Abstract: The ultrastructural changes of the surface and subcutaneous tissue were observed through scanning and transmission electron microscopy using resistant varieties‘Jonathan’and susceptible cultivars‘Golden Delicious’and their hybrid seedings（Jonathan × Golden Delicious）including highly resistant 02-24-036 and highly susceptible 02-38-071 as materials inoculated by the strong pathogenic Ls1 strain [Botryosphaeria dothidea（Moug.）Ces. et de Not.]. It found that parents and 02-24-036 all produced special secretions after infection. The secretions of Jonathan and 02-24-036 significantly inhibited the invasion and reproduction of hyphae on fruit surface，while secretions of Golden Delicious couldn’t do that. Results showed that these special secretions were connected with bacteriostasis and resistance to invasion. After hyphae invaded tissue through lenticel and wound，accumulation of osmiophilic globule was found in Jonathan and 02-24-036，while this phenomenon was not observed in Golden Delicious and 02-38-071. These results suggested that the resistance in Jonathan and 02-24-036 to apple fruit ring rot disease is induced resistance，which performed both anti-intrusion and resistance to expansion.

Key words: Malus domestica, fruit, Botryosphaeria dothidea, resistance