bluuebunny/crossref_metadata_2025 huggingface dataset:
Genotype Effects and Genotype by Environment Interactions for Traits of Elite Switchgrass Populations
Authors: Hopkins Andrew A. , Vogel K. P. , Moore K. J. , Johnson K. D. , Carlson I. T.
Published: July 2010

Switchgrass (Panicum virgatum L.) is used as a forage species and has shown potential for use in production of fuel ethanol from cellulosic biomass. Objectives of this research were to determine performance differences between elite switchgrass populations for agronomic, forage quality, and biofuel traits and to determine the magnitude of genotype × environment (G× E) interactions for these traits across midwestern environments. Twenty elite switchgrass populations, consisting of cultivars and advanced breeding populations, were planted in sward trials at Mead, NE, Ames, IA, and West Lafayette, IN, during 1990 and were evaluated in 1991 and 1992. Forage samples were taken at a vegetative growth stage, at heading, and at the end of the season. Plots were harvested for forage yield at heading and at the end of the growing season. Forage composition and in vitro dry matter digestibility was determined using near infrared reflectance spectroscopy. Significant differences (P < 0.05) between populations for forage yield were found at individual locations but not across locations, except at the P = 0.10 probability level, because of G × E interactions. Genotype × environment interactions were significant for hemicellulose plus cellulose (holocellulose) yield, a potentially important biofuel trait. In vitro dry matter digestibility was more stable than both forage yield and holocellulose yield. Despite large G × E interaction effects, a few populations consistently ranked high in forage yield and holocelulose yield. Multiple location, multiple year sward trials will be needed to develop switchgrasses broadly adapted to the midwest.
Yield, Quality, and Nitrogen Use of Inbred Corn with Varying Numbers of Leaves during Detasseling
Authors: Wilhelm W. W. , Johnson B. E. , Schepers J. S.
Published: July 2010

Detasseling is used in hybrid corn (Zea mays L.) seed production to ensure harvested seeds have the desired genetic complement. Both mechanical and hand detasseling result in loss of some leaf tissue and plant N. The objective of this study was to determine if seed yield and quality and N content of grain and stover were affected by leaf removal during detasseling. The treatments evaluated were removal of tassel only, tassel plus one leaf, tassel plus two leaves, tassel plus three leaves, tassel plus four leaves, and no tissue removed (control). The leaf area index (LAI) declined linearly, about 0.16 LAI units per leaf removed. Grain and stover yield also declined linearly with number of leaves removed with the tassel (r 2 = 0.97 and 0.92, respectively). Each leaf removed reduced grain yield about 0.36 Mg ha−1. Yield reduction was caused by decreased kernel size. Grain and stover N concentration and amount of N in stover did not vary among detasseled treatments. However, total N in the grain declined linearly as number of leaves removed increased (r 2 = 0.97). Warm and cold germination and warm germination after accelerated aging were not affected by leaf removal during detasseling. Results reported here suggest that when leaves are removed from the plant at detasseling, the loss of photosynthetic capacity, the ability to intercept fight, and plant N all contribute to grain yield reduction.
Stand Establishment Response of Soft White Winter Wheat to Seedbed Residue and Seed Size
Authors: Chastain T. G. , Ward K. J. , Wysocki D. J.
Published: July 2010

The adoption of soil‐conserving management systems in dryland soft white winter wheat (Triticurn aestivum L.) production areas is limited by concerns that seedbed residues contribute to suboptimal stand establishment. Field trials were seeded in 1990 (Trial 1) and 1991 (Trial 2) near Pendleton, OR, to ascertain seedbed crop residue, seed size, and cultivar effects on emergence, early growth and development, and yield of soft white winter wheat. Seedbeds were much drier in Trial 2 than in Trial 1. Seed‐soil contact was probably reduced in high residue cover, but emergence rate was reduced by seedbed residue in Trial 2 only when seed zone water content was <120 g kg −1. Consequently, plant growth and development were responsive to seedbed residues only in Trial 2. Final stand density and grain yield were not sensitive to seedbed residue level in either trial. Seed size had no effect on laboratory germination, but seedlings from large seed emerged more rapidly in the held. Plants grown from large seed were taller, heavier, and had more tillers than plants grown from small seed. Planting large seed had no effect on grain yield in Trial 1, but plants grown from large seed produced 4.2% greater grain yield than from small seed in Trial 2. Cultivar performance was determined by genetic potential, seed size, and seed quality, and was not differentially influenced by seedbed residue level. Emergence was influenced by coleoptile length which differed among cultivars, but coleoptile length was not related to seed size. Higher levels of seedbed surface residues required to reduce soil erosion in dryland crop production systems do not reduce stand Establishment or yield of soft white winter wheat.
Genetic Diversity and Vulnerability of St. Augustinegrass
Authors: Busey Philip
Published: July 2010

St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze, expanding rapidly as a lawn grass, due especially to urban development in warm coastal areas, where it is best adapted. Although first discovered in South Carolina, in 1788, St. Augustinegrass may not be native to North America. The six other species of the genus are endemic to the Old World, and are still confined mainly along shorelines from Africa to the South Pacific. The first recorded use of St. Augustinegrass was in 1880, as a lawn in Florida. Cultivars were named beginning in the 1920s. The first cultivar of known parentage was released in 1980. Genetic diversity in the urban landscape is reduced by reliance on a few vegetatively propagated cultivars. Among breeding collections of St. Augustinegrass, considerable diversity exists for diploids, but not for polyploids. A related species, pembagrass, S. dimidiatum (L). Brongn., is resistant to the southern chinch bug, Blissus insularis Barber, and the sting nematode, Belonolaimus longicaudatus Rau., which are pests of St. Augustinegrass. Currently, only 26 foreign introductions of Stenotaphrum are found in the National Plant Germplasm System. Untapped germplasm potential of polyploid St. Augustinegrass and related species should be explored in southern Africa, where potential sources of resistance to chinch bugs and drought, and shade tolerance might be found. For new problems that will be discovered, genetic diversity must be deployed so as to deter resistance‐breaking pest strains. This will require better knowledge of the biological relationships.
Performance of Related Indeterminate and Tall Determinate Soybean Lines in Short‐Season Areas
Authors: Cober E. R. , Tanner J. W.
Published: July 2010

Determinate growth habit (dt1dt1) is useful in reducing plant height and lodging but can result in excessive dwarfing in early‐maturing soybean [Glycine max (L.) Merr.] lines. When the genotype E1E1e3e3e4e4 is combined with dtldt1, the result is nondwarf, early‐maturing determinate soybean lines (tall determinate). This study was conducted to compare the agronomic characteristics of Maturity Group 0 and I, tall determinate and indeterminate breeding lines. Thirty‐five pairs of lines with contrasting growth habit, with each pair of similar maturity and from the same cross, were selected from 16 populations and evaluated in three environments. Tall determinate lines significantly outyielded indeterminate lines in two environments, while in the third, there were no differences. The tall determinate lines were shorter, had higher bottom pods, and had decreased 100‐seed weight. Lodging and seed quality were not affected by growth habit. Tall determinate lines flowered later and matured earlier, resulting in a reduced reproductive period. High‐yielding lines of each type were identified. These results suggest that breeding for high‐yielding, tall determinate soybean lines adapted to short‐season areas is possible and that the tall determinate phenotype could prove beneficial because of the height increase of the bottom pods.
Cotton Resistance to Root‐Knot Nematode: I. Penetration and Reproduction
Authors: Creech R. G. , Jenkins J. N. , Tang B. , Lawrence G. W. , McCarty J. C.
Published: July 2010

Nematode parasitism of cotton (Gossypium hirsutum L.) has become increasingly important because of yield losses and increased distribution across cotton production regions. Penetration and reproduction of root‐knot nematodes, Meloidogyne incognita (Kofoid & White) Chitwood, Race 3, was compared on three cotton genotypes differing in level of resistance: M‐8, susceptible to root‐knot; M‐78 (M‐78RNR), moderately resistant; and M‐315 (M‐315RNR), resistant. Responses were characterized by penetration of plant roots by root‐knot nematode juveniles and by reproduction, measured as number of eggs, egg‐masses per plant, and eggs per egg‐mass. Susceptible, moderately resistant, and highly resistant cotton genotypes were penetrated about equally by juveniles. Production of egg‐masses, eggs per egg‐mass, and eggs per plant by nematodes were different among the three cotton genotypes. The development of egg masses was delayed in M‐78 and M‐315 as compared with M‐8, with the greatest delay and prevention of the formation of significant numbers of egg‐masses in the highly resistant M‐315. Production of eggs and second‐stage infective juveniles in the moderately resistant M‐78 were sufficient to contribute significantly to the build‐up of the next generation of root‐knot populations in cotton production fields. Reproduction on M‐315 was so low that nematode populations would be expected to decrease significantly under continuous culture. M‐315 possesses two major genes for resistance and is a valuable source of root‐knot nematode resistance for cotton improvement programs. These genes in combination do not alter penetration of the root‐knot nematode juvenile stage into cotton roots, but do have major negative effects on survival and reproduction of the nematodes.
Cotton Resistance to Root‐Knot Nematode: II. Post‐Penetration Development
Authors: Jenkins J. N. , Creech R. G. , Tang B. , Lawrence G. W. , McCarty J. C.
Published: July 2010

Root‐knot nematode (RKN), Meloidogyne incognita (Kofoid and White) Chitwood, damages cotton, Gossypium hirsutum L., roots, affecting water and nutrient uptake and predisposing the plants to other soilborne pathogens. Post‐penetration development of RKN was compared on three genotypes. Susceptible M‐8, moderately resistant M‐78, and highly resistant M‐315, were grown in a greenhouse in a Wickham sandy soil (a fine, loamy, mixed thermic, Typic Hapludult) and inoculated with second‐stage juveniles. RKN in each of 7 developmental stages were counted every 2 d for 44 d. At 18 DAI, 70, 45, and 6% of RKN present were adults in M‐8, M‐78, and M‐315, respectively. In addition to slower development of RKN in M‐315, resistance is expressed by significantly fewer developing third and fourth stage juveniles at 8 DAI and fewer developing to mature females at about 24 DAI. Most RKN that penetrated M‐315 failed to establish and/or maintain giant cells. However, a few females established giant cells. At 44 DAI, the numbers of egg‐laying females on M‐8, M‐78, and M‐315 were 299, 144, and 5, respectively. There were significantly fewer root galls on M‐315 than on M‐78 or M‐8 beginning 10 DAI, and significantly fewer on M‐78 than on M‐8 at 40 DAI. Galls were significantly smaller on M‐315 than on M‐78 or M‐8 beginning 8 DAI, and significantly smaller on M‐78 than on M‐8 beginning 18 DAI. Thus, the post‐penetration development of root‐knot nematode was slower, fewer developed to adult females, and root galls were fewer and smaller on the resistant genotypes than on the susceptible M‐8.
Inheritance of Foot Rot Resistance in Winter Rye
Authors: Miedaner Thomas , Ludwig Werner F. , Geiger Hartwig H.
Published: July 2010

Foot rot in winter rye (Secale cereale L.) caused by Pseudocercosporetta herpotrichoides, Fusarium spp., and Microdochium nivale (syn Fusarium nivale) can be controlled best by host resistance. In this study, the inheritance of foot rot resistance was examined using 15 diallel and 11 factorial crosses tested along with their parent inbred lines. Four out of six test environments in southern Germany were artificially inoculated with either P. herpotrichoides, F. culmorum, or M. nivale. In the other two environments, naturally occurring field epidemics were used. At milk ripening, 50 stems per plot were rated individually for foot rot on a 1 to 9 scale. Significant estimates of genotypic variance and high heritabilities (h2 = 0.82–0.92) were observed in all genetic materials. General combining ability (GCA) was the main source of genetic variation among crosses, while specific combining ability was negligible. Considerable environmental effects and significant genotype × environment interactions were found. Strong phenotypic correlations (r ≈0.9) existed between line per se performance and GCA effects. Heterosis was not important. For optimizing disease assessment, h2 was estimated for varying numbers of steins, environments, and replicates. For inbred lines tested in two environments with two replicates or for single crosses tested in four environments with two replicates, a sample size of 15 plants per plot should result in a h2 of about 0.7. In conclusion, substantial progress can be expected from selection for foot rot resistance in hybrid rye on the basis of line per se performance by rating unspecific foot rot lesions.
Effect of Growth Habit on Yield Components of Late‐Planted Soybean
Authors: Sohédjié Ouattara , Weaver David B.
Published: July 2010

Late‐planted soybean [Glycine max (L.) Merr.] yields are usually lower than full‐season soybean yields. Indeterminate growth habit may be superior to the traditional determinate growth habit for late planting in the southeastern USA. The objective of our study was to determine the effect of determinate and indeterminate growth habit genes on yield components of late‐planted near‐isogenic fines of soybean. Twenty‐three determinate and 23 indeterminate near‐isogenic lines (near‐isolines) of soybean from three populations were compared in the field at Brewton, Tallassee, and Shorter, AL, in 1991 and 1992. Determinates had lower lowest‐pod heights, more mainstem branches per plant, and more two‐seeded pods than indeterminates. Growth habit did not affect total pods per plant, mainstem or branch pods per plant, seeds per plant, seed mass, or number of three‐seeded pods per plant. The growth habit × population and growth habit × location interactions were significant for most traits, but the growth habit × year interactions were nonsignificant or small. Number of mainstem pods was the only yield component correlated with yield (r = 0.36**). We conclude that (i) growth habit genes have little consistent effect on most yield component traits, (ii) growth habit effects are site‐ and population‐specific in the southeastern USA, and (iii) seed yield is not correlated with yield component traits in late‐planted soybean.
Vegetative Growth Analysis of a Drought‐Resistant Soybean Plant Introduction
Authors: Hudak C. M. , Patterson R. P.
Published: July 2010

Although soybean [Glycine max L. (Merr.)] Plant Introduction 416937 (PI) is known to maintain turgidity under desiccating conditions during podfilling, the mechanism(s) underlying this drought hardiness is uncertain. The objective of the present study was to determine whether PI develops drought‐resistant morphology during early vegetative growth. ‘Forrest’ was chosen as the control genotype since it is a commonly grown cultivar of similar phenology. A randomized complete block design with eight replications of each genotype was employed. Field conditions, including water, were optimized so that near maximal vegetative growth could be obtained. During 1988 to 1990, plants were excavated from the upper 38 cm of soil at 7‐ to 14‐d intervals. The PI's drought hardiness did not appear to depend upon reduced leaf area development, since annual estimates of its limiting growth values were 25% greater than those of Forrest. At maximum vegetative development, PI was characterized by having a small number of very large leaves, while Forrest had a large number of comparatively small leaves. At most harvests, PI's root mass, root volume, and relative surface area exceeded that of Forrest, and the relative growth rate of PI roots declined more slowly than that of Forrest, resulting in a 24% greater limiting root mass. PI may have a potential yielding disadvantage in that it develops a limited number of branch nodes and is susceptible to lodging. The PI's utility in breeding programs may reside in its potential to increase morphological diversity in soybean.
Effects of Root Temperatures on Leaf Gas Exchange and Growth at High Air Temperature in Phaseolus acutifolius and Phaseolus vulgaris
Authors: Udomprasert Nawarat , Li Paul H. , Davis David W. , Markhart Albert H.
Published: July 2010

Heat stress influences plant growth, development, and productivity. This research was initiated to determine whether differential root sensitivity to heat is important in determining differences in plant heat tolerance. Tepary bean (Phaseolus acutifolius Gray) and heat tolerant (GNUI 59) and heat sensitive (BBL 47) genotypes of common bean (P. vulgaris L.) were used to study leaf gas exchange and growth after exposure to high air temperature combined with either high or low root temperature. The effect of temperature on endogenous abscisic acid (ABA) levels in leaves and roots was determined using an enzyme‐immunoassay technique. High shoot/root temperature (45/45°C) for 5 h reduced carbon exchange rate (CER) and subsequent growth in all genotypes. Maintaining root temperature at 25°C restored CER to nearly the control level. High root temperature decreased endogenous ABA levels in the roots in all genotypes, but increased ABA in the leaves in the tepary bean and BBL 47 without stomatal closure. Water stress or exogenous ABA pretreatment prior to high temperature treatment induced stomatal closure at high air temperature. There were no differences in leaf temperatures between the two root temperatures, suggesting that the lower levels of CER, mesophyll conductance, and growth under high root temperature were due to root rather than to leaf temperature.
Morphological and Climatological Predictors of Forage Quality in Tall Fescue
Authors: Hill N. S. , Cabrera M. L. , Agee C. S.
Published: July 2010

Forecasting quality losses of standing forage may aid producers when making harvest decisions. The objectives of this research were to compare morphological, climatological, and chronological models as predictors of forage quality in ‘Kentucky‐31’ and ‘All‐Triumph’ tall fescue (Festuca arundinacea Shreb.) receiving three N treatments; and test those models for their ability to predict forage quality. Pure stands of Kentucky‐31 and AU‐Triumph tall fescue were fertilized to meet University of Georgia (UGA) Cooperative Extension Service recommendations with all nutrients except N. Stands were divided into individual plots which received either 50, 100, or 200 kg N ha−1, and harvested weekly after initiation of spring growth. In 1990 and 1991, tillers were counted, staged for morphological development, and weighed. Samples were ground, scanned with a near infrared reflectance spectrophotometer (NIRS), and a subset was analyzed chemically to develop calibrations for forage quality. Near infrared spectrophotometric quality values were regressed with mean stage count, mean stage weight, growing degree days (MSC, MSW, and GDD, respectively) and calendar day, and regression equations were validated with samples harvested from plots in 1992 and 1993. The MSC and MSW equations had poor fit in AU‐Triumph (range of R2 from 0.28–0.35 and 0.58–0.61, respectively) and were not validated. Calendar day and GDD had predicted quality better (range of R2 from 0.76–0.90 and 0.74–0.87, respectively); validation statistics of those equations had intercepts equal to 0.0 and linear coefficients equal to 1.0 for in vitro dry matter disappearance (IVDMD) and occasionally for crude protein (CP), but not for neutral (NDF) or acid (ADF) detergent fiber.
Genetic Improvement in Yield of Semidwarf Rice Cultivars in Colombia
Authors: Cuevas‐Perez Fęderico E. , Berrio Luis E. , Gonzalez Daniel I. , Correa‐Victoria F. , Tulande E.
Published: July 2010

The narrowing gap between commercial and experimental yields in irrigated rice (Oryza sativa L.) has renewed interest in genetic yieldimprovement. Evaluation of past gains is useful for identifying areas with potential for further enhancement. Tall rice cultivar Bluebonnet 50, introduced semidwarfs ‘IR8’ and ‘IR22’, and 13 semidwarfs developed locally from 1971 to 1989 were grown in Colombia under irrigation and rainfed conditions with and without blast (Pyricularia grisea, Sacc.) control during 1992 and 1993. The objective was to estimate progress from introduction and breeding of semidwarfs. Both types of semidwarfs yielded 80 and 122% more than Bluebonnet 50 under irrigation and rainfed conditions with blast control, respectively. Without blast control, the yield advantage (126%) was significant only in 1993. Tillering of semidwarfs was higher in all environments, ranging from 379 to 721 panicles per square meter versus 173 to 392 panicles per square meter for Bluebonnet 50. Panicles were smaller, ranging from 61 to 95 filled grains per panicle versus 118 to 187 filled grains per panicle for Bluebonnet 50. Mean grain yields of introduced and local semidwarfs were similar, but the latter were 10 to 15 cm taller. Linear regressions of means of local cultivars on year of release were nonsignificant (P > 0.05) for the irrigated and rainfed‐with‐blast control environments. For rainfed conditions without blast control, yield increased 0.13 ± 0.041 ba−1 yr−1; panicle size (1.1 ± 0.4 grains yr−1) and plant height (1.1 ± 0.2 cm yr−1) also increased. Breeding in Colombia has improved adaptation of semidwarf rice to rainfed environments.
Recurrent Selection for Grain Protein in Hard Red Spring Wheat
Authors: Delzer B. W. , Busch R. H. , Hareland G. A.
Published: July 2010

Grain protein concentration (GPC) of bread wheat (Triticum aestivum L.) is important because it partially determines bread‐making properties and nutritional value of wheat flour. Ten hard red spring wheats selected for high GPC and other traits were intermated to form the initial population. Twenty to 25 F3 lines were selected and recombined to initiate each successive cycle. Selection intensity for the parents of each cycle ranged from 3.5 to 8%. Four cycles of recurrent selection for increased GPC were evaluated. Direct response to selection for GPC and indirect responses of agronomic and breadmaking quality traits were determined. About 50 random F3‐derived lines from Cycles 0, 2, and 4 were evaluated at two locations for 2 yr to provide an estimate of gain from selection. The average realized gain for GPC was 2.7% per cycle of selection. Flour protein concentration, mixogram water absorption, and kernel hardness increased linearly with selection for GPC. Although recurrent selection effectively increased GPC linearly over cycles, this gain was associated with lower grain yield. We observed a linear decrease in grain yield of 3.2% per cycle at the target location, but no linear trend was detected at the other location. Lines which combine high GPC and high grain yield may be useful as germplasm sources.
Effect of Seed Maturation and Genotype on Seed Vigor in Maize
Authors: TeKrony D. M. , Hunter J. L.
Published: July 2010

High quality seed is the goal of all corn (Zea mays L.) seed producers. The objective of this investigation was to relate several indicators of seed maturity [black layer (BL), milk line (ML)], to seed vigor (cold test and conductivity) over a wide range of dent corn genotypes and environments. Two inbreds (B73, Mo17), four single and modified single cross hybrids, and seven open pollinated, double and three way cross hybrids were produced at two locations (Lexington and Danville, KY) from 1985 to 1989. In 1986 and 1987, a complete plant defoliation treatment was also imposed on inbred, single and double cross hybrids. Seed harvests were started at approximately 30 d after pollination and continued at short intervals (≈4 d). Seed vigor reached maximum levels at physiological maturity (PM) which occurred at black layer Stage 4 for single and double cross progeny. Maximum seed vigor occurred slightly later for inbreds between black layer Stages 4 and 5. There was a significant quadratic relationship between seed vigor (cold test and conductivity) and black layer maturity across all years in each genotype grouping including stay‐green hybrids. When plants were stressed by defoliation or high temperatures during seed development, the seed weight was reduced, seed maturation was accelerated, but maximum seed vigor occurred at the same stage (BL4) as for nonstressed plants. Maximum seed vigor levels consistently occurred at physiological maturity as determined by black layer (or milk line), which can be used by seed producers to estimate the date of harvest.
Induction and Stability of Phenotypic Variation in Sugarcane as Affected by Propagation Procedure
Authors: Burner D. M. , Grisham M. P.
Published: July 2010

Sugarcane (Saccharum L. spp. hybrids) propagated in vitro from shoot tips is generally assumed to be less phenotypically variable than from callus culture. The objectives of this research were to study stalk, milling, and morphological variant characteristics of plants of ‘CP 74‐383’ from callus culture, direct regeneration, shoot tip culture, and conventional bud propagation, and to assess the phenotypic stability after vegetative propagation. Plants were evaluated in plant‐cane and first‐ratoon crops (Experiment 1). Plants with normal or off‐type phenotypes selected from Exp. 1 were similarly evaluated in two successive plant‐cane crops (Experiment 2). The frequency of variants was high for all tissue culture (TC) treatments. The frequency of normal TC plants was 10 and 22% in plant‐cane and first‐ratoon crops, respectively, showing that some variation was transitory. However, phenotypes of normal or off‐type selections were stable with vegetative propagation. The TC plants had low mean plant height, stalk diameter, and stalk weight. Normal TC plants and controls (from bud propagation) were similar for stalk number and plant height, but normal selections had thinner, lighter stalks. Treatments did not differ in milling characteristics in either experiment, indicating that morphology was independent of cane composition. The results demonstrated that shoot tip culture of this cultivar induced considerable phenotypic variability. Little useful in‐vitro induced variability occurred for important phenotypic characteristics.
Germplasm Enhancement in Winter Wheat × Triticum tauschii Backcross Populations
Authors: Cox T. S. , Sears R. G. , Bequette R. K. , Martin T. J.
Published: July 2010

Backcross populations derived from direct hybrids between common wheat (Triticum aestivum L.) and the wild diploid T. tauschii (Coss.) Schmal. have utility for germplasm evaluation, but also can furnish genetic material directly into a germplasm‐enhancement program. Three hundred ninety‐one BC2F2‐derived lines from winter wheat × T. tauschii crosses were selected on the basis of disease resistance and general phenotype from populations undergoing field evaluation to determine whether resistant lines agronomically similar or superior to their recurrent parents could be developed. The selected backcross lines were evaluated for yield and grain‐quality traits under light to moderate infection by leaf rust (caused by Puccinia recondita f. sp. tritici Rob. ex Desm.) and heavy infection by wheat soilborne mosaic and spindle‐streak mosaic viruses at two locations in 1991. Approximately 50% of the lines were selected for further field evaluation at two locations in 1992, and three lines were entered in advanced yield trials in a total of eight environments in 1992 and 1993. At all stages of selection, BC2F2‐derived lines were identified with disease resistance, grain yield, and grain quality superior to those of their recurrent parents. Lines differing from their recurrent parents in grain yield, either positively or negatively, occurred in both the disease‐resistant and disease‐susceptible classes. In advanced yield trials where leaf rust did not affect grain yield, leaf rust‐resistant BC2F2‐derived lines yielded similarly to their recurrent parents and to cultivars currently grown commercially over large areas. Despite the wide differences in phenotype between common wheat and T. tauschii, two backcrosses were sufficient to transfer resistance genes while almost completely restoring the wheat parent's phenotype.
Meiotic Stability of Intersubspecific Hybrids of Snake River × Thickspike Wheatgrasses
Authors: Jones Thomas A. , Wang Richard R‐C. , Li Li‐Hui
Published: July 2010

Based on genomic makeup and partial hybrid fertility, Snake River wheatgrass (proposed name Elymus lanceolatus ssp. wawawaiensis) has been recognized since 1986 as a subspecies of E. lanceolatus (Scribn. & J.G. Smith) Gould. Thus it is conspecific with thickspike wheatgrass [E. lanceolatus ssp. lanceolatus (Scribn. & J.G. Smith) Gould]. However, these two wheatgrasses display distinct morphological features, physiological traits, geographical distributions, and habitat preferences. Hybridization of the two subspecies generates valuable germplasm with considerable heterosis, but the hybrids are partially male sterile. Our objective was to determine the degree and nature of hybrid male sterility. Mean chromosome pairing (and pollen stainability) was 0.11 I + 13.90 II + 0.02 IV (84%) for ‘Secar’ Snake River wheatgrass and 0.10 I + 13.83 II + 0.01 III + 0.05 IV (78%) for ‘Bannock’ thickspike wheatgrass, the parents in the original cross, 0.60 I + 13.61 II + 0.01 III + 0.04 IV (55%) for three F1 hybrid populations, and 0.09 1 + 13.92 II + 0.01 III + 0.03 IV (80%) and 0.441 + 13.66 II + 0.01 Ill + 0.05 IV (64%) for backcross populations to Bannock thickspike wheatgrass and BBR‐syn Snake River wheatgrass, respectively. The low frequency of multivalents in the hybrids indicated that male sterility resulted from some degree of genetic incompatibility rather than a major chromosomal rearrangement. Because hybrid and backcross populations possessed reasonable levels of pollen stainability and chromosome abnormalities were absent, they should respond readily to selection for high pollen stainability.
Genotype × Environment Interactions for Specific Gravity in Diploid Potatoes
Authors: Haynes K. G. , Wilson D. R. , Kang M. S.
Published: July 2010

In a clonally propagated crop, such as potato (Solanum tuberosum L.), an estimate of genetic variance as a proportion of the total phenotypic variance (broad‐sense heritability) is desirable. Because of its importance to the processing industry, tuber specific gravity has been widely studied. Earlier estimates of narrow‐sense heritability for specific gravity in a diploid hybrid population of Solanum phureja × Solanum stenotomum (PHU‐STN) were moderate. The purpose of this study was to identify stable, high specific gravity clones for future population improvement efforts and to estimate broad‐sense heritability based on clonal means in this PHU‐STN population. From 1990 to 1992, 72 diploid hybrid PHU‐STN clones were grown in replicated field plots in Presque Isle, ME, and evaluated for specific gravity. There were significant differences among clones. There was also a significant replication (year) effect and clone × year interaction. From the analysis of variance on specific gravity, broad‐sense heritability based on clonal means was estimated as 0.66, with a 95% confidence interval of 0.50 to 0.78. Stability‐variance statistics calculated for each clone were used to identify stable high specific gravity clones. There was no correlation between average specific gravity during 3 yr and the stability‐variance statistic, indicating that selecting for high specific gravity.
Sucrose Phosphate Synthase: An Enzyme with Heterotic Activity Correlated with Maize Growth
Authors: Causse Mathilde , Rocher Jean‐Paul , Pelleschi Sandrine , Barrière Yves , de Vienne Dominique , Prioul Jean‐Louis
Published: July 2010

Identification of biochemical determinants linked to growth that can be quantitated early in seedling development may be important for breeding purposes. Carbohydrate metabolism is a good candidate for such an approach. The genetic variation and inheritance of the activity of two key enzymes of carbohydrate metabolism, sucrose phosphate synthase (SPS) and ADP glucose pyrophosphorylase (ADPGppase), were studied in maize (Zea mays L.) third and fourth leaves in a half 5 × 5 diallel design, Early greenhouse growth traits (estimated in two trials) and field performances (2 locations × 2 years) were also measured. Genetic variation was observed in greenhouse‐grown leaf tissues for SPS activities under limiting and nonlimiting substrate concentrations, representing the phosphorylated and unphosphorylated state of the enzyme, respectively. Heterosis for SPS was significant in both conditions. In hybrids, SPS activity in the fourth leaf was significantly correlated with the forage dry matter yield measured in the field in 1991 (r = 0.89***, 0.87***, 0.71*, and 0.42 ns, depending on the location), suggesting that SPS activity could be a limiting factor of maize development; but no significant correlations were detected between SPS activities and forage yield measured the next year in two locations. The ADPGppase activity of hybrids was not significantly different from that of parental lines.
Effect of Irrigation Frequency on Cotton Yield in Short‐Season Production Systems
Authors: Chu Chang‐chi , Henneberry Thomas J. , Radin John W.
Published: July 2010

In irrigated desert areas of the southwestern USA, fruiting of cotton (Gossypium hirsutum L.) typically peaks in July. Water management during the fruiting period can influence cotton lint yields. This study tested the hypothesis that small frequent irrigations during the July peak fruiting stage would increase fruit set and yields compared with the same amount of water applied less frequently. During 3 yr under a short‐season production system, irrigation intervals of 5‐d with 42 mm of water applied at each of six irrigations increased lint yield by S to 11% compared with irrigation intervals of 10‐ and 15‐d with 81 and 130 nun of water applied at each of three and two irrigations, respectively. Average stomatal conductance of 1989 and 1991 was higher for the 5‐d‐irrigation interval than for 10‐ or 15‐d intervals. For 1990 and 1991 average leaf water potentials were higher and average leaf temperatures were lower for the 5‐d‐irrigation interval than for the other two irrigation intervals. The results show that with the same amount of water conventionally applied through furrow irrigation, small frequent irrigations during cotton fruiting were effective in reducing water deficit during critical growth stages and increasing lint production. The small frequent irrigations did not increase soil salt content in the top 15 cm of soil after 3 yr of study.
Genetic Variation for Phosphorus Efficiency of Common Bean in Contrasting Soil Types: I. Vegetative Response
Authors: Yan Xiaolong , Lynch Jonathan P. , Beebe Stephen E.
Published: July 2010

Phosphorus deficiency is a primary limitation to bean (Phaseolus vulgaris L.) production in the tropics. Bean genotypes differ in their P efficiency, defined as growth and yield in low P soil. Traits conferring P efficiency may be useful only in specific soil types, or may represent more general adaptations to low P availability. This information is essential in selecting and breeding more P efficient bean germplasm. Our objective was to determine if P efficiency in bean is limited to specific soil types. Sixteen contrasting genotypes were grown in pots of Andosol, Ultisol, and Oxisol soil at three levels of applied P in the tropics. At 35 d after planting, shoot growth, root growth, P accumulation, and symbiotic status were evaluated. Genotypes differed significantly in P efficiency. The relative ranking of genotypes for shoot biomass, root biomass, root length, or P accumulation under all P levels was not affected by soil type and was not related to the degree of rhizobial or mycorrhizal infection. Large‐seeded Andean genotypes were superior to small‐seeded Mesoamerican genotypes, especially under low P. Small‐seeded Mesoamerican genotypes were more responsive to added P. We conclude that (i) large genetic variation for P efficiency exists in tropical bean germplasm, (ii) this variation reflects a general adaptation to low P availability rather than an interaction with specific soil types or soil microbes, (iii) large‐seeded germplasm appears to have superior P efficiency under low P availability, and (iv) Mesoamerican genotypes are more responsive to added P.
Frost‐Induced Movement of Potassium to the Apoplast May Increase Bloat in Ruminants Grazing Alfalfa
Authors: MacAdam Jennifer W. , Hill Jennifer , Whitesides Ralph E.
Published: July 2010

Exposure of alfalfa (Medicago sativa L.) to frost reportedly increases the frequency of bloat in ruminants grazing the forage. Our objective was to investigate changes in leaves of the plant that occur with freezing that could be related to ruminant bloat. A high occurrence of bloat is associated with elevation in the ratio of potassium (K+) to sodium (Na+) in the rumen, which is thought to cause flocculation of chloroplast membrane particles, producing a stable foam that results in bloat. In several plant species, exposure to frost temporarily inhibits ATPase activity, resulting in the movement of water and K+ from the protoplast of plant cells into the apoplast. Our hypothesis was that an overnight frost causes movement of K+ into the apoplast of alfalfa leaves, and leaching of this extracellular K+ from the foliage would increase the ratio of K+ to Na+ in rumen fluid of livestock grazing the alfalfa. To test this hypothesis, we slowly froze detached alfalfa leaves to −2°C, and nucleated extracellular ice formation. We then thawed the leaves and leached them in distilled, deionized water. The mean increase of 1.061 g K+ kg−1 t leaf flesh weight leached from frozen‐thawed alfalfa was sufficient to increase the occurrence of bloat according to evidence from other studies. Compared with control leaves, calcium and magnesium were also elevated by 1.821 and 0.425 g kg−1 leaf fresh weight, respectively, in leachate from frozen‐thawed alfalfa, but relatively little Na+ was found in this leachate. A similar increase in leachate ion concentration was found when the study was repeated.
Cytoplasmic Diversity in Old Domestic Varieties of Soybean Using Two Mitochondrial Markers
Authors: Hanlon Regina , Grabau Elizabeth A.
Published: July 2010

Modern soybean [Glycine max (L.) Merr.] cultivars are derived from a limited number of plant introductions, which restricts germplasm diversity at both the nuclear and cytoplasmic levels. This study was conducted to use molecular techniques to assess the extent of cytoplasmic diversity available to soybean breeders. We have surveyed a collection of old domestic soybean varieties with a cloned 2.3 kilobase (kb) HindIII mitochondrial DNA fragment from the cultivar Williams 82 and the mitochondrial ATP synthase subunit 6 (atp6) gene to determine sources of cytoplasmic diversity present within this collection. This strategy revealed unique mitochondria! DNA (mtDNA) polymorphisms and polymorphism combinations. In several cases, the mtDNA polymorphisms provided a different classification than was predicted from recorded pedigrees. Variability was also detected among cultivars assigned the name Peking that were introduced independently into the USA soybean collection. The results of this survey coupled with previous studies can be used to define additional cytoplasmic groups in soybean.
Molecular‐Marker‐Mediated Characterization of Favorable Exotic Alleles at Quantitative Trait Loci in Maize
Authors: Ragot M. , Sisco P. H. , Hoisington D. A. , Stuber C. W.
Published: July 2010

Exotic maize (Zea mays L.) germplasm, shown to be useful for developing improved temperate cultivars, has remained little used partly because of many inherent shortcomings. Five F2 populations, developed from South American and U.S. germplasm, were used to detect favorable factors of exotic origin at quantitative trait loci (QTL) with isozymes and RFLPs. A number of traits of agronomic importance, including grain yield, were measured on F2 individuals and/or F3 families grown in several environments. Many QTLs, mostly with small effects, were identified. Major QTLs for grain yield and number of ears per plant were located on chromosomes 3 and 6. Stability of QTLs across environments was high. Favorable alleles of exotic origin were found at QTLs for several traits including grain yield and number of ears per plant. Most of these alleles also showed undesirable effects on other traits, however. Nevertheless, the superiority of exotic alleles over adapted alleles was demonstrated clearly at a few QTLs, re‐affirming the usefulness of exotic germplasm for temperate maize breeding.
Soybean Pedigree Analysis Using Map‐Based Molecular Markers: I. Tracking RFLP Markers in Cultivars
Authors: Lorenzen L. L. , Boutin S. , Young N. , Specht J. E. , Shoemaker R. C.
Published: July 2010

The history of soybean [Glycine max (L.) Merr.] cultivar development is relatively short. Approximately 80% of the germplasm present in modern cultivars can be traced back to just 12 ancestral lines which were introduced into the USA in the early 1900s. This limited number of ancestral contributors and short history make soybean a promising system for marker‐facilitated, pedigree‐based, genetic analysis. The overall objectives of this project were to (i) identify a core set of markers that would be useful for pedigree‐based analyses of elite soybean cultivars, (ii) trace markers and chromosomal regions from ancestral to descendent cultivars, (iii) determine if the observed and theoretical contribution of parental genomes to cultivar progeny were comparable, and (iv) demonstrate the utility of pedigree‐based or codescent mapping in the detection of putative linkages between molecular markers and phenotypic traits. Sixty‐four soybean lines including ancestral and milestone cultivars were analyzed at 217 RFLP loci to identify a core set of markers to use in evaluating these, and other elite breeding lines. A core set of 97 polymorphic loci were identified for genetic analysis. Results demonstrated that genomic regions contributed by a parent can be traced, often for more than a generation. Six generations of cultivar development were included in this analysis, and one RFLP allele, R013‐l‐b, could be traced through all six generations. Results also revealed that two pedigrees, that of Lincoln and Ogden, could not be supported by RFLP analysis, although it is possible that the pedigrees reported are correct and the incorrect accessions are maintained in the USDA collection. Comparison of the predicted amount of germplasm contributed by a parent, and the amount observed by RFLP analysis revealed that in only four out of 26 instances did one parent provide more genetic information than expected. Codescent analysis of markers and phenotypes demonstrated putative linkages with B and Dtl. The ability to follow regions of chromosomes from parent to offspring through multiple generations should provide an understanding of what transpired at the molecular level during the breeding of cultivars over the last 55 yr. Graphical genotypes of the cultivars analyzed in this study, and the raw RFLP data, are available for electronic transfer.
Leaf Greenness and Photosynthetic Rates in Soybean
Authors: Ma B. L. , Morrison M. J. , Voldeng H. D.
Published: July 2010

Leaf photosynthesis is a complex process. Determination of photosynthetic rate is too time‐consuming to be used as a field selection criterion for cultivar development. Two field experiments were conducted in 1994 to quantify the relationships of leaf photosynthetic rates and other leaf characteristics (greenness, area, specific weight) of soybean [Glycine max (L.) Merr.] at several growth stages to identify possible indirect indicators of soybean leaf photosynthesis. Our results showed that leaf greenness, as non‐destructively measured by a handheld portable chlorophyll meter (SPAD‐502) was positively correlated with leaf photosynthesis at growth stages R4 to 3 to 10 d after R5 in 16 genotypes. In one experiment involving two genotypes with similar backgrounds, the correlation coefficient was 0.77 at R4, 0.91 at R5 + 5 d, and non‐significant (0.22) at R6 + 10 d, respectively. In a second experiment with 14 genotypes developed during 50 yr of seed yield improvement in Ontario, leaf photosynthesis at R4 + 2 d and R5 + 7 d was consistently correlated with SPAD‐502 chlorophyll meter readings (r ≥ 0.64). Partial correlation coefficients having the same sign and similar magnitude of significance confirmed the positive correlation between the two variables. Relationships between photosynthesis and leaf area or specific leaf weight were not significant (P >0.05) or inconsistent across growth stages. These results suggest that chlorophyll readings are quick, reliable, and repeatable indicators of leaf photosynthetic rate that can be used for screening soybean genotypes.
Development, Identification, and Characterization of a Glyphosate‐Tolerant Soybean Line
Authors: Padgette S. R. , Kolacz K. H. , Delannay X. , Re D. B. , LaVallee B. J. , Tinius C. N. , Rhodes W. K. , Otero Y. I. , Barry G. F. , Eichholtz D. A. , Peschke V. M. , Nida D. L. , Taylor N. B. , Kishore G. M.
Published: July 2010

Glyphosate (N‐phosphonomethyl‐glycine) is the active ingredient the nonselective herbicide Roundup. The sensitivity of crop plants to glyphosate has limited its in‐season use as a postemergence herbicide. The extension of the use of Roundup herbicide to allow in‐season application in major crops such as soybeans [Glycine max (L.) Merr.] would provide new weed control options for farmers. A glyphosate‐tolerant soybean line, 40‐3‐2, was obtained through expression of the bacterial 5‐enolpyruvylshikimate‐3‐phosphate synthase (EPSP synthase, EPSPS) enzyme from Agrobacterium sp. strain CP4. Line 40‐3‐2 is highly tolerant to glyphosate, showing no visual injury after application of up to 1.68 kg acid equivalent (a.e.) ha−1 of glyphosate under field conditions. Molecular characterization studies determined that the single genetic insert in line 40‐3‐2 contains only a portion of the cauliflower mosaic virus 35S promoter (P‐E35S), the Petunia hybrida EPSPS chloroplast transit peptide (CTP), the CP4 EPSPS gene, and a portion of the 3' nontranslated region of the nopaline synthase gene (NOS 3') terminator. Inheritance studies have shown that the transgene behaves as a single dominant gene and is stable over several generations.