SCREENING FOR RESISTANCE TO EARLY BLIGHT (ALTERNARIA-SOLANI) IN POTATO (SOLANUM-TUBEROSUM L) USING TOXIC METABOLITES PRODUCED BY THE FUNGUS

The phytotoxic components of the culture filtrate of the fungus Alternaria solani Sor., which causes early blight in potato, were used in this study to differentiate between resistant and susceptible genotypes selected to represent a range of reactions when screened in the field. Detached leaflet assays, using spores and toxic metabolites from the culture filtrate, were compared with field ratings and a whole-plant glasshouse test. Rank correlations between several-detached leaflet tests were highly significant (P < 0.01) but the correlations between these tests and the glasshouse and field tests were poor. The disease ratings obtained in the various tests were clustered into four groups and assigned to resistance classes. For many of the genotypes there was a good correspondence between resistance classes for all test methods. Divergent results between tests were associated with foliage maturity characteristics of the genotypes.