Caracterização de resistência de cultivares de soja à Phakopsora pachyrhizi

Abstract

Soybean (Glycine max (L) Merrill) is the Brazilian agricultural crop that most expanded in the last three decades. Asian Soybean Rust (ASR), caused by the fungus Phakopsora pachyrhizi Sydow and Sydow, represent a major threat to soybean production in the main producing regions of the world, where significant losses have been reported, losses ranging from 10 to 90%. Several management strategies can be used to control Asian soybean rust, such as the adoption of a period without cultivation, sowing at recommended times, elimination of voluntary plants, chemical control, genetic resistance, among others. Genetic resistance is an alternative that involves the implantation of naturally resistant genes, which help reduce application costs and facilitate handling. Therefore, this study aims to characterize the control of Asian soybean rust through the use of commercial soybean cultivars and PI's, with different gene sources, regarding resistance to Phakopsora phachyrhizi. Nineteen soybean genotypes (PIs – plant introduction and commercial cultivars) carrying different genes of resistance to asian soybean rust were evaluated. The experiment was carried out in the experimental area of the Federal Technological University of Paraná – Campus Pato Branco. The experimental design was randomized blocks with three replications, with ten leaves from the middle third of each experimental unit being analyzed, and phenotypic analyzes were carried out, classifying the lesions as hypersensitivity reactions (RB - reddish brown), immune and susceptible. Disease severity assessments were performed to determine the area under the disease progress curve (AUDPC) and the rate of disease progress. In addition, the evaluations of resistance characteristics were: number of lesions with uredia (NoU), frequency of lesions with the presence of uredia (%LU) and sporulation level (NE). In addition, grain yield (GR) and thousand weight seeds (TWS) were quantified. All genotypes with Rpp1b genes showed high levels of resistance, therefore, using the Rpp1b gene as a source of resistance may be a promising strategy for breeding programs, aiming at higher levelsof resistance, especially against ASR isolates from South America. In addition, the commercial cultivars BRS531 and BRS539 were the only ones responsive to the pathogen attack.