bluuebunny/crossref_metadata_2025 huggingface dataset:
A PRECISE GRAVIMETRIC METHOD FOR SIMULATING DROUGHT STRESS IN POT EXPERIMENTS
Authors: Earl Hugh J.
Published: July 2010

Many different approaches have been used for the simulation of drought stress in pot studies. An ideal technique should (i) maintain uniform soil water content within the rooting zone, (ii) allow the rate at which stress develops to be precisely controlled, regardless of differences in plant size or variations in environmental conditions, (iii) permit a range of physiologically distinct stress levels to be imposed and maintained indefinitely, and (iv) provide a means of accurately quantifying the stress level. In the present study, a computer automated null‐balance lysimeter was evaluated against these criteria. Separate experiments were conducted with soybean [Glycine max (L.) Merr.] and cotton (Gossypium hirsutum L.) growing in 2.5‐L pots. Single plant water use was quantified gravimetrically by frequent, automated recording of pot weights, and transpired water was replaced by a computer controlled watering system such that relative soil water content (RSWC) was maintained within a narrow range. In this way, pots were held at four RSWC levels ranging from 20 to 75%. Despite the frequent additions of small amounts of water at the tops of the pots, soil water distribution within the pots was found to be remarkably uniform, suggesting that bulk RSWC was a suitable indicator of the soil water deficit experienced by the roots. Measurements of whole plant water use indicated that the four RSWC levels represented four statistically distinct levels of water stress. It is concluded that null balance lysimetry is a useful approach to simulating drought stress in greenhouse experiments, with specific advantages over other available techniques.
Concepts of Intrinsic Value and Integrity of Plants in Organic Plant Breeding and Propagation
Authors: van Bueren E. T. Lammerts , Struik P. C. , Tiemens‐Hulscher M. , Jacobsen E.
Published: July 2010

The natural approach taken by organic agriculture obviates the use of synthetic agrochemicals and emphasizes farming in accordance with agroecological principles. Also implicit in this approach is an appreciation for theintegrityof living farm organisms, with the integrity being evaluated from a biocentric perspective. The ethical value assigned to integrity of organisms has challenged us to develop criteria for evaluating both integrity and breeding techniques. For cultivated plants, integrity refers to their inherent nature, their wholeness, completeness, species‐specific characteristics, and their being in balance with their (organically farmed) environment. We evaluate integrity using criteria derived from four different perspectives: integrity of life, plant‐specific integrity, genotypic integrity, and phenotypic integrity. These criteria were used to assess whether existing breeding and propagation techniques violate the integrity of crop plants. In vitro techniques and techniques that engineer at the DNA level appeared to be incompatible with the integrity of crops, with the exception of use of DNA markers. On the other hand, breeding techniques that work at the level of breeding, evaluation, and selection for whole plant performance, and which do not break reproductive barriers between species, may conform to the principles of organic farming. In the selection process, the so‐calledbreeder's eyecan be developed to become a more consciously applied instrument for perceiving and assessing aspects of the wholeness or phenotypic integrity of a plant. Thus, the challenge given by the organic community to breeders implies the further development of scientific approaches, evaluation, and choice of breeding techniques, and the systematic development of the respectful and artful eye of the individual breeder.
Root Growth Parameters of Converted Race Stocks of Upland Cotton and Two BC2F2 Populations
Authors: Basal H. , Bebeli P. , Smith C. W. , Thaxton P.
Published: July 2010

Genetic modification of the rooting system may lead to more drought tolerant upland cotton, Gossypium hirsutum L. This experiment was designed to evaluate rooting traits at the seedling stage for 68 Converted Race Stocks (CRS) compared with TAM94L‐25 and ‘Lankart 142’, and to investigate the recoverability of robust rooting traits in two BC2F2 populations derived by crossing a robust (M‐9044‐0031) and a nonrobust (M‐9044‐0057) rooting CRS donor parent with TAM94L‐25. Initial screen of the CRS showed that genetic variation occurred among the 68 accessions for root length (RL), lateral root number (LRN), root fresh weight (RFW), lateral root dry weight (LRDW), and total root dry weight (TRDW). There was a 2.3‐, 2.6‐, 4.6‐, 4.8‐, and 4.4‐fold difference among the 11 most robust and 11 least robust rooting CRS accessions for RL, LRN, RFW, LRDW, and TRDW, respectively. However, no CRS were identified that were superior to the elite germplasm and BC2F2 recurrent parent, TAM94L‐25. The robust rooting population of M‐9044‐0031/3*TAM94L‐25 produced longer RL and more LRN per plant than the nonrobust rooting population of M‐9044‐0057/3*TAM94L‐25. However, no differences were observed between the two BC2F2 populations for root weight parameters. Results suggest that the day‐neutral CRS accessions have useful genetic variability for root growth parameters, that robustness of seedling rooting parameters can be recovered easily, and that seedling rooting robustness can be improved by crossing robust rooting parents.
Dominance and Genetic Drift
Authors: Edwards Jode W. , Lamkey Kendall R.
Published: July 2010

Many public sector maize recurrent selection programs have been designed based on additive genetic expectations. Populations have been managed as large metapopulations with the assumption that population size must be very large because inbreeding due to finite size causes a linear reduction in genetic variance; we show that in BS13(S)C0 such predictions are inaccurate and discuss some implications. The objective of this study was to predict the effects of subdividing a maize population, BS13(S)C0, into finite subpopulations with previous estimates of genotypic variance‐covariance components in the BS13(S)C0 population. Changes in variance among subpopulations, genetic variances within subpopulations, and mean values of subpopulations were predicted. Predicted variance among subpopulations increased approximately linearly with the inbreeding coefficient, in accordance with additive genetic expectations. Additive genetic theory predicts a linear decline in both total and additive genetic variance within subpopulations. Predicted total genetic variance within subpopulations initially increased, then decreased when the inbreeding coefficient was between 0.2 and 0.4 for most traits. Predicted additive genetic variance within subpopulations for grain yield decreased little at inbreeding coefficients <0.5. Predicted additive genetic variance for other traits decreased in approximate accordance with additive genetic expectations. These results provide model‐based predictions that inbreeding BS13(S)C0, that is, genetic drift, will not lead to linear reductions in total genetic variance or additive genetic variance as typically expected. Implications of these results for agricultural selection programs are discussed.
Postanthesis Water Deficits Enhance Grain Filling in Two‐Line Hybrid Rice
Authors: Yang Jianchang , Zhang Jianhua , Wang Zhiqing , Liu Lijun , Zhu Qingsen
Published: July 2010

Two‐line hybrid rice (Oryza sativa L.) is a hybrid from a thermosensitive genetic male sterile line and its corresponding restoring line. This hybrid rice shows strong heterosis but a slow grain‐filling rate, as a result of unfavorably delayed senescence. This study investigated the possibility that a moderate water deficit imposed during grain filling may enhance plant senescence, and therefore facilitate the remobilization of reserve C to the grains and improve grain filling. Two two‐line indica hybrids were grown in both the pot and field. Three levels of soil water potential, well watered (WW), moderate water deficit (MD), and severe water deficit (SD), were imposed from 9 d after anthesis to maturity in both pot and field experiments. Results showed that Chlorophyll content and photosynthetic rate of the flag leaves declined more quickly as plants approached maturity for MD and SD plants than for WW plants, indicating the water deficits enhanced senescence. The remobilized C reserve and reallocation of pre‐fixed 14C from stems to grains increased by 1.5‐ to 2‐fold and 55 to 67%, respectively, for water deficit plants, when compared with WW plants. The water deficit treatments shortened the grain‐filling by 5 to 17 d and increased the grain‐filling rate by 0.09 to 0.27 mg d−1 grain−1 The grain yield of MD plants in both experiments was increased by 8.2 to 10% but that of SD plants in the pot was reduced. We conclude that if water deficit is properly controlled during the grain filling, whole‐plant senescence is enhanced. The enhanced senescence can facilitate remobilization of C reserves, accelerate grain filling, and increase grain yield in the two‐line hybrid rice.
How to Succeed by Doing Nothing
Authors: Wilson Lewis J. , Sadras Victor O. , Heimoana Simone C. , Gibb Dallas
Published: July 2010

Clarifying the amount of pest damage that can be tolerated without justifying insecticidal control will be useful in reducing insecticide use and in development of integrated pest management (IPM) systems. This study investigated the ability of irrigated, high‐yielding cotton (Gossypium hirsutum L.) to recover from artificially applied damage simulating that of early season insect pests. Six experiments were done across five cotton‐growing seasons. Damage included defoliation, terminal damage, and flower bud removal in a range of timings, combinations, and intensities. Crop yield was unaffected by defoliation applied before first flower buds appeared, even when 100% of true leaves were removed on three occasions (Nodes 2, 4, and 6). Crop maturity was affected by sustained high levels of leaf loss with a peak delay of 10 d after 100% defoliation three times. Up to three light tip damage events or one heavy damage event had no effect on yield and only a slight effect on crop maturity (<5‐d delay to harvest). Heavy early fruit loss (100% fruit removal from the first four fruiting branches) did not affect yield but caused a delay in maturity of ≈7 d. Equations describing the relationship between damage type, intensity, and repetition and the yield and maturity of cotton were developed and used in sensitivity analysis to define tentative damage thresholds for IPM systems in cotton.
Testcross Performance of Semiexotic Inbred Lines Derived from Latin American Maize Accessions
Authors: Tarter J. A. , Goodman M. M. , Holland J. B.
Published: July 2010

Tropical maize (Zea mays L.) represents the most diverse readily available source of germplasm to broaden the limited genetic base of temperate maize in the USA. One objective of this study was to determine if exotic‐derived alleles contributing to enhanced testcross agronomic performance were maintained in semiexotic lines created by inbreeding and pedigree selection. A second objective was to determine if first‐generation semiexotic lines could produce hybrids with agronomic performance comparable to commercial U.S. hybrids. One hundred sixty‐four semiexotic inbred lines were developed from crosses between temperate‐adapted inbred line Mo44 and 23 Latin American maize accessions. Mo44 and each semiexotic line were testcrossed to temperate hybrid LH132 × LH51 for evaluations. In first‐stage replicated yield trials, testcrosses of 18 semiexotic lines, representing six different races, had significantly greater grain yields than the Mo44 testcross. Advanced yield evaluations were performed on check entries and 33 selected semiexotic line testcrosses in three additional environments. Across 10 environments, 12 semiexotic line testcrosses exhibited significantly greater grain yield than the Mo44 testcross, indicating recovery of favorable exotic alleles. Semiexotic testcrosses were not competitive with commercial hybrids for grain yield but were similar to or better than commercial hybrids for grain moisture and lodging resistance. Many superior accessions represent relatively recent introductions into regions from which they were collected. Tropical landraces seem to be a good source of exotic germplasm that can be used to broaden the genetic base of modern U.S. maize production and improve productivity.
Development and Utilization of SSRs to Estimate the Degree of Genetic Relationships in a Collection of Pearl Millet Germplasm
Authors: Budak H. , Pedraza F. , Cregan P. B. , Baenziger P. S. , Dweikat I.
Published: July 2010

Pearl millet [Pennisetum glaucum (L.) R. Br.] cultivars derive from a narrow gene pool, and studies of genetic diversity in Pennisetum germplasm suggest promising opportunities for the use of undomesticated materials for improving pearl millet varieties. However, efficient utilization of wild germplasm will require effective DNA marker‐based fingerprinting strategies for rapid assessment of genetic relationships. The present study aims at development and utilization of a collection of microsatellite (SSR, simple sequence repeat) markers for assessing the genetic diversity of 53 lines of millet. A small insert genomic library was screened with a (CT)15 oligonucleotide probe. A total of 34 (CT)n–containing clones were identified, and specific primers were designed for 18 of these. Of 18 new microsatellites developed as a part of this work, 11 were used to estimate the genetic diversity, along with 19 from other sources. Cluster analysis by the unweighted pair‐group method with arithmetic averages (UPGMA) showed two major and eight minor clusters, suggesting that the millet germplasm could readily be distinguished by UPGMA. The coefficients of genetic distance among germplasm lines were high and averaged D = 0.60 (range 0.28–0.92). Genetic diversity averaged 0.38. These results demonstrated that genotypes with potential traits are maximally different from the cultivated gene pool and could readily be distinguished. Development and utilization of polymerase‐chain‐reaction‐(PCR)‐based markers such as SSRs is a valuable asset for estimating genetic diversity, the identification of unique genotypes as potentially important new sources of alleles for enhancing important characteristics, and analyzing the evolutionary and historical development of cultivars at the genomic level in pearl millet breeding programs.
Cytology and Fertility of Advanced Populations ofElymus lanceolatus(Scribn. & Smith) Gould ×Elymus caninus(L.) L. Hybrids
Authors: Jensen Kevin B.
Published: July 2010

Within the wheatgrasses and wildryes, amphiploids are frequently made as a means for introgressing desirable traits and restoring fertility in hybrids between diverse species. This study reports the cytology, fertility, and morphological characteristics ofElymus lanceolatus(Scribn. & Smith) Gould,E. caninus(L.) L., their F1hybrids, advanced generations (F7and F8), and three generations of advanced amphiploid progenies (C1, C2, and C3). Meiotic chromosome associations ofE. lanceolatusandE. caninusare typical of allotetraploids. Chromosome pairing in the F1hybrids suggests a close relationship between the two parents. Bivalent associations most frequently observed in the F7and F8were 14 bivalents. After multiple generations of harvesting available seed each generation from 10 plants, an increase in meiotic regularity was observed in the advanced F generations. Aneuploidy in the amphiploids (C generation) was observed in the C2and C3generations with chromosome numbers ranging from 47 to 56. The C1generation had significantly fewer univalents per cell than the C2and C3generations. Combined across chromosome numbers, there was a significant decrease in the number of bivalents from 22.48 to 21.36 to 20.27 in each succeeding C generation, respectively. After seven generations of seed increase, pollen stainability increased from less than 1% in the F1hybrid to 87 and 85% in the F7and F8generations, respectively. Chromosome doubling significantly reduced pollen stainability in the C1, C2, and C3generations as compared to the parents and advanced F generations. Cluster analysis was able to separate the parents and the different hybrid populations.
Wheat‐Alien Species Derivatives: A Novel Source of Resistance to Fusarium Head Blight in Wheat
Authors: Oliver R. E. , Cai X. , Xu S. S. , Chen X. , Stack R. W.
Published: July 2010

Fusarium head blight (FHB), caused mainly by Fusarium graminearum Schwabe, is a destructive disease of wheat (Triticum spp.) in humid growth conditions throughout the world. Genetic resistance of the host plant is considered the most effective and sustainable method of defense against FHB; however, only limited sources of resistance are available in wheat. Relatives of wheat have proven to be an invaluable gene pool for wheat improvement. The objective of this study was to explore relatives of wheat for FHB resistance. We evaluated 293 lines derived from the crosses of wheat with its relatives for resistance to spread of FHB infection over two greenhouse seasons. of these 293 derivatives, 66 were susceptible, 153 appeared moderately resistant, and 74 lines exhibited a level of resistance comparable with T. aestivum L. ‘Sumai 3’, the most widely used source of resistance to FHB. Alien species involved in development of these derivatives include T. tauschii (Coss.) Schmal., Roegneria kamoji C. Koch, R. ciliaris (Trin.) Nevski, Leymus racemosus Lam., Thinopyrum ponticum (Podp.) Barkworth & D.R. Dewey, Th. elongatum (Host) D.R. Dewey, Th. junceum (L.) Love, Th. intermedium (Host) Barkworth & D.R. Dewey, Dasypyrum villosa L., Secale cereale L., and oat (Avena sativa L.). The wheat‐alien species derivatives identified as resistant to FHB include wheat‐alien species amphiploids, synthetic hexaploid wheat lines, and wheat‐alien species substitution and translocation lines. These derivatives could serve as novel sources to enhance resistance of wheat to FHB.
Balancing Investment Incentives and Social Benefits when Protecting Plant Varieties
Authors: Lesser W. , Mutschler M. A.
Published: July 2010

This paper examines the most recent (1991) UPOV modification of Plant Variety Protection systems to provide incentives for prebreeding. We conclude the system is unworkable as presently interpreted and, at a minimum, recommend that national bodies be established to manage minimum enhancements for initial variety status. A more fundamental limitation is the application of a single approach for improvements controlled by single or by multiple gene traits; a relatedness requirement is appropriate for the latter but not the former. We recommend different criteria be applied depending on the type(s) of innovation that characterizes a new variety. Absent that, the incentive structure applies pressure against the use of competitors’ materials in a breeding program, which can delay breeding advances, while not providing significant incentives to encourage introduction of new traits through prebreeding.
Covariation for Microsatellite Marker Alleles Associated withRht8 and Coleoptile Length in Winter Wheat
Authors: Bai Guihua , Das Modan K. , Carver Brett F. , Xu Xiangyang , Krenzer Eugene G.
Published: July 2010

Wheat (Triticum aestivumL.) cultivars with greater coleoptile elongation are preferred in low‐precipitation dryland regions and in early‐planted management systems of the Great Plains, but the presence of GA3 (gibberellin)‐insensitive dwarfing genes tends to restrict coleoptile elongation. The agronomic value ofRht8 and the discovery of its diagnostic microsatellite marker, Xgwm 261, have accelerated breeders’ interest inRht8 as an alternative dwarfing gene. Our objectives were to determine allelic distributions at the marker locus in contemporary samples of hard winter and soft red winter wheat relative to samples of Chinese accessions from aRht8‐rich geographic region, and to compare coleoptile elongation in the presence or absence ofRht8 determined by the Xgwm 261 marker. The 165‐bp (primarily hard winter wheats) and the 174‐bp (primarily soft red winter wheats) alleles of Xgwm 261 were most frequent. About 8% of all U.S. accessions carried the 192‐bp allele diagnostic forRht8, compared with 64% of the Chinese accessions. Coleoptile length varied among accessions from 4.4 to 11.4 cm. Frequency distributions for 192‐ and non‐192‐bp genotypes showed no advantage of the 192‐bp allele to coleoptile elongation. None of the 192‐bp genotypes from the Great Plains showed greater coleoptile length than ‘TAM 107’, a hard red winter cultivar withoutRht8often chosen over contemporary cultivars for its greater emergence capacity with deeper seed placement. Since coleoptile elongation may be controlled by several quantitative trait loci, identifying only the presence of 192‐bp allele of Xgwm 261 may be misleading if the primary motivation for its deployment is to increase coleoptile length in a semidwarf plant type.
Estimation of Combining Ability for Resistance to Fusarium Stalk Rot in Grain Sorghum
Authors: Tesso Tesfaye , Claflin Larry E. , Tuinstra Mitchell R.
Published: July 2010

Fusarium stalk rot (caused by Fusarium spp.) is an important disease of grain sorghum [Sorghum bicolor (L.) Moench]. The objectives of this study were to identify genetic sources of Fusarium stalk rot resistance and estimate combining ability. Six sorghum R‐lines, representing commercial parent lines and potential sources of stalk rot resistance, Tx2737, Tx435, SC33, SC35, SC599 and SC1158, and three standard seed parents, ASA3042, AWheatland, and ARedlan, were intercrossed in a Design II mating scheme. The inbred parent lines and corresponding hybrids were evaluated in field trials at Manhattan and Hesston, KS, in 1999 and 2000. Three randomly selected plants in each plot were artificially inoculated in the pith tissue of the basal stalk with liquid cultures of F proliferatum at 14 d after flowering. One additional plant in each plot was inoculated with distilled water as a control. At 28 d after inoculation, plants were harvested and scored for disease severity. Significant differences in disease reactions were noted among parent lines and hybrids. Among hybrids, significant male and female parent effects and interactions were detected. SC599 consistently had very low mean disease scores, followed by SC1158. Hybrids produced with SC599 were also highly resistant, indicating that genes for resistance had a dominant mode of inheritance in this genotype. SC599 represents an excellent source of resistance to F. proliferatum for use in breeding programs.
Primitive Accession Derived Germplasm by Cultivar Crosses as Sources for Cotton Improvement
Authors: McCarty Jack C. , Jenkins Johnie N. , Wu Jixiang
Published: July 2010

Primitive accession derived germplasm of cotton, Gossypium hirsutum L., may provide useful traits for cultivar improvement. The ability to predict advanced generation performance when crossed with commercial cultivars would enhance their utility and encourage their use in breeding programs. Our objective for this study was to predict genetic effects for day‐neutral derived lines derived from primitive accessions and crossed to cultivars using a mixed linear model approach. Parents and F2 populations were grown at two field locations in 1998 and 1999 and parents and F3s were grown at two locations in 2000. Lint yield, yield components, and fiber quality traits were evaluated. An additive‐dominance additive × additive (ADAA) model was used for genetic analysis. A mixed linear model, minimum norm quadratic unbiased estimation (MINQUE) was used to predict genetic effects and genotype values. Generally, the female cultivar parents had higher additive effects for lint yield and lint percentage; however, these females generally had lower additive effects for fiber strength. Significant AA effects widely existed among parents and F2 populations for lint percentage, boll weight, and fiber strength. The correlation coefficients between observed values and predicted values were mainly high among traits and environments. These data suggest that it is appropriate to use the ADAA genetic model to predict genetic effects and hybrid genotypic values for advanced generations. Our study showed that fiber strength may be significantly improved over that of the female parents, while the lint yield was slightly but not significantly predicted to be less than their female parents. This study suggested that day‐neutral primitive germplasm accessions provided a valuable gene resource for selecting high yielding lines with significantly improved fiber strength.
Effect of Multiple Copies of Puroindoline Genes on Grain Softness
Authors: See D. R. , Giroux M. , Gill B. S.
Published: July 2010

End use quality in wheat (Triticum aestivum L.) is primarily determined by grain hardness or texture. The puroindoline genes Pina and Pinb are the main components of the 15‐kDa friabilin protein, which is associated with kernel softness. Pina and Pinb are expressed in diploid wheat species but are silent in tetraploid wheat. The active puroindolines in hexaploid, or bread wheat, were derived from Aegilops tauschii Coss., the D genome diploid donor. The focus of this study was to incorporate active puroindoline genes into the A and B genomes of bread wheat and analyze their impact upon grain softness. Functional copies of Pina and Pinb in disomic substitution lines of T. monococcum L. chromosome 5Am for 5A of T. aestivum and 5Ss of Aegilops searsii Feldman & Kislev ex K. Hammer for 5B of T. aestivum were used to produce lines that contained four copies (5Am, 5D; 5Ss, 5D) and six copies (5Am, 5Ss, 5D) of the puroindolines. There was a direct correlation in grain softness with the increase in copy number of the puroindolines. Northern blots showed increased expression of both Pina and Pinb Extraction of TX114 soluble proteins indicated that levels of both proteins were also increased. Single kernel characterization system (SKCS) analysis showed a decrease in kernel hardness by approximately 10 points below the value of 71 for ‘Chinese Spring’ (CS) for each additional copy of Pina and Pinb added. These results indicate that increasing the functional copy number of the puroindolines can impact grain softness in bread wheat.
Modeling Rice Growth with Hyperspectral Reflectance Data
Authors: Yang Chwen‐Ming , Chen Rong‐Kuen
Published: July 2010

Field experiments were conducted to study the seasonal changes of rice reflectance spectra and approaches to model rice (Oryza sativa L.) growth with high‐resolution reflectance data. Ground‐based remotely sensed canopy spectra and growth parameters of rice plants, including fresh weights of leaves and shoots, dry weights of leaves and shoots, plant height, and leaf area index, were measured regularly during the first and the second cropping seasons in 2000 to 2002. Spectral indices of RRED/RNIR ratio, RGREEN/RNIR ratio, RRED/RGREEN ratio, and normalized difference vegetation index (NDVI) were calculated, where spectral characteristic RGREEN is reflectance at green light (490–560 nm) maximum (GREEN), RRED is reflectance at red light (640–740 nm) minimum (RED), and RNIR is reflectance at near‐infrared (740–1300 nm) peak (NIR). Seasonal patterns of these spectral attributes and growth parameters implied the existence of developmental effects as well as environmental impacts. Generally, growth parameters reached the maximum near heading when the vegetative growth was greatest, and decreased thereafter. Modeling between spectral attributes and growth parameters can be improved by separating growing period into the preheading and postheading phases. Some of the selected spectral attributes were shown to have significant relationships with growth parameters. Models established by the multiple linear regression (MLR) analysis also indicated the feasibility for estimating rice growth. These MLR models combining spectral reflectance from more than two wavebands provided flexibility in choosing the individual narrow bands, exhibited a greater sensitivity to phenological variation, and improved the models’ ability to estimate plant growth.
Physiological Adaptation of Kentucky Bluegrass to Localized Soil Drying
Authors: DaCosta Michelle , Wang Zhaolong , Huang Bingru
Published: July 2010

This study was designed to investigate effects of surface soil drying (SD) on water relations, gas exchange, growth characteristics, and abscisic acid (ABA) content of leaves and roots for Kentucky bluegrass (Poa pratensis L.), and to examine whether physiological adaptation to SD is associated with hydraulic or chemical regulation. ‘Award’ and ‘Nuglade’ were subjected to three soil moisture treatments in a growth chamber: (i) well‐watered control; (ii) SD (0–20 cm); and (iii) full soil profile (0–40 cm) drying (FD). Under SD, turf quality (TQ), relative water content (RWC), photosynthesis, and cell membrane stability remained the same as the controls, but stomatal conductance (gs) declined by 35 and 45%, and shoot growth rates were reduced by 50 and 40% for Award and Nuglade, respectively. Root DW decreased in 0‐ to 20‐cm dry soil, but increased compared with controls in the 20‐ to 40‐cm wet soil under SD. The ABA content increased by four to sixfold in roots at 0‐ to 20‐cm drying soil and did not change in the 20‐ to 40‐cm wet soil under SD conditions. The ABA content was also higher in leaves of SD plants. The results suggested Kentucky bluegrass adapted to localized soil drying by maintaining TQ, photosynthesis, leaf water status (WS), and root growth using water in the deeper soil profile. Decline in gs and shoot growth was independent of leaf WS, and could be hormonally controlled, which could help maintain favorable WS in leaves by reducing water loss under SD conditions.
Nitrogen Fertilization and Stocking Rate Affect Stargrass Pasture and Cattle Performance
Authors: Garay A. Hernández , Sollenberger L. E. , McDonald D. C. , Ruegsegger G. J. , Kalmbacher R. S. , Mislevy P.
Published: July 2010

Stargrass (Cynodon nlemfuensis Vanderyst) is an important tropical forage, but the interaction of stocking rate (SR) and N fertilizer rate on stargrass pastures is not well understood. The objective was to determine the effects of three SR (2.5, 5.0, and 7.5 bulls ha−1) and three N rates (112, 224, and 336 kg ha−1 yr−1) on stargrass pasture characteristics and performance of Jamaica Red Poll (Bos taurus × B. indicus) weanling bulls at St. Ann, Jamaica. Soil was a bauxitic clay loam, and pastures were rotationally stocked (7‐d grazing and 21‐d rest period). Pregraze herbage mass increased as SR decreased (2.0‐4.8 Mg ha−1 in Year 1 and 3.3‐8.3 Mg ha−1 in Year 2). Herbage crude protein (CP) and in vitro digestible organic matter (IVDOM) generally increased with increasing SR and N rate. Bull daily gain decreased curvilinearly from 0.70 to 0.26 kg in Year 1 and 0.65 to 0.35 kg in Year 2 as SR increased from 2.5 to 7.5 head ha−1 Daily gain increased linearly as N rate increased from 112 to 336 kg ha−1 The N fertilizer rate had little effect on gain per hectare at the lowest SR, but gain increased with fertilization up to 224 kg N ha−1 for a SR of 5 head ha−1 and up to 336 kg N ha−1 for a SR of 7.5. In conclusion, economic return from N fertilization of stargrass pastures is dependent upon SR, with greater N rates more likely to be profitable if SR is high.
Identification of Microsatellite Markers Associated with a Stem Solidness Locus in Wheat
Authors: Cook J. P. , Wichman D. M. , Martin J. M. , Bruckner P. L. , Talbert L. E.
Published: July 2010

Wheat stem sawfly (WSS), Cephus cinctus N., is a major insect pest of winter and spring wheat, Triticum aestivum L., in areas of the northern Great Plains. The primary control measure is use of resistant cultivars containing solid stems. Environmental effects on expression of the trait can be problematic, thus genetic markers would be useful. In this study, a doubled haploid (DH) winter wheat population derived from a ‘Rampart’ (solid stems) × ‘Jerry’ (hollow stems) cross was analyzed to identify molecular markers linked to genes controlling stem solidness. The DH population was genotyped with GWM and BARC microsatellite primers that spanned the wheat genome. To genotype the population efficiently, bulked segregant analysis (BSA) was used to identify polymorphism between groups of solid stem and hollow stem individuals. Four microsatellite markers (GWM247, GWM340, GWM547, and BARC77) were found linked to a single solid stem QTL (designate Qss.msub‐3BL) on chromosome 3BL. However GWM247, GWM340, and GWM547 were found to be more closely linked to the QTL than BARC77. Single marker analysis showed Qss.msub‐3BL contributes at least 76% of the total variation for stem solidness. Additionally, no significant relationship existed between Qss.msub‐3BL and other agronomic traits, including yield. These microsatellite markers (GWM247, GWM340, and GWM547) will be useful for selecting solid‐stemmed wheat cultivars to help control the wheat stem sawfly.
Microsatellite Markers Linked to the Stb2 and Stb3 Genes for Resistance to Septoria Tritici Blotch in Wheat
Authors: Adhikari Tika B. , Wallwork Hugh , Goodwin Stephen B.
Published: July 2010

Septoria tritici blotch (STB) of wheat (Triticum aestivum L.), caused by the fungal pathogen Mycosphaerella graminicola (Fuckel) J. Schröt. in Cohn (anamorph: Septoria tritici Roberge in Desmaz.), occurs naturally in all wheat production areas around the world. Two genes for resistance to this disease, Stb2 and Stb3, have been identified in wheat germplasm and together confer resistance to the most prevalent strains of M. graminicola in Australia and the USA. However, so far neither gene has been mapped in the wheat genome and their linkage relationships to other markers are not known. The objectives of this study were to identify molecular markers linked to the STB resistance genes Stb2 and Stb3 and to map these genes in the wheat genome. Genetic families of doubled‐haploid populations segregating for Stb2 and Stb3 were evaluated in the greenhouse for STB reaction during the spring and fall seasons of 2002 and 2003. Genomic DNA isolated from each segregating population was analyzed with microsatellite or simple‐sequence repeat (SSR) markers in bulked‐segregant analysis to identify those that cosegregated with the STB phenotypes. Linkage analysis identified five SSR markers near the Stb2 gene on the distal region of the short arm of chromosome 3B. Loci Xgwm389 and Xgwm533.1 were approximately 1 cM distal to Stb2, which itself was 3.7 cM distal to Xgwm493 In addition to Stb2, this genomic region contains multiple genes conferring resistance to taxonomically diverse fungal pathogens of wheat, including a major quantitative trait locus for resistance to Fusarium head blight (caused by Fusarium graminearum Schwabe). The SSR marker Xgdm132 was linked to the Stb3 gene at a distance of approximately 3 cM on the short arm of chromosome 6D. The microsatellite markers identified in this study should facilitate marker‐assisted selection and pyramiding of Stb2 and Stb3 with other STB resistance genes for more durably resistant wheat.
A Haplotype‐Based Method for QTL Mapping of F1 Populations in Outbred Plant Species
Authors: Cervantes‐Martinez Cuauhtemoc , Brown J. Steven
Published: July 2010

The integration of quantitative trait loci (QTL) analysis into breeding strategies rather than being seen as separated processes has been proposed to increase the power and accuracy of QTL detection and to allow the two activities to be joined. The main objective of this research is to develop a specific scheme for mapping QTL in actual breeding F1 populations of outbred plant species with a high degree of accuracy. The proposed method groups populations by common founders and statistically associates founder‐origin probabilities that trace the common founder haplotypes in a given region of the progeny genome with the phenotypic expression, using a linear model with a structured covariance matrix. The method was applied to computer simulated data sets, corresponding to five F1 populations of 100 individuals each obtained from the crosses of a common founder with several other founders. We are currently using this scheme with cocoa (Theobroma cacao L.) crosses, using selected clones resistant to specific diseases to widen the genetic base of disease resistance. The results indicate that the position and effect of QTLs in the common founder, that explain each at least 14% of the phenotypic variance, can be estimated with good precision and accuracy. The theoretical assumptions on which this approach was developed render the method appropriate for outbred plant species that are highly heterozygous, which is often the case in tropical tree crops like cocoa, and have phenotypic traits that show few interlocus interaction effects.
Sugarcane Photosynthesis, Transpiration, and Stomatal Conductance Due to Flooding and Water Table
Authors: Glaz Barry , Morris Dolen R. , Daroub Samira H.
Published: July 2010

Sugarcane (Saccharum spp.) is the primary crop on the Histosols of the Everglades Agricultural Area (EAA), where periodic floods and undesirably high water tables are increasing in occurrence and duration. Improved understanding of the physiologic responses of sugarcane to these conditions could help develop strategies to sustain high yields. The purpose of this study was to evaluate the effects of periodic flooding followed by drainage to different depths on single‐leaf net photosynthetic rate (Ps), transpiration (Ts), and stomatal conductance (SC) of sugarcane. In 2000 and 2001, two sugarcane genotypes were planted as split plots in 12 lysimeters filled with Pahokee muck soil. Responses of Ps, Ts, and SC to four water‐table treatments were measured for four 21‐d cycles each year. Three treatments consisted of 7‐d flooding followed by 14‐d drainage to depths of 16, 33, or 50 cm. The fourth treatment was a continuous 50‐cm water table. Analyses of individual cycles and analyses repeated over cycles generally identified neutral or positive responses of Ps, Ts, or SC to flood. Drained water‐table depth did not consistently affect Ps, Ts, or SC, but when differences occurred, 16 cm was often a favorable drainage depth. These neutral and sometimes positive responses to short‐duration flood or long‐duration high water tables support previous reports of acceptable and sometimes enhanced yields from sugarcane exposed to high water tables. Previous findings were supported that time of formation of stalk aerenchyma in sugarcane may be a key factor for sustaining high yields after exposure to flood.
Kentucky Bluegrass Response to Potassium and Nitrogen Fertilization
Authors: Fitzpatrick Richard J. M. , Guillard Karl
Published: July 2010

The response of Kentucky bluegrass (Poa pratensis L.) to potassium (K) fertilization has been inconsistent. The objective of this research was to determine the effects of K fertilization across varying nitrogen (N) rates and clipping management on Kentucky bluegrass clipping yields, quality, tissue K concentrations, apparent N recovery, and N use efficiency. A 2 × 4 × 4 factorial was arranged in a split‐plot design and repeated across two years. Main plots were clipping treatments (returned vs. removed) and subplots were N rates (0, 98, 196, and 294 kg ha−1 yr−1) in combination with K rates (0, 81, 162, and 243 kg ha−1 yr−1). There was no positive effect of K on clipping yields and quality even though soil extractable K levels tested low. Higher K rates, however, increased N recovery and use efficiency for all but the highest N rate. Tissue K response to K fertilization was nonlinear. Yield and quality responses were not correlated to tissue K concentration. Nonexchangeable K levels were high in the native soil, and may have provided an additional source of K for bluegrass. The results suggest that extractable K values alone may not adequately predict available K to Kentucky bluegrass in this sandy loam soil.
Development of DNA Markers Suitable for Marker Assisted Selection of Three Pi Genes Conferring Resistance to Multiple Pyricularia grisea Pathotypes
Authors: Fjellstrom Robert , Conaway‐Bormans Concetta A. , McClung Anna M. , Marchetti Marco A. , Shank A. Robert , Park William D.
Published: July 2010

Rice blast, caused by the fungus Pyricularia grisea (Cooke) Sacc., is a serious rice (Oryza sativa L.)disease causing considerable economic damage worldwide. DNA markers for rice blast resistance have been developed, but most are not suitable for routine use in a marker‐assisted selection breeding program involving large numbers of progeny. After identifying candidate microsatellite markers from public database sources, we have mapped these markers near the blast resistance genes Pi‐b, Pi‐k, and Pi‐ta2 on rice chromosomes 2, 11, and 12, respectively, using segregation information from hundreds of progeny in several crosses. Two microsatellite markers, RM208 and RM224, were found to cosegregate with the Pi‐b and Pi‐k genes, respectively, while additional microsatellites were found to closely flank these two genes and the Pi‐ta2 gene. The new markers are polymorphic in the narrow crosses characteristic of applied breeding programs and appear to be ideally suited for marker assisted selection for blast resistance in rice because of their tight linkage with resistance genes and ease of use through analysis of amplification products. A dominant marker indicating the presence of the Pi‐b gene, Pibdom, has also been developed on the basis of the sequence of the cloned Pi‐b gene. These markers should facilitate the introgression and pyramiding of these three blast resistance genes into new rice cultivars and elite lines.
Engineering Soybean for Enhanced Sulfur Amino Acid Content
Authors: Krishnan Hari B.
Published: July 2010

Soybean [Glycine max (L.) Merr.] is an important protein source in human diets and animal rations. Additionally, human consumption of soybean protein is reported to provide specific health benefits. Since methionine and cysteine contents limit the nutritional value of soybean, efforts involving both traditional breeding and genetic engineering have been employed in attempts to increase the presence of these essential amino acids. Traditional breeding has been primarily utilized to increase the total protein content but not to enhance the sulfur amino acid content of soybean. Although mutagenesis in conjunction with traditional breeding is a viable approach for enhancing the sulfur amino acid content of soybean, genetic engineering appears to be a more realistic approach. Introduction of methionine‐rich heterologous proteins has resulted in a modest increase of this amino acid in soybean. Either elevating the expression of endogenous methionine‐rich proteins or introducing synthetic proteins containing a high percentage of essential amino acids are other possible approaches that may increase the nutritional quality of the seed. Even though considerable progress has been made in enhancing the methionine content of soybean, several obstacles remain. A thorough understanding the sulfur assimilatory pathway in soybean is a prerequisite for improving the sulfur amino acid content. Expression of feedback‐insensitive forms of serine acetyl transferase and O‐acetylserine (thiol) lyase, two key enzymes in sulfur assimilatory pathway, could lead to an increase in the availability of sulfur amino acids. An adequate supply of sulfur amino acids in developing seeds may facilitate accumulation of sulfur‐rich proteins to a level sufficient to meet the nutritional requirement of livestock and poultry.
Mineral Composition of the Grains of Tropical Maize Varieties as Affected by Pre‐Anthesis Drought and Rate of Nitrogen Fertilization
Authors: Feil B. , Moser S. B. , Jampatong S. , Stamp P.
Published: July 2010

Breeding for higher concentrations of minerals in food crops is one option for improving the health of humans suffering from the consequences of mineral deficiency. The plant breeding approach requires that varietal differences are stable across different environmental conditions. The main objective of our research was, therefore, to determine whether differences in the concentration of grain minerals (P, K, Mg, Ca, Mn, Zn, and Cu) among tropical maize varieties are affected by the level of water and N supply. A 3‐yr study with two water regimes (preanthesis drought vs. irrigation throughout the vegetation cycle), three levels of N fertilization (0, 80, 160 kg N ha−1, applied as ammonium sulfate), and four varieties (Suwan 1, La Posta Sequia, KTX2602, DK888) was conducted in the tropical lowlands of Thailand. The water regime did not affect the mineral composition of the grains. Application of N fertilizer reduced the concentrations of Ca and Zn, and increased the concentration of Mn in the grains. The top yielder, DK888, had the lowest concentrations of N, P, Mg, and Cu in the grain. The varietal differences in the concentrations of grain N and minerals were fairly stable across the levels of N and preanthesis water supply. The varieties that differed most in the grain N and P concentrations (DK888 and KTX2602) had almost the same endosperm/germ dry weight ratio. It remains to be determined whether breeding for high grain yield inevitably lowers the concentrations of grain minerals and protein.
Population Density and Low Nitrogen Affects Yield‐Associated Traits in Tropical Maize
Authors: Monneveux P. , Zaidi P. H. , Sanchez C.
Published: July 2010

Worldwide, tropical maize (Zea mays L.) is commonly exposed to low N conditions. Identification of low N tolerance‐related traits would help to develop indirect selection for yield and marker assisted selection under stress. Tolerance to high plant population density has been proposed as an alternative breeding strategy to improve stress tolerance in maize. A better understanding of mechanisms underlying tolerance to high plant population density and low N is, however, needed. For this purpose, elite CIMMYT open‐pollinated varieties (OPVs), inbred lines, and hybrids were grown under optimal, high plant population density and low N conditions. Yield, yield components, and a set of morpho‐physiological traits (secondary traits) were assessed in the different treatments and germplasm types. Emphasis was placed on anthesis‐silking interval and traits related to senescence, dry matter partitioning, and ovule and grain number. Association was observed under low N conditions between grain yield and anthesis‐silking interval, delayed senescence as expressed by either chlorophyll concentration or the number of green leaves above the ear, and ear/tassel weight ratio. Under optimal, high‐plant population density and low N conditions, final grain number depended more on abortion rate than on the total number of ovules at anthesis. Under low N stress, grain yield was significantly negatively correlated with abortion rate. Under high plant population density, a positive association was noted between ovule number and abortion rate, suggesting a source limitation for C products. The effect of stress on yield components and the strength of association between secondary traits and yield varied greatly according to germplasm type.