Pythium oligandrum (PO) has the ability to activate defense-related gene expression and induce resistance against pathogens in dicot plants such as sugar beet, tomato, potato and Arabidopsis thaliana. To elucidate the ability of PO to activate the defense reaction in rice, we studied the induction of defense gene expression and the induced resistance to a bacterial pathogen, Burkholderia glumae, in PO-treated rice seeds. Treatment of rice seeds with oospore suspension of PO after inoculation with B. glumae reduced the severity of seedling rot. The expression of a defense-related gene, OsPR10a/PBZ1, a marker for disease resistance in rice, was induced in both rice seeds and seedlings treated with an oospore suspension of PO. In rice seedlings treated with the PO oospore suspension, the expression of jasmonic acid (JA)-responsive OsPR10b and OsPR6 was also induced. A global gene expression analysis of the roots treated with the cell wall protein (CWP) fraction extracted from PO, a resistance elicitor, indicated that CWP enhanced expression of genes encoding lipoxygenase and allene oxide synthase, key enzymes for JA synthesis, in addition to OsPR10a/PBZ1, OsPR10b and OsPR6. However, salicylic acid-responsive genes were not upregulated. These findings suggest that PO activates a JA-signaling-mediated defense reaction and induces resistance in rice against infection by B. glumae.
Isolates of a fungus isolated from anthracnose lesions on mango fruits in Okinawa produced perithecia on potato dextrose agar and were identified as Glomerella cingulata Group A (anamorph: Colletotrichum gloeosporioides) based on cultural and morphological characteristics, PCR assay using specific primers and glycerol-3-phosphate dehydrogenase (GPDH) sequence homology. Pathogenicity of the isolates to mango was demonstrated by placing mycelial disks on wounded healthy leaves and fruits and reisolating the fungus from the diseased fruit. This is the first report of confirming the production of perithecia by G. cingulata causing anthracnose of mango fruits in Japan.
A severe postharvest rot of mango fruits has been found in Okinawa Prefecture, Japan since 2000. A fungus frequently isolated from the diseased fruits was identified as Lasiodiplodia theobromae sensu stricto based on morphological and cultural characteristics and sequence homology of EF1-α region. The isolates reproduced the symptoms on mango fruits in an inoculation test and were reisolated from the inoculated fruits. This report is the first of stem-end rot of mango caused by L. theobromae in Japan, and we propose the name "jikugusare-byo" in Japanese.