bluuebunny/crossref_metadata_2025 huggingface dataset:
Genertion Mean Analysis of Resistance to Race 3 of Soybean Cyst Nematode
Authors: Mansur L. M. , Carriquiry A. L. , Rao‐Arelli A. P.
Published: July 2010

The soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is a serious pest of soybean [(Glycine max (L.) Merr.]. Most genetic studies of resistance in soybean to SCN have used qualitative models, although continuous distributions of phenotypes from zero to many cysts have been observed. We investigated the mode of inheritance for resistance to Race 3 of SCN by weighted least squares regression analysis of generation means for genetic models having additive and dominance parameters. Reaction to SCN was determined by counting the white females present on plant roots 30 d after inoculation. Four crosses, including one reciprocal, were made between resistant and susceptible genotypes. The ancestry of the resistant genotypes (‘A20’, ‘Jack’, and ‘Cordell’) traces to different sources of SCN resistance. Six generation means (P1, P2, Fl, F2, BCp1, and BCP2) in three of the crosses, and four in one (Pl, P2, F1, F2), were used to estimate the genetic effects contained in the means. The data were transformed for analysis because they were not normally distributed. The results indicated that an additive genetic model was sufficient to explain most of the genetic variation for resistance to Race 3 in each cross. Analysis of the pooled data from all crosses, however, indicated the presence of dominance effects as well. Recovery of parental phenotypes in the F2 and backcross populations indicated that no more than four genes were involved in the inheritance of the trait. Estimates for broad sense heritabilities on single plant basis ranged from 0.48 to 0.81. The relatively high heritability and additive genetic control indicate that breeder should be able to select genotypes with an intermediate level of resistance.
Activity of Phenylalanine Ammonia‐Lyase, Tyrosine Ammonia‐Lyase, and Cinnamyl Alcohol Dehydrogenase in the Maize Stalk
Authors: Morrison T. A. , Buxton D. R.
Published: July 2010

The relation between the activities of lignification enzymes and deposition of cell‐wall components during progressive stages of development has not been demonstrated. In this study, phenylalanine ammonialyase (PAL), tyrosine ammonia‐lyase (TALI, and cinnamyl alcohohNADPH dehydrogenase (CAD) activities were determined in maize (Zea maize L.) internodes at several development stages, and the activities were correlated with cellulose, hemicellulose, and lignin concentrations. Growth‐chamber grown maize was harvested at the fourteenth leaf stage, enzyme activities were quantified, and cell‐wall components were determined by the detergent system of fiber fractionation from the lower, middle, and upper sections of Internodes 7 through 14. Internode 7 was the second internode above the groundline. Cell‐wall maturation proceeded basipetally within each internode or the stalk, and appeared to be regulated by a coordinated and basipetal sequence of enzyme activities. Activity of PAL and TAL was highest in internodes undergoing rapid elongation and differentiation (Internodes 14‐13) and progressively diminished in Internodes 11 through 7, which were maturing following cessation of elongation. CAD activity was lowest in upper Internodes 14 through 12, but progressively increased in internodes that were halting elongation (Internodes 11‐7) and were commencing cell‐wall fiber deposition. The degree of lignification increased as CAD activity increased; hemicellulose, cellulose, and lignin depositions correlated strongly with CAD activity rather than with PAL and TAL. CAD activity appears committed to lignification specifically, and to secondary cell‐wall formation, in general, whereas PAL and TAL activities appear to have no direct regulatory role.
Leaf and Spikelet Primordia Initiation in Salt‐Stressed Wheat
Authors: Grieve C. M. , Lesch S. M. , Maas E. V. , Francois L. E.
Published: July 2010

Salt stress is known to affect adversely shoot apex development in cereals. This study was conducted to determine rate and duration of leaf and spikelet primordia initiation as related to final leaf and spikelet numbers in salt‐stressed wheat (Triticum oestivum L.). Early shoot development of two hard red spring wheat cultivars, Yecora Rojo and Anza, was studied in both greenhouse sand cultures and outdoor field lysimeters. In each case, two saline treatments were compared with a nonsaline control treatment. The sand cultures were irrigated with complete nutrient solutions to which NaCI and CaCI2 (2:1 molar ratio) were added to achieve electrical conductivities (K1W) of 1.7, 12.2, and 15.1 dS m−1. Lysimeters were irrigated with tap water salinized to KlW levels of 0.8, 11.4, and 17.1 dS m−1. Timing of primordium initiation was expressed in accumulated thermal time measured in the soil (°C dsoil). A three‐piece linear‐spline model was developed to facilitate the statistical analysis and interpretation of primordium initiation. Parameters of the model corresponded to morphologically significant events. In both experimental locations, each genotype exhibited a similar response to increasing salinity. The rate of leaf primordium initiation decreased while the duration of this phase was unchanged. Salinity had no effect on the rate of spikelet primordium initiation of the genotypes, but the duration of this phase was shortened. As a result, the number of leaves on the main stem and the number of spikelets per spike were significantly reduced by salinity and the yield potential of both genotypes was severely limited.
Selection within Alfalfa Cultivars for Persistence under Continous Stocking
Authors: Smith S. R. , Bouton J. H.
Published: July 2010

Alfalfa (Medicago saliva L.) has been predominately used as a hay crop in North America and most cultivars do not persist under grazing. The objectives of this research were to determine if grazing tolerance could be improved within alfalfa cultivars and to determine population shifts that occurred during selection. The original and selected populations of ‘Apollo’, ‘Florida 77’, ‘Alfagraze’, ‘Spredor II’, and ‘Travels’ were evaluated in central Georgia under 17 to 22 wk of continuous close grazing by beef cattle for 2 yr. Experiments I and II were comprised of two seasons of continuous close grazing and Exp. Ill was comprised of two seasons management for hay production. In addition, eight released, multiple‐pest‐resistant cultivars were also evaluated in Exp. II and III. Stand persistence was measured with plant density measurements and forage production was measured under exclosures. All selected populations, with the exception of Alfagraze, had better stand persistence and yield than their original populations when grazed, but yield and persistence were similar when managed for hay production. Although several fungal pathogens influenced plant mortality there was an inconsistent relationship between disease resistance and stand persistence under grazing. This research indicated that at least two seasons of continuous grazing are required to achieve a consistent ranking for grazing tolerance. In conclusion, this study suggests that grazing tolerance can be improved within existing cultivars without sacrificing forage yield.
Calcium and Relative Humidity Effects on Soybean Seed Nutrition and Seed Quality
Authors: Keiser J. R. , Mullen R. E.
Published: July 2010

Reduced seed calcium concentrations have been observed in soybean [Glycine max (L.) Merr.] seed lots with reduced seed germination. Soybean plants were grown hydroponically at Ames, IA, 1991, to determine if the Ca concentration of the root medium and relative humidity (RII) could influence seed Ca concentration and, subsequently, seed quality. Plants were grown in solution culture in a controlled environment growth chamber, with Ca concentrations of 0, 0.6, 1.2, and 2.5 mM in the root medium from beginning seed (R5) to beginning maturity (R7). In addition, concentrations of 0.6 and 2.5 mM Ca and RH of 55 and 95% were applied from R5 to R7 to plants grown in sand culture in the greenhouse. Treatments were arranged in a randomized compete‐block design in both studies, with the blocks replicated in time in the growth‐chamber study. Seed Ca concentrations increased with increased Ca supply to the plant. Relative humidity had not effect on either seed Ca concentration or germination. A decrease in the percentage of normal seedlings from 96.7 to 41.8% coincided with a decrease in seed Ca from 2.37 to 0.87 mg g−1. Reduced germination of low‐Ca seeds was primarily due to an increase in the percentage of abnormal seedlings. The percentage of normal seedlings was significantly and positively correlated with Ca (r = 0.83) and negatively correlated with the B/Ca ratio and B (r = ‐0.97 and −0.83, respectively) in seeds. Results indicate that reduced Ca supply to the plant may reduce seed Ca concentration in addition to altering other seed nutrients. Reduced seed Ca was associated with poorer seed germination, but additional studies are needed to clarify the role of Ca and other nutrients in the germination of seeds and seedling establishment.
Plant Regeneration from St. Augustinegrass Immature Embryo‐Derived Callus
Authors: Kuo Yu‐Jen , Smith M. A. L.
Published: July 2010

Development of efficient methods for plant regeneration from callus broadens the opportunities for genetic manipulation of new turfgrass selections through tissue culture. This study was conducted to induce callus formation and plant regeneration from embryo explants of St. Augustine grass [Stenotaphrum secundatum (Walt.) Kuntze ‘Texas Common’]. Immature embryo explants incubated in the dark produced yellow, amorphous callus on Murashige and Skoog (MS) agar solidified medium with 30 g L−1 sucrose and 1 or 5 mg L−1 dichlorophenoxyacetic acid (2,4‐D). Subculture to medium with 0.25 L−1 2,4‐D and 0.5 mg L−1 kinetin and introduction of a 14‐h photoperiod under fluorescent lamps (16μmol−2 s−1 photosynthetic photon flux [PPF]) induced formation of white, friable, embryogenic callus. Scanning electronic microscopy revealed that plants regenerated via somatic embryogenesis. Complete plant regeneration was achieved from 33% of the original explants after transfer to 0.5 × MS medium without growth regulators. These rooted plantlets were transplanted to a soil mix in the glasshouse with 100% acclimation success. This system for efficient regeneration of St. Augustine grass from callus could be applied to improved cultivar selection after environmental stress testing at the cell level.
Prediction of Maize Single‐Cross Performance Using RFLPs and Information from Related Hybrids
Authors: Bernardo Rex
Published: July 2010

Methods for predicting hybrid yield would facilitate the identification of superior maize (Zea mays L.) single crosses. Best linear unbiased prediction of the performance of single crosses, based on (i) restriction fragment length polymorphism (RFLP) data on the parental inbreds and (ii) yield data on a related set of single crosses, was evaluated. Yields of m single crosses were predicted as YM = C V−1 yP, where: yM = m × 1 vector of predicted yields of missing (i.e., no yield data available) single crosses; C = m × n matrix of genetic covariances between the missing and predictor hybrids; V = n × n matrix of phenotypic variances and covariances among predictor hybrids; and yP = nn × 1 vector of predictor hybrid yields corrected for trial effects. From a set of 54 single crosses, made between six Iowa Stiff Stalk Synthetic (SSS) and nine non‐SSS inbreds, 100 different sets of n = 10, 15, 20, 25, or 30 predictor hybrids were chosen at random. Pooled correlations between predicted and observed yields of the remaining (54 − n) hybrids ranged from 0.654 to 0.800. The correlations were slightly higher when dominance variance was included in the model or when coefficients of coancestry were determined from RFLP rather than pedigree data. The correlations remained relatively stable across different, arbitrary values of genetic variances. The results suggested that single‐cross yield can be predicted effectively based on parental RFLP data and yields of a related set of hybrids.
Diversity of Historically Important Sweet Corn Inbreds as Estimated by RFLPs, Morphology, Isozymes, and Pedigree
Authors: Gerdes J. T. , Tracy W. F.
Published: July 2010

Historical records indicate that sweet corn (Zea Mays L.) germplasm is largely derived from the Northern Flint race of corn. In addition, most of the publicly available inbreds were derived from three cultivars: ‘Stowell's Evergreen’, ‘Country Gentleman’, and ‘Golden Bantam’. In order to better understand sweet corn germplasm, 43 historically important sweet corn inbreds and three dent corn inbreds were examined by pedigree information, restriction fragment length polymorphisms (RFLPs), isozyme markers, and morphological traits. Data sets were developed from 71 RFLP probes, 27 isozyme loci, 24 morphological traits, and pedigree coefficients of relationship, and these data sets were subjected to cluster analysis. Isozymes and especially morphology did not accurately group these inbreds according to known pedigree relationships. The RFLP distance showed good agreement with pedigree distance (r = 0.54**). Based on cluster analysis of these two data sets this sweet corn germplasm can be divided into two major groups, inbreds that contain Golden Bantam germplasm, and inbreds with Stowell's Evergreen, Country Gentleman germplasm, or both. Several inbreds were not closely aligned with either group, and these unique inbreds have been widely used by sweet corn breeders. The amount of genetic diversity present in this material, with an average of 2.22 alleles per isozyme locus and RFLPs averaging 4.14 variants per probe, is within the range of diversity reported for Corn Belt Dent inbreds.
RFLP Analysis of Soybean Breeding Populations: I. Genetic Structure Differences due to Inbreeding Methods
Authors: Keim P. , Beavis W. D. , Schupp J. M. , Baltazar B. M. , Mansur B. M. , Freestone R. E. , Vahedian M. , Webb D. M.
Published: July 2010

Segregating soybean [Glycine max (L.) Merr.] breeding populations are frequently inbred by either single‐seed descent or by bulking progeny at each generation. During inbreeding, repetitive sampling of individual genotypes, or natural selection, may decrease the potential for genetic gain in a population. This is most likely to occur in populations that are inbred by the bulk method. This study examines the genetic structure of two soybean populations, each containing 261 segregating lines. One population was derived from a cross of two elite lines and was inbred by a multiple‐seed descent (MSD) strategy that is frequently employed by soybean breeders. A second population was derived from an elite × unadapted genotype cross that was inbred by single‐seed descent (SSD). The genetic composition of each line and the genetic distances among lines were estimated using 100 RFLP markers. The genetic contribution of each parent to each population was equivalent regardless of the inbreeding procedure. No individual in either population obtained greater than 75% of its genes from a particular parent. Close genetic relationships among lines were not observed in the SSD population, but were common in the MSD population. Cluster analysis of individual lines within the MSD population indicated that about 18% of the lines were due to repetitive sampling and, therefore, did not represent independent lineages. The repetitive sampling appeared to be caused by stochastic processes, as opposed to systematic factors such as differential fecundity among genotypes. Genetic marker analysis of population structure provides a method for directly assessing the effectiveness of inbreeding strategies.
Role of Leaf Appearance Rate and the Coleoptile Tiller in Regulating Production
Authors: Skinner R. H. , Nelson C. J.
Published: July 2010

Forage production in tall fescue (Festuca arundinacea Schreb.) depends on elongation of existing leaves and production of new leaves and tillers. Genetic selection for high leaf elongation rate (LER), however, results in plants with limited tillering capacity. Our objective was to examine how the development of individual leaves and tillers affects total tiller production in populations of tall fescue selected for high or low LER. Seedlings were grown for 32 to 70 d in controlled environment chambers (500 μmol m−2 s−1 PPFD, 14‐h photoperiod). The low LER (high tillering) population produced twice as many coleoptile tillers as the high LER population, and coleoptile tillers and their progeny accounted for 80% of the difference between populations in tillers per plant after four tiller production cycles. With the exception of the coleoptile tiller, no difference in site usage (number of tillers appearing per axillary bud produced) was observed between populations. Site usage was greater than 0.80 in both populations during the first 30 to 35 days after planting (DAP), but decreased to ≈0.20 by 70 DAP. Both populations had similar leaf and tiller phyllochrons until 30 to 35 DAP. Thereafter, rate of leaf and tiller appearance slowed significantly, beginning first in the high LER population. Thus, tillering differences between populations were initially due to differences in coleoptile tiller production, but after 30 to 35 DAP differences in leaf appearance rate also contributed to differences in potential number of tillers per plant.
Water Status and Development of the Maize Endosperm and Embryo during Drought
Authors: Westgate Mark E.
Published: July 2010

Drought during rain filling decreases final kernel mass in maize (Zea mays L.). Lack of assimilates or an unfavorable water status within the embryo or endosperm could limit kernel development. To test these possibilities, remobilization of reduced C and N as well as kernel and embryo water status were measured in plants exposed to a water deficit during rain fill. Irrigation was withheld from field‐grown plants after final kernel number was established. This treatment resulted in a soil moisture deficit of 224 mm and decreased endosperm and embryo mass by 16%, compared with controls. The water deficit shortened the effective filling period, but did not alter the rate of dry matter accumulation in either the endosperm or embryo. Carbohydrate reserves in leaf and stalk tissues as well as N stored in the leaves were remobilized to support kernel growth. However, grain filling ceased before these reserves were depleted completely. Grain filling continued in both well.watered and water‐deficient plants until the moisture content of the endosperm and embryo decreased to 280 and 430 g kg−1 fresh wt., respectively. Water‐deficient plants reached these values 10 d earlier because water loss from the endosperm began sooner after anthesis and maximum water content of the embryo was lower, compared with the controls. Kernel and embryo osmotic potentials (ψs) decreased rapidly late in grain filling and were − 2.2.to − 2.6 MPa when growth ceased. The results indicate that kernel water status is affected directly by drought and may be an important determinant of kernel development. They suggest that a water deficit after anthesis shortens the duration of grain filling by causing premature desiccation of the endosperm and by limiting embryo volume.
Stability of the Relationship between Specific Leaf Area and Carbon Isotope Discrimination across Environments in Peanut
Authors: Rao R. C. Nageswara , Wright G. C.
Published: July 2010

In previous experiments, specific leaf area (SLA) was shown to be correlated with both carbon isotope discrimination (Δ) and water use efficiency in peanut (Arachis hypogaea L.) suggesting that SLA can be used to screen genotypes for W. However, very little information is available on the stability of the relationship between SLA and Δ across environments. The present study was conducted to examine genotype × environment (G × E) interaction for the relationship between SLA and Δ. Four peanut genotypes (Chico, McCubbin, Shulamit, and Tifton‐8) with contrasting carbon isotope discriminating characteristics were grown in the field either under adequately irrigated or rainfed conditions at two locations in Queensland, Australia. The seasonal changes in Δ and SLA were examined by sampling leaves at monthly intervals. The values of Δ and SLA were significantly influenced by the location, genotype, and irrigation treatments. Genotype × location interaction effects on the relationship between Δ and SLA were not significant. The positive relationship between SLA and Δ was maintained when data were combined over sites and treatments (r2 = 0.87, P < 0.01) indicating stability of the relationship across environments. The SLA was negatively correlated with nitrogen content per unit leaf area (SLN) which in turn was negatively correlated with Δ. The results suggested that SLA can be used as a surrogate for Δ.
Leaf Anatomy of Two Lycopersicon Species with Contrasting Gas Exchange Properties
Authors: Kebede Hirut , Martin Bjorn , Nienhuis James , King Gretchen
Published: July 2010

Lycopersicon pennellii (Cor.) D'Arcy possesses greater drought resistance and higher water use efficiency (WUE) than the domesticated tomato L. esculentum Mill. A previous report suggested three restriction fragment length polymorphism markers for whole plant WUE. This study identifies species differences in anatomical, biochemical, and physiological characteristics of leaves related to leaf gas exchange and whole plant WUE, which can later be tested with the molecular markers. Lycopersicon pennellii exhibited 29% lower stomatal frequency, more even distribution of stomata between the upper and the lower leaf surfaces, and a 54% thicker leaf with 31% greater air space volume relative to total leaf tissue volume than L. esculentum. Trichomes were fewer, but longer, and the ratio of air exposed mesophyll surface area relative to external leaf area was 41% greater for leaves of L. pennellii. However, this species contained 13% less chlorophyll and had 11% lower ribulose‐l,5‐bisphosphate carboxylase/oxygenase (rubisro) activity per unit leaf area than L. esculentum. The mean stomatal resistance (r8) was greater and substantially less variable among leaves of L. pennellii, but those leaves of L. pennellii and L. esculentum that had the same rs also operated at the same photosynthesis rate (A) and WUE. Therefore, differences in and WUE among the two tomato species could be fully explained by contrasting stomatal properties. Either the differences in individual leaf anatomical, biochemical, and physiological characteristics negated each other and did not substantially alter A and WUE, or the expression of the characters was linked to r8 in the same way in both species.
Photosynthetic Differences among Lycopersicon Species and Triticum aestivum Cultivars
Authors: Martin Bjorn , Kebede Hirut , Rilling Christel
Published: July 2010

Leaf photosynthesis rate (A) and water use efficiency expressed as A/gs (gs, stomatal conductance) are controlled by stomatal properties and leaf internal anatomical and biochemical/physiological characteristics. Two germplasm entries were selected from each of the genera Triticum and Lycopersicon with contrasting drought resistance. Both drought resistant entries (L. pennellii and T. aestivum cv. TAM W‐ 101) had the greater A/gs within each pair. Of the two entries with high A/gs, L. pennellii had lower A and TAM‐101 had higher A than the respective counterpart with low A/gs (L. esculentum and T. aestivum cv. Sturdy, respectively). Comparison of photosynthetic stomatal supply capacities and mesophyll biochemical demand capacities suggested that differences in mean A and A/gs in contrasting tomato species were dependent on the lower mean gs of L. pennellii than L. esculentum, because in leaves with equal gs the balance between stomatal supply and mesophyll demand was identical. In wheat leaves operating at identical gs, however, TAM W‐101 had greater mesophyll capacity than Sturdy. Lower A and A/gs of Sturdy than TAM W‐101 was correlated with lower carboxylation efficiency and lower light and CO2 saturated A, factors associated with the photosynthetic biochemistry of mesophyll tissue. At identical gs, the balance between mesophyll and stomatal capacities and limitations of TAM W‐101 was the same as for the two tomato species. This suggested that for these three entries (L. esculentum, L. pennellii, and TAM W‐101), the differences in A and A/gs resulted from differences in the mean and range of gs. Sturdy was unique by having low A and low A/gs, a result of poor mesophyll capacity compared to the other entries.
Remobilization of Carbon and Nitrogen in Wheat as Influenced by Postanthesis Water Deficits
Authors: Palta Jairo A. , Kobata Tohru , Turner Neil C. , Fillery Ian R.
Published: July 2010

Preanthesis stored C and N in wheat (Triticum aestivum L.) are important in a mediterranean climate because grain filling frequently depends on the remobilization of preanthesis assimilates. We determined the effect of the rate of development of postanthesis water deficits on the remobilization of C and N to the grain using stable isotopes of C and N accumulated in the plant during the vegetative phase. Plants were grown in pots with adequate water and under similar temperature and humidity conditions until anthesis, and then were transferred to two temperature and humidity regulated greenhouses, and watering was stopped. One greenhouse was maintained at minimum relative humidity of 80% and the other at 40%. Within 6 d of anthesis the rates of development of plant water deficits became different and for the first 19 d after anthesis they were 0.10 and 0.18 MPa d−1 for the high and low humidity regimes, respectively. Total grain C with fast development of water deficits was reduced by 24%, relative to the slow rate, because postanthesis C assimilation was reduced by 57%, while remobilization of preanthesis stored C was increased by 36%. Total grain N was not affected by the rate of development of water deficits because there was a greater retranslocation of preanthesis N with fast relative to slow development of water deficits and because there was a smaller loss of preanthesis N with fast development of water deficits. Fast development of water deficits reduced losses of preanthesis N from 25% to 6%. The absolute contributions of preanthesis C and N to the grain were 449 and 35 mg plant−1, respectively, with fast development of water deficits. These contributions accounted for 64 and 81% of the total grain C and N, respectively. The gain in grain 13C and 15N in the mainstem and Tiller 1 of plants exposed to rapid development of water deficits, arose not only from remobilization from the straw of those shoots, but also seemed to be supplemented by C and N remobilized from Tillers 2 and 3.
Receptacle and Ovary Assimilate Concentrations and Subsequent Boll Retention in Cotton
Authors: Heitholt James J. , Schmidt John H.
Published: July 2010

Assimilate supply or flux to developing cotton (Gossypium hirsutum L.) bolls (fruits) may help determine whether those bolls are retained or abscised. Most bolls that abscise tend to do so within a few days post anthesis (DPA), and little is known about the relationship between assimilate levels in young fruiting forms and their relationship to boll retention. Therefore, the objective of this study was to determine the relationships of young receptacle and ovary assimilate levels to boll retention among genotypes and sympodial branch positions. Eight genotypes of cotton (four cultivars and four leaf‐type isolines) were grown in the field in 1989 and 1990 using conventional cultural practices. Boll retention percentages (bolls/tagged flowers) and assimilate concentrations of excised receptacles and ovaries at Fruiting Positions 1, 2, and 3 were determined at 5 d preanthesis, 0 DPA, and 2 DPA. Position 1 boll retention (54 to 75%) was greater than that of Position 2 (19 to 45%) but the concentrations of soluble sugars in their excised receptacles and ovaries were similar. Variation in retention among genotypes at Position 1 was either small or nonsignificant but was significant at Position 2. Boll retention, glucose, and starch concentration of Position 2 MD 65‐11 super okra‐leaf bolls were lower and N concentration higher than the other genotypes. However, assimilate levels did not appear to explain the variation in retention among the eight genotypes. Other factors, such as C metabolism in ovules, may need to be examined in order to explain the physiological reasons for differences in boll retention.
Behavior of Maize Stem Diameter during Drying Cycles: Comparison of Two Methods for Detecting Water Stress
Authors: Katerji Nader , Tardieu François , Bethenod Olivier , Quetin Philippe
Published: July 2010

Changes in stem diameter are frequently used to assess plant water status. We have compared two ways of data processing, analyzing either the changes in daily stem contraction (the most commonly used method) or the changes in daily maximum stem diameter (DMSD). Changes in stem diameter of adult maize (Zea mays L.) plants were measured during drying cycles either in the field or in a pot experiment, together with predawn leaf water potential, noon‐time stomatal conductance, noon‐time leaf water potential, and fraction of soil transpirable water. Close relationships, common for field and pot experiments, were observed between changes in DMSD and predawn leaf water potential (r2 = 0.91), and noon‐time stomatal conductance (r2 = 0.81). Relationships also existed between DMSD and the fraction of soil transpirable water (r2 = 0.84 and 0.87 in the field and pot experiments, respectively). In contrast, the daily stem contraction showed complex and loose relationships with soil and plant water status, and with stomatal conductance. This is consistent with the facts that (i) maize day‐time plant water status undergoes relatively little changes during drying cycles, and (ii) stomatal conductance is linked to the soil water status, and is therefore correlated to measurements characterizing night‐time plant water status such as DMSD or predawn leaf water potential. A practical consequence would be that changes in DMSD should be used rather than daily stem contraction for characterizing plant water status of maize, or for triggering the beginning of irrigation in automatic systems.
Seed Size and Water Potential Effects on Germination and Seedling Growth of Winter Wheat
Authors: Mian M. A. R. , Nafziger E. D.
Published: July 2010

Published reports on the effects of seed size on wheat (Triticum aestivum L.) vigor are conflicting. The interactive effects of seed size and water stress on germination and early growth of wheat are perhaps important in this regard. Experiments were conducted to measure the effects of seed size and water potential on germination and seedling growth of the soft red winter wheat genotypes ‘Auburn’ and ‘Howell’. In a growth chamber germination test using solutions of mannitol, germination percentage (GP) was not affected by seed size, but osmoticum of −300 kPa reduced GP to 69 compared to 88 and 89 for the 0 and −100 kPa treatments, respectively. In greenhouse soil, shoot dry weight (SOW), root dry weight (ROW), and number of tillers (NT) of 4‐wk‐old seedlings from large seeds (35 mg seed−1) were larger than those of seedlings from medium (26 mg seed−1) and small (17 mg seed−1) seeds. Soil water potentials of −100 and −300 kPa decreased all three parameters compared to the control (−10 kPa). The GP in the greenhouse was reduced by low water potential, but was not affected by seed size. The genotype × water potential interaction was significant for SOW and ROW, but not for GP and NT; Howell was more susceptible to water stress than Auburn. At −10 kPa, 4‐wk‐old plants from small seeds had SDW and ROW that were 30 and 39% smaller, respectively, than those from large seeds, while at −300 kPa, SOW and ROW of plants from small seeds were 75 and 78% smaller, respectively, than those of plants from large seeds. The ability of larger seeds to produce larger seedlings than smaller seeds thus appears to be more pronounced under drought than under well‐watered conditions. While it is not known whether larger seedlings (with larger roots) would enhance water supply to the plant by exploring more soil, or would decrease the supply through more transpiration, faster early growth from larger seeds may be advantageous in establishing plants under dry soil conditions.
Cytological Evaluation of Tobacco Doubled Haploids for Presence of Amplified Homologous Chromosomal Regions
Authors: Reed Sandra M. , Burns Joyce A. , Wernsman E. A.
Published: July 2010

Atypical quadrivalents, resulting from pairing between homologous amplified chromosome segments, have been observed in hybrids between low‐yielding, second‐cycle doubled haploid (DH) lines of tobacco (Nicotiana tabacum L.) and their source cultivars. The first objective of this study was to determine if homologous amplified chromosome segments are present in other DHs, such as those that have been through only one cycle of anther culture and those that are only moderately depressed in yield. The second objective was to trace the development of amplified chromosomal regions through consecutive cycles of anther culture. Chromosome pairing was studied in DH × cultivar hybrids involving high‐ and low‐yielding first‐cycle DHs and second‐cycle DHs derived from the high‐yielding first‐cycle DHs. There appeared to be no correlation between multivalent formation and yield. The one DH that was found to contain homologous amplified chromosome segments was a low‐yielding first‐cycle DH, NC95 DHL. NC95 DHL was then crossed to two second‐cycle DHs derived from it that had previously been determined to have homologous amplified chromosome segments. Cytological analysis of these DH × DH hybrids indicated that the amplified chromosomes in NC95 DHL passed unchanged to one of its second‐cycle derivatives. In contrast, a number of modifications occurred in another of its derivatives during the second cycle of anther culture.
Endosperm Type Effects on Biomass Production and on Stalk and Root Quality in Sweet Corn
Authors: Treat C. L. , Tracy W. F.
Published: July 2010

In maize (Zea mays L.), a strong reproductive (grain) sink has been associated with increased stalk and root lodging. A weak reproductive sink may result in reduced production of photosynthate. Endosperm mutants sugary1 (su1) and shrunken2 (sh2) reduce the strength of the reproductive sink. Our objective was to examine stalk and root quality, biomass production, and reproductive sink size using su1 and sh2 in near‐isogenic backgrounds. In 1989 and 1990, seed of two half‐diallels made from six inbreds was planted. The same inbreds were used; however, one diallel used su1 versions of the inbreds and the other, sh2 versions. Each diallel was planted twice; in one planting the su1 and sh2 diallels were pollinated with su1 pollen and in the other, they were pollinated with sh2 pollen. This resulted in four sets of hybrids that varied only for endosperm type. Stalk and root quality and biomass and partitioning traits were measured. Percentage root lodging, root pull resistance, stalk diameter, stalk section weight, and grain yield differed significantly between starchy and sh2 endosperm types. Hybrids with sh2 had less grain yield and root lodging, higher root pull resistance and stalk section weight. Starchy types had a slightly higher harvest index than the su1 endosperm types. There were no significant differences in biomass among the four groups. The significant reduction in reproductive sink caused by the sh2 endosperm was not associated with decreased biomass.
Russian Wheat Aphid Resistance in Barley: Inheritance and Linked Molecular Markers
Authors: Nieto‐Lopez Rosa M. , Blake Thomas K.
Published: July 2010

Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is an important pest of small grains cereals in many areas throughout the world. This research was conducted to determine the inheritance of resistance and to identify molecular markers of resistance in the barley (Hordeum vulgare L.) lines PI366444 and PI366453. Artificial infestation was performed in the field and growth chamber. Sodium dodecyl sulphate‐polyacrylamide gel electrophoresis, Southern blotting, and polymerase chain reaction (PCR) techniques were used to determine plant genotypes. The PI366444 and PI366453 lines were intercrossed and each was also crossed with the susceptible cultivars Stark and Bearpaw. Allelism tests of F2 progeny showed that the resistant lines shared common or tightly linked resistance genes. Segregation ratios from crosses among resistant and susceptible plants, measured using F3 families, indicated that there were at least two resistance genes in both of the P1 lines. Two different regions in the barley genome were associated with RWA resistance genes. Variation for both leaf chlorosis and leaf rolling in F2 plants from crosses with both resistant lines was associated with the sequence‐tagged‐site (STS) PCR markers B‐hordein and D14 on the short arm of Chromosome 5. The STS‐PCR marker ABG8 on Chromosome 2 was associated with leaf rolling in one cross. Barley breeding programs throughout North America have devoted significant time and resources to backcrossing RWA resistance genes into acceptable cultivars. The molecular markers described in this report may assist barley breeding programs in introgression and fixation of linked resistance genes into useful germplasm.
Selection among Haploid Sporophytes for Resistance to Black Shank in Tobacco
Authors: Campbell K. G. , Wernsman E. A.
Published: July 2010

Black shank, caused by Phytophthora parasitica Dast var. nicotianae [Breda de Haan] Tucker, is a common disease of tobacco (Nicotinna tabacum L.). Selection for genetic resistance to black shank within an F1‐derived haploid population is more efficient than selection within an F2 diploid population. Our objectives were to identify black shank resistance in three segregating haploid tobacco populations and to verify that disease resistance assessed on haploids corresponded to that of doubled haploids (DHs). Population 1 was derived from ‘McNair 944’ × ‘ZA 692’, Populations 2 from ‘Coker 371‐Gold’ (C 371‐G) × ‘K 326’, and Population 3 from ‘VA 509’ × breeding line MDH 410. Haploids were transplanted into a disease nursery and disease incidence was recorded weekly throughout the growing season. We observed segregation for resistance in all three haploid populations. Rescue and chromosome doubling was successful for 85% of selected haploids. In the flue‐cured populations (1 and 2), all but one selected haploid was resistant as a DH. Transgressive segregation for resistance was identified in Population 1. The resistance of a population produced by Intel‐mating Population 1 DHs was equal to that of McNair 944, the resistant parent. Resistance of Population 2 DHs derived from selected haploids was equal to that of C 371‐G, the resistant parent. Selected DHs from Population 2 were significantly more resistant than both K 326 and an unselected DH population derived from the same cross. In Population 3, the hurley population, differences between parents and among DHs were difficult to detect and should be assessed in multiple environments.
Using Climatological, Geographical, and Taxonomic Information to Identify Sources of Mature‐Plant Salt Tolerance in Alfalfa
Authors: Smith S. E. , Johnson D. W. , Conta D. M. , Hotchkiss J. R.
Published: July 2010

Performance under salinity stress has been improved in elite populations of alfalfa (Medicago sativa L. sensu lato) by mass selection. Use of unimproved germplasm may permit additional gains in salt tolerance or access to unique tolerance mechanisms. Resources would be used more efficiently if germplasm with specific traits could be identified from large collections using taxonomical, climatological, or geographical data. Our objective was to determine whether such information could be used to identify M. sativa accessions in the U.S. plant introduction (PI) collection likely to have improved response to salinity. We evaluated forage yield for three harvests in 630 Pis under saline (80 mMNaCI) and nonsaline irrigation in greenhouse trials. Passport data were used to classify climate (Trewartha's system) at the collection site. No significant differences were found in mean salt tolerance (forage yield with saline irrigation/nonsaline irrigation) among the subspecies of M. sativa sampled extensively (falcata, caerulea, varia, and sativa). Accessions considered either tolerant or with high saline yield (high forage yield with saline irrigation; highest 15.1% of accessions for these traits) were present in all subspecies. Mean salt tolerance and saline yield for accessions, and the proportion of accessions considered tolerant or with high saline yield did not differ between accessions from six basic climate groups (Tropical, Arid, Subtropical, Temperate, Boreal, Highland). An increased proportion of tolerant accessions was found from arid environments where alfalfa is usually grown without irrigation. The effects of agronomic practices seems to represent a major limitation to use of climatological data in identifying germplasm with improved performance under salinity stress.
White Clover Seed Production: I. Crop Water Requirements and Irrigation Timing
Authors: Oliva R. N. , Steiner J. J. , Young W. C.
Published: July 2010

White clover (Trifolium repens L.) seed production may be increased by soil‐water deficits during flowering. This study was conducted on a Woodburn silt loam (fine‐silty, mixed, mesic Aquultic Argixeroll) in 1990 and 1991 to determine white clover seed crop water requirements and supplemental irrigation timing. A crop water stress index (CWSI) was calculated and the fraction of available soil‐water used was used to determine white clover seed crop water requirements. Under minimal‐stress conditions, depleted soil‐water was replenished twice weekly to field capacity with the water amount used since the last application. Four treatments had a single water replacement to 100% field capacity when 25, 46, 68, and 84% of the available water was used in 1990 and 30, 57, 64, and 79% in 1991. A nonirrigated control was also maintained. We identified two distinct CWSI non stressed baselines for canopy‐air temperature differences versus vapor pressure deficit that were related to crop aging but not to canopy floral display. Maximumse ed yield water‐use efficiency was obtained in 1990 when water application was delayed until 68% of the available soil‐water was depleted and CWSI was 0.46. In contrast to 1990, in 1991 none of the single water application treatments affected seed yield because flower production was reduced by dense stolon production. The CWSvI alues across all treatments in both years weren egatively related to leaf water potentials (r = −0.86).
Recurrent Selection for Maize Grain Yield: Dry Matter and Nitrogen Accumulation and Partitioning Changes
Authors: Moll R. H. , Jackson W. A. , Mikkelsen R. L.
Published: July 2010

Recurrent full‐sib family and reciprocal recurrent selection have resulted in significant increases in grain weight of crosses between the varieties of maize (Zea mays L.) Jarvis Golden Prolific and Indian Chief. The objectives of this study were to (i) compare increases due to 14 cycles of recurrent full‐sib family selection, and reciprocal recurrent selection for yield in maize and (ii) determine whether increased grain weights were accompanied by parallel increases in total dry matter and total N accumulation. Unless total dry matter acquisition increases in parallel with grain weight during selection, sustained root and shoot functions would be restricted by excessive diversion of carbohydrates to grain. After 14 selection cycles on sandy soils of the North Carolina coastal plain, grain weight, dry matter accumulation, and N accumulation in the population hybrid increased 23, 12, and 4%, respectively, with full‐sib family selection and 27, 21, and I0%, respectively, with reciprocal recurrent selection. Greater proportions of the dry matter and N accumulated were partitioned to grain after full‐sib family selection than after reciprocal recurrent selection. Therefore, photosynthate production after full‐sib family selection was not sufficient to fully satisfy both the demand by grain and the requirements for root and shoot processes. Reciprocal recurrent selection resulted in a greater increase in photosynthate production, so that the hybrid population was able to meet the demand for carbohydrate by higher grain yield and still sustain N acquisition by roots. The conclusions were also supported by heterosis for grain weight, total dry matter, and total N accumulation, which was greater after reciprocal recurrent selection than after full‐sib family selection. Selection to increase grain weight will result in efficient N acquisition only when the greater grain weight is supported by an adequate increase in photosynthate production.
Genetics of Maize Tolerance of Striga hermonthica
Authors: Kim Soon‐Kwon
Published: July 2010

A parasitic weed, Striga hermonthica (Del.) Benth., infects millions of hectares of arable land in sub‐Saharan Africa, and it threatens production of cereal crops. The objectives of this study were to investigate inheritance in maize (Zea mays L.) inbred lines of tolerance and resistance to S. hermonthica, based on visible host plant symptoms and Striga emergence counts. A diallel cross involving 10 inbreds was tested under Striga infested fields at Mokwa, Nigeria, for 5 yr. Host plant response was rated on a scale of 1 (no symptoms) to 9 (plants dead or dying). Ratings for the crosses ranged from 3.6 (TZi 11 × TZi 12) to 8.3 (TZi 9 × TZi 10). General combining ability (GCA) mean square was roughly twice specific combining ability (SCA) mean square. Data on S. hermonthica emergence counts were taken from the 45 F1 crosses for 2 yr. Average Striga emergence of the 45 crosses ranged from 7.5 (TZi 9 × TZi 12) to 41.0 (TZi 2 × TZi 10). The SCA mean square was roughly 3.5 times greater than the GCA mean square. The results of this study reveal that genetic control for tolerance and resistance of maize genotypes tested to S. hermonthica is polygenic and that the inheritance is quantitative.
Photosynthetic Response to Chilling in Peanut
Authors: Bell M. J. , Micheals T. E. , McCullough D. E. , Tollenaar M.
Published: July 2010

Recent evidence suggests peanut (Arachis hypogaea L.) may be sensitive to relatively mild night temperature in terms of both dry matter accumulation and yield. The objective of this research was to quantify the effects of a range of night temperatures (9–20 °C) on leaf CO2 exchange rate (CER) of unhardened plants and to study the mechanisms involved in the contrasting response of peanut cultivars to differing night temperature. Four peanut cultivars (Ontario Agricultural College [OAC] Ruby, OAC Garroy, Chico, and Early Bunch) were grown in either controlled‐environment cabinets or outdoors during August and September at Guelph, Ontario. Results of the outdoor study indicated a linear decline in CER as ambient night temperature fell from 20 to 13 °C for all cultivars except OAC Garroy, with OAC Ruby less sensitive to low night temperature than Chico or Early Bunch. Limitations to CER after chilling at 10 °C in the dark were greater for Chico and Early Bunch (CER reduced by ≈35%) than for OAC Ruby and OAC Garroy (CER reduced ≈15%). All cultivars showed the ability to recover CER within 24 to 48 h of alleviation of chilling conditions. Cultivars grown indoors showed differing responses to one or two successive chilling nights (Chico was more affected than all others), but after four successive chilling nights, all cultivars showed a similar linear response to night temperature (i.e., CER = 0.693 × Train + 11.8 ; r2 = 0.90). An analysis of the relative contribution of stomatal and mesophyll constraints to CER in indoor studies (chilled at 9 °C) indicated significant limitations due to each component, with the relative importance dependent on cultivar and chilling period duration. Results suggest that night temperatures may be an important factor in determining relative cultivar performance in cool production environments.