Ecological Studies on the Soft-Rot Bacteria of Vegetables

Abstract

Thirty species of crop plants belonging to ten families were grown in the field. On the 67th and 82nd days after seeding, the rhizosphere populations of each plant were analized by the dilution plate method and the enrichment technique using a selective medium.Bitaminna (Brassica sp.) and one variety of turnip had already been infected by soft rot disease before examination. The preferential stimulation of the soft-rot bacteria (Erwinia sp.) was observed in the following crops; Chinese cabbage, three varieties of Brassica chinensis L., teosinte, Chinese chives and tomato. No similar effect was noted with all the seven species of leguminous crop plants.Furthermore, fifteen species of weeds which grew naturally in the field where chinese cabbages were grown were tested. The selective action on the soft-rot bacteria was also demonstrated with cow-thistle, pigweed and spiderwort.Of the plants tested, the preferential effect on the soft-rot bactoria was most pronounced with the crops belonging to the cruciferous plants.It seems that the soft-rot bacteria are one member of the specific rhizosphere microflora in some of the cruciferous plants.