Sites of contamination and numbers of Erwinia carotovora present in stored seed potato stocks in Scotland

SUMMARY Forty‐eight bulk and crate stored commercial seed potato stocks from the east of Scotland were examined for contamination by Erwinia carotovora in 1967 and 1968. Both E. carotovora var. carotovora and E. carotovora var. atroseptica were present, the latter, the blackleg pathogen, being detected four times more frequently. Most contamination was located on the tuber surface and in the lenticels; it was rare in the vascular ring and the organism was never detected in the cortex. The level of contamination of lenticels was only slightly affected after winter storage, which, however, substantially reduced surface contamination. More than 103 cells were detected on the surface of tubers in over half the stocks and in half the stocks each lenticel sampled contained more than 102 bacteria.