Effect of the extracts and exudates from Chinese cabbages [Brassica chinensis] on the growth of soft rot bacterium, Erwinia carotovora subsp. carotovora

Nutrient substances leaked from the roots of Chinese cabbages (Brassica campestris, Pekinensis group) have been commonly assumed to play an essential role in the preferential growth of soft rot bacterial pathogen, Erwinia carotovora subsp. carotovora in rhizosphere of the plant from its late wrapping stage and continuous maintenance of high population level as 10**5-10**7 cfu/g of soil in the site to harvest time. To make clear the mechanism of the growth and its maintenance, the present study was carried out to examine the effect of water-exudated and water-extracted solution of the roots and petioles of the plant on the growth of the organism. The high population level of about 10**5-10**7 cfu/g of soil in the rhizosphere declined rapidly by cutting the upper grand part of the plants. Thus, it was thought that the growth of the organism was closely concerned with some nutrient substances leaked from the root, which depended on photosynthesis of the plant. The organism hardly grew in water-exudated soil solution. Addition of water-exudated or water extracted solution of roots or petioles of the plant to the water-exudated soil solution enhanced the growth of the organism and attained to a level of 10**7 cfu/ml at 25degC for 24 hrs. However, the efficacy of the adding the water exudated or water extracted solutions to the soil solution extracted by autoclaveing (120degC, 2 hrs.)was unclear. The results may indicate that some substances which can rise the preferential growth of the organism are contained in the tissues of roots and petioles of Chinese cabbage. Moreover, the growth of the organism was enhanced by addition of some nutritive substances contained in tissues of Chinese cabbages and in soil solution extracted by heating treatment as autoclaving. Sixteen kinds of amino acids and two sugars detected in the materials from tissues of the plant though they were variable according to growing stage of the plant and degree of cutting the upper ground part of the plant, seven kinds of polyphenollike substances were also detected. There was a tendency that they were more abundant in the extracted solution than the exudateion quantatively and quantitatively. Some of amino acids such as asparatic acid and the two sugars, glucose and fructose were confirmed to induce the preferential growth to the organism by adding in synthetic medium and soil. A role of polyphenol-like substances in the growth of the organism was not examined. It may be concluded that the roots and the petiole of the plant contain amino acids and sugars inducing the preferential growth of the organism. Further study should be need to determine whether or not the substances leaked from the roots and petioles in a field and actually attribute to the preferential growth of the organism and maintenance of high population level in rhizophere of the plant.