Lactobacillus plantarum; a deleterious contaminant of plant tissue cultures

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Abstract
Lactobacillus plantarum was isolated from in vitro plant cultures of Hemerocallis Stella d'ora, Catherine Woodbury and Stafford. Infected cultures deteriorated rapidly during three subcultures (15 weeks) when grown in vitro, showing chlorotic white shoots and grey calli. Weaned plants developed normally when transferred to the soil. The drop in multiplication rate of plant cultures coincided with a decrease in pH of the growth media. Uninfected plants of Hemerocallis Stella d'ora showed the same symptoms after inoculation with L. plantarum. Lactobacillus plantarum was reisolated from inoculated plant cultures that showed symptoms, thus fulfilling Koch's postulates. In plants inoculated with L. plantarum both the amount of dl‐lactic acid formed and the number of plants showing symptoms increased with increasing numbers of bacteria in the inoculum, wheras plant multiplication rate and pH decreased. These effects could be reproduced by adding dl‐lactic acid to the multiplication medium of plants free from L. plantarum, suggesting that the bacterial production of lactic acid was responsible for the changes in infected plants.