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Improving shade tolerance is critical for development of new turfgrass cultivars in the United States. Comparing turfgrass coverage under reduced sun exposure is a popular and effective method for determining shade tolerance, but requires years to evaluate. The objectives were to (i) compare phenotypical differences of experimental genotypes and cultivars of bermudagrass (Cynodon spp.), St. Augustinegrass (Stenotaphrum secundatum), and zoysiagrass (Zoysia spp.) grown under 73% shade and (ii) identify whether genetic improvement for shade adaptation was made in these species. This 3‐year study conducted in Tifton, GA, found phenotypic differences among genotypes within species for turfgrass coverage when exposed to 73% shade. The experimental bermudagrass, 11‐T‐56, possessed the superior combination of high green turfgrass coverage, low canopy height, and season long dark green color under shade. Experimental genotypes in St. Augustinegrass exhibited genetic improvement compared to commercially available cultivars; however, these genotypes should be examined under more intense shade to elicit differences before further selection. Performance of experimental zoysiagrass genotypes from several turfgrass breeding programs did not indicate significant improvement in the shade persistence within Zoysia spp. There appears to be genetic differences in the speed at which newer zoysiagrasses can initially spread by rhizomes and stolons when grown under shade. Further research should be conducted to determine if juvenile growth is an indicator of shade tolerance under natural tree shade or structures. Overall, results indicated that canopy heights cannot be used to directly predict shade tolerance but can be used to identify turfgrasses with reduced mowing frequency requirements. Core Ideas: Experimental bermudagrass, 11‐T‐56, had greater coverage, lower canopy height, and darker green color under shade.Experimental St. Augustinegrasses showed genetic improvement compared to commercial cultivars grown under shade.Newer zoysiagrasses can initially spread faster when grown under shade compared to older cultivars.Research identified turfgrasses with reduced mowing needs when grown in shade environments. [ABSTRACT FROM AUTHOR]

Little is known about the variation of 2C nuclear DNA content in zoysiagrass (Zoysia Willd.). Therefore, a glasshouse study including 20 cultivars and 16 experimental genotypes of Zoysia japonica Steud., Z. macrantha Desv., Z. matrella (L.) Merr., Z. minima (Colenso) Zotov, Z. pacifica (Goudswaard) M. Hotta & Kuroki, Z. pauciflora Mez, and select interspecific hybrids was conducted in 2008 at Gainesville, FL. Nuclei were stained with propidium iodide, and flow cytometry (FCM) analysis was conducted with a laser cytometer. Genotypes from Z. minima and Z. matrella had the largest (0.96 pg) and smallest (0,77 pg) 2C nuclear DNA content, respectively. The observed 0.19 pg spread between zoysiagrass species was less than variation reported in other tetraploid warm-season grasses within the same species. Results further suggest that midparent values for 2C nuclear DNA content of interspecific hybrids between Z. minima and other Zoysia spp. may be statistically detectable. Zoysiagrasses have one of the smallest genome sizes but are extremely diverse with respect to morphology, growth habit, and response to abiotic and biotic stresses. This information supports the large genome constraint hypothesis that species with small genome sizes are better able to adapt to environmental changes due to a lack of evolutionary limitations associated with large amounts of repetitive DNA. doi: 10.2135/cropsci2009.08.0425

Sting nematodes (Belonolaimus longicaudatus) can injure roots of many warm-season turfgrasses in sandy, welt-drained soils and on artificial, sand-based putting greens. Resistant or tolerant grasses could reduce the need for chemical control. This research was initiated to assess the host status and relative tolerance of six warm-season genotypes--four zoysiagrasses (Zoysia Wiild.), one St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze], and one bermudagrass [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy]-to the sting nematode by two screening methodologies in sequential glasshouse trials in 2007. All entries were hosts with final sting populations 1.7 to 11.0 times greater than initial inoculation levels. Results indicate that evaluating root lengths of unestablished sprigs under sting nematode pressure may improve the identification of genotypes with greater genetic tolerance than in methods using established plants. Total root lengths were not reduced by sting nematodes in UFZ-10, indicating greater tolerance than found in other entries. Treatments of 'Empire', 'Cavalier', 'Emerald', ,TifEagle', and 'Floratam' inoculated 45 d after planting exhibited total root length reductions of 24, 29, 29, 32, and 37%, respectively, when compared with uninoculated controls, The observed variability suggests that gains from selecting for sting nematode resistance or tolerance are possible in zoysiagrass. doi: 10.2135/cropsci2008.11.0672

Zoysiagrasses (Zoysia spp.) are widely adapted and highly variable; however, information is lacking regarding the heritability and potential for improvement of numerous performance characteristics. Three individual replicated field studies, which included 90 very fine, 108 fine, and 126 coarse-textured zoysiagrass genotypes, respectively, were conducted near Gainesville, FL, to determine the response and broad-sense heritabilities of 10 turfgrass performance and stressrelated characteristics. Genotypic variance largely contributed to the wide range in expressed phenotypic response for plot coverage, turf density, turf quality, genetic color, and seedhead density, which resulted in higher broad-sense heritability estimates (0.62 [less than or equal to]_[H.sup.2][less than or equal to] 0.94). Fall dormancy and spring greenup were influenced more by the environment and had lower heritabilities (0.32[less than or equal to] [H.sup.2][less than or equal to] 0.58). Turf quality was also rated considering the effects of glufosinate [2-amino4-(hydroxymethylphosphinyl)butanoic acid] herbicide application, Bipolaris incidence, and mole cricket (Scapteriscus spp.) damage. Large error variances and low broad-sense heritablities were typical for these stress-related traits. Potential exists for improvement of characteristics that exhibited large amounts of genetic variation and were less influenced by the environment. Broadsense heritability estimates indicate the possibility of combining desirable traits in superior clonalty propagated [F.sub.1] hybrids. doi: 10.2135/cropsci2008.12.0705

Competition from foreign grown cotton (Gossypium hirsutum L.) and artificial fibers have increased the demand for improved fiber quality. The genetic potential for effecting change in many traits can be judged by previous gains from selection. Nine upland cotton cultivars developed over the past century were grown during 2004 and 2005 in five plant densities to evaluate varying levels of interplant competition on genetic gain estimates for high volume instrument fiber properties. The rates of genetic gain since 1905 among this set of genotypes for fiber length and strength were significantly higher under the greatest planting densities, implying that genetic gains for these characteristics have been made for tolerance to interplant competition as well as for the fiber trait per se. Both fiber elongation and uniformity index appear to be largely unaffected by the stresses of increased interplant competition. Plant density impacted genetic gain in micronaire but cultivars were essentially unchanged over the century, reflecting that the market demands fiber micronaire to be within a range that neither maximizes nor minimizes this trait. Caution should be practiced in the interpretation of these data since the capability to objectively measure these traits has been widely available to breeders only since the 1980s and because selection pressure for these traits has been sporadic with little concentrated effort to maximize or minimize each characteristic.

Genetic gain studies have been used to evaluate the historical improvement of different traits, to provide insights into magnitudes of gain possible in future cultivars, and to defend the role of genetics during periods of stagnant or decreasing yield trends. This study was conducted over a 2-yr period and included nine current or obsolete cotton (Gossypium hirsuturn L.) cultivars grown in five plant densities to evaluate genetic gain with varying levels of interplant competition. The rates of genetic gain for lint yield were highest in the commercial, 1 by 0.3 m, and 1 by 1 m plant spacing treatments with slopes of 8.7, 8.2, and 7.1 kg [ha.sup.-1] [yr.sup.-1], respectively. Slopes were reduced in the 2 by 2 m and 3 by 3 m spacing treatments with gains of 3.6 and 1.5 kg [ha.sup.-1] [yr.sup.-1], respectively, implying that for lint yield, genetic gains have been made for tolerance to interplant competition and not only yield potential per se.

Zoysia japonica Steud. (2 n = 4 × = 40) is a C turfgrass well-adapted for the warm-humid and transitional climatic zones of the USA. Its use is limited to warmer climates because of a relative lack of winter hardiness compared to C grasses. Molecular markers associated with this trait would be useful for effective selection of winter hardy germplasm before field testing. A pseudo-F mapping population of 175 individuals was developed from crosses between Z. japonica cultivars 'Meyer' (freeze-tolerant) and 'Victoria' (freeze-susceptible) and used to generate a high-density genetic map of 104 SSR markers and 2359 sequencing-derived SNP markers. The map covers 324 Mbp and 2520 cM as well as the 20 chromosomes for the zoysiagrass haploid genome. Phenotypic data on winter injury, establishment, and turf quality collected in North Carolina and Indiana in 2014-2016 were used in conjunction with this map to identify quantitative trait loci (QTL) associated with winter hardiness. Fifty-six QTL associated with winter injury, establishment, and turf quality were identified over six environments. Twelve of those were identified in two or more environments. Furthermore, seven regions of interest were identified on chromosomes 8, 11, and 13 where co-location of QTL for three or more traits occurred. Within these regions, analysis with NCBI basic local alignment search tool (BLAST) identified proteins related to cold and other abiotic stresses tolerance. These QTL and associated markers could be valuable in implementing marker-assisted selection for winter hardiness in zoysiagrass breeding programs. [ABSTRACT FROM AUTHOR]

Since its introduction into the United States in 1892, zoysiagrass (Zoysia spp. Willd.) has made a tremendous impact on the US turfgrass industry. Three species of zoysiagrass [Z. japonica Steud., Z. matrella (L.) Merr., and Z. pacifica (Goudswaard) M. Hotta & S. Kuroki] collected from East Asia and the Pacific Islands were introduced into the United States and are used directly as turf or by turfgrass breeders in the development of advanced lines. Golf courses, lawns, grounds, sod farms, athletic fields, roadsides, and airports are some of the many locations where zoysiagrass is used. While almost 50 improved cultivars of zoysiagrass have been developed to date, active efforts to improve zoysiagrass further and expand its utilization are ongoing. These continued improvements in stress and pest tolerance allow for expanded use of this low-input turf species. This review summarizes the history of zoysiagrass in the United States; summarizes species introduction and utilization; addresses and discusses strengths and shortcomings of the species; evaluates breeding history, methodology, and challenges; and suggests future prospects and potential for zoysiagrass. [ABSTRACT FROM AUTHOR]

Selection during varietal improvement has been shown to reduce genetic diversity in several different crop species. A reduction in genetic diversity can be detrimental to future breeding efforts and increase susceptibility to biotic stresses. The purpose of this study was to analyze changes in levels of allelic diversity at the gene and population levels in 40 zoysiagrass (Zoysia spp. Willd.) cultivars released between 1910 and 2016 using simple sequence repeat (SSR) markers. Fifty-six SSR primer pairs were used to determine whether allelic diversity has changed among cultivars released over a century of modern plant breeding. While no significant differences were observed for total numbers of alleles or genetic similarity values between the initial and most recent time periods, our results demonstrate that genetic diversity among zoysiagrass cultivars has fluctuated over time. Allelic diversity declined during the 1990s and then recovered during 2000s. STRUCTURE analysis revealed five subpopulations with varying levels of admixture and that, for the most part, good representation of these subpopulations has been maintained over the different decades of release. These findings illustrate that plant breeding has not resulted in a substantial decline in zoysiagrass genetic diversity, but also that the potential exists for increasing diversity through future germplasm collections and the inclusion of less-used Zoysia species to create new combinations of alleles. [ABSTRACT FROM AUTHOR]