Effect of Intercropping and Mixed Cropping of Gramineous Crops on Multiplication of Soft Rot Bacteria in Field Soils and Incidence of Soft Rot in Chinese Cabbage

Abstract

To investigate the effect of non-host plants on the multiplication of Erwinia carotovora subsp. carotovora (Ecc) in field soil and the incidence of soft rot in Chinese cabbage, a field which had previously been used for continuous cropping of Chinese cabbage was dressed with sandy soil. The effects of intercropping Chinese cabbage and wheat and of a mixed cropping of Chinese cabbage and oats were then studied for three years. Ecc could be detected in the soil near the roots of spring-sown Chinese cabbage within the first year. In summer-sown Chinese cabbage, regardless of the type of non-host plants, the multiplication rate of the bacteria was the same as that in continuously cropped Chinese cabbage. The results of the third year were similar. However, in the second year, the bacteria were not detected before the Chinese cabbage was harvested. In contrast to multiplication rates, the incidence of soft rot in both the first year spring and summer-sown Chinese cabbage was the same as that for the continuously cropped field. However, disease severity did not increase with successive cropping. Instead, the onset of the disease was somewhat delayed, the disease was less severe, and disease severity tended to decline. Cultivating Chinese cabbage with a non-host plant to enable intercrossing between the root systems of the two species for three years; the non-host plants appeared to have no effect on the multiplication of Ecc or on the incidence of soft rot.