Bacterial galls were found on roots of tomato (Solanum lycopersicum), cabbage (Brassica oleracea), shepherd’s purse (Capsella bursa-pastoris var. pinnata), bog yellowcress (Rorippa palustris), purple deadnettle (Lamium purpureum) and corn speedwell (Veronica arvensis) in Shizuoka Prefecture from December 2007 to July 2008. Galls had formed on the main or secondary roots, and bacterial aggregates were often observed on the surface of the galls. Bacterial isolates from the plant galls formed white, rough colonies and had properties identical to those of Rhizobacter dauci. Phylogenetic analysis based on 16S rDNA sequence showed that the isolates had the highest homology (similarity of 100%) with that of the type strain of R. dauci. Pathogenicity of the isolates was confirmed by inoculating the roots of carrots and the original host species. After 4 weeks, galls had formed on the roots of the plants, and the bacterium was reisolated. This report is the first of bacterial galls caused by R. dauci on tomato, cabbage, shepherd’s purse, bog yellowcress, purple deadnettle and corn speedwell. To investigate the host range of R. dauci, 20 vegetable crop species of seven families were planted in a field infested with the bacterium. After 1.5 months, galls had formed on the roots of nine vegetables representing four families, and a bacterium that forms white, rough colonies was isolated from the infested plants. Pathogenicity of the isolates was confirmed by inoculating the roots of carrots; galls formed on the roots, and the bacterium was reisolated. After direct inoculation of 77 plant species from 24 families with the carrot isolate R. dauci O1, galls formed on the roots, stems or tubers of 46 plant species of 20 families, and the inoculated bacterium was reisolated. These results suggested that R. dauci has an extremely wide host range. It may commonly inhabit the roots of various plants in the field.
Direct sowing of iron-coated rice seeds into flooded paddy fields has been widely applied to save on labor and cultivation costs; however, seedlings grown from iron-coated rice seeds often develop seedling rot in the field. We identified Pythium arrhenomanes as one of the causal agents of the disease based on fungal morphology and a DNA sequence analysis of internal transcribed spacer region on ribosomal DNA. This study is the first report of Pythium arrhenomanes causing a rot on rice seedlings from directly sown iron-coated seeds.
A protocol to quantify ustiloxin A (ustA) in a bulk sample of false smut balls of rice (J. Vet. Med. Sci. 71: 239-241) was modified to quantify ustA in single balls collected from a paddy field after natural infection and in balls formed after rice plants were inoculated with either of two isolates of Ustilaginoidea virens isolated from different commercial fields in Fukui Prefecture. To test whether these isolates differed in their capacity to produce ustA, we compared the mean quantity of ustA that each produced in individual balls. The two isolates varied greatly in ustA production; the differences in ustA in balls between the two ranged from 42-fold to 115-fold. Such massive differences in ustA production indicate that the pathogenic isolate is an important contributing factor to the quantity of ustA produced in false smut balls.
In tomato, induced resistance mediated by Pythium oligandrum (PO) is accompanied by enhanced production of ethylene and expression of a gene encoding β-cyanoalanine synthase (β-CAS), which catalyzes the detoxification of cyanide to β-cyanoalanine. We analyzed the activity of β-CAS in tomato after treatment with PO and the defence reactions by examining gene expression of tomato treated with β-cyanoalanine. The β-CAS activity significantly increased in tomato roots treated with an oospore suspension of PO, and the β-cyanoalanine treatment activated the expression of the jasmonic acid (JA)-related defence gene, LePR6. Increased activity of β-CAS and subsequent production of β-cyanoalanine may thus activate the JA-dependent defence reaction in PO-treated tomato plants.