Development and validation of a standard area diagram set as assessment aid for estimating the severity of bacterial spot on tri-lobed leaves of yellow passion fruit

Anne Pinheiro Costa,Michelle Souza Vilela,José Ricardo Peixoto,Luiz Eduardo Bassay Blum,Wagner A Vendrame

doi:10.14393/bj-v35n6a2019-42435

Anne Pinheiro Costa, Michelle Souza Vilela + Show 3 more

Open Access

https://doi.org/10.14393/bj-v35n6a2019-42435

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Abstract

Bacterial spot (Xanthomonas axonopodis pv. passiflorae) significantly reduces yellow passion fruit (Passiflora edulis Sims) yield and longevity. A standard area diagram set (SADs) for severity assessment of bacterial spot on tri-lobed leaves of yellow passion was developed and validated in this study. The SADs consisted of eight severity levels (2; 4; 9; 18; 35; 58; 80; and 94%). For its validation, 20 raters, who initially estimated the disease severity without the aid of the SADs, were divided into four groups (G1 and G3, inexperienced; G2 and G4, experienced). Subsequently, G1 and G2 performed the second evaluation without the SADs, and G3 and G4 completed the second evaluation with the proposed SADs. The accuracy and precision of the assessments were determined by simple linear regression and by the Lin’s concordance correlation coefficient (LCCC). The proposed SADs allowed accurate and precise quantification of bacterial spot severity, increasing the agreement between estimated and actual values. Inexperienced raters benefited the most from the use of the SADs. The increase in accuracy and precision in the non-aided groups, when present, was less pronounced than those increments observed in the SADs-aided groups. The LCCC confirmed the increases in accuracy and precision detected by the linear regression analysis.

Highlights

Bacterial spot (Xanthomonas axonopodis pv. passiflorae) is a disease of difficult control and, as a consequence, is responsible for significant production losses in yellow passion fruit (Passiflora edulis Sims) (ISHIDA et al, 2017)
Subjectivity and error in estimates can be minimized by standard area diagram sets (SADs)
Development of the SADs Fifty tri-lobed leaves of yellow passion fruit (BRS Gigante Amarelo, Yellow Master FB200, and genotypes in breeding process) showing symptoms of bacterial spot were collected at Paraná Farm commercial orchard, located in Nucleo Rural Pipiripau, Planaltina, DF, Brazil (47°29’56,92’’ S and 15°30’15,08’’ W, 955 m)

Summary

Introduction

Bacterial spot (Xanthomonas axonopodis pv. passiflorae) is a disease of difficult control and, as a consequence, is responsible for significant production losses in yellow passion fruit (Passiflora edulis Sims) (ISHIDA et al, 2017). The disease causes intense defoliation and terminal branch drought These symptoms drastically reduce fruiting, cause plant death, and may result in total orchard loss (CARVALHO et al, 2015). Bacterial spot is commonly evaluated by visual estimates of disease severity and descriptive keys (VIANA et al, 2014; CASTRO, 2015; NOGUEIRA, 2016). Such keys are prone to various errors due to the inherent subjectivity of the method, which does not allow visual acuity adjustment in the evaluation of the severity levels (CAMPBELL; MADDEN, 1990), compromising accuracy and precision of the estimates. Subjectivity and error in estimates can be minimized by standard area diagram sets (SADs)

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