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Association of Bipolaris sorokiniana, Fusarium graminearum Group 2, and F. culmorum on Spring Wheat Differing in Severity of Common Root Rot. Carol E. Windels, Associate Professor, Northwest Experiment Station, University of Minnesota, Crookston 56716. C. Holen, Area Crop Pest Management Extension Specialist, Northwest Experiment Station, University of Minnesota, Crookston 56716. Plant Dis. 73:953-956. Accepted for publication 2 May 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0953.

Forty fields of spring wheat (wheat planted after wheat) in the early-milk to ripe stages were sampled in northwestern Minnesota during 19851987. Subcrown internode ratings (03 scale, where 0 = healthy, 3 = ≥50% discolored) during the 3 yr averaged 0.9. In 1985 and 1986, Bipolaris sorokiniana was isolated from significantly fewer subcrown internodes in disease classes 0 and 1 than in disease classes 2 and 3; in 1987, recovery of this fungus was the same for all disease classes. Isolation of B. sorokiniana from crowns of the same plants in classes 0, 1, 2, and 3 and from plants with no subcrown internodes did not differ significantly in each of the 3 yr and averaged 76%. Fusarium graminearum group 2 was recovered from 7% of the subcrown internodes and 9% of the crowns, whereas F. culmorum was isolated from 2% of the subcrown internodes and 4% of the crowns. Although subcrown internode ratings were low, B. sorokiniana, F. graminearum group 2, and F. culmorum were isolated from symptomless and lesioned subcrown internodes and crowns of roots in all disease classes.

Keyword(s): Cochliobolus sativus, Gibberella zeae, Triticum aestivum.