First Report of Leaf Curl on Celery (Apium graveolens var. dulce) Caused by Colletotrichum fioriniae in New York

An outbreak of foliar disease on celery cultivar Tango was reported in Erie County, New York, in September 2018. Disease incidence was approximately 85%. Diseased plants were stunted and twisted, and older leaves were downward curling. Brown to orange-colored lesions were observed on the margins of leaves and stalks, and chlorotic spots were present on the upper surface of leaves. Microscopic observation of the lesions on the leaves and stems identified acervuli typical of Colletotrichum spp. Conidia from acervuli were spread on 2% water agar (plus 0.02% w/v ampicillin) and incubated at 20°C. Cultures were transferred onto potato dextrose agar (PDA; Difco Laboratories, Detroit, MI). After 7 to 10 days, gray-colored colonies with pink conidiomata typical of Colletotrichum spp. were observed (Damm et al. 2012). Twenty isolations were conducted from diseased celery leaves and stalks, resulting in the same fungus. Conidia (n = 50) of an isolate Cl18-03 were cylindrical, 8.84 μm (6.66 to 10.77 μm) long and 3.63 μm (2.86 to 4.22 μm) wide, and slightly tapered on one end. To confirm the identity of the isolate, polymerase chain reaction was performed to amplify the internal transcribed spacer (ITS) region, actin (ACT), and portions of the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes using primer pairs ITS1/ITS4 (White et al. 1990), Act512F/Act738R (Carbone and Kohn 1999), and GDF1/GDR1 (Templeton et al. 1992), respectively. Pairwise alignment of the sequences showed 99.8% similarity within the ITS and 100% similarity to the GAPDH and ACT sequences of C. fioriniae ex holotype CBS128517. Sequences of the isolate Cl18-03 were deposited in GenBank with accession numbers MK558808 (ITS), MK558809 (ACT), and MK558810 (GAPDH). For pathogenicity testing, Cl18-03 was grown on 0.2× PDA at room temperature and a 16-h photoperiod. Conidia were harvested after 7 days by flooding the plate with sterile type I water (ultrapure). The conidial suspension was passed through double-layered cheese cloth. Spores were counted, and the suspension was diluted to 1 × 10⁶ (plus 0.01% polysorbate-20) spores/ml. Five celery plants of cultivar Tango were sprayed with the inoculum until run-off. After inoculation, the plants were covered with a plastic bag for 96 h. Similarly, noninoculated control plants were sprayed with 0.01% polysorbate-20 and bagged. Plants were placed in a misting chamber and exposed to alternating 25°C light/18°C dark temperatures with a 16-h photoperiod. Mist was applied for an hour every day to maintain at least 85% relative humidity. After 8 days, symptoms of leaf curl including marginal and necrotic spots on the petiole were observed on all inoculated plants with complete collapse in two of the five inoculated plants. No symptoms were observed in the control plants. Symptomatic leaves were detached and placed in a moist chamber for 2 days, and brown acervuli without setae were observed in 75% of the lesions. Spores isolated from the lesions showed similar morphology and dimensions to the original isolate. To our knowledge this is the first report of C. fioriniae on celery associated with leaf curl in New York. The pathogen appears to be emerging in importance and previously reported on garlic in New York (Hay et al. 2018). Leaf curl is also an emerging, serious disease of celery reported in surrounding states including Ontario (Canada; Reynolds et al. 2019), Pennsylvania (Pollok et al. 2012), and Michigan (Rodriguez-Salamanca et al. 2015) and in Australia (Heaton and Dullahide 1993; Wright and Heaton 1991), and considering the low tolerance of disease, it may represent a significant threat to celery production in New York.