Excised chestnut shoots were inoculated with Phytophthora sp. strains to assess the resistance of 31 different Castanea clones, including Euro-Asiatic hybrids, to this fungus. The length of the necrosis caused by the fungus is considered negatively proportional to the resistance to Phytophthora sp.
Clone classifications made with two different Phytophthora sp. strains were identical for the most resistant clones. Clonal heritability of resistance to Phytophthora sp. calculated for the more vigorous fungal strain was high, with a value of 0.82 for the joint analysis of the four repetitions. Therefore the test can be replicated quite well.