Disease Minority Report

Wisconsin lab tests method for pinpointing disease early

Published in the June 2009 Issue Published online: Jun 05, 2009 Fungicide, Insecticide Tyler J. Baum, Editor

The movie Minority Report, directed by Steven Spielberg, showed a world where criminals were caught even before they committed a crime.

In a way, a Wisconsin lab may have figured out how to catch crop pests before they've even struck.

Pest Pros Inc. is an independent crop consulting firm and plant disease diagnostic laboratory located in Plainfield, Wis. Pest Pros provides a range of crop management services to assist growers in solving production problems. Founded as an IPM scouting services provider in 1984, they've evolved to offer a full line of crop and pest management advice and testing services including nematode testing and molecular (DNA) plant disease diagnostics.

In 2004, Pest Pros began collaborating with Dr. Walt Stevenson and Dr. Zahi Atallhah, potato disease specialists at the University of Wisconsin-Madison, in the Department of Plant Pathology. They agreed to a project to test pre-harvest storage disease risk-a system that could eventually be fast-tracked for commercial applications.

In the fall of 2008, commercial testing began. According to Randy Van Haren, Pest Pros lead pest management specialist, tuber samples from each field were tested last fall. Forty-two fields involving Russet Burbank, Norkota, Gold Rush, FL 1879, FL 1867, White Pearl, Snowden and Dakota Pearl were sampled seven to ten days prior to digging, using real-time Polymerase Chain Reaction (RT-PCR) for background loads of soft rot, pink rot and pythium leak inoculum.

A storage disease risk assessment was made for each field. Fields were indexed, using a scale developed by Randy Van Haren, from 1-5 (from very low to high risk) for disease risk and the storage bins monitored and rated from 1-5 (from very low rot to high rot) for the development of storage rot. Only non-symptomatic tubers were tested for disease potential. Samples were taken of three tubers every 10 acres, by walking an inner and outer wheel track of each pivot, digging in two adjacent hills.

Each sample was first cleaned, then a thick slide was cut from the middle of each tuber to include the bud and stolon end, and DNA was extracted. Storage bins were monitored all winter for the development of rot.

After a long winter of waiting, mid-April came around, when the actual storage rot outcomes were determined. Randy's comparison of the "Storage Potato Disease Risk Index" to the storage rot outcome in mid-February showed that 74 percent of the forecasted disease predications were either in complete agreement or very close to the final disease outcome in storage.

Van Haren noted that none of the indexes produced false negatives-no fields were rated as safe for rot with subsequent rot development in storage. However, false positives occurred in 25 percent of the fields-slightly less rot developed than was predicted. He noted that these results were produced in an average to slightly below average year for storage rot in Wisconsin."

"It is only a single year's worth of data," he points out.

The ultimate goal is to provide a means for growers to segregate risky potatoes from the rest, by variety in storage and manage the healthy potatoes for quality in long-term storage.

This is still a work in progress, Randy points out.

"[We're] not trying to promote the system aggressively outside of Wisconsin yet, but would like those in the industry to be aware of what we are doing," he says. "It will be interesting to see how the disease indexing will perform in a more severe storage rot season."

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