What makes Weed Populations more or less susceptible to Resistance ?
A lack of fitness or decreased competitive ability of resistant weeds is frequently mentioned, as compared to susceptible populations, as yet another factor that delays the development of herbicide resistance. When a gene (the one that confers resistance) substitutes another (the one responsible for the susceptibility) in a population, the new individual is commonly less fit because it has some physiological disadvantage in relation to the original one (Holt, 1989). These disadvantages keep the new gene in a very low frequency within the population. Therefore, it is logical to conclude that if the resistant individuals were more fit, in the absence of selective pressure (herbicide), they would be the dominant type within the population, and the herbicide would never have effectively controlled the weed species in the first place. Thus fitness could be defined as the reproductive success or the proportion of genes that an individual leaves in the genetic pool of a population. Its two ma
