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Scientists Collaborate to Study Phomopsis

Tuesday, November 1, 2011
filed under: Disease

Public researchers are “few and far between” these days, as reductions in government funding take their toll. According to Tom Gulya, research plant pathologist with the USDA-ARS Sunflower and Plant Biology Research Unit in Fargo, N.D., the number of publically funded full-time sunflower pathologists around the world can be counted on two hands.

This small group of specialized scientists makes every effort to collaborate whenever possible. Such was the case this season when Sue Thompson from Australia spent two weeks in the U.S. with Gulya, evaluating sunflower disease nurseries in the Dakotas and Minnesota. But, in fact, Thompson and her co-workers have been have been cooperating with Gulya and his fellow USDA scientists for a good part of the past decade.

Sue Thompson is a state-employed plant pathologist in Agri-Science Queensland (DEEDI), Australia, who has been working on sunflower diseases for more than 15 years — particularly on powdery mildew, rust and Phomopsis stem canker.

A severe outbreak of Phomopsis stem canker occurred in Australia two years ago, and it is her task to identify the species responsible for the disease. An investigation quickly determined that the Australian isolates were not P. helianthi, the most damaging Phomopsis species presently recorded on sunflower in the U.S and Europe. To date, her group has identified three previously undescribed species of Phomopsis associated with stem cankers on sunflower in Australia. Further studies are needed to determine whether these species are also present in other sunflower growing regions internationally.

Thompson’s visit to the U.S. was to confer with Gulya and North Dakota State University pathologists, and for the groups to share their knowledge on Phomopsis. The disease has been of economic significance in the U.S. the past several years — especially in wet seasons — and appears to be increasing in incidence in Australia. Infection occurs via the leaves and then travels down the petiole, where a lesion develops at the node. Pith damage weakens the stalk, making it vulnerable to lodging and can restrict the flow of nutrients to the head — both leading to yield loss.

Thompson spent a good part of her two-week visit in Gulya’s Phomopsis nurseries, participating in the rating of more than 2,300 plots — an ideal opportunity for both scientists to compare and discuss the range of symptoms exhibited by the causal fungus in both countries and to brainstorm on possible management and future research strategies.

Gulya and his team planted 270 USDA Plant Introductions in two Minnesota locations, one location in North Dakota and another in South Dakota. They also planted another 75 U.S. hybrids and 10 hybrids from Novi Sad, Serbia (whose hybrids are specifically selected for Phomopsis resistance), at Rothsay and Crookston, Minn. Those areas had severe Phomopsis epidemics in 2010 and presumably would have natural infection this year.

Thompson and Gulya together rated all 2,300 rows of sunflower in the multiple nurseries. They also made disease surveys and collected “disease specimens” from commercial fields. The data are now being analyzed; but results from one trial indicate a clear differentiation between susceptible and resistant lines/hybrids.

For Thompson it was a great learning experience to see P. helianthi expression in North America, in multiple locations and hundreds of lines — especially since the growing environment in the U.S. Upper Midwest is very different from that of Queensland. For Gulya, the assistance and camaraderie were invaluable. “It is so good to make these assessments in the field with another scientist who has experienced the disease first hand,” he says.

Thompson also had the opportunity to present her research to NDSU, USDA and seed company researchers in two seminars she presented in Fargo. As breeders begin to breed for resistance, it is necessary to know which species of the disease they are targeting. She also had a chance to meet and interact with Dr. Lisa Castlebury, a USDA-ARS mycologist from Beltsville, Md., who specializes in the taxonomy of the genus Phomopsis/Diaporthe.

The National Sunflower Association is supporting Febina Mathew, an NDSU Ph.D. student who is determining which species of Phomopsis are present and their distribution in the U.S. sunflower production area. This is similar work to what Thompson is doing in Australia. Thompson and Mathew had an opportunity to share their techniques and research plans and to ensure that their efforts would be complementary.

NSA is also funding work by Dr. Sam Markell, NDSU extension plant pathologist, who is coordinating Phomopsis fungicide trials with a number of his co-workers at various North Dakota locations. Thompson was able to spend time with Markell going over his protocols.

Thompson, who has a wonderful Aussie brogue, was delighted to meet and interact with all of the U.S. specialized pathologists and breeders from the public sector and private companies. “It was a great learning experience to be able to interact with other dedicated sunflower pathologists and breeders with a passion for sunflower. There is a great deal of research activity in the public and private sectors in the U.S. on this disease,” said the energetic Thompson. Gulya was equally appreciative of Thompson’s work while she was here. “We covered lots of miles and evaluated thousands of plants in a short time frame. Her assistance was invaluable. Plus, we all learned a great deal from her,” he says.

— Larry Kleingartner
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