Of the many potential targets of domestication for a sustainable perennial oilseed in Minnesota, the perennial prairie composite, Silphium integrifolium, stands out for its drought tolerance, large seed size relative to other native prairie plants, and generally agronomically favorable morphology (Van Tassel & DeHaan, 2013). We aim to use modern genome-empowered breeding methods to rapidly domesticate S. integrifolium to serve as a sustainable, perennial oilseed crop for the Midwest. This work represents an interdisciplinary collaboration between research groups that focus on plant breeding, natural variation, agronomy, and food science.
In addition to obtaining water from depths of soil via a distinctive deep root system, silphium has agronomically desirable traits including erect stems, relatively large seeds, and high competitiveness with annual weeds. (Van Tassel & DeHaan, 2013). Subsequent analysis has revealed seed oil composition comparable to traditional sunflower (Hulke, unpublished data, Kowalski & Wiercinski, 2004). Silphium could serve as a component of a perennial agricultural system and provide other ecosystem services including supporting pollinators and other wildlife (Fiedler and Landis, 2007a, Fiedler and Landis, 2007b). Because these systems would have a perennial component, they have the potential to deliver an economically valuable product and important ecosystem services that will protect Minnesota’s natural resources. Silphium incorporated into a polyculture system could mimic the natural mixed prairies where wild silphium is found, and provide further ecosystem benefits.
The traditional route taken to develop perennial agronomic crops has been to introduce perenniality into existing crop species through hybridization with wild perennial relatives. However, because perenniality is often a complex trait, involving a number of physiological factors, we believe that our approach- identifying a perennial wild plant and improving agronomic qualities through breeding will be more effective.
Our approach is to domesticate this species as quickly as possible given the resources available. This requires tackling several genetics/genomics, agronomic, and plant breeding approaches in parallel.
An important early investment is in selective breeding targeted at traits that make a species easier to work with. While high yields are our ultimate breeding objective, our ability to make progress on yield will be improved for many years by initial attention to traits that make wild plants expensive (especially in terms of labor and time) to breed. Improvements resulting from selection will allow breeders to accelerate selections cycles and establish new plots by directly seeding untreated seed. Some of the traits being examined include selecting for earlier flowering time and reducing the amount of dormancy necessary for germination. In parallel with traditional selection for these traits, we will exploit genomics tools as they become available to employ marker-assisted breeding and genomic selection to improve other traits including seed yield, oil composition, harvestability, and disease resistance (Lorenz et al. 2011).
Silphium breeding program at the University of Minnesota
Recent advances in sequencing technology and genomics, including the identification of genomic regions associated with desirable traits (e.g. yield and developmental time) and traits involved in local adaptation (e.g. cold environments) could greatly accelerate genetic improvement of a wild species by enabling marker assisted selection (see breeding, below). However making the most of these advances requires substantial effort in generating relevant genomic and genetic resources, and characterizing genomic diversity across the ranges of Silphium species in the primary and secondary gene pool of S. integrifolium. Thus our early priorities include developing an integrated genetic-physical map and a reference genome for S. integrifolium, and to use these resources to identify the genetic basis of targeted traits traits while maintaining genetic diversity in our novel domesticate, and to identify locally adapted genetic variants from across the range of S. integrifolium and its close relatives to ensure that the product of domestication is well suited to the climate conditions of the northern midwest prairie.
At the other end of the agronomic spectrum, we must develop recommendations for farmers since wild perennial species have never been used as oilseeds. This work has been initiated and includes three major experiments. First, looking at optimum nitrogen fertilizer application rates for seed production. Optimum nitrogen application rates have been determined for the production of S. perfoliatum forage production, and will be determined for S. integrifolium seed production (Gansberger et al 2015). Next, the ideal planting densities that will increase yields of S. integrifolium will be determined.
Last, in an attempt to determine the optimum seeding date for the plant, a once-monthly planting of the seeds from fall to spring has been undertaken. A component of this seeding date experiment is that seeds that overwinter would flower during the next year instead of needing a full year of growth to flower the next year. This decreases the amount of time needed to collect seed from initial planting. Silphium species have been highly ranked among native flowering plants for supporting native pollinators and other beneficial species (Fiedler and Landis, 2007a, Fiedler and Landis, 2007b). Thus another major goal of our work is to design silphium cropping systems that provide an attractive balance of ecosystem services and oilseed production.
Crop domestication by the ancients took generations, however, using modern breeding tools, it is possible have more rapid progress. Knowledge gained about the domestication process could be used to harness the potential of even more native Minnesota species, and help increase the diversity of crops grown on the landscape. We must also invest in research that increases the consumer demand for silphium. However, farmers will be reluctant to plant the crop if there is not a strong market for these crops, and this market pull cannot be established unless the crop is developed for food use. Diverse collections of S integrifolium and related species as well as breeding populations developed through this project will be screened for chemical characteristics, storage stability, physiological/nutritional benefits, sensory/flavor quality, and food applications. This research will benefit all Minnesotans by providing a new crop with potential use on landscapes with the goal of conserving environmental resources and providing wildlife habitat.
Yaniv Brandvain, Assistant Professor, Department of Plant Biology
Kevin Dorn, Post-Doctoral Research Associate, Kansas State University
Shawn Goggins, Research Assistant, Department of Plant Biology
Pam Ismail, Associate Professor, Department of Food Science and Nutrition
Gregg Johnson, Associate Professor, Department of Agronomy and Plant Genetics
Devin Peterson, Professor, Department of Food Science and Nutrition
John Hill Price, Research Assistant, Department of Agronomy and Plant Genetics
Sydney Schiffner, Research Assistant, Department of Agronomy and Plant Genetics
Tonya Schoenfuss, Associate Professor, Department of Food Science and Nutrition
Craig Sheaffer, Professor, Department of Agronomy and Plant Genetics
Kevin Smith, Professor, Department of Agronomy and Plant Genetics
Don Wyse, Professor, Department of Agronomy and Plant Genetics
David van Tassel, The Land Institute, Salina KS