Camellia reticulata is the world-famous ornamental flower (Wang et al. 2021). In February 2021, the infected flowers of C. reticulata 'Shizitou' were collected in Zixi Mountain, Chuxiong city, Yunnan province, China (24°9'95″ N, 101°42'53″ E). Flower rot disease incidence ranged from 40% to 75% in the garden. The infected flowers showed symptoms of varying degrees of yellow-browning, dry or wet rot to the whole flower wilted and even dropped (Figure 1A, B, C). Three symptomatic flowers were randomly collected in the garden. Tissues from the infected flowers (cut to 5×5 mm size) were surface-disinfected by 75% ethyl alcohol for 30s, rinsed in sterile water for 3 times to air dry, and cultured in Potato Dextrose Agar medium (PDA) at 25℃±2 in the normal light for 5-7 days (Fang, 1998). Similar fungal colonies were isolated from 50%-75% of the infected flowers. Three isolates from different flowers showed similar colony morphology. After sub-culturing of hyphal tips on PDA for 5-7 days, the initially yellow colored colonies showed abundant white aerial mycelium, with sporulation (Figure 1E, F). The asci (Figure 1G) sporulation site is 24(-37) ×7(-14) μm, and the stalk length is 17-42 μm, with 8 biseriate acuminate ascospores. The mature ascospores (Figure 1H) are olive-brown or brown, lemon-like, double-pointed, with slightly umbilical protrusions at both ends, flat on both sides, 9(-11.5) × 7(-9) × 5.5(-7) μm in size, with germ holes on the top (Wang et al. 2016). These morphological features are consistent with Chaetomium pseudocochliodes. The genomic DNA was extracted from the isolated strains. To identified this fungal pathogen genetically, sequence analyses were conducted using the ITS1/ITS4 (Henson et al. 1993), NL1/NL4 (Liu et al. 2011), EF1-938F /EF1-2218R (Tan et al. 2016) primers for the internal transcribed spacer (ITS), large ribosomal subunit (LSU), and elongation factor 1-α (EF1-α) genes. The obtained sequences were deposited in GenBank with accession numbers MZ817067 (ITS), MZ817072 (LSU), MZ820167 (EF1-α). The phylogenetic trees (Figure 2) were constructed to determine the phylogenetic relationships based on MEGA 6.0 maximum likelihood method. In order to confirm the pathogenicity, the tests were conducted with fungus plug (5 mm) from a 7-day-old colony placed onto the surface of healthy petals. The sterile water-absorbent cottons place onto healthy petal surface near fungus plug and plastic wraps cover in petri dish were used for moisturizing. A total of 3 replicates in each of 3 groups were included (3 healthy petals for a group, 1 for wounded inoculation, 1 for unwounded inoculation, and 1 for sterile PDA plug). A sterile PDA plug was placed onto the surface of healthy petals as a control. After incubation at room temperature for 5 days (Ren. 2019), 3 replicates in each of 2 groups of treated healthy petals for wounded inoculation showed obvious symptoms (Figure 1D), and no symptoms appeared in the control, and healthy petals unwounded showed symptoms for 7-10 days. The fungus was re-isolated from the lesions of inoculated tissues. The re-isolated fungal colonies showed identical morphology and high sequence similarity with ITS, LSU and EF-1α of the initial isolate. No fungus was isolated from the controls. The first extraction of C. pseudocochliodes was also obtained from the roots of the Panax notoginseng in Wenshan, Yunnan (Wang et al. 2016). To our knowledge, this is the first report of flower rot caused by C. pseudocochliodes on C. reticulata in China.
Keywords: Camellia reticulata; Chaetomium pseudocochliodes; flower rot disease.