Weedy plant species can develop herbicide resistance through different
mechanism such as gene flow of herbicide resistance, transgenes from crops
into compatible weedy species or by natural evolution. Previous studies
suggest that sub-lethal levels of the herbicide glyphosate can alter the
pattern of gene flow between glyphosate resistant canola (Brassica napus)
and other glyphosate-sensitive varieties of Brassica.

Sub-lethal doses of herbicides glyphosate and glufosinate were utilized to
treat Brassica crop and weed species. Phenological and developmental changes
were recorded after treatment. Several vegetative and reproductive traits of
these plants were also evaluated under greenhouse conditions. Exposure of
Brassica species to sub-lethal dose of herbicides resulted in altering
flowering phenology. Flowering was significantly delayed and male fertility
was suppressed in all sensitive varieties. Higher, but still sub-lethal,
levels of herbicide typically contributed to an increase in the magnitude of
phenotypic changes.

Implications of altering flowering phenology would include very different
pollination patterns between species as well as an altered pattern of gene
flow which can prevent transgene escape to weedy relatives. However, there
is also the potential for increased glyphosate resistance through natural
evolution in weedy communities exposed to sub-lethal glyphosate.

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