First report of Fusarium oxysporum f. sp. coriandrii causing Fusarium wilt in Coriander in Brazil.

Abstract

Coriander (Coriandrum sativum L.), an aromatic leafy vegetable from the Apiaceae family, is globally renowned for its flavorful leaves and medicinal properties (Mahleyuddin et al. 2022). In Brazil, coriander cultivation faces challenges like seedling damping-off and leaf burn, symptoms frequently linked to Fusarium wilt, caused by F. oxysporum, in other countries (Koike and Gordon, 2005; Li et al., 2021). Since 2018, a rise in leaf chlorosis, wilting, and mortality has been noted in coriander cultivars Verdão and Verdão Super in Maranhão, Brazil, particularly in the municipalities of São Luís (2°34'01"S, 44°16'00"W) in August 2018 and Formosa (4°50'60"S, 46°44'00"W) in March 2021, affecting up to 70% of 20-25-day-old field plants. To investigate it further, ten symptomatic plants were randomly collected from Formosa and ten from São Luís, then sent to the Plant Pathology Laboratory at the State University of Maranhão. From symptomatic tissues of each sample, vascular fragments (1 x 1 cm) were disinfected (70% alcohol, 1% sodium hypochlorite, and sterile water) and cultivated on Potato Dextrose Agar, then incubated (25°C - 12 h light/dark cycle). After five days, rapidly growing pink colonies appeared in all isolated fragments, and then microscope slides were prepared to observe the fungal structures, where short monophialides and unicellular, elliptical microconidia were observed, measuring 14-25 µm in length (mean = 20.55 µm) and 36.4-55.4 µm in width (mean = 48.6 µm) (n = 20). Macroconidia, slightly curved with three septa, measured 116-467 µm in length (mean = 370 µm) and 28.8-51.3 µm in width (mean = 42.78 µm) (n = 20). Chlamydospores were also observed terminal or intercalary in hyphae. Single-spored isolates were molecularly identified and tested for pathogenicity. DNA was extracted using Zymo Research® kit, and TEF-1α, ITS, and IGS regions were amplified using PCR. The primers used were EF1-728R/EF2 for TEF-1α (Carbone & Kohn, 1999), ITS1/ITS4 for ITS (White et al., 1990), and Inl11/FoIGS-R for IGS (O'Donnell et al., 2009). Amplicons were sent to ACTGene company and sequenced by Sanger, submitted to GenBank, and analyzed phylogenetically. The accession numbers are MGSS 305 (OR102500, OR859840, PQ468316), MGSS 415 (OR102501, OR859842, PQ468317), and MGSS 416 (OR102502, OR859841, PQ468318). Bayesian analysis confirmed that the isolates belong to the F. oxysporum species complex. Pathogenicity tests involved two coriander varieties (Verdão and Verdão Super), totaling 200 plants, with 25 per isolate (MGSS 305, MGSS 415, MGSS 416 and control)/ variety combination. Thirty-day-old seedling roots were dipped in a conidial suspension of 1 x 106 conidia/mL for 20 min; while the control group was treated with sterile water (Reis et al., 2004). Plants were grown in 3 L pots with sterilized soil, in a greenhouse at 25 ± 2°C, 60% RH, and a 12 h photoperiod. After 21 days, wilt incidence occurred in the inoculated plants: MGSS 415 and MGSS 416 infected both varieties, where we observed an incidence between 80% and 92% in Verdão and 96 and 100% in Verdão Super, and MGSS 305 showed less than 20% incidence in both varieties. Control plants remained healthy. Reisolation confirmed the pathogen via morphology, molecular data (Figures 1 and 2), and pathogenicity, identifying it as F. oxysporum f. sp. coriandrii (Gilardi et al. 2017; Koike and Gordon 2005). The experiment was conducted twice at different times, and similar results were observed. This finding underscores the need for further research and the development of mitigation strategies to protect this crop.