Identification and inheritance characterization of Rdc2, a novel resistance gene against Diaporthe caulivora in soybean

Soybean stem canker (SSC) is a destructive disease that can cause plant death, affecting crop yield and phytosanitary quality. It is attributed to two causal agents: Diaporthe aspalathi (syn. Diaporthe phaseolorum var. meridionalis) and D. caulivora (syn. D. phaseolorum var. caulivora, Dc). SSC-Dc has emerged as one of the most prevalent soybean diseases in South America, and the Rdc1 gene represents the only reported source of resistance against D. caulivora. In this work, inheritance studies were conducted to characterize the resistance to SSC-Dc in H32, a local soybean genotype that behaved consistently as resistant to Dc in different pathogenicity assays. After phenotyping several segregating populations and performing allelism tests under different environmental conditions, a novel and independent locus conferring resistance to Dc was identified, characterized as a major, dominant resistance gene, and proposed to be named Rdc2. Considering the potential damage caused by this disease, coupled with the absence of genetic resistance in Argentinian commercial varieties, the strategy objective is to introgress Rdc2 and to stack the Rdc/Rdm genes into elite germplasm. The final goal is to generate a broader and more durable resistance, aim to mitigate the impact of SSC on crop performance, and consequently increase yield and seed phytosanitary quality.