Comparing tar spot epidemics in high-risk areas in the U.S. and Honduras

Authors: GONHORA-CANUL, CARLOS - PURDUE UNIVERSITY; PUERTO, CARLOS - ZAMORANO, PANAMERICAN SCHOOL OF AGRICULTURE; JIMENEZ-BEITIA, FIDEL - ZAMORANO, PANAMERICAN SCHOOL OF AGRICULTURE; TELENKO, DARCY - PURDUE UNIVERSITY; KLECZEWSKI, NATHAN - UNIVERSITY OF ILLINOIS; ROSAS, J.C. - ZAMORANO, PANAMERICAN SCHOOL OF AGRICULTURE; AVELLANEDA, CAROLINA - ZAMORANO, PANAMERICAN SCHOOL OF AGRICULTURE; SANDERS, ARIE - ZAMORANO, PANAMERICAN SCHOOL OF AGRICULTURE; RODRIGUEZ, IVETH; Goodwin, Stephen - Steve; FERNANDEZ-CAMPOS, MARIELA - PURDUE UNIVERSITY; LEE, DA-YOUNG - PURDUE UNIVERSITY; CRUZ, ANDRES - PURDUE UNIVERSITY; CRUZ, CRISTIAN - PURDUE UNIVERSITY

Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2023
Publication Date: 2/1/2024
Citation: Gonhora-Canul, C., Puerto, C., Jimenez, F., Telenko, D.E., Kleczewski, N.M., Rosas, J., Avellaneda, C., Sanders, A., Goodwin, S.B., Dalla-Lana, F., Cruz, C.D. 2024. Comparing tar spot epidemics in high-risk areas in the U.S. and Honduras. Canadian Journal of Plant Pathology. https://doi.org/10.1080/07060661.2023.2300077.
DOI: https://doi.org/10.1080/07060661.2023.2300077

Interpretive Summary: Tar spot is a fungal disease of corn that causes significant production losses in the Americas. However, relatively little is known about how epidemics begin and develop. To fill this gap, the temporal dynamics of tar spot epidemics were assessed in six field experiments in the United States and Honduras during the 2019 and 2020-2021 growing seasons. The disease took longer to develop from first symptoms to maximum severity in the U.S. (57 days) compared to Honduras (41 days) and progressed from the lower to the upper canopy in both countries. The analyses showed that the disease has multiple cycles of infection and there were differences between the parts of the plant canopy that were affected in each country. These results will be useful to plant pathologists trying to understand and manage this disease.

Technical Abstract: Tar spot is a fungal disease of corn that causes significant production losses in the Americas. However, relatively little is known about its epidemiology. To fill this gap, the temporal dynamics of tar spot epidemics were assessed in six field experiments in the United States and Honduras during the 2019 and 2020-2021 growing seasons. In the U.S., the time from initial visible signs (stromata) and symptoms (onset of disease at 67 days after planting (DAP) and VT-R1 growth stage) to maximum severity (ymax) at 124 DAP and R5-R6 was 57 days, compared to 41 days from 35 (V5-V6) to 90 DAP (R2-R4) in Honduras. In all experiments, the disease progressed from the lower to the upper canopy. Highest AUDPC levels were observed in the middle canopy in the U.S. (up to 1,600) but the lower canopy in Honduras (up to 4,000). The Gompertz model best described the disease progress curves, indicating a polycyclic-like disease. The Gompertz infection rate (rG*) was lower in the U.S. (0.05 day-1) than in Honduras (0.06 day-1). In the U.S., the highest rG* (0.06 day-1) and correlation among epidemiological parameters occurred in the upper canopy, while in Honduras these occurred in the lower canopy (0.08 day-1). Multi-treatment meta-analysis showed that yons, rG*, and AUDPC were higher in Honduras than the U.S (Cohen’s D effect size = 0.47, 0.23 and 0.6, respectively), and ymax was higher in the U.S. than Honduras (-0.48). These analyses identified differences in epidemiological dynamics in high-risk areas in North and Central America.