Severity evaluation methods for southern polysora corn rust

Fernando Cezar Juliatti,Adriana Andrade Figueiró,Élcio Oliveira Alves

doi:10.14393/bj-v32n4a2016-33730

Fernando Cezar Juliatti, Adriana Andrade Figueiró + Show 1 more

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https://doi.org/10.14393/bj-v32n4a2016-33730

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Journal: Bioscience Journal	Publication Date: Jan 1, 2016
Citations: 1	License type: cc-by

Affiliation: Pioneer (United States)

Abstract

Among the biotrophic organisms that attack the corn crop the most important for Central Brazil is the Puccinia polysora Underw, which is the causal agent of polysora corn rust. Due to the need to study the methods used in the assessments better, this work was performed. An experiment to identify the best methodology for assessing polysora rust was set up in Itumbiara – Goias - Brazil, with 22 hybrids and an experimental randomized block design with three replications. So as to evaluate disease severity in relation to the leaf area affected, the Area Under the Disease Progress Curve (AUDPC) and a single evaluation were used, while also considering the severity of the disease on the leaf area affected, 30 days after flowering (30 d.a.f.) Both based on a proposal diagrammatic scale from Agroceres with grades ranging from one (highly resistant) to nine (highly susceptible), which were employed considering the plot as a whole. So as to calculate the AUDPC five evaluations of disease severity at intervals of 10 days which begun 50 days after sowing were carried out. It was found that it was possible to determine the level of genotype resistance by using the AUDPC or by using the single assessment at 30 d.a.f., with the assessment of disease severity by means of the AUDPC calculation allowing for better understanding of the evolution of the disease in time and that the one only or single assessment at 30 d.a.f. allows us to work with a greater number of genotypes, due to the practicality of the methodology.

Highlights

Since the beginning of the 1980s, polysora rust, Puccinia polysora Underw, has been a serious problem in the corn crop in south-west regions of Goias, in the Triângulo Mineiro and more recently in the northwest of São Paulo, in the East and in the North of Paraná and in Mato Grosso do Sul in Brazil
At 50 d.a.s. only some/slight symptom of polysora rust was noted in the trial
There was a great uniformity in the severity of polysora rust among all plants of the plot, allowing for an optimal evaluation of the disease both by Area Under the Disease Progress Curve (AUDPC) as well as by assessing the severity at a single time, at 30 d.a.f

Summary

Introduction

Since the beginning of the 1980s, polysora rust, Puccinia polysora Underw, has been a serious problem in the corn crop in south-west regions of Goias, in the Triângulo Mineiro and more recently in the northwest of São Paulo, in the East and in the North of Paraná and in Mato Grosso do Sul in Brazil. It is considered to be the most aggressive and destructive among corn diseases and can cause rapid necrosis of the plant. Under favorable conditions and in susceptible cultivars, this rust may occur with severe presence in the leaves, stems, straw, and cause a marked reduction in the size of the corn cobs and grains (FANTIN, 1997). The severity of the disease can be assessed by subjective methods such as counting the number of lesions per leaf or the measurement of the affected area, but these methods are usually very time consuming. As corn breeding or improvement programs are very dynamic, and produce a large number of new varieties each year, it is necessary to evaluate the behavior of these materials in relation to this disease. This, so as to direct future work of breeding/improvement, in order to obtain resistant cultivars, and to act as a guide in the selection and recommendation of cultivars for different regions (VON PINHO et al, 2001)

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