Reproductive Fitness and Virulence of Heterodera glycines Races on Resistant and Susceptible Soybean Genotypes

Abstract

Reproductive fitness and virulence of Heterodera glycines races were evaluated on resistant and susceptible soybean genotypes to understand host–pathogen interactions and variability in nematode adaptation. Greenhouse experiments were conducted using standardized inoculation techniques, and nematode development was assessed through cyst formation, egg mass production, and reproductive factor (RF) across different soybean genotypes carrying distinct resistance backgrounds. Significant variation in nematode reproduction was observed among races, indicating differential virulence potential against host resistance genes. Susceptible soybean genotypes supported higher cyst density and elevated reproductive factors, while resistant genotypes significantly suppressed nematode development, although partial reproduction was still observed in certain race–genotype combinations. This suggests the presence of virulence variability within H. glycines populations capable of overcoming host resistance. Fitness analysis revealed trade-offs in virulent populations, with increased reproductive success on resistant hosts accompanied by reduced efficiency on susceptible genotypes in some cases. Pathogenic variability among races highlighted the dynamic evolution of virulence in response to selective pressure imposed by resistant cultivars. The findings emphasize the risk of resistance breakdown under continuous monoculture of single resistance sources and underline the importance of deploying diverse resistance genes in integrated nematode management strategies. Understanding reproductive fitness and virulence patterns of H. glycines is essential for developing durable soybean resistance and improving long-term nematode control in agricultural systems.