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First Report of Leaf Spot Disease on Pineapple Caused by Fusarium solani in China

    Affiliations
    Authors and Affiliations
    • Y. Zhang1
    • H. Y. Ma1
    • S. H. Liu2
    • H. Q. Hu1
    • L. Ren1
    • Y. Y. Wang1
    1. 1Department of Biotechnology, College of Coastal Agricultural Sciences of Guangdong Ocean University, Zhanjiang, Guangdong, China 524088
    2. 2South Subtropical Crop Research Institute, China Academy of Tropical Agricultural Sciences, Zhanjiang, Guangdong, China 524088

    Pineapple (Ananas comosus) is an economically important tropical fruit in Guangdong Province, China. The plants were seriously infected with a year-round leaf spot disease. During September to November 2022, the leaf spot disease of pineapple was found in Xuwen City and Zhanjiang City of Guangdong Province. A disease survey of 1 ha revealed that pineapple was affected at an incidence ranging from 30 to 50%. The disease caused economic loss because of the disease control with chemicals. The initial symptoms were observed after 1 month of planting in October and included yellow spots and brown necrotic lesions. The leaves of pineapples showed large brown necrotic lesions, especially on the tip of basal leaves. The diseased leaves were collected and surface disinfected in 1% NaClO for 2 to 3 m, rinsed with sterilized water, air dried, placed on potato dextrose agar (PDA) medium, and incubated for 3 to 5 days at 28°C. Two isolates (PLF1 and PLF2) were collected and purified using the single-spore method. Colonies developing on PDA were in a circle with abundant white, densely fluffy aerial mycelium, pale to colorless after 3 days, and pale orange 5 to 15 days later. Cultures of the isolates produced macroconidia which were falcate, 1 to 3 septate, hyaline, and 18.2 to 43.4 × 4.8 to 6.8 μm (n = 50). Cultures of the isolate also produced a large amount of conidia, which were hyaline, oblong, no septate, and 5.2 to 10.6 × 2.7 to 5.2 μm (n = 50). These characteristics were consistent with the description of Fusarium sp. (Chitrampalam et al. 2018). For molecular identification, the genomic DNA of the two isolates was extracted. The fragments of internal transcribed spacer (ITS), translation elongation factor 1α (EF1α), and β-tubulin were amplified and sequenced using the primer pairs ITS4/ITS5, EF1/EF2 (OʼDonnell et al. 2008), and T1/T2 (O’Donnell and Cigelnik 1997), respectively. These sequences were deposited in GenBank (OR501466 and OR501467 for ITS; OR499874 and OR499875 for EF1α; OR499876 and OR499877 for β-tubulin). Phylogenetic trees were constructed in MAGA 11 using the maximum likelihood method based on the concatenated sequences of ITS, EF1α, and β-tublin. The two isolates were grouped with Fusarium solani A01-1 (GCA_027945525.1) with a bootstrap value of 100 in the phylogenetic tree. The morphology and multigene phylogenetic analysis indicated that the new isolates are F. solani. The two isolates were selected for pathogenicity tests to fulfill Koch’s postulates. Six plants at the seven-to-ten-leaf stage were inoculated with each isolate separately. Three sites of each leaf were wounded with a sterile needle and covered with a piece of cotton drenched with 200 μl of spore suspension (107 spores/ml) from each isolate cultured in PDA medium. Leaves inoculated with PDA medium served as negative controls. The inoculated plants were placed in an incubator at 28°C and 80% relative humidity under a 12-h light/dark cycle for 7 days. After 7 days of incubation, necrotic spots were observed in all the inoculated plants except the negative control. The pathogenicity tests were conducted three times with similar results. The strains were then reisolated from the lesions, found to be F. solani, and confirmed to be the same as the inoculated pathogen. F. ananatum, F. guttiforme, and F. subglutinans have been reported to infect all parts of pineapple to cause fusariosis disease (Jacobs et al. 2010; Stępień et al. 2013; Ventura et al. 1993). To our knowledge, this is the first report of fusariosis on pineapple caused by F. solani. Identification of F. solani as a disease agent on pineapple will assist in disease management for this important fruit.

    The author(s) declare no conflict of interest.

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    Funding: Funding was provided by the National Natural Science Foundation of China (2022A1515012128).

    The author(s) declare no conflict of interest.