Herbicide-resistant crop plants hold the promise of new weed control strategies that will reduce the negative impact of herbicides on the crop and the environment. 230 weed species have been reported to be resistant to one or more of 17 classes of herbicides. The response of a plant to herbicides is a heritable trait. Terms used to describe response of plants to herbicides. Tolerance is the ability of a plant population to remain uninjured at the herbicide doses normally used.
Susceptibility indicates that the plant population dies at the herbicide doses normally used.
Tolerance and susceptibility are what we expect to see when a selective herbicide is used on a mixed population of plant species that results from differential retention, penetration, translocation, or metabolism. Resistance is the ability of a formerly susceptible plant population to survive herbicide doses above those that were once used to control the original plant population. Resistance is most frequently caused by a single gene mutation that modifies the herbicide binding site on an enzyme or protein. Multiple resistance - weed populations that are resistant to two or more herbicides from different chemical groups with different modes of action. Multiples resistance is less frequent than cross resistance and is frequently attributed to differential retention, penetration, translocation, or metabolism rather than to site of action.