bluuebunny/crossref_metadata_2025 huggingface dataset:
Potato Leafhopper‐Induced Injury on Growth and Development of Alfalfa
Authors: Hutchins Scott H. , Pedigo Larry P.
Published: July 2010

Yield of irrigated cotton (Gossypium hirsutum L.) increases as the interval between water applications is decreased, even if the total amount of water applied is unchanged. Experiments were undertaken to compare season‐long water relations of high‐frequency dripirrigated cotton (I‐ to 2‐d intervals) to cotton irrigated at approximately 2‐wk intervals. The crop was grown at two locations in central Arizona on a Mohall sandy loam (fine‐loamy, mixed, hyperthermic Typic Haplargid) and an Avondale clay loam (fine‐loamy, mixed, hyperthermic Typic Torrifluvent) soils. In 2‐yr trials at each location, irrigation frequency had inconsistent effects on midday leaf water potential (ψw) during vegetative growth. When the crop developed a heavy fruit load, however, ψw of plants on the longer cycles was much lower than that of drip‐irrigated plants, even after irrigation when ample soil moisture should have been available. Plant hydraulic conductances, estimated from regressions of single‐leaf transpiration rate against ψw, were high in both treatments early in the season. Hydraulic conductance decreased greatly during fruiting in plants on long irrigation cycles but less so in drip‐irrigated plants. Late in the season, after fruit maturation and daring plant regrowth, conductances were again high and similar in the two treatments. The results imply that during heavy fruiting, mild water stress associated with long irrigation cycles triggers deterioration of the root system that is very slow to be reversed. High‐frequency drip irrigation, by preventing cyclical stress, apparently minimized this deterioration during fruit filling.
Phosphorus Requirement of Azolla pinnata: Effects of Low Concentrations on Growth and Nitrogen Fixation
Authors: Sah R. N.
Published: July 2010

There are conflicting reports about the critical P requirements for growth and N2 fixation of Azolla pinnata‐Anabaena azollae association (azolla). This study was conducted to determine critical concentrations of media P and tissue P for optimum growth and N2 fixation of azolla. Continuous flow‐through experiments using media‐P levels ranging from 0 to 500 μM were conducted in a greenhouse. There were no differences in growth and N 2 fixation of azolla grown at media‐P concentrations between 0.5 and 500 μM. Azolla initially high in tissue P (13 to 15 g P kg‐I dry wt.) grew in the Pfreemedium at the optimum rate for about I0 d. For the optimum growth of azolla, media P between 0 and 0.5 μM and about 1.0 g tissue P kg‐1 dry wt. appeared to be the critical concentration. The critical medium‐P concentration was significantly lower than the reported value, 2 μM. Nitrogen fixation correlated with growth, but tissue‐N and P concentrations did not. Increasing media‐P concentrations decreased P utilization efficiency. Results suggest that the difference between deficient and sufficient media‐P and tissue‐P levels may be very narrow.
Development of Winter Wheat under Increased Atmospheric CO2 and Water Limitation at Tillering
Authors: Schönfeld Manette , Johnson Richard C. , Ferris Davis M.
Published: July 2010

Atmospheric CO2 concentrations are increasing world‐wide and are expected to double within the next century. This study was conducted to determine the combined effects of CO2 enrichment and dehydration stress on development of ‘TAM W‐101’ winter wheat (Triticum aestivum L.) at the tillering stage. Seedlings (one per pot) were grown in growth chambers maintained at 350 (ambient) or 700 (enriched) fiL L‐1 CO2, and subjected to three levels of soil moisture (well watered, medium stress, and severe stress). Plastochron (the developmental time for one leaf) decreased 2 to 3% at all water levels under CO2 enrichment. Averaged over CO2 treatments, water limitation increased plastochron from 90 thermal units under well‐watered conditions to 126 under medium stress and 141 under severe stress. Similarly, water limitation reduced tiller number from 26 to 14 and 12 under medium and severe stress, respectively. The ratio of leaf dry wt. to leaf area (specific leaf wt.) and water use efficiency were significantly higher in plants grown under CO2 enrichment. Although CO2 enrichment had positive effects on growth and development of winter wheat at tillering, these were insufficient to counterbalance the debilitating effects of water limitation.
Identification of Inbred Lines as a Source of New Alleles for Improvement of Elite Maize Single Crosses
Authors: Mišević Dragan
Published: July 2010

The identification of inbred lines as sources of favorable alleles not already present in an elite single cross is an important part of the pedigree maize (Zea mays L.) breeding program. The objectives of this study were to identify lines for improvement of elite hybrids. A diallel set of 15 maize inbred lines, which included eight USA (US) public and seven Maize Research Institute “Zemun Polje”, Yugoslavia, proprietary lines were evaluated in 1986 and 1987 in Yugoslavia. Seven hybrids representing Stiff Stalk Synthetic (SSS) ✕ Lancaster, SSS ✕ other US, SSS ✕ Yugoslavian (YU), Lancaster ✕ other US, Lancaster ✕ YU, other US ✕ YU, and YU ✕ YU heterotic patterns were designated as targets for improvement. Significant differences in grain yield were found among lines in minimally biased estimates (μG) of favorable alleles present in a donor inbred, but not present in a recipient hybrid, minimum upper bound (UBND) estimate and predicted threeway performance (PTC) each of the seven hybrids were designated as a target. The highest values for all estimators of new favorable alleles were found for donor lines that belonged to a different heterotic group than the parents of the target hybrid. In most cases (C+F)‐(D+E) values agreed with expectation based on pedigree information. Simultaneous increases in yield and decreases in grain moisture appear to be possible for most target hybrids. Correlations among three estimators of new favorable alleles were high, positive, and significant. The highest correlations, which frequently exceeded 0.95, were found between μG and PTC indicating that PTC also provides reliable information.
Measurement and Use of Excised‐Leaf Water Status in Wheat
Authors: McCaig T. N. , Romagosa I.
Published: July 2010

Water status of intact and excised leaves has been reported to be related to drought resistance. Automation of leaf weighing has enabled more rapid and detailed examination of water content and water loss following excision than was previously possible. Our objective was to evaluate these measurements as screening techniques in tetraploid wheat (Triticum turgidum L.) and hexaploid wheat (Triticum aestivum L.) breeding programs. Among eight genotypes, those adapted to dryland exhibited high initial water content (IWC) (dry weight basis) and/or low rate of water loss (RWL) suggesting that both characters may contribute to the maintenance of leaf water status during periods of severe drought. Differences among tetraploid genotypes, for IWC and RWL, were more consistent than among hexaploid types. Both IWC and RWL of the most recently fully expanded (MRFE) leaf decreased as a function of thermal time indicating that maturity differences among genotypes must be considered. Genotypic differences were more pronounced when sampling was carried out prior to heading. Leaf selection was also important since the RWL of the MRFE leaf of the main stem was lower than that of the penultimate leaf. Controlled environment (well‐watered) results were similar to those obtained from the field (rainfed), indicating that screening may be possible in growth chambers. Phenological, genotypic, and environmental effects on these parameters are further discussed, including procedures and cautions concerning the use of these techniques.
Seed Yield of Grazing‐Tolerant Alfalfa Germplasms
Authors: Smith S. R. , Bouton J. H.
Published: July 2010

Alfalfa (Medicago sativa L.) cultivars tolerant to grazing usually have poor seed yields. This study compared grazing‐tolerant alfalfa cultivars and germplasms to hay‐type cultivars for seed yield in Georgia and determined the relationship of certain plant characters to seed yield. Hay‐type (‘Apollo’ and ‘Florida 77’) and grazing‐type (‘Spredor II’ and ‘Travois’) cultivars and two alfalfa germplasms selected for survival under continuous grazing in Georgia (GA‐GC and GA‐WCG) as well as the representative base populations of GA‐WCG were established as replicated spaced plants for seed production over a 2‐yr period. Measurements of raceme number, seeds per pod, and seed weight did not attain biologically significant correlations with seed yield. Grazing‐tolerant germplasms, GA‐GC and GA‐WCG, produced seed and forage yields higher than the grazing‐type cultivars and equivalent to the hay‐type cultivars. Comparisons between GA‐WCG and its base population indicate that seed and forage yields were maintained while the population was shifted toward a more decumbent growth habit and earlier fall dormancy. In this experiment alfalfa seed and forage yields were not sacrificed in the development of grazing‐tolerant cultivars.
Bermudagrass Encroachment into Creeping Bentgrass as Affected by Herbicides and Plant Growth Regulators
Authors: Johnson B. J. , Carrow R. N.
Published: July 2010

Bermudagrass (Cynodon spp.) encroachment into creeping bentgrass (Agrostis stolonifera var. palustris Huds.) golf greens is a severe problem where both grasses are grown. Research was initiated to determine the effects of dates and frequency of herbicide‐plant growth regulator (PGR) treatments on tolerance of creeping bentgrass and encroachment of three bermudagrass cultivars under golf green conditions. Treatments were arranged in a split‐plot design with frequency of herbicide‐PGR application as main plots and bermudagrass cultivars as subplots. Soil type was an artificial rootzone mix. Creeping bentgrass was injured more when treated with various herbicide‐PGR combinations in September than in April. However, creeping bentgrass injury was unacceptable (>30%) with mefluidide {N‐[2,4‐dimethyl‐5‐[[(trifluoromethyl)‐sulfonyl] amino]phenyl]acetamide} applied in sequence with siduron [N‐(2‐methyl‐cyclohexyl]‐N‐phenylurea] or ethofumesate [(±)2‐ethoxy‐2,3‐dihydro‐3,3‐dimethyl‐5‐benzofuranyl methanesulfonate] at either date. In general, herbicide‐PGR treatments applied in April suppressed foliage and stolon growth of bermudagrass equal to or better than treatments applied in September and April. Bermudagrass growth was effectively suppressed until late May or early June when treated with siduron, siduron with flurprimidol {α‐(1‐methylethyl)‐α‐[4‐(trifluoromethoxy)‐phenyl]‐5‐pyrimidine‐methanol}, or ethofumesate with flurprimidol. There generally was no difference in foliar growth suppression from treatments applied to ‘Tifway’, ‘Tifgreen’, both C. transvaalensis Burtt‐Davy ✕ C. dactylon (L.) Pers., and common bermudagrass, C. dactylon (L.) Pers. When chemicals were applied only in April, the length and number of bermudagrass stolons were effectively suppressed for several weeks but stolon growth recovered and increased rapidly from mid‐May until June. The suppression of stolon growth of all bermudagrass cultivars in June was as good or better when treated with ethofumesate plus flurprimidol than with other treatments.
Maximum Temperature for Nitrogen Fixation in Common Bean
Authors: Hernandez‐Armenta R. , Wien H. C. , Eaglesham A. R. J.
Published: July 2010

The upper temperature limit for nodulation and N2 fixation by common bean (Phaseolus vulgaris L.) is not well defined. Controlled‐environment experiments were conducted to address this issue and to determine the relative importance of shoot and root temperatures. Bean cultivars Redkloud and Jutiapa were grown in sand culture and exposed to day temperatures (13 h d−1) of 26, 32, and 38 °C from sowing or 26, 32, 34, 36, and 38 °C for 5 to 10 days during vegetative growth. In other experiments, day shoot‐root temperatures of 26‐26, 26‐38, 38‐26, and 38‐38 °C were compared. Night temperature was 22 °C in all instances. Transferring plants from a 26 °C to a 38 °C environment resulted in elimination of acetylene reduction activity (ARA) (controls reached over 12 nmol plant−1 s−1), severe N deficiency (55 ± 3 mg shoot‐N plant−1 after 10 d compared with 177 ± 7 mg in controls), and virtual cessation of leaf expansion. Ten days at 32 °C decreased (P ≤ 0.05) shoot‐N content relative to controls. Nodulation was inhibited at 38 °C when treatment was started immediately after inoculation of established plants or seeds but not when it was applied after nodules were initiated. At root temperature of 38 °C, N2 fixation was inhibited regardless of shoot temperature. Conversely, at root temperature of 26 °C, nodulation and shoot‐N accumulation were unaffected even when shoot temperature was 38 °C. It appears that only high soil temperature would constrain N2 fixation by bean; the critical temperature was 32 °C for nodule function and 38 °C for nodulation.
Implication of Fatty Acids and Seed Dormancy in a New Screening Procedure for Cold Tolerance in Rice
Authors: Majumder M. K. , Seshu D. V. , Shenoy V. V.
Published: July 2010

Developing a suitable screening technique to identify appropriate genetic donors, and segregants is a requisite to the successful incorporation of cold tolerance into high yielding, semidwarf rice (Oryza sativa L.) cultivars. This study investigated relationships between cold tolerance and unsaturated fatty acids (USFAs); between seed dormancy and short‐chain saturated fatty acids (SCSFAs), specifically, nonanoic acid (C9); and between cold tolerance and seed dormancy in rice. The cold‐tolerant cultivars accumulated higher quantities of USFAs in 40‐d‐old leaves and mature grains compared to the cold‐susceptible cultivars under the optimum (29/21 °C day/night) and the low (22/18 °C) temperatures in the phytotron. The tolerant cultivars also showed a null allelic situation at the esterase 2 locus (20). The susceptible and the less tolerant cultivars had either the esterase 21 or the esterase 22 allele. The esterase 21 and the esterase 22 allozymes utilized the choline ester precursors of USFAs to liberate free USFAs, reportedly the precursors of the SCSFAs in plants. The strongly dormant cultivars had the esterase 21 allele and accumulated higher levels of SCSFAs in the mature seeds compared to the nondormant cultivars. Nonanoic acid was the most effective seed dormancy imposer of the four SCSFAs tested. For the artificial imposition of dormancy, the seeds of cold‐tolerant cultivars needed more nonanoic acid than the cold‐susceptible cultivars. Thus, based on germination response to nonanoic acid and the esterase 2 allozyme pattern, a reliable two‐tier screening technique has been developed to identify cold‐tolerant rice cultivars.
Genetic Allelism of Nodulation Response Genes Rj1, Rj2, and Rj4 in Soybean
Authors: Devine T. E. , O'Neill J. J.
Published: July 2010

Several qualitatively inherited genes (Rj1, Rj2, and Rj4) controlling nodulation response have been reported in soybean, Glycine max (L.) Merr. This study was undertaken to determine whether these alleles were located at distinct genetic loci, or whether one or more were located at the same locus. The F3 progeny from crosses of genetic stocks of each allele were evaluated for nodulation response. The responses due to the Rjl allele were evaluated in the field. The responses due to the Rj2 allele and the Rj4 allele were evaluated in sterile vermiculite in growth trays following controlled inoculation with bradyrhizobial strain USDA 7 or USDA 61, respectively. The F3 seed lots were subdivided to permit assay for more than one allele. Genotypes of F2 plants were rationalized from F3 progeny. Allelism tests established that the Rjl, Rfl and Rj4 alleles were distinct in their segregation and must be located at three distinct genetic loci. The Rjl gene has been located 40 ± 2 centimorgans from the F gene. Both Rj2 and Rj4 were found to segregate independently of the F locus, confirming that they are not at the Rjl locus. Therefore, soybean breeders have the option of constructing soybean genotypes containing all or any combination of these alleles if desired.
Evaluation of F2 ✕ F2 and BC1 ✕ BC1 Maize Interpopulation Crosses
Authors: Bernardo Rex , Johnson G. R. , Dudley J. W. , Meghji M. R.
Published: July 2010

Further improvement in the performance of elite maize (Zea mays L.) hybrids is an important objective of maize breeding programs. Introgression of broadbase germplasm to improve the elite single cross B73 ✕ Mo17H was considered. Estimates of genetic parameters in a [B73 ✕ B Composite]F2 ✕ [Mo17H ✕ A Composite]F2 Design 2 population and a [B73(B73 ✕ B Composite)]BC1 ✕ [Mo17H(Mo17H ✕ A Composite)]BC1 Design 2 population were obtained. Proportion of broadbase germplasm had a linear effect on means with the order of performance (most favorable to least favorable) for all traits being B73 ✕ Mo17H, the BC1 interpopulation cross, the F2 interpopulation cross, and A Composite ✕ B Composite. Estimates of half‐sib covariances (CovHS) and specific combining ability variance (VarSCA) for grain moisture and plant and ear heights were greater in the F2 than in the BC1 interpopulation cross as expected for a one‐locus, two‐allele genetic model. Contrary to expectations, estimates for grain yield of CovHS in the population related to B73 and of VarSCA were two and four times greater, respectively, in the BC1 than in the F2. The large estimates of CovHS and VarSCA for grain yield in the BCt interpopulation cross were consistent with expectations for a model in which B73 and Mo17H are homozygous for an allele at a modifier locus, which causes complete dominance at a quantitative trait locus. Frequency of the modifier allele in the two composites would be near zero under this model. The VarSCA results suggested the use of backcross populations for selection procedures that exploit specific combining ability effects. Together with higher frequencies of BC1 ✕ BC1 testcrosses superior to B73 ✕ Mo17H, they indicated a higher probability for immediate derivation of superior single crosses from the BC1.
Genetic Variability and Selection for Acetylene Reduction in Peanut
Authors: Arrendell S. , Wynne J. C. , Rawlings J. O.
Published: July 2010

Effective manipulation of the symbiotic relationship between peanut (Arachis hypogaea L.) and Bradyrhizobium is aided by an understanding of the genetic mechanisms governing the host contribution. This study was conducted to obtain genetic variance estimates and evaluate the effectiveness of selection for acetylene reduction. The population under study consisted of 80 F5 lines derived from the single cross of the Virginia‐type ‘Florigiant’ and the Spanish‐type ‘CES 101’. Estimates of genetic variance components for acetylene reduction were obtained at three sampling dates at each of two locations. Standard errors of the estimates were generally large; however, the tendency was for additive genetic variance to be important at Dates 1 and 3 and for the additive ✕ additive genetic variance to be important at Date 2. The five lines with the highest mean acetylene reduction and the five with the lowest mean acetylene reduction were selected and evaluated in the F6 generation. The mean acetylene reduction of the high selection group, 79.1 μmoles C2H4 plant−1 h−1, was significantly greater than the mean of the low selection group, 52.2 μmoles C2H4 plant‐1 h‐1, but not different from the mean of the better parent, 89.9 μmoles C2H4 plant−1 h−1. Twenty‐eight vegetative, fruit, and seed characters were used to assign the selected lines and original parents to morphological groups. Variability for these traits existed within each of the selection groups. selected lines, regardless of selection group, did not group with either parent. Adequate genetic variability existed in this late generation population and host genotypes with differing abilities to fix N2 were identified by selection. When the breeding objective is improvement of the N2‐fixing ability of Spanish‐type peanuts, direct selection for morphological characters may be required if the base population has been derived from a Virginia ✕ Spanish cross.
Divergent Phenotypic Recurrent Selection for Nitrate Reductase Activity in Maize. I. Selection and Correlated Responses
Authors: Eichelberger K. D. , Lambert R. J. , Below F. E. , Hageman R. H.
Published: July 2010

The use of biochemical or physiological traits as accessory criteria for selection of high‐yielding maize (Zea mays L.) genotypes has been proposed. In this study, direct and correlated responses to eight cycles of divergent phenotypic recurrent selection for high and low levels of postanthesis leaf‐lamina nitrate reductase activity (NRA) in the maize synthetic Super Stiff Stalk (BSSS) were valuated fertilizer‐N rates of 112, 224, and 336 kg ha−1, Cycle 0, 3, 6, and 8 of the high‐ and low‐NRA strains were evaluated in 1985 for NRA to determine the direct response to selection. Cycles 0, 3, and 6 of the high‐ and low‐NRA strains were evaluated for correlated responses in grain yield, yield components, harvest index, days to anthesis, and days to silk emergence in 1983, 1984, and 1985 at one location each year. Cycle 8 was an additional treatment in 1985 only. Relative to Cycle 0, eight cycles of selection resulted in a 46% increase in NRA in the high‐NRA strain and a 62% decrease in the low‐NRA strain, averaged over supplemental‐N rates. Divergence of NRA was maintained late into the grain‐fill period. Cycle 6 of the high‐ and low‐NRA strains had grain‐yield reductions of 5.6 and 16.8%, respectively, relative to Cycle 0, averaged over supplemental‐N rates. The large grain‐yield reduction for Cycle 6 of the low‐NRA strain was due primarily to a reduction in kernels plant−1. Estimates of inbreeding depression could account for essentially all of the yield reduction for Cycle 6 of the high‐NRA strain, but for only a fraction of the yield reduction for Cycle 6 of the low‐NRA strain. Both NRA strains showed reductions in the harvest index and increases in days to flower.
Divergent Phenotypic Recurrent Selection for Nitrate Reductase Activity in Maize. II. Efficient Use of Fertilizer Nitrogen
Authors: Eichelberger K. D. , Lambert R. J. , Below F. E. , Hageman R. H.
Published: July 2010

Improving the efficiency of absorption and utilization of soil‐applied N by maize (Zea mays L.) cultivars should be an important goal of maize breeders. This study was conducted to determine the relationship between nitrate reductase activity (NRA) and reduced N, N harvest index, N uptake, N utilization, N‐use efficiency and grain N accumulation of maize. Eight cycles of divergent phenotypic recurrent selection for high and low levels of postanthesis leaf‐lamina NRA were completed in the maize synthetic Super Stiff Stalk (BSSS). Cycles 0, 3, and 6 of the high and low NRA strains were grown at N rates of 112, 224, and 336 kg ha−1 in 1983, 1984, and 1985 at Urbana, IL, and were evaluated for the above N traits. The 1985 experiment included Cycle 8 high and low NRA. Selection for high NRA had little effect on the N traits evaluated. In contrast, selection for low NRA resulted in significant reductions for many of the N traits examined. Reductions in grain N content for Cycle 8 low NRA were 9, 21, and 19% with 112, 224, 336 kg N ha−1, respectively, relative to Cycle 0, were observed. Nitrogen‐use efficiency of Cycle 8 low NRA decreased 21, 16, and 13%, relative to Cycle 0, at the three respective N rates. These results indicate selection for low NRA has adversely affected nitrate metabolism in this population, resulting in lower grain N production and less‐efficient use of soil‐applied N to produce grain.
Rht1 and Rht2 Semidwarf Genes Effect on Hybrid Vigor and Agronomic Traits of Wheat
Authors: Keyes Geoff , Sorrells Mark E.
Published: July 2010

The ‘Norin 10’ dwarfing genes, Rhtl and Rht2, have been an effective source of stature control in commercial cultivars of hexaploid wheat (Triticum aestivum L.). Various and conflicting studies have reported on the yield effects associated with these genes. The present study was undertaken to examine pleiotropic effects on yield and yield related characters in inbreds and F1 hybrids near‐isogenic for Rht1 and Rht2. Isogenic series for six diverse cultivars at three levels of dwarfing; tall (no Rht alleles), semidwarf (2 Rht alleles), and double‐dwarf (4 Rht alleles) were intercrossed in all possible combinations within each dwarfing level, without reciprocals, to construct three near‐isogenic series of 15 F1 hybrids. Parents and hybrids were grown in replicated field trials in each of two locations for two years. Mean grain yield of all genotypes declined significantly as a linear function of the number of Rht genes. Negative effects of Rht were a consequence of significantly reduced kernel weights that were not offset by other yield components. Midparent heterosis for one measure of yield was greatest for tall hybrids (14%), followed by semidwarfs (10%), and double‐dwarfs (2%). The Norin 10 Rht alleles appear to limit the expression of hybrid vigor.
Determining Alfalfa Resistance and Yield Losses Associated with Verticillium Wilt Infestations
Authors: Papadopoulos Y. A. , Christie B. R. , Boland G. J.
Published: July 2010

Twenty‐four alfalfa (Medicago sativa L.) cultivars and experimental synthetics were evaluated for resistance to verticillium wilt (Verticillium albo‐atrum Reinke & Berth) in controlled environments (utilizing aseptically grown seedlings prior to inoculation with V. albo‐atrum) and field conditions to determine the ability of controlled environment methods to evaluate disease resistance and the influence of verticillium wilt on alfalfa forage production. Foliar disease symptoms first appeared in the field prior to the second cut of the first production year (1 yr after planting). Substantial differences in foliar disease symptoms and reductions in healthy plant populations and herbage dry matter yield were detected among the entries by the third harvest of the second production year. Field disease ratings were positively correlated with growth chamber disease ratings and negatively correlated with herbage dry matter yield. Twenty to 56% of the variation in herbage yield among cultivars in the V. albo‐atrum infested field was attributed to the influence of disease as determined by correlation analysis. The results indicate that controlled environment evaluations of cultivar resistance to verticillium wilt of alfalfa were in agreement with the cultivars' reaction in the field following natural infection and that verticillium wilt causes substantial yield reduction in susceptible cultivars. It is estimated that alfalfa cultivars should possess levels of resistance comparable to that of the check cultivar Vertus to avoid yield losses due to verticillium wilt.
Application of the Near‐Isogenic Line Gene Mapping Technique to Isozyme Markers
Authors: Muehlbauer G. J. , Specht J. E. , Staswick P. E. , Graef G. L. , Thomas‐Compton M. A.
Published: July 2010

Near‐isogenic lines (NILs) have been proposed as a genetic resource that can be used to identify linkages between molecular and conventional markers. If the donor parent (DP) and the recurrent parent (RP) possess an allelic contrast for the molecular marker, and if the DP allele is still present in the NIL, then presumptive evidence of linkage between that molecular marker and the intro‐gressed gene can be inferred. The objective of this study was to evaluate this NIL gene‐mapping technique using isozyme markers and a collection of 63 soybean [Glycine max (L.) Merr.] NILs. The electrophoretic isozyme banding patterns of eight enzymes (12 loci) were examined in 35 ‘Clark’ and 28 ‘Harosoy’ RP/NIL/DP trio sets, where each NIL possessed an introgressed conventional gene. Of the 756 combinations of 12 isozyme loci and 63 trio sets evaluated, 256 exhibited RP/DP isozyme allelic differences. Of these 256, seven (four in Harosoy, three in Clark, total of five conventional markers) exhibited an RP/NIL contrast and a corresponding NIL/ DP equality for an isozyme allele. The five different presumptive linkages were: Enp – In, Mpi – dt2, Aco4 – dt2, Mpi – ln, and Pgi – d2. The F2 cosegregation data confirmed the presumed linkages of Enp with ln (9.38 ± 1.55%) and Mpi with dt2 (16.07 ± 6.43%), but refuted the presumed linkages of Aco4 – dt2 and Mpi – ln. The Enp locus is therefore part of Linkage Group 4, which is currently comprised of the v1, ln, and P2 loci. Neither Mpi nor dt2 have been assigned to an existing linkage group, and thus represent a new linkage group. The presumed linkage of Pgi with d2 was not tested, but other data indicated that this presumption was probably erroneous. The confirmation of two of the five presumptive linkages was consistent with the numbers expected based on a previously published theoretical analysis of the NIL gene‐mapping technique.
Pollen Size and Pollen Viability in Big Bluestem as Related to Spikelet Type
Authors: Springer T. L. , Taliaferro C. M. , McNew R. W.
Published: July 2010

The utilization of big bluestem, Andropogon gerardii Vitman, for revegetation is limited by seed availability. Although several factors influence seed production in cross‐pollinated species, effective pollination is essential for seed set. Objectives of this study were to compare pollen grain size and viability from pedicellate and sessile spikelets of six big bluestem accessions in each of 2 yr. Coulter Counter measurements of mean pollen diameter varied significantly with spikelet type and year. The mode pollen diameter varied with accession, spikelet type, and year. Mean and mode pollen diameters were consistently larger in sessile than pedicellate spikelets. Differences in pollen viability were attributable to accession, spikelet type, and an accession by spikelet interaction. Among accessions, pedicellate‐spikelet pollen viability varied from 4 to 78% averaged over years, and in two accessions was nearly as high as the sessile spikelet. Phenotypic variation in pedicellate‐spikelet pollen viability suggests that selection for this trait should be effective, assuming heritable variation of sufficient magnitude.
Standard Errors for Heritability and Expected Selection Response
Authors: Hanson W. D.
Published: July 2010

Confidence statements for response expected from selection are needed. The first order approximation in Taylor's expansion was used to develop standard errors for heritability and expected progress. Both standard errors contain adjustments for level of heritability. They offer criteria for establishing approximate confidence intervals for these two estimated parameters.
Inheritance of Grain Dormacy in White‐Kernelled Wheat
Authors: Paterson A. H. , Sorrells M. E.
Published: July 2010

Preharvest sprouting is a serious problem for seedsmen, growers, and processors of white‐kernelled wheat (Triticum aestivum L. em Thell). Grain dormancy identified in several white‐kernelled wheats may provide genetic variation necessary to breed sprouting‐resistant white wheats. We have investigated the inheritance of grain dormancy from white‐kernelled wheats ‘dark's Cream’ and NY6432‐ 18, in crosses with white‐kernelled wheats ‘Geneva’ and ‘Houser’. Germination tests were performed on mature seed from several generations, with multilocation testing in advanced generations. Dormancy from each of the two sources shows largely dominant genetic effects, modification by background genotype, and a strong influence of environment. Large variation in dormancy among F5 single‐seed descent lines derived from dormant but otherwise divergent parents, indicates that multiple dormancy mechanisms remain in the gene pool of domestic white‐kernelled wheats. Because of dominance and substantial nongenetic variation, selection for grain dormancy from these sources is best practiced among near‐homozygous genotypes replicated over environments.
Genotype ✕ Popping Method Interaction for Expansion Volume in Popcorn
Authors: Dofing S. M. , Thomas‐Compton M. A. , Buck J. S.
Published: July 2010

Expansion volume, defined as the volume of popped corn per gram of unpopped corn, is considered the most important quality trait in popcorn (Zea mays L.). The increasing popularity of microwave popcorn has necessitated the development of cultivars for use in both conventional and microwave popping. Information on expansion volume of popcorn genotypes using both popping methods is not available in the literature. This study investigated the presence of a genotype ✕ popping method interaction for expansion volume and its components in popcorn. Eleven commercial popcorn hybrids, one flint corn ✕ popcorn inbred line cross, and one open‐pollinated popcorn variety were grown in isolation in 1988. Seed harvested from each genotype was divided equally into large‐ and small‐kernel samples that were evaluated for expansion volume, popped kernel (flake) size, and percent unpopped kernels in conventional and microwave popping. All genotypes performed better in conventional popping than in microwave popping. Significant differences existed among genotypes for expansion volume and flake size. A significant genotype ✕ popping method interaction was detected for expansion volume, flake size, and percent unpopped kernels. Therefore, breeders utilizing germplasm similar to that which we studied with the dual objective of developing cultivars for conventional and microwave popcorn markets should conduct evaluations for expansion volume using both popping methods.
In Vitro Digestibility of Fresh Leaves and Stems of Small‐Grain Species and Genotypes
Authors: Bruckner P. L. , Hanna W. W.
Published: July 2010

Comparative studies examining relative forage digestibilities of small‐grain species and genotypes are lacking. Pattern and extent of digestion and microanatomical characteristics of fresh leaves and stems were evaluated in two genotypes each of rye (Secale cereale L.), soft red winter wheat (Triticum aestivum L.), oat (Avena sativa L.), and triticale (✕ Triticosecale Wittmack). Field grown plants (mid‐boot) were sampled in 1987 and 1988 at Tifton, GA. In 1987, leaf and stem anatomy were compared microscopically in fresh nondigested samples. Fresh leaf and stem segments (2.5 cm) were digested 36 h in buffered rumen fluid, serially sectioned, and examined microscopically to examine the ease and extent of digestion in specific tissues. In 1988, in vitro dry matter disappearance (IVDMD) was determined in ground (1 mm) and intact stem and leaf sections (1 cm) digested for 12, 24, 36, and 48 h. No microanatomical variation was observed among genotypes of the same species. Variation was observed among species in stem signification, stem sclerenchyma cell‐wall thickness and arrangement, compaction, and shape of leaf mesophyll cells. Signified stem tissue was greatest in wheat and triticale and least in oat and rye. Rye leaf mesophyll cells were the least compact with the largest intercellular spaces. Variation was observed among species in digestibility of leaf and stem bundle sheath cells. Differentiation among genotypes for leaf IVDMD was greater in sectioned samples digested 12 to 36 h than in ground samples digested 48 h. Species varied in leaf and stem IVDMD. Oat had the lowest stem digestibility but the highest leaf digestibility. Variation for forage digestibility was observed among genotypes of all species except triticale. Variation in forage digestibility was not associated with variation observed for stem signification or arrangement and compaction of leaf mesophyll cells. Adequate variability exists within rye and oat to suggest that selection for leaf IVDMD would be effective in improving small‐grain forage quality.
Cotyledon Cell Number and Size in Birdsfoot Trefoil
Authors: Fonseca M. L. , McGraw R. L. , Beuselinck P. R.
Published: July 2010

Birdsfoot trefoil (Lotus corniculatus L.) has small seed compared with many other forage or grain legumes. Small seed is largely responsible for poor seedling vigor that limits usage of this important forage crop. Factors influencing seed size and cotyledon expansion during seedling growth have not been studied in birdsfoot trefoil. Two studies were conducted to determine if: (i) variation in seed size is due to changes in cotyledon cell number and/or cell size, and (ii) cell division and/or cell enlargement is responsible for cotyledon expansion in growing seedlings. In the first study, cotyledons of MU‐81 and ‘Norcen’ birdsfoot trefoil from three seed‐size classes were macerated in chromic acid. Cells were counted in aliquots of suspended cells. Cell size was estimated by measuring cell area and by calculating the number of cells per milligram of cotyledon dry mass and the dry mass of an individual cell. Cell number per seed increased by 44 and 50% and cell area increased by 47 and 34% from the small to large seed class in Norcen and MU‐81, respectively. In the second study, seeds of MU‐81 were germinated and grown in a growth chamber. The number and area of cells in the expanding cotyledons were measured every 4 d for 20 d using methods similar to the first study, except that cotyledons were pretreated with a dilute pectinase solution prior to maceration in chromic acid. Cotyledon expansion was associated with an increase in cell size but not in cell number. Thus, the maximum size an expanding cotyledon could attain was limited by the number of cotyledon cells in a mature seed and their ability to enlarge.
Genotypic Differences in Carbon Isotope Discrimination by Cowpea under Wet and Dry Field Conditions
Authors: Hall A. E. , Mutters R. G. , Hubick K. T. , Farquhar G. D.
Published: July 2010

Theory and empirical evidence have demonstrated that 13C discrimination (∆) by leaves of C3 plants may be associated with intrinsic water‐use efficiency or productivity. Consequently, selection for ∆ has potential value in breeding plants with improved adaptation. This study evaluates genotypic differences in ∆ among cowpea [Vigna unguiculata (L.) Walp.] and genotype ✕ drought level interactions, and compares ∆ measured in leaves and grains. Sixty cowpea accessions were subjected to drought by growing them on stored soil moisture in six randomized blocks, and genotypes differed significantly (P < 0.001) in leaf ∆. Seventeen cowpea accessions were grown under weekly irrigation (wet) and stored moisture (dry) conditions in four randomized‐split blocks. Genotypes differed significantly in ∆ under both conditions using either leaves or grains. Plants under dry conditions had lower ∆, which theory predicted could be associated with 62% higher water‐use efficiency. The same plants showed a 62% higher ratio of CO2 assimilation rate to leaf diffusive conductance. Genotypic rankings for ∆ were similar under wet and dry conditions for most genotypes, but a significant (P < 0.05) genotype ✕ drought interaction was observed, which was mainly due to one genotype. Correlations between ∆ in grain and subtending leaves were highly significant (P < 0.001), but two genotypes exhibited substantial differences in ranking for ∆ determined in grain compared with leaves. Genotypic differences were more readily detected in leaves than grains with broad sense heritabilities of 0.76 and 0.35, respectively. Heritabilities were similar under wet and dry conditions.
Fructan Accumulation and Sucrose:sucrose Fructosyltransferase Activity in Stems of Spring Wheat Genotypes
Authors: Dubois D. , Winzeler M. , Nösberger J.
Published: July 2010

Stems of wheat (Triticum aestivum L.) accumulate water‐soluble carbohydrates (WSC) during the first 3 wk after anthesis. These reserves can later contribute to grain filling. Two spring wheat genotypes (‘Kolibri’ and breeding line D) were tested in growth chambers to determine if they differ in the accumulation of WSC components and in the activation of sucrose:sucrose fructosyltransferase (SST) in stem tissue. Concentration of CO2 was supplied at 1000 or 300 μL CO2 L−1 after anthesis to alter photosynthate production. The WSC accumulation in the penultimate internode during the first 18 d post anthesis (DPA) was substantially higher in Genotype D than in Kolibri. The WSC accumulation up to 7 DPA was due to increases in hexoses and sucrose. Sucrose concentration was initially lower in Kolibri than in Genotype D, but increased to a comparable level for both genotypes and both CO2 treatments. Fructan synthesis was initiated at 7 DPA. At 18 DPA, fructan was the dominant component of WSC. Under both CO2, treatments Genotype D accumulated substantially higher fructan concentrations than Kolibri. In a second experiment, induction of SST activity was observed during the first 9 DPA in the penultimate internode of plants grown at 1000 and 200 μL CO, L−1. There was a positive relationship between sucrose concentration and in vivo SST activity, suggesting that sucrose induced SST activity; however, Kolibri exhibited a much lower SST activity at given sucrose concentration. Thus, the low fructan synthesis of Kolibri is associated with an initial lower sucrose concentration and with a less effective activation of SST by sucrose.
Resistance to Hessian Fly from North African Durum Wheat Germplasm
Authors: Amri Ahmed , Hatchett J. H. , Cox T. S. , El Bouhssini M. , Sears R. G.
Published: July 2010

The development of new virulent biotypes continuously forces entomologists and breeders to search for new sources of resistance to protect common wheat (Triticum aestivum L.) from the Hessian fly, [Mayetiola destructor (Say)]. Two hundred and seventeen durum wheats (T. turgidum L. var. durum) from Tunisia were evaluated in a greenhouse for resistance to biotypes of GP, D, and. L of Hessian fly. Of these, 88, 86, and 59% were considered potential sources of resistance to biotypes GP, D, and L, respectively. Twenty‐five durum wheats from Morocco also were tested for resistance to biotypes D and L, and 60% were resistant to one or both biotypes. Four resistant Moroccan durum wheats, land races Oued Zenati and BD 1026 and cuitivars Jori and Hajj Mouline, were intercrossed and crossed to either or both of the susceptible checks ‘Zeramek S’ and ‘ACSAD 65’. Results from testing F2 populations, F2:3 families, and testcross F1:2 families to biotype D showed that Oued Zenati possesses two independent dominant genes for resistance. The other land race, BD 0126, has a single dominant gene apparently allelic or closely linked to one of the genes in Oued Zenati. Resistance in Jori and Hajj Mouline is controlled by the same single dominant gene, independent of the genes in Oued Zenati and BD 0126 and of the H9 and H10 genes in the durum wheat ‘Elva’. Thus, the three genes in the Morocco durum wheats appear to be different from the previously designated genes H1 through H13, based on species of origin and reactions to biotypes D and L and to populations of Hessian fly in Morocco. The identification of a large number of Hessian fly‐resistant durum wheats from Tunisia and Morocco, along with the presence of three independent genes in a sample of only four durum wheats from Morocco, indicates that North African durum germplasm is a rich source of new genes for resistance to Hessian fly in the USA.
Genetics of Kidney Seed in Gossypium barbadense L.
Authors: Turcotte E. L. , Percy R. G.
Published: July 2010

The Gossypium barbadense L. germplasm collection contains over 600 accessions listed in The National Collection of Gossypium Germplasm catalog. Kidney cotton, a distinctive type in which the seeds of each locule are conjoined into a single kidney‐shaped mass (kidney seed), represent more than 20% of the photoperiodic, shortday stocks in the barbadense collection. Several of these kidney cottons are characterized by a complex of traits and are known collectively as G. barbadense var. braziliense (Rafinesque) Fryxell. The objectives of the present study were to determine the inheritance of the kidney seed and its linkage relationships with other Gossypium mutants, and to reexamine the complex of traits associated with vat. braziliense. A day‐neutral stock with the kidney seed trait was derived from accession K0004 of vat. braziliense from Guatemala, and was crossed in appropriate combinations with day neutral, free seed ‘Pima S‐5’ for inheritance studies and with several genetic marker stocks for linkage studies. A survey was made of records of currently available descriptors of accessions of kidney cotton to determine what characteristics were associated with them. Experiments indicated that the kidney seed trait was under genetic control, that it is inherited as a monogenic recessive, and that it is not linked with 21 Gossypium mutant genes. The gene symbol k is assigned to the kidney seed trait. An expanded complex of characters was found to be associated with G. barbadense vat. braziliense.
Microspectrophotometry of Phenolic Compounds in Bermudagrass Cell Walls in Relation to Rumen Microbial Digestion
Authors: Akin D. E. , Ames‐Gottfred N. , Hartley R. D. , Fulcher R. G. , Rigsby L. L.
Published: July 2010

The amount and location of phenolic compounds within plant cell walls are important factors in limiting forage digestibility. The present study was undertaken to evaluate phenolic compounds within plant cell wall types that differed in digestibility in leaf blades of ‘Coastal’ (CB) and ‘Coastcross‐1’ (CX) bermudagrasses [Cynodon dactylon (L.) Pers]. The ultraviolet (UV) spectra of the cell wall types in bermudagrass leaf blades were obtained by microspectrophotometry and the results related to their digestibilities (measured by microscopy after in vitro incubation in rumen fluid) and to their histochemical reactions for phenolic compounds. Cell walls of all tissues gave three absorption peaks in the ranges of 317 to 324, 285 to 293, and 244 to 254 nm. Indigestible cell walls (sclerenchyma and mestomc sheath) had high UV absorbance (ca. 1.8 at 320 nm) and had positive tests with histochemical reagents for phenolics. In contrast, totally digestible cell walls (mesophyll and phloem) had low UV absorbance (ca. 0.2 at 320 nm) and had negative or weak reactions for phenolics. Partially digestible cell walls (parenchyma bundle sheath and epidermis) had intermediate UV absorbance (ca. 0.45 at 320 nm) and were positive for phenolics with chlorine‐sulfite and diazotized sulfanilic acid reagents. Comparison of cell wall types in leaf blades of CB and the more highly digestible CX showed that corresponding tissues of the two cultivars had similar UV absorbance values, with the exception of parenchyma bundle sheath; the parenchyma bundle sheath cell walls of CX had approximately two‐thirds the UV absorbance values of those of CB and were more digestible. Hence, improved digestibility of CX leaf blades appears to result from a lower concentration of phenolic compounds within cell walls of parenchyma bundle sheaths.
Two Methods for Characterizing Rooting Depth of Forage‐Legume Seedlings in the Field
Authors: Brar G. S. , Matches A. G. , Taylor H. M. , McMichael B. L. , Gomez J. F.
Published: July 2010

Because rooting characteristics are difficult to investigate, little research has been done on the root development of legume seedlings. Both the growth pouch and slant tube methods may provide rapid and relatively inexpensive methods for investigating seedling root development. Our objective was to determine the relationship between rooting depths of forage legumes grown in growth pouches and slant tubes with rooting depths in the field. Forage legumes were grown in slant tubes in the greenhouse and in growth pouches held in the dark at constant temperatures ranging from 10 to 30 °C and compared with rooting depths of the same legumes grown in the field. At 10 d after planting (DAP), root length in pouches for 20 and 25 °C were correlated (P < 0.01) with rooting depth (r2 = 8.87) in the field at 32 DAP. Root lengths in slant tubes at 14, 18, and 25 DAP were correlated (P < 0.01) with field rooting depth at 32 DAP and r2s were 0.69, 0.71, and 0.62, respectively. Thus, both growth pouches and slant tubes appear useful for screening rooting characteristics of forage legume seedlings.