bluuebunny/crossref_metadata_2025 huggingface dataset:
Reproductive‐Stage Heat Tolerance, Leaf Membrane Thermostability and Plant Morphology in Cowpea
Authors: Ismail Abdelbagi M. , Hall Anthony E.
Published: July 2010

High night temperatures during reproductive development can reduce yields of cowpea [Vigna unguiculata (L.) Walp.]. Screening whole plants for degree of flowering and pod set in hot environments has been effective in breeding for heat tolerance, but suitable screening environments often are not available. An indirect screening technique was evaluated involving relative electrolyte leakage from leaf tissue sampled at the end of the dark period with incubation at temperatures that are hot for night‐time conditions. This technique was tested with four different pairs of cowpea lines with similar genetic backgrounds but different heat sensitivities during reproductive development. Plants were grown in growth chambers at optimal temperatures. Additional tests were conducted with plants grown in moderately hot and extremely hot field environments. Three sets of three genotypes were used that are either heat susceptible during both early flowering and pod set or heat tolerant during early flowering and heat susceptible during pod set or heat tolerant during both early flowering and pod set. Similar genotypic differences in electrolyte leakage were obtained from plants grown in the growth chamber or field environments. Genotypes with heat tolerance during flowering and pod set had less leaf electrolyte leakage than either genotypes with heat susceptibility during flowering and pod set or genotypes having heat tolerance only during early flowering. Leaf electrolyte leakage, as a measure of leaf membrane thermostability, may provide an efficient indirect screening technique for reproductive‐stage heat‐tolerance genes that can be used with plants grown in a range of field nursery environments.
Assessment of Drought Resistance of Crop Genotypes by Means of the Water Potential Index
Authors: Karamanos A. J. , Papatheohari A. Y.
Published: July 2010

The evaluation of crop genotypes for their adaptability is often performed by means of regression techniques of yields against some kind of an environmental index as independent variable. The weakness of these techniques lies in the lack of a direct assessment of a given environment by specific environmental factors. In this work, a new index, the water potential index (WPI), is suggested as a measure of the total water stress experienced by any crop in a given environment for a specific time interval. The index is derived from the integral of the course of leaf water potential over time. Its usefulness is demonstrated in evaluations of field‐grown bread wheat [Triticum aestivum (L.) em. Thell] and faba bean (Vicia faba L.) genotypes of contrasting characteristics by yield vs. WPI linear regression analysis. In these regressions, the intercept represents the “potential” yield at no stress conditions and the slope represents the “adaptability” of each genotype. It was found that the dwarf wheat cultivars Yecora and Siette Cerros exhibited higher potential yields and lower adaptability in comparison with the tall cultivar Generoso. In faba beans, the smaller the seed size of a cultivar, the lower was the potential yield and the better the adaptability. On the basis of this regression analysis, different response scenarios of hypothetical crop genotypes are described. Furthermore, the “relative adaptability” concept is presented, in which the potential yield effect is removed from the adaptability of any genotype. Examples of the use of WPI for obtaining information on the involvement of water shortage in specific growth stages of the wheat crop or for assessing the sensitivity of faba bean yield components to water shortage are presented.
Variation in Agronomic and Morphological Traits among Russian Wildrye Accessions
Authors: Berdahl J. D. , Mayland H. F. , Asay K. H. , Jefferson P. G.
Published: July 2010

Russian wildrye [Psathyrostachys juncea (Fischer) Nevski] accessions in the U.S. National Plant Germplasm System have not been adequately characterized for agronomic and morphological traits. Such characterization would be helpful in development of improved cultivars. Objectives of this study were to (i) measure consistency of dry‐matter and seed yields as well as plant height and vigor of 65 Russian wildrye accessions and four cultivars at three diverse test sites, (ii) characterize phenotypic diversity among these accessions using cluster analysis, and (iii) define needs for future evaluation and collection of Russian wildrye germplasm. Field tests were conducted at Logan, UT; Mandan, ND; and Swift Current, Saskatchewan, Canada. Dry‐matter and seed yields were not consistent among accessions and cultivars at the three locations, and testing at each location was necessary to identify accessions that were best suited to a specific location. Variance component estimates were small and of little consequence for accession × year interaction effects. The 69 entries were grouped into 10 clusters based on multivariate analysis of 17 classification variables. Accessions in Cluster 3 averaged well above the overall test mean for dry‐matter yield, seed yield, and plant vigor and have high utility in plant breeding programs in North America. Only four accessions had high levels of resistance to Septoria spraguei Uecker & J.M. Krupinsky, an important foliar disease. Accessions from a defined geographic area tended to cluster, but some accessions from a particular area were spread among several clusters. This emphasizes the value of sampling diverse collection sites within a defined geographic area.
Effects of Phosphorus and Water Supply on Yield, Transpirational Water‐Use Efficiency, and Carbon Isotope Discrimination of Pearl Millet
Authors: Br ü ck H. , Payne W. A. , Sattelmacher B.
Published: July 2010

Several studies have identified low soil P and water availability as major constraints to pearl millet [Pennisetum glaucum (L.) R. Br.] production in semi‐arid West Africa. To evaluate the effects of phosphate and water supply on yield, transpirational water‐use efficiency (WUET), and carbon‐isotope discrimination (Δ), two varieties of pearl millet were cultivated in pots in a glasshouse at the ICRISAT Sahelian Centre, near Niamey, Niger. Phosphate and water supply had significant effects on yield, WUET, and Δ. Compared with the control plants, which had adequate water and P availability, yield was reduced 34% by low water supply and 48% by low P supply. Under high P‐supply, water stress increased WUET by approximately 37%. Under low P‐supply, no effect of water supply on WUET was observed. Water stress increased Δ by approximately 0.6‰ for low P plants, and 0.9‰ for high P plants. Added P increased Δ by 0.3 to 0.4‰. WUET and Δ did not differ significantly between varieties. Differences in Δ between green and necrotic leaves were found within both P treatments under low water supply. We attribute changes in Δ to changes in the ratio of external to internal concentration of CO2, (pi/pa), leakage rates of CO2 out of bundle‐sheath cells, respiration rates, or chemical composition of the plant material.
Competitive Ability in Mixtures of Small Grain Cereals
Authors: Juskiw P. E. , Helm J. H. , Salmon D. F.
Published: July 2010

Morphological and physiological differences in competitive ability among species and genotypes can affect the growth, development, and subsequent composition and value of feedstuffs produced from small grain cereal mixtures. Our objective was determine the final grain yields of the components of mixtures and compare these yields with those expected based on the yields of the monocrops. Three field studies were conducted to evaluate the productivity of barley (Hordeum vulgare L.), oat (Avena sativa L.), triticale (× Triticosecale rimpaui Wittm.), and rye (Secale cereale L.) grown as monocrops and mixtures. Seeding rates ranging from 250 seeds m−2 to 750 seeds m−2 were evaluated to determine their effect on competitive ability of genotypes and species of small grains. Differences in competitive ability were found. The semi‐dwarf barley ‘Kasota’ was less competitive than the standard‐height ‘AC Lacombe’ and ‘Seebe’. ‘Noble’ barley was more competitive than ‘AC Mustang’ oat or ‘Wapiti’ triticale. ‘Prima’ winter rye was more competitive than ‘Pika’ winter triticale. Relative grain yields were generally not different than 1.0 g g−1, but when significantly different they were usually higher than one, indicating that the yields of those mixtures were better than expected based on yields when the cultivars were grown as pure stands. Seeding rates had little effect on competitive ability. The specific factors that lead to better than expected grain yields of mixtures and to good competitive ability of cultivars and species are difficult to predict and must be evaluated on a case‐by‐case basis.
An indirect test using oxalate to determine physiological resistance to white mold in common bean
Authors: Kolkman Judith M. , Kelly James D.
Published: July 2010

In common bean (Phaseolus vulgaris L.), the detection of physiological resistance to white mold [Sclerotinia sclerotiorum (Lib.) de Bary] in the field is confounded by environmental factors and plant avoidance mechanisms. Development of a reliable screening procedure is needed to identify resistant bean germplasm and to develop resistant cultivars. The objective of this study was to determine if oxalate, a primary pathogenicity factor of S. sclerotiorum, could be used to indirectly screen for physiological resistance to white mold in common bean. Cut bean seedlings were placed in a 20 mM oxalate solution in the greenhouse. Genotypes were rated based on differences in wilting response to oxalate. Oxalate ratings of the 27 genotypes were correlated with field ratings of a white mold disease severity index and incidence , and negatively correlated with yield . The oxalate test is an efficient method to indirectly test for physiological resistance to white mold in common bean.
Association of Fusarium Head Blight Resistance with Gliadin Loci in a Winter Wheat Cross
Authors: Ittu Mariana , S a ˜ ulescu Nicolae N. , Hagima Ioana , Ittu Gheorghe , Must a ˜ tea Pompiliu
Published: July 2010

Fusarium head blight (FHB) is one of the major diseases of wheat (Triticum aestivum L.). Genetic control of resistance to Fusarium spp. has been studied in resistant Chinese spring wheat cultivars, but little is known about inheritance of lower but useful levels of resistance found in winter wheat. This study was undertaken to characterize the genetic control of FHB resistance and to identify possible associations of resistance with several marker loci in winter wheat. Recombinant inbred lines were derived from the cross of a susceptible winter wheat, F1054W, with a moderately resistant parent, Sincron, not related to the Chinese germplasm. The parents had different alleles at five marker loci, RhtB1, Rht8, W2, GliB1, and GliD1. Recombinant inbred lines were classified for alleles at the RhtB1 and Rht8 loci by plant height and seedling response to exogenous gibberellic acid. Alleles at the GliB1 and GliD1 loci were determined from the gliadin spectrum detected by starch gel electrophoresis and alleles at the W2 locus by phenotypes in the field. The area under disease progress curve (AUDPC) and relative weight of inoculated spikes (RWIS), following injection of Fusarium graminearum Schwabe inoculum into central florets of flowering spikes, were determined for 3 yr in the field. A significant increase in resistance was associated with the allele GliR1, suggesting location of a Fusarium head blight resistance quantitative trait locus (QTL) on chromosome T1BL.1RS. A smaller but significant increase in resistance was associated with allele GliD1b, indicating the presence of another QTL on chromosome 1D. No association between Fusarium resistance and RhtB1, Rht8, or W2 was found. The effects of favorable alleles on chromosomes 1B and 1D were cumulative. Selection for genotypes possessing GliR1 and GliD1b in this population would increase the probability of obtaining lines with higher resistance to Fusarium head blight.
Effect of Stem Termination on Soybean Traits in Southern U.S. Production Systems
Authors: Kilgore‐Norquest L. , Sneller C. H.
Published: July 2010

Southern U.S. soybean [Glycine max (L.) Merr.] are primarily determinate and are grown in a diverse array of environments. Understanding the yield response of different plant types to southern environments may lead to improved yield. Our objective was to determine if varying stem termination could increase yield in some environments. Eleven pairs of isolines varying for determinate and indeterminate growth habit were derived from two crosses. All lines and controls were grown at two locations for 2 yr, planted in May and June and with or without irrigation. Seven pairs were grown for a third year. Yield, height, lodging, and maturity data were collected. In all crosses and production systems, determinate lines were shorter, earlier maturing, and had less lodging than indeterminate lines. Yields of determinate and indeterminate lines were equal in all irrigation–planting date combinations. There was a trend for determinate lines to yield better than indeterminate lines with early planting and irrigation. The yield difference between growth habits was conditioned primarily by a complex interaction of random genetic and environment effects. The indeterminate growth habit may confer a yield advantage over the determinate growth habit in environments with limited yield and growth potential. This was due to the lower yield response to increasing environment productivity of indeterminate vs. determinate lines. Perhaps 10 to 15% of southern production environments have conditions where indeterminate types may yield better than determinate types. The yield advantage of indeterminate types in such environments appears small. The success of deploying indeterminate cultivars to low‐yield, low‐growth southern environments to maximize yield will depend on accurately predicting where these environments will occur.
Variation among Maize Inbred Lines and Detection of Quantitative Trait Loci for Growth at Low Phosphorus and Responsiveness to Arbuscular Mycorrhizal Fungi
Authors: Kaeppler Shawn M. , Parke Jennifer L. , Mueller Suzanne M. , Senior Lynn , Stuber Charles , Tracy William F.
Published: July 2010

Maize (Zea mays L.) growth at low soil P levels is affected both by inherent physiological factors as well as interactions with soil microbes. The objectives of this study were (i) to quantify differences among maize inbred lines for growth at low P and response to mycorrhizal fungi, and (ii) to identify quantitative trait loci (QTL) controlling these traits in a B73 × Mo17 recombinant inbred population. Shoot dry weight and root volume were measured in the greenhouse after 6 wk of growth in a factorial experiment of 28 inbred maize lines using treatments of low vs. high P and mycorrhizal vs. nonmycorrhizal treatments. Shoot dry weight for the low P treatment in the absence of mycorrhizae ranged from 0.56 to 3.15 g. Mycorrhizal responsiveness based on shoot dry weight ranged from 106 to 800%. Shoot dry weight in the low P–nonmycorrhizal treatment was highly negatively correlated with mycorrhizal responsiveness. Plants grown at high P in the presence of mycorrhizae accumulated only 88% of the biomass of plants grown at high P in the absence of mycorrhizae, indicating that mycorrhizae can reduce plant growth when not contributing to the symbiosis. Percentage of root colonization was not correlated with mycorrhizal responsiveness. B73 and Mo17 were among the extremes for growth at low P and mycorrhizal responsiveness, and a B73 × Mo17 population of 197 recombinant inbred lines was used to detect QTL for growth at low P and mycorrhizal responsiveness. Three QTL were identified which controlled growth at low P in the absence of mycorrhizae based on shoot weight and one QTL which controlled mycorrhizal responsiveness. This study indicates that there is substantial variation among maize lines for growth at low P and response to mycorrhizal fungi. This variation could be harnessed to develop cultivars for regions of the world with P deficiency and for reduced‐input production systems.
Correcting for Classification Errors when Estimating the Number of Genes Using Recombinant Inbred Chromosome Lines
Authors: Eskridge K. M. , Shah M. M. , Baenziger P. S. , Travnicek D. A.
Published: July 2010

Techniques based on intercultivar chromosome substitution lines in wheat (Triticum aestivum L.) have been used to identify and locate the genes controlling quantitative traits on a specific chromosome. For a particular trait, the number of segregating loci affecting differences between two parental lines are generally determined by the frequency distribution of recombinant inbred chromosome lines (RICLs). Recombinant inbred chromosome lines are the inbred progeny of crosses between a chromosome substitution line and its parent cultivar. The determination of the presence and the number of segregating loci becomes difficult (i) when the distribution exhibits no clear discrete classes, (ii) when there is a considerable chance of misclassifying lines into parental and recombinant types, and (iii) when loci are linked. We describe an approach to estimate the number of segregating loci responsible for the difference between a chromosome substitution line and parental cultivar using the derived RICLs when classification errors are likely. We also discuss the effects of linked loci on the estimates. The method was used to estimate the number of genes on chromosome 3A controlling grain yield, kernels spike−1, kernel weight, spikes m−2, grain volume weight, plant height and anthesis date in wheat.
Evaluation of Perennial Glycine Species for Resistance to Soybean Fungal Pathogens That Cause Sclerotinia Stem Rot and Sudden Death Syndrome
Authors: Hartman G. L. , Gardner M. E. , Hymowitz T. , Naidoo G. C.
Published: July 2010

The cultivated soybean [Glycine max (L.) Merr.] has a relatively narrow genetic base and most commercial cultivars are susceptible to Sclerotinia sclerotiorum (Lib.) de Bary and Fusarium solani (Mart.) Sacc. f. sp. glycines, which, respectively cause Sclerotinia stem rot (SSR) and sudden death syndrome (SDS). The objective of this study was to screen all the available accessions of the perennial Glycine species for resistance to the pathogens that cause SSR and SDS. For SSR evaluations, five seedlings of each of 787 accessions were screened once in a series of eight non‐replicated runs. Seedlings were inoculated with an agar plug cut from the edge of a 1‐d‐old fungal culture by placing the plug next to the stem. Of the 787 accessions, 183 had partial resistance with 144 of these accessions being G. tabacina (Labill.) Benth. A selected set of 53 accessions was further screened in two replicated trials with five plants per each of four replications. Glycine tabacina had several accessions that were consistently rated as partially resistant. For SDS evaluations, five plants of each of 767 accessions were screened once in a series of eight runs. Plants were inoculated by a layered technique in which infested sorghum seed were placed below the transplanted seedlings. In the initial evaluation of 767 accessions, 134 had partial resistance with 65 of these accessions being G. tomentella Hayata. In a replicated set of selected accessions, G. tomentella had several accessions that were consistently rated as partially resistant. These perennial Glycine species represent potential untapped sources for improving disease resistance in soybean.
Differences in Tillering of Long‐ and Short‐Leaved Perennial Ryegrass Genetic Lines under Full Light and Shade Treatments
Authors: Bahmani I. , Hazard L. , Varlet‐Grancher C. , Betin M. , Lemaire G. , Matthew C. , Thom E. R.
Published: July 2010

There is uncertainty among plant breeders as to which characteristics to select for to optimize grass growth dynamics. The objective was to study the relationship between leaf length and tillering in perennial ryegrass (Lolium perenne L.). Two long‐leaved and two short‐leaved genetic lines were grown in simulated shade and near‐full sunlight (control) environments. The genetic lines were New Zealand cultivars Ellett (long‐leaved) and Grasslands Ruanui (short‐leaved), both early flowering. The other two were late‐flowering divergent selections ‘LL’ (long‐leaved) and ‘SL’ (short‐leaved). Differences between genetic lines in leaf length were attributable mainly to higher leaf elongation rate (LER) in the two long‐leaved genetic lines, and leaf elongation duration (LED) did not differ significantly between genetic lines. Grasslands Ruanui had a higher tiller number per plant than Ellett in both light environments, explained by higher site filling but similar leaf appearance rate (AL). In contrast, LL had a higher tiller number per plant than SL, arising from a higher AL in LL. This difference decreased during the experiment under the control treatment because SL tended to have a higher site filling ratio than LL. However, in the shade treatment, differences in tiller number between LL and SL were more mediated by AL than site filling. Therefore, selection for high LER and long lamina length, even though associated with reduced site filling in all treatments, did not necessarily result in reduced tiller number per plant.
Growth and Carbohydrate Metabolism of Creeping Bentgrass Cultivars in Response to Increasing Temperatures
Authors: Huang Bingru , Gao Hongwen
Published: July 2010

High temperature is a major factor limiting growth of creeping bentgrass (Agrostis palustris Huds.). Physiological causes of turf growth and quality decline with increasing temperature is not well understood. The objective of the study was to examine responses of growth and carbohydrate metabolisms to increasing temperatures in three creeping bentgrass cultivars. Sods of ‘Penncross’, ‘ISI‐AP‐89150’, and ‘SR 1020’ were grown in growth chambers and exposed sequentially for 20 d to each of the following temperatures: 20, 24, 30, 34, and 38°C. Evaluation and measurements were made at 10 and 20 d after each sequential temperature increase. Decreased root viability and root dry matter production of all cultivars was observed after a 10‐d exposure at 30°C and continued to decline with increasing temperatures. A decline in turf quality and leaf chlorophyll content (Chl) was observed at a 20‐d exposure to 30°C. Turf quality, Chl content, and root viability of SR 1020 were higher than those of Penncross after a 10‐d exposure at 30°C and 20 d at 34°C, and 10 d at 38°C, respectively. Canopy net photosynthetic rate (Pn) decreased with temperature in all cultivars. Dark respiration rates of whole plants (Rplant) increased with temperature up to 34°C, and then declined at 38°C. Daily carbon consumption to production ratio increased dramatically with temperature after 30°C, and Rplant exceeded Pn when temperature increased to 34 or 38°C in all cultivars. Plants grown at 30, 34, and 38°C had lower total nonstructural carbohydrate than those grown at 20 or 24°C. Results suggest that a decline in root activity of creeping bentgrass occurred before a decline in turf quality at temperatures above 30°C, and could be related to the imbalance between photosynthesis and respiration, and limited carbohydrate availability.
Mapping Yr28 and Other Genes for Resistance to Stripe Rust in Wheat
Authors: Singh R. P. , Nelson J. C. , Sorrells M. E.
Published: July 2010

Stripe (yellow) rust, caused by Puccinia striiformis West., is an important constraint to wheat production in cool environments. With the purpose of identifying genes for resistance to the disease, a RFLP mapping population of recombinant inbred lines developed from a synthetic [Triticum turgidum L. × Aegilops tauschii (Coss.) Schmal.] × T. aestivum L. cv. ‘Opata 85’ cross was visually evaluated for seedling infection type in three greenhouse inoculation tests and for adult‐plant disease severity in four field tests at Celaya and Toluca, Mexico. A previously unidentified gene from Ae. tauschii, designated as Yr28, was located on chromosome arm 4DS. Although Yr28 strongly influenced seedling resistance, it showed a strong effect in adult plants at only the warmer of the two field sites. A second gene showed high environmental sensitivity in seedling tests, with resistance associated with Opata marker alleles near the adult‐plant resistance (APR) gene Yr18 on chromosome arm 7DS. Gene Yr18, known to be present in Opata, strongly reduced disease response in field trials and was tightly linked with leaf‐rust resistance gene Lr34 Three other regions from Opata on chromosome arms 3BS, 3DS, and 5DS were also associated with APR.
QTL Analysis of New Sources of Resistance to Erwinia carotovora ssp. atroseptica in Potato Done by AFLP, RFLP, and Resistance‐Gene‐Like Markers
Authors: Zimnoch‐Guzowska E. , Marczewski W. , Lebecka R. , Flis B. , Schäfer‐Pregl R. , Salamini F. , Gebhardt C.
Published: July 2010

The two most important bacterial diseases of cultivated potato, blackleg of stems and tuber soft rot, are caused by Erwinia species. Genetic resistance currently present in cultivars is insufficient to protect the crop. New sources of polygenic resistance to Erwinia carotovora ssp. atroseptica (van Hall) Dye (Eca) have been selected in diploid hybrids originating from intercrossing Solanum tuberosum L with the wild species S. chacoense Bitter and S. yungasense Hawk. One F1 hybrid population derived from these materials was used to locate, on the molecular map of potato, quantitative trait loci (QTL) for resistance of tubers and leaves to Eca. A linkage map was constructed based on AFLP and RFLP markers including three resistance‐gene‐like (RGL) markers. Clustering of AFLP markers in putative centromeric regions was observed. QTL analysis revealed complex inheritance of resistance to Eca. Genetic factors affecting resistance to Eca were located on all 12 potato chromosomes. Putative QTL for tuber resistance were identified on 10 chromosomes. The QTL with the largest and most reproducible effect on tuber resistance mapped to chromosome I. Effects on leaf resistance were less reproducible than effects on tuber resistance. Putative QTL for leaf resistance were identified on 10 chromosomes. Inheritance of tuber and leaf resistance to Eca was largely independent. Several QTL for resistance to Eca were linked to RGL loci. Four of those QTL mapped to genomic segments that have been shown to contain factors for qualitative and quantitative resistance to different pathogens in potato, tomato (Lycopersicon esculentum Mill.), or tobacco (Nicotiana tabacum L.).
Estimation of Pollen Viability in Grain Sorghum
Authors: Tuinstra M. R. , Wedel J.
Published: July 2010

Male fertility of crop plants is a function of pollen production and viability. Differences in pollen production can be evaluated by simple observation, but pollen viability is more difficult to quantify. The objective of this study was to develop an in vitro pollen germination assay for sorghum [Sorghum bicolor (L.) Moench]. In experiments evaluating common germination media substrates, large differences in germination were observed in response to changing concentrations of sucrose, boric acid, and calcium nitrate in agar‐based media. In vitro germination was maximized following incubation on agar supplemented with 0.9 M sucrose, 2.43 mM boric acid, and 2.12 mM calcium nitrate. The effect of incubation temperature was also significant. Pollen germination was not affected by changes in temperature between 20 and 40°C, but germination was significantly reduced at 10°C.
Free‐Air CO2 Enrichment and Drought Stress Effects on Grain Filling Rate and Duration in Spring Wheat
Authors: Li Ai‐Guo , Hou Yue‐Sheng , Wall Gerard W. , Trent Anthony , Kimball Bruce A. , Pinter Paul J.
Published: July 2010

Wheat grain weight is a function of rate and duration of grain growth and is affected by photosynthate supply. Drought stress reduces photosynthate production because of stomatal closure. However, this might be partially overcome by an increase in air CO2 concentration. This study was conducted to evaluate elevated CO2 and drought stress effects on grain‐filling rate and duration for spring wheat (Triticum aestivum L.). Spring wheat (cv. Yecora Roja) was grown at two CO2 concentrations, 550 (elevated) or 370 (ambient) μmol mol−1 and two water treatments in a Free‐Air CO2 Enrichment (FACE) system at the University of Arizona Maricopa Agricultural Center. Plant samples were collected every 3 to 4 d from 6 d after anthesis until plant maturity. Main stem spikes were separated into upper, middle, and lower sections. Grain weight data for the intact main stem spike, each of its sections, and intact tiller spikes were fitted to a cumulative logistic model. Both elevated CO2 and water treatments significantly influenced the grain‐filling processes. Under drought stress conditions, elevated CO2 increased grain weight in the upper and lower sections of the main stem spike by 10 and 24%, respectively. In well‐watered plants, final grain weight in the midsection of the main stem spike was 8% higher than that measured under drought stress conditions. Grain weight increase under elevated CO2 was due to a faster rate of grain filling. Effects of elevated CO2 on the statistically derived duration of grain filling were inconclusive because of the confounding effect of blower‐induced temperature changes on the process. An increase in grain weight of well‐watered plants was due to a longer grain‐filling period. Later‐formed tiller spikes were more responsive to elevated CO2 and drought stress than main stem spikes. Information from this study will help us understand the grain growth of wheat and provide information to establish grain growth mechanism.
White Clover Seed Production: III. Cultivar Differences under Contrasting Management Practices
Authors: Medeiros R. B. , Steiner J. J.
Published: July 2010

Information is needed to determine the optimal combinations of agronomic practices for white clover (Trifolium repens L.) seed production in humid temperate marine climatic conditions. Effects on seed yield were determined for two stand ages (first and second seed year of production), six cultivars varying in leaf size (ladino large‐leaf type: Canopy, California Ladino, Osceola, and Regal; and intermediate leaf‐type: Louisiana S‐1 and White Dutch), grown with and without spring herbage removal, and with and without supplemental irrigation. The experiment was arranged in a modified split‐split‐split‐plot design with four replications. First year seed was harvested in 1997, and first and second year seed was harvested in 1998. Intermediate‐leaf size cultivars reached initial bud and flower stages earlier than large‐leaf types, but there were no differences between the two leaf types at the time of seed harvest. The number of flowers produced early in the reproductive period for nonirrigated plants was highly correlated with seed yield. Supplemental irrigation delayed flower maturity, but herbage removal did not. First seed year yields were greater than second seed year yields for all cultivars except Osceola, which had similar yields both seed years. Supplemental irrigation only increased seed yields of Canopy. In first seed year stands, White Dutch was the only cultivar that did not recover lost seed yields due to herbage removal when supplemental irrigation was applied. Herbage removal and supplemental irrigation treatments generally did not increase white clover seed yields under the conditions of this experiment, so maximal yields were generally achieved with minimal management inputs.
Molecular Markers Useful for Detecting Resistance to Brown Stem Rot in Soybean
Authors: Klos K. L. E. , Paz M. M. , Marek L. Fredrick , Cregan P. B. , Shoemaker R. C.
Published: July 2010

Brown stem rot (BSR) causes vascular and foliar damage in soybean [Glycine max (L.) Merr.]. Identification of plants resistant to BSR by inoculation with Phialophora gregata (Allington & W.W. Chamberlain) W. Gams is laborious and unreliable because of low heritability. Molecular markers linked to the resistance gene could be used to screen for resistant individuals and hasten the development of BSR resistant genotypes. The objective of this study was to develop molecular markers for efficient identification of BSR resistant plants in a breeding program. Seventeen resistant and 29 susceptible cultivars and plant introductions as well as recombinant inbred lines derived from a cross between BSR 101 and PI 437.654 were assayed by PCR‐based markers derived from RFLPs K375I‐1 and RGA2V‐1, Satt244, or developed from bacterial artificial chromosome (BAC) sequences. The DNA markers that were developed tag the BSR locus and are informative in a diverse range of soybean germplasm. Markers detected different banding patterns between resistant and susceptible genotypes. The PCR‐based markers will most likely be useful in screening for BSR resistance and allow soybean breeders to transfer rapidly resistance derived from Rbs3 to improved cultivars or soybean lines. The markers are relatively easy‐to‐use, inexpensive, and highly informative. Soybean breeding efforts can now be designed to incorporate the use of marker information when parental genotypes possess contrasting banding patterns.
Total and Seasonal Distribution of Dry Matter Yields for Pearl Millet × Wild Grassy Subspecies Hybrids
Authors: Hanna Wayne W.
Published: July 2010

The wild grassy subspecies Pennisetum glaucum (L.) R. Br. subspecies monodii (Maire) Brunken has been used as a source of germplasm for improved disease resistance and cytoplasmic diversity for improving pearl millet [P. glaucum (L.) R. Br.] cultivars. The objective of this research was to evaluate a portion of the monodii germplasm to determine if this germplasm could be used to increase the dry matter yield and extend the growing period of pearl millet forage hybrids. Seventy‐nine monodii accessions from Niger, Mali, Senegal, and Burkina Faso were crossed with Tift 85DA1, a cytoplasmic‐nuclear‐male‐sterile (CMS) pearl millet used in commercial hybrid production. These hybrids along with `Tifleaf 2' (a popular commercial hybrid) and `Gahi 3' were tested for 2 yr on a fine, loamy, thermic Plinthic Kandiudult soil at Tifton, GA, latitude north 31.48° and longitude west 83.53°. The best experimental hybrid yielded up to 31% more dry matter than Tifleaf 2. A significant hybrid × year effect on total yield indicated that some of the hybrids showed a differential response during the 2 yr. Tifleaf 2 produced between 23 and 32% of its total yield in the last harvest, whereas a number of the experimental hybrids produced significantly more (up to 50%) of their dry matter in the last harvest. The experimental hybrids were consistent across years in their superior late‐season production. Variation was also observed among hybrids for production of dry matter in the first harvest. Early production would be especially valuable in areas that have distinct wet and dry seasons. This research indicates that genes for enhancing level and distribution of yield in cultivated pearl millet are present in the wild grassy subspecies, monodii
Comparison of Bioclimatic Indices for Prediction of Maize Yields
Authors: Jeutong F. , Eskridge K.M. , Waltman W.J. , Smith O.S.
Published: July 2010

Yield prediction across a target production zone with varying strategies of agronomic practices has been a challenging problem to plant breeders when testing new genotypes for release. This study focused on comparing the importance of a new bioclimatic index called biological windows and six other traditional environmental indices as predictor variables of maize yields across sites (farmers' fields) and years, using a simple linear regression model. The yield data were collected for six hybrids evaluated in strip tests at 57 to 186 sites throughout Iowa during 1987–1994. The biological windows index was based on the Newhall Simulation Model and estimated the number of days the soil was moist and above 5°C. The environmental indices were July precipitation, temperature, the product of July precipitation and temperature, and the equivalent values for August. Because the actual values for the indices were not recorded at each site, all the indices were estimated for each site as the weighted averages of the data from 112 Iowa weather stations. Across years and within the Iowa sites, the mean percentiles of R‐square distributions showed that biological windows had less predictive value for maize yields than the more traditional indicators such as August precipitation and temperature. For all indices, across years and within sites had much greater mean R‐squares than across sites and within years, which had very low predictive values. For predicting yield across years within sites, there appeared to be an advantage in using August precipitation or the product of August precipitation and temperature over the five other indices. The R‐square values for these two indices were at least 0.60 in 80% of the test sites for five hybrids.
Agronomic and Phenological Differences of Soybean Isolines Differing in Maturity and Growth Habit
Authors: Curtis D. F. , Tanner J. W. , Luzzi B. M. , Hume D. J.
Published: July 2010

The effects of maturity genes (E genes) on flowering, maturity, and the seed filling period of soybean [Glycine max(L.) Merr.] have previously been described. However, little work has been done to quantify the effect of maturity and growth habit genes on morphological and phenotypic traits. This study quantifies the effects of maturity and growth habit genes on morphological and phenotypic traits to understand better how these genes may be most agronomically beneficial in northern short‐season breeding programs. Four near‐isogenic pairs consisting ofe1e3e4,e1e3E4,e1E3E4, andE1e3e4maturity gene combinations containing either indeterminate (Dt1) or determinate (dt1) stem termination type were grown near Woodstock, ON, in 1994 and 1995. When averaged across growth habit, the presence of an additional dominant maturity gene significantly increased the time to the start of the seed filling period (SSFP) and days to maturity. Lines with dominant E genes exhibited increased height, final node number, and lodging, and decreased harvest index. Indeterminate growth habit caused increased days to SSFP in 1995, and increased days to maturity, height, and lodging and decreased harvest index in both years. A positive relationship between whole‐plant seed filling rate (SFR) and yield occurred in theDt1lines in both years and occurred in thedt1lines in 1994. There was a positive relationship between whole‐plant seed filling period (SFP) and yield in thedt1lines in 1995. TheE1dt1line consistently had the highest seed filling rate of any isoline. The data indicated that theE1dt1combination may have unrealized potential in short‐season breeding programs.
Molecular Variation and F1 Performance among Strains of the Sweet Corn Inbred P39
Authors: Tracy W. F. , Talbert L. E. , Gerdes J. T.
Published: July 2010

Some maize (Zea mays L.) inbreds produce morphological variants at unexpectedly high frequencies. In some cases, heterosis has been observed in crosses between variants and the progenitor inbred. Causes of such variants and resulting heterosis are unclear. Unique materials for addressing these questions are strains of the sweet corn inbred P39. Several morphologically distinct strains of P39 have been identified. Molecular variation of P39 strains was analyzed by means of three types of molecular markers, including four probes that hybridize to multiple sequences, 78 single copy restriction fragment length polymorphisms (RFLP), and 671 amplified fragment length polymorphisms (AFLP). All crosses were made among seven P39 strains. Ear weight and plant and ear height of the crosses were measured in 2 yr with one location and eight replications per year. Ten‐ear weight ranged from 0.49 to 0.84 kg. Significant levels of molecular variation were observed among the strains. Summing polymorphisms per inbred pair over the multiple sequence probes resulted in a range among pairwise comparisons of 0 to 18. RFLPs ranged from 6 (7%) to 28 (35%) polymorphisms per inbred pair. AFLPs between inbred pairs ranged from 3 (0.5%) to 145 (22%). Ten‐ear weight was correlated with the number of polymorphisms between pairs of strains for the multiple copy probes. RFLP variation was correlated with plant height
and ear height
but not ear weight. AFLP variation was correlated with ear weight
While initial isolation of some of the P39 strains was due to a mutation at a single gene, the amount of molecular variation was unexpectedly high. The molecular variation and changes in combining ability indicates the occurrence of alterations throughout the genome.
Identification of Soybean Genotypes with N2 Fixation Tolerance to Water Deficits
Authors: Sinclair T. R. , Purcell L. C. , Vadez V. , Serraj R. , King C. Andy , Nelson R.
Published: July 2010

Symbiotic N2 fixation in soybean [Glycine max (L.) Merr.] has been shown to be very sensitive to drying soil. Since this loss of N2 fixation activity has a negative impact on crop yield under many cropping situations, alleviation of this response would be a major benefit. The objective of this research was to screen a large number of plant introduction lines in an effort to identify soybean germplasm that might have substantially decreased sensitivity of N2 fixation to water deficits. A three‐stage screening process was developed to narrow successively the number of candidate lines for tolerance in this trait. The first‐stage screen involved the measurement of petiole ureide levels in a large number of plant introductions (approx. 1000 per year). Approximately 10% of the lines with low petiole ureide levels, which are generally associated with N2 fixation tolerance, were selected. The second‐stage screen involved subjecting field plots of each selected plant introduction to a sustained water deficit of approximately 3 wk and measuring N accumulation during this period. Again, about 10% of these lines were selected for the intensive third‐stage screen based directly on an acetylene reduction assay during a cycle of soil drying. From an initial population of about 3000 plant introduction lines, eight lines were identified as having substantial tolerance of N2 fixation to soil drying. These eight lines are to be used in physiological studies to investigate the basis of their tolerance, and in breeding efforts to incorporate this trait into commercial germplasm.
Repeatability of Large‐Scale Germplasm Evaluation Results in Durum Wheat
Authors: Annicchiarico Paolo , Pecetti Luciano , Boggini Gaetano , Doust Mohammad A.
Published: July 2010

Large‐scale trait evaluation may enhance the utilization of germplasm collections by breeders. However, there is concern that this information may not be repeatable outside the area of testing because of large genotype × location interaction. Our objective was to assess the repeatability of large‐scale evaluation results for durum wheat [Triticum turgidum (L.) Thell. ssp. turgidum conv. durum (Desf.) MacKey] across two areas of the Mediterranean region. A subset of 600 entries from a world collection was evaluated for six agronomic traits at one site in northern Syria and one in Sicily. Pearson's and Spearman's rank correlations of entry values between locations indicated that the repeatability as measured by both coefficients was high for heading time (r ≥ 0.73), moderately high for kernel weight and plant height (0.48 ≤ r ≤ 0.57), relatively low for grain yield and kernels per spike (0.18 ≤ r ≤ 0.30), and non‐significant for early vigor score. Comparison between phenotypic and genetic correlations suggested that not only genotype × location interactions but also experimental errors contributed substantially to departures from complete repeatability. When each location alternated as the selection site and the other as the test site, at least 50% of the advantage shown by the top 10% entries over the remaining accessions at the selection site could be maintained at the test location for early or late heading, high kernel weight, and short or tall stature, for which 30 to 57% of selected entries were common to both sites. At least 20% of the selection advantage was maintained for high kernels per spike and grain yield. The results support the potential usefulness of large‐scale germplasm evaluation trials for crop improvement.
Comparison of Hemp Varieties Using Random Amplified Polymorphic DNA Markers
Authors: Forapani Silvia , Carboni Andrea , Paoletti Claudia , Moliterni V. M. Cristiana , Ranalli Paolo , Mandolino Giuseppe
Published: July 2010

The objective was to study the genetic structure and degree of variability of hemp (Cannabis sativa L.) varieties. Six varieties of hemp were analyzed by random amplified polymorphic DNA (RAPD) analysis, using 10 plants per variety. The varieties were a dioecious landrace, a dioecious selection from it, a cross‐bred cultivar, a monoecious variety, a drug strain, and an inbred female line. The genetic complexity of each cultivar was investigated by determining the number of bands produced by the primers used, the number of fixed and polymorphic loci, the average allele frequency, and the heterozygosity. A good correlation was found between these parameters and the genetic origin and breeding strategy of each variety. The average polymorphism over all varieties and loci was 97.1%; the single cultivar polymorphism ranged from 31.1 to 85.5%. Heterozygosity ranged from 0.05 (inbred female line) to 0.26 (cross‐bred Fibranova). The average heterozygosity calculated over all 102 loci and all plants studied was 0.29. The Fst (Wright's fixation index) value calculated for all loci was 0.48, and only 33.3% of the scored loci had higher values and can be considered informative for cultivar identification. A Fisher's test based on allele frequencies suggested complete differentiation among all varieties, with the exception of the Italian dioecious varieties Carmagnola and CS, for which no discriminating alleles were found. The correlations among the molecular data and the genetic structure of the different cultivars and the consequences in relation to variety discrimination in hemp are discussed.
An Improved Whole‐Seed Assay for Screening Wheat Germplasm for Polyphenol Oxidase Activity
Authors: Anderson James V. , Morris Craig F.
Published: July 2010

Polyphenol oxidase (PPO) causes darkening and discoloration of wheat (Triticum aestivum L.) foods such as noodles. Consequently, a simple, nondestructive, quantitative assay for determining PPO on one to a few wheat seeds could identify superior germplasm and eliminate inferior breeding lines, thus greatly assisting the development of wheat cultivars with superior noodle color. We sought to (i) examine current PPO whole‐seed assays and develop an improved assay that would facilitate rapid, efficient evaluation of wheat breeding lines and cultivars, be amenable to single seeds, and not adversely affect seed viability; (ii) use the assay to evaluate a large collection of wheat germplasm with the aim of identifying lines with very low PPO levels for crossing; and (iii) gain additional information on the location of PPO gene(s). Phenol, L‐tyrosine, catechol, methyl catechol, 3,4 dihydroxyphenyalanine (L‐DOPA), and caffeic acid were evaluated as potential substrates. Kinetic studies indicated that L‐DOPA and catechol at pH 6.5 produced the greatest enzyme activity. L‐DOPA did not reduce seed viability, whereas catechol is reportedly toxic to seeds. A standard assay [1.5 mL of 10 mM L‐DOPA in 50 mM 3‐(N‐morpholino) propane sulfonic acid (MOPS) buffer, pH 6.5, with 3 to 5 seeds constantly rotated in a 2‐mL microcentrifuge tube for 0.5 or 1 h at room temperature] was used to screen 1953 germplasm accessions grown in a common environment. Lines with low levels of PPO (i.e., 10% of the population) were identified; 24 of 66 lines displayed low PPO when evaluated under a second environment. Lastly, chromosome 2D was identified as a location of PPO gene(s) based on ‘Langdon’ durum/‘Chinese Spring’ D‐genome substitution lines, and homoeologous group 2 nullisomic/tetrasomic stocks of Chinese Spring. The L‐DOPA standard assay described here provides a robust and efficient method of evaluating germplasm and cultivars for PPO.