VIEW ARTICLE

Ecology and Epidemiology

The Effects of Temperature and Dew Period on Germination and Infection by Uredospores of Phakopsora pachyrhizi. M. A. Marchetti, Research Plant Pathologist, Agricultural Research Service, U. S. Department of Agriculture (ARS, USDA) Northeastern Region, Plant Disease Research Laboratory, Frederick, Maryland 21701, Present address of senior author: ARS, USDA, Southern Region, Texas A & M University, Agricultural Research and Extension Center, Beaumont 77706; J. S. Melching(2), and K. R. Bromfield(3). (2)(3)Research Plant Pathologists, Agricultural Research Service, U. S. Department of Agriculture (ARS, USDA) Northeastern Region, Plant Disease Research Laboratory, Frederick, Maryland 21701. Phytopathology 66:461-463. Accepted for publication 27 October 1975. DOI: 10.1094/Phyto-66-461.

Uredospores of Phakopsora pachyrhizi germinated between 10 C and 28.5 C, with a broad optimum in the range 15-25 C. Spores of isolates from Australia, India, Indonesia, and Taiwan germinated over similar temperature ranges, but the optimal temperature range for the Indian isolate was narrower than that for the other isolates. Maximal infection of Wayne soybean leaves occurred at 20-25 C with 10-12 hours of dew and at 15-17.5 C with 16-18 hours of dew. The minimal dew period for infection was 6 hours at 20-25 C, and 8-10 hours at 15-17.5 C. Infection did not occur above 27.5 C. It appears that temperature-moisture requirements for infection of soybeans by uredospores of P. pachyrhizi would not preclude the establishment of the soybean rust fungus in major soybean growing areas of the U. S.