The evolutionary ecology of resistance to herbicides: insights into the role of plant fitness

VILA AIUB, MM; BUSI, R.; POWLES, SB

Conferencia; Global Herbicide Resistance Challenge Conference; 2013

Australian Herbicide Resistance Initiative

An evolutionary and ecological theoretical framework for improving the understanding of herbicide resistance in plants is formulated. Considering the evolutionary ecology of herbicide resistance in agro-ecosystems requires the assessment of plant fitness (W) of herbicide resistant (R) and susceptible (S) genotypes in the presence (WR(h), WS(h)) and absence (WR, WS) of herbicide selection. Two conditions must be met for resistance to evolve: a herbicide resistance trait must endow a fitness (W) advantage over the wild type under herbicide (h) selection (i.e. resistance benefit, RB), and this advantage should exceed any fitness or ecological disadvantage associated with the resistance trait in the absence of herbicide selection (i.e. resistance cost, RC). Provided a positive net fitness difference (RB>RC), then rapid herbicide resistance evolution is possible, especially if the resistance traits endow a significant fitness benefit under herbicide selection and show no or negligible resistance cost in the absence of herbicide selection. The fitness difference (RB>RC) informs about the occurrence probability of resistance evolution and the magnitude of the difference has been shown to be a function of the precise selected resistance mechanism, gene(s) or allelic substitution. Within these favourable conditions for resistance selection (RB > RC), there will be fitness combinations for the R and S genotypes that will maximize the selection intensity (SI) and subsequent rate of herbicide resistance evolution. Estimation of fitness of a herbicide resistant (R) genotype under herbicide selection (WR(h)) is usually expressed as relative to the fitness in the herbicide free environment (WR). This involves the quantification of resistance decay (RD), a useful parameter for ranking the efficiency (i.e. weak vs. strong) of resistance alleles to protect the plant from damage exerted by a particular herbicide and dose. Resistance benefit (RB), cost (RC) and decay (RD) are different aspects of plant fitness all required for a proper estimation of selection intensity (SI) and dynamics of herbicide resistance alleles in agroecosystems.