Late wilt of corn - Magnaporthiopsis maydis
EEffective: July 29, 2013 - September 15, 2014
Resources:
Pest Tracker
CAPS Pest Datasheet
Screening Aids:
Taxonomic Position:
Magnaporthales : Magnaporthaceae
Pest Type:
Fungi
Pest Code (NAPIS):
FGDNCGZ
This pest is a member of the following lists:
| Corn |
|---|
These Approved Methods are appropriate for:
2015
Major Hosts identified in the Host Matrix:
Corn
This list includes important economic or environmental hosts but does not represent all major hosts of the pest. Check CAPS pest datasheet for complete list of hosts.
This list includes important economic or environmental hosts but does not represent all major hosts of the pest. Check CAPS pest datasheet for complete list of hosts.
Pest is vectored by:
No known vector.
Survey
Approved Method(s):
| Method | Instructions | NAPIS Survey Method |
|---|---|---|
| Visual | Collect symptomatic plant material. |
3031 - General Visual Observation |
Signs:
No specific signs are present.
Symptoms:
The first symptom is a moderately rapid wilting of plants usually at about the time of flowering until shortly before maturity. Wilting progresses from lower to upper portions of the plant. Leaves first become dull green, eventually lose color, and become dry as though suffering from lack of water. Vascular bundles in the stalk become reddish-brown, and lower internodes also assume this color. In advanced stages of the disease, lower portions of the stalk become dry, shrunken, and hollow. Secondary infection by other pathogens frequently progresses into stalk rot.
Key Diagnostics
ID/Diagnostic: Multiple
Morphological: Pathogen may be identified morphologically by examination of the shape and size of conidia and conidiophores, color and type of colony, and temperature requirements (Samra et al., 1963).
PCR primers have been developed for differentiating H. maydis (=Cephalosporium maydis) from some of its relatives (Acremonium, Cephalosporium, Gaeumannomcyes, and Phialophora) (Saleh and Leslie, 2004). The PCR assay can be used as a preliminary screen for potential morphological positives. Final confirmation would occur via PCR and sequencing at a national diagnostic laboratory.
Update: Two diagnostic assays have been developed for Harpophora maydis, causal agent of late wilt of maize, by CPHST Beltsville. They are currently being validated and subjected to a ring test with a collaborator in Israel, where H. maydis is an established plant pathogen. Work Instructions for both the conventional and qPCR assays have been written, and are in the process of being reviewed prior to their approval for general use in CPHST. Both of the conventional PCR and qPCR assays target a segment of the Ribosomal Internal Transcribed Spacer (ITS) of H. maydis. The conventional PCR assay has been optimized as a stand-alone (singleplex) assay. The ITS region of H. maydis has been cloned into a pCR2.1-TOPO vector and constitutes the positive control for this assay. The qPCR assay has been optimized as a stand-alone (singleplex) assay, and as a multiplex assay combining a diagnostic PCR assay specific for H. maydis, and an internal control (IC) assay targeting a known plant DNA locus (COX). We expect to have these Work Instructions validated by the collaborator in Israel before the end of FY-2013, and be released for screening in FY-2014.
PCR primers have been developed for differentiating H. maydis (=Cephalosporium maydis) from some of its relatives (Acremonium, Cephalosporium, Gaeumannomcyes, and Phialophora) (Saleh and Leslie, 2004). The PCR assay can be used as a preliminary screen for potential morphological positives. Final confirmation would occur via PCR and sequencing at a national diagnostic laboratory.
Update: Two diagnostic assays have been developed for Harpophora maydis, causal agent of late wilt of maize, by CPHST Beltsville. They are currently being validated and subjected to a ring test with a collaborator in Israel, where H. maydis is an established plant pathogen. Work Instructions for both the conventional and qPCR assays have been written, and are in the process of being reviewed prior to their approval for general use in CPHST. Both of the conventional PCR and qPCR assays target a segment of the Ribosomal Internal Transcribed Spacer (ITS) of H. maydis. The conventional PCR assay has been optimized as a stand-alone (singleplex) assay. The ITS region of H. maydis has been cloned into a pCR2.1-TOPO vector and constitutes the positive control for this assay. The qPCR assay has been optimized as a stand-alone (singleplex) assay, and as a multiplex assay combining a diagnostic PCR assay specific for H. maydis, and an internal control (IC) assay targeting a known plant DNA locus (COX). We expect to have these Work Instructions validated by the collaborator in Israel before the end of FY-2013, and be released for screening in FY-2014.
Mistaken Identities:
Symptoms can be confused with drought stress.
When culturing, the fungus may be confused with other more rapidly growing Harpophora and Gaeumannomyces species.
When culturing, the fungus may be confused with other more rapidly growing Harpophora and Gaeumannomyces species.
In Progress / Literature-based Diagnostics:
Molecular: Culture the fungus in complete medium (CM) broth and incubate on an orbital shaker for 3 days at room temperature. Harvest mycelia for DNA extraction.
Ward and Bateman (1999) use a pair of PCR primers that amplify a segment of the ribosomal gene locus from many members of the Gaeumannomyces and Phialophora fungal pathogens from maize and other host plants. The PCR product from Harpophora maydis (=Cephalosporium maydis) can be distinguished from that of other members of the group on the basis of its unique size (490 bp) relative to that of other species.
Ward and Bateman (1999) use a pair of PCR primers that amplify a segment of the ribosomal gene locus from many members of the Gaeumannomyces and Phialophora fungal pathogens from maize and other host plants. The PCR product from Harpophora maydis (=Cephalosporium maydis) can be distinguished from that of other members of the group on the basis of its unique size (490 bp) relative to that of other species.
References
- Saleh, A.A., and Leslie, J.F. 2004. Cephalosporium maydis is a distinct species in the Gaeumannomyces-Harpophora species complex. Mycologia 96(6): 1294-1305.
- Samra, A.S., Sabet, K.A., and Hingorani, M.K. 1963. Late wilt of maize caused by Cephalosporium maydis. Phytopathology 5: 402-406.
- Ward, E. and Bateman, G.L. 1999. Comparison of Gaeumannomcyes- and Phialophora-like fungal pathogens from maize and other plants using DNA methods. New Phytologist 141: 323-331.