First Report of Leaf Spot of Chenopodium album Caused by Fusarium equiseti in China

Abstract

Chenopodium album L. (commonly known as bathu) is one of the most troublesome weeds associated with crops in the world. In June 2018, leaf spot on C. album was observed in soybean and corn fields in Yanshou County (45°26′N, 128°18′E), Heilongjiang Province, China, with 20 to 40% incidence. The disease was not observed on soybean or maize. Initial symptoms were brown necrotic spots with a white center. Lesions rapidly expanded (1 to 10 mm diameter), contained concentric rings, and became necrotic. Ten C. album leaves were collected for fungal isolations. Diseased tissues were surface sterilized with 0.1% HgCl₂ for 1 min, rinsed in sterile distilled water, and cultured on potato dextrose agar at 26°C. After 5 days, six fungal isolates were obtained and subcultured by transferring hyphal tips. The colony had abundant white aerial mycelia and became peach-orange in color with age on potato dextrose agar. Macroconidia were mostly five- to seven-septate, slightly curved with a tapered and elongated apical cell and prominent foot-shaped basal cell, 23.2 to 31.8 μm in length, and 3.1 to 4.92 μm in width on carnation leaf agar medium. No microconidia were observed. Chlamydospores were abundant in clumps or chains, ellipsoidal or subglobose. Morphological characteristics of the isolates were consistent with those of Fusarium equiseti (Jacobs et al. 2018). Genomic DNA was extracted from single conidial cultures of the representative isolate H5, and the internal transcribed spacer regions (ITS) and translation elongation factor 1-α gene (TEF1) were amplified with primers ITS1/ITS4 (White et al. 1990) and EF1-728F/EF1-986R (Akbar et al. 2018), respectively, and sequenced. The DNA sequence of the isolate was identical, and the representative isolate H5 was deposited in GenBank (accession nos. MN241064 and MK990601). BLAST analysis showed that the obtained sequence for the ITS amplicon shared 99.6% similarity with F. equiseti isolate KA (accession no. JQ690085.1), whereas the sequence of the TEF1 amplicon shared 99% similarity with F. equiseti strain G17WX1-5-2 (accession no. MG670196.1). To determine pathogenicity, C. album plants were grown in 15-cm pots containing a commercial potting mix (one plant/pot). After the eight-leaf stage, three plants (two leaves/plant) were inoculated with 50 μl of a conidial suspension (4 × 10⁶ spores/ml). Three plants treated with sterile distilled water served as a control. All plants were placed in a humidity chamber (>95% relative humidity) at 26°C for 48 h after inoculation and then kept in a greenhouse at 22/28°C (night/day). After 10 days, all inoculated leaves showed symptoms similar to those observed in the field. No disease occurred on control plants. Five same fungal isolates were reisolated from five diseased leaves and confirmed to be F. equiseti. To our knowledge, this is the first report of leaf spot on C. album caused by F. equiseti in China.