bluuebunny/crossref_metadata_2025 huggingface dataset:
Hypersensitive Response to Striga Infection in Sorghum
Authors: Mohamed A. , Ellicott A. , Housley T. L. , Ejeta G.
Published: July 2010

Availability of appropriate laboratory procedures that reveal the specific interactions between the parasitic striga (Striga spp.) and host genotypes in the early stages of infection facilitates characterization of the specific mechanisms of resistance. Our objective was to use an in vitro extended agar gel assay (EAGA) to characterize hypersensitive response (HR) to parasitic invasion of sorghum [Sorghum bicolor (L.) Moench] genotypes. The HR was characterized by expression of necrotic lesions at the haustorial attachment sites which discouraged further penetration of the parasite into host roots. We examined the HR reaction of seven cultivated, five wild, and 95 BC3F4 genotypes derived from a wild resistant (P47121) and two susceptible male sterile based populations (CK60 and KP9). The susceptible genotypes showed no necrosis. In contrast, resistant cultivars Framida and Dobbs, and a wild accession, P47121, showed necrosis in >67% of attached striga In each of these lines, attached striga were discouraged from penetration and further development. P47121 had the highest level of necrosis (89.9%) and discouraged haustoria penetration (83.1%), followed by Framida (71.4, 56.7%) and Dobbs (67.8, 49.4%). However, resistant genotypes SRN‐39, IS9830, and 555 with low striga germination distance did not exhibit any HR. Only Framida possessed both a low germination distance and high HR. Nine BC3F4 genotypes had a moderate to high HR. These results suggest that use of P47121 and other resistant genotypes would further enhance development of striga‐resistant sorghum cultivars through directed introgression.
Challenges in Comparing Transgenic and Nontransgenic Soybean Cultivars
Authors: Raymer Paul L. , Grey Timothy L.
Published: July 2010

Genetically modified soybean [Glycine max (L.) Merr.] cultivars containing herbicide resistance have become the predominant cultivars marketed in the USA. This technology dramatically changed weed management strategies in the USA and created controversy and new challenges within various segments of the industry. This review seeks to summarize many of the issues that arose within the soybean industry surrounding the introduction of the world's first major transgenic crop. Hopefully, the experiences gained during this transition period will benefit future efforts to commercialize transgenic crops. Initially, the new transgenics made the already difficult, yet critically important, task of cultivar selection even more arduous and confusing. Lack of university data, high cultivar turnover rates, and the added burden of factoring in technology fees, yield lag, and weed control costs into the decision of which cultivar to plant were frustrating to most producers. Industry's early insistence on separate cultivar performance trials for Roundup Ready (RR) cultivars taxed limited testing resources and increased the size of the already massive data sets generated. Most often, the end result did not provide a direct comparison with popular conventional cultivars. As this new technology has become fully accepted and assimilated into our industry, comparisons with conventional cultivars are less important since most farmers are selecting only among RR cultivars. The current literature indicates that soybean variety test (SVT) programs with limited resources can effectively compare soybean cultivar performance using combined trials treated only with conventional herbicides with little risk of yield loss or herbicide × cultivar interactions. However, the use of a systems approach or separate RR trials to evaluate the performance of soybean cultivars is now commonplace in the USA due to the sheer dominance of RR cultivars. Many larger SVT programs will soon consider discontinuing separate trials for conventional cultivars as their numbers and importance diminish.
Shifts in Pest Resistance, Fall Dormancy, and Yield in 12‐, 24‐, and 120‐Parent Grazing Tolerant Synthetics Derived from CUF 101 Alfalfa
Authors: Sledge M. K. , Bouton J. H. , Kochert G.
Published: July 2010

Selection for grazing tolerance has been reported to be accompanied by changes in resistance to blue alfalfa aphid (Acyrthosiphon kondoi Shinji) and fall dormancy in alfalfa (Medicago sativa L.). This study was conducted to determine changes in pest resistance, fall dormancy, grazing tolerance, and yield between ‘CUF 101’ alfalfa and three experimental, grazing tolerant synthetics. A 120 parent experimental synthetic was derived from CUF 101 after two cycles of selection for grazing tolerance. Two synthetics composed of 12 and 24 parents were selected from the 120 grazing tolerant parents on the basis of the genetic dissimilarity of amplified fragment length polymorphism (AFLP) markers. There were no significant differences between the three experimental synthetics for grazing tolerance; however, all experimental synthetics were more grazing tolerant than CUF 101. All experimental synthetics had lower levels of resistance to blue alfalfa aphid, but generally higher levels of resistance to five other diseases in comparison to CUF 101. All experimental synthetics were more fall dormant than CUF 101. No consistent differences in yield were documented among the synthetics at testing locations in Georgia or California. In conclusion, this study underscores the need for further evaluation, after selection for grazing tolerance, to document fall dormancy and blue alfalfa aphid resistance ratings and to practice reselection for these traits if necessary.
A Rapid and Direct Approach to Identify Promoters That Confer High Levels of Gene Expression in Monocots
Authors: Yang Meizhu , Bower Robert , Burow Mark D. , Paterson Andrew H. , Mirkov T. Erik
Published: July 2010

Direct screening of genomic libraries for highly expressed genes is an efficient way to identify promoters that confer high levels of gene expression. To test the efficacy of this approach to isolate promoters for directing high levels of gene expression in sugarcane, 11 genomic clones were isolated after screening a sugarcane genomic library with radioactively labeled first strand cDNA probes synthesized from sugarcane leaf mRNA. Hybridization analysis with pooled first strand cDNA indicated that eight of the clones probably contain genes with expression levels similar to or higher than ubiquitin (which was also isolated in this screen). The coding regions of these 11 genomic clones were isolated from a cDNA library, sequenced, and found to represent parts of five different genes including elongation factor 1α, α‐tubulin, an aquaporin, a proline‐rich protein, and one novel gene. Southern and Northern results showed that the sugarcane proline‐rich protein‐encoding gene (SPRP1) was the best candidate to isolate a promoter that would direct high levels of expression, although the other four are also good candidates. Two genomic clones of the sugarcane proline‐rich gene and a sugarcane elongation factor 1α (SEF1α) gene, which contain both the promoter and coding regions, were subcloned, sequenced, and promoter regions defined by comparison of cDNA and genomic DNA sequences. Both the SEF1α and SPRP1 promoter/β‐glucuronidase (GUS) fusions resulted in high levels of GUS expression when reintroduced into embryogenic sugarcane callus, and also resulted in high levels of transient GUS expression in wheat embryos. This approach has value as an efficient technique to find promoters that confer high‐level gene expression in monocots.
Resistance to Russian Wheat Aphid Damage Derived from STARS 9301B Protects Agronomic Performance and Malting Quality When Transferred to Adapted Barley Germplasm
Authors: Bregitzer Phil , Mornhinweg Dolores W. , Jones Berne L.
Published: July 2010

Infestations of Russian wheat aphid (RWA), Diruaphis noxia (Mordvilko), reduce grain yield and quality of barley, and have induced producers in some areas to cease growing barley (Hordeum vulgare L.). No RWA‐resistant barley cultivars that are adapted to North America exist. Resistance from the germplasm line STARS 9301B was transferred into adapted germplasm via backcrossing. Our objective was to determine the potential utility of this resistance for the protection of yield and malting quality in adapted germplasm. We studied the effect of RWA infestations on grain yield and malting quality of STARS 9301B, the susceptible adapted parents 88Y315 and ‘Garnet’, and five backcross‐derived progeny. Four of the backcross‐derived lines were rated as highly resistant and one as moderately resistant, and were superior to STARS 9301B and similar to their recurrent parents with respect to agronomic performances and, to a lesser extent, malting qualities. When infested at the boot to heading stage, STARS 9301B, and the highly resistant progeny lines had negligible reductions in agronomic performances and malting qualities; slightly greater reductions were observed for the susceptible parents and the moderately resistant progeny line. When infested at the three‐ to six‐leaf stage, STARS 9301B and the resistant backcross‐derived lines showed relatively small reductions in their agronomic performances and malting qualities. In sharp contrast, however, the susceptible parents, and to a lesser extent the moderately resistant progeny line, showed moderate to severe leaf streaking and rolling, head trapping, and reductions in their agronomic performances and malting qualities. STARS 9301B should provide a valuable source of resistance to RWA damage.
Cold Hardiness of Saltgrass Accessions
Authors: Shahba M. A. , Qian Y. L. , Hughes H. G. , Christensen D. , Koski A. J.
Published: July 2010

Freezing tolerance is an environmental adaptation that significantly influences plant geographical distribution. Since differences in winter survival among saltgrass ecotypes have been observed in the field at Fort Collins, CO, the objective of this study was to determine the relative freezing tolerance, seasonal changes in the freezing tolerance, and winter survival of six accessions of saltgrass [Distichlis spicata var. stricta (L.) Greene]. Saltgrass accessions A65 and A29 were originally collected from Denver, CO, while C66 was from Humbolt Sink, NV, 32 from Wanship, UT, 55 from Hereford and 48 from Farmingdale, SD. These accessions were established in a field nursery at Fort Collins, CO. Rhizomes were sampled at monthly intervals from October 1999 through April 2000 and from October 2000 through April 2001 and subjected to laboratory freezing tests. Cold hardiness of the saltgrass accessions increased gradually during the fall with maximum hardiness occurring at midwinter. During midwinter, freezing tolerance was significantly different among accessions. Ranking of accessions for subfreezing temperature resulting in 50% mortality [LT50 (°C)] during January 2000 was A29 = 48 (−20.0) < 55 (−17.0) ≤ 32 (−15.5) ≤ A65 = C66 (−14.0). In January 2001, they were ranked with 48 = 55 (−26.0) < A65 = 32 (−23.0) < A29 (−20.0) = C66 (−18.5). In December and January sampling dates of the first season, accessions A29, 48, and 55 exhibited the highest relative regrowth when exposed to temperatures ≈ −20.0°C. In midwinter of the second season, accession 55 showed the highest regrowth after being subjected to temperatures ≈ −25.0°C. Accession C66 had the lowest regrowth potential after freezing treatments in both seasons. Winter survival in the field correlated negatively with LT50 value, with accessions 48, A29, and 55 demonstrating greater winter survival while C66 had the lowest percentage survival. The difference in freezing tolerance among accessions is in part associated with their origin‐inherited adaptation. This information is useful for defining the potential adaptation range of saltgrass and in saltgrass breeding projects to select and develop freezing tolerant saltgrass.
Relationships of Soluble Carbohydrates and Freeze Tolerance in Saltgrass
Authors: Shahba M. A. , Qian Y. L. , Hughes H. G. , Koski A. J. , Christensen D.
Published: July 2010

Information is lacking regarding the changes of endogenous soluble carbohydrates of saltgrass [Distichlis spicata (L.) Greene] during cold acclimation. The objective of this study was to quantify soluble carbohydrates and their relationships to freezing tolerance in six saltgrass accessions (A65, A29, C66, 32, 55, and 48). The study was performed at monthly intervals under natural acclimation in two consecutive winter seasons (October 1999–April 2000 and October 2000–April 2001) at Fort Collins, CO. Concurrent with LT50 (subfreezing temperature resulting in 50% mortality) assessment, soluble carbohydrates, including sucrose, fructose, glucose, raffinose, and stachyose were measured by gas chromatography (GC). Results indicated significant differences among accessions and sampling dates in LT50 and carbohydrate content. Sucrose was the predominant sugar, but did not show a clear seasonal trend and had no correlation with freezing tolerance. Fructose, glucose, raffinose, and stachyose exhibited clear seasonal changes, reaching highest concentrations during midwinter. In December of both seasons, higher concentration of fructose and glucose were observed in 48 and 55 as compared with other accessions. Accession A29 had the highest concentration of raffinose in December and January in both seasons. A29 also had the highest stachyose content in midwinter of 1999‐2000. Higher fructose, glucose, or raffinose concentrations were frequently observed in accessions of 48, 55, and A29, which coincided with their lower LT50 as compared with the other accessions. In contrast, C66 had the lowest sugar concentrations, which related to its sensitivity to low temperatures. These results indicate that fructose, glucose, raffinose, and stachyose may play important roles in saltgrass freezing tolerance.
Inheritance of Dollar Spot Resistance in Creeping Bentgrass
Authors: Bonos Stacy A. , Casler Michael D. , Meyer William A.
Published: July 2010

The dollar spot disease incited by Sclerotinia homoeocarpa F.T. Bennet. is a common and destructive disease of both cool‐ and warm‐season grasses throughout the world. Genetic resistance to dollar spot is an important control strategy; however, the genetic mechanism of dollar spot resistance in turfgrasses is unknown. The first objective of this study was to determine broad‐sense heritability and predicted gain from selection of dollar spot resistance in creeping bentgrass (Agrostis stolonifera L.). This was completed through dollar spot disease evaluation of 265 randomly selected creeping bentgrass clones arranged in a randomized complete block design with six and five clonally propagated replicates in each of two locations evaluated over 2 yr. Five isolates of S. homoeocarpa were used to inoculate the field studies and applied at a rate of 1.75 g m−2 of prepared inoculum. The second objective was to evaluate inheritance characteristics of dollar spot disease resistance. Major gene calculations, heterosis, maternal effects, chi square analysis of segregation ratios, and number of effective factors were determined through the evaluation of dollar spot disease resistance of progeny from controlled crosses between fixed resistant and susceptible bentgrass clones. These progenies along with parental clones were established in field trials and inoculated with dollar spot. The continuous population distribution of phenotypes for clones and progeny indicated that dollar spot resistance may be quantitatively inherited. Broad‐sense heritability estimates (0.56 on a single plant basis and 0.90 on an 11‐plant clonal mean basis) indicated replication increased selection efficiency and that improvement in dollar spot resistance in creeping bentgrass should be possible. A minimum of two to five effective factors depending on the cross may be associated with dollar spot resistance.
Pyramiding and Validation of Quantitative Trait Locus (QTL) Alleles Determining Resistance to Barley Stripe Rust
Authors: Castro Ariel J. , Chen Xianming , Corey Ann , Filichkina Tanya , Hayes Patrick M. , Mundt Christopher , Richardson Kelley , Sandoval‐Islas Sergio , Vivar Hugo
Published: July 2010

The use of molecular and quantitative trait locus (QTL) analysis tools initially lent support to the idea that relatively few genetic factors were the principal determinants of complex traits, including quantitative resistance (QR) to plant diseases. However, there are concerns regarding bias in QTL estimation and reproducibility of QTL effects in different genetic backgrounds. We are interested in mapping determinants of QR, and pyramiding resistance alleles at QTL loci may lead to durable resistance as well as provide independent validation of QTL effects and estimation of QTL interactions. We used molecular marker information to validate effects of resistance alleles at three QTL conferring QR to barley stripe rust (caused by Puccinia striiformis West. f. sp. hordei). Two of the QTL [one on chromosome 4(4H) and one on chromosome 7(5H)] trace to one parent, while another QTL on chromosome 5(1H) traces to a different parent. The pyramids of these QR alleles provide independent estimates of QTL effects, influence of genetic background on QTL effects, QTL × QTL interaction, and QTL × environment interaction. Our results validate QTL effect estimates, showing that a small number of QTL explained 94% of the genetic variation in trait expression in a new genetic background. Original QTL estimates were quantitatively biased, but that did not preclude the achievement of selection responses. We also confirmed the additive effects of the QTL alleles, as well as the consistent effects of QTL alleles across environments.
Genetic Dissection of Silicon Content in Different Organs of Rice
Authors: Dai Wei-Min , Zhang Ke-Qin , Duan Bin-Wu , Zheng Kang-Le , Zhuang Jie-Yun , Cai Run
Published: July 2010

Quantitative trait loci (QTLs) analysis for Si content in rice (Oryza sativa L.) was performed to study the inheritance of Si content in rice. A recombinant inbred line (RIL) population of 244 lines derived from the indica rice cross ‘Zhenshan 97B’ (ZS97B)/‘Milyang 46’ (MY46) were grown in 2003 with two replications. Silicon content in the hull (HUS), flag leaf (FLS), and stem (STS) were measured. On the basis of a linkage map consisting of 207 DNA marker loci, a total of 10 QTLs showing significant additive effects and 14 digenic interactions having significant additive‐by‐additive (AA) epistatic effects were detected. The number of QTLs and AA interactions for individual traits were four and four for HUS, four and four for FLS, and two and six for STS, respectively. General contributions to the phenotype variance due to additive effects and AA effects were 29.3 and 18.6% for HUS, 14.8 and 13.6% for FLS, and 8.6 and 28.6% for STS, respectively. This indicates that gene actions at both the one‐ and two‐locus levels play an important role to genetically control Si content in rice. In addition, it was shown that the detection of QTLs at the one‐locus level, as well as magnitude and direction of the additive effect, might be influenced greatly by digenic interactions involving loci linked to the given QTL. By comparing these results with other reports, genetic association between QTLs for Si content and QTLs for yield component traits and lodging‐tolerance related traits were evident.
Phylogenetic Relationships among North American Popcorns and Their Evolutionary Links to Mexican and South American Popcorns
Authors: Santacruz‐Varela A. , Widrlechner M. P. , Ziegler K. E. , Salvador R. J. , Millard M. J. , Bretting P. K.
Published: July 2010

To determine genetic relationships among representative popcorns (Zea mays L.) of the New World, 56 maize populations from the USA and nine Latin American countries were characterized for 29 morphological traits, 18 isozyme loci, and 31 SSR loci. Cluster and principal component analyses were performed upon standardized morphological data and allelic frequencies from isozyme and SSR loci to elucidate relationships among populations within a geographical and historical context. Three groups of popcorn, with distinctive morphological characteristics and genetic profiles, were identified in the North American populations. The first group includes the North American Yellow Pearl Popcorns, which are currently the most important for U.S. commercial production. This group could be derived from introductions of the race Curagua from Chile into New England in the 19th Century. The second group includes the North American Pointed Rice Popcorns, which probably originated from the complex of traditional races of pointed popcorns from Latin America, such as Palomero Toluqueño, Confite Puntiagudo, Canguil, and Pisankalla, which diffused from the highlands of central Mexico into northern Mexico and then into southwestern USA. The third group includes the North American Early Popcorns, which show a marked influence of Northern Flint maize, from which they probably acquired the trait of early maturity. This third group also shows genetic influences of maize from northwestern Mexico and even from early European varieties of popcorn introduced late in the 19th Century. We propose that the three groups of North American popcorn identified in this study be recognized taxonomically as distinct races, and we provide characteristic traits as well as isozyme and SSR alleles to define the new races.
Fiber Length Development in Near‐Long Staple Upland Cotton
Authors: Braden Chris A. , Smith C. W.
Published: July 2010

Advanced Fiber Information System (AFIS) mean fiber length by weight (Lw), fiber length development period (FLDP), and average daily fiber length growth rates (ADGR) were determined for four experimental strains and three cultivars of upland cotton, Gossypium hirsutum L., in 1998 and 1999 in College Station, TX. TAM 94L‐25 and TAM 94M‐14, near‐long staple sib lines developed by the Texas Agricultural Experiment Station (TAES), were compared with five upland cotton genotypes that varied in high‐volume instrument (HVI) upper half mean (UHM) fiber length. The FLDP was determined as the number of days postanthesis (DPA) until fibers reached a Lw greater than or equal to their Lw at boll opening. Final average daily growth rate (FADGR) was calculated as the average Lw d−1 from anthesis to open boll. Length by weight was determined at 3‐d intervals from 16 DPA until boll opening. With a higher FADGR and longer FLDP, TAM 94L‐25 and TAM 94M‐14 exhibited the longest final Lw TAM 94L‐25 had a higher FADGR than the commercial cultivars Suregrow 125 and Tamcot CAMD‐E, while TAES strain 94WD‐17 exhibited the lowest FADGR. The broad‐sense heritability estimate for final Lw across years was 0.88.
Grain Composition and Productivity of Maize Hybrids Derived from the Illinois Protein Strains in Response to Variable Nitrogen Supply
Authors: Uribelarrea Martín , Below Fred E. , Moose Stephen P.
Published: July 2010

The Illinois Long‐Term Protein Selection strains of maize (Zea mays L.) have been employed in a variety of studies investigating the genetic and physiological control of maize grain composition. These prior studies, however, have not assessed the grain composition and yield potential of these strains in hybrid combinations with an elite tester, or in response to supplemental N. Our objective was to study the interactive effect of genotype and N supply on productivity and grain quality for hybrids with a wide divergence in grain protein. Hybrids derived from the Illinois Protein Strains were evaluated in a 2‐yr field experiment where N rates were varied from 0 to 235 kg ha−1 (in eight 34‐kg increments), along with a current commercial hybrid sharing the same female parent (FR1064). The Illinois Protein Strain hybrids produced grain protein concentrations that reflected the strain parents, with all hybrids except Illinois Low Protein showing increased grain protein in response to increasing N supply. Many other strain attributes were also manifested at the hybrid level, including the relative differences in kernel weights and the inverse relationship between grain protein to both starch concentration and grain yield. Nitrogen supply positively enhanced grain yield in all hybrids, primarily by increasing kernel number. Nitrogen supply also impacted the yield–protein relationship by stimulating protein synthesis rather than by inhibiting starch production. These results demonstrate the strong genetic control of grain composition in maize hybrids, which can be modulated by the positive effects of N on reproductive sink capacity and seed protein synthesis.
Gene Diversity among Botanical Varieties in Peanut (Arachis hypogaea L.)
Authors: Ferguson M. E. , Bramel P. J. , Chandra S.
Published: July 2010

For the first time, sufficient numbers of molecular markers that reveal polymorphism in cultivated peanut (Arachis hypogaea L.) have become available for diversity assessments. In this study, the amount and distribution of genetic variation within and among six peanut botanical varieties, as well as its partitioning among three continents of origin, was assessed at 12 simple sequence repeat (SSR) loci by means of 10 sequence‐tagged microsatellite site (STMS) primers. Eighty‐nine alleles were revealed, varying from 2 to 17 per locus with an average of 7.4 alleles per locus. Greater differentiation was observed between varieties (Fst = 0.33), compared with between continents (Fst = 0.016). However, maximum differentiation was observed among continents within varieties (Fst = 0.366) for three varieties. Rogers' modified distance among varieties revealed the similarity of three varieties of subspecies fastigiata Waldron, namely fastigiata, vulgaris C. Harz, and aequatoriana Krapov. & W.C. Gregory. It did not support the inclusion of var. peruviana Krapov. & W.C. Gregory in this grouping. In addition, the results suggest that subsp. hypogaea var. hypogaea and var. hirsuta Köhler are not closely related and therefore should not hold the same subspecific ranking. Discriminant function analysis reveals a high degree of accordance between variety delimitation on the basis of morphological and molecular characters. Landraces from Africa and Asia were more closely related to each other than to those from South America. Nei's unbiased estimate of gene diversity revealed very similar levels of diversity within botanical varieties. Landraces from South America had the highest diversity, and possessed 90% of alleles, compared with Africa (63%) and Asia (67%).
Sorghum Kernel Weight
Authors: Gambín Brenda L. , Borrás Lucas
Published: July 2010

The influence of genotype and panicle position on sorghum [Sorghum bicolor (L.) Moench] kernel growth is poorly understood. In the present study, sorghum kernel weight (KW) differences during grain filling were analyzed by kernel water relationships previously described in other crops. Eight commercial genotypes differing in KW were used, and KW, water content, kernel volume, kernel moisture content, and kernel density were measured in two positions within the panicle (apical and basal) throughout the grain‐filling period. At physiological maturity (PM), KW ranged from 16.5 to 25.1 mg kernel−1, and a significant (p < 0.05) genotype × position interaction was detected. Independently of final KW, apical kernels always exhibited a higher rate (p < 0.001) and a shorter duration of grain filling (p < 0.001) than basal kernels. Maximum water content was related to kernel growth rate but not to final KW. Basal kernels reached maximum kernel volume after attaining maximum water content, with dry matter accumulation affecting kernel volume determination. Kernel density increased with a similar pattern regardless of genotype or panicle position when related to the kernel moisture decline, but at PM, basal kernels were always more dense than apical ones. Differences in the kernel desiccation pattern and in the critical moisture content for biomass accumulation helped explain differences in the grain‐filling duration between positions. A general kernel growth curve based on kernel moisture content was impossible to obtain because of the differences in kernel growth patterns within the panicle.
Tall Fescue Photomorphogenesis as Influenced by Changes in the Spectral Composition and Light Intensity
Authors: Wherley B. G. , Gardner D. S. , Metzger J. D.
Published: July 2010

The influence of deciduous foliage shade on turfgrass development has not been fully investigated. Previous research neglects changes in spectral distribution, e.g., red:far‐red light (R:FR) ratios common of foliage shade. Turfgrass plants may respond simultaneously but in different ways to changes in light intensity and spectral composition. A field study was conducted in 2001–2002 at the Ohio Turfgrass Research and Educational Facility, Columbus, OH. Two tall fescue (Festuca arundinacea Schreb.) cultivars of differing shade tolerance were established under low photosynthetic photon flux (PPF) in approximately 8% of full sunlight with high (>1) and low (<1) R:FR ratios to distinguish between developmental effects of R:FR ratio (spectral composition) and PPF (light intensity) on turfgrass photomorphogenesis. Few morphological differences in shade tolerance between the two cultivars were observed during the 2‐yr study. However, under low PPF, high R:FR ratios led to increased tillering, leaf blade width and thickness, and chlorophyll contents. Root mass declined under reduced PPF regardless of R:FR ratio. Results suggest that while turfgrass photomorphogenesis in shade is influenced by changes in PPF, many characters are further influenced by changes in the R:FR ratio.
Heritability of Waterlogging Tolerance in Wheat
Authors: Collaku A. , Harrison S. A.
Published: July 2010

Tolerance of wheat (Triticum aestivum L.) to waterlogging is related to many morphological and physiological traits that are under a strong environmental influence. Often their genetic control is confounded by environmental stress. The objective of this study was to estimate narrow‐sense heritability for grain yield and yield components under waterlogging conditions and to provide selection criteria for waterlogging tolerance in early generations. We studied 80 families derived from four segregating soft red winter wheat populations in the F2 generation. The experiment was conducted under the effect of 5 wk of waterlogging stress. The Restricted Maximum Likelihood (REML) method was used to estimate genetic variance components. In contrast to traditional methods, REML has no limitations on the mating design and accounts for the relationships among families in a breeding population. Grain yield had the lowest heritability (h2 = 0.25). The highest heritability estimates were found for kernel weight (0.47), chlorophyll content (0.37), and tiller number (0.31). Strong genetic correlations were observed between grain yield and kernel weight (r = 0.56), and between grain yield and tiller number (r = 1). Selection for a relatively highly heritable trait, such as kernel weight, would be an effective way to improve waterlogging tolerance in early generations, as grain yield has a low heritability. Genetic and phenotypic information about traits was used to construct selection indices. A yield improvement of 17% is expected by selection on the basis of the index: grain yield‐kernel weight‐tiller number.
DNA Fingerprinting of Seeded Bermudagrass Cultivars
Authors: Yerramsetty Praveen Nagh , Anderson Michael P. , Taliaferro Charles M. , Martin Dennis L.
Published: July 2010

Bermudagrasses (Cynodon spp.) are important for turf and forage in temperate and tropical climates, with cultivars historically propagated clonally. Over the past two decades the number of seed‐propagated commercial cultivars has dramatically increased, but information is lacking on the extent of the genetic diversity among these new cultivars. Accordingly, this research was undertaken to assess the genetic relatedness of 17 seed‐propagated turf‐bermudagrass cultivars using DNA amplification fingerprinting (DAF). Four DAF and four Minihairpin‐DAF (MHP‐DAF) primers were used in this study. The DAF and MHP‐DAF primers amplified 90 and 131 amplicons, respectively. A total of 13 out of the 17 cultivars were practically indistinguishable using the DAF primers with an average similarity [similarity coefficient (SC)] of 0.982 while the MHP‐DAF primers distinguished all cultivars readily. Results from the DAF and MHP‐DAF analysis indicated that 14 out of the 17 cultivars were related to Arizona common germplasm with average SC of 0.833 in the MHP‐DAF analysis. Arizona common germplasm is naturalized to the Colorado River Valley production areas of Arizona and California. The three most distinct cultivars—‘Princess 77’, ‘Yukon’, and ‘SWI‐11’—had an average SC of 0.668. The most distinct cultivar was Yukon with an average SC of 0.604. Yukon showed 59 DNA signatures not observed in the other cultivars studied with DAF and MHP‐DAF. These results indicated that a majority of seeded‐type bermudagrasses developed over the past two decades depend on a narrow genetic base and that several recent cultivars are markedly genetically distinct, indicating a recent and significant broadening of the germplasm.
Seasonal Poa annua L. Seedling Emergence Patterns in Maryland
Authors: Kaminski John E. , Dernoeden Peter H.
Published: July 2010

Annual bluegrass (Poa annua L.; ABG) can be a major weed problem in golf course turf. Research‐based information on the seasonal emergence patterns of ABG is limited. The objectives of this four‐year field study were (i) to determine seasonal ABG emergence patterns in Maryland, (ii) to determine peak period(s) of ABG emergence, and (iii) to determine the date and estimated percentage of seedlings emerged when the rate of emergence declines. Annual bluegrass seedlings were found to emerge between August and May in two Maryland golf course roughs. A majority (50–70%) of seedling emergence occurred between late September and mid‐October, and peak germination generally was observed in early October. The linear increase in ABG seedling emergence generally ended by early November; however, 24% of all seedlings emerged between November and May. No major ABG emergence cycles were observed during the spring in any year. Mean daily temperatures generally were ≤20°C during peak ABG emergence periods, and germination was stimulated by precipitation. Since the genetic diversity of ABG is well known, these findings may only be applicable to Maryland and regions with similar environmental conditions.
Genetic Relatedness of Portuguese Rice Accessions from Diverse Origins as Assessed by Microsatellite Markers
Authors: Jayamani P. , Negrão S. , Martins M. , Maçãs B. , Oliveira M. M.
Published: July 2010

Simple sequence repeat (SSR) markers detect a significantly high degree of polymorphism in rice (Oryza sativa L.) and are particularly suitable for evaluating genetic diversity among closely related cultivars. A total of 176 rice accessions originating from 19 countries in the Portuguese working germplasm collection and two standard rice varieties (IR36‐indica and Nipponbare‐japonica) were analyzed for DNA profile using 24 SSR loci covering two loci per chromosome. A total of 184 alleles were detected. The number of alleles per locus ranged from 3 to 16, with an average of 7.7, and the PIC value ranged from 0.179 to 0.894 with an average of 0.667. All the loci were polymorphic among the accessions and clearly distinguished the indica and japonica subspecies. At 20% similarity, cluster analysis of the 178 accessions revealed three major groups, japonica, basmati, and indica (Groups I, II, and III, respectively). The japonica group contained 87% of the accessions and showed a wide range of similarity values (0.21–0.92), revealing a high degree of diversity among the accessions. Many of the accessions included in this study are morphologically similar and lack pedigree information. Hence, identification of genetic distances among the accessions should improve their use in breeding programs. As a result of this study, genetically diverse parents can be identified, increasing the usefulness of germplasm collections by broadening the genetic base of rice varieties.
Probabilistic Models for Collecting Genetic Diversity: Comparisons, Caveats, and Limitations
Authors: Lockwood Dale R. , Richards Christopher M. , Volk Gayle M.
Published: July 2010

Methods for collecting genetic diversity from in situ populations are important tools for plant conservation. Many quantitative collection strategies for sampling populations without a priori information regarding the ecology, reproductive biology, or population genetic structure of the taxa have been proposed, but their different assumptions regarding the collection scale and the basis for diversity often make them difficult to compare. Understanding the limitations of the different strategies enables collectors to make more informed choices when implementing conservation and restoration projects or collecting for germplasm improvement. We compare two genetically based strategies under a common set of assumptions and extend the probabilistic arguments of the strategies to accommodate rare alleles, multiple loci, and multiple populations. The recommendations of many models are based on a single locus, but larger numbers of individuals must be collected to assure with a high probability (>0.95) the acquisition of alleles at multiple independent loci within a population. Sampling from multiple populations linked by gene flow may offset this increase. Additionally, the likelihood of capturing rare alleles remains high when sampling for multiple loci or across multiple populations. Comparison of the models provides germplasm collectors with a basis to evaluate risks of over‐ and undersampling to capture genetic diversity within a species.
Relationship of Flag Leaf Characteristics to Economically Important Traits in Two Spring Wheat Crosses
Authors: Blake N. K. , Lanning S. P. , Martin J. M. , Sherman J. D. , Talbert L. E.
Published: July 2010

Selection in unreplicated head rows for traits that affect yield potential is an objective for many wheat (Triticum aestivum L. ) breeding programs. Flag leaf characteristics provide a potential target for selection. In this experiment, we determined flag leaf and yield characteristics for recombinant inbred lines (RIL) from two crosses, McNeal/Thatcher and McNeal/Reeder. McNeal is intermediate between Thatcher and Reeder for green flag leaf duration after heading. Flag leaf characteristics had heritability greater than 0.70 for all traits. Heading date was positively associated with yield for one cross in dryland and irrigated environments but tended to be negatively associated with grain volume, kernel weight, and kernel protein in both crosses. The duration of green leaves after heading was positively correlated with yield, grain volume, and kernel weight in both sets of environments in the McNeal/Thatcher RIL. This trait was positively correlated with grain volume, kernel weight, and grain protein in dryland environments in the McNeal/Reeder RIL. Our results suggest that selection against late heading and for a long duration of green flag leaves after heading should result in gains in yield potential, grain volume, and kernel weight for spring wheat.
Pollen Dispersion within a Population, Nonrandom Mating Theory, and Number of Replications in Polycross Nurseries
Authors: Nyquist W. E. , Santini J. B.
Published: July 2010

A breeder is uncertain how many replications to include in a polycross. Our objective was to develop a method to answer the question. Four isolated, space‐planted nurseries on a 0.91‐m grid of 29 rows by 35 plants were established of ryegrass (Lolium perenne L.), a wind‐pollinated species, with rows in each nursery oriented differently with respect to the compass. The middle row was homozygous for the dominant fluorescent marker gene. Seeds from the seven middle plants in the seven rows closest to the middle row on both sides were observed for the frequency of the dominant gene. From these observations a two‐parameter exponential pollen dispersal function was fitted for the mean of all eight directions combined. The variance among the cross‐pollination frequencies qjk was calculated under two pollination assumptions: (i) pollination confined within each replication and (ii) pollination across all replications. After bulking equal quantities of seed from all replications we have the variance of the mean cross frequencies The square root of this variance, , was used as a measure of the closeness to random mating. The required number of replications to achieve specific levels of closeness to random mating is given for 3 to 100 clones for Assumption 1. The measure of closeness to random mating is given for 3 to 100 clones and up to 30 replications for Assumption 2. When pollination is assumed to occur across replications, a 70% reduction in the variance of is obtained compared to pollination within replications. Hence, fewer replications are required in this case.
Analysis of Genotype‐by‐Environment Interaction in Wheat Using a Structural Equation Model and Chromosome Substitution Lines
Authors: Dhungana P. , Eskridge K. M. , Baenziger P. S. , Campbell B. T. , Gill K. S. , Dweikat I.
Published: July 2010

The presence of genotype‐by‐environment interaction (GEI) complicates selection of superior genotypes and an understanding of environmental and genotypic causes of significant GEI is important in all stages of plant breeding. We present a systematic approach for understanding GEI of complex interrelated traits by combining chromosome substitution lines that allowed us to study the effects of genes on a single chromosome with a structural equation model that approximated the complex processes involving genes, environmental conditions, and traits. We applied the approach to recombinant inbred chromosome wheat lines grown in multiple environments. The final model explained 74% of the yield GEI variation and we found that spikes per square meter (SPSM) GEI had the highest direct effect on yield GEI and that the genetic markers were mostly sensitive to temperature and precipitation during the vegetative and reproductive periods. In addition, we identified a number of direct and indirect causal relationships that described how genes interacted with environmental factors to affect GEI of several important agronomic traits which would not have been possible with previously used methods.
Optimization of the Marker‐Based Procedures for Pyramiding Genes from Multiple Donor Lines: I. Schedule of Crossing between the Donor Lines
Authors: Ishii T. , Yonezawa K.
Published: July 2010

Recent exploitation of DNA markers of desirable trait genes facilitates construction of high‐degree, gene‐pyramided lines via assembling markers from multiple donor lines. In such a program, a plant that has all the target markers in a heterozygous state must be produced first. Efficient procedures for that are discussed. When pyramiding the genes onto the genetic background of a particular recipient line, the backcross should be performed separately for each donor before the crossing between the donors. The plants produced through the backcross should be crossed in a schedule with structure and disposition of the plants as symmetric as possible. When four such plants (A, B, C, and D) are produced, for instance, they should be crossed in a schedule like (A × B) × (C × D) in which the number of target markers of A plus B should be as similar as possible to that of C plus D. Ideal‐type schedules in the presence of four to eight donors are presented. A contrastingly different guideline applies when the donors themselves are crossed without the backcross; they should be crossed in a schedule with completely tandem structure in which donors with fewer target markers enter the schedule in earlier stages. The disposition of donors in the schedule should be modified in the presence of linked or redundant markers. Donors should be disposed in a pattern to minimize the occurrence of repulsion linkages. Formulae for the modification under a high redundancy are presented.
Historical Foundations of Causal Inference in Epidemiology
Authors: Steven S.Coughlin
Published: July 2010

Empiricist philosophers such as Francis Bacon, John Locke, and David Hume believed that knowledge is gained through observations of natural phenomena. In contrast to deductive logic, inductive logic is not self-contained and therefore is open to error. On the other hand, deductive logic cannot by itself establish a theory of prediction since it has no connection to the natural world. Hume observed that inductive inference does not carry a logical necessity. He challenged the notion that causality could be proved, while highlighting the subjectivity of knowledge and the fallibility of inductive reasoning. In the nineteenth century, Robert Koch provided a framework for identifying acute diseases associated with microorganisms. In the twentieth century, following World War II, efforts were made by Sir Austin Bradford Hill and others to systematize and justify causal inference in observational research. More recent authors, including Mervyn Susser, have offered refined accounts of causal criteria. The Bradford Hill criteria for causal inference or subsets of the criteria are still widely used as a heuristic aid for assessing whether associations observed in epidemiologic research are causal. The model of sufficient component causes proposed by Kenneth Rothman is widely used in epidemiology as a framework for teaching and understanding multicausality.
Contemporary Epidemiologic Concepts Regarding Causality
Authors: Steven S.Coughlin
Published: July 2010

There have been many important developments in quantitative models for assessing causality in the last two decades as well as important related developments in epidemiology, statistics, philosophy, and computer science. Writers have conceptualized causality using deterministic models, quasi-deterministic models, and probabilistic models. In epidemiology, a probabilistic model of causation holds that a cause increases the probability that a disease or other adverse health condition will occur. There has been extensive discussion of probabilistic causation in the literature on the philosophy of science. Under a probabilistic model of causation, a cause may be neither necessary nor sufficient for the disease to occur. In contrast, a deterministic model holds that diseases have causes and if these causes are present then diseases will follow. Both probabilistic and deterministic models of disease causation can be linked to sufficient-component models of disease causation. Sufficient-component models of disease causation are especially suitable for understanding the complex causation of many chronic diseases. Approaches for warranting causal claims in epidemiology include quantitative models such as the counterfactual model and structural models.
Seeking Causal Explanations in Epidemiology Subdisciplines
Authors: Steven S.Coughlin
Published: July 2010

Much of the literature on causal inference in epidemiologic research has dealt with causal inference in the field of epidemiology as a whole, or has focused on causal inference in certain areas such as chronic diseases and environmental causes of diseases and adverse health outcomes. In recent years, however, several authors have dealt with causal inference within a variety of epidemiologic subdisciplines including nutritional epidemiology, genetic epidemiology, infectious disease epidemiology, and social epidemiology. Although criteriabased approaches are still widely cited and used, enthusiasm for the Bradford Hill criteria or subsets of the criteria appears to be waning in some areas of epidemiology (or among some groups of epidemiologists). An increasing number of authors have argued that traditional criteria for causal inference in observational research do not apply to particular epidemiology subdisciplines or that certain criteria should be modified. A large and growing literature has dealt with quantitative models for estimating causal parameters using data from observational studies (for example, counterfactual models and structural equation models).