the causal agent of Asian soybean rust. CD 214 RR soybean cultivar was inoculated with the following polyoxyethylene sorbitane monolaurate concentrations: 0, 30, 60, 120, 240, 480 and 960 µL.L-1 water, as well as a fixed uredospore concentration of 2 x 10(4) spores.mL-1. In a second phase, the inoculum concentrations of 0, 5 x 10³, 1 x 10(4), 2 x 10(4), 4 x 10(4), 8 x 10(4) and 16 x 10(4) uredospores.mL-1 were evaluated, and the spreader concentration of 240 µL.L-1, selected in the previous experiment, was fixed. The spreader concentration of 240 µL.L-1 can be used in artificial inoculation studies, as well as up to 4 x 10(4) uredospores.mL-1. In this work, there was a correlation between uredia and lesion density. Thus, the use of lesion density is recommended to assess disease intensity for its accuracy and less time consuming. There was also a positive correlation between uredia and lesion density.

Quantification of incubation, latent and infection periods of Phakopsora pachyrhizi in soybean, according to chronological time and degree-days

ABSTRACT In experiments conducted in a growth chamber, the chronological time and the accumulated degree-days were determined for the duration of incubation, latent and infectious periods of Phakopsora pachyrhizi cultivars BRSGO 7560 and BRS 246 RR. Detached soybean leaflets were placed in gerbox-type acrylic boxes and inoculated with 20 x 103 uredospores/mL. The study was conducted at 12-h photoperiod and temperatures of 10ºC, 15ºC, 22ºC, 25ºC and 30°C for 30 days. Lesions and uredia/cm2were evaluated and the number of uredia per lesion was quantified after the beginning of sporulation. The sporulation potential was also quantified for cultivars BRSGO 7560 and BRS 246 RR. The steps of the infection process can be quantified based on both the chronological time and the accumulated heat. The cultivar BRSGO 7560 produced 4,012.8 spores/cm2 and BRS 246 RR, 7,348.4 uredospores/cm2. The largest number of uredia was produced at 25ºC in both cultivars; however, BRS 246 RR presented 372.7 uredia/cm2 and BRSGO 7560, 231.6 uredia/cm2. At 10ºC and 30°C, leaf infection did not occur in both cultivars.

Efeito de indutores bióticos e abióticos na atividade de quitinase e peroxidase e no controle da ferrugem causada por Puccinia psidii em eucalipto

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

Impacto do aumento da concentração de CO2 atmosférico sobre o período latente e o controle biológico da ferrugem do cafeeiro

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Controle da ferrugem asiática da soja (Phakopsora packyrhizi) com óleo de café e bacillus spp

Pós-graduação em Agronomia (Proteção de Plantas) - FCA

Controlling Asian soybean rust (Phakopsora pachyrhizi) with Bacillus spp. and coffee oil

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

The infection of soybean leaves by Phakopsora pachyrhizi during conditions of discontinuous wetness.

The ability of Phakopsora pachyrhizi to cause infection under conditions of discontinuous wetness was investigated. In in vitro experiments, droplets of a uredospore suspension were deposited onto the surface of polystyrene. After an initial wetting period of either 1, 2 or 4 h, the drops were dried for different time intervals and then the wetness was restored for 11, 10 or 8 h. Germination and appressorium formation were evaluated. In in vivo experiments, soybean plants were inoculated with a uredospore suspension. Leaf wetness was interrupted for 1, 3 or 6 h after initial wetting periods of 1, 2 or 4 h. Then, the wetting was re-established for 11, 10 or 8 h, respectively. Rust severity was evaluated 14 days after inoculation. The germination of the spores and the formation of the appressoria on the soybean leaves after different periods of wetness were also quantified in vivo by scanning electron microscopy. P. pachyrhizi showed a high infective capacity during short periods of time. An interruption of wetness after 1 h caused average reductions in germination from 56 to 75% and in appressorium formation from 84 to 96%. Rust severity was lower in all of the in vivo treatments with discontinuous wetness when compared to the control plants. Rust severity was zero when the interruption of wetness occurred 4 h after the initial wetting. Wetting interruptions after 1 and 2 h reduced the average rust severity by 83 and 77%, respectively. The germination of the uredospores on the soybean leaves occurred after 2 h of wetness, with a maximum germination appearing after 4 h of wetness. Wetness interruption affected mainly the spores that had initiated the germination.