Incidence of tuber diseases in classified seed potatoes harvested In England and Wales, 1974–77

Seed potato tuber inspections were inaugurated in England and Wales as a training exercise daring 1974–77, preparatory to the operation of seed potato classification under statutory authority as from 1978. The number of stocks inspected varied from 359 for the 1976 harvest (38% of those classified) to 536 for the 1975 harvest (52%). The proportion of stocks meeting the required standards progressively increased from 82% for 1974 crops to 91% for 1977 crops. The diseases most commonly causing the failure of stocks to meet the required standards were gangrene (Phoma exigua var. foveata) for crops harvested in 1974, 1975 and 1977, and non-bacterial soft rots for 1976 crops. Over the 4 years the proportion of stocks failing to meet the required standards for diseases were respectively: 1.2% for tuber blight (Phytophthora infestans); 0.6% for bacterial soft rots (Erwinia carotovora subspp.); 2.0% for non-bacterial soft rots (including Phytophthora erythroseptica and Pythium ultimum); 0.8% for dry rots (Fusarium spp.); 4.0% for gangrene; 0.1% for skinspot (Polyscytalum pustulans); 0.1% for black scurf (Rhizoctonia solani); 0.1% for powdery scab (Spongospora subterranea) and 1.6% for common scab (Streptomyces spp.).