Metabiosis and pH of Moldy Fresh Tomatoes

Two hundred twenty eight locally grown, garden variety, moldy tomatoes were examined. The dominant molds were Alternaria , Fusarium and Cephalosporium . Geotrichum , Epicoccum and Mucor were seen in a small number of tomatoes. Seventy eight per cent of the tomatoes were infected with a single mold, and mixed infections were seen in 21% of tomatoes. The pH at the site of infection varied from 4.4 to 8.1, with pH less than 4.8 observed in only 21 moldy tomatoes. The pH of sound tissue increased as pH at the site of the lesion increased. Bacteria were seen in wet mounts from the site of the lesion of 26% of the tomatoes. Bacteria were cultured from an additional 38% of the tomatoes at the site of the lesion and from 13% of the juice cavities at the site across from the infection. Most bacteria were members of the acid tolerant genera Erwinia and Enterobacter . Members of the genera Pseudomonas , Flavobacterium and Alcaligenes were also isolated. Leuconostoc mesenteroides , rennin-proteolytic Streptococcus faecalis and yeasts were obtained in culture, but were not seen in wet mounts. Gram-negative bacteria were seen in two of 13, and recovered in culture from 6 of 13 severely bruised, non-molded tomatoes. The bacteria appear to be present in a metabiotic relationship in which the molds created a favorable pH for bacterial growth.