2022 article
Validation of Standard Area Diagrams to Estimate the Severity of Septoria Leaf Spot on Stevia in Paraguay, Mexico, and the United States
Sanabria-Velazquez, A. D., Enciso-Maldonado, G. A., Maidana-Ojeda, M., Diaz-Najera, J. F., Thiessen, L. D., & Shew, H. D. (2022, November 22). PLANT DISEASE.
author keywords: disease severity; phytopathometry; Septoria steviae; Stevia rebaudiana
MeSH headings : United States; Stevia; Mexico; Reproducibility of Results; Paraguay; Ascomycota / genetics
UN Sustainable Development Goal Categories
2. Zero Hunger
(Web of Science)
13. Climate Action
(Web of Science)
Source: Web Of Science
Added: June 26, 2023
Septoria leaf spot (SLS) affects stevia leaves, reducing their quality. Estimates of SLS severity on different genotypes are made to identify resistance and as a basis to compare management approaches. The use of standard area diagrams (SADs) can improve the accuracy and reliability of severity estimates. In this study, we developed new SADs with six illustrations (0.5, 1, 10, 25, 40, and 75% severity). The SADs were validated by raters with and without experience in estimating SLS. Raters evaluated 40 leaf photos with SLS severities ranging from 0 to 100% without and with the SADs. Agreement (ρc), bias (Cb), precision (r), and intracluster correlation (ρ) coefficients were significantly closer to “true” severity values when the SADs was used by inexperienced (ρc = 0.89; Cb = 0.97; r = 0.90, ρ = 0.81) and experienced (ρc = 0.94; Cb = 0.99; r = 0.95, ρ = 0.91) raters. The SADs were tested under field conditions in Paraguay, Mexico, and the United States, with inexperienced raters assigned to two groups, one SADs trained and the other not trained, that estimated SLS severity three times: first, all raters without SADs and no time limit for the estimates; second, only the SADs-trained group used SADs and no time limit; and third, only the SADs-trained group used SADs, with a time limit of 10 s imposed per specimen assessment. Agreement and reliability of SLS severity estimates significantly improved when raters used the SADs without a time limit. The use of the new SADs improved the accuracy, precision, and reliability of SLS severity estimates, enhancing the uniformity in assessment across different stevia programs.