Assessment of Seedborne Stagonospora nodorum in New York Soft White Winter Wheat. D. Shah, Former Graduate Student, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. G. C. Bergstrom, Associate Professor, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Plant Dis. 77:468-471. Accepted for publication 11 December 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0468.

Stagonospora nodorum, incitant of Septoria nodorum blotch, is the predominant foliar pathogen of winter wheat in New York. Previous field surveys indicated that seedborne inoculum may be a significant factor in the initiation of epidemics. To ascertain the extent of seedborne S. nodorum in New York winter wheat, 50 seed lots per year were selected randomly from those produced and submitted for certification (i.e., germination testing) in 1990 and 1991. Lots sampled in 1990 were screened for percentage of seed infected by S. nodorum using both a wet-blotter seedling symptom test and a fluorescence test on a selective medium. Results of both assays were highly correlated (r = 0.82). Consequently, lots sampled in 1991 were assayed by the fluorescence test only. Germination was not affected significantly by infection by S. nodorum, but was decreased significantly by infection by Fusarium species in several 1990 lots. S. nodorum was detected in all lots in 1990 and in all but nine lots in 1991. The average incidence of infected seed in the lots was 23% (range of 1–71%) in 1990, a moist season with moderate to severe Septoria nodorum blotch, and 2% (range of 0–19%) in 1991, an atypically dry season with low levels of Septoria nodorum blotch. All sampled lots met New York certification standards and were marketed to wheat producers. The results suggest that most winter wheat sown in New York has a potential source of seedborne inoculum of S. nodorum, with the extent of seed infection varying widely by the year in which seed was produced and the specific lot.

Keyword(s): Leptosphaeria nodorum, Phaeosphaeria nodorum, seed health test, Triticum aestivum.