Resistance of tomatoes to late blight (Phytophthora infestans)

Abstract

SUMMARYRace T1 of Phytophthora infestans was first isolated in Central Europe. Tomato varieties carrying the dominant gene Ph were easily infected by T1 but showed a different degree of field resistance. In September 1967 more than 80% of all isolations from the experimental plots at Greifswald were determined as the aggressive race T1. This race was also isolated in a large screening test over several provinces of the GDR from potato and tomato fields where no plants carrying dominant resistance genes were present in the neighbourhood.The fungus was able to pass from potato leaves or tubers to detached tomato leaves or intact tomato plants (cv. Fanal) without any reduction in sporulation.The field‐resistant tomato variety Ružový Ker and the highly field‐resistant variety Atom were crossed. In F2 and subsequent generations, young plants were selected following inoculation of 14 mm leaf‐discs. Weak sporulations on the leaf‐discs were almost invariably correlated with a reduced level of infection of fruit in the field. Data from crosses of Atom with more or less susceptible varieties suggested the presence of incompletely dominant genes. It is concluded that at least two genes in the variety Atom control field resistance and the gene‐symbols Phf and Phf‐2 are proposed for them.