Carol E. Windels

Economic and social impacts of fusarium head blight: changing farms and rural communities in the northern great plains.

Fusarium head blight, also known as scab, can be a devastating disease on all classes of wheat and barley. Among the species of Fusarium that cause scab, F. graminearum is the predominant pathogen. Wheat and barley are highly susceptible to infection when the crop is in the flowering to soft dough stages and when weather includes frequent precipitation, high humidity, or heavy dews. Multiple symptoms occur: reduced yields, discolored and shriveled kernels (tombstones), depressed seed weights, and reduced seed quality and vigor. The mycotoxin deoxynivalenol (DON, commonly known as vomitoxin) also can be produced by F. graminearum on infected grain. Grain contaminated with DON often is unsuitable for flour, cereals, or malt and is too toxic as feed for nonruminant animals (19). Distribution of Fusarium head blight. In recent years, Fusarium head blight has reemerged worldwide as a disease of economic importance (19). In the United States and Canada, the reemergence of Fusarium head blight in the 1990s has caused epidemics of varying severity on barley and on all classes of wheat. It is documented as causing epidemics in 26 states (19) and the Canadian provinces of Quebec (A. Comeau, Agriculture and Agri-Food Canada, Ste. Foy, Quebec, Canada, personal communication), Ontario (A. W. Schaafsma, University of Guelph, Ridgetown College, Guelph, Ontario, personal communication), and Manitoba and Saskatchewan (R. Clear, Canadian Grain Commission, Winnipeg, Manitoba, personal communication). The United States Department of Agriculture (USDA) ranks Fusarium head blight as the worst plant disease to hit the nation since the stem rust epidemics of the 1950s (35). Wheat and barley losses caused by scab epidemics in the United States during the 1990s are estimated at close to

Phylogenetic relationships among plant and animal parasites, and saprotrophs in Aphanomyces (Oomycetes)

3 billion. American wheat farmers lost over 500 million bushels of wheat valued at about

Reaction of Soybean Cultivars to Isolates of Fusarium solani from the Red River Valley

2.5 billion (T. Sayler, Prairie Ag Communications, Fargo, ND, personal communication) and Midwestern barley producers lost

Variability in sensitivity to metalaxyl in vitro, pathogenicity, and control of Pythium spp. on sugar beet

400 million on barley (J. Mittleider, North Dakota Barley Council, Fargo, personal communication). Economic losses to wheat producers in Canada in the 1990s are estimated in U.S. dollars at

Fusarium Species Stored on Silica Gel and Soil for Ten Years

220 million in Quebec and Ontario (A. Comeau, Agriculture and Agri-Food Canada, Ste. Foy, Quebec, personal communication) and, from 1993 to 1998, at

Remote Sensing for Assessing Rhizoctonia Crown and Root Rot Severity in Sugar Beet

300 million in Manitoba (A. Tekauz, Agriculture and Agri-Food Canada, Winnipeg, Manitoba, personal communication). Why Fusarium head blight has been so severe. The disease has been favored by a combination of factors including unseasonably wet weather, particularly when plants are most susceptible. The increased practice of conservation tillage has favored inoculum of the pathogen to survive in residues of host crops such as wheat, barley, and corn. A high percentage of land has been planted to small grains, with short intervals between crops. Also, plant resistance to scab has been limited or absent in wheat and barley cultivars. These factors have resulted in the buildup and abundance of inoculum of F. graminearum. “Breadbasket of the World” under siege. The Northern Great Plains has a short growing season, so much of the land is tied to cereal production that includes hard red spring wheat, durum wheat, winter wheat, and barley. Beginning in 1993, northwestern Minnesota, eastern North Dakota, northeastern South Dakota, and southern Manitoba in Canada were particularly hard hit by Fusarium head blight and disease severities reached 20 to 80% (19). Epidemics of Fusarium head blight, however, have continued to reoccur every year from 1993 to 1998 at varying intensities, particularly in northeastern North Dakota, northwestern Minnesota, and southern Manitoba. In the last couple of summers, F. graminearum has spread further westward across North Dakota (M. McMullen, North Dakota State University, Fargo, personal communication) and from western Manitoba into Saskatchewan (R. Clear, Canadian Grain Commission, Winnipeg, Manitoba, personal communication). In the 1999 season, Fusarium head blight was a minor disease problem in Minnesota and North Dakota (although infections occurred as far west as the central portion of the state) and less of a problem in Manitoba compared with previous years. The Red River Valley, which I refer to occasionally in this presentation, is a 40to 60-mile region on each side the Red River that separates North Dakota and Minnesota and flows north into Manitoba. The flatlands of the Red River Valley are the lake bed of the prehistoric Lake Agassiz. It’s black loamy soil is among the richest farmland in the world. This region is the “Breadbasket of the World” and farmers here typically are prosperous. I live and work in northeastern North Dakota and northwestern Minnesota and have witnessed the impact of Fusarium head blight on the region. It has severely crippled the wheat and barley industries, driven producers to financial ruin and human hardship, and resulted in rural communities dwindling away. The epidemic has generated nearly

Perithecium production in Fusarium graminearum populations and lack of correlation with zearalenone production

10 million in new public and private funding to support Fusarium head blight research and education in the United States (T. Sayler, Prairie Ag Communications, Fargo, ND, personal communication) and also has resulted in lobbying to change agricultural policies. In this address, I will focus on the development and impact of this crisis, with an emphasis on northeastern North Dakota and northwestern Minnesota. The summer of 1993 held great promise. Fields of wheat and barley were lush and green, and yield potentials promised to meet or exceed the bumper crops harvested in 1992. At harvest, growers were stunned and distressed when they found severe scab infecContribution No. 9910102 of the Minnesota Agricultural Experiment Station.

Spatial Distribution of Aphanomyces cochlioides and Root Rot in Sugar Beet Fields

Molecular phylogenetic relationships among 12 species of Aphanomyces de Bary (Oomycetes) were analyzed based on 108 ITS sequences of nuclear rDNA. Sequences used in the analyses belonged to the major species currently available in pure culture and GenBank. Bayesian, maximum likelihood, and maximum parsimony analyses support that Aphanomyces constitutes a monophyletic group. Three independent lineages were found: (i) plant parasitic, (ii) animal parasitic, and (iii) saprotrophic or opportunistic parasitic. Sexual reproduction appeared to be critical in plant parasites for survival in soil environments while asexual reproduction seemed to be advantageous for exploiting specialization in animal parasitism. Repeated zoospore emergence seems to be an advantageous property for both plant and animal parasitic modes of life. Growth in unspecific media was generally faster in saprotrophs compared with parasitic species. A number of strains and GenBank sequences were found to be misidentified. It was confirmed molecularly that Aphanomyces piscicida and Aphanomyces invadans appear to be conspecific, and found that Aphanomyces iridis and Aphanomyces euteiches are closely related, if not the same, species. This study has shown a clear evolutionary separation between Aphanomyces species that are plant parasites and those that parasitize animals. Saprotrophic or opportunistic species formed a separate evolutionary lineage except Aphanomyces stellatus whose evolutionary position has not yet been resolved.

First Report of Fusarium oxysporum Causing Yellows on Sugar Beet in the Red River Valley of Minnesota and North Dakota

Five isolates of Fusarium solani, originally isolated from diseased soybean roots in the Red River Valley (RRV) of Minnesota and North Dakota, were evaluated for their ability to cause symptoms on 10 genetically diverse soybean cultivars. Taproots of 2-week-old plants were inoculated with F. solani-infested oat kernels, and 3 and 10 weeks later, plants were evaluated for root rot and foliar symptoms. At 3 weeks after inoculation, taproots of all cultivars had extensive reddish brown to black lesions; root rot severity (1-6 scale) ranged from 4.8 to 5.1, and 3.5% of the plants had died. Foliar symptoms were not observed. At 10 weeks after inoculation, all cultivars showed extensive decay of taproots and >50% of lateral roots were necrotic; root rot severity (1-4 scale) ranged from 2.7 to 3.7, and 42.5% of the plants had died. Foliar symptoms were first observed between the R-1 to R-6 growth stages (about 5 weeks after inoculation) on the lower leaves and consisted of chlorosis at the margins that progressed inward. Veins initially were green, but leaves eventually became chlorotic, then necrotic, and fell with petioles still attached to the stem. In some cases, all of the foliage died. There was no significant (P = 0.05) isolate × cultivar interaction for root rot at 3 or 10 weeks after inoculation or for severity of foliar symptoms. Thirty-three cultivars commonly grown in southern Minnesota and the RRV were evaluated for reaction to one isolate of F. solani. Root rot severity ranged from 4.2 to 5.7 (1-6 scale) and 3.5 to 4.0 (1-4 scale), at 3 and 9 weeks after inoculation, respectively, and >50% of the plants died by 9 weeks after inoculation. Severity of foliar symptoms was low. These results indicate that isolates of F. solani from the RRV cause root rot and foliar symptoms on soybean and that cultivars grown in the region lack resistance to this pathogen. Foliar symptoms were not identical to those associated with sudden death syndrome.

Characterization and Pathogenicity of Thanatephorus cucumeris from Sugar Beet in Minnesota

Pythium ultimum var. sporangiiferum (76 isolates) and P. aphanidermatum (21 isolates) cultured from diseased sugar beet seedlings in Minnesota and North Dakota were tested for sensitivity to metalaxyl, pathogenicity on sugar beet, and disease control by metalaxyl seed treatment. Sensitivity to metalaxyl (effective concentration causing 50% growth inhibition [EC50]) was determined by linear growth on corn meal agar amended with 0, 0.01, 0.1, 1, 10, and 100 μg a.i. metalaxyl ml-1 after 48 h in the dark at 21 ± 1°C. Variation among isolates was significant (P = 0.05) within and between species, and EC50 values averaged 0.16 (range: 0.05 to 1.30 μg ml-1) for P. ultimum var. sporangiiferum and 2.06 (range: 1.19 to 3.12 μg ml-1) for P. aphanidermatum. In pathogenicity tests on sugar beet, most isolates of P. ultimum var. sporangiiferum (72 of 76) and all of P. aphanidermatum significantly (P = 0.05) decreased final stands compared to the noninoculated control. There was no correlation between aggressiveness in the absence of metalaxyl and in vitro sensitivity to metalaxyl. When Pythium-infested soil was planted with seed treated with metalaxyl at the standard (0.625 g a.i. kg-1) or half rate, some isolates that were least sensitive to metalaxyl in vitro resulted in a significant (P = 0.05) reduction in disease control. These results may explain, at least in part, why producers do not attain expected stands when they plant metalaxyl-treated sugar beet seed.