bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimation of Pollen Viability, Shedding Pattern, and Longevity of Creeping Bentgrass on Artificial Media
Authors: Fei S. , Nelson E.
Published: July 2010

An estimation of pollen viability is needed to determine pollen daily shedding pattern and longevity. Both parameters provide valuable information for plant breeding and contribute to the risk assessment of pollen‐producing transgenic crops. Pollen viability of ‘Crenshaw’ creeping bentgrass (Agrostis stolonifera L.) was estimated through pollen germination on media containing sucrose (1‐alpha‐D‐glucopyranosyl‐2‐beta‐D‐fructofranoside, at 0.25, 0.5, 1.0 M), H3BO3 (1.0, 2.0, or 4.0 mM), and CaCl2 (1.0, 2.0, or 4.0 mM). The highest pollen germination percentage was obtained on a medium containing 1.0 M sucrose, 1.0 mM H3BO3, and 2.0 mM CaCl2 Concentrations of all three medium components had significant effects on pollen germination. No two‐way or three‐way interactions among sucrose, H3BO3, and CaCl2 were observed. A high sucrose concentration of 1.0 M severely inhibited pollen tube growth, causing shorter and thicker pollen tubes. Pollen‐tube length of pollen germinated on medium containing 1.0 M sucrose averaged 137 μm, while those germinated on medium containing 0.5 M sucrose averaged 248 μm. The daily shedding pattern of pollen of Crenshaw creeping bentgrass was determined by collecting and germinating pollen from 0800 through 1700 h at 1‐h intervals. The results indicated there were two peaks of pollen viability, with the first one occurring at 0900 h and the second peak at 1400 h. The longevity of Crenshaw and ‘Penncross’ pollen was assessed by storing the pollen in a desiccator at 21°C and a relative humidity of 64 to 66%. Our results showed that creeping bentgrass pollen lost viability dramatically within the first 1.5 h of storage and lost viability completely after 3 h of storage.
An Empirical Model for Pollen‐Mediated Gene Flow in Wheat
Authors: Gustafson D. I. , Horak M. J. , Rempel C. B. , Metz S. G. , Gigax D. R. , Hucl P.
Published: July 2010

The extent of pollen‐mediated gene flow (PMGF) in wheat (Triticum spp. L.) as a function of distance from a pollinator source has been measured in recent field studies. Wheat is primarily self‐pollinated; however, some cross‐pollination can occur depending on biological, agronomic, and environmental factors. The complexity of these interactions restricts attempts to develop a workable mechanistic model; therefore, we pursued an entirely empirical modeling approach. We fit a simple empirical regression model to all available observed data and then used it to make general predictions about the effects of field size, blending at harvest, and isolation distances on PMGF in wheat. The empirical model was derived by fitting a least squares regression line to the gene flow data when plotted as the logarithm of PMGF versus the square root distance from the edge of the source field. Linear behavior was observed when either the maximum or mean PMGF was plotted in this manner. A “General Wheat Model” (GWM) of this same mathematical form is given which provides a conservative (“high‐end”) prediction of PMGF in the general case: , where PMGF is the percent gene flow at a particular point in the field (without blending), and x is the distance (m) from the edge of the source field. The GWM was used to show that the effect of source field size is minimal for sources of 10 ha or larger, where asymptotic levels of PMGF are obtained. The model was also applied to show that harvest‐blending produces PMGF at the field level 10 to 50 times lower than the highest level observed at the edge of the receptor field. Significantly, isolation buffers of 0 to 10 m were predicted by the GWM to have only a minimal impact on harvest‐blended PMGF, when the receptor field had an overall width of 100 m or greater. Without any isolation buffers, the harvest‐blended PMGF between neighboring commercial‐sized (>10 ha) fields was less than 0.1% (well below commercial thresholds for foreign material in wheat seed and grain). This is also well below any existing standards for labeling the presence of approved biotech traits in food or seed distributed or sold as conventional.
Soybean Maturity and Pubescence Color Genes Improve Chilling Tolerance
Authors: Takahashi Ryoji , Benitez Eduardo R. , Funatsuki Hideyuki , Ohnishi Shizen
Published: July 2010

Exposure of soybean [Glycine max (L.) Merr.] to chilling temperatures (10–18°C) at flowering reduces seed yield and induces browning around the hilum region and cracking of the seed coats. Previous studies revealed that alleles at maturity loci E1 to E5 and E7 were associated with the intensity of pigmentation and cracking, and that genotypes with the pubescence color allele T are associated with less seed yield reduction under low temperature conditions. The first objective of this study was to evaluate the combination effect of maturity genes between E1 and E3E4 on the intensity of seed coat pigmentation and cracking. The second objective was to evaluate the combination effects of E1, E3E4, and T on weight of seed per plant under chilling treatments. For the seed quality experiment, soybean cv. Harosoy (e1e2E3E4e5E7t) and its near‐isogenic lines (NILs), Harosoy‐E1, Harosoy‐e3e4, and Harosoy‐E1e3e4, were exposed to 15°C for 2 wk beginning 8 d after flowering. Harosoy‐E1e3e4 had an intermediate degree of pigmentation and cracking relative to Harosoy‐E1 and Harosoy‐e3e4, suggesting that the effects of E1 and E3E4 may be additive. For the yield component experiments, Harosoy, Harosoy‐T, Harosoy‐E1e3e4, and Harosoy‐E1e3e4T were exposed to 15°C in 2002 and 18/13°C with 55% shading in 2003 for 4 wk from flowering. Weight of seed per plant in NILs with E1e3e4 was higher than NILs with e1E3E4 under chilling treatments. Further, NILs with T produced higher weight of seed per plant compared with NILs with t under chilling treatments. The above results suggest that allelic combination of E1e3e4 is preferable to e1E3E4 to enhance quality and yield of seeds under chilling conditions. The dominant T allele may also be useful to further improve chilling tolerance.
Fagopyritol Accumulation and Germination of Buckwheat Seeds Matured at 15, 22, and 30°C
Authors: Horbowicz Marcin , Obendorf Ralph L.
Published: July 2010

Common buckwheat (Fagopyrum esculentum Moench; Polygonaceae) embryos accumulate six fagopyritols in two unique series: fagopyritol A1, fagopyritol A2, fagopyritol A3, fagopyritol B1, fagopyritol B2, and fagopyritol B3. Fagopyritol A1 is isosteric to a putative insulin mediator believed to be deficient in subjects with noninsulin dependent diabetes mellitus (NIDDM) and polycystic ovary syndrome (PCOS). Fagopyritols accumulate during seed development, and accumulation is enhanced in response to cooler temperatures. The objective was to test the hypothesis that seed maturation at cooler temperature enhances fagopyritol accumulation, improves seed quality, and increases yield of desirable fagopyritols for dietary treatment of NIDDM and PCOS. Seeds from buckwheat plants grown at 15, 22, or 30°C were harvested at 8, 12, 16, 20, and 28 d after pollination (DAP) and analyzed for soluble carbohydrates in the embryos. Remaining seeds were dried and tested for germination and seedling growth. Embryo dry weight increased rapidly between 8 and 12 DAP at 30°C, 12 and 16 DAP at 22°C, and 16 and 20 DAP at 15°C. Seed dry weight declined (–0.86 mg per 1°C) when maturation temperature increased. Total soluble carbohydrates remained constant across seed maturation temperatures, but the composition of carbohydrates changed in response to different maturation temperatures. Fagopyritol A1 and fagopyritol B1 were highest in seeds matured at 15°C, whereas fagopyritol A2, fagopyritol B2, fagopyritol A3, raffinose, and stachyose were higher in seeds matured at 30°C. At harvest, seeds matured at 30°C had highest germination. Cool temperatures during buckwheat seed maturation can result in increased seed size and yield of fagopyritol A1 and fagopyritol B1 in embryos for nutritional and medicinal applications.
Morphological and Molecular Characterization of Common Bean Landraces and Cultivars from the Caribbean
Authors: Durán L. A. , Blair M. W. , Giraldo M. C. , Macchiavelli R. , Prophete E. , Nin J. C. , Beaver J. S.
Published: July 2010

Little information is available regarding the relationship of Caribbean bean landraces with the Andean and Mesoamerican gene pools of common bean (Phaseolus vulgaris L.) While small‐seeded Mesoamerican black beans are prevalent in parts of the Caribbean, many of the regionally preferred red mottled and medium‐to‐large‐seeded bean landraces found there are postulated to belong to the Andean gene pool. To test this hypothesis, we analyzed the morphological characteristics, phenological traits, phaseolin status, and random amplified polymorphic DNA (RAPD) banding patterns of 54 red mottled or large‐seeded bean landraces and cultivars from the Caribbean (16 from the Dominican Republic, 14 from Haiti, 1 from Jamaica and 23 from Puerto Rico) compared with 11 Andean bean lines from other regions. To estimate phylogenetic relationships among the lines, distances were calculated and dendrograms constructed for morphological and/or phenological and molecular characteristics by the complete clustering method. The landraces were grouped into two clusters morphologically: one with Mesoamerican characteristics, which included all the red mottled lines from Haiti and three landraces from the Dominican Republic collected near the Haitian border and the other with Andean characteristics, which included all the lines from Puerto Rico and the remaining lines from the Dominican Republic. RAPD and phaseolin polymorphisms identified three groups, one corresponding to the genotypes with Mesoamerican morphologies, one to those with Andean morphologies, and another that had Andean phenotypes but proximity to the Mesoamerican group, suggesting possible introgression between the gene pools. Phaseolin variability agreed with other molecular and morphological data allowing the assignment of genotypes to a Mesoamerican or Andean gene pool. Knowledge of this variability may provide useful information concerning the potential value of Caribbean landraces to Andean bean breeding programs.
Disease and Insect Resistance in Cultivated Barley Accessions from the USDA National Small Grains Collection
Authors: Bonman J. Michael , Bockelman Harold E. , Jackson Lee F. , Steffenson Brian J.
Published: July 2010

Cultivated barley (Hordeum vulgare subsp. vulgare L.) accessions from the USDA‐ARS National Small Grains Collection (NSGC) have been tested systematically for the past 20 yr for disease and insect resistance. In this study, we analyzed the resistance to barley yellow dwarf (BYD), spot blotch (SB) caused by Cochliobolus sativus (Ito and Kuribayashi) Drechs. ex Dastur, net blotch (NB) caused by Pyrenophora teres f. teres Drechs., stripe rust (SR) caused by Puccinia striiformis Westend. f. sp. hordei, and Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), with respect to (i) geographic origin of resistant accessions, (ii) relationship to other NSGC descriptor data, and (iii) relationships among resistances. “Centers of concentration” for certain resistances were identified: eastern Africa for several diseases, western Turkey and the Caucasus for SR resistance, eastern Asia for adult plant resistance to NB, and south‐central Asia for RWA resistance. Stripe rust resistance was also associated with accessions originating from high altitude in eastern Africa (Ethiopia). Various associations between resistances and grain descriptors, plant habit, and landrace status were also found. Forty‐eight accessions showed multiple resistances on the basis of the field disease data and the RWA greenhouse data. Many of these resistant accessions were from Ethiopia, and many were of unknown origin. Stripe rust testing in California and Bolivia supported the conclusion that winter‐habit accessions were more resistant to the disease than were spring‐habit accessions. Information from this study will be used to guide future NSGC acquisition and evaluation efforts.
Plant Species Diversity and Management of Temperate Forage and Grazing Land Ecosystems
Authors: Sanderson M. A. , Skinner R. H. , Barker D. J. , Edwards G. R. , Tracy B. F. , Wedin D. A.
Published: July 2010

More than a century since Charles Darwin stated that diverse grasslands produce more herbage than monocultures, scientists still debate the relationship between species diversity and ecosystem function. Postulated benefits of diversity in experimental grasslands include greater and more stable primary production along with more efficient nutrient use. These benefits have been extrapolated to forage and grazing land systems with little supporting objective data. Most information on the potential benefits of increased plant diversity comes from studies of synthesized grasslands that have not included domestic grazing animals. We explore this debate relative to the management of temperate forage and grazing lands. Plant species diversity refers to the number of species (richness) and their relative abundance (evenness) within a defined area. Plant relations influence biodiversity responses through positive (e.g., facilitation, N2 fixation, hydraulic lift) and negative interactions (e.g., competitive exclusion, allelopathy). Early 20th century research on complex mixtures of forage species (limited to grasses and legumes) for pasture indicated equivocal results regarding benefits of species‐rich mixtures and typically recommended using the best adapted species in simple grass–legume mixtures. Recent research indicates potential herbage yield benefits from species‐rich mixtures for pastures. Limited animal productivity research on species‐rich mixtures indicates variable responses and much more research is needed. Grazing land productivity is a primary focus for biodiversity benefits because of the direct economic relevance to producers. However, taking a broader view of the multifunctionality of grazing lands to include environmental and aesthetic benefits to humans reveals a great scope for using biodiversity in grazing land management.
Hybridization and Introgression between Bread Wheat and Wild and Weedy Relatives in North America
Authors: Hegde S. G. , Waines J. G.
Published: July 2010

Introgression between cultivars and wild relatives is common in several angiosperm taxa including the grass family Poaceae. Bread wheat (Triticum aestivumL.) is a domesticated allohexaploid species (genome formula BBAADD) without any known wild hexaploid relative in the genusTriticumBread wheat is also related to the genusAegilopsL., which has probably contributed two of the three genomes of bread wheat. A few tetraploidAegilopsspecies, includingAe. cylindricaHost. andAe. triuncialisL., occur as weeds both in the Mediterranean basin and in West Asia. Introduced populations of these weeds are also known to occur in North America. These species have been known to introgress occasionally with bread wheat when grown near wheat fields. Similarly, rye (Secale cerealeL.), a species from a distant genus, has a potential to introgress with bread wheat. A few natural introgressive hybrids between herbicide resistant wheat andAe. cylindricaand between wheat and rye have been created or recovered in North America. Natural hybrids between wheat andAe. triuncialishave not been observed in North America. The available data do not suggest the prevalence of large‐scale introgression between bread wheat and its wild relatives in North America. Nevertheless, with modern bread wheat cultivars being developed with novel traits, such as herbicide and disease resistance, an in‐depth evaluation of the extent and nature of introgression between weedyAegilopsor Secalespecies and bread wheat is useful both for assessing potential ecological risks that may be associated with trait presence in hybrids and for formulating strategies to manage gene transfer to hybrids. In this review, we discuss the existing literature on reproductive ecology of bread wheat and on introgression between bread wheat and its wild relatives in the generaAegilopsandSecalethat occur in North America. We also discuss the implications of introgression in consideration of the current and possible future development of transgenic wheat.
Selection for Silage Quality in the Wisconsin Quality Synthetic and Related Maize Populations
Authors: Frey T. J. , Coors J. G. , Shaver R. D. , Lauer J. G. , Eilert D. T. , Flannery P. J.
Published: July 2010

Maize (Zea mays L.) silage is a high‐quality forage for ruminants, but there have been few significant breeding efforts specifically dedicated to improving maize forage yield or quality by breeders in the USA. The objective of this study was to evaluate the forage yield and quality of the Wisconsin Quality Synthetic (WQS) and related populations developed by the University of Wisconsin Maize Breeding Program for agronomic and nutritional attributes. Three cycles of divergent S1 recurrent selection have been completed for stover fiber, silica, and lignin concentration for populations WFISIHI (Wisconsin‐fiber‐silica‐high) and WFISILO (Wisconsin‐fiber‐silica‐low). The third cycle (C3) of WFISILO was crossed to two high‐quality inbred lines, Mo17 and H99, to create WQS C0, which then underwent two cycles of S2–topcross selection for improved forage yield and quality. All cycles of selection for WFISIHI, WFISILO, and WQS were evaluated for forage yield and quality at two field locations in Wisconsin in 2000 and 2001. Results for WFISIHI and WFISILO demonstrated that S1 selection for stover composition altered both stover and whole‐plant composition in the anticipated directions. Selection for whole‐plant yield and composition of S2–topcrosses was also effective for WQS, especially when using selection indices incorporating whole‐plant yield, neutral detergent fiber (NDF), neutral detergent fiber digestibility (NDFD), crude protein (CP), and starch. WQS C2 whole‐plant and stover in vitro true digestibility (IVTD), whole‐plant and stover acid detergent lignin, and milk yield per megagram dry matter (DM) were similar to the brown‐midrib check hybrid, F657. WQS C2 whole‐plant and stover NDFD were lower than F657 but higher than other commercial check hybrids. In addition, WQS population testcrosses improved over cycles of selection for whole‐plant yield and most quality attributes. Our results indicate that it is feasible to develop silage maize germplasm with both high whole‐plant yield and excellent nutritional quality.
Identification of Molecular Markers Linked to the Fertility Restorer Genes for CMS‐D8 in Cotton
Authors: Zhang Jinfa , Stewart James McD.
Published: July 2010

The identification of molecular markers closely linked to restorer genes of the cytoplasmic male sterile (CMS) D8 system could facilitate the development of parental lines for hybrid cotton (Gossypium hirsutum L.). Our objective was to develop molecular markers closely linked to the two independent dominant restorer genes, Rf1 from the D2 restorer line transferred from G. harknessii Brandegee (D2 genome) and Rf2 from the D8 restorer line. Bulked segregant analysis was used to identify random amplified polymorphic DNA (RAPD) markers that were linked to the restorer genes. Three testcrosses were used for mapping Rf2 and two for Rf1 relative to the markers. Two RAPD markers, UBC1113000 and UBC188500, were associated with Rf2 in coupling phase. UBC188500 was closely linked to Rf2 with an average genetic distance of 2.9 cM. A survey of cotton species and cultivars revealed that UBC188500 was absent in normal cotton cultivars and most Gossypium spp. However, it was present in the D8 restorer line, G. raimondii Ulbr. (D5), G. trilobum (DC.) Skovst. (D8), and selected wild species from Australia, indicating that Rf2 and the DNA fragment yielding the RAPD marker were both introgressed into the tetraploid cottons from the D8 genome. A new RAPD marker, UBC169700, and a previously identified RAPD marker, UBC6591500, cosegregated with Rf1 in the two populations examined. The three RAPD markers, UBC188500, UC169700, and UBC6591500 were converted into reliable and genome‐specific sequence tagged site (STS) markers on the basis of their sequence information. These markers are restorer‐specific and should be useful in marker‐based selection for developing restorer parental lines and constructing a high‐resolution linkage map containing Rf1 and Rf2
Primitive Accession Derived Germplasm by Cultivar Crosses as Sources for Cotton Improvement
Authors: McCarty Jack C. , Jenkins Johnie N. , Wu Jixiang
Published: July 2010

Cotton, Gossypium hirsutum L., is grown primarily for its spinnable fibers. To meet textile mill requirements and producer demands, both fiber quality and yield must be improved. This study was conducted to compare yield and fiber quality when exotic derived lines were crossed to cultivars. Fourteen germplasm lines with high fiber strength derived from selected primitive accessions were crossed as male parents to each of five cultivars. The F2 populations and parents were grown at two different field locations in 1998 and 1999. Parents and F3s were grown at two locations in 2000. Parents, F2, and F3 populations were evaluated for yield, yield components, and fiber quality traits. Combination of location and year was considered an environment for data analyses. An additive‐dominance, additive × additive (ADAA), and genotype × environment interaction genetic model was used for data analysis. A mixed linear model approach, minimum norm quadratic unbiased estimation (MINQUE) was used to estimate genetic variance components on the basis of the ADAA model. Cultivars had higher yields and lint percentages than germplasm lines. Fiber strength for germplasm lines exceeded cultivars. Lint percentage, boll weight, micronaire reading, elongation, and fiber length were similar between F2 and F3 populations and near mid‐parent values. Both additive and additive × additive (AA) epistatic effects significantly controlled all agronomic and most fiber traits. Significant dominance effects were detected for all traits except fiber elongation. Additive × environment and dominance × environment interaction effects were detected for most traits. Significant AA × environment interaction effects were detected for agronomic traits but not fiber traits. The additive × environment effect was significant; however, it made a small contribution to the total variance. This study suggest that crosses between day‐neutral derived lines from photoperiodic primitive accessions and commercial cultivars may allow both the utilization of heterosis and the use of genetic variation for pure line development.
Genetic Diversity of Public Inbreds of Sorghum Determined by Mapped AFLP and SSR Markers
Authors: Menz Monica A. , Klein Robert R. , Unruh Natalie C. , Rooney William L. , Klein Patricia E. , Mullet John E.
Published: July 2010

The objectives of this study were (i) to assess the level of genetic diversity in elite sterility‐maintaining (B) and fertility‐restoring (R) sorghum [Sorghum bicolor (L.) Moench] lines as compared with a group of exotic and converted germplasm (IS) from the World Collection, (ii) to compare the classification of germplasm on the basis of estimates of genetic similarities obtained by means of AFLP and microsatellite (SSR) markers, and (iii) to compare the classification of germplasm obtained by different classes of molecular markers. A set of 100 SSRs, 1318 EcoRI/MseI AFLP, and 496 PstI/MseI AFLP markers with known map positions were utilized to determine the genetic similarity in a group of B, R, and IS public inbreds. Cluster analysis of genetic similarity estimates (GSij) revealed that the classification of sorghum inbreds is based on the sorghum working groups, Zera‐zera, Kafir, Kafir‐Milo, Durra, and Feterita. Cluster analyses failed to give a clear differentiation between B‐ and R‐lines, suggesting that R‐ and B‐lines do not represent well‐defined heterotic groups in this set of public lines. By comparing the different classes of molecular markers (SSRs, AFLPs, combinations of SSRs and AFLPs), we determined that the distribution of the markers and the coverage of the genome by the markers did affect the classification of genotypes. Dendrograms of genetic similarity (GS) based on PstI/MseI AFLP markers, or a set of markers spaced at 1‐ to 2‐cM intervals across the genome, produced clusters that were in better agreement with pedigree information than the analysis based solely on the EcoRI/MseI AFLP or SSR markers used in this study.
New Sources of Resistance to Greenbug in Barley
Authors: Porter David R. , Mornhinweg Dolores W.
Published: July 2010

Most biotypes of the greenbug [Schizaphis graminum (Rondani)] are extremely damaging to barley (Hordeum vulgare L.). However, greenbug biotype G has been reported to be unable to successfully feed on barley, and is described as the first greenbug avirulent to ‘Wintermalt’ barley (which is susceptible to all other greenbug biotypes). The objective of this study was to determine the pest status of greenbug biotype G in barley by characterizing the response of select barley cultivars and germplasm to greenbug biotype G feeding. Eight barley and four wheat (Triticum aestivum L.) cultivars and germplasm were challenged with biotype G and damage ratings recorded after 22 d of infestation. Barley is indeed a host of biotype G and genetic diversity exists within barley for reaction to attack by greenbug biotype G. Three barley cultivars were killed by biotype G, while five were resistant to feeding damage. These new sources of resistance to greenbug biotype G in barley should prove useful in the development of new greenbug‐resistant barley cultivars.
Agronomic Effect of Wheat‐Rye Translocation Carrying Rye Chromatin (1R) From Different Sources
Authors: Kim W. , Johnson J. W. , Baenziger P. S. , Lukaszewski A. J. , Gaines C. S.
Published: July 2010

The confounding effect of wheat (Triticum aestivum L.) genetic background has been addressed as the major factor in inconsistent agronomic performances of 1RS translocation. The objective of this study was to test the effects of centric translocations of chromosome 1 in various rye (Secale cereal L.) sources on agronomic performance of wheat grown in humid southeastern conditions in North America. Various 1R substitution, 1RS translocation, and 1RL translocation lines in ‘Pavon 76’ were evaluated for agronomic performance. The 1RS translocation line was most favorable for agronomic performance when compared with those of substitution, 1RL translocation, and controls. The 1RS significantly increased grain yield. However, the effect of source of rye chromatin was greater than its position effect in wheat genome. Among translocation lines, those with 1RS derived from ‘E12165’ (CIMMYT) and ‘Amigo’ induced higher mean grain yield and T1DL·1RS derived from ‘BH1146/Blanco rye’ had the lowest grain yield. The mean grain yield of 1RL translocation lines was lower than that of 1R substitution. Thus, selection of 1RS source is important in producing constantly higher grain yield in 1RS translocation lines. Genetic recombination among different 1RS may also be used to create more genetic variation.
AFLP and AFLP‐Derived SCAR Markers Associated with Striga gesnerioides Resistance in Cowpea
Authors: Boukar O. , Kong L. , Singh B. B. , Murdock L. , Ohm H. W.
Published: July 2010

Cowpea, Vigna unguiculata (L.) Walp., is an important grain legume grown in tropical and subtropical regions, primarily Africa. The parasitic weed Striga gesnerioides (Willd.) Vatke is one of the most important constraints to cowpea production. Host plant resistance is the only practical control method. Five virulence genotypes (races) of S. gesnerioides have been identified in different regions of Africa. Several host resistance genes have also been identified that are effective against specific races of S. gesnerioides The rapid spread of this parasitic weed creates an urgent need for cowpea varieties with multiple resistance genes. A recently identified cowpea breeding line, IT93K‐693‐2, has resistance to all known races. The objective of this research was to develop DNA markers that are useful for marker‐assisted selection (MAS) in breeding cowpea for resistance to S. gesnerioides An F2 population developed from the cross between IT93K‐693‐2 and the susceptible cultivar IAR1696 was characterized for resistance against race 3 of S. gesnerioides for genetic analysis and molecular mapping. IT93K‐693‐2 was found to have a single dominant gene for resistance. Four amplified fragment length polymorphism (AFLP) markers, designated E‐ACT/M‐CTC115, E‐ACT/M‐CAC115, E‐ACA/M‐CAG108 and E‐AAG/E‐CTA190, were identified and mapped 3.2, 4.8, 13.5 and 23.0 cM, respectively, from Rsg1, a gene in IT93K‐693‐2 that gives resistance to race 3 (or Nigerian strain) of S. gesnerioides The first two markers were validated in a second F2 population developed from crossing the same resistant parent with ‘Kamboinse local’, a different susceptible cultivar. The AFLP fragment from marker combination E‐ACT/M‐CAC, which is linked in coupling with Rsg1 was cloned, sequenced, and converted into a sequence characterized amplified region (SCAR) marker named SEACTMCAC83/85, which is codominant and useful in breeding programs.
St. Augustinegrass Response to Plant Growth Retardants
Authors: McCarty Lambert B. , Weinbrecht Jan S. , Toler Joe E. , Miller Grady L.
Published: July 2010

St. Augustinegrass [(Stenotaphrum secundatum (Walt.) Kuntz.] is the preferred warm‐season turfgrass for Florida's commercial and residential landscapes with an estimated 0.7 million hectare under growth and management. Limited published information is available on St. Augustinegrass response to plant growth retardants (PGRs). A 2‐yr study was implemented to monitor St. Augustinegrass turf quality, lateral stolon growth, percent cover, mowing frequency, cumulative turfgrass clippings, and seedhead suppression following PGR application. Treatments were applied on 23 June 1995 and 22 June 1996 as a single application (SIA) at label use rate (LUR) or as twin split applications (TSA) at half LUR each: the sequential application was only used when mowing interval equaled the untreated. The PGRs and rates were flurprimidol [α‐(1‐methylethyl)‐α‐[4‐(trifluoro‐methoxy)phenyl]‐5‐pyrimidine‐methanol] and paclobutrazol [(+/−)‐(R*,R*)‐β‐[(4‐chloro‐phenyl)methyl]‐α‐(1,1‐dimethylethyl)‐1H‐1,2,4‐triazole‐1‐ethanol] at 1.12 kg ha−1 for SIA and 0.56 kg ha−1 for TSA, trinexapac‐ethyl [4‐(cyclopropyl‐α‐hydroxymethylene)‐3,5‐dioxocyclohexane carboxylic acid ethylester] and mefluidide [N‐[2,4‐dimethyl‐5‐[[trifluoromethyl)sulfonyl]amino]phenyl]acetamide] at 0.28 kg ha−1 for SIA and 0.14 kg ha−1 for TSA, and imazapic [(±)‐2‐[4,5‐dihydrol‐4‐methyl‐4‐(1‐methylethyl)‐5‐oxo‐1H‐imidazol‐2‐yl]‐5‐methyl‐3‐pyridine‐carboxylic acid] at 0.028 kg ha−1 for SIA and 0.014 kg ha−1 for TSA. Responses were observed for a 12‐wk period following initial application, and turf quality was acceptable (>7) for all PGRs. Turf quality for imazapic was generally better than the untreated for Weeks 6 to 10. Greatest control of lateral stolon growth 10 wk after initial application was achieved with TSA of imazapic (68%) and mefluidide (61%). Percent cover 12 wk after initial application was lowest for SIA and TSA imazapic (66 and 53%, respectively). Greatest reduction in mowing frequency was provided by trinexapac‐ethyl (50%), while flurprimidol and mefluidide reduced mowing frequency by 26 and 20%, respectively. The only PGR that reduced cumulative turfgrass clippings (CTC) was trinexapac‐ethyl (63%). Greatest seedhead inhibition during peak production (about 35%) was provided by imazapic and mefluidide. The two most effective PGRs were trinexapac‐ethyl (reduced mowing frequency and CTC) and imazapic (controlled lateral stolon growth and seedhead production), while mefluidide demonstrated some potential. Combinations of these products could be examined in future studies.
Carbon Dioxide Content in Golf Green Rhizosphere
Authors: Chong S.‐K. , Boniak Richard , Indorante S. , Ok C.‐H. , Buschschulte D.
Published: July 2010

Anaerobic soils limit the amount of free oxygen available in the rhizosphere, and therefore will impede grass root development and restrain nutrient availability for turf growth. An in situ study was conducted on existing greens to investigate the relationship between CO2content in the rhizosphere and turf quality. Nine greens were selected in the study. On each green, five 1‐m‐diam. circular plots were randomly selected for conducting the experiment. The greens were sampled seven times from August 1998 to August 1999. Data collected from each plot included turf quality index (TQI), CO2content, and physical properties of the rooting mixtures. Turf quality declined drastically when CO2content in the rhizosphere increased to 5 to 6 μL L−1during the late summer season. The CO2content increased as water content in the root zone increased, but was inversely related to infiltration rate. Cultivation of a golf green may reduce CO2content in the rhizosphere, but the benefit of cultivation decreased with time.
Mapping As You Go
Authors: Podlich Dean W. , Winkler Christopher R. , Cooper Mark
Published: July 2010

The advent of high throughput molecular technologies has led to an expectation that breeding programs will use marker–trait associations to conduct marker‐assisted selection (MAS) for traits. Many challenges exist with this molecular breeding approach for so‐called complex traits. A major restriction to date has been the limited ability to detect and quantify marker–trait relationships, especially for traits influenced by the effects of gene‐by‐gene and gene‐by‐environment interactions. A further complication has been that estimates of quantitative trait loci (QTL) effects are biased by the necessity of working with a limited set of genotypes in a limited set of environments, and hence the applications of these estimates are not as effective as expected when used more broadly within a breeding program. The approach considered in this paper, referred to as the Mapping As You Go (MAYG) approach, continually revises estimates of QTL allele effects by remapping new elite germplasm generated over cycles of selection, thus ensuring that QTL estimates remain relevant to the current set of germplasm in the breeding program. Mapping As You Go is a mapping‐MAS strategy that explicitly recognizes that alleles of QTL for complex traits can have different values as the current breeding material changes with time. Simulation was used to investigate the effectiveness of the MAYG approach applied to complex traits. The results indicated that greater levels of response were achieved and these responses were less variable when estimates were revised frequently compared with situations where estimates were revised infrequently or not at all.
Simulating Potential Kernel Production in Maize Hybrid Seed Fields
Authors: Fonseca Agustin E. , Lizaso Jon I. , Westgate Mark E. , Grass Lahcen , Dornbos David L.
Published: July 2010

In maize (Zea mays L.) hybrid seed production, achieving the optimum seed yield per unit land area often is based on limited information about the quantity of pollen shed by the male and practical experience synchronizing pollen shed by the male inbred with silk emergence by the female inbred. We recently reported that kernel production per hectare could be simulated fairly accurately under pollen‐limited conditions from simple measures of pollen shed and silking dynamics. The objective of this study was to determine whether a simple mechanistic description of the flowering dynamics of male and female inbreds could be used to simulate and optimize kernel production in seed production fields. We estimated kernel production on the basis of flowering dynamics in six commercial seed fields located near Washington, IA, in 2002, which differed in the quantity of pollen production and silk emergence. In all cases, the fields were managed and harvested by standard seed industry methods. Harvested kernel number varied from 8.4 to 23.1 million kernels per female hectare. Simulated kernel number was closely correlated with these measured values (r2 = 0.98). This result indicates that relative differences in kernel production can be assessed directly from inbred flowering dynamics. Examples are provided to show how inbred management can be modeled to optimize harvested kernel number for a given inbred pair. Model simulations, however, overestimated harvested kernel number by 11%, on average, which implies that other plant factors, such as pollen viability, prolificacy, pollen capture by the canopy, or kernel abortion in response to leaf removal during detasseling might have limited kernel production across the six seed fields. Information about these variables can be incorporated readily into the kernel set model to improve its accuracy. This study indicates that kernel production in a hybrid seed field can be simulated from simple measures of inbred flowering dynamics. The model is a useful tool for optimizing harvested kernels for an established inbred pair or for defining initial management protocols for new combinations of inbreds.
Light and Heavy Turfgrass Seeds Differ in Germination Percentage and Mean Germination Thermal Time
Authors: Larsen Søren U. , Andreasen Christian
Published: July 2010

Seed weight is often related to germination percentage (GP) and mean germination time (MGT) within seed lots, but the relationships are poorly described. In this study, we described these relationships in the species slender creeping red fescue (Festuca rubra L. subsp. litoralis Vasey), perennial ryegrass (Lolium perenne L.), and Kentucky bluegrass (Poa pratensis L.). Seeds from one seed lot of each species were graded into nine seed weight fractions in an air separator. For each seed weight fraction, the 1000‐seed weight (TSW) was determined and the weight distribution was described for each seed lot. Seeds from each seed weight fraction were germinated in standard laboratory tests at 5/15°C and 15/25°C. For each species and temperature regime, the relationship between TSW and GP and between TSW and MGT could be described for whole populations by two different nonlinear functions, with GP increasing and MGT decreasing with increasing TSW. When the seed fraction with the lightest seeds was excluded, both relationships could be described for the remaining seeds by linear functions with positive effect of TSW on GP and negative effect on MGT in all but one case. Mean germination thermal time (MGTT) was calculated for the two temperatures. With exclusion of the lightest seeds, there was a linear relationship between TSW and MGTT for the two temperatures with light seeds of all three species requiring more degree days for germination than heavy seeds.
Physiological Recovery of Kentucky Bluegrass from Simultaneous Drought and Heat Stress
Authors: Wang Zhaolong , Huang Bingru
Published: July 2010

Drought and heat are two major factors limiting growth of cool season grasses. Rapid recovery from the combination of those stresses is important for the persistence of perennial turfgrasses. The study was designed to examine physiological factors associated with the persistence and recovery of Kentucky bluegrass (Poa pratensis L.) exposed to combined drought and heat stress following rewatering and/or temperature drop. Two cultivars differing in drought and heat tolerance, ‘Midnight’ (tolerant) and ‘Brilliant’ (sensitive), were exposed to drought and heat stress (35°C) simultaneously in a growth chamber until most plants became brown and completely desiccated (14 d). Plants were then subjected to three recovery treatments: (i) rewatered but exposed to heat stress (rewatering); (ii) returned to optimum temperature (20°C) but unwatered (cooling), and (iii) rewatering and cooling. Leaf photochemical efficiency (Fv/Fm), chlorophyll content, and activities of superoxide dismutase (SOD) and catalase (CAT) declined, while electrolyte leakage (EL) and lipid peroxidation increased rapidly during the combined stress. The adverse impact of the combined stress was more severe for Brilliant than for Midnight. Following rewatering or in combination with cooling, all parameters except chlorophyll content fully recovered for Midnight. However, for Brilliant, most of the parameters did not recover completely; Fv/Fm recovered partially. There was no recovery for any parameters of either cultivar when plants were returned to the optimum temperature but still unwatered. The results suggested that simultaneous drought and heat stress could cause permanent physiological damage for Kentucky bluegrass, particularly for the stress‐sensitive cultivar. Rewatering was essential for physiological recovery from the combined stress, regardless of temperature conditions. Rapid resumption of Fv/Fm, cell membrane stability, and antioxidant activities were important factors contributing to the recovery of Kentucky bluegrass.
Cytokinin‐Containing Seaweed and Humic Acid Extracts Associated with Creeping Bentgrass Leaf Cytokinins and Drought Resistance
Authors: Zhang Xunzhong , Ervin E. H.
Published: July 2010

Drought continues to be a major limiting factor for creeping bentgrass (Agrostis palustris Huds. A.) quality and persistence on golf course fairways, greens, and tees. Little breeding specifically aimed at improving bentgrass drought resistance has been completed. However, a number of reports indicate that treatment with natural products such as seaweed extracts and humic acids improve cool‐season grass drought resistance possibly by hormonal up‐regulation of plant defense systems against oxidative stress. This study was conducted to determine the response of exogenous natural product treatment of three creeping bentgrass cultivars subjected to drought. ‘Penn G‐2’, ‘L‐93’, and ‘Penncross’ creeping bentgrass were treated with seaweed extract (SWE) at 0.5 kg ha−1, humic acid (HA; 80% a.i.) at 1.5 kg ha−1, alone or in combination, and maintained in a greenhouse at approximately field capacity (−0.01 MPa) or allowed to dry until near the permanent wilting point (−1.5 MPa). Unashed samples of SWE and HA contained 66 μg g−1 and 57 μg g−1 zeatin riboside (ZR), respectively, while ashed samples contained no detectable cytokinins as determined by enzyme‐linked immunosorbent assay (ELISA). There were no significant differences between cultivars in response to drought, except for ZR concentration, which was higher in Penn G‐2 than in L‐93 or Penncross foliage. Turf quality and photochemical efficiency began to decline 14 d into the dry‐down for the control and at 21 d in the natural product‐treated bentgrass. The combination of HA + SWE enhanced root mass (21–68%), and foliar α‐tocopherol (110%) and ZR (38%) contents. This is the first known report indicating that these natural products contain cytokinins and that their application resulted in increased endogenous cytokinin levels, possibly leading to improved creeping bentgrass drought resistance.
Relationships between Water Use Efficiency, Carbon Isotope Discrimination, and Turf Performance in Genotypes of Kentucky Bluegrass during Drought
Authors: Ebdon J. S. , Kopp K. L.
Published: July 2010

Carbon‐13 discrimination (Δ) and water use efficiency (WUE) have been largely ignored in turfgrass. Turfgrass performance under drought may be improved by selecting for low Δ, which has been shown to be negatively correlated with WUE. The objectives of this 2‐yr greenhouse study were (i) to compare Δ and WUE in 12 genotypes of Kentucky bluegrass (Poa pratensis L.) with evapotranspiration (ET) and rooting for assessing turf performance under drought, and (ii) to determine the relative importance of ET in drought resistance by comparing diverse ET genotypes (6 low and 6 high) during drydown. Clipping dry weight to ET ratio (WUE) was evaluated with sand‐filled weighing lysimeters (20‐cm diam. by 65‐cm depth) during two 4‐d periods (Days 1 to 4 and 5 to 8) in 2002 and 2003. Carbon (13C/12C) analysis of leaf clippings was used to derive Δ values. Time domain reflectometry (TDR) was used to measure changes in volumetric soil moisture content (VSMC) at the 8.25‐, 17.5‐, 35.0‐, and 52.5‐cm depths to indicate moisture uptake and rooting activity. Drought resistance was visually assessed as wilt and leaf‐firing symptoms. Low‐ and high‐ET genotypes were similar in wilt and leaf firing, suggesting low ET may not be relevant in drought survival. Deep rooting at the 52.5‐cm depth and higher ET as soils dried were associated with less leaf firing. The WUE at Days 5 to 8 was comparable in some years with rooting. The Δ was not always reliable in assessing WUE, but turf performance under drought was correlated with Δ. Low Δ values were associated with less wilt (r = 0.59, P ≤ 0.05) and leaf firing (r = 0.58, P ≤ 0.05), suggesting that Δ may be a useful selection criterion for superior performance under limiting soil moisture.
Selection for Deep Root Production in Tall Fescue and Perennial Ryegrass
Authors: Bonos Stacy A. , Rush Debra , Hignight Kenneth , Meyer William A.
Published: July 2010

The identification and selection of germplasm with improved drought tolerance will play an important role in developing turfs with better performance and persistence during drought stress periods. The objectives of the study were to: (i) determine the feasibility of simultaneously selecting plants with low‐shoot‐to‐high‐root ratios and increased root mass in lower sand profiles using flexible tubes under greenhouse conditions, and (ii) determine gain from two cycles of selection for increased root production within the flexible tubes. Seeds from two populations of tall fescue (Festuca arundinacea Schreb.) and perennial ryegrass (Lolium perenne L.) were germinated in 29.5% (−1.4 MPa osmotic potential) and 28.5% (−1.2 MPa osmotic potential) polyethylene glycol (PEG), respectively, for each cycle of selection. The most vigorous seedlings were transferred to flexible root tubes, 63.5 cm long filled with silica sand, to evaluate for deep root production in the greenhouse. Clippings were collected weekly and root weights were determined after approximately 8 to 12 wk of growth in the flexible root tubes. The top 2 to 4% of the populations were selected for the following characteristics: clipping weights at or below the mean of the population and root weights (in the bottom 30 cm) at least 1 SD above the mean of the population for the turf‐type tall fescue and perennial ryegrass populations. After two cycles of selection for increased root mass in the lower 30 cm, gain from selection was approximately 41% in a narrow population and 81% in a broad population of tall fescue and 130% in a turf‐type and 367% in a forage‐type perennial ryegrass. This technique should be very successful in developing turfgrasses with improved rooting characteristics.
EFFECT OF SOYBEAN STEM GROWTH HABIT ON HEIGHT AND NODE NUMBER AFTER BEGINNING BLOOM IN THE MIDSOUTHERN USA
Authors: Heatherly Larry G. , Smith James R.
Published: July 2010

There are two broad types of stem growth habit in soybean [Glycine max (L.) Merr.]: indeterminate [generally maturity group (MG) IV and earlier] and determinate (generally MG V and later). Field studies of irrigated April and May plantings were conducted on Sharkey clay soil (very‐fine, smectitic, thermic Chromic Epiaquert) at Stoneville, MS (lat. 33°26′N), to determine if current expectations for stem growth habit are valid in genetic backgrounds of indeterminate MG IV and determinate MG V cultivars that are used in the early soybean production system (ESPS) in the midsouthern USA. All cultivars increased height and node number between beginning bloom (R1) and stem termination (ST), but the increases were greater for MG IV cultivars. Height and node number were greater at R1 for MG V than for MG IV cultivars, and greater for MG IV cultivars at ST. Averaged across planting date and year, MG V cultivars increased height and node number after R1 by 23 cm and 3.7 nodes, respectively. These results indicate that determinate MG V cultivars are capable of producing significant increases in height and node number after R1.