bluuebunny/crossref_metadata_2025 huggingface dataset:
Variability in Root‐Knot Nematode Resistance within the Genus Alysicarpus1
Authors: Taylor S. G. , Baltensperger D. D. , Quesenberry K. H. , Dunn R. A.
Published: July 2010

Root‐knot nematodes (Meloidogyne spp.) are a major limiting factor in the establishment and growth of many forage legumes, including alyceclover [Alysicarpus vaginalis (L.) DC.], which is highly susceptible to three Meloidogyne species. An extensive collection of Alysicarpus germplasm was evaluated for variability in Meloidogyne susceptibility to determine the feasibility of developing resistant cultivars. Germplasm was evaluated in two field (Arredondo fine sand) and two greenhouse tests. Variation in response to Meloidogyne spp. was identified in the Alysicarpus germplasm. Accessions FL‐1, FL‐4, FL‐5, and FL‐7 had overall mean gall scores of less than 2.0 (0 = no galls; 5 = more than 100 galls) when infested with M. incognita race 3. Accessions FL‐1, FL‐3, and FL‐4 received mean gall scores of less than 1.0 in response to M. javanica, while FL‐2, FL‐5, and FL‐7 had ratings of less than 2.0. M. arenaria race 1 was the most aggressive pathogen as only FL‐3 had a mean gall score of less than 2.0. No one line was highly resistant to all three Meloidogyne spp., suggesting the need for hybridization. Galling was highly correlated (r = 0.98) with egg mass production in the a!yceclover germplasm. Greenhouse and field results were also highly correlated (r = 0.61 to 0.89), so accessions resistant in the greenhouse were also field resistant. The level of Meloidogyne infestation achieved in Field Experiment 2 did not adversely affect yield, nodulation, or crude protein percentages. Broad sense heritabilities (47 ‐ 78%) indicate a large percentage of the existing variation is genetic. Thisuggests that hybridization and selection programs to improve populations could be successful.
Selection‐Induced Differences among Strains of Iowa Stiff Stalks Synthetic Maize1
Authors: Oyervides‐Garcia Manuel , Hallauer A. R.
Published: July 2010

Different recurrent selection methods have been used for the improvement of traits in maize (Zea mays L.). The relative performance of nine strains of Iowa Stiff Stalk Synthetic (BSSSCO) derived different methods of recurrent selection for different traits were determined by evaluating strains per se, diallel crosses among strains, and Sl generations of strains and strain crosses. Objectives were to determine selection. induced differences among the nine strains and the direct and indirect effects of selection for yield, grain moisture, root and stalk lodging, and dropped ears. Replicated field trials were conducted in six environments. BS13(S)C2 had the highest yield per se (7.83 Mg ha‐1) and the highest yielding $1 generation (5.82 Mg ha‐1). Inbreeding depression for yield was less for the highly selected strains and for crosses involving those strains. Selection for resistance to European corn borer (Ostrinia nubilalis Hübner) did not significantly affect yield, but selection for resistance to corn rootworm (Diabrotica virgifera Le Conte) did have a significant negative correlated effect on grain yield. Changes in frequency of additive effects due to selection for yield improvement were more important for BSI3(S)C2 (seven cycles half‐sib and two cycles S2 selection) than for BSSS(R)C8 (eight cycles reciprocal recurrent selection). Greater changes were observed in frequency of alleles with dominance effects in BSSS(R)C8 than in BS13(S)C2. After removal the effects of drift, rate of realized gain per cycle was 0.279 Mg ha‐1 (4.4%) for BS13(S)C2 and 0.259 Mg ha‐1 (4.1%) for BSSS(R)C8. Yield of the 36 strain crosses ranged from 6.10 Mg ha‐1 for BSSSCO ✕ BSSS(RW)C2 to 9.37 Mg ha‐1 for BSSS(R)C8 ✕ BS13(S)C2. Average midparent heterosis for yield was 11.7%. Yield differences among strains and level of heterosis expressed in crosses suggested selection‐induced genetic diversity among strains of BSSSCO.
Selection of Barley for Slow Rusting Resistance to Leaf Rust in Epidemics in Different Severity1
Authors: Andres M. W. , Wilcoxson Roy D.
Published: July 2010

Slow rusting resistance is of great potential value because it may be more stable than resistance recognized by infection types. However, the conditions necessary for most effective selection for slow rusting resistance are not well defined. The barley (Hordeum vulgare L.) cultivars Gus, Larker, Vada, Volla, Gold, and the lines MN9062, MN7572 and MN7544, known to differ in slow rusting resistance, were evaluated in the field during severe and mild epidemics of race 4 of Puccinia hordei. The area under the disease progress curve (AUDPC), used to estimate slow rusting, was larger for all cultivars and lines in a severe epidemic than in a mild one. The differences among the eight cultivars and lines for AUDPC were more distinct in the severe epidemic. The ranking of the cultivars and lines according to AUDPC was similar in both epidemics as indicated by Spearman's coefficient of rank correlation (0.86, significant at P = 0.01). It is suggested that selection for slow rusting resistance preferably be done in severe epidemics with the inclusion as controls, cultivars that are known to rust slowly or rapidly.
Induction of Leaf Red‐Speckling by Phosphorus on Sorghum Grown under Controlled Conditions1
Authors: Furlani A. M. C. , Clark R. B. , Sullivan C. Y. , Maranville J. W.
Published: July 2010

Studies were conducted to better understand the enhancement and properties of a red‐speckling that was induced on the lower leaves of young sorghum [Sorghum bicolor (L.) Moench] plants grown in nutrient solutions with various levels of P. Severity of leaf red‐speckling was enhanced as solution P level increased. Phosphorus as low as 1.2 to 2.5 μnol per plant induced red‐speckling. At comparably low levels of P, organic sources (phenyl‐, glyceryl‐, and ethylammonium phosphate) induced more severe symptoms than did inorganic sources [potassium dihydrogen, calcium (dibasic‐, tribasic‐, meta‐, and pyro‐), ferrous, ferric, and aluminum phosphate]. A redspeckled fourth leaf (from the plant base) of ‘Martin’ had lower photosynthetic rates, chlorophyll concentrations, chlorophyll a/b ratios, and leaf areas than a comparable nonspeckled NB9040 leaf. Except at high P, a comparable nonspeckled fifth leaf of Martin and NB9040 had similar photosynthetic rates. Reduced leaf photosynthetic rates were associated with severe red‐speckling, which in turn was induced in Martin plants grown at high levels of P. Martin accumulated more P, developed severe leaf red‐speckling, and was more adversely affected by P than NB9040. Some of the unusual or abnormal red colorations that appear on leaves of young sorghum plants may be caused by P. Excess P disorders or toxicities occurred on sorghum leaves at P levels lower than had normally been considered.
Effect of Elevated Growing‐Point Temperature on Maize Growth and Yield1
Authors: Jeppon R. G. , Crookston R. Kent
Published: July 2010

Clipping of early leaves has been shown to increase the harvest index (HI) or maize (Zea mays L.). In a preliminary greenhouse study, we found that early leaf clipping increased the growing point (GP) temperature of the plant. The objective of this study was to determine if leaf clipping of corn resulted in GP heating in the field, and to determine if the previously observed increase in HI of corn following early leaf clipping was associated with altered GP temperature. Field experiments were conducted in 1978 and 1979 at St. Paul, MN. Growing point heating treatments were designed to simulate the effect of increased GP temperature following early clipping without actually removing the leaves. Clipping at the five‐leaf stage (LS) increased GP temperature in the field by as much as 5°C when measured at midday. Clipping and heating increased HI by 18 and 15%, respectively, when averaged over both years. Clipping and heating at the five‐LS reduced leaf area by 14 and 7%, respectively. Averaged over both years, both clipping and heating at the five‐LS significantly reduced tillering. It appears that the effect of early leaf clipping on corn growth may in part be a response to altered GP temperature. We propose a physiological hypothesis for the effects observed following both early leaf clipping and GP heating.
Germplasm and Physiologic Effects on Induction of High‐Frequency Hormone Autonomous Callus and Subsequent Shoot Regeneration in Sugarbeet1
Authors: Saunders J. W. , Shin K.
Published: July 2010

The availability of adapted germplasm capable of regenerating shoots from callus may affect the speed with which tissue culture‐mediated genetic improvements can be brought to commercial usage. To assess the shoot regeneration capability in Beta vulgaris L., 17 germplasm sources including sugarbeet, table beet, fodder beet and leaf beet were screened for callus‐forming ability and shoot regeneration. Petiole and blade explants from in vitro shoot cultures grown with 6‐benzyladenine (BA) as the only growth regulator were challenged to initiate callus on a Murashige‐Skoog basal medium (MS) with 0.25 or 1.0 mg L−1 BA. Bud regeneration was scored on the callus induction medium or after transfer of primary callus to MS + 1.0 mg L−1 BA + 0.3 mg L−1 3‐indoleacetic acid. Some individual genotypes from each of the 17 germplasm sources produced callus, and bud regeneration from callus was seen in 14 of the 17 germplasm sources, indicating that this ability is widespread in the species. Direct adventitious budding on petioles was also found within all germplasm sources. Use of BA as the sole growth regulator induced buds on callus within the range 0.1 to 3.0 mg L−1. Kinetin and tzeatin alone induced buds, but at the higher concentrations of 30 and 10 mg L−1, respectively. Environmental conditions and leaf part affected callus induction frequency on explants. Leaf blade segments were considerably more responsive than petiole segments. Explants cultured at 31°C initiated callus at least five times more frequently than those at 23°C. Highest frequency of callus induction with one genotype occurred in the dark, and no callusing occurred in 200 μmol m−2 s−1 light from fluorescent lamps. An uncomplicated procedure for shoot regeneration evolved through these experiments, permitting lone explants to initiate callus and subsequently regenerate shoots on MS + 1.0 mg L−1 BA without transfer. This system is applicable to a wtde range of B. vulgaris L. germplasm.
Effects of High Temperatures and Starter Nitrogen on the Growth and Nodulation of Soybean1
Authors: La Favre A. K. , Eaglesham A. R. J.
Published: July 2010

Until recently it was believed that soil temperatures in excess of 30°C are likely to inhibit the establishment of root nodules on soybean [Glycine max (L.) Merr.]; however, using diurnally cycling thermoperiods rather than constant‐temperature techniques, we previously found that a root temperature of 45°C is required to suppress soybean nodulation. Considering that the level of soil N also affects growth and nodulation, in this work we examine the effects of daily maxima of 30 to 45°C in combination with different levels of N (KNO3) applied at planting, using sand‐cultured ‘Wilkin’. Plant growth, on combined N or symbioticaily fixed N, was severely inhibited by temperature maxima >41°C, but was improved by 36°C maximum for 9 h daily. With 21‐day‐old plants, maxima >36° adversely affected nodulation only in the presence of combined N, and after depletion of N excellent nodulation was obtained. Growth and nodulation at 35 days were less adversely affected by temperature stress when a small (e.g., 90 mg N plant‐1) application of N had been made at planting than under N‐free conditions. The results show that inhibition of nodulation of soybean by high temperature is exacerbated by: (i) the presence of available N, and (ii) the complete absence of applied N.
Somatic Embryogenesis and Plant Regeneration in ErUca Sativa1
Authors: Ashloowalia B. S.
Published: July 2010

Eruca sativa (Mill) Thell is a speciality oilseed crop. The objective of this study was to develop a suitable method of in vitro plant regeneration for genetic modification of eruca through tissue culture techniques. Zygotic embryos at various stages of development were taken from immature seeds and cultured on modified Murashige and Skoog's RM medium (MS) supplemented with 0.5 mg/L naphathelene acetic acid and 5.0 mg/L benzylaminopurine. All embryos, except those at the torpedo stage and younger, showed organogenesis from the hypocotyls; in addition, a few produced somatic embryos on the lower surface of the cotyledons. Further subculture of these responsive embryos produced either shoots or somatic embryos depending upon the medium used. Subculture of the responsive embryos on half‐strength MS (half‐MS) medium for 3 weeks resulted in meristem proliferation and formation of many shoots that rooted on half‐MS medium and could be transferred into soil. However, subculture of responsive embryos on MS medium supplemented with 100 mg/L asparagine and 60 g/L sucrose produced somatic embryos from the surface of the proliferated stems. Primary somatic embryos formed secondary somatic embryos from the upper surface of cotyledons. Somatic embryos germinated when subcultured on half‐MS medium, and plantlets were transferred into soil. It is concluded that plant regeneration in eruca can be achieved via organogenesis and somatic embryogenesis.
Cell Wall Carbohydrates of Flaccidgrass Plant Parts. III. Near Infrared Reflectance Spectroscopy Determination, Rate, and Extent of Fermentation1
Authors: de Ruiter J. M. , Burns J. C.
Published: July 2010

Cell wall carbohydrate fractions of forage plants strongly influence their rate and extent of fermentation. Two different analytical methods were evaluated to establish the rate and extent of structural carbohydrate in vitro fermentation in a subtropical forage grass species, flaccidgrass (Pennisetum flaccidum Griseb.). The procedures involved either chemical determination [cell wall hydrolysis with trifluoroacetic acid (TFA), derivatization and analysis by gas‐liquid chromatography], or near infrared reflectance spectroscopy (NIRS) of partially fermented cell wall residues. The chemical hydrolysis products were carbohydrate monomers of noncellulosic origin. Coefficients in a fermentation model derived from chemical data indicated major differences in the in vitro disappearance of cell wall xylose and glucose. Cell wall xylose disappearance was 32% slower than glucose when averaged over the range of flaccidgrass maturities. In addition, between 41 and 73% of the xylose was fermented, compared with 82 to 98% of the cell wall glucose hydrolyzed by TFA. Plant maturity and plant part (leaf, sheath, or stem) had pronounced effects on the digestion model coefficients. When averaged over all plant parts, total cell wall monosaccharides losses from mature plants were 26% less than in immature plants, with an overall 40.5% reduction in the disappearance rate. There was an average of 19% difference in the extent of fermentation of leaf and sheath, while stems fermented 38% slower than leaf. Fermentation losses and the cell wall carbohydrate components remaining at different fermentation periods were predicted accurately and rapidly by NIRS. Predicted and observed values for the level of fermentation were highly correlated (r = 0.95) as were carbohydrate monomers (r > 0.73). The method can be used to estimate the digestion (in vitro and in vivo) of forage species on the basis of their structural composition, provided calibrations are precise. Both the digestion model and NIRS method gave good predictions of the concentration of carbohydrates in partially fermented cell walls, as well as the extent of dry matter loss during fermentation.
Forage Quality of Perential Glandular‐Haired and Eglandular Medicago Populations
Authors: Lenssen A. W. , Sorensen E. L. , Posler G. L. , Harbers L. H.
Published: July 2010

Current alfalfa (Medicago sativa L.) cultivars have inadequate resistance to the alfalfa weevil [Hypera postica (Gyilenhal)] and the potato leafhopper [Empoasca fabae (Harris)], the two most injurious arthropod pests of alfalfa in North America. Resistance to both insects has been documented in other Medicago species having erect, glandular hairs. These hairs have been transferred to alfalfa. The effects of glandular hairs and their exudates on forage quality of alfalfa are unknown. A field trial was established in 1985 to determine the effects of erect glandular hairs and their exudates on forage quality of some perennial Medicagos. Glandular and eglandular plant populations were selected from the diploids M. glandulosa David and M. prostrata Jacq. and tetraploids M. glutinosa Bieb., M. sativa (MS4n) × M. glutinosa, and MS4n × M. prostrata. (Medicago glutinosa is the first label given to PI 346919, a plant introduction from Russia. In 1978, USDA Tech. Bull. 1574 identified it as a mixture of the following M. sativa L. subspecies: sativa, praefalcata, glomerata, and X varia.) Eglandular M. sativa ‘Riley’ and diploid M. sativa subsp. caerulea (Less. ex Ledeb.) Schmalh. were included as controls. The test was planted in an area mapped as Wymore silty clay loam (fine, montmorillonitic, mesic Aquic Argiadolls) 1 to 4% slopes. Foliar diseases and insects were controlled. Leaves were separated from stems for three harvests in 1985 and one harvest in 1986. In vitro dry matter disappearance (IVDMD) and crude protein (CP) were determined on each component. The presence of glandular hairs on the wild Medicago species (glandulosa, prostrata, and glutinosa) did not significantly affect the IVDMD or CP contents of leaves or stems. Stem digestibilities and crude protein contents of the diploid populations exceeded those of Riley.
Selection for Sucrose Yield in Stressed Sugarbeet Seedlings
Authors: Doney Devon L.
Published: July 2010

Progress in improving sucrose yield in sugarbeet (Beta vulgaris L.) has been slow, due to large environmental variation associated with root yield and a negative correlation between root yield and sucrose concentration. Appropriate stress applied on segregating populations could increase performance differences among genotypes and increase the genetic variance. Stress that forces defoliated plants to grow new leaves from their stored root reserves logically ought to select for increased photosynthate storage and, therefore, increased sucrose yield. Stress was imposed in greenhouse tests by trimming the leaves from 3‐ to 4‐wk‐old sugarbeet seedlings and covering them with black plastic, thereby forcing the plants to grow new leaves from their stored root reserves. When this stress was imposed on seedlings of a series of cultivars varying in root yield and sucrose potential, those cultivars with the highest potential sucrose yield had the greatest survival rate (fewest plants dying). The correlations between percent survival after stress and total sucrose yield were 0.96 and 0.90 for field and greenhouse replicated trials, respectively. Open‐pollinated seed increases of the surviving plants in two heterogeneous populations resulted in increases in field root yield, sucrose concentration and total sucrose yield. These increases, although in a favorable direction, were not always at the desired probability of significance. Data combined over 2 years of testing gave significant increases in total sucrose yield for the two new stress selection populations over their parents at the 0.07 and 0.14 probability levels. This method shows promise as a quick, inexpensive technique for improving both root yield and sucrose concentration.
Measurement of Resistance to Fusarium Wilt/Root and Crown Rot in Birdsfoot Trefoil Populations
Authors: Zeiders K. E. , Hill R. R.
Published: July 2010

Fusarium wilt disease [caused by Fusarium oxysporum (Schlect) Snyd. & Hans.] has been identified as an important factor in stand decline in birdsfoot trefoil (Lotus corniculatus L.) seed production fields in the Champlain Valley of New York and Vermont. In response to this problem, studies to develop resistance to F. oxysporum were initiated. In greenhouse inoculations tests, two broad‐based populations of birdsfoot trefoil were subjected to two cycles of recurrent phenotypic selection for resistance to wilt/root and crown rot caused by F. oxysporum. In a cycle comparison test, plants were rated for disease severity four times at 30‐d intervals after inoculation. The objectives were to evaluate the effectiveness of selection and to compare different methods of measuring resistance to the pathogen. Disease resistance was measured by: (i) disease progress curves based on visual wilting/stunting ratings of individual plants (DSW); (ii) frequencies of plants rated > 2 (DSD) (where 1 = no disease to 5 = plant dead), indicating moderate or greater wilting/stunting; (iii) area under the disease progress curve (AUDPC) calculated from curves in method ii; and (iv) root and crown rot ratings (RCR) of individual plants at the end of the experiment. Analyses by each of the four measures of resistance indicated that recurrent selection increased resistance to F. oxysporum in birdsfoot trefoil. Cycle 0 plants of each population were among the most susceptible, and Cycle 2 plants were among the most resistant of all entries in the evaluation test. Analyses of DSW and DS2 indicated similar responses to selection. Disease severity increased until Day 90 of the test with little or no increase thereafter. Analysis of AUDPC was more sensitive to larger increases in disease severity early in the evaluation trial. Analysis of RCR ratings indicated less progress from selection than with the other measures of resistance.
Field Evaluation of Soybeans for Mexican Bean Beetle Resistance. I. Maturity Groups VI, VII, and VIII
Authors: Kraemer M. E. , Rangappa M. , Benepal P. S. , Mebrahtu T.
Published: July 2010

Field screening of soybean, Glycine max (L.) Merr., germplasm for resistance to insect defoliation was undertaken because of the many new additions to the USDA germplasm collection in recent years and because of the narrow genetic base of resistance currently available to plant breeders. All soybean plant introductions (PIs) available by 1980 (to PI 424595) in maturity groups VI, VII, and VIII were screened at the Randolph Research Farm of Virginia State Univ., Petersburg, VA, for resistance to feeding by the Mexican bean bettle (MBB), Epilachna varivestis Mulsant. Resistance was determined by estimating the percent defoliation caused by the MBB. All soybean accessions were initially tested in 1984 and selected lines were retested in 1985 (three replicates) and 1986 (four replicates). The least defoliated lines of each maturity group (MG) were identified and compared with three susceptible genotypes from their respective maturity groups. Although no PI had a higher level of resistance than the previously identified PIs 171451 and 229358, several accessions had nearly equal levels of resistance. These include two PIs (417061 and 417136) in MG VIII which had less defoliation than the standard resistant line of this MG, PI 227687. Also, sources of resistance were identified for the first time in MG VI: FC 31665, and PIs 379621, 416925, and 416937.
Prediction of Kentucky Bluegrass Root Growth Using Degree‐Day Accumulation
Authors: Koski A. J. , Street J. R. , Danneberger T. K.
Published: July 2010

The ability to predict the progression of turfgrass root formation would be of interest to both researchers and turfgrass practitioners. This capability would allow for improved evaluation of the effects that the timing of various management practices could have on turfgrass root production. The purpose of this study was to develop a model, based on accumulated degree‐days (ADD) calculated from soil temperature, which could predict the accumulation of ‘Baron’ Kentucky bluegrass (Poa pratensis L.) root growth during the period of January to June. Temperature at the 10 cm depth (fine quartz sand) and cumulative root length (CRL) data collected in the rhizotron facility at The Ohio State University during 1981, 1982, and 1985 were used to develop the model. Within the confined cultural and environmental conditions of this study, the model accounted for 95% of the observed variation in CRL and the actual equation was: CRL = 5.269 + 0.032(ADD) + 0.0000138(ADD2). Under field conditions, other factors besides temperature and heat unit accumulation would be expected to display strong and independent effects on turfgrass root growth. The development of a widely usable model would include provisions for variations in edaphic conditions and for the great diversity of management practices and maintenance intensity levels which are utilized today.
Symbiotic Relationship between Bradyrhizobium Strains and Peanut
Authors: Alwi N. , Wynne J. C. , Rawlings J. O. , Schneeweis T. J. , Elkan G. H.
Published: July 2010

Significant host ✕ strain interactions for the amount of N fixed were found in previous factorial experiments of peanut (Arachis hypogaea L.) and Bradyrhizobium strains. The results suggested that specific host‐strain combinations should be identified to maximize N fixation. The objectives of this study were to determine if methodology could be developed to reduce the testing required to identify specific host‐strain combinations that maximize N fixation. Sixteen peanut cultivars representing four morphological groups inoculated with 29 Bradyrhizobium strains known to be effective on peanut were used to determine if grouping of host genotypes or strain genotypes could be used to limit testing to groups of genotypes instead of individual genotypes. The peanut cultivars grouped using numerical taxonomy of morphological characters reflected the differences in response to rhizobial strains; however, cultivars were not homogeneous within groups for symbiotic traits. Strain variability was the largest component of the phenotypic variability for all traits, and the host plant had larger variability than the cultivar ✕ strain interaction for nodule number, nodule weight, and nodule size. The biplot of shoot weight ratio classified the strains and peanut cultivars into five and four groups, respectively. All cultivars received enough N to appear normal when they were inoculated with effective strains but were quite different in response to symbiotic N. These results suggest that the amount of plant testing required to identify specific strains for a host genotype can be reduced considerably by first classifying the symbionts into groups and eliminating some groups from further testing.
Inheritance of Resistance to Barley Yellow Dwarf Virus Detected by Northern Blot Analysis
Authors: Lorens G. F. , Falk B. W. , Qualset C. O.
Published: July 2010

Development of wheat (Triticum aestivum L.) cultivars tolerant to the barley yellow dwarf virus disease (BYD) has been limited by lack of precision in rating plants for response to infection, usually done by visual scoring of plant symptoms under field conditions. Other methodologies have been developed to study the host/pathogen relationship and to assess resistance or susceptibility. In this study northern dot blot analysis was used to determine barley yellow dwarf virus (BYDV) UNA concentrations of six wheat cultivars that differed in visual BYD symptom expression. Plants were infected with the NYPAV (PAY) isolate of BYDV in the greenhouse. At several dates after inoculation crude plant extracts were blotted on nitrocellulose and hybridized with a 32P‐labeled probe of the pPA8 cDNA clone of BYDV. Scintillation counts of a dilution series of purified plasmid were used to determine PAY RNA concentration (PRC). Seri 82, a susceptible cultivar, had statistically greater PRC than NS 879/4, a cultivar showing tolerance based on symptom expression in the field. The frequency distribution for PRC for 122 F2 plants from the cross of these two cultivars was multimodal, but showed no discrete classes. The F2 mean PRC was greater than the mean of either parent. Selection of F2 plants with either high PRC or low PRC resulted in good bidirectional response to selection in the F3 generation, demonstrating genetic control of PRC. The F3 data also indicated that variation for greater susceptibility than either parent in the F2 generation was genetically controlled. Both NS 879/4 and Seri 82 appear to each have genes for reduced PRC and these genes are probably at different loci. The distribution of PRC for the F2 population was compared to the distribution of BYD visual symptom scores for 403 F2 plants of a similar F2 population of NS 879/4 ✕ Seri 82 under field conditions. The results were qualitatively similar, suggesting that northern dot blot analysis to measure PRC may be useful in understanding the genetics of resistance to BYD. This technique, when incorporated into breeding programs, could be important in the development of highly tolerant wheat cultivars with reduced losses to BYD.
Preplant Tillage Effects on Population Dynamics of Soybean Insect Pests
Authors: Funderburk J. E. , Wright D. L. , Teare I. D.
Published: July 2010

Tillage operations can modify soil and plant characteristics where many insects reside dudag at least part of their life cycle. However, information relating tillage and subsoiling to soybean [Glycine max (L.) Merr.] insect pests is very scarce or inconclusive. The objective of this study was to determine the effect of tillage and subsoiling on population cycles and densities of foliage‐inhabiting insect pests in soybean. Soybean was grown on a Norfolk sandy loam soil (fineloamy, siliceous, thermal Typic Kandiudult) and tillage treatments were (i) disk (no subsoil), (ii) disk (subsoil), (iii) conservation (no subsoil), and (iv) conservation tillage (subsoil). Planting curred immediately after disking or in conjunction with conservation tillage. Subsoiling consisted of a chisel plow located on a planter directly under the soybean row. Plots were sampled for insects by beating the soybean plants on both sides of the row onto a ground cloth. Population densities of velvetbean caterpillar (VBC), Anticarsia gemmatalis Hubner, increased at R4 and peaked at soybean Growth Stage R5.5; green cloverworm (GCW), Plathypena scabra (Fabricius) in 1985 and 1986 were greatest at Growth Stage R1 and R2.6, respectively, but remained low in 1987. Preplant tillage treatments usually caused no significant effect on the population dynamics of VBC or GCW. The population densities and cycles of southern green stinkbug (SGSB) nymphs and adults, Nezara viridula (L.), were similar for each preplant tillage treatment in 1985, 1986, and 1987. Since insect pests were not affected by tillage operations at planting, the tillage operation can be selected to promote beneficial insect predators that have shown to be favored by conventional tillage.
Inhibition of Corn Callus Growth by Helminthosporium carbonum Race 1 Toxin
Authors: Wolf S. J. , Earle E. D.
Published: July 2010

Plant tissue culture has potential application in the development of disease‐resistant crops and also in the study of host‐pathogen interactions in vitro. Pathogen‐produced toxins (phytotoxins) can be used as pathogen surrogates in such work. Helminthosporium carbonum Race 1, the causal agent for Helminthosporium leaf spot of corn (Zea mays L.), produces a phytotoxin (HC toxin) known to be the pathogenicity factor for that disease. Tissue cultures were established from corn genotypes susceptible or resistant to H. carbonum Race 1. A toxin preparation with an effective dose (ED50,) of 2 μg mL‐1 for seedling roots was incorporated into callus growth and regeneration media. Growth of callus derived from genotypes susceptible to the pathogen was inhibited at 5 μg mL‐1 toxin, whereas callus from a resistant genotype was inhibited only at 50 μg mL‐1 toxin. Regeneration of plants from callus of susceptible genotypes was also inhibited at 5 μg mL‐1 toxin, but regeneration of a resistant genotype was not inhibited at 20 μg mL‐1 toxin. A total of 5676 calli from the susceptible lines were exposed to toxin concentrations of 2, 5, and 10 μg mL‐1. Both 3 and 15‐mo old calli were used. Some cultures were treated with the mutagens sodium azide and ethyl methane sulfonate before exposure to toxin. No resistant callus or plants were recovered from any of the treatments. Failure to recover resistant callus might be due to an inability to identify resistant cells within a relatively slow‐growing callus cell population.
Root Characteristics Associated with Divergent Selection for Seedling Aluminum Tolerance in Soybean
Authors: Hanson W. D.
Published: July 2010

Soybean (Glycine max [L.] Merr.) roots are susceptible to A1 toxicity. This study tested the hypothesis that seedling characteristics could serve as selection criteria for plant tolerance to A1. Phenotypic‐recurrent, divergent selection programs for seedling tolerance to A1 were completed within two broad‐base soybean populations based on a laboratory screen. Genotypes differing in seedling tolerance to A1, rate of electron release (and, H+ release) from the root surface, and root thickness (g cm‒1) were identified. Root penetration from a soil horizon with low A1 into soils with high A1 was selected to measure A1 tolerance for greenhouse‐grown plants. Selection pressure for seedling root growth under A1 within these two populations evolved a number of apparent mechanisms affecting seedling root growth in solutions containing A1. Selecting genotypes for differences in A1 seedling tolerance gave inconsistent associated responses for root penetration into soils with high A1. High electron release rates and small roots (and seeds) were associated with selection for low A1 seedling tolerance. Selecting genotypes for differences in electron release rate or for differences in root thickness did not create an associated response in root penetration into soils with high A1. Preconditioning of seedling roots to A1 increased tolerance to A1 proportionately in tolerant and nontolerant selections, when tolerant and nontolerant selections were grown in different A1 concentrations selected to yield ≈75% reduction in root growth. Genetic variability available was not such as has been associated with the inducible A1‐binding proteins proposed for wheat (Triticum aestium L.). New genetic sources for A1 tolerance and information on the nature of this tolerance are needed to develop selection criteria for A1 tolerance.
New Sources of Resistance to Greenbug in Wheat
Authors: Porter D. R. , Webster J. A. , Burton R. L. , Puterka G. J. , Smith E. L.
Published: July 2010

A new greenbug [Schizaphis graminum (Rondani)] Biotype G (GBG) damages all known sources of resistance in wheat (Triticum aestivum L.) and poses a potential new threat to wheat production. Resistance to GBG was detected in germplasm originating from hybridizations using x‐ray irradiated pollen of wheat/rye (Secale cereale L.) hybrids to pollinate hard red winter wheat females. Te GBG‐resistant wheat germplasms exhibited high levels of resistance to all economically important greenbug biotypes (i.e., B,C,E, and G) at the seedling stage. This germplasm should be extremely valuable in the development of new multibiotype greenbug‐resistant cultivars.
Inheritance of Stem Canker Resistance in Soybean Cultivars Crockett and Dowling
Authors: Bowers Glenn R. , Ngeleka Kadima , Smith Olin
Published: July 2010

Stem Canker caused by Diaporthe phaseolorum (Cooke & Ellis) Sacc. var. caulivora K. L. Athow & R. M. Caldwell (Dpc) has become a serious disease of soybean [Glycine max (L.) Merr.] throughout the southeastern USA. Sources of resistance have been identified and information on the inheritance of resistance is needed for each source. The objective of this work was to study the inheritance of resistance to stem canker in ‘Crockett’ and ‘Dowling’ soybean. Crockett, Dowling, and ‘Tracy‐M’ were crossed with each other and with two susceptible cultivars, Coker 338 and Johnston. Disease reactions of parent and progeny populations were studied in the greenhouse following artificial (toothpick) incoculation with a southern isolate of Dpc. Crosses between either Dowling or Crockett and the two susceptible parents resulted in segregating F2 populations that fit a 3 resistant : 1 susceptible ratio, and F2:3 families that fit a 1 resistant : 2 segregating : 1 susceptible ratio. The cross between Crockett and Dowling resulted in a 15:1 ratio in the F2 and a 7:8:1 ratio in the F3 generation. Crosses between Tracy‐M and Crockett or Dowling resulted in segregation ratios of 63:1 in the F2 and 37:26:1 and F3. These results suggest that Crockett and Dowling each have a major dominant gene, and that these two genes are different from RdC1 and RdC2 found in Tracy‐M. The gene symbols Rdc3 and Rdc4 are proposed to identify genes controlling resistance to stem canker in Crockett and Dowling, respectively.
Regulatory DNA of Ribosomal RNA Genes and Control of Nucleolus Organizer Activity in Wheat
Authors: Flavell R. B. , O'Dell M. , Sardana R. , Jackson S.
Published: July 2010

A molecular genetic analysis of wheat (Triticum aestivum L.) ribosomal RNA (rRNA) gene locus expression is described. Locus activity was estimated by cytological assays of nucleolus organiser volume. Gene structure was determined from DNA sequencing and restriction endonuclease mapping of isolated genes. Relative nucleolus organiser activity is correlated with the number of 135 base pair (bp) repeats that lie upstream of the gene promoter. A model is proposed in which gene and locus‐relative activity is determined by the ability of the 135 bp and other promoter sequences of the genes in a locus to compete for regulatory proteins in limiting concentration in the nucleus. Active loci are enriched with genes which have unmethylated cytosines at specific sites in the promoter and the 135 bp repeats and in which chromatin structure is perturbed. It is concluded that the processes that produce different numbers of regulatory DNA sequences between rRNA genes are responsible for the differential expression of nucleolus organisers in hexaploid wheat and in interspecies hybrids.
Backcross (BC2‐BC4)‐Derived Fertile Plants from Glycine max and G. tomentella Intersubgeneric Hybrids
Authors: Singh R. J. , Kollipara K. P. , Hymowitz T.
Published: July 2010

Wild perennial relatives of the soybean [Glycine max (L.) Merr.] have not been utilized to broaden the genetic base of the crop. This study provides information on production, morphology, cytology, and breeding behavior of backcross (BC2 to BC4)‐derived fertile plants from soybean (2n = 40, genome GG) and G. tomentella Hayata (2n = 78, genome DDEE). The main hurdle was to obtain BC~ plants (G. max cv. Altona) × (G. tomentella, Pl 483218)] → F1, 2n = 59, genome GDE → colchicine treatment (CT) → 2n = 118, GGDDEE × soybean cv. Clark 63 → BC1, 2,n = 76 (expected 2n = 79). Three sterile BC2 plants (2n = 58, 2n = 56, 2n = 55) were produced. Procedures for immature seed‐rescue were utilized to obtain F, amphiploid, BC1 and BC2 plants. Soybean cv. Clark 63 was used as the recurrent parent in the backcrossing programs. The range of chromosome number among BC3 plants was 2n = 41 to 2n = 52, and among BC4 plants was 2n = 40 to 64. A hypertriploid (2n = 64) in BC4 plant originated after fertilization of an unreduced egg (n = 44) by a normal haploid (n = 20) male gamete. Phenotypes of BC3 and BC4 plants were dissimilar but generally resembled closely to the soybean cv. Clark 63. We expect to isolate a series of aneuploid lines from BC3 to BC6 generations that may open up the path to introgress desired traits from wild perennial Glycine species to the cultivated soybean.
Oxalic Acid Effects in Exudates of Sclerothinia trifoliorum and S. sclerotiorum and Potential Use in Selection
Authors: Rowe D. E.
Published: July 2010

Sclerotinia crown and stem rot caused by Sclerotinia trifoliorum Eriks. or S. sclerotiorum (Lib.) de Bary is a serious problem on crimson clover (Trifolium incarnatum L.), berseem clover (T. alexandrinum L.), and alfalfa (Medicago sativa L.) in temperate climates. The inability to develop cultivars resistant to this disease indicates more detailed research is needed on factors causing disease by either fungus. The objectives of this study were to determine what deleterious effects fungal exudates have on the seed of these legumes and attempt to measure the importance of oxalic acid in the fungal exudates. The percent seed germination and length of germinated seedlings of four cultivars each of crimson clover, berseem clover, and alfalfa were measured in five environments. Seed was placed in a host‐pathogen interaction system and exposed to exudates of S. trifoliorum or S. sclerotiorum on water agar acidified with oxalic acid to a pH of 3.3, and water agar as a control (pH 6,2). In contrast to a control, fungal exudate caused a 51 to 60% reduction in seedling length and an average of two‐thirds of this reduction appeared to be caused by oxalic acid. The seedling length on oxalic acid amended agar was correlated with that of seedlings exposed to exudates from S. trifoliorum (r 0.71, 10 dr) and S.sclerotiorum (r = 0.83, 10 di~. Oxalic acid appeared to have potential value in selection of resistance to either fungus in alfalfa or resistance to S. sclerotiorum in crimson clover.
Diallel Analysis of Head Rice Percentage, Total Milled Rice Percentage, and Rough Rice Yield
Authors: Gravois Kenneth A.
Published: July 2010

The value of rough rice (Oryza sativa L.) is often determined by the percentage of head rice and total milled rice produced after milling. The objective of this study was to obtain information on general combining ability (GCA), specific combining ability (SCA), and high‐parent heterosis for head rice percentage, total milled rice percentage, and rough rice yield. An eight‐parent diallel (F1 crosses plus parents) was evaluated in 1991 at two Arkansas locations: Stuttgart and Marianna. Genetic variation among the hybrids for total milled rice percentage was nonsignificant. The GCA effects were more important than SCA effects for head rice percentage, indicating the importance of additive genetic effects in the inheritance of head rice percentage. It is postulated that head rice percentage SCA effects were due predominantly to additive × additive epistatic effects rather than dominance effects. Additive and additive × additive epistatic types of gene action are most easily exploited by producing homozygous genotypes. Single cross performance for head rice percentage could largely be predicted by GCA effects or mid‐parent means. Average heterosis, as indicated by the Parent vs. Hybrid mean squares, was nonsignificant for head rice percentage, but significant for rough rice yield. High‐parent heterosis for rough rice yield, head rice percentage, and head rice per plot averaged 21, −5, and 22%, respectively. High‐parent heterosis, obtained from the hybrids of this eight‐parent diallel, for head rice per plot was due primarily to rough rice yield heterosis rather than head rice percentage heterosis. Based on the yield of head rice per plot, hybrid rice production would be feasible.
Yield‐Determining Processes in Relation to Cultivar Seed Size of Common Bean
Authors: Sexton Peter J. , White Jeffrey W. , Boote Kenneth J.
Published: July 2010

Cultivar seed size and yield potential of common bean (Phaseolus vulgaris L.) are negatively associated. Large‐seeded cultivars are predominately of Andean background, while small‐seeded cultivars are predominately of Mesoamerican background. Crop growth analyses were conducted to examine the association of cultivar seed size with crop growth rate (CGR), seed growth rate (SGR) on a land‐area basis, intensity of partitioning to seed (land‐area SGR divided by CGR), and effective seed‐filling period. Sixteen cultivars, ranging in seed size from 190 to 540 mg seed−1, were grown at two sites in Colombia at elevations of 1000 m (warm) and 1800 m (cool). The seed size groups did not differ in CGR at either site. At the warmer site, the small‐seeded Mesoamerican lines had greater mean partitioning to seed (1.29 vs. 0.97 for the Mesoamerican and Andean lines, respectively), greater land‐area SGR (11.7 vs. 8.3 g m−2 d−1), and higher yield ( 2030 vs. 1750 kg ha−1) than did the large‐seeded Andean lines. At the cool site, the seed size groups did not differ in any of these variables. At both sites, the Mesoamerican lines flowered ≈6 d later and acquired more total N than did the Andean lines. It is postulated that the greater land‐area SGR and yield of the Mesoamerican lines at the warmer site was due to their greater accumulation of N, which allowed them to sustain greater rates of canopy photosynthesis during seed‐filling.
Quantitative Inheritance of Forage Quality Traits in Intermediate Wheatgrass
Authors: Berdahl J. D. , Karn J. F. , Dara S. T.
Published: July 2010

Knowledge of heritability and inheritance of nutritive quality traits in intermediate wheatgrass [Thinopyrum intermedium (Host) Barkw. & D.R. Dewey] would be helpful in choosing effective selection techniques. This study assesses variation and heritability of traits associated with hay quality in intermediate wheatgrass, ascertains the relative magnitude of general and specific combining ability (SCA and GCA) for these traits, and examines relationships among important agronomic and quality traits. Six parent clones and the 15 progenies from a diallel cross (reciprocal crosses not included) were evaluated in a replicated field test for in vitro digestible organic matter (IVDOM), neutral detergent fiber (NDF), and N concentration of whole plants, leaf blades, and stems (stem plus leaf sheath). Spike emergence date, plant height, and leaf/stem ratio were also measured. Variation among progenies was significant for all traits except leaf IVDOM and whole‐plant N. Leaf/stem ratios varied from 0.22 to 0.28 among progenies, with stems contributing more to whole‐plant IVDOM than did leaf blades. Low variation in whole‐plant N concentration limits the potential for forage N improvement. Spike emergence date, a measure of relative plant maturity, was correlated positively with IVDOM (r = 0.75**) and negatively with NDF (r = −0.61*). Narrow‐sense heritability estimates were moderately high for whole‐plant IVDOM and for IVDOM, NDF, and N of stem and leaf fractions. Variance components for GCA were generally higher than those caused by SCA. Year effects for IVDOM and NDF were high, but year × GCA and year × SCA interaction effects for these traits were not significant. Selection for high whole‐plant IVDOM in a single environment employing recurrent phenotypic selection or other selection techniques that utilize additive genetic variance should be effective in improving digestibility of intermediate wheatgrass hay.