Pathogenicity of bacteria causing spear (head) rot of calabrese (broccoli) in Scotland
1994
Harling, R. | Kellock, L.J. (Scottish Agricultural College, Edinburgh (United Kingdom)) | Chard, J.
Spear rot is a major disease of calabrese in Scotland. This work presents new data on the causal agent(s) of this disease in the UK. Isolations from affected crops in 1992 showed that the predominant bacteria present on rotted heads were fluorescent Pseudomonads. A smaller proportion of the population comprised Erwinia carolovora and, as yet unidentified, non-fluorescent Gram-negative bacteria. Out of 72 fluorescent Pseudomonas isolates tested, 13 (18 percents) were capable of causing a rapid spreading rot when inoculated onto calabrese heads in an in vitro pathogenicity test. Pathogenic isolates were mostly classified as Groups IVa and IVb fluorescent Pseudomonas. Pathogenicity of the Pseudomonas isolates was correlated with their surfactant and pectolytic abilities. A small number of Erwinia carotovora isolates was obtained from diseased spears: these isolates were all strongly pathogenic but did not produce surfactant. None of the unidentified Gram-negative group were capable of causing disease. Conjugated polyclonal antiserum produced against one of the pathogenic Pseudomonas isolates showed very high specificity for its homologous isolate. Antisera raised against two Erwinia isolates cross-reacted with several pathogenic and non-pathogenic fluorescent Pseudomonas isolates.
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