Abstract
Various mutations altering the herbicide target site (TS), can lead to structural modifications that decrease binding efficiency and results in herbicide resistant weed. In most cases, such a mutation will be associated with ecological fitness penalty under herbicide free environmental conditions. Here we describe the effect of various mutations, endowing resistance to acetyl-CoA carboxylase (ACCase) inhibitors, on the ecological fitness penalty of Lolium rigidum populations. The TS resistant populations, MH (substitution of isoleucine 1781 to leucine) and NO (cysteine 2088 to arginine), were examined and compared to a sensitive population (AL). Grain weight (GW) characterization of individual plants from both MH and NO populations, showed that resistant individuals had significantly lower GW compared with sensitive ones. Under high temperatures, both TS resistant populations exhibited lower germination rate as compared with the sensitive (AL) population. Likewise, early vigor of plants from both TS resistant populations was significantly lower than the one measured in plants of the sensitive population. Under crop-weed intra-species competition, we found an opposite trend in the response of plants from different populations. Relatively to inter-population competition conditions, plants of MH population were less affected and presented higher reproduction abilities compared to plants from both AL and NO populations. On the basis of our results, a non-chemical approach can be taken to favor the sensitive individuals, eventually leading to a decline in resistant individuals in the population.
Highlights
Major parts of cultivated land in the world (∼70%) are occupied by cereal crop-plants such as bread wheat (Triticum aestivum), corn (Zea maize), and rice (Oryza sativa) (FAOSTAT, 2016)
Individuals from all three L. rigidum populations were analyzed for their response to herbicides from three chemical classes of acetyl-CoA carboxylase (ACCase) inhibitors: diclofop-methyl, pinoxaden, and cycloxydim
Plants from NO population did not show 50% decrease in shoot fresh weight (FW) and ED50 value could not be extracted under diclofop-methyl treatment (Figure 1D and Supplementary Table S2)
Summary
Major parts of cultivated land in the world (∼70%) are occupied by cereal crop-plants such as bread wheat (Triticum aestivum), corn (Zea maize), and rice (Oryza sativa) (FAOSTAT, 2016). Rigid ryegrass (Lolium rigidum Gaud.) is among the worldwide most noxious grass weed species infesting winter cereal-crops worldwide (Heap, 2017). Field studies in Australia have shown that L. rigidum can cause yield reductions of more than 40% (Pannell et al, 2004). Shifting Fitness-Penalty under TS Resistance control is the most cost efficient method to reduce the yield losses associated with weeds infestation. In recent years, increasing abundance of herbicide-resistant weed populations endanger food security for the ever-increasing world population. Herbicide resistance of Lolium species has been reported in various habitats; agricultural fields, orchards, vineyards, road sides, and more (Heap, 2017). L. rigidum was found to be the species that developed resistant to the highest number of different modes of action (MOA; Heap, 2017), which can be consequence of the obligate outcrossing nature of this specie (Mccraw et al, 1983)
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