The extent and survival of contamination of potato stocks in Scotland by Erwinia carotovora var. carotovora and E. carotovora var.atroseptica*

SUMMARY The following results were obtained when fifty‐seven bulk and crate‐stored commercial seed potato stocks from the East of Scotland were examined in 1966‐8 for contamination by pectolytic Erwinia spp. (1) Most tubers of all the cultivars and stocks examined, irrespective of whether they were obtained from blackleg‐infected or blackleg‐free crops, were contaminated with E. carotovora; (2) some 80% of the Erwinia isolates obtained were identified as var. atroseptica, the rest being var. carotovora; (3) the organisms survived in and on tubers for 6–7 months of bulk storage over the winter and up to planting time the following spring; (4) contrary to what is generally thought, the high incidence of contamination of all stocks, while suggesting that the seed itself is the major source of E. carotovora for the growing crop, emphasizes that other factors affect manifestation of blackleg in the field and soft rot in store.