Dana Lauenroth's scientific contributions

The recurrent exposure to herbicides in agricultural landscapes forces weeds to adapt in a race against extinction. What role newly arising mutations and pre-existing variation play in this evolution of herbicide resistance is critical for developing management strategies. Here, we present a model of rapid adaptation in response to strong selection, capturing complex life cycles of sexual and asexual reproduction and dormancy in a perennial weed. Using a multitype Galton-Watson process, we derive the probability of herbicide resistance evolution and the waiting time distribution until resistant plants appear in the field. We analyse the effect of seed bank dynamics and details of the reproductive system in defining the probability and timing of resistance adaptation in Sorghum halepense. Further, we investigate key factors determining the primary source of adaptive variation. We find that even small fitness costs associated with resistance reduce adaptation from standing genetic variation. For herbicide resistance inherited in a (incompletely) dominant fashion, self-pollination also diminishes standing variation for herbicide resistance by increasing the homozygosity. Our study highlights the importance of seed banks for weeds' adaptive potential, preserving genetic information of forgone selection and prolonging the period in which the population can adapt.

Herbicide-resistant weeds pose a substantial threat to global food security. Perennial weed species are particularly troublesome. Such perennials as Sorghum halepense spread quickly and are difficult to manage due to their ability to reproduce sexually via seeds and asexually through rhizomes. Our theoretical study of S. halepense incorporates this complex life cycle with control measures of herbicide application and tillage. Rooted in the biology and experimental data of S. halepense, our population-based model predicts population dynamics and target-site resistance evolution in this perennial weed. We found that the resistance cost determines the standing genetic variation for herbicide resistance. The sexual phase of the life cycle, including self-pollination and seed bank dynamics, contributes substantially to the persistence and rapid adaptation of S. halepense. While self-pollination accelerates target-site resistance evolution, seed banks considerably increase the probability of escape from control strategies and maintain genetic variation. Combining tillage and herbicide application effectively reduces weed densities and the risk of control failure without delaying resistance adaptation. We also show how mixtures of different herbicide classes are superior to rotations and mono-treatment in controlling perennial weeds and resistance evolution. Thus, by integrating experimental data and agronomic views, our theoretical study synergistically contributes to understanding and tackling the global threat to food security from resistant weeds.

Perennial weed species like Sorghum halepense are a bane of agriculture and lead to significant economic losses. Such weeds can spread quickly and are particularly hard to control due to their ability to reproduce sexually via seeds and asexually through rhizomes. The growing problem of herbicide resistance imposes an additional major challenge on the weed management. Our theoretical study of Sorghum halepense incorporates the complete complex life cycle along with control measures of herbicide application and tillage. We evaluate the extent of control that the different strategies provide and the evolution of herbicide resistance. Our analysis indicates that the natural frequency of target-site resistance mainly depends on the resistance cost and less on its dominance. The sexual phase of the life cycle, including self-pollination and seed bank dynamics, contributes substantially to the persistence and rapid adaptation of the weed. For example, the seed bank significantly increases the probability of escape from control while maintaining genetic variation. We also extend our analysis to study herbicide mixtures, rotations and treatment combinations and how they contribute to reducing control failure. Our model is rooted in observational and experimental data on Sorghum halepense. Still, the general methodology developed herein is extendable to other perennial weeds comprising a complex life cycle. This approach shows how an integrated interdisciplinary view can synergistically contribute to understanding and tackling the global threat to food production presented by resistant weeds.