Soft rot Erwinia bacteria in surface and underground waters in southern Scotland and in Colorado, United States

An anaerobic liquid enrichment method followed by plating on a selective medium revealed that the soft rot coliform bacterium Erwinia carotovora subsp. carotovora was generally present in water from drains, ditches, streams, rivers and lakes (including reservoirs) in southern Scotland and in Colorado, United States, in mountainous, upland and arable areas through the year. Many sites were remote from susceptible or diseased crops. Erwinia carotovora subsp. atroseptica was isolated much less frequently and no Erwinia bacteria were isolated from underground waters. Erwinia bacteria were also found in rain-water in Scotland, in winter snow from mountain passes in Colorado, and in sea water from the west and east coasts of Scotland and from the coasts of Oregon, California, Texas, Louisiana and Florida. The significance of the occurrence of these bacteria in water is discussed in relation to the control of blackleg and soft rot diseases of potato by production of Erwinia -free stocks.     

Soft rot Erwinia bacteria in the rhizosphere of weeds and crop plants in Colorado, United States and Scotland

The soft rot coliform bacteria Erwinia carotovora subsp. carotovora and E. carotovora subsp. atroseptica were isolated by an enrichment method from the rhizosphere of many weed species and crop plants, collected in commercial potato fields either currently in potatoes or in a different crop as part of the rotation. Erwinia carotovora was isolated from 24 plant species in Colorado and 47 species in Scotland. Weeds contaminated with E. carotovora were found in fields growing other crops in which potatoes had not been grown for 1–2 and sometimes much longer. Weeds collected from virgin land in Colorado were not contaminated with E. carotovora but in Scotland virgin soils containing weed roots yielded E. carotovora subsp. carotovora . In general, the numbers of contaminated weeds rose from nil or low levels in spring and early summer to considerably higher levels during mid-season, and fell to progressively lower levels later. Erwinia carotovora subsp. carotovora was the predominant organism recovered from the rhizosphere, but E. carotovora subsp. atroseptica was less common, especially in Scotland, and its incidence varied in different seasons depending on factors such as temperature and moisture conditions. The bacteria could apparently persist in the root zone for an extended period of time and may be a source of inoculum to contaminate soft rot erwinia-free seed potato stocks; the origin of the bacteria was uncertain.