Breeding a Better Bahiagrass

Bahiagrass has been a staple for Florida turf use for decades.  Originally introduced from South America in the early 1900s as a forage grass that could perform well in sandy soils, it soon gained popularity for turf applications that focused on low cost and the ability to survive without supplemental irrigation and fertilization.

These characteristics have made it appealing to those advocating for “native” landscapes (based on the misperception that it is a Florida native grass) as well as those who are concerned with water and fertilizer use.  The particularly low cost of bahia also made it the grass of choice for applications like highway shoulders and medians, moderate-cost home builders, and large turf areas with little traffic.  The grass has also very few disease or pest issues.

Bahia is not without its drawbacks.  Most of the Bahia in Florida is still produced as forage (Florida’s cattle industry is among the largest in the United States) and is harvested every 3-5 years from existing pasture lands on a rotational basis as herds are moved to adjacent lands.  And while many cattle producers have developed a process to prepare the grass for harvest, the quality of the grass and its suitability for home lawn or commercial applications can vary widely (it’s also not unheard of for a load of Bahia delivered for a home lawn installation to contain some – well – surprises).

The Bahia cultivars currently used in Florida do not form a dense turf, but have an open growth habit which can make lawns look sparse.  It can also allow for weed intrusion, which can be difficult to treat, as many readily available home-use lawn products are either ineffective or damaging to the grass.  It’s best mowed at 3-4 inches, and its tough, fibrous stalk is hard on mower blades. And homeowners can be unpleasantly surprised by a lawn that turns yellow-brown and goes dormant in dry or cool weather.

Watering and fertilizing to maintain the green color can be counterproductive; UF studies have shown that over-fertilizing or too much supplemental irrigation can actually weaken the grass, encouraging weed intrusion and negating water savings.

Finally, although good seed heads are a plus for existing grasses – seed can be harvested and sold separately for establishing pastures or allowed to remain to reseed the area – seed heads in a home lawn can be unappealing and unsightly.

Some Florida growers have produced Bahia- grass on the farm along with other varieties, but market conditions and perception have made it difficult to compete cost-wise with inexpensive pasture-harvested Bahia.

So can we develop a Bahiagrass that retains the best qualities of existing varieties – drought tolerance, low maintenance, pest and disease resistance – while improving on some of the less desirable characteristics, creating a denser growth habit, minimizing seedheads, and improving the overall appearance?

Breeding Progress

In 2008, with financial support provided by TPF, the turf-type bahiagrass improvement project was initiated at the University of Florida. This project focused on the improvement of tetraploid bahiagrass (a.k.a. Argentine bahiagrass). Tetraploid bahiagrass was selected for improvement because the resulting turf stand is more uniform than turf produced from diploid bahiagrass (a.k.a. Pensacola bahiagrass). Because tetraploid bahiagrass plants reproduce through apomixis (clonal propagation through seed) it is not possible to make crosses to generate variation as would occur in a conventional breeding program. To produce variation, apomictic plants are exposed to mutagenic substances that cause changes in their DNA that might randomly result in desirable attributes in the mutant progeny lines.

Initially, 2000 mutant plants were produced by exposing seed and rhizomes of two tetraploid (apomictic) bahiagrass cultivars (Argentine and Wilmington) to gamma radiation, x-rays, ethyl methanesulfonate or cells in tissue culture to sodium azide. These plants were grown in the field for three years, until selections were made for reduced flowering, darker green color and higher turf density in the summer of 2011. In 2012, approximately 70 selected plants were planted in a replicated study for better assessment of turfgrass performance. In 2014-2015 with funding from the United States Golf Association, eleven plants were advanced for establishment in larger plots at Citra and Jay, FL. Data from these two trials has been collected for turfgrass performance (quality, color and density), and seed head density. Overall the advanced lines include grasses that could enter the market as follows: 1) seed produced with the primary use as a forage and secondary use as a turf (with slight improvements in turf performance compared to Argentine), 2) seed produced and used only as a turf, and 3) vegetative production only and used only as a turf.

In December 2015, the plots at Citra were used to dig sprigs which were transferred to a collaborating sod producer and planted in 20 × 40 ft blocks to assess the ability of these advanced lines to establish vegetatively and to learn if these lines can be produced using conventional sod production practices. This information is critical because a few of the advanced lines with superior turf quality do not produce enough seed heads or viable seed to warrant seed production. In short, these grasses will only become commercially available if they can be produced and sold as sod. In October 2016, the blocks ranged from 80 to 95 percent established, providing good indication that sprigged sod fields could be produced in 12 months. The original intent for 2017 was to take two or three of best experimental lines and expand to 0.5 acre blocks and begin testing these grasses in landscapes by early 2018. Unfortunately, as a result of excessively dry conditions and subsurface irrigation from fall 2016 through spring 2017 significant salts accumulated in these blocks. The salt level at the soil surface was near the levels found in sea water. These conditions resulted in significant dieback of the experimental lines. Observations of the eleven different plots under high soil salinity clearly identified that the Wilmington mutants were more sensitive to the salt compared to the Argentine mutants. The Wilmington mutants are those with the highest turf quality, darker green color and fewer seed heads. Secondarily, these plots were planted in a low area and the excessive rain that fell through the summer of 2017 resulted in water logged soils and essentially wiped out these blocks.

 

Moving Forward

We are very confident that these mutant bahiagrasses can establish quickly enough for sod production; however, questions remain regarding herbicides, sod strength and regrowth. Additionally, testing in landscapes remains as a critical component that must be evaluated. One of the mutant Wilmington lines has by far, the best turfgrass performance (i.e. high turf quality, dark green color, good density and very few, short seed heads). In 2018, this line named WEMS12, will be expanded at two farms with a goal of having enough material to conduct landscape testing in 2019. In addition, a graduate student, Agustin Boeri, under the direction of Bryan Unruh will evaluate herbicide responses and sod strength for several of the advanced lines.

This project is briefly described below:

In July 2017, sprigs from plots at the West Florida Research and Education Center, Jay, FL were collected to conduct a herbicide tolerance study. Under greenhouse conditions, nine advanced lines and Argentine bahiagrass were sprayed with 12 commercial herbicides at 1X and 2X labeled rates. Treatments were sprayed within a DeVries Research Track Sprayer which provides a very precise application. Visual ratings of damage and turf color were assessed. In addition, dry weights were collected to detect differences in growth after the herbicide application. In general, almost of the improved lines showed a response similar Argentine bahiagrass. FLDW 5-1 demonstrated greater herbicide tolerance. The most susceptible line was 3 FPEN8. From the 12 herbicides tested, Acclaim, Celsius and MSM (metsulfuron methyl) were the most damaging.

In spring 2018, these 10 lines will be tested for drought response to assess whether the improved lines are as drought resistant as conventional bahiagrass cultivars. These experiments will be performed by growing the grasses at different levels of moisture stress. Photosynthetic responses will be tested using a LI-COR LI-6800 Photosynthesis System. Furthermore, evapotranspiration (ET) and weekly visual ratings of TQ and leaf firing will be evaluated.

In 2018, new plots will be established to test sod production characteristics. Establishment of sprigged plots will be assessed using digital image analysis; and subsequently, sod will be harvested and evaluated for sod tensile strength.