VIEW ARTICLE

Effect of Soil Temperature on Virulence of Pythium aphanidermatum and Pythium myriotylum to Rye and Tomato. R. H. Littrell, Assistant Professor of Plant Pathology, University of Georgia, College of Agriculture Experiment Stations, Coastal Plain Station, Tifton 31794; S. M. McCarter, Assistant Professor of Plant Pathology, University of Georgia, College Experiment Station, Athens 30601, Former affiliation of junior author: Research Plant Pathologist, Crops Research Division, ARS, USDA, Tifton. Phytopathology 60:704-707. Accepted for publication 18 November 1969. DOI: 10.1094/Phyto-60-704.

Optimum temperature for mycelial growth of Pythium aphanidermatum and P. myriotylum on V-8 juice agar was 35 C; slight growth occurred at 15 and 43 C. When seeds were planted in infested soil, both species reduced stands of rye 100% at 27 C and above, but caused no damage at 15 C. P. aphanidermatum was most virulent to tomato at 27-35 C. P. myriotylum caused almost complete stand loss in tomato at 35 C and was less virulent than P. aphanidermatum at 23-31 C. P. myriotylum caused root and crown rot and reduction in wet wt of established rye plants at 23 C, and virulence increased as soil temperature increased to 35 C. P. aphanidermatum caused little damage to established rye plants below 31 C. Both species were about equally damaging to established tomato plants above 23 C, and disease was most severe at 35 C. Rye kernels were more readily infected by P. aphanidermatum than by P. myriotylum. Seventy-three per cent of the kernels were infected after exposure in P. aphanidermatum-infested soil for 24 hr at 35 C, as compared to 15% infection with the other species. Tomato seed were relatively resistant to invasion, as indicated by failure to recover either species after exposure in infested soil for 48 hr at 31 C.