bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperate Maize Inbreds Derived from Tropical Germplasm: I. Testcross Yield Trials
Authors: Uhr David V. , Goodman Major M.
Published: July 2010

Tropical maize (Zea mays L.) has been suggested as a germplasm source to improve yield and disease resistance for U.S. breeding programs. Our objective was to compare the performance of testcrosses between tropical‐derived lines and an elite U.S. tester with the performance of adapted commercial hybrids. A group of 190 lines was derived from seven tropical commercial hybrids and intercrosses among them using two cycles of pedigree selection for adaptation to North Carolina. Ear‐to‐row sib‐mating and selfing were used to develop the lines. Visual selection of each generation concentrated on silk‐tassel synchrony, earliness, standability, lower ear height, and ear quality. No selection for combining ability was made during line development. Lines were topcrossed onto the public U.S. single cross B73Ht/Mo17Ht. Testcrosses were evaluated in yield trials at three locations during 2 yr. Among 190 testcrosses, 16 were within the LSD (0.05) of the commercial checks for yield, standability, and grain moisture. Most genetic variation for yield, standability, and grain moisture was accounted for by differences among pedigrees rather than differences among lines within a pedigree. Seventeen testcrosses yielded more than the tester, B73Ht/ Mol7Ht. The inbreds B73 and Mo17 represent two dominant heterotic groups utilized by U.S. maize breeders. Since tropical‐derived lines appear to combine well with B73/Mo17, they could be used as a source of disease resistance for either heterotic group. In addition, they have potential to enhance the combining ability of inbreds representing these two heterotic groups.
Release of Flavonoids and Betaines from Seeds of Seven Medicago Species
Authors: Phillips Donald A. , Wery Jacques , Joseph Cecillia M. , Jones A. Daniel , Teuber Larry R.
Published: July 2010

Germinating alfalfa (Medicago saliva L.) seeds release flavonoids and betaines that induce transcription of nodulation (nod) genes in Rhizobium meliloti and promote growth of R. meliloti and mycorrhizal fungi. Defining how these beneficial signal molecules vary among alfalfa cultivars and other Medicago species is one step toward improving agronomic management of rhizosphere microbes. This project quantified flavonoids and betaines released from seeds of seven Medicago species and measured their biological activities in R. meliloti. Seed compounds were separated by HPLC, identified by spectroscopic methods, and quantified by comparison with authentic standards. Regulatory activities of seed rinse fractions were measured as NodD1‐ or NodD2‐dependent transcription of a nodC‐lacZ fusion in R. meliloti. The betaines trigonelline and stachydrine were released from all species examined (M. sativa, M. falcata, M. littoralis, M. polymorpha, M. orbicularis, M. ruthenica, and M. truncatula), and the amount of trigonelline correlated positively (r2 = 0.60; P < 0.05) with NodD2‐dependent nod‐gene induction. Luteolin and luteolin‐7‐O‐glucoside flavonoids were released from all species except M. littoralis, M. ruthenica, and M. truncatula. NodD1‐dependent nod‐gene induction correlated positively (r2 = 0.74; P < 0.05) with the total amount of those compounds. Exudation kinetics of the flavonoid nod‐gene inducer chrysoeriol in alfalfa differed greatly from other flavonoids and may reflect a metabolic event rather than simple solubilization. Variation in the amounts of flavonoids released from the limited number of alfalfa cultivars tested suggested that plant selection techniques may increase these beneficial, but sometimes limiting, compounds.
Soybean Lipoxygenase Mutants and Seed Longevity
Authors: Trawatha S. E. , TeKrony D. M. , Hildebrand D. F.
Published: July 2010

Lipid peroxidation and the generation of free radicals may contribute to seed deterioration. Lipoxygenase (LOX) is thought to be a major contributor to lipid peroxidation and free radical generation. This investigation was initiated to determine whether inactivation of one or two of the three LOX isozymes would alter soybean [Glycine max (L.) Merr.] seed storability. Seed from three soybean near‐isogenic LOX null isolines and ‘Century’ were produced at Lexington, KY, in 1991, stored at 120 g kg−1 seed moisture and 30°C, sampled periodically for 155 d, and tested for seed vigor and viability. Embryonic axes excised from deteriorated seeds were tested for LOX activity, total and free fatty acid content, and production of six‐carbon aldehydes. Century and all the LOX genotypes had high initial seed quality and lost germination and vigor (accelerated aging and cold tests) in a similar manner during storage. As seed vigor and viability declined during storage, there was a concurrent rise in free fatty acid content and E‐2‐hexenal formation for all genotypes. Free linoleic and linolenic acids and E‐2‐hexenal were inversely related to seed vigor as measured by accelerated aging and cold tests (r ≥ 0.71), and this relationship did not vary among LOX isolines. Seed from the LOX mutants did not show greater or less longevity in the same storage environment. Thus, the loss of one or two of the three LOX isozymes had no effect on soybean seed deterioration.
Classifying Japonica Rice Cultivars with RAPD Markers
Authors: Mackill David J.
Published: July 2010

Two major subspecies of rice (Oryza sativa L.), indica and japonica, are widely recognized. Japonica rice, which includes temperate and upland (tropical) cultivars, has been less well characterized by DNA markers than indica rice. The present study was undertaken to quantify genetic diversity with random amplified polymorphic DNA (RAPD) markers in a sample of 134 predominately japonica cultivars and two wild species (O. nivara Sharma et Shastry and O. rufipogon Griffith). Ten oligonucleotide primers produced 30 bands showing clear polymorphisms. The indica and japonica cultivars were classified into separate groups by cluster analysis. Clustering was less pronounced within the japonica group. Tropical japonicas (including U.S. long‐grain types) usually clustered together but no firm boundary was found between the tropical and temperate types. Canonical discriminant analysis indicated that the distance between the indica group and each japonica subgroup was approximately equal and was much greater than the distance between the two japonica subgroups. Additional primers led to better resolution of closely related cultivars. Genetic distances estimated from RAPDb anding patterns were correlated with those estimated by coefficients of parentage (r = 0.59, P < 0.001). conclusion, RAPDasr e useful for classification of japonica rice cultivars, but many primers will be needed to resolve closely related japonica cuitivars. Maximumge netic diversity for gene mapping or exploiting F1 hybrid vigor within japonica cultivars can be obtained in crosses between selected temperate (or U.S. short and medium grain) and tropical (or U.S. long grain) parents.
Variability of Thirteen Isozyme Loci in the USDA Soybean Germplasm Collections
Authors: Griffin Jeffrey D. , Palmer Reid G.
Published: July 2010

Surveys of variability at loci that condition simply inherited, phenotypically neutral characters can be used to investigate relationships among accessions in germplasm collections. We performed a survey of isozyme variability among 1005 domesticated soybean [Glycine max (L.) Merr.] and 258 wild soybean [G. soja (L.) Siebold & Zucc.] accessions from the USDA soybean germplasm collection. By using eight activity stains, we detected polymorphisms conditioned by 13 isozyme loci. The average gene diversity of the Asian G. max accessions in this study was 0.198, while that of the G. soja accessions was 0.235. The relatively high variability of this set of loci made it possible to investigate relationships among groups of accessions from six diverse geographic regions in Asia: China, India and South‐Central Asia, Japan, Korea, Manchuria‐Siberia, and Southeast Asia. The G. max and G. soja accessions fell into two separate groups, based both on genetic distance and canonical discriminant analysis. Publicly developed soybean cultivars released for production in North America clustered with the G. max accessions from northeast Asia. The group of accessions from India and South‐Central Asia was the G. max group most closely related to the G. soja accessions and may include some primitive agronomic types. The group of G. max accessions from Southeast Asia stood out from the other G. max groups. This difference was due to high frequencies of the Aco3‐b, Dial, and Enp‐a alleles among accessions in Maturity Groups VII through X. The accessions in the later maturity groups may represent a distinct population, relative to the accessions in the earlier maturity groups.
Relationship of Test Weight and Kernel Properties to Milling and Baking Quality in Soft Red Winter Wheat
Authors: Schuler Steve F. , Bacon Robert K. , Finney Patrick L. , Gbur Edward E.
Published: July 2010

Although test weight is used as a grading criterion and an indication of quality in wheat (Triticum aestivum L.), its relationship to specific quality parameters in soft wheat is not well documented. Seed characteristics, flour yield, and baking quality were studied in 24 soft red winter wheat (SRWW) genotypes grown in six environments to determine their relationship to test weight. Flour yield, flour protein, alkaline water retention capacity (AWRC), and softness equivalent (SEQ) were evaluated by the micro‐procedures of the USDA‐ARS soft wheat early‐generation milling and baking quality evaluation program. Despite removal of shriveled kernels prior to evaluation, environmental effects had a significant impact on quality parameters, ranging from 68% of total variability (SEQ) to 5% (AWRC). Test weight was correlated with flour yield, but was significantly correlated with flour protein content (r = 0.54, P < 0.05) as was kernel density (r = 0.49). Thousand‐kernel weight, diversity of seed size, proportion of large seed, and average kernel length and width were not correlated with flour yield or other quality parameters. Test weight did not predict flour yield in SRWW when shriveling was absent, but it was related to flour protein content, which is associated with baking quality. Kernel size or size distribution did not affect end‐use quality. The best predictive model based on the characters above explained little of the total variation in flour yield (R2 = 0.22).
Homozygous Variation in Rice Somaclones: Nonrandom Variation Instead of Mitotic Recombination
Authors: Xie Q. J. , Rush M. C. , Oard J. H.
Published: July 2010

Mitotic recombination has been postulated by some researchers as a mechanism to explain the lack of segregation for certain traits in plants derived from tissue culture. Three genetic marker lines were used to examine whether mitotic recombination could be detected from plants regenerated from rice (Oryza sativa L.) tissue culture. One line, CI 11014, had two dominant genes An (awned) and Gl (pubescence) in linkage group 12. The other two, CI 11020 and CI 245714, had two corresponding recessive genes an (awnless) and gl (glabrous). A total of 1788 R1 plants regenerated from immature panicles of F1 plants from the crosses CI 11020 × CI 11014 and CI 245714 × CI 11014, and from the parental lines, were evaluated from 1988 to 1990 in the greenhouse, and 360 R2 lines derived from these F1 plants and parental lines were evaluated in the field. No mitotic recombination occurred for the genes investigated in this experiment. A high somaclonal variation frequency (47.5%) for the awnless characteristic was observed. The variation was not due to mutation of the dominant gene An, but was apparently caused by mutation of an inhibitor gene. Results from these experiments suggested that somaclonal variation was not always random and that specific loci had higher mutation rates during the somaculture procedure. Previous suggestions that changes in DNA methylation pattern caused by the tissue culture process were not random were consistent with the data from our studies.
Stem and Crown Rust Resistance in the Wisconsin Oat Selection X1588‐2
Authors: Harder D. E. , Chong J. , Brown P. D.
Published: July 2010

The Wisconsin oat (Avena sativa L.) selection X1588‐2 has reacted either with mesothetic (moderately resistant) or 0;1 (highly resistant) infection types to races of Puccinia graminis Pers. f. sp. avenae Eriks. & E. Henn. (stem rust). This selection also is resistant to some pathotypes of P. coronata Corda f. sp. avenae Eriks. (crown rust). The objectives of this study were to identify the genes in X1588‐2 responsible for the rust resistance and to determine the usefulness of this line as a source of resistance in oat breeding. Tests with 45 races of P.g. avenae showed that X1588‐2 was highly resistant to races that were avirulent to genes Pg3 and/or Pg4 and was moderately resistant to all other races. These results and the pedigree of X1588‐2 indicated the presence of stem rust resistance genes Pg3, Pg4, and Pg10 in X1588‐2. The presence of these genes was further indicated in tests of seedlings of segregating BC1F1 and BC1F2 populations from a cross of X1588‐2 with the susceptible cultivar Makuru. Resistance to crown rust in X‐1588‐2 was conferred by a gene designated as Pc95. The resistance conferred by Pc95, however, was not effective against a sufficient range of pathotypes of P. coronata to be a useful source of resistance. Genes Pg3 and Pg4 are ineffective against current North American populations of P.g. avenae. Gene Pgl0, however, appears to confer a moderate but very broad range of resistance and may be a useful source of resistance in oat breeding.
Genotypic Differences in Nitrate Uptake and Nitrogen Utilization for Spring Wheat Grown Hydroponically
Authors: Oscarson P. , Lundborg T. , Larsson M. , Larsson C.‐M.
Published: July 2010

The physiological background for variation in grain protein content of cnitivars of spring wheat (Triticum aestivum L.) is still unclear. This study was performed to investigate whether differences in nitrate uptake and nitrogen utilization could explain the observed differences. Four cultivars of spring wheat were grown hydroponically to maturity. Growth was controlled by daily additions of growth‐limiting amounts of nitrate at preset and step‐wise decreased relative rates. The plants showed a relevant ontogeny when compared to field‐grown plants. The kinetics of net nitrate uptake were measured regularly from 16 to 102 d of culturing. The maximal net nitrate uptake rate of the plant, i.e., Vmax, increased until anthesis, and subsequently decreased. There were no major changes in the affinity for nitrate, i.e., Km during the development. When uptake capacity was put in relation to the need of the plant in order to maintain growth rate and tissue‐nitrogen concentration, it was clear that the plants had a substantial overcapacity for net nitrate uptake at all times. There were no major genotypic differences in either Vmax or Km. Frequent sampling of plants made it possible to calculate the remobidization of nitrogen from vegetative tissues to the grains, and these data could be used to discuss further differences in grain protein yield.
Genetic Variation for Phosphorus Efficiency of Common Bean in Contrasting Soil Types: II. Yield Response
Authors: Yan Xiaolong , Beebe Stephen E. , Lynch Jonathan P.
Published: July 2010

Phosphorus deficiency is a primary constraint to common bean (Phaseolus vulgaris L.) production in the tropics. Bean genotypes differ in their P efficiency, defined as growth and yield in low P soil. The objectives of this study were to evaluate genetic variation in diverse bean germplasm for P efficiency in soil types with contrasting P chemistry and to assess possible relationships between dry matter distribution, P partitioning, and yield. Experiments were conducted at two sites in Colombia, one an Andosol in which P availability is limited by allophane and recalcitrant organic matter and the other an Ultisol in which P availability is limited by Fe and AI oxides, with three levels of P fertilization. Twelve contrasting genotypes were evaluated for yield components, harvest index, and P partitioning. Genotypes yielded differently under P stress. Andean germplasm was often higher yielding under P stress than Mesoamerican germplasm but less responsive to added P fertility. Genotypic rankings for P efficiency did not differ in the two soil types. Reproductive parameters such as harvest index, yield components, and P allocation among plant parts at maturity were not related to P efficiency. We conclude that (i) there is no evidence for specific adaptation to low P availability in volcanic or mineral soils in beans; (ii) Mesoamerican and Andean genotypes respond differently to P availability; and (iii) vegetative and reproductive responses to low P availability are not always correlated. Further studies of P acquisition mechanisms related to root traits and efficiency of P use are warranted.
Environmental Control of Floral Induction and Development in Kentucky Bluegrass
Authors: Carlson JoAnn M. , Ehlke Nancy J. , Wyse Donald L.
Published: July 2010

Kentucky bluegrass (Poa pratensis L.) floral induction requires a lengthy, uninterrupted period of cold temperature with a short photoperiod. Our objective was to develop an deficient artificial vernalization procedure to facilitate breeding experiments. The stage of plant development and length of vernalization period necessary for floral induction was determined for six cultivars: Abbey, Aspen, Midnight, Park, Rugby, and Trenton. Plants were exposed progressively to three temperature and light‐controlled environments: (i) seedlings were grown in a 12‐h photo‐ and thermal period with a 20°C day/14°C night temperature regime and high irradiance of 30 W m−2 from germination until 3, 5, 9, or 13 wk after emergence (approx. 8, 26, 145, and 198 leaf stage, respectively); (ii) plants were then vernalized for an 8‐h photoperiod at 5°C constant temperature and low irradiance of 7 W‐2 for 4, 8, or 12 wks; and (iii) plants were transferred panicle development conditions of 18‐h photoperiod and 12‐h thermal period with a 18°C day/15°C night temperature regime and high irradiance of 30 W−1 for 16 wk. No panicles were observed on plants with the 4‐wk vernalization treatment. For all cultivars except Midnight, the 9‐wk plant development and 12‐wk vernalization treatment resulted in floral induction of all plants. The same four cultivars responded to this treatment with a mean panicle number greater than five panicles per plant and the time from seedling emergence to 75% of the panicles emerged was approximately 28 wk. This study has demonstrated that an artificial vernalization procedure could be developed that would make reproductive material of Kentucky bluegrass available throughout the year independent of season or climate.
Development of a Core Collection for Perennial Medicago Plant Introductions
Authors: Basigalup D. H. , Barnes D. K. , Stucker R. E.
Published: July 2010

The size and heterogeneity of world germplasm collections often have hindered their evaluation and utilization. Most of the diversity of germplasm collections could be represented by core collections (or core subsets), which are representative samples of the genetic diversity of a crop species and its relatives. Individual accessions not included in the core are retained as reserve subsets. The objectives of this research were to evaluate selection procedures for designating a core collection of plant introduction accessions (P.I.s) and to designate U.S.P.I. core collection for alfalfa (Medicago sativa L. sensu lato). About 1100 perennial Medicago P.I.s collected from 47 countries were classified into 18 geographical groups based on passport data from the Germplasm Resources Information Network (GRIN) System. data file was developed for 50 agronomic, forage quality, root and crown morphology, pest resistance, and stress tolerance traits. Eight methods for developing a 200‐entry core were compared by nonparametric procedures with the original P.I. collection. The methods included multivariate procedures, random and/or directed selection of entries, and a totally randomly selected core. The sign test was used to compare the means and the variances for 38 traits having the most complete data sets among the cores developed by the eight methods. None of the methods changed the trait means; but nearly all methods, with the exception of the randomly selected core, significantly increased the variance for most traits. Two methods were the best for designating a core collection. One method combined cluster analysis based on principal components within each geographical group with randoms election of entries within each cluster (Method 3), the other method was direct selection of entries within each geographical group (Method 8). Method 3 needs a complete data set and extensive computer facilities. Method 8 can utilize incomplete data sets and does not require computer facilities. Method 8 was chosen for designating the core collection for perennial Medicago spp. P.I.s because it retained the greatest variability for all traits. This 200‐entry core was one of the first designated for any crop in the GRIN System.
Influence of Tillage Systems on Weed Population Dynamics and Management in Corn and Soybean in the Central USA
Authors: Buhler Douglas D.
Published: July 2010

Species composition and population densities of weed communities of arable land reflect agronomic practices. The trend toward reducing tillage in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] production changes the environment where weeds are managed, survive, and reproduce. The shift from tillage systems that include extensive annual soil disturbance to systems that minimize soil disturbance will cause major changes in weed population dynamics. These changes often reduce the effectiveness of weed control practices. Reduced herbicide efficacy has slowed adoption of conservation tillage because many conservation tillage systems rely heavily on herbicides for weed management. Poor understanding of weed population dynamics and lack of suitable control alternatives often result in increased herbicide use in conservation tillage systems. While results have varied among experiments, some general trends in weed population dynamics have arisen as tillage is reduced. These include increased populations of perennial, summer annual grass, biennial, and winter annual species. Densities of large‐seeded dicot species often decrease. The ecological and management aspects of these changes are varied and complex. Effective, economical, and environmentally sound weed management in conservation tillage systems will require integration of new information with established principles of weed management. New management systems and control technologies are needed to develop integrated weed management systems for the altered ecosystems created by conservation tillage production systems.
Comparison of Related Wheat Stocks Possesing 1B or T1BL·1RS Schromosomes: Grain and Flour Quality
Authors: Carver Bett F. , Rayburn A. Lane
Published: July 2010

The agronomic advantage of the T1BL. 1RS translocation and the potential importance of chromosome 1BS to end‐use quality of bread wheat (Triticum aestivum L.) warrant a more precise definition of the relationship of T1BL‐1RS to bread wheat quality. This study was conducted to determine the effect of TIBL. 1RS from ‘Aurora’ on grain and flour quality in multiple near‐isoline pairs with varying genetic background, and to examine the genetic variation among random inbred lines selected only for 1B or T1BL 1RS. Two experiments were conducted, each with a different set of genetic materials derived from the same pair of crosses. In one experiment, 25 pairs of F5‐derived near‐isolines homozygous for either 1B or T1BL‐ 1RS were evaluated in at least two environments; in the second experiment, plants homozygous for either 1B or T1BL‐1RS were selected in the F2, and 40 inbred lines per chromosome type in each cross were evaluated in four environments. The near‐isolines showed high isogenecity for all traits based on comparison of duplicate lines within pairs. The translocated chromosome, on the average, increased grain protein concentration and decreased mixogram rating, mlxogram band width, and sedimentation volume in both crosses. Kernel hardness, flour yield, and mixing time either decreased or did not change in the TIBL 1RS isolines depending on the cross. Water absorption did not change. The T1BL‐1RS and 1B isolines showed similar mixograph properties in eight of the 25 pairs. Genetic variance of TIBL IRS random inbred lines was not reduced for those traits where deleterious effects were most notable, e.g., mixing tolerance and sedimentation volume. Hence, the detrimental effect of T1BL‐ 1RS on dough properties might be mitigated, relative to non‐TIBL 1RS genotypes with equivalent pedigree, by rigorous selection of background genotype. Special attention must be given to mixing tolerance and sedimentation.
Simultaneous Selection for Major and Minor Resistance Genes
Authors: Cox T. S.
Published: July 2010

In many crop species, genes that confer resistance to diseases or insects often exhibit strong dominance and epistasis. As a result, it is generally considered difficult or impossible to accumulate, or pyramid, resistance genes with both large and small effects in a single population or cultivar. Availability of differential disease or insect cultures or molecular markers linked to major resistance loci may allow such loci to be pyramided efficiently, along with minor genes. A deterministic model was used to simulate recurrent selection by truncation in a population segregating at multiple loci with intra‐ and interlocus interactions similar to those that occur in systems of resistance genes. Selection at major loci generated large nonadditive genetic variances and gametic disequilibria. Phenotypic selection at minor loci was generally ineffective when major genes were also present; pleiotropic penalties on resistance genes caused minor resistance alleles to be eliminated from the population, illustrating the Vertifolia effect. The most effective method by which frequencies of both major and minor genes could be increased simultaneously was to use data from differential cultures or linked markers to discard all individuals with more than one major allele and then select the most resistance of the remaining individuals in each cycle, based on means of their selfed progenies. This methodology increased the frequency of desired genotypes to a level at which use of the population in a breeding program would be practical.
Nitrogen Defeciency in Maize: I. Effects on Crop Growth, Development, Dry Matter Partitioning, and Kernel Set
Authors: Uhart Sergio Adolfo , Andrade Fernando Héctor
Published: July 2010

Variations in N availability affect growth and development of maize (Zea mays L.) and may lead to changes in crop physiological conditions at flowering and in kernel set. The objectives of this study were (i) to establish the effect of N availability on crop development, crop radiation interception, radiation use efficiency, and dry matter partitioning; and (ii) to study the relationship between kernel number and crop growth at flowering and between kernel number and crop N accumulation at flowering. Three experiments with a commercial hybrid (DK636) were carried out under field conditions at the INTA Baicarce Experimental Station, Argentina, without water limitations. The treatments consisted of different radiation levels, obtained by shading, combined with different levels of N availability obtained by the addition of N fertilizer or organic matter to inmobilize N. Nitrogen deficiencies delayed both vegetative and reproductive phenological development, slightly reduced leaf emergence rate, and strongly diminished leaf expansion rate and leaf area duration. Nitrogen deficiencies reduced radiation interception as much as radiation use efficiency and their effects on the ear dry matter/total dry matter ratio at harvest were associated with crop growth rate reductions at flowering. Dry matter partitioning to reproductive sinks at flowering and the ear dry matter/total dry matter ratio at harvest were reduced by N shortages. Significant relationships between kernel number and N accumulation rate or crop growth rate at flowering were fitted by linear + plateau functions with thresholds above which kernel number and grain yield did not increase.
Seedling White Clover Response to Defoliation
Authors: Kang J. H. , Brink G. E. , Rowe D. E.
Published: July 2010

Defoliation during the early stages of seedling development can influence growth of white clover (Trifolium repens L.). Our objective was to determine the response of cultivars with diverse leaf sizes to defoliation across a range of seedling growth stages. ‘Regal’ (large‐leaf), ‘Louisiana S‐1’ (medium‐large‐leaf), ‘Grasslands Huia’ (medium‐smallleaf), and ‘Aberystwyth S184’ (small‐leaf) were grown in the greenhouse and were initially clipped to remove all leaf (except cotyledons) and petiole tissue (1.0‐cm stubble) when seedlings attained a unifoliolate leaf or one, two, four, and eight trifoliolate leaves. Seedlings were subsequently clipped in the same manner every 7 or 28 d for the next 28 d. Plant response to defoliation was assessed 7, 14, 21, and 28 d after the last clipping. Seedling shoot dry weight of all cultivars increased linearly in response to initial leaf stage when subsequent clipping occurred every 7 d after the initial defoliation. When subsequent clipping was delayed 28 d, defoliation after the four‐trifoliolate stage did not influence shoot weight of any cultivar except Regal. Despite fewer numbers of leaves after regrowth, seedling leaf area of Regal was always greater than that of the other cultivars. Number of stolon branches of Regal and Louisiana S‐1 increased in response to leaf stage at initial defoliation (0.15 branches stage−1), while that of Grasslands Huia and Aberystwyth S184 was relatively unchanged after the four‐ to six‐trifoliolate stage. Permitting white clover seedlings to attain advanced leaf stages before initial defoliation and increasing the time interval before subsequent defoliation will enhance seedling growth and potential survival.
Mineral Composition of Triticale Grains as Related to Grain Yield and Grain Protein
Authors: Feil Boy , Fossati Dario
Published: July 2010

Little has been published about the composition of mineral elements in triticale (× Triticosecale Wittm.) grains. Our study deals with the following questions: (i) How do increases in grain yield, resulting from growing triticale in more productive environments or growing more productive cultivars, affect the concentrations of minerals in the grains? (ii) Do genotypes exist whose grains are exceptionally high or low in minerals? (iii) To what extent are the concentrations of protein and minerals related? To answer these questions, 10 hexaploid winter triticale lines/cultivars were grown at three locations in western Switzerland for 2 yr. Whole grains were analyzed for protein (N ✕ 5.7), P, K, Mg, Ca, Fe, Mn, Zn, and Cu. With the exception of Mn and Zn, the variation in mineral element concentrations among lines/cultivars was as great as or greater than the variation caused by environmental factors. Except for Mg, concentrations of mineral elements were significantly lower in the year in which the grain yield was higher. Except for Ca, high grain yields of cultivars were associated with low concentrations of minerals, indicating that one‐sided selection for high grain yield tends to reduce the nutritional quality of triticale grain. Concentrations of protein and minerals were positively correlated, suggesting that breeding for elevated levels of protein is likely to increase the concentrations of minerals.
Remark on a Desirability Index for Selecting Genotypes
Authors: Piepho Hans‐Peter
Published: July 2010

Plant breeders are often interested in simultaneously selecting for yield performance and stability. Recently, a desirability index called the “area under the function” has been proposed, which combines mean yield and regression slope. In this note, it is argued that the desirability index does not appropriately incorporate the distribution of potential environments. A corresponding modification is shown to lead to the simple mean yield as a selection criterion. Reference is given to alternative ways of combining performance and stability.
Genetic Diversity of U.S. Upland Cotton Cultivars Released between 1980 and 1990
Authors: May O. Lloyd , Bowman Daryl T. , Calhoun D. Steve
Published: July 2010

Sustained genetic advance requires that genetically diverse parents be mated to form segregating populations for selection. Genetic diversity of U.S. cotton (Gossypium hirsutum L.) cultivars has not been extensively quantified. We assessed diversity among 126 Upland cotton cultivars released between 1980 and 1990 by use of coefficient of parentage (CP). In computing CP, we utilized assumptions appropriate for self‐pollinated crops. Mean CP among the 126 cultivars was 0.07, implying a genetically diverse group. However, cluster analysis revealed 12 distinct gene pools, with mean within‐cluster CP = 0.25 and between‐cluster CP = 0.04. Overall, clusters corresponded to area of cultivar origin. The CP analysis indicates that Acala‐type cultivars are more diverse than those bred in the Mississippi Delta or southeastern USA. A trend in germplasm usage in the late 1980s was the repeated mating of genetically related material, or reselection within germplasm, to develop proprietary cultivars. To ensure continued progress in cotton improvement, we suggest that cotton breeders consider the pedigree of parents prior to population synthesis.
Relationships among Specific Leaf Weight, Photosynthetic Rate, and Seed Yield in Soybean
Authors: Thompson Jeffrey A. , Nelson Randall L. , Schweitzer Lee E.
Published: July 2010

Increasing leaf apparent photosynthesis (AP) may improve seed yield in soybean [Glycine max (L.) Merr.]. Selection for high specific leaf weight (SLW) may increase AP. The objectives of this study were to (i) incorporate extremes in SLW from exotic germplasm into adapted soybean lines with high agronomic potential, (ii) compare the time course of SLW in lines known to vary in SLW, and (iii) evaluate the relationships among SLW, AP, and seed yield. In 1991 and 1992, 16 genotypes representing extremes in SLW were grown at Urbana, IL, and West Lafayette, IN. The SLW and AP were measured at the R2, R4, and R5 growth stages. At the R5 growth stage in 1992, AP was also measured at approximately twice ambient CO2 concentrations. A subset of lines was sampled weekly for SLW from R1 until R7. High SLW lines displayed a greater rate of increase in SLW than low SLW lines beginning after R2 and continuing until R6. Significant class mean differences (P < 0.01) in SLW were observed on all sample dates across locations. Class mean differences in AP at ambient and twice ambient CO2 concentrations were observed at Urbana, although ranking of SLW classes was inconsistent across years. Leaf rugosity was negatively correlated with AP and seed yield. A high SLW line with low rugosity, LG89‐1917, expressed high AP and produced yields very similar to the adapted cultivars Chapman and Elgin 87. Lines with high SLW and low leaf rugosity may hold the greatest potential for high AP and yield improvement.
Club and Common Wheat Yield Component and Spike Development in the Pacific Northwest
Authors: Zwer P. K. , Sombrero A. , Rickman R. W. , Klepper B.
Published: July 2010

The superior end‐use qualities and reputation for emergence in poor seed bed conditions has maintained club wheat (Triticum compactum Host) as an important, though small class, of wheat in the Pacific Northwest. Our objectives were to determine yield component development in two agronomic zones representative of the fallow/wheat growing region of the Pacific Northwest and to characterize and compare yield component and spike development in two club and two common wheat (Triticum aestivum L.) genotypes. The experiments were conducted at Moro and Pendleton, OR, in 1988 and 1989, where data were collected on yield components and on spike and kernel characters of identified culms. Yields were significantly higher at Pendleton than Moro. Lower floret fertility at Pendleton resulted in fewer and heavier seeds. Kernel weight was apparently the yield component associated with the yield advantage at Pendleton. Early tiller development at Pendleton also favored the development of spikes with greater capacity for yield component compensation. Differences were identified for yield component development in the cultivars Tres, OR8218, Hill 81, and Stephens; however, total grain yield was not significantly different. Although club spikes were one‐half the length of common spikes, spikelet number was not different between classes. Moreover, the number of fertile spikelets and the percentage of fertile spikelets per spike was significantly greater in club genotypes compared with common genotypes. The club genotypes produced more kernels in 1989 than the common genotypes. Kernel weight was consistently less for club lines. These differences were found in the mainstem and tillers T1 to T4. Kernel weight may play an important role in the early seedling establishment in regions where soil moisture is inadequate at planting.
Relationship between Leaf Photosynthesis and Nitrogen Content of Field‐Grown Rice in Tropics
Authors: Peng Shaobing , Cassman Kenneth G. , Kropff Martin J.
Published: July 2010

A field‐derived relationship between maximum single leaf net photosynthetic rate under saturating light (Amax) and leaf N content per unit leaf area (Na) is not available for rice (Oryza sativa L.). The rice simulation model ORYZA1 estimates aboveground dry matter production based on the relationship between Amax and Na determined previously under greenhouse‐growth chamber conditions. The objectives of this study were to establish to relationship between Amax and Na under field conditions and to determine whether the field‐derived relationship could improve ORYZA1 estimation of aboveground dry matter production of tropical irrigated rice. Rice plants were grown in the field with different N rates in the 1993 dry season. The Amax and Na were determined at 38 and 88 d after transplanting. Aboveground dry matter was determined at physiological maturity. Dry matter production data at physiological maturity from four other field experiments were used for model evaluation. There was a close correlation between Amax and Na under field conditions (r2 = 0.88). Compared with the relationship between Amax and Na as determined under greenhouse‐growth chamber conditions in previous studies, higher Amax was observed at low Na in this field study. When the field‐derived relationship between Amax and Na was used, ORYZA1 estimation of dry matter production was improved for rice grown in tropical irrigated environments.
Phytotoxicity of Extracts from Sorghum Plant Components on Wheat Seedlings
Authors: Ben‐Hammouda Moncef , Kremer Robert J. , Minor Harry C.
Published: July 2010

Wheat (Triticum aestivum L.) yield is depressed when the crop is grown after grain sorghum [Sorghum bicolor (L.) Moench], known allelopathic species. Since little is known about the variability of allelopathic potential among sorghum hybrids on wheat, six sorghum hybrids were selected from a 1989–1990 sorghum‐wheat sequence for further study. The range in yield depression observed was 16%. The six hybrids were grown in 1991 and separated into plant parts at maturity. A bioassay using wheat seedlings to detect allelopathic potential was developed. Bioassays of water extracts from mature seeds, glumes, leaves, stems, and roots of sorghum were conducted to (i) quantify the allelopathic potential of sorghum on wheat; (ii) compare allelopathic potential of individual Sorghum hybrids; and (iii) identify the plant paris that are the most important sources of allelopathic substances. Wheat radicle growth response to water extracts revealed a highly allelopathic hybrid and two hybrids with low allelopathic potential. These were retained for study in 1992. All plant parts, regardless of hybrid, contained water‐soluble materials inhibitory to wheat seedling growth. Stems, leaves, and roots were the most inhibitory components of a sorghum plant, reducing wheat radicle elongation by 74.7, 68.5, 64.0%, respectively. Within a sorghum hybrid, an individual plant part was not consistently allelopathic at the same level across years. Bioassays can rapidly detect the differences in allelopathic potential that may occur within and among hybrids. These results have implications for using sorghum‐wheat rotations where residues of certain sorghum hybrids might negatively influence growth and development of wheat, possibly resulting in decreased wheat yields.
Influence of Irrigation on Susceptibility of Selected Soybean Genotypes to Soybean Looper
Authors: Lambert Lavone , Heatherly Larry G.
Published: July 2010

Soybean [Glycine max (L.) Merr.] is usually grown under water deficit conditions in the southern USA and is often attacked by defoliating insects. Field studies were conducted during a 2‐yr period with ‘Centennial’ (insect susceptible) and D75‐10169 (insect resistant) bean genotypes. Plants were grown either with or without irrigation to determine the influence of water‐stressed plants on soybean looper [Pseudoplusia includens [(Walker)] oviposition, development, survival, and damage to plants. There were no significant (P < 0.05) differences in egg deposition on the two plant genotypes, and effect of irrigation on egg deposition was not consistent. At 2 wk after insect release on plants, neither genotype nor irrigation treatment significantly affected number of larvae. Larvae developing on nonirrigated plants of both genotypes were significantly smaller than those developing on irrigated plants. All surviving larvae on Centennial pupated and all larvae on D75‐10169 died by 18 d after the onset of oviposition. Defoliation by insects of irrigated plants of both genotypes was more than 50% greater than defoliation of nonirrigated plants. Without insects, seed yields of the two genotypes were similar and were greater from irrigated than from nonirrigated plants. Insect infestation significantly reduced yield of both genotypes, but the decrease in Centennial yield was greater. Yield reduction resulting from insect infestations was greater for irrigated than for nonirrigated plants. These findings show that soybean plants growing under water deficit conditions may allow a delay in initiation of soybean looper control measures, especially since yield potential and resulting profit potential are low.
Modified Convergent Improvement: A Breeding Method for Multiple Trait Selection
Authors: Henning John A. , Teuber Larry R.
Published: July 2010

Breeders need efficient multiple trait selection schemes that allow selection for each trait within its respective optimum environment. This report describes such a breeding procedure entitled, “modified convergent improvement,” and compares theoretical predictions of genetic gain per cycle (Δq/cycle) for the following schemes: modified convergent improvement, tandem selection in two dissimilar populations followed by a population cross (strain crossing), recurrent selection for single traits in dissimilar populations followed by a multiple population cross (multiple strain cross), and independent culling. Estimates of Δq/cycle were calculated for both additive and dominant gene action when selecting for three to six traits. Modified convergent improvement (Δq/cycle = 0.13) and independent culling (Δq/cycle 0.11) exhibited highest average Δq/cycle for traits controlled by recessive genes (P≤ 0.05). Independent culling exhibited the highest average Δq/cycle when selecting for traits controlled by dominant genes (Δq/cycle = 0.13) or by additive gene action (Δq/cycle = 0.20). Modified convergent improvement proved superior to independent culling when selecting for traits controlled by additive gene action or by recessive genes when gene frequency was low (q = 0.04−0.12). Theoretical Δq/cycle values for multiple strain cross and strain crossing were consistently lower than those obtained for either independent culling or modified convergent improvement.We propose that modified convergent improvement is a superior method for multiple trait selection when traits must be evaluated in dissimilar environments or during the initial stages of germplasm development. This procedure confers additional benefits including reducing inbreeding potential and/or disequilibrium over that observed in single population breeding procedures.
Estimation of Parthenogenesis Frequency in Kentucky Bluegrass with Auxin‐Induced Parthenocarpic Seeds
Authors: Mazzucato Andrea , den Nijs Anton P. M. , Falcinelli Mario
Published: July 2010

To estimate the frequency of apomixis in Kentucky bluegrass (Poapratensis L.) by use of traditional embryo sac classification and progeny testing methodologies is difficult and time consuming. This study was conducted to test the applicability of the auxin test, a recently developed technique that allows the asexual potential to be estimated quickly as the frequency of auxin‐induced, endospermless grains containing one or more parthenogenetic embryos. Frequency of parthenogenesis was estimated by the auxin test for eight clones in two seasons and two locations. The 2,4‐D (2,4‐dichlorophenoxyacetic acid) induction of endospermless grains ranged from 50 to 100%. Two clones were 100% sterile, while the others presented sterility ranging from 2 to 63%. Expression of parthenogenesis was fairly stable within and between environments, suggesting a strong genetic control. Differences in parthenogenesis frequency between clones were evident. Statistical analysis based on pooled data discriminated highly (87–89%), intermediate (78%), and moderate (69–73%) parthenogenetic clones. Estimates of parthenogenesis frequency obtained by embryo sac analysis were similar to or lower than those from the auxin‐induction test. Estimates of apomictic reproduction by progeny tests were usually higher than both estimates of parthenogenesis. Auxin‐induced grains of one clone were analyzed by histological sections. Most of the embryos in the parthenogenetic ovules and grains (80%) seemed normal with regard to position, shape, and cell pattern. It is therefore concluded that the auxin test is a workable technique for determining the percentage of parthenogenesis in breeding programs.