Standard area diagrams set for assessment of anthracnose severity on cucumber leaves

BRAINER MARTINS, R; MICHEREFF, S. J.; NICOLI, A; CONFORTO, C.; CAPUCHO, A

Recife

Congreso; 51º Congresso Brasileiro de Fitopatología; 2019

Sociedade Brasileira de Fitopatologia

Anthracnose, caused by Colletotrichum orbiculare complex species is a destructive disease of cucumber in the coastal region of northeastern Brazil. The objective of this study was to develop a standard area diagrams set (SADs) to improve the assessment of anthracnose severity on cucumber leaves. To develop the SADs, leaves of cucumber with different levels of anthracnose severity were collected and scanned for determine the actual severity. The SADs was produced according to the symptoms of the disease, aiming to represent the form, frequency and standard of distribution of disease lesions. After, the raters with no previous experience estimate the severity of the disease on 50 images of leaves, without and with use of SADs elaborated. The precision and accuracy were determined based on Lin´s concordant correlation analysis (LCCC, ρc). The reproducibility was determined by analysis the distribution of absolute errors and coefficient of determination (R2) of the linear regression among combinations of raters combined in pairs. The SADs elaborated was composed for anthracnose severity ranged from 2% to 54% and the LCCC demonstrated that estimates by the raters with SADs were closer to perfect agreement (variables, μ = 0, υ = 1, Cb = 1, r = 1, rho or ρc = 1). The LCCC combines both measures of precision (r) and accuracy (Cb) to measure agreement with the true value. Cb is a function of height shift (μ) and slope shift (υ). Furthermore, the equivalence test showing that the variables were statistically different when compared without SADs. The reproducibility was highly improved, with mean R2 among the combinations of raters using SADs different that without SADs and the mean deviations were closer to zero (below 5%), as evidenced by the significant reduction in absolute error values. Therefore, the SADs developed can be used to estimate the anthracnose severity on cucumber.