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Single-pustule inoculation to examine diversity of the Brazilian orange rust pathogen from various origins and uredia

Lis Porto: Federal University of Sao Carlos

<div>The orange rust of sugarcane (<em>Puccinia kuehnii</em>) has caused elimination of important cultivars in Brazil since the main strategy of control is through resistant genotypes. The effectiveness of this measure is dependent on the knowledge of pathogen diversity. Nevertheless, the few studies in this area employed fungi collected from multiple lesions. In this process, variants present at lower frequency may not be detected. Therefore, the present study aimed to employ single uredium to examine diversity of <em>P. kuehnii</em> from different cultivars as well as among uredia from the same leaf. A total of 285 single uredium from three susceptible cultivars were inoculated on four cultivars and lesion area measured by Assess software, 21 days after inoculation. Genetic variants among uredinium DNA of 24 pustules from the same leaf were genotyped with four SSR markers. Phenotypic data, based on diseased area, identified different variants ranging from 3.12 to 6.45% in these inoculum sources demonstrating that diverse pathotypes of <em>P. kuehnii</em> were affecting each of the susceptible cultivars. Genotypic variation were observed among uredia of the same leaf when using SSRs. Therefore, single-pustule inoculation proved to be effective in detecting variants of the pathogen, even present at very low frequency. Grant: FAPESP (2017/14351-0)</div>