First Report of Cercospora cf. flagellaris causing leaf spot on Ivyleaf morning glory ( Ipomoea hederacea ) in Iowa

Ivyleaf morning glory ( Ipomoea hederacea Jacq.) is a common weed in Convolvulaceae in Iowa corn-soybean systems. In October 2023 and 2025, round, necrotic leaf lesions (approx. 3-4 mm diam.) with dark borders and tan centers were observed near senescence in Boone County, Iowa. Incidence was ~25%, with 5-30% severity. Leaves with >10% lesion severity were surface-sterilized and incubated in humid chambers at 25°C under a diurnal cycle to induce sporulation. After 2 days in humid chambers, Cercospora -like sporulation developed. Conidia were transferred to diluted V8 medium (DV8; 4% juice V8; Matthiesen et al. 2016), producing white colonies with purple pigmentation. Conidiophores measured 127-169 x 3-5 µm (mean 143 x 4 µm) and conidia 105-342 x 3-5 µm (mean 238 x 4 µm). Only one other Cercospora species has been reported from Convolvulaceae, C. convolvulicola on field bindweed ( Convolvulus arvensis ) (Bakhshi et al. 2015). Based on cultural characteristics, isolates were initially identified as C. kikuchii -like. For identification, DNA from isolates CLB-M1-2023, CLB-M3-2023, and CLB-32-2025 was sequenced for ITS, ACT , CAL , and H3 loci using primers of Shrestha et al. (2024). Sequences were aligned with representative Cercospora sequences from phylogenetic clades closely related to C. kikuchii (two isolates per clade) for multilocus phylogenetic analysis using ModelFinder (Kalyaanamoorthy et al. 2017) in PhyloSuite v2 (Zhao et al. 2025) clustering with C. cf. flagellaris with posterior probability value of 1. BLAST search of sequences against the NCBI database revealed 100% identity with C. cf. flagellaris . Additionally, CAL amplicons were digested with MluCI as described by Shrestha et al. (2024) with positive results for C. cf. flagellaris . Then, sequences deposited in GenBank (PZ359595-PZ359597, PZ464607-PZ464609, PZ452806-PZ452808, and PZ452802-PZ452803). For pathogenicity, plants of 6 weeks, grown in pots with 50:50 Sunshine mix ® from surface-disinfested seeds, were foliar sprayed separately for each isolate as da Silva et al. (2026) with conidial suspension of 10 4 conidia/ml of water at 0.0025% Tween 20 ® plus gelatin at 0.5% w/v as the vehicle, and control with only vehicle. Post-inoculation, plants were kept at 24-h dark incubation with >90% RH. Plants were kept at average 27°C, >90% RH, under a 12-h photoperiod at 75% light intensity; and were trained vertically by plastic sterile stakes. Pots were fertilized 2 weeks after sowing, with 1 g Osmocote Plus ® and with 6 ml FAFAGRASS ® liquid fertilizer per each liter of watering. Conidia production was enhanced and harvested as described by da Silva et al. (2026) using instead DV8 plates. The experiment was conducted twice. Lesions developed at 8 DAI, and controls remained symptomless. Similar C. cf. flagellaris isolates were re-isolated, from diseased leaves on DV8 medium by plant tissue method and no isolates obtained from control. Koch’s postulates were completed. Isolates clustered with Cercospora cf. flagellaris with strong posterior probability support; and restriction enzyme testing was positive for this species. In the U.S., C. cf. flagellaris occurs on soybean (Shrestha et al. 2024) and hemp (Doyle et al. 2019; Swift et al. 2024). This report identifies ivyleaf morning glory as a potential inoculum reservoir in soybean systems in the U.S. and represents the first report of C. cf. flagellaris on I. hederacea and in Convolvulaceae worldwide.