| | Smooth cordgrass tolerates a wide range of salinity from slightly brackish to seawater. (Photo by Prasanta K. Subudhi) |
| | | California bulwhip, also known as California bulrush, tolerates deeper flooding than most species used in coastal restoration projects. (Photo by Prasanta K. Subudhi) |
| | | Sea oats prefer a high dune environment, and most East Coast lines are not well-adapted to the low profile sand dunes characteristic of the Louisiana coast. (Photo by Prasanta K. Subudhi) |
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Stephen A. Harrison, Niranjan Baisakh, Michael D. Materne, Carrie Knott, Prasanta K. Subudhi and Herry S. Utomo
The application of proven plant breeding methods to enhance the usefulness of native plants for coastal reclamation has tremendous potential. The LSU AgCenter has put together a multi-disciplinary team of plant breeders, geneticists and ecologists to determine the potential of native coastal plants for reclamation activities. Each plant species has distinctive characteristics for adaptation and survival in coastal environments, but most also have traits that limit their widespread use in conservation and preservation activities. The first step is to determine genetic variability and identify traits within each of the candidate species that might be enhanced. Proven plant breeding and genetic methods are applied to overcome such limitations as poor seed set, reduced vigor, slow growth or lack of salt tolerance.
The LSU AgCenter Coastal Plant Program, in cooperation with the Natural Resources Conservation Service, has jointly released several varieties for vegetative and wildlife restoration of barrier islands, saline and brackish marshes. These varieties are widely used for contract restoration by government and private agencies and are the basis of a developing Louisiana wetlands nursery industry. Variety and population development activities are well under way for smooth cordgrass, sea oats and bulwhip. Genetic improvement activities have been expanded to include additional species important to Louisiana’s coastal environments, and a full-time plant breeder was hired in April 2007 to direct variety development activities for coastal plants.
Developing Spartina Varieties
Smooth cordgrass (Spartina alterniflora) has received the most research attention because it is the predominant marsh grass and tolerates a wide range of salinity from slightly brackish to seawater. A single plant grows to a clump of several feet in diameter during a summer, and it thrives in coastal marshes and intertidal regions along the Gulf Coast. The dense canopy of smooth cordgrass provides a significant buffer against wave energy. It controls erosion, traps suspended sediments and produces significant amounts of organic matter. It grows parallel to the shore in water up to 18 inches deep and in clumps on mud flats.
The majority of restoration contracts specify that the variety Vermilion should be used since it is the only released variety along the Gulf Coast. The widespread use of Vermilion is a cause for concern because of genetic vulnerability. Restored areas planted exclusively to Vermilion lack the ability to buffer against changes in the environment or insect and disease pests. Vermilion is not a particularly good seed producer and, therefore, does not lend itself to large-scale seed harvest and planting.
An initial collection of seed was harvested from 126 sites across the Gulf Coast. These were planted at several locations in south Louisiana and evaluated for vegetative vigor, spread, pest resistance, adaptation and seed production. They were evaluated over a number of years and locations. Thirteen of these have been chosen as candidates for release as vegetative varieties. These selections have excellent vegetative growth and are good seed producers. They are diverse in geographic origin and have been shown to be genetically diverse using molecular marker technology. The release of new smooth cordgrass varieties is significant because it gives restoration practitioners the ability to plant diverse populations that are proven performers. An excellent strategy for utilization of these lines will be to transplant them in clusters dispersed throughout large open mudflats. The clusters should cross-pollinate, produce lots of seed, and reseed the open areas with a superior and diverse population within a short time.
The superior smooth cordgrass lines can be planted in a randomized manner within flooded rice fields for seed production, which may spawn a seed-based restoration industry. The resulting seed harvested from these ponds can be flown across large areas of the marsh to produce a genetically diverse population of vigorously growing plants. Seed production ponds can be re-established from foundation plants of these elite lines in a prescribed manner to ensure quality and purity.
Other Coastal Plant Species
California bulwhip (Schoenoplectus californicus), also known as California bulrush, tolerates deeper flooding than most species used in coastal restoration projects. It has an extensive network of rhizomes and forms dense colonies. It traps sediment effectively, reduces wave energy and provides better conditions for the establishment of other vegetation along the shoreline. The potential for use of California bulrush is limited by its low salt tolerance. California bulrush with greater salt tolerance would have an expanded range and will be useful in brackish wetland preservation and restoration efforts. Preliminary greenhouse research identified eight native bulwhip lines with improved salt tolerance, which will be used to initiate a genetic improvement program to develop even more tolerant lines. Twenty genotypes of California bulrush are being evaluated in coastal environments for salt tolerance and vegetative vigor. These include nine elite lines in freshwater from a previous trial, eight lines selected as salt-tolerant under greenhouse conditions, one line selected as an intermediate, one line selected as a poor performer and the variety Restorer.
An additional 756 regenerated plants of California bulrush derived from cells selected for improved salt-tolerant levels were grown under flooded conditions and continuously exposed to salt concentrations of zero, 6, 12 and 18 parts per thousand for nine months. Lines selected for salt tolerance in the greenhouse will be advanced to marsh site testing. Selected lines will be increased for further field testing. Superior lines for vegetative growth and salt tolerance will be released as varieties for use in coastal wetland restoration activities and will form the foundation of a breeding and genetic improvement program.
Sea oats (Uniola paniculata) are dune-loving plants with extensive root systems that trap sand and stabilize sand dunes. Sea oats prefer a high dune environment, and most East Coast lines are not well-adapted to the low profile sand dunes characteristic of the Louisiana coast. Production of sea oats plants in large numbers is a challenge for coastal restoration managers because of poor seed set, poor germination and seed dormancy. Sea oats are commonly propagated in nurseries from field-collected seeds, but limited seed production by the native populations is a barrier to the success along the Louisiana coast. Seed production in the Louisiana populations of sea oats is extremely low compared to the population along the southeastern United States. Many of the sand dunes along the Louisiana coast have been lost to tropical storms, and few native Louisiana sea oats populations are left. The possibility of collecting enough seeds is low because of the disappearance of natural stands.
A large collection of sea oats germplasm, representing eight southeastern Atlantic and Gulf coast states (Virginia, North Carolina, South Carolina, Florida, Alabama, Mississippi, Louisiana and Texas), was characterized at the molecular level. There was significant genetic variation in lines among states, among lines within states and among individual plants. The relationship between genetic diversity and geographic source of sea oats populations of the United States as revealed through this study will be helpful for the resource managers and commercial nurseries in selecting, moving and mixing suitable plant materials for restoration of new areas without compromising the adaptation and genetic diversity.
Replicated field trials at Holly Beach and Biloxi, Miss., before the 2005 hurricanes showed that Florida and Louisiana lines performed relatively well in Louisiana. Elite materials were harvested from each site and are under increase for additional trials. Superior lines will serve as the foundation of a genetic improvement program aimed at developing populations and varieties with superior tolerance of the dune environment in Louisiana, greater seed production, increased genetic diversity and strong vegetative growth. Varieties developed by this effort should be better adapted to Louisiana and will be useful in restoring and preserving barrier islands.
A number of other species are under preliminary investigation, including black mangrove and bitter panicum. Elite lines will be used to form the foundation of continued genetic improvement activities.
Plants provide a self-sustaining, environmentally sound and aesthetically pleasing approach to controlling coastal erosion that can persist indefinitely. Commercial enterprises to supply marsh plant material will expand as coastal reclamation activities increase over the next decade. The coastal plants project will play an important role in developing genetically superior varieties and improved technology to protect our valuable coastal ecosystem.
Stephen A. Harrison, Professor; Niranjan Baisakh, Postdoctoral Researcher; Michael D. Materne, Instructor; Carrie Knott, Assistant Professor; Prasanta K. Subudhi, Assistant Professor, School of Plant, Environmental & Soil Sciences, LSU AgCenter, Baton Rouge, La.; and Herry S. Utomo, Assistant Professor, Rice Research Station, Crowley. La.
(This article was published in the spring 2007 issue of Louisiana Agriculture.) |