Evidence for facultative pathogenicity on Korean pine roots by <i>Sparassis latifolia</i> and metabolic utilization of the host monolignol glucoside coniferin

Sparassis latifolia thrives in natural Pinus koraiensis (Korean Pine) forests, but its artificial cultivation remains inefficient due to poor substrate utilization. Its nutritional strategy, long presumed to be saprotrophic, is poorly defined, impeding domestication efforts. We integrated taxonomic identification, pathogenicity assays, computerized tomography scanning, laser scanning microscope, Scanning electron microscopy (SEM)/Transmission electron microscopy (TEM) visualization of root colonization, and carbon utilization profiling to elucidate S. latifolia's trophic mode. By analysis the morphological characteristics of the basidiocarps and the isolations from infected roots, and in combination with molecular data, identified as S. latifolia. This fungus was demonstrated pathogenic on P. koraiensis seedlings, causing root rot with intracellular colonization of sieve cells. Mycelial growth was quantified in minimal media supplemented with host-derived compounds. S. latifolia showed striking carbon source specificity, growing significantly only on glucose or monolignol glucoside coniferin. Coniferin drove faster radial expansion and higher biomass yield than glucose. This specificity correlates with high coniferin levels in fresh P. koraiensis lateral roots, markedly reduced in dried substrates. Our findings provide strong evidence supporting S. latifolia as a facultative parasite of P. koraiensis, reliant on host-derived coniferin as a premium carbon source. This coniferin-centric strategy underpins its efficient colonization in living roots and may partially explains long cultivation cycle in coniferin-decreased artificial substrates. Our findings resolve its nutritional ecology and expose the critical bottleneck for domestication.