The role of plant size in pesticide selection intensity and resistance evolution

VILA AIUB, MM; GUNDEL, P.E.; ROMERO, I; DEVOTO-GALLARDO, S; POWLES, SB

Conferencia; Global Herbicide Resistance Challenge Conference; 2013

Survival and growth of herbicide resistant (R) and susceptible (S) Sorghum halepense populations to glyphosate selection at different plant sizes (i.e. germinating seeds, seedlings, young and adult plants) was evaluated. Glyphosate resistance was evident at all plant stages. More glyphosate was required to have the same impact on fitness components of R and S individuals under increments of plant size. However, glyphosate R individuals exhibited higher survival rates and growth in response to glyphosate with increments in plant size. Under coexistence of similar-sized R and S individuals, selection intensity increased with higher herbicide doses and was higher at the seedling and young stage of both R and S plants. The same outcome was observed when young R plants coexisted with adult S plants. Only when R seedlings coexisted with larger S plants (young or adult) no selective advantage for resistance was observed. Knowledge of the size class structure in perennial populations enables a better prediction and understanding of selection intensity and evolutionary dynamics of resistance traits. Decisions taken in the management of herbicide resistance in terms of selection timing and doses of herbicides can provide contrasting results depending on the plant size distribution and consequent attained fitness traits of populations.