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Eric Watkins and William A. Meyer

Recently, turfgrass breeders have developed many improved turf-type tall fescue (Festuca arundinacea Schreb.) cultivars. Due to the large number of cultivars currently available to turfgrass managers and researchers, we have classified turf-type tall fescue cultivars into six groups based primarily on several morphological measurements. This type of classification is important for turfgrass breeders because many breeding decisions are made based on observations in a spaced-plant nursery. The major objective of this study was to classify tall fescue cultivars and selections based on spaced-plant measurements and to then compare those results with turf performance. A spaced-plant nursery consisting of 36 cultivars and selections was established in September 1998 at Adelphia, N.J. Plant height, panicle length, flag leaf width and length, subtending leaf width and length, and subtending internode length were measured 10 days after anthesis in 1999 and 2000. Additionally, a turf trial was established at North Brunswick, N.J., that included the same 36 cultivars and selections. The turf plots were evaluated for several traits including overall turfgrass quality, density, and susceptibility to brown patch disease. Based on principal component analysis of morphological measurements, along with turf trial data, all cultivars and selections were assigned to one of six groups: forage, early-standard, standard, early semi-dwarf, semi-dwarf, and dwarf. In turf plots, the semi-dwarf, early-semi dwarf, and dwarf groups were the top-performing types in terms of overall turfgrass quality, and the forage and early-standard cultivars had the lowest overall quality ratings. The dwarf types did not perform well under summer stress, especially in terms of brown patch disease incidence. The results of this study suggest that when developing cultivars for higher maintenance situations, turf-type tall fescue breeders should focus on the development of semi-dwarf cultivars.

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Eric Watkins, Bingru Huang, and William A. Meyer

Tufted hairgrass [Deschampsia cespitosa (L.) Beauv.] is receiving increasing attention as a low-maintenance turfgrass for use in areas with reduced fertility or reduced sunlight. The objectives of this study were to examine physiological responses of tufted hairgrass to heat and drought stress and to distinguish whether better summer performance was related to better heat or drought tolerance. Four germplasm lines were chosen based on summer performance in field plots (two lines resistant to summer stress and two lines susceptible to summer stress) and were grown in growth chambers [14-hour photoperiod, 20/15 °C (day/night)]. Plants were exposed to either drought stress or heat stress (35/30 °C, day/night) for up to 49 days. Control plants maintained under normal conditions (20/15 °C, day/night, well watered) were included for both treatments. During the course of the study, single-leaf photosynthetic rate, photochemical efficiency, and relative water content were measured, and turf quality was visually rated. All parameters for all tufted hairgrass lines decreased under drought stress and heat stress, and the decline was more severe for summer stress-susceptible lines than for resistant lines. Lines that were previously considered resistant to summer stress exhibited superior photochemical efficiency under heat stress compared with the susceptible lines. When subjected to drought stress, the lines exhibited little or no differences in the measured parameters. These results suggest that observed variation in field summer performance among various tufted hairgrass germplasm lines may be mainly the result of their differences in heat tolerance. These results suggest that selecting for heat-tolerant germplasm could be important for further improvement in turf performance of tufted hairgrass during the summer.

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Josh A. Honig, Stacy A. Bonos, and William A. Meyer

Kentucky bluegrass (Poa pratensis L.) is an important facultative apomictic temperate perennial grass species used for both forage and cultivated turf. Through apomixis, this species is able to propagate diverse and odd ploidy levels, resulting in many genetically distinct phenotypes. A wide range of diverse cultivars and accessions of kentucky bluegrass have been previously characterized based on common turf performance or morphological characteristics as well as by random amplified polymorphic DNA (RAPD) markers. Although previous characterization efforts have provided valuable information, the use of both morphological characteristics and RAPD markers for genetic diversity analysis has limitations. In the current report, we developed and characterized 88 novel microsatellite markers for kentucky bluegrass. Polymorphism for each marker was assessed in 265 kentucky bluegrass cultivars, experimental selections, collections, and hybrids. The number of alleles for individual microsatellites ranged from four to 81 with an average of 38.3 alleles per simple sequence repeat. These polymorphic microsatellite markers would be useful tools for investigating genetic diversity, creation of genetic linkage maps, assessment of levels of apomixis in cultivars and experimental varieties, and identification of aberrant progeny in apomictic kentucky bluegrass breeding programs.

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Stacy A. Bonos, William A. Meyer, and James A. Murphy

The apomictic breeding behavior of Poa pratensis L. provides an opportunity to study many unique genotypes that can vary dramatically in characteristics such as disease resistance, stress tolerance and growth habit. The classification of Kentucky bluegrass into types is based on common growth and stress performance characteristics gathered from field turf trials. These classification types include the Compact, Bellevue, Mid-Atlantic, BVMG (`Baron, `Victa', `Merit', and `Gnome'), Common, and Aggressive types. A spaced-plant nursery trial was established in May 1996 to quantify morphological and growth characteristics of 45 cultivars and selections representing the major types of Kentucky bluegrass. Plant height, panicle height, flag leaf height and length, subtending leaf length and width, rhizome spread, and longest extending rhizome were measured 10 days after anthesis. Compact type cultivars had a lower, more prostrate growth habit than the Common, Mid-Atlantic, and Bellevue types. Mid-Atlantic type cultivars had a wider rhizome spread than Compact type cultivars. Principal component analysis of morphological measurements made on spaced-plants supports the classification types of the Common, Compact, Bellevue, Mid-Atlantic, and BVMG, but not necessarily the Aggressive type.

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Zhaolong Wang, Bingru Huang, Stacy A. Bonos, and William A. Meyer

Drought is a major factor limiting plant growth, which has been associated with the accumulation of absicsic acid (ABA) in various species. The objective of the study was to determine the relationship between ABA accumulation and drought tolerance for kentucky bluegrass (Poa pratensis L.) during short-term drought stress. Eight kentucky bluegrass cultivars (`Midnight', `A82-204', `RSP', `Alpine', `Moonlight', `Brilliant', `Washington', and `Baruzo') were subjected to drought stress in a growth chamber. Water relations, gas exchange rate, and ABA content of leaves were determined at various times during drought stress. Turf quality decreased with drought duration for all eight cultivars. Leaf ABA content increased linearly with drought stress within 11 days of treatment; the rate of the increase was negatively related to the rate of turf quality decline. The rate of ABA accumulation during drought stress was positively correlated with the rates of decrease in turf quality (r 2 = 0.6346), increase in electrolyte leakage (r 2 = 0.7128), and decrease in relative water content (r 2 = 0.5913). There were highly significant negative correlations between ABA content and leaf water potential (r 2 = 0.9074), stomatal conductance (r 2 = 0.6088), transpiration rate (r 2 = 0.6581), net photosynthesis rate (r 2 = 0.6956), and a positive correlation between ABA content and electrolyte leakage (r 2 = 0.7287). The results indicate that drought tolerance is negatively related to ABA accumulation during shortterm drought stress. ABA accumulation in response to drought stress could be used as a metabolic factor to select for drought tolerance in kentucky bluegrass.

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Robert R. Shortell, William A. Meyer, and Stacy A. Bonos

The apomictic breeding behavior of Kentucky bluegrass (Poa pratensis L.) results in many unique cultivars. A classification system was previously developed to characterize the large number of Kentucky bluegrass cultivars into different types. However, many new cultivars have been released since the last refinement of the classification system. The objectives of this study were to determine differences in morphological and agronomic characteristics among select Kentucky bluegrass cultivars representing the major classification types and to determine broad-sense heritability estimates for important morphological (plant height, panicle length, flag leaf height, and flag leaf length and width) and agronomic (rhizome spread) traits in Kentucky bluegrass. A spaced-plant nursery trial was established in the spring of 2003 at Adelphia, NJ. One hundred seventy-three cultivars and selections were planted in a randomized complete block design with three replications. The morphological and agronomic traits listed were measured on spaced plants. High Density type cultivars (formerly the Aggressive type cultivars) had the most prostrate growth habit with plant heights of 33 and 43 cm in 2004 and 2005, respectively. Mid-Atlantic and Texas × Kentucky bluegrass hybrids had the widest rhizome spread (Mid-Atlantic = 73 and 121 cm; Texas × Kentucky bluegrass hybrids = 72 and 122 cm) in 2004 and 2005, respectively. Broad-sense heritability estimates were high for plant height (H = 0.84), panicle length (H = 0.88), flag leaf height (H = 0.85), and rhizome spread (H = 0.85); moderate for flag leaf length (H = 0.71); and low for flag leaf width (H = 0.11). This study characterizes new cultivars into respective groups and identifies the genetic inheritance of important morphological and agronomic traits in Kentucky bluegrass.

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Jonathan M. Bokmeyer, Stacy A. Bonos, and William A. Meyer

Brown patch, caused by Rhizoctonia solani Kühn, is a devastating disease of tall fescue (Festuca arundinacea Schreb.). Developing genetic resistance is a viable long-term control strategy; however, the genetic mechanism of brown patch resistance in tall fescue is not known. The objectives of this study were to determine the broad-sense heritability and stability analysis of brown patch resistance in tall fescue. To complete these objectives, 230 tall fescue genotypes were arranged in a randomized complete block design with six clonal replications at two locations and evaluated for brown patch resistance over 2 years. Two isolates of R. solani were used to inoculate both field trials at a rate of 0.8 g·m−2 of prepared inoculum. The lack of complete resistance and the observation of a continuous distribution of phenotypes suggest that brown patch resistance is quantitatively inherited. The broad-sense heritability estimates (0.25 on a single plant basis and 0.74 on 12-plant clonal mean basis) indicate that resistance is influenced by the genotype and also illustrate the importance of replication in selecting for brown patch resistance in tall fescue. Stability analysis resulted in the identification of tall fescue genotypes that were stable over multiple environments for brown patch resistance.

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Josh A. Honig, Vincenzo Averello, Stacy A. Bonos, and William A. Meyer

Kentucky bluegrass (Poa pratensis L.) is an important facultative apomictic temperate perennial grass species used for both forage and cultivated turf. Through apomixis, this species is able to propagate diverse and odd ploidy levels, resulting in many genetically distinct phenotypes. A wide range of diverse cultivars and accessions of kentucky bluegrass have been previously characterized based on pedigree, common turf performance, and morphological characteristics to create a kentucky bluegrass cultivar classification system. The objectives of the current study were to assess the amount of genetic divergence among kentucky bluegrass cultivars, experimental selections, and plant collections and revise/update the original pedigree, turf performance, and morphological characteristics kentucky bluegrass classification system using recently described kentucky bluegrass microsatellite [simple sequence repeat (SSR)] markers. In this study, 247 kentucky bluegrass cultivars, experimental selections, and collections were genotyped using 25 SSR markers. SSR markers showed a strong correlation between genetic relatedness as assessed by molecular markers and the original kentucky bluegrass classification system and also provided justification for a revision/update of the classification system. Traditional classification types that were supported by the current SSR analysis include BVMG, Compact, Compact-America, Julia, Mid-Atlantic, Midnight, and Shamrock types. Newly proposed classification types included Cynthia, Jefferson/Washington, Limousine, P-105, Sydsport, and three Eurasian types. The majority of cultivars, experimental selections, and collections were uniquely identified with the current set of SSR markers. Genetic relationships of individuals as assessed by SSR markers closely matched known pedigrees. The current set of SSR markers can be used to rapidly genotype and assign new cultivars/accessions to kentucky bluegrass classification types and assess genetic relatedness among individuals and should be considered for use in a kentucky bluegrass plant variety protection program.

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Lisa A. Beirn, William A. Meyer, Bruce B. Clarke, and Jo Anne Crouch

Rusts are destructive fungal diseases that can cause severe thinning and unattractive discoloration of kentucky bluegrass (KBG; Poa pratensis L.). Currently, turfgrass breeding programs rely on field evaluations to screen KBG germplasm for rust resistance; methods that are expensive, labor intensive, and require large turf areas. The availability of a greenhouse-based assay to perform prescreening of KBG germplasm for resistance to rust diseases before field trials would allow breeders to remove the poorest performing plants before field evaluations thus enhancing breeding efficiency. In this study, we set out to develop a reliable, low-cost greenhouse inoculation protocol for the two most common rust pathogens of KBG in temperate growing regions: Puccinia coronata and Puccinia graminis, the causal agents of crown and stem rust, respectively. Using a modified inoculation assay and custom-built plexi-glass chambers adapted from protocols used for cereal rust pathogens, urediniospores of crown and stem rust fungi developed on inoculated plants 10 to 14 days postinoculation. Real-time polymerase chain reaction (PCR) assays, disease symptomology, and morphology of urediniospores confirmed the presence and identity of both rust pathogens from inoculated host tissue. The inoculation protocols described here represent an effective method to accelerate screening of KBG germplasm for resistance to crown and stem rust diseases. Infection of KBG plants in the greenhouse will also allow breeders to maintain populations of crown and stem rust fungi throughout the year, providing a reliable and ongoing source of pathogen inoculum for experimentation and screening in the future.

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James W. Cross, Stacy A. Bonos, Bingru Huang, and William A. Meyer

Heat and drought are two major abiotic stresses causing a decline in quality in cool-season turfgrasses during the summer. The objectives of this study were 1) to determine whether genotypic variations in turf performance during summer stress in New Jersey is related primarily to heat tolerance or drought tolerance of tall fescue; and 2) to make selections of plants tolerant to summer stress for breeding efforts. Twenty-four tall fescue genotypes exhibiting differential performance during summer months in field conditions (12 summer stress-tolerant and 12 summer stress-sensitive) were selected from the germplasm pool present at the New Jersey Agricultural Experiment Station. Plants of these 24 genotypes were exposed to heat, drought, or heat + drought. There were generally no significant differences in turf quality, photochemical efficiency, relative water content, or electrolyte leakage between summer stress-tolerant and -sensitive genotypes, except in the heat treatment in which the summer stress-tolerant selections performed significantly better. The results indicate that the superior performance of the summer stress-tolerant plants under field conditions is mainly the result of superior heat tolerance.