This study was performed to investigate the causes of bacterial brown blotch in Agaricus bisporus by analyzing environmental factors using sensors and growth factor characteristics. We found no direct correlation between the CO2 concentration and bacterial brown blotch among the evaluated cultivation environmental factors. However, maintaining the CO2 concentration at 500–2,000 ppm during the harvest period increased the hardness of the mushrooms. Ventilation for 40 min at dawn every day during this period helped prevent the development of bacterial brown blotch by reducing water condensation inside the grower. The incidence of browning disease was reduced to 1% when the medium layer humidity index was decreased to approximately 10 at harvest time and the leaf sensor moisture index was maintained at 430–490.

Fluorescent bacteria were isolated from sporocarps that browned into various mushrooms during survey at places of the production in Korea. We examined the pathogenicity, biodiversity, and genetic characteristics of the 19 strains identified as Pseudomonas tolaasii by sequence analysis of 16S rRNA and White Line Assay. The results emphasize the importance of rpoB gene system, fatty acid profiles, specific and sensitive PCR assays, and lipopeptide detection for the identification of P. tolaasii. As a result of these various analyses, 17 strains (CHM03~CHM19) were identified as P. tolaasii. The phylogenetic analysis based on the 16S rRNA gene showed that all strains were clustered closest to P. tolaasii lineage, two strains (CHM01, CHM02) were not identified as P. tolaasii and have completely different genetic characteristics as a result of fatty acids profile, specific and sensitive PCR, lipopetide detection, rpoB sequence and REP-PCR analysis. Pathogenicity tests showed 17 strains produce severe brown discolouration symptoms to button mushrooms and watersoaking of sporophore tissue within three days after inoculation. But two strains did not produce discolouration symptoms. Therefore, these two strains will be further investigated for correct species identification by different biological and molecular characteristics.