bluuebunny/crossref_metadata_2025 huggingface dataset:
Conversion of Fertility Restoration of the Sorghum IS1112C (A3) Male‐Sterile Cytoplasm from Two Genes to One Gene
Authors: Tang H. V. , Pring D. R.
Published: July 2010

The restoration of male fertility in sorghum [Sorghum bicolor (L.) Moench] lines carrying the IS1112C male‐sterile cytoplasm is characterized by limited seed set. Restoration requires complementary gametophytic action of two restoring alleles, Rf3 and Rf4, for individual gamete viability, and an F1 heterozygous for the two restoring loci is expected to exhibit 25% viable pollen. The objective of this study was to demonstrate the feasibility of converting restoration to single gene behavior. Single‐seed descent B3Tx398/IS1112C F5:6 lines were used to generate homozygosity at the rf3 and rf4 loci, and critical segregants were identified by progeny tests, assays for action of the Rf3 allele, and genomic markers for the rf4 locus. Using these criteria, we constructed the genotypes Rf3Rf3rf4rf4 and rf3rf3Rf4Rf4 in normal, male‐fertile cytoplasm lines, and in IS1112C male‐sterile cytoplasm lines. Pollination of either male‐sterile line with a matching male‐fertile line resulted in about 25% pollen staining in the F1, demonstrating complementation of the two restoring loci. Pollination of either male‐sterile line with IS1112C, Rf3Rf3Rf4Rf4, resulted in about 50% pollen staining. These characteristics substantiate complementary action of the restoring alleles, and are consistent with successful conversion to a single gene fertility restoration system.
Measurements of Representativeness Used in Genetic Resources Conservation and Plant Breeding
Authors: Vencovsky Roland , Crossa Jose
Published: July 2010

This paper reviews some measurements of representativeness such as the effective population size (Ne) useful in genetic resources conservation and plant breeding research. Some easy‐to‐use expressions for estimating Ne in a number of practical conditions are given. For the case of several subpopulations, Ne is scarcely influenced by the total inbreeding. Thus, Ne becomes mostly dependent on the allelic diversity among subpopulations and the number of subpopulations sampled. When, under natural conditions, levels of interpopulation allelic divergence are low, it is misleading to believe that a small number of subpopulations will be sufficient to attain adequate effective population sizes. When a single population is considered and seeds being sampled have a family structure, at the limit Ne depends only on the number of seed parents and the coancestry coefficient among sibs within families. Accession regeneration is the case where the reference population is of finite size. Gametic control is a major factor in regeneration. The loss of up to 20% of seeds may be recovered in terms of Ne when female gametic control is applied. This is not attainable with random sampling of seeds. When studying Ne in recurrent selection schemes, results showed that the gain in Ne through gametic control is very small when selection is intensive. When comparing effective population sizes for the single seed descent (SSD) method versus the bulk system, results showed that SSD maintains genetic drift at a low level and offers a much better protection against random loss of alleles during selfing generations. Estimating population parameters, through codominant genetic markers is fundamental for obtaining reliable estimates of effective population size.
Clarification and Reevaluation of Population‐Based Diallel Analyses
Authors: Murray Leigh W. , Ray Ian M. , Dong Haiying , Segovia‐Lerma Armando
Published: July 2010

Plant breeders and geneticists often use diallel mating designs to obtain genetic information about a trait of interest from a fixed or randomly chosen set of parental lines. Diallel analyses of broad‐based populations have frequently been conducted by means of three analyses presented by Gardner and Eberhart in 1966. The original paper of Gardner and Eberhart used sequential model fitting to obtain estimates of effects and corresponding sums of squares. This approach, although having a long history, suffers from shortcomings which have led to confusion about what hypotheses the analyses actually test. The objectives of this paper were to delineate clearly all models implicitly required to perform Gardner and Eberhart Analyses II and III, and to present explicit formulas for effects in terms of the population means which are fundamental and unambiguous. While developing formulas of effects, we discovered a typographic error associated with variety effects in the original example of Analysis II. Our results also indicate that Analyses II and III effect formulas are rather nonintuitive both biologically and genetically, and incorporate multipliers that are functions of the number of parents. Another specific result shows that the varietal effects obtained in Gardner and Eberhart's Analysis III are “unconstrained” estimates, while those from the Analysis II are estimates constrained by the assumption of “no heterosis.” These results have implications for the use and interpretation of such effects. A SAS computer program for analyzing diallels among broad‐based populations according to Gardner and Eberhart's Analyses II and III is also reported.
Early Plant Selection Effects on Crown Traits in Pensacola Bahiagrass with Selection Cycle
Authors: Blount A. R. , Gates R. N. , Pfahler P. L. , Quesenberry K. H.
Published: July 2010

A positive relationship between crown traits of greenhouse‐grown plants and crown development in the field would allow for the efficient evaluation of large populations of bahiagrass (Paspalum notatum Flügge) for rapid stand establishment. The objective of this study was to determine if young plants exhibiting greater crown vigor (expressed as rapid crown area growth and profuse tillering) in the greenhouse would result in larger, more vigorous plants when grown in the field. Fifty young bahiagrass plants, from each of four cycles (C0, C4, C9, and C23) resulting from recurrent restricted phenotypic selection (RRPS), were evaluated in the greenhouse for plant vigor, crown width, crown wet weight, and tiller number. Plants were transplanted to the field and crown area was determined at 6 and 15 mo after establishment. Crown vigor of greenhouse plants was greatest for C4 and C9 plants. Vigor ratings for C9 plants were smaller (P < 0.05) than C4 in Exp. 2, but larger than C0 and C23. Crown area, crown wet weight, and tillering of the greenhouse plants favored plants from C4 populations. Greenhouse plants of C23 generally had smaller crowns and less tillering. Crown area of individual plants from greenhouse plants, for all cycles, was positively correlated with crown area in the field after 6 mo following transplanting (r = 0.74 to 0.87 for Exp. 1 and 0.75 to 0.93 for Exp. 2). At 15 mo after transplanting to the field, bahiagrass crowns had filled the area between spaced plants. Selecting young superior bahiagrass plants in the greenhouse should aid breeders in developing germplasm that could hasten field establishment.
The Pd2 and Lf2 Loci Define Soybean Linkage Group 16
Authors: Devine Thomas E.
Published: July 2010

Despite progress made in constructing the molecular map of soybean [Glycine max (L.) Merr.], many genes remain to be located on the classical map. The genetic linkage studies reported here were undertaken to advance the construction of the classical genetic map. Hybridizations were made in the field and the F2 and F3 generations were produced and classified in the greenhouse or field at Beltsville, MD. Data were tested by chi‐square for single‐factor segregation and linkage. Recombination estimates were made by the maximum likelihood method. The Lf2 locus (controlling leaflet number) segregated independently of the T, Ln, W1, Rj1, F, Y17, Df4, Fr2, and Pc loci. The Pd2 locus (controlling pubescence density) segregated independently of the W1 locus. The chi‐square for Lf2 and Pd2 strongly indicated linkage. The recombination frequency between the Lf2 and Pd2 loci was estimated at 12 ± 2.2%. Soybean breeders attempting to couple or decouple the Lf2 and Pd2 alleles in their breeding populations should take cognizance of this linkage association in estimating the population sizes required to achieve their goals.
Selection Index for Improving Helminthosporium Leaf Blight Resistance, Maturity, and Kernel Weight in Spring Wheat
Authors: Sharma R. C. , Duveiller E.
Published: July 2010

Helminthosporium leaf blight [HLB, caused by spot blotch, Cochliobolus sativus (Ito & Kuribayashi) Drechs. ex Dastur, and/or tan spot, Pyrenophora tritici‐repentis (Died.) Drechs.], is the most serious disease constraint to wheat (Triticum aestivum L.) yields in the warmer plain areas of South Asia. A selection strategy is needed to identify early maturing, HLB‐resistant genotypes, given that most early maturing wheat cultivars in the region are either susceptible or have low levels of HLB resistance. A study was conducted to determine whether three traits could be simultaneously improved with a selection index (IS) combining the area under disease progress curve (AUDPC) as an assessment of disease severity, days to heading (DHD), and thousand‐kernel weight (TKW). Results from replicated field tests at two sites in Nepal in 2002 showed that selection in the F3 generation with the low and high IS was effective in identifying F4 lines with low and high AUDPC, respectively. The use of low IS was associated with higher grain yield and higher TKW, without significantly affecting DHD and plant height. The AUDPC was reduced by 579 to 837, depending on location and population, while TKW was increased by 7.8 to 12.7 g, and grain yield by 786 to 1491 kg ha−1 The use of IS also produced positive response in biomass and grain yields. There was an average 43% increase in grain yield of the low IS group compared with the high IS group. The results suggested that selection for early maturing, HLB‐resistant wheat lines with high grain yield and kernel weight is possible with a IS
Comparative Chromosome Banding Studies of Nondormant Alfalfa Germplasm
Authors: Bauchan Gary R. , Campbell T. Austin , Hossain M. Azhar
Published: July 2010

A cytogenetic investigation was conducted on four historically putatively distinct nondormant alfalfa germplasm sources, African, Chilean, Peruvian, and Indian tetraploid alfalfa [Medicago sativa ssp. sativa (L.) L. & L.; 2n = 4x = 32]. C‐banding, image analysis, and cluster analysis was used to test the hypothesis that chromosome structure differed among the four nondormant alfalfa populations. Cytogenetic analyses revealed polymorphisms for heterochromatic DNA in the number and location of constitutive heterochromatic DNA both within and among genotypes. However, this variability did not prevent recognition of homologous chromosomes. Karyotypes of Peruvian and Indian populations were developed. The reference African population was used to compare the karyotypes of Peruvian and Indian populations as well as the previously published Chilean population. In general, the number of heterochromatic DNA bands was similar for the African, Chilean, and Peruvian populations; however, the Indian population had significantly fewer heterochromatic bands than the other three. Cluster analysis based on all eight chromosomes yielded no clear separation of the nondormant alfalfa populations possibly because of the lack of chromosomal rearrangements, similar genetic backgrounds of the initial introductions, intercrossing of the different sources, genetic drift during maintenance, and/or common genetic backgrounds of the original parental germplasm sources.
Short Periods of Water Stress during Seed Filling, Leaf Senescence, and Yield of Soybean
Authors: Brevedan R. E. , Egli D. B.
Published: July 2010

The effects of short periods of water stress during seed‐filling on leaf senescence, seed‐fill duration, and yield of soybean [Glycine max (L.) Merrill] are not well understood. Short stress periods were investigated in two greenhouse experiments with cultivar Elgin 87 grown in soil‐filled pots. All pots received adequate water until the beginning of growth stage R6 when a continuous water‐stress treatment (pots received 40% of the water needed to bring controls to pot capacity) was initiated and maintained until maturity. Water stress was relieved in other pots (watered as the control) after 5 or 13 d in Exp. 1 and 3 or 6 d in Exp. 2. Each treatment was replicated six to eight times in a completely randomized design. The carbon exchange rate was rapidly reduced by continuous water stress resulting in earlier maturity, significantly lower yield (39%), and smaller seeds (25–33%). The carbon exchange rate rapidly increased to near control levels in the early stress‐relief treatment, but it was always less than the control for the rest of seed filling. These plants matured sooner and produced significantly lower yields (10–23%) and smaller seeds (9–17%) than control plants. Late stress relief also reduced yield and seed size relative to the control. Yield and seed size of both stress relief treatments, however, were greater than the continuous stress treatment. Water stress‐induced acceleration of senescence could not be stopped by eliminating the stress after a short period. Short periods of water stress during seed filling may, therefore, have larger than expected effects on yield.
Optimizing Marigold (Tagetes erecta L.) Petal and Pigment Yield
Authors: Bosma Theresa L. , Dole John M. , Maness Niels O.
Published: July 2010

African marigold (Tagetes erecta L.) flower pigments can be extracted and used as a natural food additive to color egg yolks orange and poultry skin yellow. Five cultivars were examined for their ability to be grown commercially and mechanically harvested. ‘E‐1236’ was consistently a top producer for three seasons in terms of flower number, flower diameter, plant and flower canopy height, plant stand, and fresh flower, dried flower, and dried petal yield. E‐1236 produced the greatest quantity of lutein, a carotenoid pigment, in 1998 (22.0 kg ha−1), and E‐1236 and ‘Orange Lady’ both produced the greatest quantities in 1999 (20.7 and 21.3 kg ha−1, respectively). Transplanted rather than direct‐seeded plants produced two more harvests in a single season resulting in greater amounts of lutein production by transplants. In 1998, one mid‐season ammonium nitrate application (28 kg ha−1) resulted in larger flower diameters with direct‐seeded plants but did not affect dried petal yield. Plants were hedge trimmed in 1999 to mimic mechanical harvesting; this resulted in a 45 to 55% reduction in flower harvest data compared with hand‐harvested flowers. Of the cultivars tested, Orange Lady produced the greatest quantity of lutein (10.6 kg ha−1) when hedge trimmed.
Microsatellite Markers Flanking the tms2 Gene Facilitated Tropical TGMS Rice Line Development
Authors: Lopez M. T. , Toojinda T. , Vanavichit A. , Tragoonrung S.
Published: July 2010

The use of thermosensitive genetic male sterility (TGMS) in the development and production of rice (Oryza sativa L.) hybrids is an alternative to the cytoplasmic‐genetic male sterility (CMS) system. This study aimed to develop TGMS lines with aromatic Thai rice background by molecular marker‐aided breeding. Four microsatellite markers (RM2, RM10, RM11, and RM214) on chromosome 7 in the vicinity of the TGMS gene tms2 and showing polymorphism between the two parents were used in genotyping the mapping population consisting of 157 F2 plants derived from a cross between Norin PL12 (a TGMS line from Japan) and KDML 105 (a popular aromatic Thai rice cultivar). The RM11 marker was approximately 5 centimorgans (cM) from tms2 while RM2 was approximately 16 cM from it. In this F2 population, the accuracy of selecting sterile plants with RM2 and RM11 markers was 92 and 97%, respectively. In three backcrosses, the accuracy of selection with markers for either homozygous or heterozygous plants was higher than 90% with RM2. Using RM11, we obtained 89% accuracy for selecting homozygous fertile plants and 59% accuracy for selecting heterozygous plants. The results demonstrated that microsatellite markers were powerful in screening large breeding populations, and these markers facilitated selection for plants possessing the tms2 in an early stage of the crop and without exposing the materials to the required temperature for TGMS gene expression. Three TGMS lines with aromatic Thai rice background were developed and showed complete pollen sterility when maximum temperature was higher than 30°C, 1 to 2 wk after panicle initiation. Up to 77% spikelet fertility was observed when these lines were exposed at temperature below 30°C during the critical stage.
Differential Response of Rice Germplasm to Straighthead Induced by Arsenic
Authors: Yan Wengui , Dilday Robert H. , Tai Thomas H. , Gibbons James W. , McNew Ronnie W. , Rutger J. Neil
Published: July 2010

Straighthead disease is a physiological disorder of rice (Oryza sativa L.) characterized by sterility of the florets leading to reduced grain yield. Knowledge of the straighthead response of new cultivars is important for producer control of this disease, and identification of resistant germplasm is essential for breeding improved cultivars. The objectives of this study were to characterize U.S. cultivar reactions to straighthead and search for resistant germplasm. Twelve lines, including 10 U.S. cultivars, a Chinese and Japanese cultivar, were tested for straighthead reaction induced by monosodium methanearsonate (MSMA) at 0, 6.7, and 9.0 kg ha−1 under nitrogen fertilizer of 0, 67, 134, and 269 kg N ha−1 in 1999 and 2000. Straighthead delayed heading date, shortened plant height, and dramatically reduced grain yield. Cocodrie, Mars, Kaybonnet, and Bengal were highly susceptible to straighthead with ratings from 7.2 to 8.0 and grain yield reductions from 80 to 96%. Wells, LaGrue, Drew, Cypress, and Japan 92.09.31 were susceptible with ratings from 5.9 to 6.7 and yield reductions from 49 to 73%. Priscilla and Jefferson were tolerant with ratings of 4.9 and 5.3, and yield reductions of 24 and 36%, respectively. The Chinese indica cultivar Zhe 733 was essentially immune to straighthead, showing neither symptoms nor detectable yield reduction. A total of 124 Chinese cultivars including 109 indica and 15 japonica were evaluated for straighthead resistance in 2001. Nineteen cultivars, 18 indica and 1 japonica, were identified as straighthead resistant. Grain yields of the resistant cultivars were not significantly reduced by their straighthead ratings of 1 to 3. Variation in yield, plant height, maturity, and endosperm type within the resistant germplasm was also observed.
Shoot Biomass Production among Accessions of Medicago truncatula Exposed to NaCl
Authors: Veatch Maren E. , Smith Steven E. , Vandemark George
Published: July 2010

Increased salt tolerance would improve utilization of salt‐sensitive crop plants such as alfalfa (Medicago sativa L.). In order for selection for salt tolerance to be more efficient, it is useful to know whether improved productivity under saline conditions is due to unique physiological responses to salinity or merely the carry over of increased yield that was selected for in a nonsaline environment. Medicago truncatula Gaertn., a self‐pollinated relative of alfalfa, was used to examine the response of specific genotypes across a range of salinities. This was done by evaluating the change in fresh shoot biomass production of greenhouse‐grown mature plants and seedlings of different accessions of M. truncatula in response to four levels of salinity imposed as NaCl. Those accessions with the highest fresh shoot biomass production under nonsaline irrigation also had the highest fresh shoot biomass production under all salinity levels. The high correlation between an accession's fresh shoot biomass under nonsaline and saline irrigation indicate no unique physiological adaptation to salinity in the accessions of M. truncatula evaluated.
Geographical Parameters and Proximity to Related Species Predict Genetic Variation in the Inbred Potato Species Solanum verrucosum Schlechtd
Authors: del Rio A. H. , Bamberg J. B.
Published: July 2010

Identification of ecogeographic parameters associated with genetic variation would help to prioritize populations within conserved species for collection and maintenance. Previous studies comparing accessions of three Solanum species representing different breeding systems, S. fendleri A. Gray (a disomic polyploid selfer), S. jamesii Torr. (a diploid outcrosser), and S. sucrense Hawkes (a polysomic polyploid outcrosser), revealed no significant associations between genetic and ecogeographic variation. Even physical separation did not predict genetic distance. These previous studies are expanded here by investigating the relationship of genetics and geographic parameters for a fourth type of breeding system: a diploid selfer, modeled by wild S. verrucosum Schlechtd (2n = 2x = 24) from Mexico. The objective was to assess whether genetic distances between accessions are predicted by differences in geographic parameters at the natural sites of origin. Twenty‐seven S. verrucosum accessions were studied using 152 RAPD markers to estimate the genetic distance between pairs of accessions. The association of genetic variation with proximity of the S. verrucosum accessions to other Mexican wild potato species (some known to be sympatric with S. verrucosum) was also analyzed. Pairwise comparisons showed that the average GD of all pairs of accessions was 12.8% (ranging from 0–29.3%). Parameters with variation significantly correlated with the average GD of S. verrucosum populations were physical separation (0.42), latitude (0.70), longitude (0.51), proximity to S. hjertingii Hawkes (0.80), S. hougasii Corr. (−0.75), and S. demissum Lindl. (−0.50). Significant effects of proximity to S. hjertingii (for example) might be caused by introgression, or the coincidence that all S. hjertingii occur in the extreme NE corner of the S. verrucosum range.
Physiological Consequences of Moisture Deficit Stress in Cotton
Authors: Pettigrew W. T.
Published: July 2010

Moisture deficits can depress cotton (Gossypium hirsutum L.) lint yield in all cotton production regions. However, most cotton physiological drought stress research has been conducted in arid production regions, growth chambers, or greenhouses. The objective of this research was to document the effects of moisture deficit stress on the physiology of cotton grown in the humid southeastern USA. Field studies were conducted under dryland and irrigated conditions from 1998 to 2001 with eight genotypes, including an okra‐normal leaftype near‐isoline pair and transgenic lines paired with their recurrent parents. Dry matter partitioning, light interception, canopy temperature, leaf water potential, gas exchange, chlorophyll (Chl) fluorescence, and leaf Chl content data were collected. Genotypes responded similarly to both soil moisture regimes. Drought stress reduced overall plant stature with a 35% leaf area index (LAI) reduction, prompting an 8% reduction in solar radiation interception. Dryland leaves had 6% greater CO2 exchange rates (CER) and 9% higher light‐adapted photosystem II (PSII) quantum efficiency than irrigated leaves during the morning. However, as water potential of the dryland plants became more depressed during the afternoon, the CER and light adapted PSII quantum efficiency of the dryland plants became inhibited and was 6 and 10% lower, respectively, than irrigated leaves. A 19% greater Chl content for the dryland leaves contributed to their higher CER during the morning. This polarity of photosynthesis throughout the day for the dryland plants relative to irrigated plants may explain some of the irrigation yield response inconsistencies in the southeastern USA.
RAPD‐Based Genetic Relationships in Kentucky Bluegrass
Authors: Curley J. , Jung G.
Published: July 2010

Kentucky bluegrass (Poa pratensis L.) is a widely used, facultatively apomictic, cool season turf and forage grass, with many known cultivars. Previously these have been classified on the basis of morphological traits in field tests. However, these determinations are lengthy, sensitive to environmental variations, and there are few traits that can be tested. Molecular markers provide an alternative way to classify these cultivars. Important advantages of molecular markers include lack of sensitivity to changes in environmental conditions, as well as a nearly unlimited potential number of markers and speed of the marker assays as compared with field tests. They can also provide additional information such as the amount of genetic divergence between Kentucky bluegrass cultivars and other genotypes, the amount of agreement between morphological and marker‐based classification, and the amount of genetic variability between seedling replicates of genotypes. Random amplified polymorphic DNA (RAPD) marker data was collected from three replicates each of 123 Kentucky bluegrass cultivars, plant introductions (PIs), experimental breeding lines, and interspecific hybrids between Kentucky and Texas bluegrass (Poa arachnifera Torr.). From these data multidimensional scaling (MDS) plots were created, and ANOVA tests of significant differences between germplasm sources were performed. The PIs were the most genetically divergent from the cultivars, while the interspecific hybrids were not as distinct. Members of two morphological trait‐based types were found to be genetically similar, and there was a wide range of genetic variability among germplasm sources. The genetic divergence of the PIs, combined with their potentially high turf utility reported in earlier studies, indicates their potential as a genetic resource. All but two of the morphological trait‐based types contained genetically diverse individuals, so that cultivar blends of all but these two types would be morphologically similar yet genetically diverse. The rather high within‐cultivar genetic variability could be due to a relatively high proportion of potentially sexually produced off‐types. Thus, this study provides further evidence for the utility of RAPD markers for turfgrass genetics, as well as important genetic information for turf breeders and managers.
Virginia Wildrye Evaluated as a Potential Native Cool‐Season Forage in the Northeast USA
Authors: Sanderson Matt A. , Skinner R. Howard , Kujawski Jennifer , van der Grinten Martin
Published: July 2010

Most forage grasses grown in the northeastern USA are introduced species. Interest in native plant species for conservation and production has increased because of new federal policies. We evaluated northeastern accessions of the native cool‐season grass Virginia wildrye (Elymus virginicus L.) for yield, persistence, and plant morphological traits. Thirteen accessions, one cultivar (Omaha), and one commercial ecotype of Elymus were transplanted into single‐row field plots in late summer of 2000 at Beltsville, MD, Rock Springs, PA, and Big Flats, NY. Two orchardgrass (Dactylis glomerata L.) cultivars were the checks. Yield and morphology (leaf width, length, mass, area, and tillers per plant) data were collected during 2001 and 2002. The Elymus accessions produced as much dry matter (28–57 g per plant) as the cultivar and commercial ecotype. Orchardgrass yielded more than twice as much dry matter than the mean of all Elymus entries (94 vs. 34 g per plant averaged for years and locations). The difference in productivity was related to reduced tillering in Elymus especially during regrowth. Yield per plant was strongly correlated (r = 0.62–0.81, P < 0.01) with the number of tillers per plant. Differences in productivity were also reflected in leaf blade traits, with Elymus having a lower leaf area and mass than orchardgrass. Leaf traits were positively correlated (r = 0.35–0.56, P < 0.05) with plant yield. Some northeastern Elymus accessions would probably perform as well as the commercial sources of Elymus in conservation plantings.
Physiological and Molecular Characterization of Mutation‐Derived Imidazolinone Resistance in Spring Wheat
Authors: Pozniak Curtis J. , Birk Iwona T. , O'Donoughue Louise S. , Ménard Christiane , Hucl Pierre J. , Singh Bijay K.
Published: July 2010

While imidazolinone herbicides are an attractive alternative for weed control, spring wheat (Triticum aestivumL.) is susceptible to most of these herbicides. Three mutant alleles conferring resistance to the imidazolinone herbicides were previously identified in spring wheat following seed mutagenesis, but little is known about the physiological and molecular basis of resistance conferred by these alleles. On the basis of acetohydroxyacid synthase (AHAS; E.C. 4.1.3.18) assays, imazethapyr resistance in genotypes TealIMI 10A (AhasL‐D1), TealIMI 11A (AhasL‐B1), TealIMI 15A, and BW755 (AhasL‐D1) was due to a herbicide resistant form of AHAS. TealIMI 15A, which is homozygous for two resistance alleles, was the most resistant at the enzyme level, suggesting resistance in wheat is additive. Nucleotide sequence analysis of clones derived from susceptible cultivar CDC Teal and resistant lines indicated the presence of three genes coding for the catalytic subunit of AHAS. Using a collection ofT. aestivumcv. Chinese Spring aneuploid and deletion lines,ahasL‐D1, ahasL‐B1,andahasL‐A1mapped to the long arm of chromosomes 6D, 6B, and 6A, respectively. Comparison of partialAhasL‐D1,andAhasL‐B1deduced amino acid allele sequences with wild‐type sequences indicated resistance was due to a Ser‐Asn substitution near the carboxyl terminal of resulting AHAS catalytic subunits. This substitution was not present on the single isolated clone ofAhasL‐A1from TealIMI 15A. This is the first report of the molecular characterization of the AHAS gene family from wheat.
Inflorescence Sampling Improves Effective Population Size of Grasses
Authors: Johnson R. C. , Bradley V. L. , Evans M. A.
Published: July 2010

Variation in seed production per plant leads to reductions in effective population size (Ne), which is a major factor promoting genetic drift of heterogenetic populations during seed collection and regeneration. The objectives of this study were (i) to compare Ne to the census population size (Nc) among different seed harvest methods; (ii) use inflorescence sampling to determine Ne/Nc for numerous heterogenetic grass species, and (iii) to predict the optimum number of inflorescences per plant to most efficiently increase Ne Estimates of Ne/Nc from rubbing whole plants, cutting whole plants, and from sampling a constant two inflorescences per plant were made on Festuca pratensis Huds., Lolium perenne L., and Pseudoroegneria spicata (Pursh) Á. Löve accessions. Inflorescence sampling was also completed on four accessions of Bromus inermis Leyss., Dactylis glomerata L., F arundinacea Schreb., L. perenne, Pseudoroegneria spicata, and Phalaris aquatica L. The mean Ne/Nc for the inflorescence method was 0.78, significantly higher then the 0.64 average for the cut or rub methods. For all species and entries, the slope of the curves describing Ne/Nc to inflorescence number was initially steep from 1 to 3 inflorescences and then leveled off asymptotically. Thus, most of the benefit occurs after sampling only a few inflorescences. The results show that sampling a constant number of inflorescences per plant promotes Ne and reduces the potential for genetic drift associated with collection and regeneration of heterogenetic grass populations.
Selection Environments for Maize in the U.S. Western High Plains
Authors: Guillen‐Portal Fernando R. , Russell W. Ken , Eskridge Kent M. , Baltensperger David D. , Nelson Lenis A. , D'Croz‐Mason Nora E. , Johnson Blaine E.
Published: July 2010

Dryland maize (Zea mays L.) production in the U.S. western High Plains is hampered by variable yields because of substantial environmental variation in this region. This study was conducted to determine the degree to which the ranking of superior maize hybrids for dryland production in the western High Plains was predictable from performance of the same hybrids in highly productive, irrigated environments in the same region. Forty‐five maize hybrids were evaluated for grain yield performance under different water regimes in western Nebraska, eastern Wyoming, and northeastern Colorado in 1998 and 1999. The value of genotypic variance was by far larger in fully irrigated test environments (0.70) than in nonirrigated test environments (0.01–0.17). The genotypic mean repeatability in fully irrigated test environments (0.63) compared with that in nonirrigated test environments (0.18–0.69, respectively), and it showed correspondence with yield performance. The genetic correlation between fully and nonirrigated environments (0.72) was lower than that observed between all‐nonirrigated environments (0.78–1.02). Thus, the proportion of direct advance in the former case (0.63) was generally lower than in the latter (0.41–0.97). However, an environmental similarity ratio (ESR) derived from crossover interaction indicated that water‐contrasting environments were as similar (ESR = 0.53) as nonirrigated environments (ESR = 0.49) in ranking the maize hybrids. Selective identification of maize hybrids in irrigated environments for production under nonirrigated environments in the western High Plains might be a useful surrogate to direct selection in the latter environments.
Response to Selection and Genetic Drift in Three Populations Derived from the Golden Glow Maize Population
Authors: Butruille David V. , Silva Heyder D. , Kaeppler Shawn M. , Coors James G.
Published: July 2010

Reciprocal recurrent selection (RRS) in maize (Zea mays L.) is used to develop populations with superior combining ability, and it is usually assumed that these populations must be genetically distinct for RRS to be effective. Starting from two randomly derived subpopulations, GG(A) and GG(B), of the open‐pollinated maize population ‘Golden Glow’ (GGC0), we conducted six cycles of full‐sib RRS for grain yield and moisture. Our objectives were to (i) document selection response; (ii) evaluate inter and intrapopulation genetic diversity; and (iii) review selection response relative to gene action, heterosis, inbreeding, and genetic drift. We performed a generation means analysis (GMA) using GG(A), GG(B), and a third population of Golden Glow developed by 21 cycles of mass selection for prolificacy, GG(MP). Field performance was evaluated at four environments in Wisconsin. We analyzed allele frequency changes using simple sequence repeats (SSRs) and amplified fragment length polymorphisms (AFLPs). Selection response for grain yield of GG(A) × GG(B) population crosses was 5.3 g plant−1 cycle−1 Grain moisture and root lodging decreased by −0.5% cycle−1 and −5.2% cycle−1, while prolificacy increased by 0.03 ears cycle−1 After six cycles of RRS, GG(A) and GG(B) diverged genetically from each other, as well as from GG(MP)C21 and Golden Glow. Gene diversity within GG(A) and GG(B) decreased. However, total gene diversity over both GG(A) and GG(B) did not change over cycles of RRS. Genetic drift did not appear to seriously impede selection response. Most of the selection response, regardless of trait, selection method, or subpopulation, was attributed to additive genetic effects.
Stability of Nonflowering Orchardgrass
Authors: Casler M. D. , Barker R. E. , Cherney J. H. , Papadopolous Y. A.
Published: July 2010

Orchardgrass (Dactylis glomerata L.) is a valuable pasture species in much of temperate humid North America. However, profuse and early flowering in spring creates management problems for graziers and reduces intake of livestock in a management‐intensive rotational grazing system. The objectives of this study were to estimate environmental stability, genotypic variability, and frequency of nonflowering and sparse‐flowering plants in two sparse‐flowering orchardgrass populations. Seven cultivars and 299 half‐sib families were evaluated for 2 yr at five locations between 42° and 47°N latitude. Sparse‐flowering populations WO‐SF‐B and WO‐SF‐C were later in maturity, produced fewer panicles per plant, and had higher frequencies of sparse‐flowering and nonflowering plants than the cultivars. Plants had varying levels of expression of the nonflowering trait, ranging from slightly sensitive (sparse flowering in one year) to highly sensitive (stable nonflowering across years), with highly sensitive plants found only within populations WO‐SF‐B and WO‐SF‐C. The nonflowering trait of orchardgrass appears to be controlled by floral‐regulation genes that are turned off by short‐day temperatures below a critical threshold. Such a threshold appears to exist for all orchardgrass plants, but is increased in those plants expressing the nonflowering trait.
Kernel Number Determination in Argentinean Maize Hybrids Released between 1965 and 1993
Authors: Echarte L. , Andrade F. H. , Vega C. R. C. , Tollenaar M.
Published: July 2010

Grain yield and the stability of harvest index are greater in newer than in older Argentinean maize (Zea mays L.) hybrids. The objective of this study was to elucidate mechanisms underlying the superior yield and harvest index stability of newer Argentinean maize hybrids using the relationship between kernel number per plant (KNP) and plant growth rate during the period bracketing silking (PGRs). Three experiments were performed at Balcarce, Argentina, during two growing seasons (1998–2000). Maize was grown under a wide range of plant densities (from 2 up to 30 plants m−2) to generate contrasting availability of resources per plant. Growth of individual plants during the period bracketing silking was estimated through a nondestructive method on the basis of relationships between actual shoot dry matter and morphometric variables, including stem and ear diameters and ear length. Detasseling and silk pollination synchronization treatments were imposed in one experiment to also modify available resources per kernel and kernel sink strength. Newer hybrids set more kernels per unit PGRs than older hybrids as is indicated by (i) the lower threshold PGRs for kernel set and (ii) greater potential kernel number at high availability of resources per plant, for newer than for older hybrids. At low and intermediate PGRs, the greater kernel set per unit PGRs in newer vs. older hybrids was attributable to greater partitioning of dry matter to the topmost ear during the period bracketing silking, whereas number of kernels set per unit of ear growth rate did not differ. In contrast, kernel set per unit of ear growth rate was greater in newer than in older hybrids when PGRs was high. Results of this study indicate that genetic yield improvement in maize is attributable, in part, to increased partitioning of dry matter to the ear during the critical period bracketing silking.
Plant Responses and Characteristics Associated with Dollar Spot Resistance in Creeping Bentgrass
Authors: Bonos Stacy A. , Casler Michael D. , Meyer William A.
Published: July 2010

Dollar spot, incited by Sclerotinia homoeocarpa F.T. Bennett, is one of the most important diseases affecting creeping bentgrass (Agrostis stolonifera L.) golf greens, fairways, and tees. Genetic resistance to dollar spot is a promising control strategy. A study was initiated to: (i) evaluate dollar spot resistance of 265 collections of creeping bentgrass in two locations; (ii) determine bentgrass clone stability of dollar spot resistance; and (iii) evaluate 10 resistant and susceptible clones for disease, turf, and leaf traits. The field experiments were arranged in randomized complete blocks with six and five clonally propagated replicates in each of two locations evaluated across 2 yr in North Brunswick, NJ. Five isolates of S. homoeocarpa were used to inoculate the field experiments. New Jersey fairway collections had the highest percentage of stable dollar spot resistant clones compared with Illinois fairway and New Jersey and New York golf green collections in this particular study. Resistant clones maintained a significantly higher turf density and percentage green turf cover and smaller dollar spot diameter sizes compared with susceptible clones.
Influence of Bt Transgenes on Cell Wall Lignification and Digestibility of Maize Stover for Silage
Authors: Jung H. G. , Sheaffer C. C.
Published: July 2010

There have been inconsistent reports that maize (Zea mays L.) hybrids with the Bacillus thuringiensis (Bt) cry1 Ab transgene contain more lignin than non‐Bt hybrids of similar genetic background. Our objective was to evaluate the impact of the cry1 Ab transgene on lignin concentration (using three different assays), yield, and forage quality traits of maize. Replicated trials were conducted at four locations in Minnesota with 12 commercial hybrids (three MON810 and three Bt11 cry1 Ab transgene event hybrids, and respective near‐isogenic controls). Whole plants and the fourth elongated, above‐ground internodes were harvested at silage maturity. Samples were analyzed for crude protein, starch, neutral detergent fiber (NDF), acid detergent fiber, 24‐ and 96‐h in vitro ruminal NDF digestibility, and lignin (acid detergent, Klason, and acetyl bromide). European corn borers (Ostrinia nubilalis Hübner) were not controlled and damage was limited to the non‐Bt hybrids, averaging 1.5 internodes plant−1 with tunnels. Environment and environment × hybrid interactions affected all measures of maize performance and quality, but comparisons of non‐Bt/Bt hybrid pairs, for both whole plants and internodes, found no consistent differences in yield, nutrient content, in vitro ruminal NDF digestibility, or lignin concentration. Differences in lignin concentration were infrequent, small in magnitude, and inconsistent between a few non‐Bt/Bt hybrid pairs at individual locations. Two non‐Bt/Bt hybrid pairs did not differ in lignin concentration at any location. Contrary to some earlier reports, presence of the cry1 Ab transgene did not alter lignin concentration or other forage quality traits of maize stover in commercial maize hybrids.
RAPD and SCAR Markers Linked to the Ur‐6 Andean Gene Controlling Specific Rust Resistance in Common Bean
Authors: Park S. O. , Coyne D. P. , Steadman J. R. , Crosby K. M. , Brick M. A.
Published: July 2010

Bean rust, caused by Uromyces appendiculatus (Pers.: Pers.) Unger, is a major disease of common bean (Phaseolus vulgaris L.). A recommended strategy to obtain durable rust resistance is to use molecular markers linked to rust resistance genes for pyramiding monogenic resistance genes into a single bean cultivar. However, markers tightly linked to Ur‐6 of Andean origin conferring specific resistance (SR) to rust present in Olathe have not been reported. Our objectives were to identify random amplified polymorphic DNA (RAPD) markers linked to Ur‐6 controlling SR to race 51 using bulked segregant analysis in an F2 population from the Middle American (MA) common bean cross Olathe (resistant) × Nebr.#1 sel.27 (susceptible), and determine the presence or absence of these identified markers in 70 MA and Andean bean cultivars and breeding lines. A single dominant gene controlling SR to race 51 was found in the F2 and confirmed in the F3 Six RAPD markers were detected in a coupling phase linkage with Ur‐6 The gene was flanked by two coupling‐phase markers OBC06.300 and OAG15.300 at 1.3 and 2.0 cM. Sequence characterized amplified region (SCAR) marker SOBC06.308 was developed based on the specific primer pair designed from the sequence of the RAPD marker OBC06.300. The RAPD and SCAR markers were also present in MA pinto bean germplasm having Ur‐6 as well as Golden Gate Wax, another source of Ur‐6 However, these markers were also present in six Andean cultivars without Ur‐6, suggesting gene pool specificity. Among five repulsion‐phase markers identified, OAY15.200 was the most closely linked to Ur‐6 at 7.7 cM. We also confirm the Ur‐6 location on linkage group 11 of the P. vulgaris map. These RAPD and SCAR markers linked to Ur‐6 identified here, along with markers for other independent rust resistance genes, could be utilized to pyramid multiple genes into a bean cultivar for more durable rust resistance.
Screening Multiple Soybean Cultivars (MG 00 to MG VIII) for Somatic Embryogenesis Following Agrobacterium‐Mediated Transformation of Immature Cotyledons
Authors: Ko Tae‐Seok , Nelson Randall L. , Korban Schuyler S.
Published: July 2010

A total of 15 soybean [Glycine max (L.) Merr.] cultivars representing maturity groups 00 to VIII were assessed for their embryogenic and transformation potentials. All cultivars were identified as embryogenic under hygromycin selection following Agrobacterium‐mediated transformation of immature cotyledons. Histochemical β‐glucuronidase (GUS) assays of induced hygromycin‐resistant somatic embryos (SEs) showed that 13 out of 15 cultivars were amenable for transformation. Wide variations among different genotypes were observed for their embryogenic capacity under hygromycin selection. Three cultivars, Cisne, Council, and Kunitz, were highly embryogenic yielding more than 50% responding explants and 1.5 to 2.4 hygromycin‐resistant SEs per responding explant. The transformation potential of multiple soybean cultivars was highly correlated with the embryogenic potential of immature cotyledons under hygromycin selection. It was possible to distinguish between highly and poorly embryogenic genotypes by visually observing the phenotype of cultured immature cotyledons. For highly embryogenic cultivars, the induction of somatic embryos mainly originated from actively dedifferentiating and browning/necrotic tissues along the margins of the abaxial side of cultured cotyledons.
Debunking Soybean Myths and Legends in the Historical and Popular Literature
Authors: Hymowitz T. , Shurtleff W. R.
Published: July 2010

The soybean [Glycine max (L.) Merr.] is one of humanity's principle food crops. Unfortunately, the historical and popular literature concerning soybean is replete with factual errors that keep recycling from one publication or website to another without documentation. In this essay we attempt to correct the most egregious errors about soybean history. The earliest known introduction of the soybean into North America was by Samuel Bowen in 1765 and not Benjamin Franklin. A royal patent 878 was issued to Bowen for making soy sauce from Chinese vetches (soybean). The 1804 date cited as the oldest introduction of the soybean into the USA is clearly in error. George Washington Carver did not play an important role in the introduction of the soybean to the USA. The soybean is not one of the world's oldest domesticated crops, has not been cultivated in China for more than 5000 yr (50 centuries), and Emperor Shennong is a mythical figure. The current oldest record for the soybean in China dates back to the 11th century BCE or perhaps a bit earlier.