First Report of Fusarium falciforme Causing Branch Rot on Jasminum sambac in China.

Abstract

Jasmine (Jasminum sambac (L.) Aiton) is a commercially important plant known for its fragrant flowers, which are used in tea production and essential oils extraction (Sun et al. 2023; Hong et al. 2024). In September 2022, branch rot symptoms were observed in a ~1300 m² jasmine plantation in Hengzhou, Guangxi, China. Approximately 35% of the plants exhibited branch rot, with about 50% of the branches on each diseased plant affected. Symptoms included wilting and defoliation of leaves and brown irregular lesions on some branches. In later stages, the disease caused branch discoloration or desiccation and plant death. Twenty infected branches were collected randomly from six plants in the most severely affected area half. Branch tissues (3 mm²) from necrotic margins were surface-sterilized (75% ethanol for 10 s, 2% NaClO solution for 2 min), rinsed three times with sterile distilled water, and then placed on potato dextrose agar (PDA) plates. After incubation at 28 °C for seven days, ten morphologically identical isolates were obtained. Two isolates (HR112-1 and HR113-1) were randomly selected for further study. Both isolates exhibited abundant white to cream aerial mycelium and produced hyaline, slightly curved macroconidia (21.2 to 46.1 × 4.4 to 8.8 µm; n = 100) with zero to three septa and oval or reniform microconidia (6.1 to 14.4 × 3.3 to 8.9 µm; n = 100) with zero to two septa on PDA. Genomic DNA was extracted from the two isolates using the CTAB method. The partial internal transcribed spacer (ITS) region, translation elongation factor subunit 1-alpha (TEF-1α) and ribosomal polymerase II second largest subunit (RPB2) gene sequences were amplified and sequenced using primers pairs ITS1/ITS4, EF1/EF2 and 5f2/7cr (White et al. 1990; O' Donnell et al. 2010), respectively. The sequences were deposited in GenBank (ITS: PQ625807 and PQ625808; TEF-1α: PV008115 and PV008116; RPB2: PQ638394 and PQ638395). BLAST analysis showed 99.08 to 99.81% identity with the ex-type strain Fusarium falciforme CBS 475.67. A maximum-likelihood phylogenetic tree constructed using MEGA X based on concatenated sequences of ITS, TEF-1α and RPB2 confirmed that both isolates (HR112-1 and HR113-1) clustered with F. falciforme. Pathogenicity tests were performed on 1-year-old healthy J. sambac plants grown in pots. Circular wounds (1 mm depth) were made on the branches using a sterilized needle and covered with wet cotton saturated with 100 μm conidial suspension (1 × 10⁶ conidia/ml). The inoculated sites were wrapped with plastic film to maintain moisture. Control plants were treated with sterile water-moistened cotton. Five plants were used for each isolate and control, with three inoculation sites per plant. All plants were enclosed in clear plastic bags and placed in a plant incubator (14 h light/10 h dark, 28 °C). After 14 days, all plants inoculated with the two isolates exhibited branch rot and browning, with leaves wilting and dropping, while the controls remained asymptomatic and healthy. F. falciforme was reisolated from the symptomatic branches and re-identified based on morphological and molecular characteristics, fulfilling Koch's postulates. F. falciforme has been reported as a pathogen causing branch dieback in tomato (Vega et al. 2019) and African eggplant (Okorley et al. 2024). To our knowledge, this is the first report of F. falciforme causing branch rot on J. sambac. Our findings provide insights for the development and implementation of effective disease control strategies.