Adaptive value of single and double spontaneous EPSPS glyphosate resistance mutations in the agroecosystem

VILA AIUB, MM

Congreso; Global Herbicide Resistance Challenge 2017; 2017

A novel double point mutation (TIPS) in the EPSPS gene endowing glyphosateresistance has recently evolved in Eleusine indica in which individuals with a singlepoint mutation (P106S) also coexist. Under controlled and field conditions both the plantresistance benefit and cost associated with the TIPS (homozygous (RR) vsheterozygous (Rr)) and P106S EPSPS variants were assessed. The P106S mutationgives modest resistance (50% mortality) under glyphosate field dose and survivorsshow a significant reduction in vegetative and reproductive growth. The RR TIPSvariant, however, endows high level glyphosate resistance (no mortality) and nosignificant impact on reproductive growth is observed. An even higher resistance fitnessbenefit is associated with the compound heterozygous Rr TIPS plants. Although bothRR and Rr TIPS plants show no plant mortality under glyphosate treatment, vegetativeand reproductive growth is significantly higher in Rr than in RR TIPS plants. Asignificant resistance fitness cost associated with the homozygous TIPS but not thehomozygous P106S EPSPS variant was identified. The resistance cost associated withthe TIPS mutation escalated to 85% (seed number) in plants under resourcecompetition. The resistance cost associated with the homozygous RR TIPS mutation isnot expressed in plants with the Rr TIPS mutation denoting the recessive nature of thecost associated with the TIPS allele. While endowing a high resistance fitness benefitwhen exposed to glyphosate, the homozygous RR TIPS resistance alleles incur asignificantly high resistance fitness cost in glyphosate-free environments. Whereas thehomozygous P106S alleles incur no resistance cost but provide a low/moderate fitnessbenefit when glyphosate-challenged, the compound heterozygous Rr TIPS allelesencode for the most favourable glyphosate resistance trait in current cropping systems.The biochemical and physiological bases of the associated resistance cost and benefitin TIPS and P106S EPSPS gene variants are discussed.