Defence responses of Aphanoregma patens (Hedw.) Lindb. to inoculation with Pythium aphanidermatum

Abstract

We examined the defensive responses of leaf surfaces, rhizoids, and protonemata of the moss Aphanoregma patens (Hedw.) Lindb. to inoculation with zoospores and encysted zoospores (cysts) of the oomycete Pythium aphanidermatum OPU849. Aphanoregma patens infected with Pythium exhibited extensive browning of the leaves and stems 4 days after inoculation. The zoospore infection sites were rhizoids and protonemata. Cysts on the rhizoids and protonemata germinated and formed elongated hyphae that invaded the cells of the moss, forming oospores and lobed sporangia. The subsequent production of new zoospores on infected plants indicates that A. patens is a suitable host for manipulating the life cycle of Pythium. However, cysts inoculated onto leaf surfaces did not germinate, and they began to show signs of disruption after only 3 hours. After 2 days, more than 80% of the cysts on leaf surfaces were completely disrupted, possibly due to the secretion of degrading enzymes. Cyst disruption was not observed on rhizoids nor on protonemata.

Keywords:

• Aphanoregma patens
• Bryophyte pathology
• Moss
• Oomycete
• Physcomitrella patens
• Pythium aphanidermatum
• Zoospore

Acknowledgements

The observation of cysts disruption was conducted in collaboration with Dr H. Toyoda, Dr Y. Matsuda, Dr T. Nonomura, and Dr K. Kakutani. We also thank these collaborators for their useful comments and suggestions on the manuscript. We thank Dr M. Tojo for providing the P. aphanidermatum OPU849.

Taxonomic Additions and Changes: Nil.