Rhizoctonia-like fungi colonization systemically induces defense response against leaf soft rot in Bletilla striata (Orchidaceae)

G. C. PUJASATRIA*, C. MIURA, H. KAMINAKA

*The United Graduate School of Agricultural Science, Tottori University, 4-101 Koyama-minami, Tottori 680-8553, Japan

Orchids associate with more than one orchid mycorrhizal fungus (OMF) during early seed germination up to maturity. However, aside from nutrient transfer, the investigation of its role in defense priming is still lacking. While it was previously discovered that both arbuscular (AM) and orchid mycorrhiza (OM) share major molecular components during mycorrhizal association, we further investigated this commonality by testing the extent of mycorrhiza-induced defense response in Bletilla striata against leaf soft rot causal agent, Dickeya fangzhongdai. Two Rhizoctonia-like fungi, Tulasnella calospora and Serendipita vermifera, were able to colonize B. striata protocorms and roots with the same pattern: T. calospora always colonizes protocorms and roots at a higher rate compared to S. vermifera. To test the change in B. striata defense responses, we measured D. fangzhongdai proliferation and other symptoms. We found that its proliferation was heavily arrested in plants colonized by T. calospora compared to S. vermifera but visible symptoms (lesion size, etc.) were not reduced. In addition, photosynthetic damage caused by the infection was also ameliorated by OMF colonization. With these results, we proved that the commonality between AM/OM extends to mycorrhiza-induced defense response, however, the similarity of the molecular mechanism underlying the defense responses requires further investigations.