Abstract
Understanding the fate of heterogenous herbicide resistant weed populations in response to management practices can help towards overcoming the resistance issues. We selected one pair of susceptible (S) and resistant (R) phenotypes (2B21-R vs 2B21-S and 2B37-R vs 2B37-S) separately from two glyphosate resistant heterogeneous populations (2B21 and 2B37) of Echinochloa colona and their fate and adaptive plasticity were evaluated after glyphosate application. Our study revealed the glyphosate concentration required to cause a 50% plant mortality (LD50) was 1187, 200, 3064, and 192 g a. e. ha−1 for the four phenotypes 2B21-R, 2B21-S, 2B37-R, and 2B37-S respectively. Both S phenotypes accumulated more biomass than the R phenotypes at the lower application rates (34 and 67.5 g a. e. ha−1) of glyphosate. However, the R phenotypes generally produced more biomass at rates of glyphosate higher than 100 g a. e. ha−1 throughout the growth period. Plants from the R phenotypes of 2B21 and 2B37 generated 32% and 38% fewer spikes plant−1 than their respective S counterparts in the absence of glyphosate respectively. The spike and seed numbers plant-1 significantly higher in R than S phenotypes at increased rates of glyphosate and these relationships were significant. Our research suggests that glyphosate-resistant E. colona plants will be less fit than susceptible plants (from the same population) in the absence of glyphosate. But in the presence of glyphosate, the R plants may eventually dominate in the field. The use of glyphosate is widespread in field, would favour the selection towards resistant individuals.
Highlights
Understanding the fate of heterogenous herbicide resistant weed populations in response to management practices can help towards overcoming the resistance issues
It is believed that overreliance on herbicides, especially those belonging to the same chemical class or site of action is a major contributor of resistance seelction[12]
It is important to evaluate R and S phenotype individuals from the same p opulation[1]. In this experiment we used paired R and S lines of Echinochloa colona selected from the same seed source collected from the same field to determine whether there were any fitness costs or gains associated with glyphosate resistance through estimation of their fate after glyphosate application
Summary
Understanding the fate of heterogenous herbicide resistant weed populations in response to management practices can help towards overcoming the resistance issues. This system often exerts strong selection pressure for resistance in weeds[1,2,3], traits that is an inherited ability of a weed plant to survive an application of herbicide at its labelled use r ate[4,5] In this evolutionary process, both survival and reproduction of individuals with resistance alleles in a population are enriched in the presence of the h erbicide[6]. It is important to evaluate R and S phenotype individuals from the same p opulation[1] In this experiment we used paired R and S lines of Echinochloa colona (awnless barnyard grass) selected from the same seed source collected from the same field to determine whether there were any fitness costs or gains associated with glyphosate resistance through estimation of their fate after glyphosate application.
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