First Report of Powdery Mildew of Cocculus orbiculatus var. mollis Caused by Erysiphe pseudolonicerae in China
Year: 2025
Type: article
Abstract: The genus Cocculus comprises diverse medicinal plants in China, including two species C. laurifolius DC. and C. orbiculatus (L.) DC., and one variety C. orbiculatus (L.) DC. var. mollis (Kunming Institute of Botany, Chinese Academy of Sciences. 1983). In January 2023, severe powdery mildew symptoms were found on C. orbiculatus var. mollis at the Huaxi Campus (26°23'04'' N, 106°37'57'' E) of Guizhou Normal University, Guiyang, China. The incidence observed was ~95% among 80 C. orbiculatus var. mollis plants. Infected leaves presented chlorotic to necrotic areas. Mycelium grew mainly on the adaxial surface of leaves. Hyphae were hyaline and 4–10 μm wide. Hyphal appressoria were lobed to multilobed, and solitary or in opposite pairs. Conidiophores were erect, straight to somewhat flexuous and 55–130 µm long (n = 40). Foot cells were subcylindrical to curved-sinuous at the base, followed by 2–4 cells. Conidia formed singly and were ellipsoid to ovoid in shape with dimensions of 28.8–54 × 13.3–17 µm (n = 50). Based on these morphological characteristics, the powdery mildew fungus (named as GZCO-1) was provisionally identified as an Erysiphe species (Bradshaw et al. 2023). To identify the species, the ITS and LSU regions were amplified using the primer pairs PM10/PM28R (Bradshaw and Tobin 2020); the CAM, GAPDH, GS, and RPB2 region were amplified using the primer pairs PMCAM1/PMCAM4R, PMGAPDH1/PMGAPDH3R, GSPM2/GSPM3R, and PMRpb2_4/ PMRpb2_6R, respectively (Bradshaw et al. 2022); the TUB region was amplified using the primers BTF5b/BTR7a (Ellingham et al. 2019). The obtained 1364-bp ITS-LSU sequence (GenBank accession no. PQ818141), 282-bp CAM sequence (PQ822234), 316-bp GAPDH sequence (PQ822231), 468-bp GS sequence (PQ822235), 763-bp RPB2 sequence (PQ822232), and 733-bp TUB sequence (PQ822233) were deposited in GenBank. Using a phylogenetic tree based on the concatenated ITS-LSU, CAM, GAPDH, GS, RPB2, and TUB sequences (Bradshaw et al. 2023), the isolate GZCO-1 was grouped in the same clade as E. pseudolonicerae. To perform pathogenicity tests, leaves of three healthy potted C. orbiculatus var. mollis plants were inoculated by gently pressing with diseased leaves. Non-inoculated plants served as controls. All plants were incubated in a greenhouse at 25 ± 2°C with 80% relative humidity. Similar powdery mildew symptoms appeared on inoculated plants 12 days after inoculation, whereas no symptoms were observed on control plants. The fungus from inoculated C. orbiculatus var. mollis plants was morphologically identical to that on originally diseased plants. In addition, ITS-LSU sequences of the fungus from the artificially inoculated plants shared 100% identity with PQ818141. Based on the morphological and molecular characterization, the powdery mildew fungus was identified as E. pseudolonicerae. This powdery mildew on this host has previously been reported from China (Bradshaw et al. 2024), however this is the first report supported by sequence analyses.
Source: Plant Disease
Institution: Guizhou Normal University
Language: English
Subfield: Plant Science
Domain: Life Sciences
Open Access status: bronze
Awards: G5514321373, G7587807427
OpenAlex ID: W4410854267