First Report of Leaf Spot Disease on Chamaedorea elegans Caused by Fusarium oxysporum in China

Plant Dis. 2023 Jan 23. doi: 10.1094/PDIS-03-22-0696-PDN. Online ahead of print.

Abstract

Chamaedorea elegans, native to Mexico and Guatemala, is a commonly planted indoor and small-scale garden ornamental due to its stately appearance, tolerance of low light levels, and its ability to improve air quality (El-Khateeb et al. 2010). In December 2021, an unknow leaf-spot disease was observed on C. elegans in Ganzhou City of Jiangxi Province, China (25.83 °N, 114.93 °E). The symptoms were small brown spots on the leaves, gradually expanded into irregular dark brown spots with necrotic tissue forming in the center of the lesions (Figure 2 A-1 and A-2). To isolate the pathogen, the diseased leaves were surface sterilized in 75% ethanol for 30 s. Small pieces of tissue (5 × 5 mm) were taken from the margin between diseased and healthy tissue, disinfected 1% NaClO for 45 s, washed three times in sterile water, and then placed on PDA at 25 ± 1°C for 5 days. Later, five isolates were purified from single spores and each of the five isolates has the same properties as described below. The isolates had abundant pale purple flocculent hyphae with purple pigmentation (Figure 2 C-1 and C-2). Macroconidia were falciform, straight or slightly curved, 1-2 septate, 11.75 to 22.99 × 3.06 to 4.44 μm (μ=16.08 μm × 3.37 μm, n=50) (Figure 2 D-1). Microconidia were oval or elliptical, a septate, 4.03 to 9.19 × 1.92 to 3.73 μm (μ=5.88 μm × 2.66 μm, n=50) (Figure 2 D-2). Chlamydospores formed singly or in pairs, and were terminal or intercalary in hyphae (Figure 2 D-3). Based on morphological characteristics, the fungus was preliminarily identified as a Fusarium sp. (Leslie et al. 2006). To confirm the identification, primers ITS1/ITS4 (White et al. 1990), RPB2-5f2/RPB2-7cr (O'Donnell et al. 2010; Liu et al. 1999) and TEF 1-αF/TEF 1-αR (O'Donnell et al. 2000) were used to amplify and sequence apportion of the ITS, RPB2 and TEF (Table 1). The sequences (Genebank accession number: OM780148, OM782679, OM782680) shared 100% idnetity with Fusarium oxysporum (Genebank accession number: MH866024.1, MH484930.1, MH485021.1). The maximum likelihood (ML) phylogenetic analysis of the concantenated ITS, RPB2 and TEF sequences was performed in MEGA7.0. (Sudhir et al. 2016), assigning the isoaltes to the F. oxysporum species complex (Figure 1). To confirm the pathogenicity, nine pots of healthy 3-year-old C. elegans plants were inoculated in the greenhouse (12 h light/12 h dark cycle, RH 90 %, three for wounded inoculation, three for nonwounded inoculation and three for control). Fifty disinfected leaves were wounded with sterile needles and fifty remained unwounded. The wounded (Figure 2 B-1 and B-2) and unwounded leaves were inoculated with a 10 μL spore suspension (1.0 × 106 conidia/ml) which was taken from each of the five isolates cultured for 7 days. Fifty leaves were mock-inoculated with sterile water (Figure 2 B-3 and B-4). After incubation for 7 days, the wounded leaves inoculated with the spore suspension had similar symptoms to the original diseased leaves, while the unwounded leaves and the control leaves did not develop symptoms. The experiment was repeated three times and the pathogens was reisolated from wound-inoculated leaves with the same morphological characteristics to the original pathogens, and identified as F. oxysporum by morphological and molecular analysis, completing Koch's postulates. F. oxysporum, a pathogen with a broad spectrum of hosts, ranks 5th among the top 10 fungal plant pathogens (Amjad et al. 2018.) and has been reported to Carpinus betulus, Citrullus lanatus, Pinus pinea (Mao et al. 2021; Muhammad et al. 2021; Monther et al. 2021). To our knowledge, this is the first report of leaf spot disease on C. elegans caused by F. oxysporum in China. C. elegans is an important ornamental plant in China with high economic value, so the disease has the potential to be a threat to its cultivation industry.

Keywords: Chamaedorea elegans; Fusarium oxysporum; Leaf Spot Disease.