First report of Ceriporia lacerata causing root rot disease of Delonix regia in Taiwan.

Abstract

Ceriporia lacerata (syn. Irpex laceratus) is a saprotrophic fungus commonly found on angiosperm branches and rotten trunks (Chen et al. 2021). It was also reported as an endophyte in some plants (Fusco et al. 2022; Lapuz et al. 2018; Martin et al. 2015 Wang et al. 2013; Yuan et al. 2011). In October 2021, a flame tree (Delonix regia) at the main campus of National Taiwan University (NTU) suddenly toppled over in no wind or rain. The canopy was weak, characterized by sparse branches, leaves, and foliar chlorosis. The roots and stem base were covered with white to cream, effused-resupinate basidiomata. The wood tissues appeared whitish and decayed. To isolate the causal agent, diseased root samples were surface disinfested with 75% EtOH, 1% NaClO, and triple rinsed with sterile water. The samples were cut into 0.5 × 0.5 cm pieces then placed onto the selective medium "MA+4" (Wu et al. 2020). After a few days, extended hyphae from tissues were transferred to potato dextrose agar (PDA) and incubated at 30℃ in the dark for 4 days. Colonies were white on the upper and reverse sides, and no spores were observed. To confirm the species identity, genomic DNA extracted from 3 isolates (TP1, TP2, TP3) were used for PCR amplification and sequencing of the internal transcribed spacer (ITS) region, 28S rDNA, RNA polymerase Ⅱ large subunit (rpb1), RNA polymerase Ⅱ second largest subunit (rpb2), and the translation elongation factor 1-α (tef1) with published primers (Chen et al. 2021) (GenBank nos. PV342505-PV342507, PV472218-PV472232). According to the phylogram of the Irpicaceae inferred from maximum likelihood (ML) analyses using the combined ITS+28S+ rpb1+rpb2+tef1 dataset, all three isolates clustered with C. lacerata (syn. I. laceratus) in a highly supported lineage (BP = 99%). To fulfill Koch's postulates, C. lacerata isolates TP1 and three isolates previously collected from basidiomata on angiosperm branches or rotten trunk in Taiwan (V00476, V00503, V00507) were used for inoculation. The inoculum was cultured on sorghum grains (100 g sorghum, 50 ml dH₂O, and 5 mg chloramphenicol) at 30℃ in the dark for 3 weeks. In the greenhouse at the First Hall of NTU (natural light), wounded and nonwounded inoculations were conducted on D. regia seedlings (Liao et al. 2023) (n = 4 in the first trial and n = 6 in the second trial). 10 g of inoculum was wrapped around the lower stem by parafilm and then covered with aluminum foil. The inoculum was removed at 14 days post-inoculation (dpi). Wilting was observed in 50% of the wounded-inoculated plants at 21 dpi, while the remaining plants exhibited no external symptoms up to 120 dpi. However, C. lacerata caused internal discoloration of all inoculated stem tissues. C. lacerata was reisolated from the bark (99% frequency from wounded and 56% from nonwounded) and interior wood tissues (79% from wounded and 11% from nonwounded), and morphological characters and ITS sequences were identical to the original one. C. lacerata can also be isolated from the 2.5-cm-segments above/below the inoculation sites, but at lower frequencies (interior wood tissues: 33% from wounded and 2% from nonwounded inoculations). Control plants inoculated with sterile grains showed no external or internal symptoms. This study reveals C. lacerata as a potential pathogen, not just a saprotroph or endophyte, highlighting its threat to urban tree health. Although symptom development may be slow after infection, the risk of root decay and tree collapse should not be overlooked.