Relationship Between Incidence and Severity of Peanut Smut and Its Regional Distribution in the Main Growing Region of Argentina

Abstract

Peanut smut caused by the soil-borne pathogen Thecaphora frezii, has increased in incidence in the main Argentine peanut growing region. Smut affected pods transforming the kernel into a mass of teliospores, which survive long-term in the soil. This study is the first wide-scale survey to determine the occurrence and distribution of peanut smut in the main growing area of Argentina. Survey was conducted in Córdoba province, in commercial peanut fields (n=217) randomly selected from the 2015 to 2020. The intensity of disease was explored, analyzing the distribution of classes of disease severity from peanut fields, and assessing the relationship between disease parameters. No field with 0% incidence was recorded, being the mean of the incidence increased from 1.66% in 2015 to 11.47% in 2020. Smut symptoms varied from a small sori to the complete transformation of the kernel (severity classes). Severely damaged pods (SDP) were considered severity class 3 and 4, where at least one or both kernels were transformed into a mass of spores, producing a high volume of spores that spread among fields increasing the inoculum in the soil. More than 80% of the infected pods in samples corresponding to SDP. A strong relationship was observed between the disease severity index and incidence (R = 0.99), and between incidence and severity class 3 and 4 (R = 0.97 and R = 0.93), being the linear regression a model that explained the data. The results obtained contribute to progress in the knowledge of the distribution of T. frezii in the peanut-growing area of Argentina. Severity can be estimated by incidence, incidence assessment is faster, more accurate, and reproducible. This is a good technical criterion for monitoring the disease annually, and it can also be used to screen materials in breeding programs or treatments implemented as management strategies for peanut smut.