Pollen-Mediated Movement of Herbicide Resistance Genes in Lolium rigidum

Abstract

The transfer of herbicide resistance genes by pollen is a major concern in cross-pollinated species such as annual ryegrass (Lolium rigidum). A two-year study was conducted in the greenhouse, under favorable conditions for pollination, to generate information on potential maximum cross-pollination. This maximum cross-pollination rate was 56.1%. A three-year field trial was also conducted to study the cross-pollination rates in terms of distance and orientation to an herbicide-resistant pollen source. Under field conditions, cross-pollination rates varied from 5.5% to 11.6% in plants adjacent to the pollen source and decreased with increasing distances (1.5 to 8.9% at 15 m distance and up to 4.1% at 25 m in the downwind direction). Environmental conditions influenced the cross-pollination both under greenhouse and field conditions. Data were fit to an exponential decay model to predict gene flow at increasing distances. This model predicted an average gene flow of 7.1% when the pollen donor and recipient plants were at 0 m distance from each other. Pollen-mediated gene flow declined by 50% at 16.7 m from the pollen source, yet under downwind conditions gene flow of 5.2% was predicted at 25 m, the farthest distance studied. Knowledge of cross-pollination rates will be useful for assessing the spread of herbicide resistance genes in L. rigidum and in developing appropriate strategies for its mitigation.

Dynamics of Glyphosate Resistance in Lolium perenne: Pollen-Mediated Gene Flow under Field Conditions in Argentina

“…Recently, the gene flow of herbicide-resistant Lolium rigidum was fitted to an exponential decay model at increasing distances. Under field conditions of Spain, the average crossing rate was 8.5% (±3.0%) in plants adjacent to the pollen source, and 2.9% (±1.7%) at 25 m (farthest distance studied) in the downwind direction [16]. Consistently, the present results indicate that the effective glyphosate-resistant gene flow reached trap plants distanced at ≤35 m from the source of pollen in L. perenne.…”

“…During the flowering period, four rain days (cumulative rainfall was 148 mm) were registered, and the average wind speed was 12.1 km h −1 , with the prevailing direction being from south (data from meteorological station from Chacra Experimental Integrada Barrow). Considering that air temperature and relative humidity are the two main environmental factors that affect pollen viability [29], along the pollination period, the average air temperature was 15.0 (±6.6) • C, and the relative humidity was 66% (±3%) (data from meteorological station from Chacra Experimental Integrada Barrow) and they would not be detrimental for pollen viability and longevity [16].…”

“…Under field conditions, pollen-mediated gene flow was detected in L. rigidum between herbicide-resistant and -susceptible plants spaced at different distances [13][14][15][16]. Considering that topographic properties, like different environmental conditions and pollinator variants, affect the pollen-mediated gene flow [13,16,19], these experiments contributed to knowledge about Lolium spp. pollen dispersal and potential cross-pollination in different environments.…”

“…The increased area sown with herbicide-resistant crops has determined that gene flow studies gain special attention [11,12]. Also, after the detection of herbicide-resistant weed populations, the dispersion of resistant genes through pollen and/or seeds has been addressed to predict the evolution of the resistance [13][14][15][16].…”

Vacuolar Sequestration of Paraquat Is Involved in the Resistance Mechanism in Lolium perenne L. spp. multiflorum

“…Herbicide resistance in LOLMU has been reported in several countries around the world to a variety of modes of action ( Heap, 2017 ). It has an obligate outcrossing, self-incompatible breeding system, which facilitates the dispersal of herbicide resistance traits within and among populations ( Loureiro et al, 2016 ) and, in some cases, results in the accumulation of herbicide resistance traits ( Mahmood et al, 2016 ).…”