Anastomosis of germ tubes and migration of nuclei in germ tube networks of the soybean rust pathogen, Phakopsora pachyrhizi

Soybean rust (SBR) survival and host availability (kudzu, Pueraria spp.) were assessed from November 2006 through April 2007 at six sites from the panhandle to southwest Florida. Micro loggers recorded both temperature and relative humidity hourly at each location. Periods of drought and cumulative hours below 0°C correlated with kudzu defoliation. Inoculum potential from detached kudzu leaves was evaluated in vitro under various temperature and relative humidity levels. Kudzu leaves with SBR kept at 4°C produced viable urediniospores with the highest germination at all moisture levels over time. Freezing temperatures (–4 and –20°C) drastically reduced spore germination. However, when leaves were incubated at low (<35%) relative humidity, inoculum potential was prolonged. Results from this study demonstrate that both temperature and relative humidity impact P. pachyrhizi in the field and in vitro, and that detached kudzu leaves have the potential to serve as an inoculum source in kudzu stands.

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Expressed sequence tag analysis of the soybean rust pathogen Phakopsora pachyrhizi

Fungal Genetics and Biology ◽

10.1016/j.fgb.2005.06.004 ◽

2005 ◽

Vol 42 (12) ◽

pp. 949-962 ◽

Cited By ~ 39

Author(s):

Martha Lucia Posada-Buitrago ◽

Reid D. Frederick

Keyword(s):

Expressed Sequence Tag ◽

Soybean Rust ◽

Phakopsora Pachyrhizi ◽

Rust Pathogen ◽

Expressed Sequence Tag Analysis ◽

Expressed Sequence

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Effects of Simplicillium lanosoniveum on Phakopsora pachyrhizi, the Soybean Rust Pathogen, and Its Use as a Biological Control Agent

Phytopathology ◽

10.1094/phyto-01-11-0031 ◽

2012 ◽

Vol 102 (8) ◽

pp. 749-760 ◽

Cited By ~ 23

Author(s):

N. A. Ward ◽

C. L. Robertson ◽

A. K. Chanda ◽

R. W. Schneider

Keyword(s):

Biological Control Agent ◽

Signs And Symptoms ◽

Control Agent ◽

Soybean Rust ◽

Phakopsora Pachyrhizi ◽

Latent Stage ◽

Leaf Surfaces ◽

Rust Pathogen ◽

Soybean Leaf ◽

Soybean Leaves

The fungus Simplicillium lanosoniveum was isolated from soybean leaves infected with Phakopsora pachyrhizi, the soybean rust pathogen, in Louisiana and Florida. The fungus did not grow or become established on leaf surfaces until uredinia erupted, but when soybean rust signs and symptoms were evident, S. lanosoniveum colonized leaves within 3 days and sporulated within 4 days. Development of new uredinia was suppressed by about fourfold when S. lanosoniveum colonized uredinia. In the presence of S. lanosoniveum, uredinia became increasingly red-brown, and urediniospores turned brown and germinated at very low rates. Assays using quantitative real time polymerase chain reaction revealed that the fungus colonized leaf surfaces when plants were infected with P. pachyrhizi, either in a latent stage of infection or when symptoms were present. However, when plants were inoculated before infection, there was no increase of DNA of S. lanosoniveum, suggesting that the pathogen must be present in order for the antagonist to become established on soybean leaf surfaces. We documented significantly lower amounts of DNA of P. pachyrhizi and lower disease severity when soybean leaves were colonized with S. lanosoniveum. These studies documented the mycophilic and disease-suppressive nature of S. lanosoniveum.

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Archaeophytopathology of Phakopsora pachyrhizi, the Soybean Rust Pathogen

Plant Disease ◽

10.1094/pdis-07-14-0772-sr ◽

2015 ◽

Vol 99 (5) ◽

pp. 575-579 ◽

Cited By ~ 2

Author(s):

James S. Haudenshield ◽

Glen L. Hartman

Keyword(s):

Pcr Primers ◽

Fungal Species ◽

The Philippines ◽

Soybean Rust ◽

Herbarium Specimens ◽

Phakopsora Pachyrhizi ◽

The Past ◽

Rust Pathogen ◽

Dna Genotyping ◽

Archival Specimens

Herbarium specimens are useful to compare attributes of the past to attributes of today and predictions into the future. In this study, herbarium specimens from 1887 to 2006 were used to identify Phakopsora pachyrhizi and P. meibomiae, the two known fungal species that cause soybean rust. Historically, these two species differed in geographic distribution, with P. pachyrhizi confined to Asia and Australia, and P. meibomiae confined to the Americas. In our analyses, herbarium specimens were used to determine whether it was possible to extract adequate useful DNA from the fungal structures. If present, quantitative PCR primers specific to P. pachyrhizi, P. meibomiae, or to a third group inclusive of many rust species could be used to speciate the fungus. Of the 38 archival specimens, 11 were positive for P. pachyrhizi, including a 1912 specimen from Japan; 15 were positive for P. meibomiae, including a 1928 specimen from Brazil and two 1923 specimens from the Philippines; and 12 (including all African accessions) were negative for both species. Five specimens were positive in the more inclusive rust assay; all had been labeled as P. pachyrhizi and none were on soybean. These results demonstrate the feasibility of DNA genotyping in archaeophytopathological investigations.

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Suppression or Activation of Immune Responses by Predicted Secreted Proteins of the Soybean Rust Pathogen Phakopsora pachyrhizi

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-07-17-0173-fi ◽

2018 ◽

Vol 31 (1) ◽

pp. 163-174 ◽

Cited By ~ 12

Author(s):

Mingsheng Qi ◽

James P. Grayczyk ◽

Janina M. Seitz ◽

Youngsill Lee ◽

Tobias I. Link ◽

...

Keyword(s):

Immune Responses ◽

Crop Production ◽

Rust Fungus ◽

Functional Characterization ◽

Rust Fungi ◽

Effector Proteins ◽

Soybean Rust ◽

Phakopsora Pachyrhizi ◽

Immune Systems ◽

Rust Pathogen

Rust fungi, such as the soybean rust pathogen Phakopsora pachyrhizi, are major threats to crop production. They form specialized haustoria that are hyphal structures intimately associated with host-plant cell membranes. These haustoria have roles in acquiring nutrients and secreting effector proteins that manipulate host immune systems. Functional characterization of effector proteins of rust fungi is important for understanding mechanisms that underlie their virulence and pathogenicity. Hundreds of candidate effector proteins have been predicted for rust pathogens, but it is not clear how to prioritize these effector candidates for further characterization. There is a need for high-throughput approaches for screening effector candidates to obtain experimental evidence for effector-like functions, such as the manipulation of host immune systems. We have focused on identifying effector candidates with immune-related functions in the soybean rust fungus P. pachyrhizi. To facilitate the screening of many P. pachyrhizi effector candidates (named PpECs), we used heterologous expression systems, including the bacterial type III secretion system, Agrobacterium infiltration, a plant virus, and a yeast strain, to establish an experimental pipeline for identifying PpECs with immune-related functions and establishing their subcellular localizations. Several PpECs were identified that could suppress or activate immune responses in nonhost Nicotiana benthamiana, N. tabacum, Arabidopsis, tomato, or pepper plants.

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Effectiveness of Resistance Genes to the Soybean Rust Pathogen Phakopsora pachyrhizi

Japan Agricultural Research Quarterly JARQ ◽

10.6090/jarq.51.199 ◽

2017 ◽

Vol 51 (3) ◽

pp. 199-207 ◽

Cited By ~ 3

Author(s):

Masayasu KATO

Keyword(s):

Resistance Genes ◽

Soybean Rust ◽

Phakopsora Pachyrhizi ◽

Rust Pathogen

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Documentation of an Extended Latent Infection Period by Phakopsora pachyrhizi, the Soybean Rust Pathogen

Plant Health Progress ◽

10.1094/php-2012-0321-01-rs ◽

2012 ◽

Vol 13 (1) ◽

pp. 22

Author(s):

N. A. Ward ◽

R. W. Schneider ◽

C. L. Robertson

Keyword(s):

Latent Infection ◽

Late Summer ◽

Soybean Rust ◽

Phakopsora Pachyrhizi ◽

Disease Symptoms ◽

Infection Period ◽

Airborne Inoculum ◽

Rust Pathogen ◽

Latently Infected ◽

Soybean Leaves

Phakopsora pachyrhizi, the soybean rust pathogen, overwinters on kudzu in the southern United States. However, even with severely affected kudzu adjacent to soybean fields, disease symptoms do not occur on soybeans until plants are in mid-reproductive stages of growth during mid to late summer. These observations suggested that soybeans are exposed to airborne inoculum of the pathogen long before symptoms occur, and we hypothesized that these plants may be latently infected. This hypothesis was confirmed by using quantitative real-time PCR (qPCR) to detect the rust pathogen in soybean leaves 18 to 60 days before symptoms were observed. Additionally, DNA of P. pachyrhizi increased only slightly until one week before symptoms developed. Results from this study documented that soybeans can become infected by the rust pathogen during early stages of plant growth, but symptoms often develop during the mid-reproductive stages. This extended latent infection period may be an optimum time for fungicide applications. Accepted for publication 12 December 2011. Published 21 March 2012.

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Combinatorially Selected Peptides for Protection of Soybean Against Phakopsora pachyrhizi

Phytopathology ◽

10.1094/phyto-12-09-0365 ◽

2010 ◽

Vol 100 (10) ◽

pp. 1111-1117 ◽

Cited By ~ 3

Author(s):

Zhiwei D. Fang ◽

James J. Marois ◽

Gary Stacey ◽

James E. Schoelz ◽

James T. English ◽

...

Keyword(s):

Germ Tube ◽

Single Gene ◽

The United States ◽

Inhibitory Effect ◽

Tube Growth ◽

Soybean Rust ◽

Cytokinin Oxidase ◽

Phakopsora Pachyrhizi ◽

Soybean Leaves ◽

Germ Tube Growth

Phakopsora pachyrhizi, the fungal pathogen that causes Asian soybean rust, has the potential to cause significant losses in soybean yield in many production regions of the United States. Germplasm with durable, single-gene resistance is lacking, and control of rust depends on timely application of fungicides. To assist the development of new modes of soybean resistance, we identified peptides from combinatorial phage-display peptide libraries that inhibit germ tube growth from urediniospores of P. pachyrhizi. Two peptides, Sp2 and Sp39, were identified that inhibit germ tube development when displayed as fusions with the coat protein of M13 phage or as fusions with maize cytokinin oxidase/dehydrogenase (ZmCKX1). In either display format, the inhibitory effect of the peptides on germ tube growth was concentration dependent. In addition, when peptides Sp2 or Sp39 in either format were mixed with urediniospores and inoculated to soybean leaves with an 8-h wetness period, rust lesion development was reduced. Peptides Sp2 and Sp39, displayed on ZmCKX1, were found to interact with a 20-kDa protein derived from germinated urediniospores. Incorporating peptides that inhibit pathogen development and pathogenesis into breeding programs may contribute to the development of soybean cultivars with improved, durable rust tolerance.

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