The success of sessile organisms has largely been linked to their ability to respond to biotic and abiotic shifts in their environment. As such, many plants have evolved trichomes, or hair-like epidermal appendages, to constantly interact with environmental cues. While research has shown that trichomes can provide defense against herbivory/ pathogen attacks, protect against UV light, regulate temperature, and prevent water loss, recent theories suggest that trichomes may serve a more expansive role for plants interacting in agricultural ecosystems. These systems can introduce novel conditions via herbicide exposure to non-crop plant populations, which has been linked to increased rates of herbicide resistance. Previous work has identified herbicide resistance mechanisms as target site resistance, involving modifications of target proteins, or non-target site resistance, involving the reduction in the amount of herbicide that reaches target proteins, yet our understanding is currently based on the knowledge of biochemical mechanisms of resistance with limited understanding of barrier/phenotypic mechanisms of resistance. Here, we explore the potential that differential trichome traits can contribute as external forms of non-target site resistance.
In a joint growth chamber – field experiment, we investigate the impact of differential trichome structures, lengths, densities, and evenness on herbicide resistance with the common weed velvetleaf (Abutilon theophrasti) as the focal species. Our findings reveal a significantly positive genetic correlation between single trichomes and herbicide resistance in the growth chamber. However, in the field this result is reversed, and we detect a significantly negative correlation between single trichomes and herbicide resistance but a significantly positive correlation between branched trichomes and herbicide resistance. Further, we identified negative selection acting upon single trichomes and positive selection acting upon branched trichomes. Due to the highly negative correlation between these two trichome traits, our results suggest they are likely developmentally linked. Overall, if these findings are to be applied more broadly, it indicates trichome relationships with herbicide resistance are environmentally dependent. More work is needed to understand the specific roles of trichome traits and due to the multi-functional nature of trichomes, shifts in trichome structure may alter community dynamics found at the agro-ecological interface.