Received for publication March 7, 1980. Contribution of Science and Education Administration, Agricultural Research, U.S. Department of Agriculture, in cooperation with the Agricultural Experiment Station, Oregon State University. Technical Paper No. 5345 of the latter.
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Plant Pathologist, USDA SEA-AR. I acknowledge the assistance of M. Sturdevant and K. Kowalczyk in taking data and F.J. Lawrence in selecting superior subclones during this study.