Diagrammatic scale for the assessment of blast on wheat spikes

Abstract

RESUMOPalavras-chave adicionais: Magnaporthe oryzae, Pyricularia grisea, ImageJ, severidade, epidemia.A qu a ntifica çã o correta da bru sone ca u sa da pelo fu ngo Magnaporthe oryzae em espigas de trigo (Triticum aestivum) é um componente importa nte pa ra o entendimento do desenvolvimento dessa doença com vistas ao seu controle. A quantificação visual baseada em uma esca la diagramática pode ser uma tarefa prática e eficiente que já tem demonstrado utilidade em diversos patossistemas, inclusive doenças da espiga do trigo como a mancha das glu mas e fusariose. Espigas apresentando diferentes valores de severidade da doença foram coletadas em u ma lavou ra com o objetivo de ela borar u ma escala diagramática para quantificar a severidade da brusone em espigas de trigo. As espigas foram fotografa das e a severidade da bru sone foi Maciel, J.L.N.; Danelli, A.L.D.; Boretto, C.; Forcelini, C.A. Escala diagramática para avaliação de brusone na espiga de trigo. Summa Phytopathologica, v.39, n.3, p.162-166, 2013. determinada usando os recursos do programa computacional ImageJ. Uma escala diagramática foi elaborada com os seguintes valores de severidade de doença: 3,7; 7,5; 21,4; 30,5; 43,8; 57,3; 68,1; 86,0; e 100,0%. Uma espiga assintomática foi adicionada à escala. A validação da escala foi realizada por oito pessoas que estimaram a severidade da brusone em imagens digitalizadas de 40 espigas de trigo. A precisão e a a cu rá cia da s a va lia ções va ria ra m de a cordo com o a va lia dor (0,82 <R 2 < 0,9 0; -6,1 2< a <2 ,94 ; 0,8 5< b<1 ,16 ), nã o ocorrendo erro sistemático na su perestimativa ou su bestima tiva da doença entre os avaliadores, demonstrando que a escala desenvolvida é adequada para a avaliação da brusone em espigas de trigo.Blast caused by the fungus Magnaporthe oryzae B. Couch (Pyricularia oryzae anamorph. dig) is one of the major limits to food production in the world, affecting several crops of agricultural importance. For South America, since the mid-1980s, when it was first reported to affect wheat plants, this disease has also been characterized as one of the most serious problems for wheat crops, especially in Brazil, Bolivia and Paraguay (5, 10, 12). Difficulties for its control are enormous. Management practices such as crop rotation, balanced fertilization and treatment of aerial parts with fungicides are not sufficient to prevent the economic damage caused by this disease, especially in seasons of severe epidemics (6, 7,13).An important problem in Brazilian wheat fields is that the cultivars available to the producers are susceptible to blast, which demonstrates that the development of cultivars with higher resistance is an indispensable component of the strategy to control this disease. Improving the process for evaluating the reaction of genotypes to the disease is also part of this strategy. Thus, an additional difficulty is the lack of a diagrammatic scale to help evaluate the disease severity on spikes. Other fungal diseases of importance to the wheat crop have had this type of to...

Multi-environment assessment of fungicide performance for managing wheat head blast (WHB) in Brazil and Bolivia

“…WHB intensity was rated as incidence (proportion of diseased head) and severity in a 100-head sample. Severity was assessed using an ordinal scale developed by Maciel et al (2013). An overall WHB disease index (DI) was given by (severity*incidence)/100.…”

Wheat Blast- A New Challenge to Wheat Cultivation in South Asia

“…The score 0 referred to nil visual symptoms, 1 for 25 % of the spike showing symptoms; 2 for 50%, for 75% and for 100% length of spike affected. Maciel et al (2013) photographed the infected spikes. The blast severity was ascertained by using resources of the software ImageJ.…”

Nitrogen fertilization effects on wheat blast epidemics under varying field environmental conditions

“…In each plot, wheat severity on spikes with typical disease symptoms (bleaching noticed above dark lesions formed in the rachis) was estimated visually aided by a diagrammatic scale containing 10 grades of severity ranging from 0 to 100% (0, 3.5, 7.5, 21.5, 30.5, 44, 57.5, 68, 86 and 100%) (Maciel et al 2013). A destructive sampling method was used to collect at least 60 spikes from two central wheat rows 0.5 m long, selected at random inside each plot, when the plants were on average in dough development (Z80 stage; Zadoks et al 1974).…”