Caracterização da resistência de genótipos de soja a patótipos Phytophthora sojae

Abstract

Soybean (Glycine max (L.) Merrill) is one of the most important agricultural crops in Brazil and worldwide, with substantial economic, social, and environmental relevance. Among the factors limiting soybean productivity, Phytophthora root and stem rot, caused by the oomycete Phytophthora sojae, is one of the most destructive diseases, leading to severe yield losses. The use of genetically resistant cultivars, mainly through the deployment of specific Rps genes, is considered the most effective and sustainable strategy for disease management. However, the high genetic variability of the pathogen and the emergence of new pathotypes have reduced the durability of resistance over time. Therefore, this study aimed to evaluate the reaction of soybean genotypes to Phytophthora root and stem rot against different P. sojae races and to infer the possible Rps genes associated with resistance. A total of 144 soybean genotypes were evaluated using pathotypes corresponding to races 1, 3, 4, 17, and 25 of P. sojae. The experiments were conducted under greenhouse conditions at GDM Seeds, Cambé, Paraná, Brazil, during 2024 and 2025. Genotypes were arranged in experimental blocks for each P. sojae race, with two replications. Inoculation was performed by inserting macerated mycelium into the hypocotyl, and disease reaction was classified based on the percentage of dead seedlings, with genotypes showing up to 30% mortality considered resistant. The results revealed variation in the frequency of resistance among the evaluated races, with the highest proportion of resistant genotypes observed for race 1 (75.69%) and the lowest for race 25 (54.86%). Gene combinations involving Rps1a + Rps3a, Rps1k + Rps3a, and Rps1c + Rps3a predominated, indicating the use of gene pyramiding strategies in soybean breeding programs. Single resistance genes occurred less frequently, while a proportion of the genotypes showed no clear identification of specific resistance genes. These findings highlight the high variability of P. sojae populations and reinforce the importance of continuous monitoring of pathotypes in soybean-producing regions. The combined use of Rps genes and quantitative resistance represents a promising strategy to enhance resistance durability and support the development of soybean cultivars better adapted to the conditions of southern Brazil.