Mitochondrial DNA sequences of greenbug (Homoptera: Aphididae) biotypes

Sequence comparisons were made for 738-bp of mtDNA cloned from seven greenbug, Schizaphis graminum, biotypes (B, C, E, F, G, H and I) obtained from laboratory colonies maintained by USDA-ARS, Stillwater, OK. These sequences include parts of the genes for 16S ribosomal subunit (16S rRNA), tRNA^leu, tRNA^ser, cytochrome b (cytb) and NADH dehydrogenase (ND) subunits one and four. Sequence data revealed considerable variation in 86 (12%) nucleotide sites over the 738-bp sequenced among the seven greenbug biotypes. Nucleotide invariance was observed within the seven greenbug biotypes from both the laboratory colonies and field collected biotype E greenbugs from Kansas, Nebraska, Oklahoma, and Texas.     

CYTOGEOGRAPHY OF PANICUM VIRGATUM IN CENTRAL NORTH AMERICA

Mc Millan , Calvin . (U. Texas, Austin.), and John Weiler . Cytogeography of Panicum virgatum in central North America. Amer. Jour. Bot. 46(8): 590–593. Illus. 1959.—For 124 clones of Panicum virgatum L. representing 44 local populations from Manitoba and eastern Montana to Texas, the chromosome number was determined. Most of the clones were grown in a transplant garden at Lincoln, Nebraska. Among the earlier-flowering clones from the northern and western area, a preponderance were tetraploids (n = 18). Among the later-flowering clones, the Iowa material was predominantly tetraploid, while those from Nebraska presented a diversity of types (n = 18, 27, 36) within each population. A series of polyploids was common in population samples from southern Kansas, Oklahoma, and Missouri. Through the complex breeding patterns resulting from the common occurrence of a range of polyploidy and the possible action of apomixis, variability within the population is maintained, and with it, genetic insurance for survival in highly unpredictable prairie habitats.     

Biotypic diversity in greenbug (Hemiptera: Aphididae): characterizing new virulence and host associations

Biotypic diversity of the greenbug, Schizaphis graminum (Rondani) (Hemiptera: Aphididae), was assessed among populations collected from cultivated wheat, Triticum aestivum L., and sorghum, Sorghum bicolor (L.) Moench, and their associated noncultivated grass hosts. Greenbugs were collected during May through August 2002 from 30 counties of Kansas, Nebraska, Oklahoma, and Texas. Discounting the presumptive biotype A, five of the remaining nine letter-designated greenbug biotypes were collected; however, biotypes C, F, J, and K were not detected. Biotypes E and I exhibited the greatest host range and were the only biotypes collected in all four states. Sixteen greenbug clones, collected from eight plant species, exhibited unique biotype profiles. Eleven were collected from noncultivated grasses, three from wheat, and two from sorghum. The most virulent biotypes were collected from noncultivated hosts. The great degree of biotypic diversity among noncultivated grasses supports the contention that the greenbug species complex is composed of host-adapted races that diverged on grass species independently of, and well before, the advent of modern agriculture.     

Belowground bud production is linked to population establishment in Sorghastrum nutans (Poaceae)

Belowground bud production mediates many responses of tallgrass prairie grasses to temporal environmental variation, and clonal spread contributes to dominance in successional plant communities. However, we know little about the importance of these regenerative traits for vegetation establishment in grassland restoration and about their regional variability. Further, geographic seed or transplant sources affect plant performance. We investigated the effects of seed source on the number of belowground buds per tiller, clonal spread (total rhizome length adjusted for plant biomass), and population establishment in the native C₄ grass Sorghastrum nutans sown into tallgrass prairie restorations using reciprocal common gardens in three sites (in Nebraska, Kansas, and Oklahoma). We characterized buds per tiller and clonal spread at the plant level and related both traits to population establishment at the restoration plot level. Plant-level bud production significantly differed among seed sources and common garden sites, and was positively associated with plot-level establishment (density and canopy cover), but plant-level clonal spread did not differ among seed sources or common garden sites and was not associated with the plot-level establishment. Our results are among the first to link bud production, which varied among source populations, to differences in plant population establishment. These results suggest that we should more often consider differences among sources in traits closely tied to post-seeding population establishment. The use of sources that possess such traits may facilitate successful establishment in restoration settings.     

Mitochondrial DNA sequences of greenbug (Homoptera: Aphididae) biotypes

Sequence comparisons were made for 738-bp of mtDNA cloned from seven greenbug, Schizaphis graminum, biotypes (B, C, E, F, G, H and I) obtained from laboratory colonies maintained by USDA-ARS, Stillwater, OK. These sequences include parts of the genes for 16S ribosomal subunit (16S rRNA), tRNAleu, tRNAser, cytochrome b (cytb) and NADH dehydrogenase (ND) subunits one and four. Sequence data revealed considerable variation in 86 (12%) nucleotide sites over the 738-bp sequenced among the seven greenbug biotypes. Nucleotide invariance was observed within the seven greenbug biotypes from both the laboratory colonies and field collected biotype E greenbugs from Kansas, Nebraska, Oklahoma, and Texas.     

Plant functional traits improve diversity‐based predictions of temporal stability of grassland productivity

Synthesis The temporal stability of plant production is greater in communities with high than low species richness, but stability also may depend on species abundances and growth‐related traits. Annual precipitation varied by greater than a factor of three over 11 years in central Texas, USA leading to large variation in production. Stability was greatest in communities that were not dominated by few species and in which dominant species rooted shallowly, had dense leaves, or responded to the wettest year with a minimal increase in production. Stability may depend as much on species abundances and functional traits as on species richness alone. Aboveground net primary productivity (ANPP) varies in response to temporal fluctuations in weather. Temporal stability of community ANPP may be increased by increasing plant species richness, but stability often varies at a given richness level implying a dependence on abundances and functional properties of member species. We measured stability in ANPP during 11 years in field plots (Texas, USA) in which we varied the richness and relative abundances of perennial grassland species at planting. We sought to identify species abundance patterns and functional traits linked to the acquisition and processing of essential resources that could be used to improve richness‐based predictions of community stability. We postulated that community stability would correlate with abundance‐weighted indices of traits that influence plant responses to environmental variation. Annual precipitation varied by a factor of three leading to large inter‐annual variation in ANPP. Regression functions with planted and realized richness (species with > 1% of community ANPP during the final four years) explained 32% and 25% of the variance in stability, respectively. Regression models that included richness plus the fraction of community ANPP produced by the two most abundant species in combination with abundance‐weighted values of either the fraction of sampled root biomass at 20–45 cm depth, leaf dry matter content (LDMC), or response to greater‐than‐average precipitation of plants grown in monocultures explained 58–69% (planted richness) and 58–64% (realized richness) of the variance in stability. Stability was greatest in communities that were not strongly dominated by only two species and in which plants rooted shallowly, had high values of LDMC, or responded to the wettest year with a minimal increase in ANPP. Our results indicate that the temporal stability of grassland ANPP may depend as much on species abundances and functional traits linked to plant responses to precipitation variability as on species richness alone.     

Early Establishment of a Native Grass Reduces the Competitive Effect of a Non‐Native Grass

Buffelgrass (Pennisetum ciliare (L.) Link), a C₄ perennial bunchgrass native to Africa and parts of Asia, has invaded broadly across the southwestern United States and northern Mexico. Buffelgrass establishment may occur earlier than the natives it displaces which may preempt resource acquisition by native species and contribute to its invasion success. In a greenhouse, buffelgrass aboveground growth was tested against Arizona cottontop (Digitaria californica (Benth.) Henr.), a native C₄ perennial bunchgrass, in pairwise combinations in a randomized complete block factorial design with 10 replications, three neighbor identities (self, other, and no neighbor), and three competition treatments (21‐day younger neighbor, 21‐day older neighbor, and same‐aged neighbor). When compared with control plants, there was no significant effect on aboveground biomass for older Arizona cottontop plants competing with younger buffelgrass plants (p > 0.05). However, when Arizona cottontop plants were of the same age or younger than buffelgrass plants, buffelgrass caused 95 and 88% reductions, respectively, in aboveground biomass (p < 0.05 in both cases). Intraspecific competition between same‐aged Arizona cottontop plants resulted in only 55% decline in aboveground biomass production (p < 0.05), thus interspecific competition with buffelgrass was more intense than intraspecific competition for Arizona cottontop when plants had similar emergence times. These results suggest that establishing native plants immediately following a disturbance event could be a practical technique for restoring or retaining diversity on sites with high potential for invasion by buffelgrass.     

Fertilization effects on species density and primary productivity in herbaceous plant communities

Fertilization experiments in plant communities are often interpreted in the context of a hump-shaped relationship between species richness and productivity. We analyze results of fertilization experiments from seven terrestrial plant communities representing a productivity gradient (arctic and alpine tundra, two old-field habitats, desert, short- and tall-grass prairie) to determine if the response of species richness to experimentally increased productivity is consistent with the hump-shaped curve. In this analysis, we compared ratios of the mean response in nitrogen-fertilized plots to the mean in control plots for aboveground net primary productivity (ANPP) and species density ( D ; number of species per plot of fixed unit area). In general, ANPP increased and plant species density decreased following nitrogen addition, although considerable variation characterized the magnitude of response. We also analyzed a subset of the data limited to the longest running studies at each site (≥4 yr), and found that adding 9 to 13 g N m⁻² yr⁻¹ (the consistent amount used at all sites) increased ANPP in all communities by approximately 50% over control levels and reduced species density by approximately 30%. The magnitude of response of ANPP and species density to fertilization was independent of initial community productivity. There was as much variation in the magnitude of response among communities within sites as among sites, suggesting community-specific mechanisms of response. Based on these results, we argue that even long-term fertilization experiments are not good predictors of the relationship between species richness and productivity because they are relatively small-scale perturbations whereas the pattern of species richness over natural productivity gradients is influenced by long-term ecological and evolutionary processes.     

The potential of genotypically diverse cultivar mixtures to moderate aphid populations in wheat (Triticum aestivum L.)

Plant species diversity has long been considered a primary driver of arthropod community structure; however, recent ecological research has demonstrated that plant genotypic diversity can also play a major role in influencing the composition of arthropod communities. Genotypic diversity has already been exploited in some agricultural systems to improve disease control and appears to hold promise for managing some insect species as well. To explore the potential for using genotypic diversity within a crop species to help manage insect pests, we used laboratory-based studies to investigate the influence of wheat (Triticum aestivum L.) genotypic diversity on aphid (Rhopalosiphum padi L.) population growth. Increasingly diverse mixtures of wheat genotypes supported lower aphid populations compared with monocultures and were equally productive as single variety plantings. In the absence of aphids, genotypic mixtures were more productive than monocultures. We also analyzed the volatile organic compounds emitted by non-infested genotypic mixtures to provide insight on a possible mechanism influencing aphid populations. Mixtures and monocultures of wheat emitted the same compounds, but mixtures emitted greater amounts of volatile compounds than monocultures. Our results suggest that genotypic mixtures can strongly influence the growth rate and size of aphid populations; therefore, cultivar mixtures appear to hold good potential to be an effective tool for managing insect pests in crop fields.     

Switchgrass Biomass Simulation at Diverse Sites in the Northern Great Plains of the U.S.

The Agricultural Land Management Alternatives with Numerical Assessment Criteria (ALMANAC) model, originally developed and tested in Texas, needs to be tested for switchgrass (Panicum virgatum L.) simulation in more northerly locations. The Northern Great Plains of the U.S. has regionally adapted native populations of switchgrass and has excellent potential for growing switchgrass as a biofuel crop. The objective of this study was to adjust switchgrass parameters (potential leaf area index (DMLA) and degree days to maturity (PHU)) for northern sites and populations and to validate the model against switchgrass data from diverse sites in this region. Three or 4 years of measured yield data were used from a ten field sites in North Dakota (ND), South Dakota (SD), and Nebraska (NE). ALMANAC realistically simulated mean annual switchgrass yields ranging from means of 4.75 to 9.13 Mg ha^?1. Mean simulated yields were within 3%, 15%, and 9% of mean measured yields for NE, SD, and ND, respectively. Sensitivity analysis with temperature and rainfall demonstrated variable responses of potential yields depending on whether season duration, soil water, or soil nitrogen was the limiting factor at a site. ALMANAC shows promise as a useful tool for switchgrass evaluation and management in the northern Great Plains and in similar latitudes with low rainfall such as the East European Plain.     

Distribution and diversity of russian wheat aphid (Hemiptera: Aphididae) biotypes in North America

Wheat, Triticum aestivum L., with Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae) resistance based on the Dn4 gene has been important in managing Russian wheat aphid since 1994. Recently, five biotypes (RWA1-RWA5) of this aphid have been described based on their ability to differentially damage RWA resistance genes in wheat. RWA2, RWA4, and RWA5 are of great concern because they can kill wheat with Dn4 resistance. In 2005, 365 Russian wheat aphid clone colonies were made from collections taken from 98 fields of wheat or barley, Hordeum vulgare L., in Oklahoma, Texas, New Mexico, Colorado, Kansas, Nebraska, and Wyoming to determine their biotypic status. The biotype of each clone was determined through its ability to differentially damage two resistant and two susceptible wheat entries in two phases of screening. The first phase determined the damage responses of Russian wheat aphid wheat entries with resistance genes Dn4, Dn7, and susceptible 'Custer' to infestations by each clone to identify RWA1 to RWA4. The second phase used the responses of Custer and 'Yuma' wheat to identify RWA1 and RWA5. Only two biotypes, RWA1 and RWA2, were identified in this study. The biotype composition across all collection sites was 27.2% RWA1 and 72.8% RWA2. RWA biotype frequency by state indicated that RWA2 was the predominant biotype and composed 73-95% of the biotype complex in Texas, Oklahoma, Colorado, and Wyoming. Our study indicated that RWA2 is widely distributed and that it has rapidly dominated the biotype complex in wheat and barley within its primary range from Texas to Wyoming. Wheat with the Dn4 resistance gene will have little value in managing RWA in the United States, based on the predominance of RWA2.     

Yield and Nutrient Removal by Bioenergy Grasses on Swine Effluent Spray Fields in the Coastal Plain Region of North Carolina

Bioenergy grasses such as giant miscanthus (Miscanthus × giganteus) and switchgrass (Panicum virgatum L.) are promising alternatives to the traditional coastal bermudagrass [Cynodon dactylon (L.) Pers.] at spray fields in Eastern North Carolina. The objective of this study was to determine the impact of different harvest practices on yield and nutrient removal of miscanthus and switchgrass in a swine (Sus scrofa domesticus) lagoon effluent spray field environment. Field trials of grasses under six single-cut and double-cut harvest practices (May/October, June/October, July/October, Aug/October, October only, and December only) were established at three commercial swine farms in Eastern North Carolina in either 2011 or 2012. Throughout the 4-year experimental period (2012–2015), both miscanthus and switchgrass produced significantly higher biomass yield than coastal bermudagrass. Two-cut harvest systems significantly improved the yields of miscanthus and switchgrass relative to a single harvest in December at spray fields. The maximum yields were 24 Mg ha^?1 year^?1 for miscanthus and 18 Mg ha^?1 year^?1 for switchgrass. Bioenergy grasses removed more nutrients under two-cut systems than under a single harvest. The significantly greater nutrient removals under two-cut harvest systems would result in lower requirements for receiver crop acreage and are more desirable from a spray field nutrient management perspective.     

Development and characterization of genomic SSR markers in Cynodon transvaalensis Burtt-Davy

Simple sequence repeat (SSR) markers are a major molecular tool for genetic and genomic research that have been extensively developed and used in major crops. However, few are available in African bermudagrass (Cynodon transvaalensis Burtt-Davy), an economically important warm-season turfgrass species. African bermudagrass is mainly used for hybridizations with common bermudagrass [C. dactylon var. dactylon (L.) Pers.] in the development of superior interspecific hybrid turfgrass cultivars. Accordingly, the major objective of this study was to develop and characterize a large set of SSR markers. Genomic DNA of C. transvaalensis ‘4200TN 24-2’ from an Oklahoma State University (OSU) turf nursery was extracted for construction of four SSR genomic libraries enriched with [CA] _n , [GA] _n , [AAG] _n , and [AAT] _n as core repeat motifs. A total of 3,064 clones were sequenced at the OSU core facility. The sequences were categorized into singletons and contiguous sequences to exclude redundancy. From the two sequence categories, 1,795 SSR loci were identified. After excluding duplicate SSRs by comparison with previously developed SSR markers using a nucleotide basic local alignment tool, 1,426 unique primer pairs (PPs) were designed. Out of the 1,426 designed PPs, 981 (68.8 %) amplified alleles of the expected size in the donor DNA. Polymorphisms of the SSR PPs tested in eight C. transvaalensis plants were 93 % polymorphic with 544 markers effective in all genotypes. Inheritance of the SSRs was examined in six F₁ progeny of African parents ‘T577’ × ‘Uganda’, indicating 917 markers amplified heritable alleles. The SSR markers developed in the study are the first large set of co-dominant markers in African bermudagrass and should be highly valuable for molecular and traditional breeding research.     

Recruitment limitation of native species in invaded coastal dune communities

Recruitment limitation may limit the ability of sites to regenerate after disturbances such as weed invasion and weed management. We investigated seed bank constraints and dispersal limitation in coastal dune communities on the east coast of Australia. The ability of sites to regenerate naturally following weed removal was assessed in coastal dune communities invaded by the invasive alien, bitou bush (Chrysanthemoides monilifera subsp. rotundata). To investigate recruitment limitation, seed banks and vegetation of invaded, native, intensively managed (selective application of herbicide and some re-vegetation) and extensively managed (large-scale, non-selective herbicide application) sites were compared. We investigated the dispersal mechanisms of species in the seed bank and vegetation to determine if communities might be dispersal-limited, i.e. contain significant numbers of species with only short-distance dispersal capabilities. Species richness and composition of soil seed banks differed from the vegetation in foredunes and hinddunes. Invasion depleted seed banks further. About half of the species had short-distance dispersal mechanisms indicating the potential for dispersal limitation. Secondary weed invasion following management was evident although alien species occurred in both seed banks and vegetation. Our results indicated that coastal dune communities suffer recruitment limitation. Native, managed and invaded dune communities appear to be both seed bank and dispersal-limited although management and invasion exacerbates recruitment. Regeneration of coastal dune communities will require active reintroduction of species, particularly those with short-distance dispersal mechanisms.     

Effects of Three Years of Regrowth Inhibition on the Resilience of a Clear-cut Northern Hardwood Forest

Clearcutting is a common silvicultural practice in the deciduous forests of northern New England. Subsequent regrowth is usually rapid, largely due to regenerative capacities of successional plants, particularly pin cherry (Prunus pensylvanica L.). The forest cover of an experimental watershed (W2) in Hubbard Brook Experimental Forest, NH was clearcut and then treated with herbicides for 3?years to prevent regrowth. This experimental treatment delayed plant growth and caused extensive nutrient losses from the watershed-ecosystem, thereby diminishing factors normally promoting revegetation. This article addresses the question of whether, or to what degree, resilience, defined here as the trajectory of recovery back to a prior state following a perturbation, was reduced by this treatment. Performance metrics for resilience were aboveground net primary productivity (ANPP) and biomass accumulation. Data collected over seven intervals for the first 31?years of regrowth show that a primary component of resilience??pin cherry density??was reduced, and that ANPP and biomass accumulation were initially below normal compared with other clear-cut sites. After approximately a decade of regrowth, however, trajectories for both ANPP and biomass fell within the lower margins of variability measured in other regional examples.     

Rumen bacterial interrelationships with plant tissue during degradation revealed by transmission electron microscopy

The mode of rumen bacterial degradation of cell walls in coastal bermudagrass [Cynodon dactylon (L) Pers.] differed with the plant tissue type. Bacteria degraded thin, primary cell walls of mesophyll and phloem apparently by extracellular enzymes and without prior attachment; thick-walled bundle sheath and epidermal cells apparently were degraded after bacterial attachment, in some types by an extracellular substance, to the plant cell walls. Rumen bacteria split the nondegraded cuticle from the epidermis by preferentially attacking the cell just underneath the cuticle. The propensity for bacterial attachment to lignified cells of the vascular tissue was low, and bacterial degradation of these cells did not occur after 72 h of incubation.     

Propagule pressure and native species richness effects drive invasibility in tropical dry forest seedling layers

Understanding the factors that encourage or inhibit plant invasions is vital to focusing limited invasive control efforts within areas where they are most practical and cost-effective. To extend the range of contexts in which invasibility is studied and aid the development of practical strategies to limit damaging plant invasions, we set out to test the relative importance of native species richness, native seedling density, and invasive propagule pressure, on the invasibility of artificial assemblages of naturally occurring tropical woody seedling communities. Our greenhouse mesocosms included a species pool of twelve trees and woody shrubs native to South Florida's tropical hardwood hammocks, and an increasingly prevalent noxious woody invader of this system, Ardisia elliptica. We found that invader propagule pressure was the single most important factor determining community invasibility. We also revealed a positive relationship between invasibility and native species richness in our polyculture mesocosms. Because A. elliptica biomass production significantly differed among different native monocultures and was not related to overyielding in native polycultures, we suggest that the effect of species richness on invasibility in this experiment was the result of sampling effects rather than a true effect of diversity.Three broad findings hold potential for application in preventing and controlling plant invasions, especially in the seedling layers of tropical dry forests: (1) effective invasive control efforts will likely benefit from measures to minimize propagule pressure; (2) managers might do well to prioritize invasive monitoring and removal efforts on the most diverse habitats within a management region; and (3) while more data are necessary to further understand our finding of a lack of association between productivity and invasibility, management regimes aimed at maximizing primary productivity might not increase invasibility, and in fact, strategies for controlling invasive plants via the management of ecosystem productivity may be ineffective.     

Impacts of introduced grasses on breeding season habitat use by northern bobwhite in the South Texas plains

Introduced grasses may affect diversity of native fauna and flora adversely, and disrupt ecosystem processes. Many rangelands in South Texas have been seeded to or have been colonized by buffelgrass (Pennisetum ciliare) and Lehmann lovegrass (Eragrostis lehmanniana), perennial bunchgrasses native to Africa. The objective of this research was to quantify impacts that these 2 species of introduced grasses may have on northern bobwhite (Colinus virginianus) habitat use on South Texas rangelands during the breeding period (Apr–Aug). We evaluated the effects of buffelgrass and Lehmann lovegrass on northern bobwhite nest habitat (n = 35 nests) and general habitat use sites (n = 86 radiomarked quail) with logistic regression and habitat selection functions based on simple saddlepoint approximations. Buffelgrass was used as a nesting substrate at 11% of nests; however, vegetation height and visual obstruction between 1 cm and 30 cm were the best predictors of nest site use. Areas of introduced grass coverage ≥15–20% were avoided by northern bobwhites at general habitat use organism-centered points, but not at nest site use points. Introduced grass coverage and forb coverage were the best predictors of general habitat use, and bobwhites avoided areas with ≥18% introduced grass cover. These results suggest that avoidance of areas with extensive introduced grass cover may indicate a reduction in usable habitat space for northern bobwhite in the western South Texas plains. Maintaining native grass stands while implementing localized control of introduced grasses could be used as a strategy to promote habitat for northern bobwhites. © 2011 The Wildlife Society.     

Exotic tree seedlings are much more competitive than natives but show underyielding when growing together

Aims Invasive species continue to be a worldwide threat to ecosystems mainly as a cause for biodiversity loss. Forest ecosystems, for example, are subject to a change in species composition due to the invasion of exotic species. Specifying the attributes that cause the strong competitiveness of several exotic species may improve the ability to understand and effectively manage plant invasions in the future. In this study the following hypotheses were tested: (1) biomass production of below- and aboveground plant components of the exotic tree species is higher than that of the natives, resulting in a higher competitiveness of the exotics; (2) the exclusion of root competition has a positive effect on the biomass production of the inferior native species; and (3) mixtures of native and exotic species yield a higher biomass production than the respective monocultures.Methods A pot experiment, containing about 2000 tree seedlings, was established. We investigated the biomass productivity and growth reactions of two native (Quercus robur L., Carpinus betulus L.) and two exotic tree species (Prunus serotina Ehrh., Robinia pseudoacacia L.) in different intra- and interspecific, competitive situations with and without the influence of root competition.Important findings The biomass production of both exotic species was significantly higher and led to a strong competitive advantage, resulting in a biomass decrease of the less competitive native species. The high belowground biomass of both exotic species had a negative effect on the biomass production. The competitive pressure of exotic tree seedlings on the native ones was largely driven by root competition. Furthermore, mixtures of native and exotic tree species had a higher productivity than their growth in monocultures would have predicted. Competition was lower for exotic species in mixtures with the less productive native species compared to the competition in monocultures or in mixture with the other highly productive exotic species. Accordingly, both highly competitive exotic species produced less biomass in mixture with each other compared to monocultures. Despite the significantly higher biomass of P. serotina in all mixtures and in monoculture, R. pseudoacacia seemed to be the dominating species. Due to its strong root competition, R. pseudoacacia significantly reduced the biomass production of P. serotina .     

Association of SSR Markers with Cold Tolerance Traits in Diverse Bermudagrass [Cynodon dactylon (L.) Pers.] Accessions

Bermudagrass [Cynodon dactylon (L.) Pers.] is a perennial and typical warm-season grass. It undergoes withering and severe damage under cold stress; thus, cold is considered as a key factor that restricts the widespread use in bermudagrass. Identification of association between molecular markers and cold tolerance-related traits would facilitate the efficient selection of cold tolerant bermudagrass cultivars. A total of 106 diverse bermudagrass accessions, including 4 commercial cultivars and 102 wild germplasms, were tested for cold tolerance and analyzed by 104 simple sequence repeat (SSR) markers. Cold significantly decreased transpiration rate, growth rate and turf quality. There were significant variations in these trait values among the accessions under cold conditions. Two subpopulations were detected in the panel of accessions based on the analysis of 1474 alleles with 104 SSR markers. Clustering analysis revealed that the genetic relationship was affected by the natural habitats. Thirty-four SSR markers were identified to be associated with two or three traits based on the corrected P values (P < 3.5 × 10⁻⁴). These markers can be used for genetic improvement of cold tolerance of bermudagrass after further validation.