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.
Highlights
A native of the Mediterranean region, Lolium rigidum Gaud. is the most important ryegrass species in Spain where it is commonly found as a major weed in winter cereal crops
Our study provides a data set on cross-pollination rates among L. rigidum biotypes under greenhouse and semi-arid field conditions
There were great differences between the two years of experiment, with average cross-pollination rates that were three times higher in 2008 than in 2007 (44% vs 14%). These differences could be attributed to environmental conditions
Summary
A native of the Mediterranean region, Lolium rigidum Gaud. (annual or rigid ryegrass) is the most important ryegrass species in Spain where it is commonly found as a major weed in winter cereal crops. (annual or rigid ryegrass) is the most important ryegrass species in Spain where it is commonly found as a major weed in winter cereal crops It is widespread across other grain-growing regions in Southern Europe, in Southern and Western Australia, in different states of the USA, and in some areas of South Africa, Chile and Argentina. It has been controlled by pre- or post-emergence herbicides. The excellent efficacy of these herbicides encouraged their widespread repeated use in several countries This selection process led L. rigidum to become a major problem because of its ability to evolve resistance to the several herbicides used for its control [1,2]. Surveys conducted in Australia [4,5,6], USA [7] and Spain [8,9] have revealed widespread occurrence of herbicide-resistant Lolium species, with biotypes resistant to almost all herbicides available for PLOS ONE | DOI:10.1371/journal.pone.0157892 June 23, 2016
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