bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport Processes of Two Lolium ✕ Festuca Hybrid Derivatives Differing in Potassium Concentration
Authors: Brauer D. , Leggett J. E. , Egli D. B.
Published: July 2010

To facilitate the development of forages with mineral composition optimal for ruminant production, knowledge of the biochemical and physiological processes determining genotypic differences in nutrient uptake is needed. Experiments were conducted to identify the mechanism(s) that regulated the difference in leaf blade K concentration between two selections of Lolium × Festuca hybriderivatives. Selection differences in rates of K uptake werestimated by measuring Rb uptake by excised roots, and the selectivity of cation uptake for K over Na was determined using intact tillers grown in modified Hoagland's solutions containing varying ratios of K:Na. Differences in Rb uptake by excised roots were of sufficient magnitude to explain differences in leaf blade K concentration. Results indicate differences in K and Na uptake between these two selections reflected an alteration in cation uptake selectivity by roots. Perturbing the plasma membrane integrity by Ca depletion treatments eliminated the difference between selections in K uptake but not in Na uptake. Differences in K uptake were associated with differences in the stimulation of the plasma membrane ATPase by K. These results were interpreted in terms of at least two transport processes contributing to the differences in leaf blade cation concentrations, one process on the plasma membrane affecting K accumulation and another affecting Na accumulation, possibly on the tonoplast membrane.
Daylength Effect on Leaf Emergence and Phyllochron in Wheat and Barley
Authors: Cao Weixing , Moss Dale N.
Published: July 2010

An understanding of the effect of environment on leaf emergence and development is necessary in order to model crop growth and development. This study was designed to determine the effect of controlled daylength on leaf emergence rate and phyllochron in winter wheat (Triticum aestivum L.) and spring barley (Hordeum vulgare L.). Two sets of experiments were conducted in growth chambers at a constant 15 °C. For the first set, 10 experiments were done at daylengths between 8 and 24 h on four wheat and four barley genotypes. The emergence of new leaves at a given daylength was a linear function of time for all genotypes and daylengths, the R2 being 0.94 or greater. However, the slopes differed among genotypes and daylengths. As daylength increased, the leaf emergence rate (leaves/day) increased and phyllochron (degree‐days/leaf) decreased, both curvilinearly. The R2 for the curve fittings were 0.98 or greater for all genotypes. The phyllochron ranged among eight genotypes from 92.4 ± 4.5 degree‐days at 8‐h daylength to 64.5 ± 5.0 degree‐days at 24‐h daylength. The phyllochron of barley was more sensitive to daylength than was that of wheat. In the second set of experiments, the phyllochron for ‘Stephens’ wheat changed quickly when plants were transferred from either 8 to 18 or 18 to 8‐h daylengths. The decrease of phyllochron as daylength increases may explain in part why the phyllochron of wheat and barley growing in natural environments varies with planting date.
Temperature and Daylength Interaction on Phyllochron in Wheat and Barley
Authors: Cao Weixing , Moss Dale N.
Published: July 2010

An understanding of how environment controls the initiation and development of leaves is required to construct dynamic crop simulation models. The leaf development process is poorly understood in cereals. This study was designed to investigate the interaction of temperature and daylength on the leaf phyllochron in winter wheat (Triticum aestivum L.) and spring barley (Hordeum vulgare L.). Growth chamber experiments were conducted at all combinations of three temperatures (10,15,20 °C) and four daylengths (6,10,14,18 on four wheat and four barley genotypes. Wheat and barley had a constant phylloehron (the number of degree‐days elapsed between successive leaves on a culm) at a given temperature and daylength combination. However, the phyllochron varied among genotypes and among temperature and daylength combinations. Phyllochron increased as temperature increased or as daylength decreased. The combined action of temperature and daylength on phyllochron could be quantified in a single term, the thermo/photo ratio (the ratio of daily degree‐days to daylength). The phyllochron for all genotypes in this study was linearly related to the thermo/photo ratio in all the temperature‐daylength combinations, with R2 values not less than 0.94. An evaluation of published field data for barley planted on different dates in two growing seasons suggests that the thermo/ photo ratio may be adequate to explain the different phyllochron values typically observed in such experiments. Our results suggest that cultivar specific coefficients will be necessary to predict the cultivar response of phyllochron to the thermo/photo ratio in wheat and barley.
Partitioning of 14C‐Photosynthate and Biomass in Relation to Senescene Characteristics of Sorghum
Authors: Victor D. M. , Cralle H. T. , Miller F. R.
Published: July 2010

The stems remaining after harvest of sorghum [Sorghum bicolor (L.) Moench] grain are a low‐cost source of biomass. Semidwarf hybrids exhibiting nonsenescent characteristics may yield more stem biomass than senescent hybrids. This study compared a nonsenescent to a senescent hybrid of semidwarf sorghum using dry wt. and partitioning of 14C‐photosynthate and 14C‐starch at three stages. A leaf was exposed to 14CO2 or 14C‐starch was injected into the middle internode of each hybriduring grain filling and at or after (post) black layer of the grain. Although dry wt. of stem internodes were significantly (P ≤ 0.05) greater for the nonsenescent compared the senescent hybrid, 14C‐photosynthate partitioning among parts did not differ between hybrids after chase periods of 5 or 7 d. Patterns of 14C‐photosynthate partitioning indicated grain, stem internodes, and lateral branches were dominant sinks at grain filling, black layer, and post black layer, respectively. Lateral branch growth comprised all of the biomass increase from black layer to post black layer. At post black layer, 47% of assimilated 14CO2 was partitioned to lateral branches. Both 14C‐photosynthate and 14C‐starch were remobilized from stem internodes to lateral branches of both hybrids after black layer. Although unmeasured in previous comparisons betweenonsenescent and senescent sorghum hybrids, lateral branch growth limited storage of 14C‐photosynthate in stem internodes and resulted in similar patterns of 14C‐photosynthate partitioning for the two hybrids after black layer in this study.
Flowering Distribution within and among Grain Sorghum Panicles
Authors: Rosenthal W. D. , Gerik T. J.
Published: July 2010

Genetic differences of the grain sorghum [Sorghum bicolor (L.) Moench] flowering process have not been fully evaluated with respect to air temperature. Flowering duration (FD), i.e., the period of progressive tip to basal spikelet anthesis on a panicle, and flowering period (FP), i.e., the period between the first panicle at tip anthesis and last panicle at basal spikelet anthesis within a field, are important components of the sorghum flowering process. An irrigated field study with 10 commercially available hybrids was conducted in 1986 and 1987 to determine if variability in FP and FD was present. Dates when tip anthesis and basal spikelet anthesis occurred were recorded for 20 consecutive plants in a row. Panicle size (seed no., panicle length, and grain wt.) were determined for each panicle at maturity. Average FD, expressed as days or heat units (base temperature = 7 °C), was significantly different among genotypes. Maximum difference in FD was approximately 0.5 d and 15 heat units (hu). The FP was not significantly different among genotypes. The FD and FP were not correlated to panicle size. Average air temperatures less than 20 °C during anthesis of the 1987 ratoon crop lengthened FD and FP, suggesting anthesis may be delayed at temperatures higher than those required for plant growth.
Genetic Variability for Mineral Element Concentration of Crested Wheatgrass Forage
Authors: Vogel K. P. , Mayland H. F. , Reece P. E. , Lamb J. F. S.
Published: July 2010

Grass tetany is a complex metabolic disorder that causes substantial livestock production losses and deaths in temperate regions of the world. It is caused by low levels of Mg or an imbalance of K, Ca, and Mg in forage consumed by animals. Development of grasses with improved mineral balance would be an economical means of minimizing losses from this malady. This study was conducted to determine if genetic variability exists among crested wheatgrasses, Agropyron cristatum (L.) Gaertner and A. desertorum (Fisher ex Link) Schultes, for forage Mg, Ca, K, Fe, Zn, Mn, Cu, Na, and concentrations. Forage of spaced plants of 10 diverse crested wheatgrass strains was harvested from replicated plots at Lincoln and Alliance, NE, which differ markedly in climate, and analyzed for these minerals. There were genetic differences among strains over locations for Ca, Mg, and Fe concentration in the forage. There were differences among strains within locations but not over locations for K. Strain differences in Zn, Mn, Cu, Na, and P concentrations of the forage were not significant (P > 0.05) when averaged over locations. Calcium and Mg were positively correlated (r = 0.40). These results indicate that it should be possible to breed crested wheatgrass with increased Mg and Ca concentrations in its forage, thus reducing grass tetany potential.
Progressive Heterosis in Autotetraploid Alfalfa: Studies Using Two Types of Inbreds
Authors: Groose R. W. , Talbert L. E. , Kojis W. P. , Bingham E. T.
Published: July 2010

Progressive heterosis is unique to autopolyploids (polysomic polyploids) where heterozygosity and heterosis are not maximal in a single‐cross hybrid of inbred parents. In an autopolyploid, heterozygosity increases with additional generations of hybridization and can result in a progressive heterotic response. This study was designed to evaluate progressive heterosis for important quantitative traits (yield of forage and seed) of autotetraploid (2n =4x = 32) alfalfa (Medicago sativa L.) using inbreds produced in two different ways. In Exp. 1, partially inbred parents (F = 0.333) were produced by colchicine doubling five genotypes of cultivated alfalfa at the diploid level (CADL). sixth CADL genotype produced 2n pollen and was used as a male parent. In Exp. 2, partially inbred parents were derived by selfing three cultivars (Vernal, Saranac, and Iroquois) the S4 generation (F = 0.518). In each experiment, populations of increasing heterozygosity were constructed by successively hybridizing the inbreds and their progenies. Single cross (SC), three‐way cross (3W), and double cross (DC) populations were constructed for Exp. 1. Single cross, DC, and double‐double cross (DDC) populations were constructed for Exp. 2. In both experiments, populations were evaluated for forage yield in direct‐seeded replicated field trials. Populations were also evaluated for yield of seed in the greenhouse and cage (Exp. 1) and in a replicated field trial (Exp. 2). The results of both experiments demonstrated progressive heterosis for yield of forage and seed in alfalfa. More heterozygous generations nearly always outperformed their more inbred progenitors. Whenever pairwise comparisons between generations were significant (P < 0.05), the more heterozygous generation exhibited superior performance. In Exp. 1, forage yields of the progressively more heterozygous 3W and DC generations were 114% and 125%, respectively, of the SC generation. Similarly, in Exp. 2, forage yields of the DC and DDC generations were, respectively, 120% and 137% of the SC generation. The results of this and previous studies indicate that successive hybridization of diverse strains might maximize the progressive heterotic response in alfalfa.
Analysis of Nitrogen Accumulation and Use in Bread and Durum Wheat
Authors: Dhugga Kanwarpal S. , Waines J. G.
Published: July 2010

Since a significant portion of applied soil N is lost by leaching and denitrification, it is desirable to breed crop cultivars with improved N use efficiency. This study was undertaken to determine the influence of soil N supply on genotypic variation for preanthesis and postanthesis shoot N accumulation, the effect of preanthesis N and grain N yield on postanthesis N accumulation, and N use efficiency. A set of 12 bread (Triticum aestivum L.) and two durum (T. turgidum L. var durum Desf.) wheat genotypes was studied over three planting dates in 2 yr with three N levels within each planting date on a Ramona type A sandy loam (coarse fine‐loamy, mixed thermic Typic Haploxeralf). Differences among genotypes for shoot N accumulation before and after anthesis became obvious at the highest soil N level. At this level, some genotypes either stopped accumulating or showed a net loss of shoot N between anthesis and maturity, which appeared to be associated with superior preanthesis N accumulation capacity and reduced grain N yield of such genotypes. Uptake efficiency (total shoot N/soil N supply) became slightly more important than utilization efficiency (grain yield/total shoot N) in determining N use efficiency (grain yield/soil N supply) with increasing soil N supply. Nitrogen harvest index (grain N yield/total shoot N) fully explained the reduced contribution of utilization efficiency at higher soil N levels. We suggest that bread wheat genotypes G4843 and ‘Anza’ should be crossed in an attempt to recombine the superior N accumulation capacity of the former with the superior grain yield of the latter to develop a cultivar with improved N use efficiency.
Response of Dry Matter Accumulation in Maize to Temperature: I. Dry Matter Partitioning
Authors: Tollenaar M.
Published: July 2010

Dry matter partitioning during early phases of development has potentially a large impact on crop growth, but the effect of partitioning on dry matter accumulation has never been quantified. This study was conducted to quantify the response of dry matter partitioning in maize (Zea mays L.) to temperature during the period from planting to the 12‐leaf stage, and to investigate the influence of partitioning on dry matter accumulation. Two maize hybrids were grown at 10 plants m−2 under controlled environment conditions at five constant (15, 19, 23, 27, and 31 °C) and five differential (15/3, 19/7, 23/11, 27/15 and 31/19 °C) day/night temperature regimes. Leaf area partition coefficient (LAPC), i.e., increase in leaf area per unit increase in total dry weight, and its components, shoot partition coefficient (SPC), leaf partition coefficient (LPC), and specific leaf area extension (SLAE), i.e., the area per g of new leaf, were calculated from plant‐component dry weights and leaf area at the 4‐, 8‐, and 12‐leaf stage. The LAPC increased linearly with temperature in the 11 to 31 °C range and declined from the 4‐ to the 12‐leaf stage. Among the components of LAPC, SLAE appeared to contribute most to the variation in LAPC. The LAPC was associated with dry matter accumulation; as much as 50% of the variation in growth rates due to temperature regimes may have been attributable to leaf area partitioning. Similarly, differences in growth rates between hybrids were associated with LAPC. This study demonstrates that dry matter partitioning varies substantially among temperature regimes and phases of development, and between hybrids, and that part of the response of dry matter accumulation to temperature may be attributable to dry matter partitioning.
Leaf Gas Exchange and Plant Growth of Winter Rye, Triticale, and Wheat under Contrasting Temperature Regimes
Authors: Winzeler M. , McCullough D. E. , Hunt L. A.
Published: July 2010

Field stands of winter rye (Secale cereale L.) often accumulate dry matter faster than wheat (Triticum aestivum L.). This study was conducted to determine whether this superiority is expressed at different temperatures and whether it is also apparent in triticale (✕ Triticosecale Wittm.), and to investigate the physiological reasons for the superiority. Rates of dry matter accumulation, dry matter partitioning, and net photosynthesis and respiration of fully expanded leaf blades were measured under controlled environment conditions of 10/7 °C and 20/15 °C day/night temperature. Total day matter accumulation rates of rye and triticale were consistently greater than for wheat irrespective of growth temperature. Intergeneric differences in light‐saturated net photosynthetic rates were evident, with rates for rye being lower than those for wheat and triticale, but they were not significantly correlated to plant dry weight. In contrast, respiration rates of fully expanded leaf blades were 63 and 36% lower for triticale and rye than for wheat under the 10/7 °C temperature regime. At 20/15 °C, leaf respiration rates did not differ between rye and triticale, although both were 50% lower than wheat. Intergeneric differences increased and were more apparent for respiration of expanded leaves of plants grown at 10/7 °C as compared to 20/15 °C. The leaf respiration rates were negatively correlated (r = −0.86) to plant dry weights. Further investigation of the significance to crop productivity of the low respiration rate trait of rye appears warranted.
Plant Regeneration of Zoysiagrass from Embryo‐Derived Callus
Authors: Al‐Khayri J. M. , Huang F. H. , Thompson L. F. , King J. W.
Published: July 2010

Tissue culture methods could enhance development of improved cultivars of zoysiagrass (Zoysia japonica Steudel). A tissue culture system for callus induction and plant regeneration of zoysiagrass was developed. Embryos were aseptically excised from seeds and over 90% produced callus. Embryogenic callus was produced on Murashige‐Skoog (MS) agar medium supplemented with 2,4‐D (2,4‐dichlorophenoxy) acetic acid, but not on N6 medium. A 2,4‐D concentration of 1.0 mg L−1 resulted in greater callus production than higher concentrations. A 16‐h photoperiod of fluorescent light (65 μmol photon m−2 s−1) increased callus production over dark conditions. Direct elimination of 2,4‐D and dark callus induction resulted in greater regeneration frequency and a higher number of plantlets per callus than gradual elimination and light callus induction. Normal plantlets were transplanted to soil and grown to maturity in the field, where overwinter survival was exhibited.
Simulated Selection for Superior Yielding Soybean Lines in Conventional vs. Double‐Crop Nursery Environments
Authors: Panter D. M. , Allen F. L.
Published: July 2010

Soybean [Glycine max. (L.) Merr.] is grown throughout the southeastern USA as both a single, full‐season crop and as a second crop following small grains. Cultivars currently grown in both systems were developed under conventional, single‐crop conditions. Since genotype ✕ environment interactions are known to be important in soybean production, the question arises as to whether cultivars selected for performance in single‐crop culture will be the best cultivars for double‐cropping. Twenty‐five determinate and 25 indeterminate F4‐derived soybean lines were evaluated for seed yield in conventional and double‐crop nursery environments to determine if: (i) relative rankings of lines for yield was similar in the two systems, and (ii) indeterminate lines were higher yielding than determinate lines under double‐crop conditions. The tests were conducted at 16 location‐year combinations from 1982 to 1986. The 50 lines were separated into two groups based on overall means: (i) a superior group of 17 lines that yielded above the mean in both types of nursery environments, and (ii) a nonsuperior group of all other lines. Line ✕ nursery environment interactions were significant (P ≤ 0.01) for both groups, but the magnitude of interaction was twice as great for the nonsnperior group. Simulated selection of the top lines from combinations of one, two, three, and four conventional or double‐crop tests in 1985 produced up to 67% of the superior lines. The best line was selected in every case. eterminates yielded significantly (P ≤ 0.01) more in double‐crop tests, but there was no difference in conventional tests. These results indicate there is no immediate need to maintain separate breeding programs to enhance the development of soybean cultivars adapted to double cropping.
Genetic Improvement in Grain Yield of Commercial Maize Hybrids Grown in Ontario from 1959 to 1988
Authors: Tollenaar M.
Published: July 2010

Analysis of crop improvement during past decades can elucidate the factors that have contributed to the genetic gain of crop cultivars and the understanding of the factors underlying genetic gain may help to sustain or improve genetic gain in the future. The objectives of this research were to estimate the genetic gain in total and machine‐harvestable grain yield of maize (Zea mays L.) hybrids representing three decades of commercial maize production in Ontario and to quantify the effect of the plant‐density :grain‐yield interaction on the genetic gain. Nine maize hybrids that had been grown in Ontario during the period 1959 to 1988 were evaluated at two locations during 1987 and 1988 at four plant densities. Total above‐ground dry matter, total grain yield, and machine‐harvestable grain yield were determined at physiological maturity. The genetic gain in total grain yield at the optimum plant density for grain yield was 1.7% yr−1, whereas the genetic gain in machine‐harvestable grain yield was 2.6% yr−1. The optimum plant density for machine‐harvestable grain yield increased with year of hybrid introduction. The optimum plant density for total grain yield increased from old to more recent hybrids, but the increase in optimum plant density did not continue for hybrids from the 1970s era to hybrids of the 1980s era. Approximately one‐third of the genetic gain in machine‐harvestable grain yield can be attributed to reduced stem lodging. A comparison of the oldest and most recent hybrids indicates that approximately 15% of the genetic gain in total grain yield can be attributed to increased harvest index. Consequently, increase in total dry matter accumulation attributed 85% to the genetic gain in total grain yield.
Genetic Control of Long Daylength Response in Soybean
Authors: Saindon G. , Voldeng H. D. , Beversdorf W. D. , Buzzell R. I.
Published: July 2010

An understanding of the genetics of the long daylength response of soybean [Glycine max (L.) Merrill] would facilitate the development of cultivars adapted to the long days of the northernmost growing areas of North America and Europe. The objective of this study was to determine the genetic control of soybean response to extension of the natural daylength to 20h using incandescent lamps. Three pairs of near‐isogenic lines (NIL) plus a long daylength insensitive check were grown outdoors and rated visually for response to incandescent long day (ILD). The same entries were further grown indoors and rated for response to extension of the natural daylength to 20h using cool white fluorescent lamps (FLD). Based on these results, entries were classified for alleles at the E3 and E4 maturity loci. Check OX619 and ILD‐insensitive NILs X2398, X2403, and X2396 were classified genotypically as e3e3 e4e4. The respective recurrent parents were all ILD‐sensitive and were classified: Evans‐e3 and Harosoy‐e3 as e3e3 E4E4 and ‘Maple Arrow’ as E3E3 e4e4. Analyses of F2 and F2:3 populations from five crosses revealed that only the e3e3 e4e4 genotype is ILD‐insensitive. Consequently, a model of two (E3 and E4), each with two alleles, each with dominance, plus epistasis of E3 on e4> is proposed to explain the ILD‐insensitivity. It was concluded that E3 is the major locus conferring long daylength insensitivity in soybean, but both E3 and E4 have to be considered when breeding for insensitivity to long daylength using ILD.
Inheritance of Reaction to Soybean Mosaic Virus in Two Soybean Cultivars
Authors: Buss G. R. , Roane C. W. , Tolin S. A. , Chen P.
Published: July 2010

Knowledge of the inheritance of resistance to major diseases is important to plant breeders. Segregation for reaction to soybean mosaic virus (SMV) was studied in two soybean [Glycine max L. (Merr.)] cultivars, Marshall and Kwanggyo, which exhibit differential reactions to strains of SMV. The objective was to determine the inheritance of resistance in each cultivar and the genetic relationship of the resistance genes. The F2‐derived F3 lines from the crosses Kwanggyo ✕ ‘Lee 68’, ‘Essex’ ✕ Marshall, Marshall ✕ Lee 68, and Kwanggyo ✕ Marshall were sown in single 0.9 m rows and resulting seedlings were inoculated with SMV. Rows were classified as all resistant, all susceptible, or segregating according to counts of susceptible and resistant plants. Necrotic plants were observed and were included with the resistant class since they were strongly associated with rows that were segregating for SMV reaction. The data indicated that both Marshall and Kwanggyo have single dominant genes for resistance and that the genes are probably alleles at a single locus. No evidence for linkage was found between the resistance gene in Kwanggyo and the T‐t gene pair, which controls pubescence color. Also, the joint segregations of the resistance gene in Marshall with the T‐t and R‐r gene pairs that regulate hilum color fit expected ratios for independent assortment.
Characteristics and Stability of a New Cytoplasmic‐Nuclear Male‐Sterile Source in Pearl Millet
Authors: Hanna W. W.
Published: July 2010

Stable cytoplasmic‐nuclear male sterile lines are desirable for producing commercial hybrids. The A1 cytoplasm in pearl millet, Pennisetum glaucum (L.) R. Br., is widely used but produces fertile revertants. The objectives of this study were to evaluate the stability of male sterility in a cytoplasm (Am) transferred from P. glaucum (L.) R. Br. subspecies monodii (Maire) Brunken and to determine if this cytoplasm differed from the A1, A2, and A3 cytoplasms. In 1983, seeds of male‐sterile ‘Tift 23A1’ and ‘Tift 23am’ were stored at 24, 5, and −5 °C. In 1984 to 1986, seeds of each line were planted in the field and observed daily at anthesis for fertile revertants. Male sterility of the line with Am cytoplasm is maintained by the maintainer lines of A1, A2, and A3 cytoplasms. Seven tester lines restored full or partial male fertility to hybrids with A1, A2, and A3 cytoplasms but only two of the testers restored male fertility to hybrids with Am cytoplasm. Plants with A1 cytoplasm are 2 or 3 d earlier than plants with A1 cytoplasm and have darker red anthers than those with A1 cytoplasm. In 3 yr, male‐sterile plants with A1 cytoplasm averaged 0.91 fertile revertant events per 1000 inflorescences, while no fertile revertants were observed for plants with Am cytoplasm. The number of fertile revertants for A1 cytoplasm increased with age of seed from 1 to 3 yr. Seeds stored at 24 °C produced plants with significantly more fertile revertants than seeds stored at 5 or −5 °C. Differences in seed germination and vigor of seedlings with A1 and Am cytoplasms were nonsignificant or of little practical significance. The new cytoplasm, desiganted A4, is different from A1, A2, and A3 cytoplasms based on fertility of hybrids, morphological characters, and stability.
Disease Severity and Grain Yield in Barley Multilines with Resistance to Powdery Mildew
Authors: Kølster Per , Munk Lisa , Stølen Olav
Published: July 2010

Superiority of yield in cultivar mixtures may be ascribed to specific and nonspecific resistance against leaf pathogens and to differential reactions of components to environment. This study was conducted to investigate the significance of specific resistance on powdery mildew (Erysiphe graminis DC.: Fr. f. sp. hordei) severity and grain yield in barley (Hordeum vulgare L.) multilines and isolines, each carrying different genes for specific resistance to powdery mildew. Multilines were composed of equal proportions of four or five isolines. In the multilines, disease levels were 50 to 80% lower than the mean level for the components grown in pure stands. The advantage of mixing increased with increasing mean level of resistance in the component isolines. Grain yield in both multilines and isolines increased with the mean level of resistance, with most resistant multilines producing higher grain yields than predicted by the mean level of the components in pure stands. The results indicate that components with higher levels of resistance gained the most benefit from utilizing them in a multiline.
Linkage between Maize Dwarf Mosaic Virus Resistance and Endosperm Color in Maize
Authors: Scott Gene E.
Published: July 2010

Maize dwarf mosaic is the most widespread virus disease of maize (Zea mays L.) in the USA. The objective of this study was to determine which, if any, of eight maize inbreds with resistance to maize dwarf mosaic virus strain A (MDMV‐A) had a gene or genes for resistance linked to the endosperm color gene (Y1) on Chromosome 6. Resistant inbreds with yellow endosperm AR234, Ark342, E663, N7B, SC54, SC278, and Tx5858 were crossed onto a susceptible inbred, Mp333, which has a white endosperm Resistant inbred KyBll0 with white endosperm was crossed onto the susceptible inbred CI21 that has yellow endosperm. The F2 kernels were separated for kernel color into dark yellow, light yellow, and white kernels. Plants from the dark yellow kernels had a significantly lower proportion of diseased to healthy plants than did plants from white kernels for all F2 populations involving resistant inbreds with yellow endosperm, indicating that each of these inbreds had a gene for resistance linked to Y1. The white inbred, KyB110, also has a gene for resistance linked to Y1 because the proportion of diseased to healthy plants was lower for plants from white kernels than for plants from dark yellow kernels. Resistance to MDMV‐A for the gene(s) linked to Y1 among the resistant parents seemed to be dominant to mostly dominant except for KyBll0. The data indicated that most of the resistant lines have additional genes for resistance to MDMV that are not linked to the Yl gene. However, crossovers between the gene for resistance to MDMV and the Yl gene and/or gene penetrance could have an effect on what conclusions can be made.
Intergenotypic Competition between Late‐Planted Determinate and Indeterminate Soybean
Authors: Sutton J. D. , Weaver D. B.
Published: July 2010

Studies of several crop plants including soybean, Glycine max (L.) Merr., have indicated a seed‐yield advantage for certain genotype mixtures over the weighted mean of the component genotypes grown in pure stand. This 2‐yr field study was designed to evaluate the performance of late‐planted soybean mixtures consisting of determinate (‘Braxton’, ‘Foster’, and ‘Gordon’)/indeterminate (G84‐ 9010, G84‐9043, and G82‐8611) genotype combinations, and to examine the nature of competition between the two growth‐habit types. Soybean genotypes differing in plant height and relative maturity were chosen to comprise the determinate/indeterminate genotype combinations. The two‐component mixtures were planted at Tallas‐see, AL in alternating 0.61‐m rows and in seed ratios of 0:1, 1:3, 1:1, 3:1, and 1:0. No significant differences in mean seed yield were observed among mixtures and pure stands. A significant quadratic regression component was observed in yield of all genotypic combinations that included G84‐9010 and G84‐9043, each indicating undercompensation (yield less than the weighted mean of the components grown in pure stand). Combinations involving G82‐8611 had no significant regression components, and were the most diverse in both height and maturity. Lack of overcompensation effects may have been related to a small range in diversity of days to maturity between the genotypes comprising each mixture (2‐7 d) as well as the general competitive ability of each genotype. Soybean planted in alternating rows tended to yield higher than 1:1 mixtures. We concluded that the nature of competition between determinate/indeterminate genotype pairs when planted late is dependent on the competitive ability of the genotypes in the pair, and is likely to be undercompensatory.
Drought‐Induced Stress Effect on Soybean Seed Calcium and Quality
Authors: Smiciklas K. D. , Mullen R. E. , Carlson R. E. , Knapp A. D.
Published: July 2010

Drought stress can lower seed quality of soybean [Glycine max (L.) Merr.], possibly from stress related changes in seed‐nutrient concentration. Determinate soybean plants were grown under a mobile weather‐shelter near Ames, IA in 1985 and 1986 to determine if the timing of drought stress could influence seed‐Ca concentration and, subsequently, seed germination and quality. A randomized complete‐ block design was used to test the effect of withholding water during flowering (R2), full pod (R4), seed formation (R5), and full seed (R6) on the quality of the harvested seed. Drought stress was quantified by monitoring leaf temperatures. Each drought‐stress period received an equivalent amount of drought stress. Seed from a R5 drought stress had 85% germination compared with 96% germination for the nonstressed seed. This reduction in seed germination coincided with a 343 μg g−1 decrease in seed‐Ca concentration from a Ca level of 1648 μg g−1 in the nonstressed seed. Electrolytic conductivity per seed and seed‐Ca concentration were negatively correlated (r = −0.50). Germination percentage was significantly correlated (r = + 0.57) with seed‐Ca concentration and negatively correlated with P, Fe, and Zn (r = −0.49, −0.44, and −0.43, respectively). Application of 2.0 g L−1 of Ca(NO3)2 to the germination media of the R5‐stressed seed improved germination to the level obtained by nonstressed seed. The application of Ca(NO3)2 also improved the germination of R6‐stressed seed, which had a concentration of seed Ca equal to the control. This suggests that seed‐Ca concentration is not solely responsible for the decrease in germination percentage of drought‐stressed seed. Results indicate that drought stress during seed formation can reduce seed‐Ca concentration, but additional work is needed to clarify the role that Ca and other seed nutrients play in the germination of drought‐stressed seed.
Divergent Phenotypic Selection Response in Smooth Bromegrass for Forage Yield and Nutritive Value
Authors: Carpenter J. A. , Casler M. D.
Published: July 2010

There has been increasing interest in breeding smooth bromegrass (Bromus inermis Leyss.) for improved nutritive value. Several studies have shown improved animal performance in forages bred for increased nutritive value. The objective of this study was to determine if phenotypic selection for improved nutritive value was possible without sacrificing dry matter yield. The study evaluated eight potential measures of nutritive value, dry matter yield, and five base selection indices. Divergent phenotypic grid selection was practiced in a population of 625 plants for neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), (ASH), cellulose (CEL), hemicellulose (HEM), crude protein (CP), in vitro matter digestibility (IVDMD), and dry matter yield. The highest lowest 75 plants for each selection criterion were crossed in semiisolation. A set of 75 randomly selected plants were bulked to form the unselected check synthetic. The synthetics were evaluated in a forage yield trial with three replicates at three locations in 2 yr. Synthetics differed significantly (P < 0.05) for IVDMD, CP, and all cell wall components except ASH. There were few genotype ✕ environment interactions for the nutritive value traits. Direct divergent selection responses were significant (P < 0.05) for IVDMD, NDF, ADF, and ADL. The divergence between synthetics appeared to be asymmetrical with progress greater in the direction of higher nutritive value. The ADL synthetic had the largest relative gain from selection. Correlated responses with ADL indicated that a 2 g kg ‐I decrease in ADL caused a 14 g kg−1 increase in IVDMD and a decrease of 10 g kg−1 NDF and 9 g kg−1 ADF. Acid detergent lignin content was an excellent chemical predictor of IVDMD in this smooth bromegrass population and was superior to selecting for IVDMD directly.
Inter‐ and Intracultivar Effects of Selection on Heterosis
Authors: Jiang Chang‐jian , Cockerham C. Clark , Moll R. H.
Published: July 2010

The effect of selection on heterosis depends on the gene action and the type of selection. Intracultivar (W) selection, full‐sib family selection within each of two cultivars, and intercultivar (R) selection, reciprocal recurrent selection between the two cultivars, were contrasted for their effects on heterosis. The cultivars were considered to be random replicate populations from an ancestral population. The relatedness of individuals within cultivars and the degree of divergence between cultivars were formalized in terms of identity by descent (IBD) measures for two, three, two‐pair, and four genes a locus and joint IBD measures for genes at each of two loci. Quantitative genetic components for a model that is general for additive, dominance, and additive by additive (a ✕ a) effects with an arbitrary number of alleles were defined for the ancestral population, and selection responses were formulated for the cultivars and the hybrid for each selection method with the aid of the IBD measures. A further analysis was made utilizing a biological building block model of gene effects. The contribution of a ✕ a effects was such that they reduced heterosis from W selection, but slightly increased heterosis from R selection. It was concluded that R selection always increased heterosis while W selection could increase or decrease heterosis, but decreased heterosis for a preponderance of the genetic parameters considered.
Nonstructural Carbohydrates in Axillary Branches and Main Stem of Senescent and Nonsenescent Sorghum Types
Authors: Vietor D. M. , Miller F. R. , Cralle H. T.
Published: July 2010

Although the concentration of nonstructural carbohydrates in main stems has been compared between senescent and nonsenescent types of sorghum [Sorghum bicolor (L.) Moench], nonstructural carbohydrates in axillary branches at upper nodes have not been compared between senescence types. The objective of this study was to test the hypothesis that nonsenescent hybrids of semidwarf sorghum accumulate more nonstructural carbohydrates in branches and in the main stem than senescent hybrids after black layer. Plants were labeled (exposed to 14CO2) 14 d before, at, and 14 d after black layer formation under field conditions. Nonstructural carbohydrates in branches and in lower and upper portions of the main stem were sampled 5 or 7 d after labeling. Comparisons between hybrids 14 d after black layer supported the hypothesis. The content of nonstructoral carbohydrates in branches increased twofold more for nonsenescent than for senescent plants between stages of labeling at and 14 d after black layer. The concentration and content of nonstructural carbohydrates in main stems of senescent plants declined 40% or more during the same period. Branches comprised 84 to 100% of the increase in content of nonstructural carbohydrates even though concentrations and 14C‐photosynthate recoveries in the nonstructural fraction of branches declined after black layer. Nonstructural carbohydrates in branches at upper nodes need to be monitored in addition to those in main stems for comparisons involving the senescence types from this study.
Leaf Water Content and Gas‐Exchange Parameters of Two Wheat Genotypes Differing in Drought Resistance
Authors: Ritchie Steven W. , Nguyen Henry T. , Holaday A. Scott
Published: July 2010

It is still unclear what parameter(s), other than grain yield, might be a suitable indicator in a wheat (Triticum aestivum L.) breeding program for drought resistance. In this study, the leaf relative water content (RWC) and gas‐exchange parameters were compared between a drought‐resistant winter wheat genotype (cv. TAM W‐101) and a drought‐susceptible genotype (cv. Sturdy) to determine if these physiological parameters contribute to drought resistance in TAM W‐101. Plants were grown under well‐watered conditions in growth chambers until drought stress was imposed by limited watering of plants at anthesis or during vegetative growth. In both growth stages, TAM W‐101 maintained a higher RWC and apparent photosynthesis (A) than Sturdy under moderate to severe drought stress. TAM W‐101 plants also maintained a higher photosynthetic capacity (higher A at a given intercellular CO2 concentration [Ci]) under stress than did Sturdy in both growth stages. Photosynthetic water use efficiency (pWUE = A/stomatal conductance) generally increased with stress severity until very severe stress levels were attained. Thus, genotypic pWUE comparisons using stressed plants should be evaluated on a water‐status basis (e.g., RWC) to avoid the confounding effect of stress severity on pWUE. TAM W‐101 tended to have higher pWUE (RWC basis) than Sturdy under moderate to severe stress conditions, but not under well‐watered conditions. High leaf RWC, A, and photosynthetic capacity are traits that may contribute to drought resistance in TAM W‐101.
Role of Heat Girdling in Early Seedling Death of Sorghum
Authors: Peacock John M. , Miller William B. , Matsuda Kaoru , Robinson David L.
Published: July 2010

High soil temperatures (>45 °C) can inhibit the field establishment of sorghum [Sorghum bicolor (L.) Moench.) seedlings in the semi‐arid tropics even when adequate soil moisture is present. The objective of this study was to demonstrate an apparatus for simulating this situation under controlled conditions. The apparatus applies a high temperature localized near the leaf intercalary meristem while maintaining an adequately moist root environment. With this technique, we tested the hypothesis that seedling death may be due to a heat‐girdling, leading to restricted translocation of carbohydrates to the root. Exposure of 10‐d‐old sorghum seedlings to heatgirdling temperatures of 52 ± 2 °C caused complete cessation of leaf elongation. At the same time, shoot carbohydrate concentrations increased while root carbohydrates declined, indicating that phloem transport from the shoot to the root may have been blocked or restricted. During the first 173 h of stress, turgor of both expanded leaves and leaf growing regions (basal 1 cm of leaf tissue) increased, indicating a favorable water balance in the seedlings. After 198 h of heat‐girdling, seedlings died. The apparatus we developed should prove useful for the large scale screening of seedlings for resistance to high soil surface temperatures.
Water‐Use Efficiency and Yield of Sainfoin and Alfalfa
Authors: Bolger T. P. , Matches A. G.
Published: July 2010

Water is often the primary limiting resource for forage production in semiarid and arid regions. Our objective was to determine yield and water‐use efficiency (WUE) of sainfoin (Onobrychis viciifolia Scop.) and alfalfa (Medicago sativa L.) as related to evapotranspiration (ET). Species were grow* in rows under an irrigation gradient. Total seasonal yields were a linear function (r2 = 0.87‐0.97) of ET for both species. Maximum sainfoin yields were 85% of alfalfa (20.7 Mg ha‐1). Sainfoin produced 58 to 63% of its total yield in the first two harvests as compared to 41 to 46% for alfalfa. When soil water was adequate for spring growth, sainfoin was ready to harvest 2 wk earlier than alfalfa. Total ET of both species was similar. Seasonlong WUE of alfalfa (18.3 kg ha‐1 mm‐1) was greater than sainfoin (10.7 kg ha‐1 mm‐'1) in 1986 due to a lack of water in spring when sainfoin yield potential and WUE is highest. In 1987, seasonal WUE of sainfoin and alfalfa was similar (18.2 vs. 16.7 kg ha‐1 mm‐1), but alfalfa had a smaller evaporation (E) component giving it greater overall WUE and yield. Sainfoin WUE was high in spring and declined in summer. Alfalfa WUE remained high throughout the spring and summer. Both species had low WUE in the fall due to dormancy responses. Differences in leaf area index (LAI) account for differences in E between sainfoin and alfalfa. Sudden death of sainfoin plants in summer was observed under low irrigation; therefore, moderate levels of summer irrigation may be necessary to prevent stand loss. In dryland areas, sainfoin's greatest utility is for early season irrigated pasture or hay.
Growth, Morphological, and Chemical Component Responses of Tall Fescue to Acremonium coenophialum
Authors: Hill N. S. , Stringer W. C. , Rottinghaus G. E. , Belesky D. P. , Parrott W. A. , Pope D. D.
Published: July 2010

A symbiotic relationship exists between the endophytic fungus, Acremonium coenophlalum Morgan‐Jones and Gains and tall fescue (Festuca arundinacea Schreb.). The response of the host planto the endophyte has been studied by comparing infected or noninfected populations in the field or by an individual plant genotype in the greenhouse. The lack of a more thorough investigation of tall fescue genotypes with and without their endophytes suggests that known responses of tall fescue plants to endophyte infection are limited to the restricted conditions by which they were tested. The objectives of this study were to determine variability in responses of tall fescue genotypes to endophyte infection for select growth characteristics, plant morphology, and chemical components. Five genotypes of tall fescue were grown in both endophyte‐infected (EI) and noninfected (NI) forms in the greenhouse under different clipping treatments. Tiller and dry matter production, crown depth, and total nonstructural carbohydrates (TNC) were measured. In addition, leaf area per plant (LAP), specific leaf weight (SLW), and ergovaline duction were measured on two diverse plant genotypes. Forage yield, tiller number, and TNC varied for EI and NI treatments among plant genotypes. Dry matter production per tiller was greater and crown depth was approximately 1‐cm lower in EI plants than NI plants. Leaf area was greater in EI plants but SLW was higher in EI Genotype 7 (3.94 vs. 3.65 mg cm−2) and lower in El Genotype 17 (4.25 vs. 4.91 mg cm‐2) compared to their NI forms. Ergovaline production was constant regardless of leaf area in Genotype 7, but increased linearly with leaf area in Genotype 17. We conclude that endophytes increased phenotypic variation in this study and thus may increase the ability of mixed EI and NI populations to adapt to diverse environments.
Medicarpin Delays Alfalfa Seed Germination and Seedling Growth
Authors: Dornbos David L. , Spencer Gayland F. , Miller Roger W.
Published: July 2010

The objective of this study was to identify a compound(s) that may be responsible, at least in part, for alfalfa autotoxicity. We found that medicarpin (3‐hydroxy‐9‐methoxypterocarpan) is a compound produced by alfalfa (Medicago sativa L.) that contributes to this. clay loam soil from a declining alfalfa stand with two plants per 930 cm2 and its 95% ethanol extract inhibited alfalfa emergence and seedlingrowth whereas extracted soil did not. The soil extracts contained at least 10 mg kg−1 medicarpin. Medicarpin, 4‐methoxymedicarpin, sativan, and 5′‐methoxysativan were isolated from alfalfa foliage with 95% ethanol, purified, identified by gas chromatography‐ mass spectroscopy, and then exogenously applied to alfalfa and velvetleaf (Abutilon theophrasti L.) seeds using an agar bioassay. Medicarpin at 1 ✕ 10−7 tool/seed reduced both alfalfa and velvetleaf seedling length by 39% after 72 h. Sativan and both methoxy derivatives had no affect on germination or seedingrowth. In a timecourse study, 2 ✕ 10−7 mole/seed medicarpin delayed germination 12 h and seedling growth 44 h, during this time the alfalfa seedlings metabolized 85% of the medicarpin. Seedling growth then resumed at the control rate. Medicarpin is produced by mature alfalfa, is present in soil from a declining alfalfa stand, and is absorbed by alfalfa seedlings where it is metabolized and exerts a transient phytotoxic effect. Medicarpin may permit established alfalfa plants to control the ecology in their immediate proximity by inhibiting seedling establishment of nearby plants, thereby gaining a competitive advantage.