Sites of entry ofphytophthora infestans (Mont.) de Bary into potato tubers in assessment of tuber blight resistance

Summary During assessment of tuber blight resistance using three test methods, the sites of entry ofPhytophthora infestans into the tuber was estimated for 41 cultivars. The trials were conducted using a mix of three highly virulent isolates at Gro? Lüsewitz 1991–1993. The influence of date of harvest and intermediate storage before inoculation was examined with two cultivars in 1993. Two levels of soil moisture and five densities of inoculum were tested in 1994. Methods of assessment of tuber blight resistance, cultivars, years and all their interactions showed a significant effect on sites of entry. Eye infections identified the highest the level of resistance and correlated best with tuber blight resistance in net bag test, r=-0.58. Soil moisture and temperature before harvest varied the ontogenic development of resistance and the relation of sites of entry of the pathogen from July to September. Intermediate storage changed the resistance and the preferred site of cultivar-specific infection. Interactions cultivar x soil moisture and cultivar x density of inoculum were significant and should be considered in the resistance assessment of cultivars.