Evaluation location: Wisconsin, United States
144 accessions representing 29 species were used in this assay to evaluate EB resistance in wild potato species. This assay uses auxin to promote senescence in detached leaves, which are inoculated with a conidial suspension of A. solani. After seedlings were transplanted to individual peat pots for about a month, the oldest healthy leaf was collected from each plant and the petiole was inserted into 0.5% agar containing 10.7 mM auxin (1-naphthalene acetic acid) and tetracycline at 10 ug/ml in a petri dish. Three leaves (from three different plants) were placed on a plate. The next day, a mister was used to apply a 47,000 CFU/ml conidial suspension of A. solani (potato isolate) to the upper surface of each leaf. Petri dishes were incubated under continuous fluorescent light at 27C. After 72 h, individual leaves were scored based on severity of lesion development, from 0 (no lesions) to 4 (severe symptoms). One week later, a second replication was performed using the same plants and an inoculums density of 48,000 CFU/ml. Again, the oldest healthy leaf was sampled. A third replication was carried out 1 week after that, using 43,000 CFU/ml inoculum. The mean score for the three replications was calculated - mean scores of less than 1 were considered to have strong resistance.