Distribution of Healthy Propagules- NCRPIS program

NPGS Curator Workshop2005 Chicago Charles C. Block, Ph.D.

Plant Pathologist

Three disease examples

• Stewart’s wilt of corn – Pantoea (Erwinia) stewartii

• Sunflower downy mildew – Plasmopara halstedii

• Squash mosaic virus of cucurbits

Stewart’s wilt disease managementThis is the top phytosanitary issue for corn seed exports

• Primary objective – to be able to certify seed as free of Erwinia stewartii. Field inspections document presence/absence of Stewart’s wilt.

• Absent in field – accession meets phytosanitary requirements for Stewart’s wilt.

• Present in field – most countries accept lab testing in lieu of field data. We do this testing in-house.

• About 90% of field positives are negative by ELISA.

Stewart’s wilt disease management

Approximate cost per accession for Stewart’s wilt lab testing

ELISA test kit $1.60 (4 wells/acc.)Buffers $0.02Student labor $1.98 (15 min.)

Tech. labor ~$1.25-1.65 (3-4 min.)~Cost per accession $4.85 - 5.25

# Accessions tested:1994 – 591995 – 821996 – 1361997 – 1341998 – 611999 – 1412000 – 432001 – 1522002 – 1242003 – 1822004 – 3772005 – 442

Sunflower downy mildew disease management

Objective: Ensure absence of downy mildew in the field.

Starting in 1990 - inspect all plots and remove infected seedlings.

1999 - present: Allegiance fungicide (metalaxyl) seed treatment – gives systemic protection.

Sunflower disease management

A minimum of two field inspections are made before flowering.

Infected plants are pulled and removed from field.

Curatorial staff observe plant health through season.

Downy mildew

Squash mosaic disease managementObjective - prevent seed infection.

1. GH seedlings are tested prior to transplanting.

2. 3-5 plants in each peat pot are tested as a group.

3. Plants in any positive pot are re-tested individually or the pot may be discarded.

4. Transplants are grown in screened cages to exclude cucumber beetles.

Cost per accession for SqMV testing

ELISA test kit $2.66 (0.38 x 7 wells)**

Sample grinding bags $1.33 (0.19 x 7 samp.)

Buffers $0.10Latex gloves $0.42Student labor at 8.00/hr $3.16 Tech labor at 25.00/hr $5.23Avg. cost per accession $12.90 **Average of 7 samples per accession and

~1500 samples per season (based on 2003 and 2004 data).

Questions?Contact: Charles C. Block, Ph.D.

Plant PathologistUSDA-ARSNorth Central Regional Plant Introduction StationIowa State University, G212 Agronomy HallAmes, IA 50011-1170Office: 515-294-4379Fax: 515-294-4880Email ccblock@iastate.edu