Complex sentence: In qualitative or discrete resistance a mutation (normally to a single gene) produces a race of a fungus with a high rieties also tend to show stability, persisting after the fungicide has been removed from the market.
Split into simpler sentences: In qualitative or discrete resistance a mutation (normally to a single gene) produces a race of a fungus with a high degree of resistance. Such resistant varieties also tend to show stability, persisting after the fungicide has been removed from the market.