Severity evaluation methods for southern polysora corn rust

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 - Goiás - 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.