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Acid soil stress limits crop productivity on nearly one-half of the nonirrigated arable land in the world. Improvement of acid soil tolerance in sorghum [Sorghum bicolor (L.) Moench] has been approached through conventional breeding programs and more recently through biotechnology. This study was initiated to determine if improved acid soil tolerant tissue culture regenerates could be developed from sensitive parental lines and whether tolerant regenerants with desirable agronomic traits could be selected under field stress conditions. Tissue culture regenerated lines of sorghum and their nonregenerated checks were field tested for acid soil [Typic Kanhapludult] tolerance (50% Al saturation at pH 4.2-4.6) near Griffin, GA, from 1986 to 1990. Two [R.sub.5] lines derived from |Hegari' and two R, lines from RTx430 demonstrated improved acid soil tolerance in 1989. Field test results indicated that these four lines had significantly higher ratings for vigor (2.6-3.4 vs. 4.8-4.9), plant survival (12-30 vs. 1), panicles harvested (2-9 vs. 0), and seed yield (20-85 g [plot.sub.-1] vs. 0) than their nonregenerated checks. During 1990, selected [R.sub.7] lines were advance tested on acid soils near Griffin with similar results. Three of these improved selections were then evaluated for early seedling development in a greenhouse soil study using the same acid soils from the field. These results showed that one Tx430 regenerated line had improved root development at low pH during the seedling stage. This research indicated that variation for acid soil stress tolerance was produced through tissue culture and that agronomically desirable genotypes were selected using appropriate field testing procedures and stress levels., Acid tolerant lines of sorghum were obtained by tissue culture selection and field tested to select for agronomically desirable lines. Initial field tests showed 1.4% of the original 212 regenerants to be acid soil tolerant. Further field testing coupled with selection for agronomically desirable traits ended with three promising lines (H2021-9, T75-46-20 and T75-46-50) that produced high grain yields under both acid soil stress and nonstress conditions. Greenhouse experiments revealed that T75-46-50 had the ability to produce a well developed root system during eary seedling stages under acid soil stress conditions.

Traffic causes shoot injury to turfgrass, with resulting inhibition of growth and reduction of quality. Turfgrasses in high traffic venues are generally selected for tolerance to traffic or for an ability to quickly outgrow the injury. However, limited knowledge exists on the mechanisms that impart wear tolerance to turfgrass, particularly for warm-season grasses. This field research was undertaken to assess overall wear tolerance within and between seashore paspalum (Paspalum vaginatum Swartz.) ecotypes and bermudagrass hybrids (Cynodon dactylon L. x C. transvaalenxis Burtt-Davy) and to determine the mechanisms that contribute to wear tolerance for both species. The research was conducted in two consecutive field trials during 1997 on seven seashore paspalum ecotypes and three hybrid bermudagrass cultivars established on a native Appling (fine, kaolinitic, thermic Typic Kanhapludult) soil at the University of Georgia Experiment Station in Griffin, GA. Regression analysis determined that the most important potential mechanism related to enhanced wear tolerance of seashore paspalum was reduced leaf total cell wall (TCW) content, which accounted for 51% of the variation. Other factors that enhanced wear tolerance in this species were low leaf strength, low stem TCW, greater leaf moisture, greater shoot density, and higher K shoot tissue concentration. In bermudagrass, high stem moisture (40.9% of variation) and reduced stem cellulose content (31.5% of variation) were associated with better wear tolerance. Other factors that enhanced wear tolerance were greater stem and leaf moisture, shoot density, leaf lignin, stem and leaf lignocellulose, and concentration of K, Mn, and Mg. Knowledge of these characteristics will assist in developing screening protocols for selection of future wear tolerance cultivars within these species., TRAFFIC IS A SOURCE OF ABIOTIC STRESS that can impose two distinct forms of injury on turf. Wear injury to shoot tissue is manifested by abrasion, tearing, or stripping of [...]

Seashore paspalum (Paspalum vaginatum Swartz) displays wide intraspecific diversity and exhibits tolerance to numerous abiotic stresses. In addition, comparatively low fertility requirements and high quality growth characteristics of many ecotypes render this grass a prospective candidate for use on golf courses, athletic fields, and landscaped areas in warm climates worldwide. The objectives of this research were to evaluate the relative growth, quality, and wear tolerance of seashore paspalum and bermudagrass. This research was conducted in two consecutive field trials during 1997 under wear and non-wear conditions on seven seashore paspalum ecotypes and three hybrid bermudagrass (Cynodon dactylon L. X C. transvaalensis Burtt-Davy) cultivars established on a native Appling sandy clay loam (clayey, kaolinitic, thermic typic Kanhapludult) at the University of Georgia Experiment Station at Griffin, GA. We found that two paspalum ecotypes, Temple 1 and SIPV-2 , ranked as high or higher than `Tifway' and `Tifsport' for visual quality, shoot density, shoot growth, and amount of verdure tissue under non-wear conditions. In addition, these two paspalum ecotypes showed the most favorable spectral reflectance data responses, indicating greatest utilization of intercepted light, and also showed rates of recovery from wear which were equal to or greater than those of the bermudagrass entries. Paspalum ecotypes Temple I and SIPV-2 appear to be suitable for use in areas where a high quality, traffic-tolerant turfgrass is required. Paspalum ecotypes with lower shoot densities were less wear tolerant., BERMUDAGRASS HYBRID CULTIVARS have been the predominant turfgrasses in use on golf courses and athletic fields throughout the southern USA and in warm climate areas worldwide. While these grasses provide [...]

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 multispectrai 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. x C. transvaalensis 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 [R.sub.935] - [R.sub.661]/[R.sub.661] + [R.sub.661]), infrared/red (IR/R) (LAI, computed as [R.sub.935]/ [R.sub.661]), Stress1 ([R.sub.706]/[R.sub.760]), and Stress2 ([R.sub.706]/[R.sub.813]) 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., Qualitative evaluations are routinely used in turfgrass research as a standard for assessing turf growth or for comparing responses to treatments. Quality may be described by both visual and functional [...]