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

Abstract

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.

Simultaneous detection and differentiation of Rice black streaked dwarf virus (RBSDV) and Southern rice black streaked dwarf virus (SRBSDV) by duplex real time RT-PCR

“…All the samples had been tested previously by RT-PCR [16], and stored at −70°C. Ninety field rice samples showing stunting, darkening of leaves, and waxy white galls along the veins on the underside of leaf blades and surface of sheaths were collected from Henan, Shandong, Hubei, Hunan, Jiangxi and Yunnan provinces of China in 2012, and stored in a freezer at −70°C.…”

“…Some studies have reported successful methods of RBSDV and SRBSDV detection, including reverse transcription-polymerase chain reaction (RT-PCR), reverse transcription loop-mediated isothermal amplification (RT-LAMP), indirect enzyme-linked immunosorbent assay (ELISA), and indirect dot-immunobinding assay (DIBA) [16-19]. Because information on the virus content in local fields is very important for forecasting and releasing warning schemes to advise farmers on the potential threat to their crops, a sensitive, reliable and quantitative method is required to detect and distinguish RBSDV and SRBSDV in rice and vector insects.…”

Taxtomina parcialmente purificada e preparações de >i<Streptomyces scabies>/i< na indução de resistência em soja à >i<Phakopsora pachyrhizi>/i<

“…As condições ideais para o fungo P. pachyrhizi são temperaturas entre 15 e 25 ºC, com molhamento foliar de 6 a 12 horas seguidas (Marchetti et al 1976). Os esporos germinam em um único tubo germinativo com apressório, sendo a penetração do tipo direta no lúmen das células epidérmicas (Furtado et al 2011), com formação dos primeiros haustórios após 24-48 horas de contato com o hospedeiro (Goellner et al 2010). Com menor frequência, o processo de penetração se inicia no espaço entre as células adjacentes e, em seguida, o fungo entra em uma destas células (Bonde et al 1976).…”

“…A capacidade de P. pachyrhizi em causar doença é dependente da umidade disponível. A interrupção no período de molhamento foliar afeta diretamente este patógeno, causando a redução da germinação e formação de apressórios e, consequentemente, há um decréscimo na severidade da doença (Furtado et al 2011). A descontinuação de períodos de molhamento afeta principalmente esporos que já iniciaram o processo de germinação com a umidade disponível inicialmente (Furtado et al 2011).…”

Avaliação de parâmetros epidemiológicos da ferrugem-asiática da soja em diferentes genótipos de soja

“…Em algumas regiões do Cerrado, o padrão de chuvas consiste em uma mistura de chuvas leves e pesadas durante o verão, o que propicia condições ideais de umidade para o desenvolvimento da cultura e da ferrugem-asiática (Del Ponte et al, 2006).De acordo com Bergamin Filho (2008) a chuva age liberando os urediniósporos da massa mucilaginosa, fornecendo água livre para germinação dos esporos e mantendo a temperatura para infecção próxima à ideal. Interrupções desse período de molhamento foliar reduzem as taxas de germinação dos urediniósporos e de formação do apressório, além de reduzir a severidade da doença em até 92%, indicando a intolerância dos esporos do fungo a períodos secos(Furtado et al, 2011). Temperaturas acima de 28ºC reduzem a taxa de progresso da doença e abaixo de 10ºC as folhas não apresentam sintomas.…”