VIEW ARTICLE

Effect of Inoculum Density of Sclerotium cepivorum and Some Soil Environmental Factors on Disease Severity. P. B. Adams, Plant Pathologist, Plant Science Research Division, ARS, USDA, Plant Industry Station, Beltsville, Maryland 20705; G. C. Papavizas, Microbiologist, Plant Science Research Division, ARS, USDA, Plant Industry Station, Beltsville, Maryland 20705. Phytopathology 61:1253-1256. Accepted for publication 26 May 1971. DOI: 10.1094/Phyto-61-1253.

Optimum temperature for white rot development on onion was 15 C. Optimum temperature for germination of sclerotia of Sclerotium cepivorum in autoclaved soil was 20 C. The optimum pH values for germination of sclerotia on agar and in autoclaved soil were 5.3 and 4.8, respectively. However, more than 50% of the sclerotia germinated in autoclaved soil at all pH levels tested between 4.5 and 7.8. At pH 5.0 or below, less than 30% of the plants were infected, whereas at 6.0 and above, 90% of the plants were infected. About 25 sclerotia/g soil were required to obtain infection of about 60% of the seedlings. Of numerous species tested, only Allium caeruleum appeared to possess significant resistance to white rot.