Diagrammatic scale to assess downy mildew severity in melon

Abstract

The downy mildew, caused by Pseudoperonospora cubensis, is an important melon disease in Northeast Brazil. Considering the lack of standard methods for its assessment, a diagrammatic scale was developed with 2, 4, 8, 16, 32, 64, 82, and 96% of affected leaf area. The scale was then checked for its accuracy, precision, and reproducibility in estimating downy mildew severity. The diagrammatic scale was validated by eight disease raters; using 50 leaves with different severity levels, previously measured using the software Assess®. Two evaluations were performed on the same set of leaves, but in a different sequence order, by the same raters, within a 15-day interval. The accuracy and precision of each rater was determined by simple linear regression between the actual and the estimated severity. The scale provided good levels of accuracy (means of 87.5%) and excellent levels of precision (means of 94%), with absolute errors concentrated around 10%. Raters showed great repeatability (means of 94%) and reproducibility (>90% in 90.3% of cases) of estimates. Therefore, we could conclude that the diagrammatic scale presented here was suitable for evaluating downy mildew severity in melon.

Development of a diagrammatic scale for the evaluation of postharvest physiological deterioration in cassava roots

“…In this case, the score overestimation may be reduced using a diagrammatic scale. Another important aspect is to correct the tendency to overestimate the stress severity by training the evaluators to use the scale (Michereff et al, 2009). Concerning the angular coefficient values (b), no significant difference (p<0.05) was found among evaluators, regardless of using the grading scale for PPD, which indicates that there were no systematic biases in the deterioration severity estimation.…”

Elaboration and validation of a diagrammatic scale to assess downy mildew severity in grapevine

“…The use of a standard system for disease evaluation is the most effective way to allow the confrontation of results from different groups, institutions, and places (BERGAMIN FILHO & AMORIM, 1996;MICHEREFF et al, 2009). Therefore, this diagrammatic scale to assess downy mildew severity in grapevine is considerated to be a valuable tool for fi eld surveys, epidemiological studies, and comparison among disease control methods.…”

“…Accuracy refers to how faithful an estimate is from the actual amount of the evaluated disease, while precision corresponds to the confi dence and/or repeatability associated to such estimate (GODOY, 2006;ANGELOTTI et al, 2008;MICHEREFF et al, 2009). However, the precise quantifi cation of infected area is a diffi cult task.…”

“…The diagrammatic scales is expected to be easy and quick for a wide range of conditions with reproducible, accurate, and precise results (MALAGI et al, 2011;SACHS et al, 2011;SANTOS et al, 2011;YADAV et al, 2012). Accuracy refers to how faithful an estimate is from the actual amount of the evaluated disease, while precision corresponds to the confi dence and/or repeatability associated to such estimate (NUTTER JR. & SCHULTZ, 1995, ANGELOTTI et al, 2008MICHEREFF et al, 2009). Downy mildew is a leaf spot and its intensity is expressed by assessing severity (percent or proportion of affected leaf area).…”

“…Downy mildew is a leaf spot and its intensity is expressed by assessing severity (percent or proportion of affected leaf area). Most of the times, disease severity is assessed visually and it is prone to large subjectivity, which can give rise to signifi cant errors in accuracy and precision (NUTTER JR. et al, 2006;ANGELOTTI et al, 2008;MICHEREFF et al, 2009). Therefore, this work aimed to develop and validate a diagrammatic scale for assessing grapevine downy mildew severity.…”