Comparative Environmental Fitness, Aggressiveness, and Extracellular Metabolic and Proteomic Profiles of a Rhizoctonia solani AG-4 HG-I Isolate from Potato in Zhejiang, China, and an AG-3 Reference Strain

Rhizoctonia solani causes stem canker and black scurf on potato, resulting in economically important losses. AG-3 is regarded as the predominant pathogenic group on potato, but little is known about the pathogenicity and metabolism of AG-4 HG-I. We isolated strain RS from diseased potato in Zhejiang Province, China, and identified it as AG-4 HG-I by morphology, ITS phylogeny, hyphal anastomosis, and AG-specific PCR. Compared with the AG-3 PT reference strain, RS used a broader range of carbon and nitrogen sources, tolerated pH 3.0–10.0, and grew better under salt stress and across tested temperatures. In pot trials, RS caused a 100% stem-base disease index versus 20% for the AG-3 strain and a tuber disease index at maturity of 83.3% versus 65.55%. RS significantly reduced biomass and tuber yield by 37.4% and 70.69%, respectively, whereas the AG-3 strain failed. Integrated extracellular metabolomics and proteomics showed that RS exhibited upregulation of carbohydrate and energy metabolism and extracellular hydrolytic enzymes, whereas the AG-3 strain exhibited upregulation of amino acid and nucleotide biosynthesis. These contrasting strategies may explain the greater aggressiveness of RS. Overall, RS may threaten potato production under warming climates and warrants strengthened monitoring and integrated management.