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.