First Report of Leaf Tip Blight Caused by Epicoccum sorghinum on Phoebe bournei in Fujian, China.

Abstract

Phoebe bournei, belonging to the family Lauraceae, is indigenous to China, where it is a protected species. In March 2022, ca. 90% of 20,000 P. bournei saplings suffered from leaf tip blight in a sapling nursery with an area of 200 m2 in Fuzhou, China. Initially, brown discoloration appeared on the tips of young leaves. The symptomatic tissue continued to expand as the leaf grew. To isolate the pathogen, 10 symptomatic leaves were randomly sampled from the nursery, and surface-sterilized in 75% alcohol for 30 s, followed by a 5% NaClO solution for 3 min, and then rinsed 3 times with sterile water. Twenty small pieces (0.3 x 0.3 cm) were excised from the margin of diseased and healthy tissue and transferred to five PDA plates amended with 50 μg/ml ampicillin. The plates were incubated at 25°C for 5 days. Finally, 17 isolates were obtained, and nine isolates with the highest isolation frequency shared the same morphological characteristics. On PDA, these colonies had aerial hyphae, white in the beginning, and became pale brown with the pigment production. Chlamydospores were observed after incubation for 7 days at 25°C, pale brown and nearly spherical, unicellular, or multicellular. Conidia were unicellular or bicellular, hyaline, and ellipsoidal, 5.15 to 9.89× 3.46 to 5.87 µm, n=50. The 9 fungi were identified as Epicoccum sp (Khoo et al. 2022a, b, c). Furthermore, strain MB3-1 was chosen randomly as the representative of the 9 isolates, and ITS, LSU, TUB sequences were amplified using the primers ITS1/ITS4, LR0R/LR5, Bt2a/Bt2b respectively (Raza et al. 2019). The sequences were submitted to NCBI and analyzed using BLAST. Results of BLAST showed that ITS (OP550308), LSU (OP550304), TUB (OP779213) sequences had 99.59% (490bp out of 492bp), 99.89% (870bp out of 871bp), 100% (321bp out of 321bp) identity to Epicoccum sorghinum sequences MH071389, MW800361, MW165323, respectively. ITS, LSU, TUB sequences were concatenated for phylogenetic analysis using the maximum likelihood method with 1000 bootstrap replicates in MEGA 7.0 software. The phylogenetic tree showed that MB3-1 was clustered together with E. sorghinum. Pathogenicity tests were performed on young leaves of healthy P. bournei saplings in vivo by inoculating with fungal conidia suspension. The conidia were eluted from the colony of MB3-1 and adjusted to 1×106 spores/ml. An amount of 20 μl conidia suspension (0.1% tween-80) was evenly sprayed on three leaves of one P. bournei sapling, 20 μl sterile water was sprayed on three other leaves of the same sapling as control, and three saplings were treated. All the treated saplings were kept at 25°C. MB3-1 caused leaf tip blight symptoms similar to those observed in nature at 6 days post inoculation (dpi). The pathogen was reisolated from inoculated leaves and identified as E. sorghinum. The experiment was repeated twice with the same results. Recently, E. sorghinum has been reported in Brazil (Gasparetto et al. 2017), Malaysia (Khoo et al. 2022a, b, c), and the United States (Imran et al. 2022). To our knowledge, this is the first report of E. sorghinum causing leaf tip blight on P. bournei. Wood from P. bournei is used to produce high-quality furniture due to its vertical grain and durability (Chen et al. 2020). And the demand for wood requires numerous saplings for afforestation. But this disease has the risk of causing insufficient saplings, which would affect the development of the P. bournei timber industry.