Investigating the Role of Soybean Genetic Resistance on the Production of Sclerotinia sclerotiorum Sclerotia

Sclerotia serve as survival structures for many plant pathogens, including Sclerotinia sclerotiorum, which causes Sclerotinia stem rot (SSR) in soybeans and leads to significant yield losses. While partially resistant soybean varieties are effective in reducing SSR incidence, the relationship between resistance and sclerotial production remains unclear. This study investigated the sclerotial production of two soybean recombinant inbred lines (RILs) with differential levels of SSR resistance under both greenhouse and field conditions. In the greenhouse, three S. sclerotiorum isolates of varying aggressiveness were used to screen the two RILs, revealing differences in disease development and sclerotial characteristics. Under greenhouse conditions, the susceptible RIL resulted in greater SSR development, higher total sclerotia production, and greater sclerotial mass per plant than the resistant RIL. Field trials in 2022 and 2023 with the same two soybean RILs, demonstrated that the susceptible RIL consistently produced more sclerotia than the resistant. Further linear regressions between the SSR incidence (DI, %) and sclerotial mass were examined for the susceptible and resistant RILs, where on the susceptible each 10% increase in DI resulted in 28.5 kg ha-1 of sclerotia produced, and on the resistant RIL each 10% increase in DI resulted in 16.2 kg ha-1. These findings provide new insights into the impact of SSR resistance in soybeans on sclerotial production and highlight the importance of selecting resistant soybean varieties to reduce potential build-up of long-lasting inoculum loads.