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Mississippi Turfgrass – Hongxu Dong

Turfgrass breeders seek to improve grasses for a variety of end uses. The ultimate goal is a variety capable of withstanding challenging environments without unnecessary inputs and pampering, all while providing an aesthetically pleasing appearance. Through plant genomics, we can sequence the genes and then study the relationships of those genes on typical characteristics. Plant genomics aims to characterize the genetic compositions, variations, structures, functions, and networks in plant genomes. Through it, we will gain better understanding of genetic mechanisms of traits of interest in order to produce better turfgrass varieties.

A superior grass growing on the plains of Africa may have value only to the cattle (Bos taurus) or wild herbivores that graze it. Although it has intrinsic value, its economic value is limited. If this plant is collected, evaluated, used in a breeding program, production tested, and released as cultivar that is planted on a large acreage, its value is greatly improved. This is the basic procedure of bermudagrass cultivar development. Bermudagrass is now the dominant warm-season turfgrass species in the southern US and has contributed billions of dollars to the economy.

Bermudagrass (Cynodon spp.) is a warm-season, fine-textured turfgrass adapted to a wide range of environmental conditions. It is a drought-tolerant, durable, and versatile turfgrass that can be used in many settings, including golf courses, athletic fields, home lawns, and as utility turfgrass. Common bermudagrass (C. dactylon) and African bermudagrass (C. transvaalensis) are the two primary species used in breeding improved bermudagrass.

Bermudagrass species are largely self-incompatible, meaning that they rely upon cross-pollination rather than self-pollination. African bermudagrass is a diploid, meaning it has two copies of chromosomes. It readily crosses with tetraploid (having four copies) and hexaploid (having six copies) common bermudagrass. Hybrid bermudagrass (C. dactylon × C. transvaalensis) has been successfully employed in the development of turf cultivars, in fact most commercial turf-type bermudagrasses are crosses of African bermudagrass and common bermudagrass parent plants. Interspecific hybrids such as ‘Tifgreen 328’ and ‘Tifway 419’ are well known standards for golf courses in warm subtropical and tropical climates.

A plant germplasm is a collection of living materials such as seeds or plants that are maintained for breeding, preservation, and other research uses. As in the example above, uncharacterized germplasm has limited value, but its value increases after it has been collected and its attributes are known.

Turfgrass breeders attempt to improve multiple traits and attributes, including turfgrass quality, genetic color, grow-in and recovery speed, density, texture, disease resistance, drought and cold tolerance, and others. Plant breeders start with a raw product, plant germplasm, and spend multiple years (in most cases, 10+ years) of selections and genetic improvement, to release products such as cultivars that are of increased value. Revenue from new cultivars must exceed the cost of development. Although great efforts and resources are devoted to this process, breeding programs risk little return from investment. Among the many factors that influence success of turfgrass breeding programs, one of the most limiting is the unknown nature of genetics within a breeder’s germplasm.

Genomics-enabled breeding is understanding and employing that genetic capability. This process leverages information from modern genomic tools that greatly accelerate breeding cycles to increase genetic gains. Plant genomics aims to characterize the genetic compositions, variations, structures, functions, and networks in plant genomes. By gaining insights into the rich genetic variations in a germplasm “panel,” breeders may explore the genetic mechanisms of many agronomic traits.

At Mississippi State University, one of our turfgrass breeding projects focuses on exploring genomic diversity in the bermudagrass germplasm using next-generation sequencing technologies. Next-generation sequencing (NGS) is a sequencing technology that offers the ability to generate large amounts of data very quickly. In addition to its application in plant breeding and genetic studies, other notable uses of NGS include clinical diagnostics such as the identification of new coronavirus strains and other pathogens. In our turfgrass breeding program, we assembled 206 bermudagrass accessions of worldwide origins and sequenced them using this technology. Over 34,000 molecular variant sites have been detected. This enormous dataset will provide unprecedented insights into the genetic variation, phylogeny, and population structure in this important turfgrass species (Figure 1). Through it, we will gain better understanding of genetic mechanisms of traits of interest through additional linkage and association analyses. The ultimate end goal is to improve breeding efficiency through marker-assisted selection and genomic selection.