There are approximately 30 different species of turfgrasses commonly found throughout the world, and each has its own set of characteristics that make it uniquely adapted for use. These adaptations can be grounded in climate, rainfall, mowing height, stress tolerance, sunlight requirements, etc., but among all of the different turfgrass species used today, few are as unique as those found in the Zoysia genus. Zoysiagrasses are thought to have originated in a region of the world that spans as far north as Japan and southeast China, and downward through Malaysia and into New Zealand. There are at least 11 recognized species within the Zoysia genus, with at least three of them commonly used as turfgrass. These include Japanese zoysiagrass (Zoysia japonica), Manilagrass (Zoysia matrella), and Mascarenegrass (Zoysia pacifica, previously identified as Zoysia tenuifolia). Historically speaking, zoysiagrass cultivars used for turfgrass have often been ‘very generally’ grouped into these three categories based mostly on leaf texture, but also on their shade tolerance and other traits. For example, coarse-textured zoysias have typically been thought of as Z. japonicas while fine-textured zoysias were considered Z. matrellas or Z. pacificas. As a result, some zoysiagrass cultivars have been misclassified with many intermediate types simply being called japonicas or matrellas. However, recent genetic research is shedding light on the inter- connectedness of these species and the diversity in traits they each produce.
Zoysiagrass species are cross-fertile and easily interbreed with one another. This is somewhat uncommon as the definition of species revolves around being reproductively isolated. While crosses between different zoysiagrass species can occur naturally, they are also often used by plant breeders as a means of mixing traits of interest into new and improved cultivars. Consequently, intermediate types between species are not unusual and a continuous range of variation exists in the Zoysia genus for many morphological traits. A few examples of this include cultivars like Cavalier, Crowne, Zeon, and Zorro. While these cultivars typically have finer texture than Z. japonicas like Zenith or Chinese Common, they don’t have texture as fine as many Z. matrellas such as Diamond or L1F. The wide range in leaf texture that exists among the zoysiagrasses listed in Figure 1 is an example of not only the variation that exists between various zoysia species, but also the shared traits in which they overlap.
These intermediate types can be difficult to classify and their relationships with other zoysia species have not always been clearly understood. In order to investigate this, researchers at North Carolina State University (Raleigh, NC), in collaboration with the University of Florida, USDA-ARS in Tifton, GA, and Blue Moon Farms conducted a study which evaluated 62 zoysiagrass cultivars and collections representing five different zoysia species: Z. japonica, Z. matrella, Z. machrostachya, Z. minima, and Z. sinica. In order to determine the true genetic relationships among these individuals, DNA markers were used to investigate their genetic constitution. Molecular or DNA markers are changes in short sequences that occur at specific locations on an individual’s DNA.
When individuals have differences in those sequences, they can be used to distinguish one individual from another. In this case, 55 DNA markers were evaluated and the relationships among the 62 zoysiagrasses included in this study were determined based on differences in their sequences. For example, if Meyer were to have a lot of markers in common with Zenith and just a few markers in common with Diamond, then Meyer would be more genetically similar to Zenith and therefore more closely related to it.
After analyzing the commonalities and differences between each pair of zoysiagrass samples, a tree of relationships was established that reflected not only the relationships among zoysiagrass species, but also the true delineation between them. This is useful
in determining where commonly used zoysiagrass varieties should be properly classified. The zoysiagrass tree of relationships presented in Figure 2 indicates that the 62 zoysiagrass samples analyzed fell into four sub- groups, or clusters. Cluster I includes true Z. japonica cultivars, while Cluster III includes true Z. matrella cultivars. Cluster II, consisting of hybrids, is right in the middle of both species.
More importantly, Cluster II is divided into two subgroups: Hybrid I which includes Z. japonica x Z. matrella hybrids that have a higher contribution of genetic material from Z. japonica, and Hybrid II which are also hybrids between the two species but have a higher contribution of Z. matrella genetic material.
To validate the DNA marker results, information on flowering characteristics from the 62 samples was also collected.
These included peduncle width, pedicel length, raceme length, number of seeds per raceme, seed length and seed width for a number of flowers per entry. This is an important step because these are the characteristics that have been traditionally used by botanists to classify the 350,000+ species of the world’s flowering plants