bluuebunny/crossref_metadata_2025 huggingface dataset:
Lowering Soil Temperatures Improves Creeping Bentgrass Growth under Heat Stress
Authors: Xu Qingzhang , Huang Bingru
Published: July 2010

High soil temperature is a major factor limiting growth of cool‐season grasses. The objectives of this study with creeping bentgrass (Agrostis palustris Huds.) were to examine growth responses to lowering soil temperatures from the supraoptimal level under high air temperature conditions, and to determine the minimum reduction in soil temperature that could improve shoot and root growth. Two creeping bentgrass cultivars, L‐93 and Penncross, were exposed to the following air and soil temperature regimes in growth chambers and water baths: (i) optimal air and soil temperatures (20/20°C, control); (ii) lowering soil temperature by 3, 6, and 11°C from 35°C at high air temperatures (35/32, 35/29, 35/24°C); and (iii) high air and soil temperatures (35/35°C). Soil temperature was reduced from 35°C by circulating cool water (18°C) in water baths at variable rates. Turf quality, leaf chlorophyll content, shoot growth rate, and root/shoot ratio (R/S) ratio increased as soil temperature was reduced from 35 to 32°C to a greater extent for Penncross than for L‐93. Significant increases in tiller density, clipping yield, root number, and fresh weight were not observed until soil temperature was reduced to 29°C. When soil temperature was reduced to 24°C, turf quality, shoot growth rate, and R/S were maintained at the same levels as in the control regime. These results suggested that reducing soil temperature by 3°C or more is effective in improving turf quality and shoot and root growth of creeping bentgrass exposed to high air temperatures.
Comparative Responses of Two Kentucky Bluegrass Cultivars to Salinity Stress
Authors: Qian Y. L. , Wilhelm S. J. , Marcum K. B.
Published: July 2010

Little information is available concerning physiological responses of Kentucky bluegrass (Poa pratensis L.) (KBG) cultivars to salinity. Growth and physiological responses of ‘Limousine’ and ‘Kenblue’ KBG to a range of salinity levels were investigated. Grasses were grown in solution culture and exposed to salinity levels of 2.2, 5.2, 8.2, 11.2, and 14.2 dS m−1 for 10 wk. Though both cultivars exhibited increased leaf firing with increasing salinity, Limousine exhibited less leaf firing than Kenblue at salinity levels above 5.2 dS m−1 In addition, salinity levels that caused 25% shoot growth reduction were 3.2 dS m−1 for Kenblue and 4.7 dS m−1 for Limousine, indicating that Limousine has better salinity tolerance. Under moderate (8.2 dS m−1) salinity stress, Limousine produced ∼50% more root growth than Kenblue. Water relations diverged between cultivars at 8.2 and 14.2 dS m−1, as Limousine had higher leaf water and osmotic potentials, as well as more positive turgor. While glycinebetaine was not detected in either cultivar, proline increased in leaves with increasing salinity, and was higher in Kenblue than Limousine at 8.2, 11.2, and 14.2 dS m−1 This suggests that compatible solute accumulation is not a salinity tolerance mechanism of KBG, and that proline accumulation is merely an indication of salt injury. Limousine maintained 52% lower shoot Na+, 30.4% lower Cl−, and 52% higher shoot K+/Na+ ratio than Kenblue at the highest salinity level. These results suggest that salinity tolerance in KBG is largely attributable to maintenance of higher root growth, and more positive turgor, higher K+/Na+ ratio, and less Cl− accumulation in shoots. These traits may serve as useful selection criteria in breeding efforts to develop salt tolerant KBG.
Performance of Meadow Fescue Accessions under Management‐Intensive Grazing
Authors: Casler Michael D. , van Santen Edzard
Published: July 2010

Meadow fescue (Festuca pratensis Huds.) is a pasture grass that has been little used in North America since the introduction of its higher yielding relative, tall fescue (F. arundinacea Schreb.). The objectives of this study were to quantify genotypic variation for traits related to performance under management‐intensive grazing (MIG) within the USDA‐NPGS collection of meadow fescue accessions, to relate that variation to the geographic sources, and to compare these meadow fescue accessions to a range of tall fescue cultivars. One hundred‐sixty meadow fescue accessions and 10 tall fescue cultivars were grazed for 2 yr under a free‐choice MIG system. Meadow fescue accessions were an average of 3.0% lower in net herbage accumulation (NHA; 8.33 vs. 8.60 Mg ha−1), but 14.7% higher in apparent intake (3.13 vs. 3.58 Mg ha−1) and 15.1% higher in apparent preference (31.7 vs. 36.4%) compared with tall fescue cultivars. Naturalized meadow fescue accessions had greater apparent intake and preference and were lower in crown rust resistance than cultivated meadow fescue accessions. Cultivated meadow fescue accessions were less variable for all traits than naturalized accessions, reflecting nearly a century of breeding activity in Europe. Most of the variability among accessions was accounted for by geographic sources. Naturalized accessions from the Russian Black Sea region generally ranked most favorably for all traits.
Removal of Perennial Ryegrass from Overseeded Bermudagrass Using Cultural Methods
Authors: Horgan Brian P. , Yelverton Fred H.
Published: July 2010

Turfgrass managers in the southeastern United States often overseed ‘Tifway’ bermudagrass [Cynodon transvaalensis Burtt‐Davey × C. dactylon (L.) Pers.] with perennial ryegrass (Lolium perenne L.) to provide a dense green turf during winter months. Although overseeding provides benefits, the spring transition from perennial ryegrass to bermudagrass can be troublesome and inconsistent. Perennial ryegrass may survive longer into the spring than is desired due to cool, wet conditions. The following experiment evaluated cultural methods for removal of perennial ryegrass from overseeded bermudagrass in the spring and early summer. The experiment was conducted at the North Carolina State University Turfgrass Field Center in Raleigh in the 1995 to 1996 and 1996 to 1997 growing seasons. Monocultures of ‘Gator’ and ‘Derby Supreme’ perennial ryegrass were overseeded into an established Tifway bermudagrass turf managed at golf course fairway conditions. It was hypothesized that various cultural treatments in the spring and summer could promote bermudagrass and/or discourage perennial ryegrass, and that the perennial ryegrass transition would differ depending on heat tolerance of the selected overseeding monocultures. The cultural treatments were biweekly vertical mowing, scalping, core cultivation, and vertical mowing/scalping, or two application timings of NH4NO3 Chemical removal of perennial ryegrass using pronamide [3,5‐dichloro‐N‐(1,1‐dimethyl‐2‐propynyl)benzamide] was included as a check treatment because it is commonly used to promote transition. Bermudagrass shoot density was consistently higher in nonoverseeded plots, illustrating perennial ryegrass competition. Cultural treatments affected perennial ryegrass cover during the spring and early summer but did not hasten its ultimate disappearance. Early or late applied NH4NO3 enhanced bermudagrass shoot density in both years. In contrast, plots receiving core cultivation had lower bermudagrass shoot density at the end of the transition period than the nontreated plots. Pronamide did hasten transition through 7 and 13 wk after initial treatment for 1996 and 1997, respectively. Regression analysis between natural perennial ryegrass disappearance over both years and air temperature or relative humidity indicates a significant association. This implies that cultural treatments alone may not consistently enhance natural transition of perennial ryegrass to bermudagrass.
Quantifying Spatial and Temporal Genotypic Changes in White Clover Populations by RAPD Technology
Authors: Gustine David L. , Sanderson Matt A.
Published: July 2010

In established white clover (Trifolium repens L.) populations, seedling recruitment is rare and plants spread by clonal growth, which could lead to low intraspecific genetic diversity. To assess how populations of white clover maintain high genetic variability in grazed swards during a growing season, we examined spatial and temporal changes in white clover clones by identifying genotypes by RAPD (random amplified polymorphic DNA) profiles. Trifoliate leaf samples were taken from plants at up to 37 specific sampling points in each of four 2.8‐m2 permanent quadrats in a grazed pasture from April to October 1997. RAPD profiles (genotype) based on 28 markers were determined for genomic DNA prepared from leaf samples. The number of sampled clones per quadrat ranged from zero to 10 and the sampled members per clone ranged from two to 34 over the growing season. Some clones were found more than once. During the study, numbers of clonal members increased or decreased, clones were found on one to three dates, and clones were found in one to two quadrats. The clonal diversity index D (probability that any two sampled plants have different genotypes) ranged from 0.89 to 0.99 for the eight dates, showing that genotypic diversity of populations was affected by number of clones and number of clonal members. We report here the first use of dominant RAPD markers to document dynamic changes of white clover population structure. These data show that white clover clones undergo dynamic spatial and temporal variability at a local scale, which accounts for much of the genetic diversity within field populations.
Core Collection of Sorghum: I. Stratification Based on Eco‐Geographical Data
Authors: Grenier C. , Bramel‐Cox P.J. , Hamon P.
Published: July 2010

ICRISAT conserves a large (36 719 entries) collection of sorghum [Sorghum bicolor (L.) Moench] accessions in India. This collection comprises cultivated and wild sorghums acquired over the past 25 years from 90 countries. However, it is difficult to characterize and assess a large collection with limited time and resources. To facilitate maintenance, assessment, and utilization of the collection, we considered the establishment of a core collection using stratified sampling strategies. Results from a study of the morpho‐agronomic diversity were used to describe the genetic structure of the collection. Morphological traits, including days to flowering and plant height, can be affected by daylength variation. These two characters were highly correlated with latitudinal and racial distributions of landraces. Thus, stratifying the entire collection for response to photoperiod, estimated by flowering date and plant height, was indicative of a major source of specific adaptation within the collection. This stratification resulted in four clusters, which described the sensitivity of genotypes to photoperiod within the latitudinal range where selection was carried out by farmers. These four clusters may serve as the basis for a random stratified sampling to establish cores in this collection.
Core Collection of Sorghum: II. Comparison of Three Random Sampling Strategies
Authors: Grenier C. , Hamon P. , Bramel‐Cox P.J.
Published: July 2010

Since 1972, the International Crops Research Institute for the Semi‐Arid Tropics (ICRISAT) has maintained a large collection of sorghum in India. The collection size has continuously increased, and the total number of accessions at present conserved in the gene bank has reached about 36 000 accessions. The need to help management was considered, and this study was conducted to establish core collections. This sorghum collection was earlier stratified into four clusters according to the photoperiod sensitivity. Then, considering the core collection strategy, we used three random sampling procedures to determine the specific accessions to be included in the core [i.e., a constant portion (Core C), a proportional (Core P), and a proportional to the logarithm (Core L)] of the photoperiod group size sampling strategy. Both the Core C and L were significantly different from the landrace collection with better representation of the smallest groups, such as landraces insensitive to photoperiod. Despite differences between the three core collections, estimates of global diversity through the Shannon‐Weaver Diversity Indices were of the same magnitude as the landrace collection. When compared, the Core C and L were significantly different. Core L sampled better for the characters, the race, and the latitudinal classes that were related to the photoperiod‐sensitive landraces. Thus, for establishing a core collection with the widest range of adaptation to photoperiod, we propose the use of a logarithmic sampling strategy, which identifies a broadly adapted set of genotypes.
A more rapid method of total sugar analysis for soybean seed
Authors: Geater Chandler W. , Fehr Walter R. , Wilson Lester A. , Robyt John F.
Published: July 2010

The total sugar content of soybean [Glycine max (L.) Merr.] cultivars is important to the soyfood industry. The method of total sugar analysis reported in the literature is labor intensive and time consuming. The objective of this study was to develop a more rapid method for the determination of total sugar in soybean seed. The original method was modified by reducing the amounts of reagents used, eliminating sample filtering, reducing the number of sample dilutions, and increasing the rate of acid hydrolysis. There was a significant difference between the original (187 g kg−1) and the rapid (224 g kg−1) method for the means of 10 samples with a broad range of total sugar, but no significant sample × method interaction was observed. The phenotypic correlation between the two methods for total sugar of the 10 samples was 0.91 (P < 0.05). The number of samples that could be analyzed in 1 d increased from 12 for the original method to 70 for the rapid method, and the estimated cost per sample was reduced from $5.34 to .92. The rapid method can be used to determine the relative differences among soybean samples for total sugar content.
Inheritance and Genetic Relationships of the D8 and D2‐2 Restorer Genes for Cotton Cytoplasmic Male Sterility
Authors: Zhang J.F. , Stewart James McD.
Published: July 2010

In cotton, cytoplasmic male sterility conditioned by the D8 alloplasm (CMS‐D8) is independently restored to fertility by its specific D8 restorer (D8R) and by the D2 restorer (D2R) that was developed for the D2 cytoplasmic male sterile alloplasm (CMS‐D2). However, knowledge of the relationship between the two restorer genes is lacking. The objectives of these studies were to determine the inheritance and genetic relationship between D2R and D8R. A series of intercrosses and test crosses were used to determine the inheritance and relationships. CMS‐D2 lines crossed with D8R resulted in all sterile F1 plants, confirming that the D8 restorer gene does not suppress D2 cytoplasmic dysfunction. A segregation ratio of one fertile to one sterile in three testcross combinations revealed that D2R contained one restorer gene, Rf, for both CMS‐D8 and CMS‐D2. The Rf gene functioned sporophytically, whereas the D8R gene is known to function gametophytically. However, Rf pollen with the D8 or D2 cytoplasm was preferentially effective in fertilization based on the low number of sterile plants obtained when alloplasmic F1 plants were self‐pollinated or used as the pollen‐parent in crosses with CMS‐D8. In tests for allelism only 8 sterile plants out of 1921 were obtained in two testcrosses of (D8R × D2R)F1 × normal cotton. Thus, the two restorer loci are not allelic but are tightly linked with an average genetic distance of 0.93 cM. The D2 gene Rf is redesignated Rf1, and Rf2 is assigned to the D8 restorer gene.
Comparative Efficiency of Two Breeding Methods for Yield and Quality in Rice
Authors: Ntanos Dimitrios A. , Roupakias Demetrios G.
Published: July 2010

A rice (Oryza sativa L.) breeder must choose a selection method that facilitates the simultaneous improvement of yield and quality. This study was conducted to compare the effectiveness of honeycomb selection (HCS) and panicle‐to‐row selection (PRS) in two F2 rice populations. Both populations were advanced to the F6 generation by both methods. Five F6 lines with high yield potential and good grain quality were selected from each population and selection method and were tested with a check cultivar (Strymonas) in a randomized complete block design for 2 yr near Kalochori, Thessaloniki, in Greece. In population GW 1992, significant differences in grain yield occurred between lines derived from the two methods as well as between selected lines and the check. In GW 2002, the differences were significant only between the HCS‐derived lines and the check. In both populations, significant genotypic differences were attributed to selection methods, and to methods vs. the check, for all quality traits studied except for total milling yield. The average superiority of the HCS method over the PRS method was 6 (GW 1992) and 5% (GW 2002) for grain yield, 18 and 9% for grain vitreosity, 1% (both populations) for grain length, and 3 and 2% for grain length/width ratio. These results indicate that honeycomb selection for yield and quality applied during generations was more effective than panicle‐to‐row selection applied in later generations.
The Response of Root/Shoot Partitioning and Root Morphology to Light Reduction in Maize Genotypes
Authors: Hébert Y. , Guingo E. , Loudet O.
Published: July 2010

In maize (Zea mays L.), increasing sowing density in early maturing genotypes modifies the root/shoot ratio, which generates more frequent lodging. The effects of available light on root emergence and biomass were thus studied to investigate the genetic variation and its interaction with light in traits related to root lodging. Isolated plants of eight hybrids of contrasting maturities and lodging resistance were grown in pots in outdoor conditions, in full sunlight and under neutral shading which captured 61% of the incident light. Plants were harvested at four sampling dates for root and shoot dry matter determination and measurement of some major traits involved in the architecture of the adventitious root system. The partitioning of biomass between root and shoot varied among genotypes. Biomass allocation was significantly affected by light treatment, and the effects varied among genotypes. Some genotypes seemed better able to maintain biomass allocation to the shoot, without major effects on root morphology, than were others. At silking, the final number of emerged roots from the first six internodes was similar across treatments. On the other internodes, the number of roots was lower in the shaded treatment, but the reduction observed (between 8 and 26%) depended on genotype and earliness. In addition, some genotypes with similar root biomass clearly differed in root morphology (58% variation in the average weight of root primary axes under shading), indicating a variation in the structure of the root system. The relationships between root biomass and root number indicated significant interactions between genotypes and shading, with possible consequences on root lodging resistance in the field.
Trinexapac‐Ethyl and Iron Effects on Supina and Kentucky Bluegrasses Under Low Irradiance
Authors: Stier J.C. , Rogers J.N.
Published: July 2010

Turf use in covered stadiums and other environments with reduced irradiance is limited due to lack of suitable turf species and management practices. This study compared the tolerance of supina bluegrass (Poa supina Schrad.) and Kentucky bluegrass (P. pratensis L.) with reduced irradiance of approximately 1 to 5 mol m−2 d−1 Treatments included trinexapac‐ethyl {[4‐(cyclopropyl‐α‐hydroxy‐methylene)‐3,5‐dioxo‐cyclohexane‐carboxylic acid ethyl ester]} (TE), foliar iron, and simulated athletic traffic inside a covered stadium simulator facility. Analysis of variance showed supina bluegrass was more responsive to TE than Kentucky bluegrass. Trinexapac‐ethyl reduced supina bluegrass clipping yields approximately 60%; Kentucky bluegrass yields were reduced by 20% or less. In non‐trafficked turf, TE increased supina bluegrass tillers by 50% and leaves by 33% but did not change tillering and leaf number of Kentucky bluegrass. Without traffic, TE‐treated supina bluegrass provided an acceptable turf at 10 to 15% solar irradiance for at least 4 to 6 mo, while Kentucky bluegrass and untreated supina bluegrass became unacceptable within 2 to 4 mo. Under traffic, TE‐treated supina bluegrass provided acceptable turf for up to 5 wk, while Kentucky bluegrass did not provide acceptable turf for more than 2 to 4 wk. Trinexapac‐ethyl enhanced supina bluegrass color and increased chlorophyll levels of both species. Foliar applications of iron had negligible effects on all of the parameters evaluated. Supina bluegrass is a useful turf for reduced irradiance situations but requires more than 5 mol m−2 d−1 to sustain traffic for periods longer than 5 wk.
Soybean Response to Water: A QTL Analysis of Drought Tolerance
Authors: Specht J.E. , Chase K. , Macrander M. , Graef G.L. , Chung J. , Markwell J.P. , Germann M. , Orf J.H. , Lark K.G.
Published: July 2010

Soybean [Glycine max (L.) Merr.] yield, when regressed on water needed to replenish 0 to 100% seasonal evapotranspiration (ET), generates an estimate of season‐specific water‐use efficiency (WUE). The impact of unpredictable water deficits might be lessened if high‐yielding genotypes had a smaller beta. Our objective was to determine the genetic basis of beta and carbon isotope discrimination (CID), a theorized indicator of transpiration efficiency (TE). A ‘Minsoy’ × ‘Noir 1’ population of 236 recombinant inbred lines (RILs), genotyped at 665 loci, was evaluated in six water treatments (100, 80, 60, 40, 20, and 0% ET) for 2 yr. Water stress was mild in 1994, but high temperatures and no rainfall in 1995 led to a drought so severe that the 100% ET treatment required 41 cm of irrigation. The 1995 yield‐to‐water regression was highly linear (28 kg ha−1 cm−1). Genotype × water (G × W) interaction was due to genotypic heterogeneity in beta The CID vs. beta correlation was low (r = 0.26), so selection for better leaf TE may not improve crop WUE. Selection of low beta (less sensitivity to drought) will be difficult, given the yield beta vs. yield correlation (r = 0.71). The major quantitative trait loci (QTL) for yield beta, yield, and CID were coincident with maturity and/or determinancy QTLs, except for a CID QTL in linkage group U09‐C2, but it had no effect on beta Genetic improvement of soybean yield performance under drought would be better achieved by coupling a high‐yield grand mean with a high‐ (not low‐) yield beta
Comparison of Phenotypic and Marker‐Assisted Selection for Quantitative Traits in Sweet Corn
Authors: Yousef Gad G. , Juvik John A.
Published: July 2010

This investigation was designed to empirically compare the efficiency of marker‐assisted selection (MAS) and phenotypic selection (PS) in enhancing economically important quantitative traits in sweet corn (Zea mays L.). Marker‐assisted selection and PS were applied to three F2:3 base populations (C0) with either the sugary1 (su1), sugary enhancer1 (se1), or shrunken2 (sh2) endosperm mutations. One cycle of selection was applied for both single and multiple traits including seedling emergence, kernel sucrose concentration, kernel tenderness, and hedonic rating (taste panel preference). Twenty percent of the families in each of the base populations were selected and intermated to constitute MAS‐ and PS‐based C1 composite populations. Selection efficiencies were evaluated on the basis of gains over one cycle and estimated evaluation costs. A total of 52 paired comparisons were made between MAS and PS composite populations. In 38% of the paired comparisons, MAS resulted in significantly higher gain than PS across the three C1 composite populations, while PS was significantly greater in only 4% of the cases. The average MAS and PS gain across all composite populations and selected traits, calculated as percent increase or decrease from the randomly selected controls, was 10.9% and 6.1%, respectively. Use of MAS is most appropriate when traits are difficult and costly to measure. However, for some traits, the higher gain from MAS can compensate for the higher costs of MAS. It was concluded that incorporating DNA markers to traditional breeding programs could expedite selection progress and be cost‐effective.
Competition and Crop Performance in a Leek–Celery Intercropping System
Authors: Baumann Daniel T. , Bastiaans Lammert , Kropff Martin J.
Published: July 2010

In an intercropping system with leek (Allium porrum L.) and celery (Apium graveolens L. var. dulce (Mill.) Pers.), weed suppression is improved through increased canopy light interception. Intra‐ and interspecific competition in the system, however, affects the performance of the crops with respect to yield and quality. The objective of the study was to quantify intra‐ and interspecific competition by leek and celeriac [Apium graveolens L. var. rapaceum (Mill.) Gaud.‐Beaup] or celery in an intercropping system. A 3 yr study was carried out to investigate the effects of plant density, relative proportion of component crop, spatial arrangement, and N input on biomass production, crop quality, and N use in an intercropping system with leek and celeriac or celery. Land equivalent ratios exceeding unity were found, indicating an improved resource use by the crop mixture. Relative yield totals around one showed that with respect to biomass production, no yield advantage was found in the crop mixture. Analyses using a hyperbolic yield density response model showed that the competitive ability of celeriac and celery was significantly higher than that of leek. Effects of intra‐ and interspecific competition resulted for both crops in a reduction of the quality. Nitrogen utilization efficiency (EU) was generally poor in all crop stands, particularly at a high N application rate. The intercropping system needs improvement with respect to crop quality, and it is suggested to apply ecophysiological crop growth models to maximize crop complementarity and competitive ability against weeds.
Seasonal Dynamics of Nonstructural Carbohydrate Partitioning in 15 Diverse Rice Genotypes
Authors: Samonte S.O.PB. , Wilson L.T. , McClung A.M. , Tarpley L.
Published: July 2010

The presence of significant variation among rice (Oryza sativa L.) genotypes in total nonstructural carbohydrates (TNC) that is related to grain yield should be of interest to rice breeders. The effects of four important yield‐determining traits (maximum number of tillers, grain weight, panicle node number, and panicle size) on the TNC concentrations of plant structures at heading and harvest were determined. Path analysis was used to determine the path coefficients of the effect of changes in TNC content (Δ TNC) in leaves or stems on Δ panicle TNC at various stages of crop maturation. Fifteen rice genotypes were used in this study (‘Lemont’, ‘Teqing’, and 13 inbred lines obtained from a Lemont × Teqing cross) to represent the combinations of low and high levels of the four important yield determinants. Field experiments were conducted during the 1994 and 1995 cropping seasons at the Texas A&M University Agricultural Research and Extension Center, Beaumont, TX. Path coefficients for the significant direct effects of Δ stem TNC on Δ panicle TNC were −0.46 for the early‐ to late‐heading period and −0.59 for the late‐heading to grain hardening period. Significant genotype × developmental stage × plant structure interaction suggested the potential for selection of rice lines with high TNC concentration in stems at heading. Linear contrasts indicated that low‐grain weight genotypes had higher stem TNC concentration at harvest, which in turn suggested for the selection of high‐grain weight genotypes.
Freezing Tolerance of Six Cultivars of Buffalograss
Authors: Qian Y. L. , Ball S. , Tan Z. , Koski A. J. , Wilhelm S. J.
Published: July 2010

Freezing tolerance is an important trait that determines geographical adaptation of a turfgrass. This study was conducted to assess the relative freezing tolerance, seasonal changes in freezing tolerance (LT50), and winter survival of six cultivars of buffalograss [Buchloë dactyloides (Nutt.) Engelm.]. The cultivars 91‐118, Tatanka, Texoka, Stampede, UCR‐95, and 609 were grown in the field at Fort Collins, CO. From September 1998 to April 1999 and from October 1999 to May 2000, stolons were sampled monthly from each plot and subjected to laboratory freezing tests. Survival and recovery following the freezing test indicated that all cultivars had similar LT50 in September and gradually increased in winter hardiness during fall. However, the capacity to acclimate and the maximum freezing tolerance were significantly different among the cultivars. Ranking of grasses for mean LT50 (°C) was Tatanka (−18.1) = 91‐118 (−18.0) ≤ Texoka (−17.1) < 609 (−14.4) < Stampede (−12.4) < UCR‐95 (−9.2) during midwinter in 1998‐1999 and Texoka (−21.7) = 91‐118 (−21.6) = Tatanka (−21.0) < 609 (−15.8) = Stampede (−15.1) < UCR‐95 (−14.0) during midwinter in 1999‐2000. Following freezing treatments, Tatanka and 91‐118 maintained a higher relative shoot and root regrowth than other cultivars. Root regrowth was reduced by freezing to a greater extent than shoot regrowth for all cultivars. Field winter survival, a measure of winter hardiness, in 1998, 1999, and 2000 was generally in agreement with laboratory test results, showing that Stampede, 609, and UCR‐95 were more susceptible to winterkill than 91‐118 and Tatanka. The differences in freezing tolerance among the cultivars tested indicates substantial intraspecific variation that may be used for breeding improvement.
Impact of Light‐Weight Rolling on Putting Green Performance
Authors: Hartwiger Christopher E. , Peacock Charles H. , DiPaola Joseph M. , Cassel D. Keith
Published: July 2010

The introduction of light‐weight rollers has contributed to the reconsideration of the practice of rolling golf putting greens. Studies were conducted in 1993 and 1994 to determine the effects of rolling on soil bulk density, putting green speed, turf quality, root mass, and thatch mass. Experimental ‘Penncross’ creeping bentgrass (Agrostis stolonifera L.) putting greens built on a United States Golf Association (USGA) specification root zone and on a Cecil gravelly sandy loam (Typic Hapludult clayey, kaolinitic, thermic) (native soil) root zone were mowed daily and subjected to four rates of rolling (0, 1, 4, or 7 times per week) with a light‐weight roller for a 10‐wk period. Soil bulk density did not change for any rolling frequency on the USGA green. Rolling rates of four and seven times per week increased bulk density on the native soil green by 4 and 3% in the first year while no changes were detected in the second year. Turf quality was diminished for rolling rates of four and seven times per week. Ball roll increased as the rate of rolling increased. Rolling rate did not alter root mass. Thatch levels were not affected by rolling frequency on the USGA green. On the native soil green, four and seven rolling treatments per week resulted in thatch levels 12 and 11% higher than the control. Rolling once per week appears to offer increased green speed without any deleterious turf effects.
Genetic Control of High Temperature Tolerance in Wheat as Measured by Membrane Thermal Stability
Authors: Ibrahim Amir M. H. , Quick James S.
Published: July 2010

Heat stress is an important production constraint of wheat (Triticum aestivum L.) affecting many plant biological activities in the cell membrane. This study determined the genetic control of heat tolerance through diallel analysis of selected wheat germplasm. Heat‐induced damage of plant membranes was assayed by the membrane thermal stability (MTS) assay, which measures electrolyte leakage from leaf tissue after exposure to high temperature. Six wheat genotypes (‘TAM 107’, ‘TAM 108’, ‘Arlin’,' Kauz', ‘Glennson 82’, and ‘Siete Cerros’) were hybridized in a complete diallel, and MTS was measured on 12 d old F1 seedlings. The mean square for general combining ability (GCA) was four times that of specific combining ability (SCA), indicating the importance of additive gene effects in acquired thermal tolerance. Maternal effects accounted for 67% of reciprocal variation, suggesting that maternal seed‐source effects may be important in hybrid seed. These results suggest that heat tolerance based on MTS can be improved using the existing genetic variability available within the germplasm evaluated in this study.
Glandular Morphology from a Perennial Alfalfa Clone Resistant to the Potato Leafhopper
Authors: Ranger Christopher M. , Hower Arthur A.
Published: July 2010

The commercial release of several cultivars of perennial, glandular‐haired alfalfa (Medicago sativa L.) for control of the potato leafhopper, Empoasca fabae (Harris), has increased the need to identify the causal mechanism of resistance. The objectives of this experiment were to examine the morphology and exudate of the glandular trichomes found on the perennial alfalfa clone FGplh13, in addition to comparing their density and distribution. Light, scanning, and transmission electron microscopy were utilized to characterize the morphology of the glandular trichomes and their associated exudate. Two distinct trichome morphologies, erect and procumbent glandular trichomes, occurred. The erect glandular trichomes consisted of multicellular stalks (5–11 cells) and gland heads, with the cells being arranged in distinct tiers. The procumbent glandular trichomes were composed of a stalk (1–2 cells) bent almost parallel to the plant surface. The procumbent gland head contained 8 to 12 cells, which were distinctly arranged in two to three tiers. Both types of trichomes released exudates that appeared to accumulate in a subcuticular space within a distal extrusion. Exudate from the procumbent glandular trichome became attached to the tibia of a potato leafhopper nymph. Entrapment of first instar potato leafhoppers by the glandular trichomes was also observed for the first time on a perennial glandular‐haired alfalfa clone. The erect glandular trichome was the most dense morphology on the stem, petiole, and leaf midvein.
Physical Map Location of the Rps1‐k Allele in Soybean
Authors: Gardner M. E. , Hymowitz T. , Xu S. J. , Hartman G. L.
Published: July 2010

Several genetic maps of soybean [Glycine max (L.) Merr.] have been developed during the past decade. Different markers have been used to construct these maps including restriction fragment length polymorphism (RFLP), amplified fragment length polymorphism (AFLP), random amplified polymorphic DNA (RAPD), simple sequence repeat (SSR), and classical markers. However, virtually none of the maps and linkage groups developed has been associated with specific soybean chromosomes. For example, there are 13 single dominant resistance genes at 7 different loci that control Phytophthora sojae These resistance genes (Rps genes) have not been located on any chromosomes, but several have been associated on classical and molecular maps. For example, the Rps1 locus is associated with molecular linkage group N. The objective of this study was to locate the Rps1 locus on a specific soybean chromosome using primary trisomic analysis. Crosses were made between 10 soybean trisomic lines and cv. Resnik (containing Rps1‐k). The F2 populations from trisomic parents were inoculated with race 3 of P. sojae to determine the ratio of resistant to susceptible plants. Nine of the F2 populations tested segregated in a normal 3:1 ratio. The F2 population of triplo 3 segregated in a 2:1 ratio, the expected segregation ratio for a single dominant gene if the gene is located on the extra chromosome, suggesting that the Rps1 locus is on chromosome 3. Thus, chromosome 3 corresponds to molecular linkage group N of the integrated genetic linkage map.
Management Strategies during the Establishment Year Enhance Production and Fitness of Seeded Bermudagrass Stolons
Authors: Munshaw Gregg C. , Williams David W. , Cornelius Paul L.
Published: July 2010

Bermudagrass [Cynodon dactylon (L.) Pers.] is an important turfgrass across the transition zone. A common concern is survival of seeded cultivars the first winter after establishment. The objective of this study was to determine the optimum seeding and N rates to enhance stolon production. The cultivar Mirage was seeded in June of 1998 and 1999 at 12.2, 24.4, 36.6, and 48.8 kg pure live seed (PLS) ha−1 Urea nitrogen was applied as a split‐plot treatment at the rates of 48.8, 195.2, 390.4, or 585.6 kg N ha−1 growing season−1 Fresh weights of stolons harvested at the end of both growing seasons were greatest at 12.2 kg PLS ha−1 rate, and decreased significantly as seeding rate increased. The same response to seeding rate was evident when measuring stolon diameters in both years of the study. In 1999, 585.6 kg N ha−1 produced more stolons than 48.8 kg N ha−1, indicating a significant positive linear response to N. The opposite was true with stolon diameters, there being a negative linear relationship with total N applied. There were no differences among seeding rates on production of total nonstructural carbohydrates (TNC), but 390.4 kg N ha−1 produced the most TNCs, showing a significant quadratic response to N. No winterkill was observed in either year of the study.
A Microsatellite Marker for Tagging Dn2, a Wheat Gene Conferring Resistance to the Russian Wheat Aphid
Authors: Miller Cynthia A. , Altinkut Ahu , Lapitan Nora L. V.
Published: July 2010

The Russian wheat aphid (RWA), Diuraphis noxia Mordvilko, is an economically important pest of wheat (Triticum aestivum L.). An effective means to control the RWA is through the use of resistant cultivars. While a phenotype‐based selection has been useful for selection of resistant plants, it has inherent limitations. Screening can only be done during cool months of the year, and symptom expression is influenced by the environment. Pyramiding of two or more RWA resistance genes is also difficult because of the presence of only one aphid biotype in the USA at present. This study was conducted to develop a DNA marker that is tightly linked to Dn2, and to test the effectiveness of the marker as a tag for Dn2 among a limited number of cultivars tested. We report mapping of five microsatellite markers linked to Dn2 The closest marker was Xgwm437 at 2.8 cM, and it distinguished lines containing Dn2 from eight susceptible cultivars and seven resistant cultivars carrying other RWA resistance genes. Xgwm437 should be effective for marker‐assisted selection of Dn2‐containing plants and for combining Dn2 with other resistance genes in a gene pyramiding program.
Development of SCAR and CAPS Markers Linked to the Beta Gene in Tomato
Authors: Zhang Yiping , Stommel John R.
Published: July 2010

Two previously identified random amplified polymorphic DNA (RAPD) markers, OPAR181100 and UBC792830, linked to the Beta (B) locus in tomato (Lycopersicon esculentum Mill.) were cloned and sequenced. Their end sequences were used to design allele specific sequence characterized amplified region (SCAR) primer pairs, SCAR18f/r and SCBC792f/r. Each of these primer pairs amplified a single product of the same size as their respective progenitor RAPD markers, but did not differentiate the two parental genotypes under a variety of polymerase chain reaction (PCR) conditions. Sequence analysis of cloned RAPD and SCAR products revealed an RsaI site mutation in the allele of the high beta‐carotene parent in the SCAR18f/r amplified DNA product which was used to develop the codominant SCAR181067 cleaved amplified polymorphic sequence (CAPS) marker. Similarly, a HinfI site mutation in the allele of the high beta‐carotene parent in SCBC792f/r amplified DNA product was used to develop the codominant SCBC792779 CAPS marker. Sequences from SCBC792f/r amplified DNA products revealed additional single nucleotide polymorphisms between the two parental genotypes. Three such polymorphisms were used to design the nested primer SCBC792f1 located 97 bp internal to the SCBC792f sequence. The SCBC792f1/r primer pair amplified the dominant SCB792682 SCAR marker present only in the high beta‐carotene parent. Linkage of the CAPS and SCAR markers to B was confirmed by means of a population of 144 F2 individuals segregating for B Using introgression line analysis, we mapped the two CAPS and the SCAR markers to the long arm of chromosome 6, consistent with the location of B on the classical linkage map of tomato.
Inheritance of Russian Wheat Aphid Resistance in Spring Barley Germplasm Line STARS‐9577B
Authors: Mornhinweg D. W. , Porter D. R. , Webster J. A.
Published: July 2010

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), has become a major pest of barley (Hordeum vulgare L.) in the western USA. STARS‐9577B (PI 591617), a six‐rowed, spring barley germplasm line with a high level of resistance to RWA, was recently released to barley breeders for barley improvement. Understanding the inheritance of RWA resistance in this germplasm line is necessary for breeders to develop an effective strategy for utilization of this germplasm in their breeding programs. This greenhouse study was conducted to determine the genetic control of RWA resistance in STARS‐9577B. Crosses were made between ‘Morex’, a susceptible, six‐rowed, malting barley cultivar, and STARS‐9577B. Genetic analyses were performed on reaction to RWA of parents, F1, reciprocal F1, F2, backcrosses (BC1F1) to both parents, and F2‐derived F3 families. Reaction was based on a visual rating scale of 1 to 9 (1 = no damage, 9 = dead plant). Segregation in the F2 and BC1F1 populations indicated multiple gene control. Seventy‐seven F3 families were found to be homozygous resistant and 18 homozygous susceptible, indicating two gene control of RWA resistance in STARS‐9577B. Analysis of data from F2 and BC1F1 populations suggested RWA resistance in STARS‐9577B is controlled by dominant alleles at two loci, with alleles at one locus conferring a high level of resistance and alleles at the other locus conferring an intermediate level of resistance only when recessive alleles are present at the first locus.
Root Growth and Yield of Differing Alfalfa Rooting Populations under Increasing Salinity and Zero Leaching
Authors: Vaughan Laura V. , MacAdam Jennifer W. , Smith Steven E. , Dudley Lynn M.
Published: July 2010

Accumulation of salinity in the root zone can be detrimental to sustained crop production. Irrigation, even with moderately saline water, pushes accumulated salts deeper into the root zone, allowing roots to proliferate in regions of relatively low salinity. Two alfalfa (Medicago sativa L.) subpopulations with low‐ and high‐fibrous rooting characteristics, MnPL‐9‐LF and MnPL‐9‐HF, were used to test the effectiveness of increased rooting on yield when plants were irrigated with saline water but without leaching. Treatments were three levels of heterogeneous root zone salinity predicted by the SOWACH model to represent 10, 20, and 30 yr of irrigation with saline water. Plants were grown for five successive harvests in 10‐cm‐diam., 130‐cm‐deep cylinders. The treatments were constructed with NaCl and gypsum. As soil became depleted to 50% extractable water, irrigation water with an electrical conductivity (EC) of 2.8 dS m−1 was applied. By the fifth harvest, soil solution EC from the top to the bottom of the profile ranged from 3 to 12 dS m−1 for the control and from 3 to 23 dS m−1 for the highest salinity treatment. Root production of the high‐fibrous root type was stimulated more at low and medium salinity than that of the low‐fibrous root type. Across salinity treatments, final root length density (cm root length per cm3 soil volume) was 24% higher for the high‐fibrous root type, and herbage yield of the high‐fibrous root type was 14% higher than that of the low‐fibrous root type. Differential rooting was greatest in the upper half of the root zone. High fibrous rooting in alfalfa is a trait with potential usefulness as a salinity stress avoidance mechanism.
Mapping and Progress toward Map‐Based Cloning of Brown Planthopper Biotype‐4 Resistance Gene Introgressed from Oryza officinalis into Cultivated Rice, O. sativa
Authors: Renganayaki K. , Fritz Allan K. , Sadasivam S. , Pammi Sujata , Harrington Sandra E. , McCouch Susan R. , Kumar S. Mohan , Reddy Avutu Sam
Published: July 2010

Brown plant hopper (BPH), Nilaparvata lugens (Stal.), is a serious insect pest of rice in Asia, causing direct losses and vectoring Rice grassy stunt virus (RGSV) and Rice ragged stunt virus (RRSV). Recombinant inbred lines (RILs) developed from a cross between ‘IR50’ and ‘IR54745‐2‐21‐12‐17‐6’ were used to identify random amplified polymorphic DNA (RAPD) markers closely linked to a BPH Biotype‐4 resistance gene [Bph13 (t)] derived from Oryza officinalis Wall. Bulked segregant analysis (BSA) using RAPD primers identified 11 polymorphic fragments. Six fragments, AJ09260a, AL05220a, AK10690a, AK10430c, AK10380d, and AJ01200a, were linked in coupling phase to the Bph13 (t) locus. The remaining five fragments, AJ09230b, AJ09180c, AJ09100d, AL05400b, and AK10340e, were linked in repulsion. The most closely linked RAPD marker, AJ09230b, was converted to a codominant linked sequence tagged sites (STS) marker. This marker mapped 1.3 centimorgans (cM) from the resistance gene and was placed on rice chromosome 3 by means of ‘IR64’ × ‘Azucena’ doubled haploid (DH) population. The tightly linked STS marker could be used for marker‐assisted selection (MAS). In addition, these markers will be useful for a positional cloning strategy to isolate the resistance gene.
Comparative Mapping of β‐Amylase Activity QTLs among Three Barley Crosses
Authors: Clancy J. A. , Han F. , Ullrich S. E. , North American Barley Genome Project
Published: July 2010

β‐Amylase (BA) is one of the starch‐degrading enzymes active in germinating barley (Hordeum vulgare L.). Unlike α‐amylase (AA), it is not synthesized de novo at the onset of germination, but accumulates during seed development. BA activity is an important malting quality parameter and is a major contributor, along with AA, to diastatic power (DP). The objectives of this study were to (i) measure and map BA activity in three crosses of North American barleys, (ii) compare quantitative trait loci (QTLs) for BA among various crosses, and (iii) determine the relationship between BA and previously mapped DP QTLs. Comparative mapping was done by means of a consensus map with common markers from F1 doubled haploid mapping populations from the crosses of ‘Steptoe’ × ‘Morex’ (S/M), ‘Harrington’ × TR306 (H/T), and Harrington × Morex (H/M). BA activity analyses were performed with field‐grown seed from the three mapping populations and parents. Relatively normal frequency distributions for enzyme activity were obtained from each of the mapping populations. QTLs for BA were identified in all three crosses and on all seven chromosomes. Seven QTLs were located in S/M, the most genetically diverse cross, while only three each were found in H/T and H/M. As expected, BA QTLs were almost always found in conjunction with previously identified DP QTLs. A survey of QTL literature of populations of diverse germplasm showed many QTLs for BA and DP in common with those identified herein and some unique QTLs as well. The results of this study suggest the benefits of identifying markers closely associated with major BA QTLs are to allow for further molecular studies and for marker assisted selection of this trait.