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Best practices for the safe transfer of wheat germplasm

Contributors to this page: CIMMYT, Mexico (Etienne Duveiller, Monica Mezzalama, Eloise Phipps, Thomas Payne, Jesper Norgaard), Independent consultant (Jesse Dubin).

In CIMMYT Mexico, ‘Rules and Regulations for the Safe Movement of wheat and maize germplasmhave been described by Dr. M. Mezzalama, Head of Seed Health Laboratory (SHL).

Since 1988 the CIMMYT SHL has been officially authorized by DGSV (Direccion General de Sanidad Vegetal) to carry out the quarantine procedures on seed introductions coming into Mexico and CIMMYT, and in April 2007 the SHL obtained accreditation under standard ISO/IEC 17025: 2005, “General requirements for testing and calibration laboratories”, as required by the Mexican government. An official DGSV inspector is assigned exclusively to CIMMYT to assist with thorough and timely seed inspection and importation.

All seed brought into CIMMYT, without exception, must be subjected to quarantine procedures in the Seed Health Laboratory. The seed introduction procedure at CIMMYT Headquarters is summarized  health flow chart

graph-1_1.jpg

The pathogen detection and identification flowchart is described below:

graph_2.jpg
 

All wheat and triticale seed, both entering and leaving CIMMYT, must pass through the seed health laboratory. All seed undergoes the same set of testing procedures, although the key target pathogens vary between incoming and outgoing seed depending on relevant quarantine regulations. There is a zero tolerance for Karnal bunt teliospores and very strict procedures are followed for moving seed within Mexico from Karnal bunt-contaminated to Karnal bunt-free areas.


CIMMYT generally uses well-established test procedures that may be found in any standard reference on seed health. The filter wash test is somewhat specialized, and the procedure are given in CIMMYT Seed Health Manual.


The tests used in CIMMYT are as follows:


  •  Physical inspection for smut sori, nematode galls, ergot sclerotia, weed seeds, insect damage, etc.

  •  Seed wash filter test, which reveals the presence of fungal spores—including bunt teliospores (Tilletia spp.), smut spores (Urocystis and Ustilago spp.), and downy mildew oospores (Peronosclerospora and Sclerophthora spp.)—and of nematode cysts. This test takes around three hours, although large volumes of samples make take longer. Composite samples of outgoing seed may be used (with rechecking of individual lines in the event of a positive result).

  • Freezing blotter test, which reveals the presence of imperfect fungi carried by seed and takes two weeks. 

  • Greenhouse germination test, for the expression, and thus detection, of seed-borne pathogens, and to check seed viability. This test takes three weeks. If symptoms appear on seedlings, further testing to identify the causal pathogen is carried out (i.e. ELISA or other tests).

  • ELISA, or enzyme-linked immunosorbent assay, to detect specific bacteria and viruses. This test takes 24 hours.

  • Immunofluoresence test, an immunological assay, taking six hours, for the detection on wheat seed of Xanthomonas translucens pv. undulosa.

     

Seed healt testing on wheat and triticale at CIMMYT

 

Test
Pathogen type(s)
detected
Pathogens of importance
in incoming seed
Pathogens of quarantine
importance in outgoing seed **

Seed wash filter test

Fungi:

bunts

smuts

Nematodes

Tilletia indica*,

Tilletia controversa*

Anguina tritici*

Tilletia indica

Tilletia spp

Ustilago spp

.

Freezing blotter test

Imperfect fungi

Alternaria triticina*

Fusarium spp.

Helminthosporium spp.

Septoria spp.

Greenhouse

germination test

Bacteria

Viruses

Pseudomonas syringae pv. atrofaciens*

Xanthomonas translucens pv. undulosa

Barley stripe mosaic virus

Wheat streak mosaic virus

P. syringae

ELISA

Viruses

Barley stripe mosaic virus

Wheat streak mosaic virus

Barley stripe mosaic virus

Wheat streak mosaic virus

Immunofluorescence
 

Xanthomonas translucens pv. undulosa

 

* Quarantined under Norma Oficial Mexicana NOM-017-FITO-1995.
** According to information reported on importing countries requirements


References and further reading

Mezzalama M. 2012. Seed Health: Fostering the Safe Distribution of Maize and Wheat Seed: General guidelines. Third edition. Mexico, D.F.: CIMMYT. Available here (0,5 MB)

Warham EJ, Butler LD, Sutton BC. 1996. Seed Testing of Maize and Wheat: A Laboratory Guide. Mexico, D.F.: CIMMYT. 84 pp

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