Studies on citrus melanose and citrus stem-end rot by Diaporthe citri (Faw.) Wolf. Part 10. Hyphal elongation of Diaporthe citri from citrus fruit pedicel to stem-end and behavior of inhibitins.

Abstract

When satsuma mandarin fruits on trees were inoculated with Diaporthe citri to their pedicels, then harvested and stored in the condition of room temperature, stem-end rot was observed on almost all the fruits at the late stage of storage. Despite hyphal penetration and elongation to the pedicel or into pedicel-end core, there was no hyphal existence between the disks and the tissues underneath where a lot of needle-like crystals were distributed. Solutions of the crude crystals at 462∼4, 620 fold dilutions showed inhibitory activity against the fungus, and higher concentration of the crystals exhibited stronger inhibition to the hyphal elongation. Though the crystals were not observed in pedicel-end of young fruits, many of them were distributed after October when they became matured. Since the crystals did not exist in the stemend at the end of storage, we assumed that they had disappeared by self-digestion of citrus fruit. A similar inclination on the antifungal activities was already observed in fruit vesicle extract. Similar crystals were also observed in the vascular bundle systems in fruit core and leaves, especially in adult leaves.