Peanut smut, caused by the soil-borne pathogen Thecaphora frezii, has increased in incidence in the main Argentinian peanut-growing regions. Smut-affected pods transforms the kernel into a mass of teliospores, which survive long-term in the soil. This study is the first large-scale (regional) survey to determine the occurrence and distribution of peanut smut in the main growing area of Argentina. Surveys were conducted in Córdoba province, in randomly selected commercial peanut fields (n = 217) grown from 2015 to 2020. A five-score severity scale has been used to quantify the smut severity on pods (0 = healthy kernels and 4 = totally smutted kernels) and a disease severity index (DSI) is calculated. Pods with severity scores of 3 and 4 are rejected by the industry and produce a high volume of spores that spread among fields increasing the inoculum in the soil. Those pods were classified as severely damaged pods (SDP). We evaluated the relative frequency of smut classes during the years and established the relationships between the yearly incidence and DSI. The mean of the incidence was variable (never zero) across the years and increased from 1.66% in 2015 to 11.47% in 2020. More than 80% of the affected pods belonged to SDP group. The variable SDP, a more time and cost-effective method for quantifying peanut smut, best explained the variation in DSI values. Our results suggest that that visual estimates of incidence and SDP should be useful for disease monitoring, screening genotypes, or treatments comparisons in smut management experiments. Our data update knowledge of the distribution of T. frezii in the peanut-growing area of Argentina.
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