ASSESSMENT OF SEED-BORNE STAGONOSPORA-NODORUM IN NEW-YORK SOFT WHITE WINTER-WHEAT

Stagonospora nodorum, incitant of Septoria nodorum blotch, is the pred ominant foliar pathogen of winter wheat in New York. Previous field su rveys 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., ge rmination testing) in 1990 and 1991. Lots sampled in 1990 were screene d for percentage of seed infected by S. nodorum using both a wet-blott er seedling symptom test and a fluorescence test on a selective medium . Results of both assays were highly correlated (r = 0.82). Consequent ly, lots sampled in 1991 were assayed by the fluorescence test only. G ermination was not affected significantly by infection by S. nodorum, but was decreased significantly by infection by Fusarium species in se veral 1990 lots. S. nodorum was detected in all lots in 1990 and in al l 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 t o 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 N ew York has a potential source of seedborne inoculum of S. nodorum, wi th the extent of seed infection varying widely by the year in which se ed was produced and the specific lot.