Elaboration and validation of diagrammatic scale for lettuce powdery mildew

Guilherme De Resende Camara,Laedio Magno Busato,Bárbara Favalessa Almeida,Willian Bucker Moraes

doi:10.1590/0100-5405/175851

Guilherme De Resende Camara, Laedio Magno Busato + Show 2 more

Open Access

https://doi.org/10.1590/0100-5405/175851

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Abstract

ABSTRACT Powdery mildew, caused by Oidium sp., is a disease of great importance in hydroponic crops of lettuce. However, in Brazil, there is scarce research focused on the epidemiological study of this disease, as standardized methods are necessary to quantify the disease severity in hydroponic systems. Thus, a logarithmic scale was developed at levels of 0.37, 1, 2, 4, 8, 16, 32 and 74% injured leaf area, testing the parameters accuracy and precision. The proposed scale was validated by eight evaluators, of whom four were experienced and four were inexperienced, and they used 50 leaves showing symptoms of the disease at different severity levels, previously measured with the aid of QUANT® software. Two evaluations were performed with a 48-h interval, in which the evaluators visually estimated distinct sequences of leaves. Linear regression was used to determine the accuracy and the precision of each evaluator. The proposed scale showed satisfactory results of accuracy and precision, and despite the inexperience of four evaluators, absolute errors were in the range of 8% after training. The proposed scale was adequate to estimate the severity of powdery mildew on lettuce.

Highlights

A mancha de oídio, causada por Oidium sp., é uma doença de grande importância em cultivos hidropônicos de alface
A escala proposta apresentou resultados satisfatórios de acurácia e precisão e, apesar da inexperiência de quatro avaliadores, os erros absolutos após o treinamento se encontraram na fixa de 8%
Since leaves are not wetted through irrigation systems, which would remove the pathogen structures, powdery mildew (Oidium sp.) is a common disease of vegetable crops and is characterized by the presence of whitish structures of the pathogen on both sides of the leaf, which evolve to a grayish color, causing chlorosis and, subsequently, necrosis of tissues, affecting the visual appearance of leaves and depreciating the final product [7; 12; 15; 20]

Summary

Introduction

A mancha de oídio, causada por Oidium sp., é uma doença de grande importância em cultivos hidropônicos de alface. A escala proposta foi validada por oito avaliadores, sendo quatro experientes e quatro inexperientes, os quais fizeram uso de folhas que apresentavam sintomas da doença em níveis diferentes de severidade, mensurados previamente com auxílio do software QUANT®. Protected cultivation allows a controlled cultivation environment and promotes an increase in productivity [7]. It is produced throughout the year, but winter and spring offer the most favorable weather conditions [21]; the variety of available lettuce cultivars is wide, showing different types, shapes, sizes and colors, of which the curly lettuce is most consumed [19]. Since leaves are not wetted through irrigation systems, which would remove the pathogen structures, powdery mildew (Oidium sp.) is a common disease of vegetable crops and is characterized by the presence of whitish structures of the pathogen on both sides of the leaf, which evolve to a grayish color, causing chlorosis and, subsequently, necrosis of tissues, affecting the visual appearance of leaves and depreciating the final product [7; 12; 15; 20]

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