Abstract:
A total of 251 bacterial isolates were isolated from blotched mushroom samples
obtained from various mushroom farms in Canada. Out of 251 stored isolates, 170
isolates were tested for pathogenicity on Agaricus bisporus through mushroom rapid
pitting test with three distinct pathotypes observed: dark brown, brovm and
yellow/yellow-brown blotch.
Phenotypic analysis of 83 isolates showed two distinct proteinase K resistant
peptide profiles. Profile group A isolates exhibited peptides with masses of 45, 18, 16
and 14 kDa and fiirther biochemical tests identified them as Pseudomonasfluorescens III
and V. Profile group B isolates lacked the 16-kDa peptide and the blotch causing
bacterial isolates of this group was identified as Serratia liquefaciens and Cedecea
davisae.
Comparative genetic analysis using Amplified Fragment Length Polymorphism
(AFLP) on 50 Pseudomonas sp. isolates (Group A) showed that various blotch symptoms
were caused by isolates distributed throughout the Pseudomonas sp. clusters with the
exception of the Pseudomonas tolaasii group and one non-pathogenic Pseudomonas
fluorescens cluster. These results show that seven distinct Pseudomonas sp. genotypes
(genetic clusters) have the ability to cause various symptoms of blotch and that AFLP can
discriminate blotch causing from non-blotch causing Pseudomonasfluorescens.
Therefore, a complex of diverse bacterial organisms causes bacterial blotch disease
