Influence of storage temperature on rate of potato tuber tissue infection caused by Phytophthora infestans (Mont.) de Bary estimated by digital imageanalysis

Potato tubers were inoculated with two biotypes of Phytophthora infestans t hen stored at 3, 7, 10 and 15 degreesC. Image analysis quantified average r eflective intensity (ARI) of diseased tissue from cut surfaces of sample tu bers. Tuber tissue infection and infection rate were measured by calculatin g Mean ARI of samples. Average tuber tissue infection and infection rate wa s minimal at 3 degreesC (P.i.-US8 or P.i.-US1). Tuber tissue infection incr eased at temperatures >3 degreesC, from 220 Mean ARI seven days after inocu lation (dai) to 190-150 Mean ARI 50 dal (depending on cultivar and biotype of P. infestans). Rate of tuber tissue infection caused by P.i.-US1 at 7 de greesC was about zero in cv. Snowden but greater than -0.2 ARI day(-1) (cvs Russet Burbank and Superior). Rate of late blight infection in tuber tissu e generally increased with temperature from -0.2 ARI day(-1) (at 7 degreesC ) in all cultivars to a maximum of -0.8 ARI day(-1) (10 degreesC).