Evaluation location: Michigan, United States
The tuber inoculations were conducted over four dates (four replications). All tubers were surface sterilized in a 5% bleach solution, rinsed, and dried overnight prior to inoculation. Tubers were each inoculated by removing a 2.5 mm plug (5 mm depth), and placing a mycelia plug (mycelia down) in the hole, and covering with a dab of petroleum jelly. The US-8 P. infestans cultures were again provided by Dr. Kirk. Tubers were held in a humid box at 10C. The tubers were scored for late blight infection ~2 months after inoculation on a 0 ? 9 scale, with zero being no late blight infection; a tuber with 100% late blight coverage received a rating of nine.