The Chloris genus is a C4 photosynthetic species mainly distributed in tropical and
subtropical regions. Populations of three Chloris species occurring in citrus orchards from
central Cuba, under long history glyphosate-based weed management, were studied
for glyphosate-resistant status by characterizing their herbicide resistance/tolerance
mechanisms. Morphological and molecular analyses allowed these species to be
identified as C. ciliata Sw., Chloris elata Desv., and Chloris barbata Sw. Based on the
glyphosate rate that causes 50%mortality of the treated plants, glyphosate resistance (R)
was confirmed only in C. elata, The R population was 6.1-fold more resistant compared
to the susceptible (S) population. In addition, R plants of C. elata accumulated 4.6-fold
less shikimate after glyphosate application than S plants. Meanwhile, populations of
C. barbata and C. ciliata with or without glyphosate application histories showed similar
LD50 values and shikimic acid accumulation rates, demonstrating that resistance to
glyphosate have not evolved in these species. Plants of R and S populations of C. elata
differed in 14C-glyphosate absorption and translocation. The R population exhibited
27.3-fold greater 5-enolpyruvyl shikimate-3-phosphate synthase (EPSPS) activity than
the S population due to a target site mutation corresponding to a Pro-106-Ser
substitution found in the EPSPS gene. These reports show the innate tolerance to
glyphosate of C. barbata and C. ciliata, and confirm the resistance of C. elata to this
herbicide, showing that both non-target site and target-site mechanisms are involved in
its resistance to glyphosate. This is the first case of herbicide resistance in Cuba.
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