Evidence for an ecological cost of enhanced herbicide metabolism in Lolium rigidum

VILA AIUB MM; NEVE P; POWLES SB

JOURNAL OF ECOLOGY (PRINT)

WILEY-BLACKWELL PUBLISHING, INC

Año: 2009 vol. 97 p. 772 - 780

0022-0477

1.In some cases, evaluation of resource competitive interactions between herbicide resistant vs.susceptible weed ecotypes provides evidence for the expression of fitness costs associated withevolved herbicide-resistant gene traits. Such fitness costs impact in the ecology and evolutionarytrajectory of resistant populations.2.Neighbourhood experiments were performed to quantify competitive effects and responsesbetween herbicide-susceptible (S) and resistant (R)Lolium rigidum individuals in which resistance is due to enhanced herbicide metabolism mediated by cytochrome P450.3. In two-way competitive interactions between the S and R phenotypes, individuals of theS phenotype were the stronger effect competitors on both a per capita and per unit-size basis.The S phenotype also exhibited a stronger competitive response to wheat plants than did the Rphenotype, displaying significantly greater (30%) above-ground biomass at the vegetative stage.When subjected to competition from wheat, R individuals produced significantly fewer reproductive tillers and allocated fewer resources to reproductive traits than individuals of the S phenotype.4.The role of potential mechanisms underlying this resistance cost driven by traits such as plantsize and tolerance to low resource availability, as well as the evolutionary implications of the results are discussed.5.Synthesis: Evolved herbicide resistance due to enhanced-herbicide metabolism mediated bycytochrome-P450 in L. rigidum has been shown to be accompanied with an impaired ability tocompete for resources. These results are consistent with the resource-based theory that predicts a negative trade-off between growth and plant defence.