Development and validation of a standard area diagram set to estimate severity of leaf rust in Coffea arabica and C. canephora

Abstract

A standard area diagram (SAD) set to aid assessment of the severity of coffee leaf rust (Hemileia vastatrix) was prepared and validated, and the characteristics of the rust lesions on Coffea arabica and C. canephora leaves were compared. The results indicated that the lesions were similar, so one scale could be used to evaluate the severity of rust on both species. The proposed SAD set contains illustrations of leaves with six disease severities (2AE5, 5, 10, 20, 40 and 80%). The SAD set was validated by 10 raters with no previous experience of disease evaluation. The severity of rust was first estimated without using the SADs, and the same raters assessed the leaves again using the SADs. Regression analysis and Lin's concordance correlation (q c ) analysis of estimated against actual disease severity showed precision and accuracy was significantly better using the SADs, for most raters, with improvements in both the slope and intercept of the regressions, and the values of u, t (components of accuracy and precision of the q c ) and q c improved to 60, 70 and 90% of raters, respectively, when the SADs were used. The absolute error was £38% without the SADs, and £22% with them. Severity estimates were more reliable using the SADs (R 2 = 0AE70-1AE00 unaided, and R 2 = 0AE80-1AE00 using the SADs). The SAD set improved rater assessments for the estimation of arabica and conilon rust severity, and can be used for assessing rust severity for many purposes, including plant breeding, fungicide screening and pathotype characterization.

Validação de escala diagramática para quantificação da severidade da antracnose do colmo do milho

“…Na avaliação de um experimento futuro, a análise estatística provavelmente será mais significativa e os tratamentos serão mais diferenciados com o uso da escala proposta, pois o intervalo em severidade entre as notas é menor em comparação ao uso da primeira escala. Portanto, os resultados aqui obtidos reforçam a importância de validação de uma escala para as futuras avaliações de doenças em plantas, conforme encontrado em vários outros estudos (STONEHOUSE, 1994;LEITE & AMORIN, 2002;GOMES et al, 2004;MICHEREFF et al, 2006;CAPUCHO et al, 2010;CAPUCHO et al, 2011;YADAV et al, 2012, RIOS et al, 2013.…”

“…Mesmo com a utilização da análise de regressão, o uso do ρ c e o teste de equivalência (95% IC) foram importantes para interpretação das avaliações realizadas pelos dez avaliadores. O coeficiente de Lin (ρ c ) tem sido usado com muito sucesso em vários trabalhos (BOCK et al, 2010;CAPUCHO et al, 2011;YADAV et al, 2012;RIOS et al, 2013), e mais recentemente o teste de equivalência também, facilitando ainda mais a conclusão dos resultados (BARDSLEY & NGUGI, 2012;YADAV et al, 2012;RIOS et al, 2013).…”

“…Os avaliadores tiveram uma tendência em superestimar a severidade da doença, a qual tem sido observada em vários outros estudos envolvendo validação de escalas (NEWTON & HACKETT, 1994;PARKER et al, 1995;DIAZ et al, 2001; LEITE & AMORIM, 2002;CAPUCHO et al, 2010;CAPUCHO et al, 2011;RIOS et al, 2013). Apenas em alguns poucos estudos tem sido verificada a severidade subestimada (MICHEREFF et al, 1998(MICHEREFF et al, , 2000GOMES et al, 2004).…”

“…Iguais alturas implicam um valor de u igual a 0. Portanto, um avaliador perfeito é aquele em que suas estimativas estão todas iguais à linha concordante, ou seja, r = 1, Cb = 1 [υ = 1, u = 0], e, consequentemente, pc = 1 (NITA et al, 2003;BOCK et al, 2010;CAPUCHO et al, 2011;YADAV et al, 2012).…”

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

“…The fi gure 3 showed the most of the assessment errors occurred in the range of 20 to 45% of severity. These results corroborated with BELASQUI JR. et al (2005), ANGELOTTI et al (2008) and CAPUCHO et al (2012) were the assessment error of citrus canker, grapevine rust and coffee leaf rust were in the range from 20 to 50% for inexperienced raters, and from 10 to 25% for experienced raters.…”