If the host plant is susceptible to the pathogen at young age and becomes resistant with age then it possesses

If the host plant is susceptible to the pathogen at a young age and becomes resistant with age then it possesses Adult plant resistance.
Resistance is the ability of a plant variety to restrict the growth and development of a specified pest or pathogen and/or the damage they cause when compared to susceptible plant varieties under similar environmental conditions and pest or pathogen pressure.