Abstract
For the laboratory assessment of the field resistance of potato tubers to infection by Phytophthora infestans, an improved inoculation method was devised using mature tubers. Mature tubers were pre-immersed in water for some hr (1-48hr). Then the pre-immersed tubers were inoculated for some hr (1-5hr) in a zoospore suspension (1-1000zoospores/ml). After washing in running tap water the inoculated tubers were incubated for 7 days under a moist condition to develop blight lesions. Results showed that almost all (<90%) lesions developed from the eye infection similarly to natural infection in the field. The infection increased with increase in the inoculum density and the periods of pre-immersion and inoculation. A combined condition of a pre-immerison period of 2hr, an inoculum density of 100zoospores/ml and an inoculation period of 4hr was suitable to assess the tuber resistance. A test using several cultivars with different degree of apparent field resistance under these conditions showed that the degree of infection reversely corresponded to their resistant characters in the field. Mature tubers could be used to assess the field resistance of the cultivars for at least three months after harvest.
