Diagrammatic scale for measuring severity of gray mould in thornless Castilla blackberry (Rubus glaucus Benth)

Abstract

Gray mould, caused by the fungus Botrytis cinerea Pers., is a disease that largely affects the crops of Rubus glaucus Benth. (Castilla blackberry) in Colombia. In spite of the economic losses that it causes in the production of Castilla blackberry at national level, a standardized method to quantify the disease severity caused by this fungus in the fruits has not yet been reported. In the present work, a diagrammatic scale was prepared to assess gray mould severity in thornless fruits of R. glaucus. The proposed scale showed the levels of 5, 10, 20, 40, 60, 80, and 100%. Photographic images were obtained for each of these levels, which were processed using the ImageJ software. The scale was validated by 13 evaluators who assessed affected fruits with and without the scale. The precision and accuracy of each evaluator was determined by simple linear regression between actual and estimated severity. The evaluators showed better precision, accuracy, and reproducibility in the assessments performed with the scale. The proposed scale is appropriate to estimate the severity of gray mould in R. glaucus fruits.

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).…”