Once Wheat spindle streak mosaic virus (WSSMV) becomes established in a field, the only available control strategy is the planting of resistant genotypes. In this study, we assessed 112 genotypes of winter wheat, rye, triticale, and barley for resistance to WSSMV in a 3-year trial in a field that had been used continuously for WSSMV evaluation for over 20 years. Because resistance to WSSMV reduces the percentage of plants that develop detectable virus titer and symptoms, we collected and analyzed disease incidence data. None of the genotypes was immune to infection. Sixty-two of the regionally adapted genotypes repeatedly expressed resistance to WSSMV, thus providing growers with a choice of cultivars resistant to WSSMV. Because of a significant interaction between genotypes and environment (year), genotypes should be assessed for incidence of symptomatic plants in multiple years, particularly when differentiating intermediate responses from highly susceptible and highly resistant responses.
Keywords: disease gradient; logistic regression.