Development of classification criteria for resistance to soybean rust and differences in virulence among Japanese and Brazilian rust populations
Naoki YamanakaYuichi YamaokaMasayasu KatoNoélle Giacomini LemosAndré Luiz de Lima PassianottoJoão Vitor Maldonado dos SantosEduardo R. BenitezR. V. AbdelnoorR. M. SoaresKazuhiro Suenaga
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In recent years soybean rust, caused by Phakopsora pachyrhizi has become one of the most serious threats to soybean production in Brazil. Breeding lines and varieties have been selected for resistance to soybean rust in Asia. However, differences in virulence between Asian and Brazilian rust populations should be considered in order to select and use resistant resources from Asia. Here, we suggest criteria for distinguishing resistant from susceptible types by the analysis of four resistance characters: frequency of lesions having uredinia, number of uredinia per lesion, frequency of open uredinia, and sporulation level, determined by the utilization of 63 genotypes. Under growth chamber conditions, a set of 13 soybean varieties were exposed to three rust populations-one from Japan and two from Brazil-and evaluated for the resistance characters mentioned above. The Japanese and Brazilian populations clearly differed in virulence, as did the two Brazilian populations. Only two resistance genes, Rpp4 from PI459025 and Rpp5 from Shiranui, commonly conferred resistance on all three rust populations. The number of resistant varieties or resistance genes useful in both countries appears limited. Therefore, a resistant cultivar that is universally effective against soybean rust should be developed by pyramiding some major resistance genes and by introducing horizontal resistance.Keywords:
Phakopsora pachyrhizi
Rust (programming language)
Soybean rust
Phakopsora pachyrhizi
Soybean rust
Urediniospore
Rust (programming language)
Aphis
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Phakopsora pachyrhizi
Soybean rust
Rust (programming language)
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Although considerable information exists regarding the importance of moisture in the development of soybean rust, little is known about the influence of temperature. The purpose of our study was to determine whether temperature might be a significant limiting factor in the development of soybean rust in the southeastern United States. Soybean plants infected with Phakopsora pachyrhizi were incubated in temperature-controlled growth chambers simulating day and night diurnal temperature patterns representative of the southeastern United States during the growing season. At 3-day intervals beginning 12 days after inoculation, urediniospores were collected from each plant and counted. The highest numbers of urediniospores were produced when day temperatures peaked at 21 or 25°C and night temperatures dipped to 8 or 12°C. When day temperatures peaked at 29, 33, or 37°C for a minimum of 1 h/day, urediniospore production was reduced to 36, 19, and 0%, respectively, compared with urediniospore production at the optimum diurnal temperature conditions. Essentially, no lesions developed when the daily temperature high was 37°C or above. Temperature data obtained from the National Climatic Data Center showed that temperature highs during July and August in several southeastern states were too high for significant urediniospore production on 55 to 77% of days. The inhibition of temperature highs on soybean rust development in southeastern states not only limits disease locally but also has implications pertaining to spread of soybean rust into and development of disease in the major soybean-producing regions of the Midwestern and northern states. We concluded from our results that temperature highs common to southeastern states are a factor in the delay or absence of soybean rust in much of the United States.
Phakopsora pachyrhizi
Urediniospore
Soybean rust
Rust (programming language)
Growing season
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In recent years soybean rust, caused by Phakopsora pachyrhizi has become one of the most serious threats to soybean production in Brazil. Breeding lines and varieties have been selected for resistance to soybean rust in Asia. However, differences in virulence between Asian and Brazilian rust populations should be considered in order to select and use resistant resources from Asia. Here, we suggest criteria for distinguishing resistant from susceptible types by the analysis of four resistance characters: frequency of lesions having uredinia, number of uredinia per lesion, frequency of open uredinia, and sporulation level, determined by the utilization of 63 genotypes. Under growth chamber conditions, a set of 13 soybean varieties were exposed to three rust populations-one from Japan and two from Brazil-and evaluated for the resistance characters mentioned above. The Japanese and Brazilian populations clearly differed in virulence, as did the two Brazilian populations. Only two resistance genes, Rpp4 from PI459025 and Rpp5 from Shiranui, commonly conferred resistance on all three rust populations. The number of resistant varieties or resistance genes useful in both countries appears limited. Therefore, a resistant cultivar that is universally effective against soybean rust should be developed by pyramiding some major resistance genes and by introducing horizontal resistance.
Phakopsora pachyrhizi
Rust (programming language)
Soybean rust
Cite
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Phakopsora pachyrhizi
Soybean rust
Rust (programming language)
Urediniospore
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Phakopsora pachyrhizi
Soybean rust
Rust (programming language)
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Phakopsora pachyrhizi is adapted to a wide range of temperatures (15 to >30 degrees C) and can cause yield losses in all regions in which leaf wetness occurs for more than 6 hours. The first lesions often are visible within 4–5 days after infection under favorable conditions and the first fruiting bodies (uredinia) and urediniospores within 6–7 days. Under severe inoculum pressure, it is almost impossible to prevent some yield loss. Severe soybean rust causes early defoliation, reduced pod set, and reduced number and size of seeds. Thus, rust affects all yield components. The extent of loss depends on the growth stage during which the plants are infected, the inoculum pressure, and the ensuing environmental conditions. Yield losses may be as high as 100%. The earlier the infection occurs, the greater and faster the defoliation and consequently the higher the yield loss and the lower the grain quality. In severe cases, when defoliation occurs during vegetative, flowering, early pod set, or the beginning of pod fill, rust can cause enough yield loss that harvesting may not be economically justified.
Soybean rust
Phakopsora pachyrhizi
Rust (programming language)
Urediniospore
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Soybean rust caused by Phakopsora pachyrhizi Sydow was first observed in the continental United States in Louisiana in November 2004 (2). As part of the national soybean rust monitoring effort, samples were collected on 3 October 2007 during the scouting of fields with green leaves in southeastern Nebraska. After incubation at room temperature for 24 h, uredinea and urediniospores were observed with microscopic examination. Urediniospores were obovoid, hyaline to pale brown, and measured 20 to 30 × 18 to 20 μm. The observed morphology was typical of P. pachyrhizi (1). In addition to microscopic observation, P. pachyrhizi was confirmed with real-time (q)-PCR with Taq DNA polymerase on 4 October 2007 with the q-PCR standard operating procedure version 1.9 outlined by the USDA-CSREES and utilized by the National Plant Diagnostic Network with appropriate positive and negative controls (1). Samples initially identified with soybean rust were from Richardson County near the town of Rulo and in Otoe County south of Nebraska City. On 12 October 2007, soybean rust was confirmed in adjacent Pawnee and Nemaha counties. Soybean rust was identified in six fields with an incidence and severity of less than 1%. In fields where the disease was identified, the disease was distributed in low-lying, shaded areas near wind breaks. Although soybean rust was detected in four southeastern Nebraska counties, soybean yields were not affected by the disease. At the time of first detection, more than 80% of the Nebraska soybean crop was harvested. To our knowledge, this is the first report of P. pachyrhizi on soybeans in Nebraska, and currently, the northwestern most find on any host in the continental United States. References: (1) R. D. Frederick et al. Phytopathology 92:217, 2002. (2) R. W. Schneider et al. Plant Dis. 89:774, 2005.
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Use of rust resistant or tolerant soybean varieties is the most economical and safe strategy for management of rust. Soybean genotypes differ in their reactions to different rust isolates. Recently, six dominant genes resistant to soybean rust were described: Rpp1, Rpp2, Rpp3, Rpp4, Rpp5 and Rpp6. Research on soybean rust reveals inheritance of rust resistance is controlled by single dominant gene in most of the cases, two dominant and single recessive genes, two and three recessive gene in few cases only. Information reviewed on soybean rust disease development, different isolates, the inheritance of rust and mapping of rust resistance genes will help in enhancing and stabilizing the yields through the development of resistant cultivars. However, limited literature is available about the molecular interaction among soybean plant and soybean rust and on the molecular pathway triggered by pathogen recognition. Since Rpp genes provides resistance against specific isolates of P. pachyrhizi, pyramiding of different rust resistance Rpp genes can help breeders to create broader or more durable resistance.
Phakopsora pachyrhizi
Soybean rust
Rust (programming language)
Inheritance
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Solutions of complex problems require intelligent systems that combine knowledge, techniques and methodologies, from different sources, considering environmental changes, for decision support improvement. Thus, it became necessary to apply robust methodologies to characterize the interaction among climatic variables related to epidemic progress. The objective of the present work was to evaluate the effects of temperature and leaf wetness in asian soybean (Glycine max L.) rust (Phakopsora pachyrhizi H. Sydow & P. Sydow) intensity in Suprema cultivar and coffee (Coffea arabica L.) rust (Hemileia vastatrix Berkeley & Broome) intensity in Mundo Novo and Catuai cultivars using linear regression (LR), nonlinear regression (NLR), fuzzy logic systems (LFS) and neuro-fuzzy systems (NFS). Comparing observed and estimated values for both diseases, NFS increased the precision and accuracy of the estimated values, following in decrease order by LFS, NLR and LR. NFS enabled to explain 85% and 99% of asian soybean rust and coffee rust monocyclic process, respectively.
Phakopsora pachyrhizi
Rust (programming language)
Soybean rust
Soft Computing
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