bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Natural Selection in Advanced Generations of Barley Composite Cross II1
Authors: Hockett E. A. , Eslick R. F. , Qualset C. O. , Dubbs A. L. , Stewart V. R.
Published: July 2010

Barley (Hordeum vulgare L.) composite‐cross II (CCII) populations that had been grown over a long period in three environments in California and Montana were tested in 16 Montana and three California environments. The populations included F15 to F37 generations of CCII previously grown with natural selection at Moccasin and Bozeman, Mont. and Davis, Calif., local check cultivars, and a mixture of the original parents of CCII (P Mix). The CCII populations were generally higher yielding than the P mix which is an indication of improvement due to natural selection. Little or no differences were found among the various CCII populations which had been grown in the widely different environments of Montana and California. Populations developed at one site were not higher yielding at that site than populations developed at another site in seven of eight cases. Far superior progress has been made by conventional breeding, for example ‘Briggs’ and ‘Atlas 68’ yielded significantly more than the best populations under the disease and high‐yield conditions at Davis. The CCII populations tested in diverse environments in Montana also yielded less than local cultivars. When tested at Moccasin and Bozeman, however, where they had a developmental history of 12 to 24 years, the best CCII populations were equal in yield to the best cultivars. Yield stability of CCII populations in the 16 diverse environments was inconsistent; however, the population grown at Moccasin for 24 generations was more stable than ‘Unitan’ and ‘Ingrid,’ while eight populations were less stable than ‘Dekap’. The Davis‐developed material had higher kernel weight and percentage of plump kernels than the Montana‐developed populations. Test weight was highest in the Moccasin‐developed populations. There were no differences among the CCII populations for heading date, plant height, grain protein, and lodging resistance.
Genetic and Environmental Variance of Water Soluble Carbohydrate Concentration, Yield, and Disease in Tall Fescue1
Authors: Burner D. M. , Balasko J. A. , Thayne W. V.
Published: July 2010

Tall rescue (Festuca arundinacea Schreb.), a widely grown forage in southeastern USA, would be more useful as a livestock feed if its energy value, when grown in summer, were increased. The primary purpose of this study was to measure genetic and environmental variance of water soluble carbohydrate (WSC) concentration of summer regrowth forage harvested from a population of tall rescue derived from a world‐wide germ plasm collection. Variances of yield and disease rating were also measured. Forty‐five genotypes from each of 30 accessions (27 foreign collections and three domestic cultivars) were randomly chosen from a source nursery and established in space‐planted nurseries at three locations in West Virginia in 1980. At each location, three blocks contained plants representative of all 30 accessions. Each accession was present in each block and was represented by two clones of five randomly selected genotypes. Variance components of WSC concentration, yield, and disease rating were estimated by equating mean squares to expected mean squares of appropriate analysis of variance models. Genetic variances of WSC concentration, yield, and disease rating were 55, 65, and 75% of the total variances, respectively, and environmental variances were 42, 36, and 29%, respectively. The area ✕ accession components of the genotype ✕ environment (G ✕ E) interaction variance for WSC concentration, yield, and disease rating were 2.1, 1.5, and 3.4% of the total variances, respectively. The block ✕ accession within area components of G ✕ E variances for the three variables were nonsignificant. The high degree of genetic variance within the population indicates that there is potential for genetic improvement in all three variables. Under conditions of this experiment, interactions between genotypes and environments were minor; therefore, a potential for wide adaptability exists within the population.
Time Course of Photosynthesis and Stomatal Conductance Following Changes in Light Flux Density1
Authors: Setter Tim Lloyd , Flannigan Brian A.
Published: July 2010

Natural fluctuations in light flux density occur in field conditions as a result of intermittent cloud cover. In this study photosynthetic CO2 exchange rates (CER) and leaf water vapor diffusive conductance (g3) were determined for the time course following light flux density transitions. Leaves of two maize hybrids at the grain‐filling growth stage in field plots were enclosed in assimilation chambers and subjected to experimental increases and decreases in light flux density according to a prescribed schedule. Step increases in light required 2 to 3 min before steady‐state CER were achieved. Stomatal opening occurring in response to the light increase showed a time course paralleling that for CER. In response to step decreases in light, photosynthetic rate declined rapidly to a new steady‐state in less than 1 min while g3 continued to decline throughout the 4.3 min measurement period. The results show that water use efficiency for periods of fluctuating light was improved by rapid stomatal adjustment.
Effect of Salinity on the Functional Components of the Soybean‐Rhizobium japonicum Symbiosis1
Authors: Singleton P. W. , Bohlool B. B.
Published: July 2010

A split‐root solution culture system was used to partition the effects of salinity on the functional components of the soybean [Glycine max (L.) Merr] ‐ Rhizobium japonicum symbiosis. Nodules were confined to half of the root system. After nodules were well developed (40 days from planting), 120 mM NaCl was applied to the half‐root systems in the following combinations: 1)unstressed, no salt to either half‐root system; 2) partially stressed shoot and unstressed nodules, salt to only the nonnodulated halfroot system; 3) partially stressed shoot and stressed nodules, salt to only the nodulated half‐root system; and 4) stressed shoot and nodules, salt to both half‐root systems. Leaf osmotic potentials (ψs) for the four treatments were: 1) −1.02; 2) −1.12; 3) −1.23; and 4) −1.83 MPa. Nodule ψs for the treatments were: 1) −0.70; 2) −0.72; 3) −1.12; and 4) −1.21 MPa. While total and specific nitrogenase activity as well as shoot N content were suppressed in treatment 3, the greatest decrease in activity and shoot N was observed when the plant was stressed by having both half‐root systems in salt (treatment 4). The rate of leaf expansion in treatment 4 was half the rate observed in the other treatments. We conclude that reduced N2 fixation by nodulated soybeans growing in saline environments was more a result of the effect of salt on leaf ψs and expansion, than the direct action of salt on the functional processes of the nitrogenase system.
Utility of Higher Plant Densities for Corn Performance Testing
Authors: Troyer A. F. , Rosenbrook R. W.
Published: July 2010

We grew 84 different corn (Zea mays L.) performance tests in paired‐density comparisons averaging 51 600 and 64 500 plants per hectare over a 9‐year period to examine the utility of higher plant densities for corn performance tests. The higher density reduced yield test means from 76 to 73 q/ha, increased ranges among hybrids from 40 to 44 q/ha, and decreased hybrid F values for tests from 3.6 to 3.2. Broken stalk test means increased from 10 to 12%, ranges among hybrids increased from 35 to 39%, and hybrid F values for tests increased from 2.5 to 2.9 with the higher density. Dropped ears showed a large period‐of‐years effect due to effective selection. Testing at above optimum plant densities increased barrenness, stalk breakage, and ear droppage; it also increased the range among entries, thereby increasing the ease of selection against these traits. We analyzed 5 years' data from 250 strip tests comparing two widely grown hybrids at three plant densities and found that increased densities reduced number of tests needed to differentiate the hybrids. On the average twenty strip tests with alternate check strips grown at plant densities at or above 56 000 plants per hectare successfully differentiated (P = ca. 0.05) 7% yield at 75 q/ha average yield, 1.8% broken stalks at 5% average broken, and 2.4% root lodged at 2.5% average lodged; the two hybrids did not differ for dropped ears. Superior commercial hybrids resulted via higher plant density testing.
Screening Soybeans for Iron Efficiency in the Growth Chamber1
Authors: Byron D. F. , Lambert J. W.
Published: July 2010

Evaluation of soybean genotypes for iron efficiency usually has been done in the field. A quick and repeatable method of evaluating soybean genotypes in the greenhouse or growth chamber is desirable due to variable results in the field and the opportunity for evaluation in the winter. Ten soybean [Glycine max (L.) Merr.] genotypes were evaluated for Fe efficiency in a Canisteo clay loam (Typic Haplaquoll, fine‐loamy mixed, calcareous) in the field and in the growth chamber. They were also evaluated in six Fe‐stress nutrient solutions in the growth chamber. The concentrations of Fe (1.8 or 3.6 µM), CaCO3 (0 or 2.5 mM), and P (130 or 200 µM) were varied in the nutrient solutions with the intent of identifying which combination of these nutrients would give chlorosis symptoms comparable to those found in the field. Visual scores ranging from 1, completely green, to 5, bleached yellow, were determined on the first four trifoliolate leaf stages in the growth chamber studies and on the fourth trifoliolate leaf stage in the field study. Plants at the second trifoliolate leaf stage in the growth chamber showed the greatest degree of chlorosis, and evaluation of genotypes was most effective at this stage. Chlorosis symptoms were much less severe in the growth chamber than in the field, when calcareous soil was the growth medium. The use of calcareous soil in the growth chamber appears to be inadequate for determining Fe‐efficiency of soybeans. The 1.8 µM concentration of Fe and the 2.5 mM concentration of CaCO3 provided an adequate medium for depicting differences among genotypes in the nutrient solutions. The low concentration of Fe and the pH control of CaCO3 resulted in an Fe‐stress similar to that in the field. The 200 µM concentration of P resulted in greater Fe‐stress but was not necessary for differentiating among genotypes for Fe‐efficiency. Of the 10 genotypes, ‘Hawkeye’ and ‘Swift’ were most Fe‐efficient; ‘Hodgson’ and ‘Chippewa 64’ were moderately Fe‐efficient; ‘Harcor’, ‘Corsoy’, ‘Hark’, ‘Anoka’, and ‘Altona’ were Fe‐inefficient; and PI 54619 as highly Fe‐inefficient.
Resource Allocation in Breeding for Fatty Acid Composition of Soybean Oil1
Authors: Hawkins S. E. , Fehr W. R. , Hammond E. G.
Published: July 2010

The objective of this study was to determine the allocation of testing resources that would provide the greatest genetic improvement for fatty acid composition in soybean [Glycine max (L.) Merr.] oil. Twenty random lines of maturity groups I to III were evaluated in two replications at seven environments in Iowa and Puerto Rico. The percentages of palmitic, stearic, oleic, linoleic, and linolenic acid were determined for two consecutive injections (analyses) of oil into a gas chromatograph from two 20‐seed samples from each of two plants per plot. Heritability estimate averages across fatty acids were 49% on a seed‐sample basis, 55% for plants, 63% for plots, and 93% for entry means. Two consecutive analyses were of little or no value for increasing the heritability of the five fatty acids compared with one analysis of an oil sample. The heritabilities for individual plant evaluation were effectively increased by analyzing more than one seed sample per plant. Evaluation of one sample from multiple plants in a plot was more effective than multiple samples from one plant when evaluating a pure line. Plot‐to‐plot variation was so small that evaluation of multiple plants in one plot was as effective as evaluation of multiple replications. The use of multiple environments was effective for increasing the heritabilities of the five fatty acids.
Growth, Development, and Alkaloid Content of Doubled Haploids vs. Inbreds of Burley Tobacco1
Authors: Kasperbauer M. J. , Legg P. D. , Sutton T. G.
Published: July 2010

Plants with improved morphological and chemical characteristics can be developed more rapidly through haploid and doubled haploid methods than through conventional inbreeding, but plants derived by the two methods need to be compared. Growth and developmental characteristics of first and second cycle doubled haploids were compared with those of highly inbred plants of five burley tobacco (Nicotiana tabacum L.) cultivars. When averaged across cultivars, doubled haploids flowered later and developed smaller plants that produced less cured leaf with lower alkaloid content than did the inbreds. Within cultivars, there were some developmental differences among first cycle doubled haploid lines derived from different microspores from a given inbred plant. Differences observed among first cycle doubled haploid lines were evident in the second generation families, indicating genetic rather than environmental cause. Some additional differences were noted among second cycle doubled haploid lines derived from anthers cultered from a given first cycle doubled haploid plant. The amount of variability among second cycle doubled haploid lines from a first cycle doubled haploid plant differed among the five cultivars, and in most cases was less than that observed among the first cycle doubled haploids of the same inbred plant. Although there were some variations among doubled haploid lines, variances among plants within plots for time of flowering and number of leaves per plant indicated that there was more uniformity among selfed progeny within doubled haploid lines than among selfed progeny within inbred lines. Haploids and doubled haploids offer an excellent meant so obtain tobacco lines with modified chemical and morphological features. However, some mutations may occur in the process, and utilization of doubled haploids should involve confirmation of the characteristics of each line before using it in physiological investigations or in plant breeding.
Alfalfa Response to Soil Water Deficits. III. Nodulation and N2 Fixation1
Authors: Carter P. R. , Sheaffer C. C.
Published: July 2010

Our objective was to determine the effect of plant and soil water deficits and forage harvest on alfalfa (Medicago sativa L.) nodulation and N2 fixation. In a field study on Typic Hapludoll (silt loam) soil, nitrogenase specific activity (NSA), nodule numbers, and shoot and root growth of irrigated and nonirrigated alfalfa were measured during a harvest/regrowth cycle. In a glasshouse study with Udorthentic Haploboroll (loamy sand) soil, NSA, nodulation, shoot and root growth, and root total nonstructural carbohydrate (TNC) concentration of nonharvested and harvested alfalfa were monitored during two successive harvest/regrowth cycles. Both harvest treatments were subjected to a range of soil and plant water deficits. Forage harvest decreased NSA and root TNC concentration for well‐watered alfalfa, but changes in NSA for water‐stressed plants were more associated with fluctuations in plant water (ψp) and soil matric (ψm) potentials than to removal of herbage or level of root carbohydrates. Nitrogenase specific activity declined linearly as ψp decreased to −3.0 MPa, at which point activity approached zero. Alfalfa nodules subjected to severe water stress were able to resume activity when soil moisture levels were restored. Nodulation was inhibited by well‐watered conditions (mean ψm of −0.015 MPa) in the silt loam and by soil water deficits (mean ψm of −0.07 to −0.51 MPa) in the loamy sand.
Role of Panicle Exsertion in Water Stress Induced Sterility1
Authors: O'Toole J. C. , Namuco O. S.
Published: July 2010

Although the sensitivity of crop species to water stress during reproductive growth stages is well documented, the causes of sterility are not understood. The role of decreased panicle exsertion as a causal factor of spikelet sterility in water stressed rice (Oryza sativa L.) was investigated. Rice cultivar IR36 was grown on a deep silty loam soil under full sprinkler irrigation for 77 days. A line source sprinkler system was then utilized during panicle exsertion and flowering to impose six continuously decreasing irrigation treatments. After the 15‐day treatment period, full sprinkler irrigation was resumed until maturity. Soil moisture extraction and plant water potential were monitored as soil and plant water stress progressed. Panicle exsertion rate was measured on tagged panicles which were later used to assess percent final panicle exsertion and percent sterility. The six irrigation treatments varied in grain yield from 5.0 t ha−1 to about 1 t ha−1 with corresponding increases in spikelet sterility of 16.6 and 74.2%. Panicle exsertion rate decreased linearly with decreasing mean daily leaf water potential. The degree of final panicle exsertion from the flagleaf sheath and percent spikelet sterility both decreased linearly with panicle exsertion rate. All spikelets left unexserted from the flagleaf sheath were sterile. Panicle exsertion rate was slightly confounded by tiller age in that late tillers in the well irrigated treatment had a slower exsertion rate and higher percent sterility than earlier tillers. The early tillers which exserted at rates of 4.5 to 5.5 cm day−1 under well watered conditions decreased to about 3.0 cm day−1 in the stressed plot and accounted for 25 to 30% spikelet sterility in the severely stressed treatment.
Leaf Injury and Peroxidase Activity in Ozone‐Stressed Tobacco Cultivars and Hybrids1
Authors: Petolino J. F. , Mulchi C. L. , Aycock M. K.
Published: July 2010

Ozone‐induced leaf injury and peroxidase activities in tobacco (Nicotiana tabacum L.) were studied under greenhouse and field conditions to determine if the stimulation in peroxidase activity could be used as a genetic marker for ozone induced biochemical stress. Greenhouse experiments involving four cultivars and six F1 hybrids of Maryland tobacco were conducted during 1979 and 1980 and field experiments involving seven cultivars and 21 F1 hybrids from a diallel set of crosses were grown in two environments at the University of Maryland Tobacco Experimental Farm during the summer of 1980. Plants were exposed to either charcoal‐filtered air or charcoal‐filtered air plus added ozone in partially open.topped fumigation chambers. Ozone levels used in the greenhouse exposures were 8.1 ✕ 10−6 mol m −3 for 6 h day−1 for 2 days. Field ozone exposures were 4.9 ✕ 10 −6 mol m−3 for 6 h day−3 for 9 days. Visual leaf injury ratings and peroxidase activities were determined for the various treatments. Ozone exposure resulted in considerable visual leaf injury. All cultivars and hybrids exhibited some degree of foliar damage and significant differences were observed among the entries in both greenhouse and field exposures. ‘Md 872’ was consistently the most tolerant entry while ‘Md 59’ and ‘Bel‐W3’ appeared most sensitive with respect to foliar damage. Peroxidase activity was significantly higher in plants exposed to ozone as compared to the controls. Stimulation in peroxidase activity upon exposure to ozone was evident in all entries regardless of the amount of visual foliar injury which suggests that this enzyme may not be a reliable marker for ozone tolerance in tobacco. There was a general lack of genotype ✕ environment interaction for visual responses to ozone stress; however, peroxidase activity appeared to be highly sensitive to environmental changes.
Field Assessment and Inheritance of Resistance to Cassava Bacterial Blight1
Authors: Umemura Yoshiki , Kawano Kazuo
Published: July 2010

Cassava bacterial blight (CBB), caused by Xanthomonas campestris pv. manihotis (Berthet and Boudar) Dye, caused 18 to 92% yield reduction on susceptible cassava (Manihot esculenta Crantz) clones relative to resistant clones depending on location, planting time, and level of simultaneous infection by superelongation disease caused by Elsinoe brasiliensis. Root dry matter content of susceptible clones was much lower than that of resistant clones. Susceptible clones did not produce planting stakes for next planting. No cassava clone under study was immune to CBB. Cultivar order of resistance was stable over years. The CBB on leaves of resistant clones spread slowly while on susceptible clones it spread rapidly causing defoliation and death of stem. Resistance appeared to be a quantitatively inherited trait (h2 = 0.63) largely controlled by additive genetic factors and was not negatively correlated with yielding ability per se. Cassava resistance to CBB is highly effective in minimizing damage caused by CBB, and use of resistant parents in hybridizations combined with simple phenotypic field selection under high natural disease pressure should effectively improve resistance of cassava cultivars.
Nitrogen Response of Panicum Species Differing in CO2 Fixation Pathways. I. Growth Analysis and Carbohydrate Accumulation1
Authors: Wilson J. R. , Brown R. H.
Published: July 2010

The apparent higher N use efficiency (NUE) of tropical than temperate grasses could be associated with the more efficient C4 cycle of CO2 fixation possessed by tropical grasses. This possible association between NUE and the CO2 fixation pathway was tested on five Panicum species with different pathways. P. maximum Jacq. (C4), P. prionitis Griseb. (C4), P. hylaeicum Mez (C3), P. laxum Sw. (C3), and also the intermediate (C3/C4) species, P. schenckii Hack. were grown at day/night temperatures of 35/30 and 24/ 19°C. Plants were grown initially in complete nutrient solutions and then in N‐free solutions. Measurements of relative growth rate (Rw), leaf expansion, and leaf CO2 exchange rate (CER) made just before and during the N withholding period. Panicum maximum maintained a higher Rw, than the other species over a wide range of plant N status and had the highest maximum NUE of 6.1 kg of dry matter kg−lN day−1. Panicum prionitis did not show the same absolute advantage in Rw nor NUE over the C3 species. However, both C4 species generally showed a smaller relative decline in growth and CER at low N status than the C3 and C3/C4 species. Leaf area expansion was more sensitive to N stress than CER and there was some evidence that the C4 species were able to continue leaf development at lower leaf N concentrations than the C3 species. Growth temperature did not cause qualitative differences in the response to N, but NUE (kg kg−1 N day−1) was higher at 35/30°C than 24/19°C, except for P. schenckii. Morphological differences between species such as stem development also appeared to contribute to changes in Rw with development of N deficiency. It is concluded that the inherently higher efficiency of the C4 photosynthetic pathway does not necessarily lead to higher NUE of dry matter production of tropical grasses.
Effects of Chronic Doses of Ozone and Sulfur Dioxide on Injury and Yield of Soybeans in Open‐Top Field Chambers1
Authors: Heagle Allen S. , Heck Walter W. , Rawlings John O. , Philbeck Robert B.
Published: July 2010

Soybeans, Glycine max (L.) Merr. ‘Davis’, were exposed for 7 h day−1 (111 days) to six concentrations of ozone (O3) and for 4 h day−1 (101 days) to four concentrations of sulfur dioxide (SO2), singly and in mixtures (24 combinations). The pollutant concentrations were selected to span those that occur in major soybean production areas of the USA. The pollutant dose‐yield response relationships were modeled using regression analyses and a Weibull model analysis. Both analyses indicated that a dose of O3 typical for soybean production areas (seasonal 7—h day−1 mean of 0.055 ppm v/v) caused a seed weight decrease of 20% compared to a control dose of 0.025 ppm O3. Sulfur dioxide at levels known to exist regionally in the USA (seasonal 4—h day−1 mean of <0.026 ppm SO2) did not cause injury or affect soybean yield. Neither pollutant changed the dose‐response relationships for the other except at high concentrations where the effect of mixtures was less than the additive effects of the pollutants singly. The dose‐response relationships were similar for each of two soil types.
Selection Indexes to Modify Protein Concentration of Soybean Seeds1
Authors: Openshaw S. J. , Hadley H. H.
Published: July 2010

The purpose of this study was t~a investigate the effectiveness of selection based upon selection indexes to modify protein concentration of soybean [Glycine max (L.) Merr.] seeds. Selection criteria were compared by evaluating F4 performance of F2‐ derived lines identified in the F3 as being in the upper 10% of the population. Smith‐Hazel indexes designed to maximize the gain in protein by including oil or oil and sugar as secondary traits were not more effective than direct selection, which resuited in changes of 1.42% protein and −1.14% oil. Smith‐Hazel indexes which gave protein and oil equal economic weights, either including or not including sugar as a secondary trait, and a desired gains index with desired gains set at 1.0% protein and 0.25% oil were all similar in results to selection based on the sum of protein + oil. Among these methods, changes ranged from 0.15 to 0.31% for protein anti from −0.01 to 0.19% for oil. An index designed to change protein by 1.25% and oil by −0.75% produced observed changes of 1.31 and −0.81%. An index designed to increase protein as much as possible while holding oil constant resulted in changes of 0.45% protein and −0.13% oil. This index was more effective than selection for protein following culling oil at the mean, which resulted in little change for either trait.
Genetic Yield Improvement of U.S. Maize Cultivars under Varying Fertility and Climatic Environments1
Authors: Castleberry R. M. , Crum C. W. , Krull C. F.
Published: July 2010

Yield of decade groups of maize (Zea mays L.) cultivars typical of those used by U.S. Corn Belt farmers in each of the decades since 1930 was evaluated across a range of soil fertility and climatic environments. This study gave estimates of the rate of genetic improvement in yield for each environment. In addition, a measure of the advisability of continued development and deployment of high yielding, management responsive single cross maize hybrids in light of potential reductions in fertilizer inputs and potentially less favorable future climatic conditions was provided. These cultivars were grown in replicated field trails in a total of 11 environments from Tennessee to Colorado in 1980 and 1981. All plots were grown according to accepted modern agronomic practices except that a low soil fertility treatment was included in both years and two limited irrigation stress treatments were included in 1981. Mean yield of cultivars from more recent decades was consistently higher than those from older decades across or within environments. Regression analysis of mean decade group yield on decade of use within each environment and on an environmental index (treatment/location/year mean yield) across environments gave significant correlations and b values which were always positive, regardless of environment. These results are consistent with the conclusion that U.S. maize production will be best served by the continued development and deployment of improved single cross maize hybrids even if less favorable soil fertility or climatic conditions should Occur.
Inheritance of Boron Status in Sunflower1
Authors: Blamey F. P. C. , Vermeulen W. J. , Chapman J.
Published: July 2010

The breeding of sunflower (Helianthus annuus L.) cultivars adapted to soils low in available boron (B) may have particular relevance since this crop has a high B requirement and B deficiency is widespread in certain sunflower‐producing areas. A field study was carried out on a Doveton clay loam (thermic Typic Rhodustult) in which six sunflower inbreds and their 15 hybrids (excluding reciprocals) were tested for differences in status as measured by the B concentration in the topmost mature leaf at flowering. The 21 entries were grown with and without B fertilization. Significant differences were recorded among parents, among offspring, and between parents and offspring with respect to B concentrations in the leaf, number of plants with B deficiency symptoms, and seed yields. Highly significant general combining ability (GCA) effects were recorded, whereas the specific combining ability effects generally were nonsignificant. Highly significant positive correlations were recorded between the means and the GCA effects of the inbreds in the characters measured. It was concluded that the susceptibility of a hybrid to B deficiency could be predicted from the performance of its parents since those inbreds with a high B status readily passed this character to their offspring.
Canopy Structure and Photosynthesis of Alfalfa Genotypes Differing in Nodule Effectiveness1
Authors: Boller Beat C. , Heichel G. H.
Published: July 2010

Photosynthesis is linked to N2 fixation and to other plant metabolic processes, but little is known of how N2‐fixation capability affects the development of the leaf canopy and leaf photosynthetic rates. Field experiments were undertaken to determine the effect of differences in N2‐fixation capability mediated by plant genes on canopy structure and apparent photosynthesis of alfalfa (Medicago saliva L.). An alfalfa genotype lacking the capability of establishing an effective symbiosis with Rhizobium was compared to normal alfalfa. Entries were grown at two rates of supplemental N (0 and 100 kg ha−1 as NH4NO5) to provide genetic‐ and culturally‐controlled differences in N2 fixation. Hostmediated genetic differences in N2‐fixation capability (ineffective vs. effective nodules) elicited pronounced changes in rates of apparent photosynthesis, canopy structure, and specific, leaf weight. Compared with alfalfa having effective nodules (Eff), alfalfa with ineffective nodules (In) averaged 17% greater specific leaf weight, but 73% less leaf area over both N regimes and three growth‐harvest cycles. For unshaded leaves at the top of the canopies, rate of apparent photosynthesis per leaf area of In was similar to that of Eff on vegetative plants 2 weeks before harvest and in canopies at 5% flower. Leaf canopies of In contained a more vertically uniform leaf area than Eff canopies unless they were supplied with 100 kg ha−1 combined N. In vegetative In plants 2 weeks before harvest, supplemental N at a rate of 100 kg ha−1 enhanced leaf area by 50%, but tended to reduce rate of apparent photosynthesis per leaf area. In Eff plants at this same growth stage, supplemental N also reduced apparent photosynthesis, but leaf area was not affected. In canopies at 5% flower, supplemental N did not change rate of apparent photosynthesis of either In or Eff. These results show that N stress induced by host‐mediated ineffective nodulation greatly reduced leaf area and photosynthetic rate per ground area, but that effective nodules were not a prerequisite for maintaining normal photosynthetic rates per leaf area even under severely limiting soil N supply.
Shade Effects on Growth, Partitioning, and Yield Components of Peanuts1
Authors: Hang A. N. , McCloud D. E. , Boote K. J. , Duncan W. G.
Published: July 2010

Peanut (Arachis hypogaea L.) may have one or more periods during development when low solar radiation intensity is particularly detrimental to high yield. The present studies were conducted in the field to determine the effect of shade on vegetative growth, partitioning of assimilates and yield components of peanut. In a 2‐year experiment, 75% shade was applied for 7, 10, 14, or 21 day periods during flowering, pegging, podding, and maturing phases. The objective was to determine which reproductive phase was most sensitive to low solar radiation intensity. Flower number, peg development, pod formation, and dry matter accumulation and partitioning were measured at regular sampling intervals. Shade during the peak flowering period reduced the number of flowers per plant and inhibited peg formation. Shade during the pegging and podding phases reduced total peg and pod number and reduced pod dry weight. Shade during the maturing phase reduced seed fill as shown by reduced shelling percentage and a lower number of fruits achieving mature pod status. On the average, over all stages, 75% reduction of light intensity decreased the growth rate of vegetative parts by 85%, the reproductive growth rate by 67%, and the total biomass growth rate by 67%. Shade prior to podding increased partitioning to vegetative growth, by 20%, whereas shade during the podding phase (83 to 104 days) increased dry matter partitioning to pods by 127%. Seventy‐five percent reduction in solar radiation intensity reduced yield of Florunner peanuts significantly only when the duration was for 14 or 21 day periods. Podding was the phase in which yield was most sensitive to shade with a 30% reduction in fruit yield from shade during 83 to 104 days of age. The maturing phase was next in sensitivity to shade, which decreased yield primarily by decreasing seed fill in existing fruits. Twenty‐one days of shade at flowering did not reduce final fruit yield, since the plants had time to recover from the loss of active flowers and subsequently bear flowers and produce a normal pod load.
Evaluation of Alien Chromosome Addition and Recombinant Isolines of Wheat1
Authors: Soliman K. M. , Qualset C. O.
Published: July 2010

Chromosome addition isolines (2n=44) and a recombinant isoline (2n=42) of common wheat (Triticum aestivum L.) were developed by selection of hemizygous or heterozygous plants having a blue aleurone (BA) gene from Elytrigia pontica (Podp.) Holub (syn. Agropyron elongatum (Host) P.B.) for 12 generations. This method of producing spontaneous interspecific chromosome recombination was simple to apply and had the advantage of simultaneously producing isolines. The BA isolines were compared to their nonblue aleurone (NBA) counterparts in field experiments. Protein and lysine percentage in the grain was enhanced by 15 to 20% in the 2n=44 BA addition lines, but no enhancement was found in the 2n=42 BA recombinant line. The enhanced protein in the addition lines was associated with lower fertility, grain yield, and kernel weight while these defects were not found in the BA recombinant line. Increased spikelet number, spike length, and rachis internode length, were expressed in BA recombinant and addition lines. Thus, those characters were intiuenced by the Elytrigia chromosome, but the enhanced protein effect was largely attributed to effects of aneuploidy. Reduced fertility in the BA addition isolines was believed to be the primary cause for lower grain yield and higher grain protein concentration than in NBA (2n=42) lines.
Effect of Recurrent Phenotypic Selection on Resistance to Purple Leaf Spot in Orchardgrass1
Authors: Zeiders K. E. , Berg C. C. , Sherwood R. T.
Published: July 2010

Genetic resistance to important diseases of forage grasses is considered to be the only practical means of reducing economic losses in yield and quality. The objective of this research was to determine the effectiveness of recurrent phenotypic selection as a method of breeding for resistance to purple leaf spot caused by Stagonospora arenaria Sacc. in orchardgrass (Dactylis glomerata L.). The initial selections were made from a source population of 28 cultivars (cycle 0). Four cycles of selection and two cycle‐comparison tests were conducted in the greenhouse. In a test comparing cycles 0, 1, 2, and 3, there were significant differences in size and frequency of purple leaf spots among entries within each cycle and among cycle means. Mean spot size and frequency for cycle 3 were markedly lower than for any previous cycle. In a four‐cycle comparison test, mean ratings for spot size and frequency were lower for cycles 3 and 4 than for previous cycles. The mean spot size and spot frequency ratings for cycle 4 were significantly lower than for cycle 3. The percentage of plants in the different severity classes shifted progressively towards higher percentages with lower ratings in each successive cycle. However, even in cycle 4, 7 to 10% of the progeny were rated susceptible. The correlation between spot size and spot frequency rating (3 df) was 0.97, significant at P < 0.01. There was a consistent significant effect of scorer on spot size rating for all tests, and in most instances on spot frequency rating. Methods of inoculation and incubation have been developed that were effective and reliable in screening for resistance to purple leaf spot. Four cycles of selection effectively increased the level of resistance to purple leaf spot in orchardgrass.
Relationships Among Male‐Sterility Inducing Cytoplasms of Sorghum1
Authors: Worstell J. V. , Kidd H. J. , Schertz K. F.
Published: July 2010

Cytoplasmic‐nuclear male steriles are used as female parents in the production of hybrid seed of sorghum, Sorghum bicolor (L.) Moench. A single male‐sterility inducing cytoplasm is most often used in the female parents, resulting in uniformity of cytoplasm in hybrids and also a restriction on nuclear diversity. The purpose of the present study was to identify diverse malesterility inducing cytoplasms. Seed set and other characteristics of hybrids of sorghum were studied to determine differences in fertility response and related characteristics among the cytoplasms of male‐sterile female parents. Thirteen near‐isonuclear female parents with cytoplasms from diverse introduced sources were crossed by eight male parents, and the progeny were grown at eight locations. From seed‐set, anther, and pollen characteristics five groups were identified. Cytoplasms from IS6271C, IS2266C, IS3579C, IS7502C, and IS6705C were not distinguished from milo cytoplasm. Cytoplasm from IS12662C differed from milo in degree of fertility restoration in hybrids and was somewhat similar to IS3063C, IS1056C, and IS2801C. Another group, composed of IS1112C and IS12565C, was distinct in that most male parents produced highly sterile hybrids when crossed with these male steriles. Another cytoplasm, from IS7920C, differed from all the other cytoplasmstudied in its effects on seed‐set, anther, and pollen characteristics. It is concluded that among these cytoplasms there are at least four distinct groups in their effects on fertility characteristics. They have potential for providing diversity among parents and hybrids in sorghum, but their utility for such purposes remains to be tested.
Photosynthate Partitioning in Pigeonpea in Response to Defoliation and Shading1
Authors: Setter Tim Lloyd , McDavid Charles R. , Lopez Francis B.
Published: July 2010

The effect of shading or defoliation on reserve carbohydrate distribution in pigeonpea [Cajanus cajan (L.) Millsp.] plants was investigated and the potential value of vegetative organs as photosynthate reservoirs was assessed. Plants were grown to the pod‐filling stage, labeled with 14CO2, and nonstructural carbohydrate levels were determined. Glucose, sucrose, and starch were present at low concentrations [less than 30 g (kg dry wt) −1 total] in roots, stems, and leaves of control plants. Defoliation reduced glucose plus sucrose levels after 24 h by 44 and 64% in stem and pod wall, respectively. Starch contents in pod walls were reduced by 53%. Shading for 24 h reduced sugar levels in leaves, stems, and pod walls by 43, 35, and 42%, respectively, and reduced starch levels in leaves by 70%. Specific radioactivities after pulse 14CO2 labeling were higher in leaves (excluding 14CO2‐fed leaves) and pod walls following shading or defoliation, consistent with the lower degree dilution from nonradioactive current photosynthate.
Stability of ‘Saratoga’ Bromegrass Populations from Different Breeder Seed Syntheses, Locations of Seed Production, and Seed Maturities at Harvest1
Authors: Rincker C. M. , Dean J. G. , May R. G.
Published: July 2010

Information is not available on the extent of population shifts, if any, in synthetic cultivars of smooth bromegrass resulting from seed multiplication in diverse environments, methods of breeder seed synthesis, or seed maturity at harvest. Objectives of our research were to determine effects of two methods of breeder seed syntheses, three diverse locations of seed production, and three seed maturities at harvest upon the population stability of ‘Saratoga’ smooth bromegrass (Bromus inermis Leyss.). Polycross seed was produced in vegetatively established nurseries at Shafter and Tehachapi, Calif., and Prosser, Wash. At each location two breeder seed lots were synthesized using 1) equal parts of pure live seed from each of the 5 parental clones, or 2) portions equivalent to relative seed yields. These lots, plus similar blends produced at Ithaca, N.Y., were used to plant four isolated increase blocks at the three western locations to produce second generation seed harvested at early, optimum, or late maturity. The second generation seed lots, including the original breeder seed blends, were evaluated in a space‐planted nursery at Prosser in 1978 and 1979. Four plant characteristics were measured: heading date, anthesis date, plant height, and rhizome spread after 2 years. Plants from second generation seed produced at Shafter tended to be taller with less rhizome spread than those from Prosser or Tehachapi. Otherwise there were no consistent trends to indicate that methods of synthesizing breeder seed or location of production affected the population characteristics. Maturity of seed at harvest had no effect on plant characteristics. Based on these results we concluded that even though the parental clones were significantly different, the Saratoga bromegrass synthetic, and perhaps other bromegrass synthetics, would be very stable under differing management and environmental conditions.
Integrated Stomatal Opening as an Indicator of Water Stress in Zea1
Authors: Fiscus Edwin L. , Wullschleger Stan D. , Duke Harold R.
Published: July 2010

A technique based on mass flow porometry is described which allows continuous monitoring of stomatal aperture in the field. The relationship between the integral of the light intensity for a 24‐h period (ILI) and the integral of the stomatal opening (ISO) of well exposed leaves for the same period provides a very sensitive indicator of the onset of stress. Experimental data from 2 years of operation in the field showed good year to year agreement between the maximum ISO values attainable at any ILI.
Performance and Stability of Doubled Haploid Lines of Upland Cotton Derived via Semigamy1
Authors: Mahill Joel F. , Jenkins Johnie N. , McCarty J. C. , Parrott W. L.
Published: July 2010

Doubled haploid lines of cotton (Gossypium hirsutum L.) derived via semigamy and colchicine doubling from diverse parental strains were evaluated for yield in several year‐location environments in Mississippi in 1980 and 1981. Experiments were conducted to determine agronomic performance and fiber properties of 15 doubled haploid lines. Selected doubled haploids, their parental strains, and commercial cultivars were evaluated in 1980 for allelochemic compounds alleged to confer resistance to the tobacco budworm, Heliothis virescens (F.). Stability parameters were determined for seed cotton yield and allelochemics using linear regression analyses to estimate regression coefficients (b values) and coefficients of determination (r2 values). A genotype was considered environmentally stable when a unit change in genotype performance corresponded to a unit change in environmental index. The hypothesis, Ho: β = 1.0, or no significant difference between the performance of a cotton line and the mean performance of all lines over environments was tested for each strain. Agronomic and fiber traits were improved for some doubled haploids but were inferior for other traits compared with their respective parental strains. Generally, doubled haploid lines were as environmentally stable for yield performance as parental strains. This was also true for within‐season variability of allelochemic compounds. Heterogeneity of a strain or cultivar was not an apparent prerequisite for environmental buffering effects. Cumulative expression of genetic traits may play a more important role in maintaining environmental stability than relative heterozygosity.
Selection for Salt‐Resistant Spring Wheat1
Authors: Kingsbury R. W. , Epstein Emanuel
Published: July 2010

Salt buildup in agricultural soils threatens irrigation agriculture in arid and semiarid regions of the world. Development of salt resistant crops may allow increased production in areas plagued by salt. Although ample sources of genetic diversity exist for most of the major crops, adequate screening methods for isolating salt‐resistant lines have yet to be developed. Wheat was chosen as a test case to investigate the current availability of salt‐resistant germplasm in the world collection. Over 5000 accessions of hexaploid wheat were screened in solution culture salinized with sea salt. Screening at 85% seawater yielded 312 individual selections capable of vigorous growth at germination and emergence. These were recovered and transferred to nonsaline conditions for seed multiplication. Subsequent screening of the next generation was done over the entire life cycle at 50% seawater, resulting in the isolation of 29 salt‐resistant lines. Salt‐sensitive lines were visually evaluated for uniformity of leaf damage at 25% seawater. Three resistant and two sensitive selections were compared with ‘Anza’ and ‘Kharchia’ for biomass production in solution cultures salinized to 20, 40, and 60% seawater. At the highest salinity, average biomass production was 6.4% of the controls for the resistant selections, 5.9% for ‘Kharchia’, 3.7% for ‘Anza’, and 1.6% for the sensitive selections. These results indicate that screening wheat at high salinities over a single generation can be effective in identifying salt‐resistant genotypes.
Heritability of Trichome Density and Droplet Size in Interspecific Potato Hybrids and Relationship to Aphid Resistance1
Authors: Mehlenbacher Shawn A. , Plaisted Robert L. , Tingey Ward M.
Published: July 2010

The heritability of three glandular trichome traits and their relationship with resistance to the green peach aphid (Myzus persicae Sulzer) was investigated in a population of Solanum tuberosum ✕ S. berthaultii hybrids. Droplet size of type B trichomes was highly heritable (64 ± 8%). Density of type B trichomes was intermediate in heritability (22 ± 5%). Density of type A trichomes was variable both within and among leaves of the same clone. A low heritability estimate (18 + 3%) was obtained when seedling counts were used as parental values, but a higher estimate (32 ± 7%) was obtained when multiple counts on field‐grown plants were used. None of the three traits taken singly was significantly correlated with suppression of Myzus persicae populations in field trials, although F2 and F3 hybrids with high levels of aphid resistance were recovered. The resistance of Solanum berthaultii Hawkes appears to be due to a complex interaction of chemical and physical factors, and should be handled by potato breeders as a quantitatively inherited trait.