Potato soft rot test

Purpose

For distinguishing pectolytic Erwiniae from nonpectolytic Erwiniae.

Materials

• Potato
• Ethanol
• 24 hour culture

Instructions

1. Wash and peel a potato.
2. Make 1 cm slices (2 slices per isolate; 2 controls).
3. Dip the slices in alcohol and flame.
4. Place a slice in a Petri dish with sterile water to a depth of 3-4 mm.
5. Make a nick in the center of the potato with a sterile tool and inoculate with a loopful of fresh culture (24 hr).
6. Incubate at 27°C for 1 day.
7. After 24 hours, run a loop across the potato slice to see how far the rot has progressed.

Expected results

• Rot extending through most of the diameter of the slice indicates a positive reaction. Slight rot at the point of inoculation indicates a negative reaction.

Notes

• Be sure to include a non-inoculated, nicked control slice.

Contributed by

From the Virginia Polytechnic Institute and State University Mediabook; contributed by Mary Ann Hansen.