Tea Camellia sinensis (L.) O. Kuntze has been cultivated in China for thousands of years and represent an economically important crop. In April 2024, tea plants exhibiting typical wilt symptoms such as leaf curling, wilting, and abscission were found in many tea gardens of southern Shaanxi Province, China. Typically, infected plants showed reduced growth, with root systems displaying rot and discoloration, ultimately leading to severe declines in yield and quality. To investigate the cause, soil samples were collected from the rhizosphere of a diseased tea plant. Fusarium strains were isolated using the dilution plating method on potato dextrose agar (PDA). A representative strain, LD-LA, was selected for further study. After 5 days of incubation at 25 °C on PDA, the colony developed white aerial mycelia with light-yellow pigmentation on the reverse. Abundant microconidia that formed on long monophialides were reniform to oval in shape and measured 4.5-24×2.5-4 µm. Macroconidia appeared after 10 days; they were appeared falcate to crescent-shaped, with 2–4 septa (mostly 3) and measured 22.5-37.5×3-4 µm. Chlamydospores were globose, intercalary or terminal, single or in chains. These morphological characteristics align with those of the F. solani species complex (Leslie and Summerell 2006). For molecular identification, the internal transcribed spacer region (ITS: 5’-TCCGTAGGTGAACCTGCGG-3’/5’-TCCTCCGCTTATTGATATGC-3’), translation elongation factor 1-alpha (TEF: 5’-GTCGTYGTYATYGGHCAYGT-3’/ 5’-ACHGTRCCRATACCACCRATCTT-3’), beta-tubulin (TUB:5’- GGTAACCAAATTGCTGCTTTC-3’/5’-ACCCTCAGTGTAGTGACCCTGGC-3’), RNA polymerase I beta subunit (RPB1: 5’- GARTGYCCDGGDCAYTTYGG-3’/5’- CCNGCDATNTCRTTRTCCATRTA-3’), RNA polymerase II beta subunit (RPB2: 5’-GGGGWGAYCAGAAGAAGGC-3’/5’-GCRTGGATCTTRTCRTCSACC-3’) and calmodulin (CAL: 5’-GARTWCAAGGAGGCCTTCTC-3’/ 5’-TTTTGCATCATGAGTTGGAC-3’) gene regions of LD-LA were amplified and sequenced (O’Donnell et al. 2010) and the PCR products were sequenced. Subsequent BLASTn analysis against the NCBI database indicated that the ITS sequence exhibited 99.27% and 99.45% similarity with reference sequences of F. solani (GenBank accession nos. KP050570.1 and OR394627.1, respectively). For the TEF gene, sequence similarity was 97.81% and 97.41% with F. solani (JF740846.1 and JF740714.1). The TUB sequence showed 96.1% similarity to both F. solani sequences (OR826265.1 and MF662655.1). Sequence similarity for the RPB1 was 93.65% and 93.60% with F. solani (LT615323.1 and JN985161.1). For RPB2, similarity values of 99.89% and 99.73% were observed with F. solani (MF276940.1 and LC745493.1). The CAL sequence exhibited 99.34% and 97.95% similarity with F. solani (MG018612.1 and PP479999.1). A concatenated phylogenetic tree based on four genes (CAL, ITS, RPB1, RPB2 and TEF) was constructed. Fusarium sequences were retrieved from NCBI (https://static.pubmed.gov/portal/portal.fcgi/) and the FUSARIOID-ID (https://www.fusarium.org/page/Sequencesindatabase) database for tree construction. The gene IDs used for building the tree are listed in the supplementary table. Multilocus phylogenetic analysis based on the concatenated sequences confirmed that LD-LA belongs to F. solani. Pathogenicity tests were conducted using one-year-old tea seedlings of cultivars 'FudingDabai' and 'Huangjinya'. Seedlings were surface-disinfested with 50% carbendazimand transplanted into sterilized soil. Each seedling was grown in 7 × 7 cm pot placed in a constant-temperature light incubator (25 ± 2°C, 16h photoperiod, 65 ± 5% humidity). For inoculation, 50 mL of LD-LA spore suspension (10⁷ spores/mL) was applied via soil drench to each seedling, whereas control plants received sterile water. After inoculation, all plants were returned to the incubator under the same conditions. A minimum of 28 seedlings were used per treatment, and experiments were independently repeated at least three times. To ensure successful infection, a second inoculation was performed seven days after the initial inoculation, for a total of two inoculations. At 40 days post-inoculation (dpi), inoculated plants exhibited symptoms such as yellow-brown leaf spots, wilting, and dieback, whereas control plants remained healthy. The fungus was re-isolated from the diseased tissues and identified as F. solani based on morphological and molecular characteristics, thereby fulfilling Koch’s postulates. F. solani has previously been reported to infect tea in Sri Lanka (Simiah et al. 2017). To our knowledge, this is the first confirmed report of F. solani causing collar rot and dieback on tea plants in Shaanxi Province, China. Given the potential of this pathogen to cause defoliation and plant death, further surveys and the development of effective management strategies are warranted.
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