Coriander (Coriandrum sativum L.) is one of the most important vegetables used as a seasoning in China. During the summer of 2019 and 2020, two-month-old coriander plants with stem and root rot were observed in commercial fields located in Tianjin, China. Symptoms were first observed when temperatures were about 24°C. Diseased plants had chlorotic lower leaves, were stunted, had rotted roots and stems, and eventually wilted and died (Fig. S1). In severe cases, disease incidence was approximately 85%. Plant samples with the same symptoms were collected from five fields by five-point sampling method (4 plants/point; 20 plants/field), out of which twenty plants were arbitrarily selected for pathogen isolation. Root tissue fragments (3 mm2; 3 fragements/plant) at the boundary of the symptomatic area were excised, washed in 1% NaClO for 2 min, rinsed in sterile distilled water (SDW), and incubated on PDA containing 50 mg/liter of streptomycin sulfate. Plates were incubated at 25°C for 5 days in the dark. 25% of the isolates were tentatively identified as Fusarium equiseti according to cultural and morphological characteristics (Leslie and Summerell, 2006). Colonies developed abundant white aerial mycelium with pale brown pigments on PDA. Microconidia were single-celled, hyaline, non-septate and ovoid, and ranged from 4.6 to 17.6 × 1.5 to 3.8 μm (n = 40). Macroconidia were mostly five-septate, slightly curved at apex, and ranged from 13.3 to 34.6 × 2.2 to 4.3 μm (n = 40). Chlamydospores with thick, roughened walls were abundant in clumps or chains, ellipsoidal or subglobose. Diseased-plant samples and pathogen isolates were deposited to China General Microbiological Culuture Collection Center (CGMCC). Species identity was confirmed by amplifying and sequencing the ITS, TEF1-α, mtSSU and RPB2 (Carbone and Kohn 1999; Li et al. 1994; Miller and Huhndorf 2005). BLASTn analyses of ITS amplicon (Genbank No. MT579854), TEF1-α (MT586131), mtSSU (MT587798) and RPB2 (MT648497) genes obtained with cognate sequences available in GenBank showed 99.8% (498 bp out of 499 bp), 100% (493 bp out of 493 bp), 99.7% (625 bp out of 627 bp) and 98.9% (656 bp out of 663 bp) identity to F. equiseti (LS479418 [ITS], KU939020 [TEF1-α], MF667972 [mtSSU] and MG839490 [RPB2]) in NCBI databases, respectively. Pathogenicity tests were conducted with each F. equiseti isolate. Plants were grown in sterilized 10-cm diameter plastic pots containing steamed peat substrate, and three replicated pots (five plants/pot) were included in each treatment. Fifteen-day-old coriander plants were inoculated with 5 mL of 1×106 conidia/mL suspension by root-drenching method. Control plants were inoculated with SDW. Each treatment was incubated in a greenhouse at 29/22°C (12h/12h, light/dark), and watered every other day to keep high humidity. After 4 days, symptoms similar to those observed in the field were observed on inoculated plants (Fig. S2), whereas control plants remained symptomless. Reisolation of F. equiseti from inoculated plants fulfilled Koch's postulates, and identification was confirmed by morphological and molecular methods. To our knowledge, this is the first report of F. equiseti causing coriander stem and root rot in China. This pathogen poses a threat to coriander production, and its accurate identification is necessary to develop effective management strategies.
Keywords: China; Coriander (Coriandrum sativum L.); Fusarium equiseti; stem and root rot.