Diagramatic scale to quantification of severity of leaf spot in Eucalyptus globulus labill. Caused by Teratosphaeria nubilosa Crous U. Braun

• Published in: Ciência florestal 2013-04, Vol.23 (2), p.521
• Main Authors: Passador, Martha Maria, Porcena, Alex Sander, Masson, Marcus Vinicius, de Pieri, Cristiane, Finkenauer, Elder, Furtado, Edson Luiz
• Format: Article
• Language: Spanish
• ISSN: 1980-5098; 1980-5098

The leaf spot (Mycosphaerella leaf disease = MLD) caused by Teratosphaeria nubilosa has caused damage in eucalypt plantations in southern and southeastern Brazil. The need to assess the disease in the field to evaluate of this damage, efficiency control, evaluation of germplasm induces to the necessity of having a visual scale for evaluation of disease. The objective was to develop a diagrammatic scale for young leaves and one for adult leaves of Eucalyptus globules for MLD. To do so, the leaves collected in the field were scanned for image analysis. The damaged area, the healthy leaf area and the external area of the same scale RGB (Red, Green, Blue) were determined. Subsequently, it was determinate the levels of severity depending on the sample distribution with seven levels for young leaves and six for adult leaves. For the visual acuity test and validate the scale, the leaves were evaluated for severity, with and without scale. With this proposed scales, the assessors showed good accuracy both for young and adult leaves with [R.sup.2]=0,98 and [R.sup.2]=0,80, respectively. The importance of the development of diagrammatic scales for assessing MLD in eucalyptus must to the fact that allows quantification of the symptoms accurately and precisely. Keywords: Eucalyptus globulus; Mycosphaerella leaf disease; disease evaluation. A mancha foliar (mancha de micosferela) causada por Teratosphaeria nubilosa tem acarretado prejuizos em plantios de eucalipto na regiao Sul e Sudeste do Brasil. A necessidade de avaliar a doenca no campo e os danos causados pela mesma, bem como a busca de formas eficientes de controle e a utilizacao de germoplasma, leva a necessidade em ter uma escala visual para quantificacao da severidade da doenca. O objetivo deste trabalho foi elaborar uma escala diagramatica com folhas jovens e com folhas adultas de Eucalyptus globulus, para avaliacao de mancha de micosferela. Para tal, as folhas coletadas em campo foram escaneadas para digitalizacao da imagem. Determinou-se a area lesionada, area foliar sadia e area total em escala RGB (Red, Green, Blue). Posteriormente, determinaram-se os niveis de severidade em funcao da distribuicao da amostra, sendo sete niveis para folhas jovens e seis para folhas adultas. Para o teste de acuidade visual e validacao da escala, as folhas foram submetidas a avaliacao da severidade, com e sem escala. Com a adocao das escalas propostas, a totalidade dos avaliadores apresentou boa acuracia, tanto para folhas jo