Simple sequence repeats (SSRs), also known as microsatellites, are highly variable DNA sequences that can be used as markers for the genetic analysis of plants. Three approaches were followed for the development of PCR primers for the amplification of DNA fragments containing SSRs from sorghum [Sorghum bicolor (L.) Moench]: a search for sorghum SSRs in public DNA databases; the use of SSR-specific primers developed in the Poaceae species maize (Zea mays L.) and seashore paspalum grass (Paspalum vaginatum Swartz); and the screening of sorghum genomic libraries by hybridization with SSR oligonucleotides. A total of 49 sorghum SSR-specific PCR primer pairs (two designed from GenBank SSR-containing sequences and 47 from the sequences of genomic clones) were screened on a panel of 17 sorghum and one maize accession. Ten primer pairs from paspalum and 90 from maize were also screened for polymorphism in sorghum. Length polymorphisms among amplification products were detected with 15 of these primer pairs, yielding diversity values ranging from 0.2 to 0.8 with an average diversity of 0.56. These primer pairs are now available for use as markers in crop improvement and conservation efforts.

Multispectral radiometry provides a method for assessing plant light reflectance in the visible and near‐infrared ranges. Reflectance of narrow wavelength ranges as well as ratios of different ranges have been highly correlated with absorbency of photosynthetically active radiation, leaf area index (LAI), and plant response to stresses. The objectives of this research were to determine if data obtained by multispectral radiometry might accurately correlate with qualitative data (used as rapid estimates of color, density, and uniformity) typically used in turfgrass research. Furthermore, it was our objective to determine whether multispectral radiometry could discriminate between stressed and nonstressed turfgrass plots. This research was conducted in two consecutive trials during 1997 on seven seashore paspalum (Paspalum vaginatum Swartz) ecotypes and three hybrid bermudagrass (Cynodon dactylon L. × C. trunsvaalensis Burtt‐Davy) cultivars established on a native Appling (clayey, kaolinitic, thermic Typic Kanhapludult) soil at the University of Georgia Experiment Station in Griffin, GA. Reflectance at 661 and 813 nm, as well as the ratios normalized difference vegetation index (NDVI, computed as R935‐ R661/R935 + R661), infrared/red (IRIR) (LAI, computed as R935/R661), Stress1 (R706/R760 nd Stress2 (R706/R813) were highly correlated with visual turf quality, shoot density, and shoot tissue injury (STI) ratings, but not with shoot clipping growth. Regression analysis also indicated very strong associations with each of these qualitative variables, but not with shoot growth data. Additionally, spectral measurements at all wavelengths except 559 and 706 nm were able to consistently distinguish between wear‐treated and untreated plots. This methodology may have applications in both turfgrass research and management to provide quantitative measures with physiological significance to traditional visual qualitative estimates of shoot aspects.

Knowledge of drought‐resistance mechanisms in turfgrasses would improve management strategies and facilitate turfgrass breeding for drought resistance. The experiment investigated root morphological and physiological characteristics in response to surface soil drying and rewatering for bermudagrass [Cynodon dactylon (L.) Pers. ‘Common’], centipedegrass [Eremochloa ophiuroides (Munro) Hack ‘Tif‐Blair’], seashore paspalum (Paspalum vaginatum Swartz, four ecotypes), and zoysiagrass (Zoysia japonica Steudel × Z. tenuifolia Steudel ‘Emerald’). Plants were grown in sectioned PVC tubes with four soil moisture regimes in a greenhouse during 1995 and 1996. Root growth was reduced when the upper 20‐ and 40‐cm soil layers dried for Emerald zoysiagrass, Common bermudagrass, and Adalayd paspalum, but only with upper 40‐cm soil drying for PI 299042, AP14, and PI 509018 paspalums, and TifBlair centipedegrass. Root dry weight recovered fully to control levels after rewatering for TifBlair centipedegrass and the three paspalum accession, but only partially for Adalayd paspalum, Common bermudagrass, and Emerald zoysiagrass. Superior drought resistance to surface soil drying for PI 509018 paspalum and TifBlair centipedegrass was associated with enhanced root growth and rapid root water uptake at deeper soil layers, maintenance of root viability at the surface drying soil, and rapid root regeneration after rewatering. Differences in these drought avoidance characteristics among turfgrasses could serve as selection criteria for improving turf drought resistance.

tween species. Warm-season turfgrass is typically more wear tolerant than cool-season turf (Youngner, 1961; Traffic causes shoot injury to turfgrass, with resulting inhibition Beard, 1973). Cultural practices, such as increased mowof growth and reduction of quality. Turfgrasses in high traffic venues are generally selected for tolerance to traffic or for an ability to ing height (Beard, 1973; Youngner, 1961), moderate N quickly outgrow the injury. However, limited knowledge exists on fertilization levels (Kohlmeier and Eggens, 1983), and the mechanisms that impart wear tolerance to turfgrass, particularly a thatch layer (Beard, 1973) can also influence wear tolfor warm-season grasses. This field research was undertaken to assess erance. overall wear tolerance within and between seashore paspalum (Pas-While some research has looked at wear tolerance at palum vaginatum Swartz.) ecotypes and bermudagrass hybrids (Cynothe intra-specific level (Beard, 1973), the data are very don dactylon L. ϫ C. transvaalensis Burtt-Davy) and to determine limited as to the degree of severity in wear tolerance the mechanisms that contribute to wear tolerance for both species.within a species, and the specific mechanisms responsi-The research was conducted in two consecutive field trials during 1997 ble for enhanced wear tolerance. Anatomical, morphoon seven seashore paspalum ecotypes and three hybrid bermudagrass logical, or physiological plant characteristics correlating cultivars established on a native Appling (fine, kaolinitic, thermic Typic Kanhapludult) soil at the University of Georgia Experiment with wear tolerance across species may not be the same Station in Griffin, GA. Regression analysis determined that the most within a particular species. important potential mechanism related to enhanced wear tolerance Shearman and Beard (1975a) evaluated interspecies of seashore paspalum was reduced leaf total cell wall (TCW) content, wear tolerance with four measurements: visual ratings, which accounted for 51% of the variation. Other factors that enhanced percentage TCW content, percentage verdure, and perwear tolerance in this species were low leaf strength, low stem TCW, centage chlorophyll per unit area. They found that visual greater leaf moisture, greater shoot density, and higher K shoot tissue wear estimates were well correlated (r ϭ Ϫ0.98) with concentration. In bermudagrass, high stem moisture (40.9% of variaquantitative evaluations when evaluating wear tolertion) and reduced stem cellulose content (31.5% of variation) were ance between species. Canaway (1981) determined that associated with better wear tolerance. Other factors that enhanced percentage of ground cover remaining after wear was wear tolerance were greater stem and leaf moisture, shoot density, leaf lignin, stem and leaf lignocellulose, and concentration of K, Mn, negatively correlated with modified acid detergent fiber and Mg. Knowledge of these characteristics will assist in developing per unit area. screening protocols for selection of future wear toleran...

ters, however, these organs can be killed when the frost zone moves below the rhizome layer. Even during rela-Seashore paspalum (Paspalum vaginatum Sw.) is a warm-season tively mild winters, the crowns and rhizomes are suscepturfgrass, best known for its superior salt tolerance. Plants are subject tible to injury due to the cold. Reestablishment of damto injury during winter conditions along the northern boundary of aged turf is expensive both in terms of labor and plant their zone of adaptation. New cultivars that are more tolerant to low temperatures are needed for use in the transition zone. Cold material. Thus, a more complete understanding of the tolerance has been correlated with the degree of unsaturation in tolerance of warm season grasses to low temperatures membrane lipid fatty acids. Unsaturated fatty acids are thought to is needed to improve their utility and extend their range. aid in maintaining membranes in a fluid state necessary for biological Whereas most temperate perennial plants can survive functioning (homeophasic adaptation). The primary objective was extensive exposure to subfreezing conditions, most tropto characterize fatty acid composition of membrane lipids in three ical and a number of subtropical plants have little or no genotypes differing in cold tolerance. A second objective was to invescapacity to withstand freezing temperatures. A plant's tigate changes in fatty acid content in these genotypes during exposure ability to alter its physiology in response to low temperato low temperatures. Cold-treated plants were exposed to a 10-h ture, such that it can survive otherwise lethal temperaphotoperiod at 8؇/4؇C day/night temperatures and light intensity of tures, is called cold acclimation (hardening). The pro-250 mol m Ϫ2 s Ϫ1 photosynthetic photon flux density for 3 wk. Rhizomes and crowns were harvested at 7-d intervals. Total lipids were cess of cold acclimation occurs seasonally when plants extracted and the polar lipids separated by thin-layer chromatography. are exposed to low, nonfreezing temperatures beforeFatty acids were identified by gas chromatography (GC) and mass the onset of winter (Levitt, 1980). Some C4 grasses have spectroscopy. In all three genotypes, the two saturated fatty acids, been shown to cold acclimate (Anderson et al., 1988, palmitic acid and stearic acid, did not change during cold treatment. 1993). The biochemical changes accompanying acclima-The triunsaturated linolenic acid increased significantly during low tion to low temperature include alterations in soluble temperature exposure. The magnitude of change was greater in the carbohydrate content, synthesis, and conformation of finer-textured and more cold-tolerant PI 509018-1 ('SeaIsle1') than in proteins and changes in membrane lipid composition the intermediately cold-tolerant 'Adalayd' or in the cold-susceptible, and fatty acid saturation (Li, 1984; Sakai and Larcher, coarse-textured PI 299042. These findings suggest that accumulation 1987; Hallgren and Oquist, 1990). Many of the new of linolenic ac...