Reliability of different parameters to estimate relative foliage blight resistance and its relation to maturity in potato

A comparative study of different parameters calculated for foliage resistance of potato to Phytophthora infestans (Mont.) de Bary was conducted on the data for 27 cultivars and one prebreeding clone in field assessment in 2003 at BAZ Groß Lüsewitz. Relationships between the parameters and maturity were determined by linear regression. The strongest associations with maturity were found for the relative area under the disease progress curve (RAUDPC), delay of attack, and attack on a determined date (r2 = 0.47-0.52). The least association with maturity was found for foliage blight resistance at Groß Lüsewitz, FBRGL (r2 = 0.03), calculated by using a maturity-dependent section of the disease progress curve. The apparent infection rate (AIR), RAUDPC and delay of attack could only explain below 50% of variability of FBRGL. The method for calculation of foliage resistance in breeding developed at BAZ and named FBRGL is described in detail, and the usefulness of the different methods for evaluation of resistance, management of plant protection and breeding is discussed.