Development and validation of a standard area diagram set to assess powdery mildew severity on watermelon leaves

Abstract

The development and validation of a standard area diagram set (SADs) was proposed in this study to assess the severity of powdery mildew (Podosphaera xanthii) in watermelon (Citrullus lanatus) leaves. The SADs proposed has twelve levels of severity, varying from 0.07 to 100%. The SADs were validated by 16 raters who had no previous experience in evaluating plant disease severity. Initially, the estimation of severity was performed without the use of the SADs in leaves with different levels of severity. In a second moment, the same raters estimated the disease severity using the SADs proposed. By Lin’s concordance correlation analysis, there was an improvement in precision (coefficient of correlation, r = 0.878 and r = 0.959, without and with SADs, respectively) and accuracy (bias correction factor, Cb = 0.830 and 0.982, without and with SADs, respectively) using SADs when compared to the non-use of SADs. The agreement (Lin’s concordance correlation coefficient, ρc = 0.734 and 0.952 without and with SADs, respectively) also improved using SADs. Severity estimates inter-rater were more reliable when using SADs (coefficient of determination, R2 = 0.681 without and R2 = 0.864 with SADs; Intra-class correlation coefficient, ρ = 0.759 and ρ = 0.928, without and with SADs, respectively). Therefore, SADs improved precision, accuracy and reliability of powdery mildew severity on watermelon leaves.

Diagrammatic scale to quantify the damage caused by bean thrips to the peanut crop

“…The severity of the damage caused by thrips to the peanut crop is usually evaluated subjectively by analyzing visually the caused symptoms (Moraes, 2005;Montes et al, 2013). Therefore, developing and validating a diagrammatic scale is useful to determine disease and pest intensity, which is important for different purposes including understanding yield loss, comparing cultivar behavior, and evaluating the effects of chemical and biological control (Bock et al, 2010;Boito et al, 2013;Vieira et al, 2014;Crenna et al, 2021).…”

How much do standard area diagrams improve accuracy of visual estimates of plant disease severity? A systematic review and meta-analysis

“…Indeed, linear regression continues to be used by some phytopathometrists for evaluating SADs (Santos et al 2017;Camara et al 2018;Trojan and Pria 2018;Arias et al 2020;Robaina et al 2020;Kublik et al 2020). The two linear regression coefficients (intercept and slope), together with the coefficient of determination (R 2 ), are usually reported for each rater in the SAD validation study, while those phytopathometrists reporting LCCC statistics have most often reported means of all raters combined (Del Ponte et al 2017;Bock et al 2020;Brás et al 2020;Nascimento et al 2020;Rivera et al 2020;Castellar et al 2021;Montero et al 2021).…”