Which one of the following types of resistance is present in a crop variety showing high degree of resistance to a pathogen but becoming susceptible to it after large scale cultivation for 4 to 5 years or so

Answer: Option A

Resistance to plant disease is either Vertical i.e. Specific or Horizontal i.e. Nonspecific. A plant variety that exhibits a high degree of resistance to a single race or strain, of a pathogen is said to be vertically resistant. This is usually controlled by a single plant gene but after large-scale cultivation, for 4 - 5 years it becomes susceptible to it.