A Field of SunflowersWild Sunflower:

Effects of Early Life History Stages and Competition
on Crop Gene Introgression in Wild Sunflower

Allison A. Snow , CoPI  snow.1@osu.edu
Kristin Mercer, CoPI mercer.97@osu.edu.
Patricia M. Sweeney sweeney.4@osu.edu

Jinguo Gao, Brian Maxwell

Collaborating Investigators: Dr. Helen Alexander (CoPI), Katie Sparks, Sarah Nodbyl, University of Kansas.

Despite numerous studies of crop-wild hybridization and the presence of crop alleles in wild populations, the processes that influence crop allele persistence are still unclear.  We plan to study the performance of wild, hybrid, and backcross sunflowers under different abiotic and biotic environments and simultaneously follow multi-year changes in crop-specific allele frequencies in experimental populations.  We focus on seed and seedling stages because our earlier work provides intriguing contrasts: low seed dormancy and early germination of crop-wild hybrid sunflowers could be maladaptive, reducing introgression.  However, these same traits could increase introgression if larger hybrid seedlings are more competitive than wild genotypes.  Our approaches and questions are:

A) Seedling Experiment - How do wild, hybrid, and backcrossed progeny differ in germination, time of seedling emergence, survival, and early growth rates when exposed to environmental variability?

B) Seed predation and soil disturbance Experiment – How do common natural processes affect the growth and fitness of hybrid and wild plants when grown alone and in mixture?

C) Introgression Experiment  - What are the relative contributions of early- and late-stage fitness differences between wild and hybrid genotypes to the persistence of crop-specific alleles in experimental populations grown at natural densities?  Founding populations will have different crop allele frequencies to mimic natural hybrid zones.

These diverse studies allow us to determine the minimum necessary information needed to make predictions of crop allele introgression over time. Such information is of specific use to regulators in design of field trial protocols and evaluation of the ‘exposure’ term in risk assessments of transgenic crops.


A Field of SunflowersWild Sunflower:
Gene flow from volunteer sunflowers 

Allison A. Snow , PI  snow.1@osu.edu
Patricia M. Sweeney sweeney.4@osu.edu
Mike Reagon reagon.1@osu.edu

Collaborating Investigators: Dr. Helen Alexander, University of Kansas, Dr. Calvin Pearson, Western Colorado Research Center,and  Dr. Diana Pilson, University of Nebraska 

To date, nearly all research on gene flow in sunflowers has focused on pollen-mediated gene flow and the use of male sterile plants has been suggested as a way to confine the flow of transgenes from GM germplasm.  However, male-sterile plants, necessarily, produce seed and in sunflower production areas, volunteer plants are common.  Thus, volunteer plants from the seeds of male-sterile GM sunflower could serve as a “genetic bridge” by which transgenes spread to wild or cultivated plants. 

Our research characterizes key fitness components of volunteer sunflower plants (nontransgenic) and compares seed longevity and fecundity of crop x crop (CC) and crop x wild volunteers (CW) with that of wild sunflowers.  We hypothesized that the CC seeds would 1. lack the dormancy exhibited by wild plants, but would still remain viable in the soil for more than one year, 2. not remain viable as long as wild or wild x crop volunteers, and 3. would survive and reproduce, but have lower fecundity than volunteer plants sired by wild plants.

Volunteer, offtype (morphologically different) and ‘pure’ wild sunflower seed were collected from Kansas and Nebraska.  Crop plants were hand crossed by wild plants from the collections to form WC F1 seed and by a second cultivar  to produce CC seed.  In November 2004, these seeds, as well as wild, normal volunteer, and offtype seed from the collections, were buried in Colorado, Kansas, and  Nebraska.   The following two springs, the buried seed was excavated and viability and dormancy was evaluated.  Results of the 2005 excavations revealed that all seed that possessed a crop parent, germinated the by the end of the 2005 experiment.  (In fact, most seed that had a crop parent had germinated prior our evacuation.) 2006 results confirmed these results.

Seedlings from the same sources described above were grown in field plots at Colorado  in 2005.  We collected fecundity and morphological data to compare crop volunteers of known parentage (CC and CW), normal volunteers, offtypes, and wild plants to determine the extent to which pollen from wild sunflowers allows crop volunteers to resemble wild and weedy sunflowers.  By characterizing the flowering phenology and time seed production of different types of volunteer plants, we will have a much better understanding of their potential cross-pollinate with other plants and to establish “feral” population de novo.


A Field of SunflowersEcological Impacts of Transgenic Sunflowers

Allison A. Snow , PI  snow.1@osu.edu
Mike Reagon reagon.1@osu.edu

Collaborator:  Dr. Diana Pilson, University of Nebraska, Lincoln, NE, USA

In the USA, cultivated sunflower (Helianthus annuus) is often sympatric with wild H. annuus, which is an agricultural weed that grows along roadsides and in other disturbed sites. We found that crop-to-wild gene flow was common (~5 - 40% hybrids) when wild plants occurred within <1,000 m of the crop, and crop-specific genetic markers persisted in wild populations for many generations. Crop-to-wild gene flow with other wild sunflower species is far less likely due to infertility barriers and non-overlapping ranges.

Field experiments with H. annuus demonstrated that F1 crop-wild hybrids typically produced fewer viable seeds than wild plants, but this disadvantage varied among plants, regions, and growing conditions, and diminished with further backcrossing. Thus, the F1 generation is not a strong barrier to introgression of transgenes into wild populations. Little is known about how introgressed transgenes will affect the population dynamics of wild plants, but we suspect that release from insect damage and disease pressure will sometimes enhance the survivorship, competitive ability, and lifetime seed production of wild suflowers, perhaps causing them to become more invasive. Our current research focuses on the ecological effects of insect seed predators and other pests in an effort to anticipate effects of transgenes for insect resistance in wild populations of H. annuus (transgenic sunflowers have not yet been marketed in the USA).


Radish Flower Wild Radish:
Potential for Transgene Escape from Crop to Wild Radishes

Lesley Campbell lgc@umd.edu
Allison A. Snow , PI 

Spontaneous hybridization between crops and related weed species can transfer crop genes coding for fitness-enhancing traits to wild populations, but little is known about how easily this takes place in various weed-crop complexes.  We are studying interspecific hybrids between wild and cultivated radishes (Raphanus raphanistrum x R. sativus), which often co-occur and share pollinators. We were initially interested in whether the F1 generation represents a strong barrier to subsequent introgression and we have compared the fitness of wild and wild-crop hybrids.  F1 hybrids had lower fitness than wild plants due to lower pollen fertility (x = 63% vs. 92-96%), fewer seeds per plant (x = 193 vs. 396 when grown in pots), and delayed flowering (22-40% of the hybrids never produced fruits in the field vs. 3-8% of wild plants).  Despite these disadvantages, hybrids contributed substantially to each population’s gene pool.  After three years, frequencies of white-flowered plants in the four artificial populations ranged from 0.08 – 0.22 and frequencies of crop-specific allozymes ranged from 0.10 - 0.27 demonstrating that crop genes persisted.

We are currently starting a new research project which will investigate the extent to which gene flow from crops can facilitate the rapid evolution of new forms of agricultural weeds.  Large-scale experiments will be conducted to determine fitness consequences of crop-wild hybridization in a serious agricultural weed, Raphanus raphanistrum.  In this project, three general biotypes will be considered: wild plants (R. raphanistrum), progeny of wild-crop hybrids, and progeny of cultivated radishes (R. sativus).  We refer to these biotypes as wild, hybrid, and feral, respectively.  In a natural selection experiment, replicated field populations will be grown in Michigan for three years (2002-2004), starting with the F2 generation.  We will compare the fecundity and phenotypic variability of the F2 and F5 generation of each biotype in two portions of the species’ range, Michigan and California.  Allozyme markers will be used to compare levels of heterozygosity and allelic diversity among F2 and F5 biotypes.  In an artificial selection experiment in the greenhouse, we will compare the ability of wild, hybrid, and feral biotypes to adapt to three generations of strong selection for a) early flowering, or b) large size/high fecundity.  For the key results from these experiments – data on fecundity, phenotypic variation, heterozygosity, allelic diversity, and adaptive responses to artificial selection - we hypothesize that: Hybrid > Wild > Feral.  A third experiment will compare the effects of five wild populations and five different cultivars as parental stock for hybrid and feral biotypes.  To our knowledge, this research represents the first comprehensive study of these topics in any weed-crop system.  Our results are relevant to many species in which the crop or its wild-crop progeny can potentially spawn new populations of weedy biotypes.


Oryza sativa plantWild Rice:

Estimating the genetic diversity of perennial wild rice,
Oryza rufipogon in the Mekong Delta of Vietnam

Allison A. Snow , PI  snow.1@osu.edu
Mike Reagon reagon.1@osu.edu

Collaborators:   Dr. Michael Cohen, Dr. Bui Chi Buu

Wild relatives of domesticated plants are an important source of genetic material for improving crop yields.  These resources are increasingly in demand as the need for higher yielding crop varieties continues to rise.  This is particularly true for cultivated rice, where the majority of genetic diversity present within the genus Oryza is preserved in wild species (Wang et al. 1992). Numerous agronomic traits, including resistance to insects and disease, and tolerance to salt, flooding and acid sulfate soils, have been derived from wild species (see Brar and Khush, 1995 for a review).  Modern breeding methods (including marker assisted selection and improved embryo rescue techniques) will make the genetic material in wild relatives more available.

Populations of wild rice species, especially, Oryza rufipogon, (the progenitor of wild rice) are threatened with extinction in many areas (Vaughn, 1990). Though loss of habitat is the primary cause of the extinction of wild rice populations, gene flow from the crop has been implicated in the loss of genetic diversity within O. rufipogon in Thailand (Akimoto et al., 1996) and Taiwan (Kiang et al. 1979).  A less well-understood consequence of gene flow is the loss of locally adapted genotypes.  Locally adapted genotypes are particularly valuable to crop breeders as they contain genetic material useful for breeding crop varieties suited to a particular environment (e.g. acid sulfate tolerance). 

The purpose of this study is to document the amount and structuring of genetic diversity in O. rufipogon populations within the Mekong Delta region of Vietnam.  The Mekong Delta encompasses a diversity of habitats and soil types, including intensive triple-cropped irrigated rice, acid sulfate soils, regions with seasonal infusion of saline water and deepwater or flood prone areas. O. rufipogon is currently widespread and abundant in the Delta though it faces increased rates of habitat loss due to development.  We will use microsatellites to compare genetic diversity among regions and habitat types.

Our experimental design will allow us to identify locally adapted genotypes (after Ohta, 1983), which may pinpoint areas in need of conservation.    The results of this research project will be of direct relevance to biosafety regulations for transgenic rice in the Mekong Delta.   We will be able to estimate the amount of hybridization that occurs between cultivated rice and its wild relatives and therefore be able to predict the potential for transgenes to “escape” cultivation.    Methodologies developed here will be applicable to other rice-growing areas where wild rices occur in abundance, such as Thailand, Malaysia, India and Nepal. 


Sorghum and its Wild Relatives:

Risk Assessment and Management of  Gene Flow in Sorghum in Africa

Allison A. Snow , PI  snow.1@osu.edu
Patricia M. Sweeney sweeney.4@osu.edu
Yifru Woldermariam  woldemariam.4@osu.edu

Collaborating Investigators: Tesfaye Tesso, Ethiopian Institute of Agricultural Research tesso1970@yahoo.com, Issoufrou Kapran, Institut National de la Recherche Agronomique du Niger(INRAN)BP  ikapran@yahoo.com Gurling Bothma, ARC-Roodeplaat, Pretoria, South Africa gbothma@vopi.agric.za Gebisa Ejeta, Dept. of Agronomy, Purdue University gejeta@purdue.edu,  Cecile Grenier - Dept. of Agronomy, Purdue University grenier@purdue.edu, Jeffrey F. Pedersen, USDA, ARS, 344 Keim Hall, East Campus, University of Nebraska, Lincoln  jfp@unlserve.unl.edu

Many concerns, ranging from safety and value to international trade are associated with the use of transgenic crops. While agricultural use of genetically modified (GM) maize (Zea mays L.) has become commonplace, there is still considerable concern regarding any future release of GM sorghum [Sorghum bicolor (L.) Moench]. Unlike maize, sorghum is known to cross with its weedy relatives. This has caused a general consensus among sorghum breeders and geneticists that field deployment of GM sorghum would present a higher degree of risk because of the possibility of gene flow through pollen to weeds. Transfer of any genes conferring adaptive fitness, especially herbicide resistance, to weed populations would be undesirable.

In addition, the deployment of transgenic sorghum on the African continent could pose the risk of contamination of sorghum germplasm resources. It is believed that sorghum originated in northeast Africa where it was domesticated about 3000 to 5000   years ago (Mann et al., 1983). Although extensive collections of sorghum germplasm are held by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) and the USDA, transgene flow from GM sorghum to wild and weedy relatives through pollen could pose significant risk to in situ germplasm, including landraces still relied upon by small-scale farmers in Africa.

Our goal is to determine the potential for gene flow from sorghum to wild relatives in the crop’s center of origin, examine possible risks associated with genetically modified (GM) sorghum and evaluate systems to reduce that risk.  Specifically, we are 1. determining the potential for co-occurrence and overlapping flowering times of wild and cultivated sorghum in major sorghum growing regions of Ethiopia, Niger, and South Africa and    providing current information on the distribution of wild sorghum species in these countries. 2. Quantifying the extent of crossing between modern cultivars (hybrid) and landraces with wild related sorghum types in controlled experiments. 3. Assessing levels of gene flow among populations and determining whether crop-to-wild gene flow already has affected the genetic diversity of wild populations. 4. Studying the population ecology of wild sorghum species to determine their potential to occur as weeds in agricultural and natural habitats, and predict whether specific transgenic traits are likely to exacerbate any existing weed problems and 5. Evaluating systems for reducing risk of genetic contamination within sorghum species.


Gene Flow within the
Genus Sorghum

Su Su
 Jill A. Johnston


Shattercane (Sorghum bicolor) is an annual weed that occurs throughout much of the USA.   It is a serious weed pest in both corn and sorghum fields because it geminates and matures at approximately the same time as the crops and also due to the long dormancy of its seed. Shattercane is the same species as sorghum, a particularly important crop in the semiarid tropics because of its tolerance to arid environments.  Shattercane and sorghum commonly co-occur throughout the Great Plains of North American.  The origins of shattercane are not known, though it may be a sorghum-sudangrass hybrid.  Although the strong likelihood exists that the two can hybridize, this has not been confirmed. 

Although sorghum can hybridize with johnsongrass (Sorghum halepense) a perennial weed, gene flow from sorghum to johnsongrass may be relatively uncommon. The two species have different numbers of chromosomes (20 and 40, respectively) and only about 10% of cross-pollinations produce seed.  Although gene flow from sorghum to johnsongrass has been studied, little is known about the role of shattercane in facilitating gene flow in this crop-weed complex. We hypothesize that a more common route for gene flow is from grain sorghum to shattercane. If hybridization occurs between shattercane and sorghum, shattercane could be “genetic bridge” from the crop to johnsongrass (Figure 1).


 In order to test our hypothesis, we will use molecular markers to study the genetic variation within and among shattercane populations and their relationship with the geographic distribution of sorghum. We expect shattercane populations near sorghum fields to be more similar to sorghum than more distant shattercane populations. We will also study the hybridization rate and the fitness of shattercane-sorghum hybrids under field conditions. 


phragmitespiccrop.JPG (204648 bytes)Native and Invasive Plants:
Invasive genotypes of cattails (Typha X glauca) and
common reed (Phragmites australis) in coastal wetlands
of the Great Lakes: genetic and ecological studies

Allison A. Snow , PI  snow.1@osu.edu
Patricia M. Sweeney sweeney.4@osu.edu
Jinguo Gao  gao.95@osu.edu
Amy Campbell  acampbell001@gmail.com

roblems caused by invasive plants in coastal wetlands of the Great Lakes are ubiquitous and well known.  Purple loosestrife (Lythrum salicaria), common reed (Phragmites australis), narrow-leaf cattail (T. angustifolia), and hybrid cattail (Typha X glauca) often have undesirable effects on habitat quality and local biodiversity.  The goals of our research are to use DNA markers to identify and study hybrid and non-native genotypes of cattail and common reed, respectively.  We are currently investigating the spread and invasiveness of hybrid cattail populations, known as Typha X glauca, relative to their parent taxa in Ohio and Michigan.  T. X glauca often represent first-generation crosses between the native T. latifolia and introduced T. angustifolia.   Many investigators assume that T. X glauca is more invasive than its parents, but rigorous studies of the hybrid status and relative invasiveness of these populations are lacking.  Therefore, we propose to survey coastal wetlands in Ohio and Michigan to: 1) document the distribution of hybrid cattail populations using DNA markers, 2) determine the extent to which these populations reproduce by seed, 3) test for backcrossing with the parent species, and 4) test the hypothesis that hybrids have faster vegetative growth rates and greater tolerance of environmental stress than their parent taxa using mesocosm experiments.

Related studies will be carried out to study the spread and ecology of native versus introduced clones of Phragmites australis.   Introduced clones along Lake Erie often produce viable seeds (A. Campbell, pers. comm.), contrary to previous reports.  These clones appear to be taller and more competitive than native genotypes.  In some cases, introduced Phragmites can be identified using morphological traits, but recent studies show that further efforts are needed to verify the utility of these morphological traits for coastal populations in Ohio and Michigan  Phragmites populations are known to differ greatly among regions, so it is useful to study the genetics and invasiveness of native and introduced genotypes on the coasts of Lake Erie, Lake Huron, and Lake Michigan, as proposed here.



Allison A. Snow , PI  snow.1@osu.edu
Patricia M. Sweeney sweeney.4@osu.edu
Jinguo Gao  gao.95@osu.edu



Collaborating Investigators:  Deborah E. Goldberg degold@umich.edu ,  Radka Wildova  radka@umich.edu   Department of Ecology and Evolution, University of Michigan, Ann Arbor, MI, 

Wetland habitats are highly vulnerable to invasive species that displace native vegetation and modify ecological processes.  Cattails are a dominant feature of many wetlands, and land-use managers are concerned about the rapid rates at which populations of T. angustifolia and T. x glauca have spread during the past few decades.  Typha x glauca appears to be a sterile, first generation (F1) hybrid between introduced T. angustifolia and native T. latifolia.  Anecdotal evidence suggests that T. x glauca is even more invasive than T. angustifolia, but this has not been tested empirically.  Our research will confirm the hybrid status of T. x glauca using molecular markers (RAPDs) and  will compare the hybrid directly with its parent species.  Reliable information about the relative invasiveness of these taxa is needed to help improve strategies for protecting native wetlands.  In a broader context, this research provides a rigorous test of the hypothesis that hybrids can be more invasive that their parent taxa. 

We plan to address the following general questions: Do opportunities for ongoing hybridization vary within or among regions due to differences in flowering times of T. angustifolia and T. latifolia? Are most T. x glauca individuals F1 hybrids or are advanced-generation hybrids also present? Does the hybrid occur over a wider range of ecological habitats than its parent species?  Is the hybrid a more aggressive invader of wetlands than its parent species and, if so, is this because of heterosis and/or greater tolerance of ecological stresses?

Our approach includes molecular marker surveys, field surveys, field experiments, and outdoor pot experiments with clonal plants.  Studies of the genetic origins and potential for ongoing hybridization will include sites in Michigan, Ohio, and Wisconsin, while ecological field studies will focus on Typha populations in northern Michigan.  We hypothesize that F1 clones have faster intrinsic growth rates (due to heterosis) and tolerate a wider range of environmental conditions than their parent species, making them more invasive.  We also suspect that advanced-generation hybrids occur, allowing cryptic gene flow from T. latifolia to T. angustifolia.  Our findings will be relevant to wetlands conservation and general theory about the evolution of invasiveness in hybrid zones.


Valeriana ciliataGenetic Variation in Prairie Valerian, 
an Endangered Species

Amy Faivre



As part of my post-doctoral research at Ohio State University, I am examining genetic variation in populations of prairie valerian (Valeriana ciliata).  Valeriana ciliata is threatened or endangered in each of the mid-western states where it occurs.  This species is endemic to prairie fens.  These limestone-rich, cold water wetlands represent glacial remnant habitats.  Prairie fens have all but disappeared in Ohio due to human development and a changing, warming climate.  In a project funded by the Ohio Department of Natural Resources (ODNR), I used allozyme electrophoresis to compare genetic variation in the two remaining, small Ohio populations to that of equally small and large populations of V. ciliata in Michigan.  The populations in Michigan represent the middle of this species range.  I am currently extracting DNA from prairie valerian samples and will use molecular markers to determine if they show the same pattern as the allozyme results.  I am contributing my data to other data gathered by ODNR and the Michigan Chapter of the Nature Conservancy to consider mechanisms for the restoration of this species.


Big Bluestem and Prairie Cone Flowers Native Plant Conservation 
& Invasive Species

Sarena M. Selbo



My research interests include the conservation of native plants and rare plant communities. I also have a great interest in the ecology and reproductive biology of invasive species. Past research endeavors have included studying the breeding system of leafy spurge and the hybridization between native and non-native cattail species.

My current research is a comparative study between native Ohio prairies and the Conservation Reserve Program (CRP) prairies in Ohio. The CRP program is operated under the USDA to encourage farmers to set land aside for conservation purposes. Much of the CRP land in Ohio is planted in grasses, some of which are native (i.e. big bluestem, Indian grass, little bluestem and switchgrass). Quite frequently the seed source for the CRP prairies is from outside of Ohio and as far away as Kansas. The conservation applications of this study dictate that non-regional seed sources have the potential to swamp out native genotypes and degrade the genetic composition of native prairies.

My study focuses on the genetic diversity of native Ohio prairies versus CRP prairies in northwest and central Ohio. RAPD (random amplified polymorphic DNA) markers will be used to ascertain genetic difference between the two prairie types. Examination of phenology (flowering times) and any measurable differences in morphology between the native and CRP prairie species will also be compared. By conducting this study, I hope to gain a greater understanding of the genetic diversity, the potential for crossing and basic fitness differences between the two prairie types in Ohio.


Last Updated:  05/13/2008