Effects of soil temperature, inoculum density, and incubation time on red root rot of vetch

Abstract

A re-analysis of data in “The Root and Stem Rot Disease of Vetch”(https://hdl.handle.net/2123/24963), a thesis leading to an award of Master of Science in Agriculture in March 1967. Field observations on the effects of sowing date and cropping history on red root rot of Vicia sativa cv. Golden Tares were corroborated with laboratory and glasshouse experiments. Optimum temperature for disease development in the glasshouse was 25.7℃, while that for the pathogen in culture was 30.5℃. The pathogen formed gemmae in culture that constituted infective colony forming units (cfu). An inoculum density of 2500 cfu ml-1 was found in severely infested soil. Disease severity increased with inoculum density in the range of 16-4000 cfu ml-1, inversely in proportion with the calculated average distance between cfu. At an average soil temperature of 17.4℃, red root rot remained mild on inoculated plants even with 4000 cfu ml-1. A mathematical model incorporating the effects of soil temperature, inoculum density, and incubation time described 95% of the variation in disease severity.