A laboratory assay for Phytophthora infestans resistance in various Solanum species reflects the field situation

Physiological and molecular research on resistance responses of Solanum tub erosum cultivars and partially resistant Solanum species to Phytophthora in festans requires a reliable resistance test that can be used in the laborat ory. Laboratory tests performed on detached leaves and intact plants were c ompared with field tests for similarity of late blight reactions. Detached leaves from field-grown plants were as resistant as detached leaves from cl imate chamber-grown plants when challenged with P. infestans. However, deta ched leaves incubated in covered trays at high relative humidity were more susceptible than detached leaves kept in open trays or leaves on intact pla nts. The incubation conditions of detached leaves in covered trays rather t han detachment itself appeared to affect the resistance expression. Detache d leaves of some wild Solanum genotypes became partially infected, whereas intact plants were completely resistant when inoculated. Inoculation of lea ves on intact plants, however, resulted in lower infection efficiencies. Th ese limitations should be taken into account when choosing the appropriate inoculation method for specific purposes. For resistance screening, laborat ory tests proved to be a good alternative for field tests. The ranking of r esistance levels for twenty plant genotypes was similar under laboratory an d field conditions.