A Histopathological Study Reveals New Insights Into Responses of Chestnut (<i>Castanea</i> spp.) to Root Infection by <i>Phytophthora cinnamomi</i>

The European chestnut (Castanea sativa) is threatened by the hemibiotrophic oomycete Phytophthora cinnamomi, causal agent of ink disease. Chestnut species have different susceptibility levels to P. with Asian (C. crenata; C. mollissima) exhibiting highest level resistance. A histological approach was used study responses exhibited susceptible and resistant genotypes characterizing early stages cinnamomi infection cellular it induces in roots. sativa (susceptible) crenata (resistant) plantlets were inoculated a virulent isolate zoospore suspension or direct contact mycelia agar pieces. Root samples collected at 0.5, 3.5, 24, 48, 72 h after inoculation (hai) for microscopic observations. Penetration observed both 0.5 3.5 hai mycelium inoculations, respectively. In methods, following penetration into rhizodermis, hyphae grew inter- intracellularly through cortex vascular cylinder. cells displayed delay pattern having fewer cell layers colonized compared sativa. At hai, collapse first cortical observed, indicating beginning necrotrophy. able respond more efficiently than restricting pathogen’s growth area activation resistance such as callose deposition around some intracellular hyphae, hypersensitive response-like death, wall thickening, accumulation phenolic-like compounds.