bluuebunny/crossref_metadata_2025 huggingface dataset:
Agronomic Potential of Synthetic Hexaploid Wheat‐Derived Populations
Authors: del Blanco I.A. , Rajaram S. , Kronstad W.E.
Published: July 2010

Wild relatives of wheat (Triticum aestivumL.) have primarily been used as sources of genes for biotic and abiotic stress resistance. A more direct approach to grain yield improvement has been sought by using exotic germplasm to enhance quantitative traits, including grain yield. This study was conducted to determine whether synthetic hexaploids, developed from artificial hybridization ofdurumwheat [Triticum turgidumssp.durum(Desf.) Husn.] withAegilops tauschiiCoss., can enhance yield or yield components of wheat. Two hundred eighty‐two BC2F2‐derived lines, involving six crosses between different synthetic hexaploids and four spring wheat cultivars, were evaluated for grain yield and its components. These synthetic‐derived lines were compared with their recurrent parent in field experiments conducted during the 1995 to 1996 and 1996 to 1997 crop seasons near Ciudad Obregón, Sonora, Mexico. More than 80% of the synthetic‐derived lines were significantly superior to their recurrent parent for kernel weight. Eight lines had significantly higher grain yield compared with their recurrent parent. Grain yields of superior lines were up to 11% higher than those of their recurrent parents. A strong association between grains m−2, biomass, spikes m−2, and grain and biomass production rates and grain yield was observed in all populations. Path coefficient analyses of yield components revealed a strong direct effect of spikes m−2and grains spike−1on grain yield. Results indicate that synthetic hexaploids can be a valuable source of alleles to improve kernel weight.
Quantitative Evaluation of Genetic Diversity in Wheat Germplasm Using Molecular Markers
Authors: Manifesto M.M. , Schlatter A.R. , Hopp H.E. , Suárez E.Y. , Dubcovsky J.
Published: July 2010

Characterization of germplasm by means of DNA fingerprinting techniques provides a tool for precise germplasm identification and a quantitative estimate of genetic diversity. This estimate is important because a decrease in genetic variability might result in a reduction of the plasticity of the crops to respond to changes in climate, pathogen populations, or agricultural practices. In this study, 105 Argentine bread wheat (Triticum aestivum L.) cultivars released between 1932 and 1995 were characterized by simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers. A selected subset of 10 highly informative SSR was used to construct an Identification Matrix that allowed the discrimination of the 105 cultivars. Data obtained from SSR markers were complemented by information derived from AFLPs. Molecular data were used to quantify genetic diversity across Argentine wheat breeding programs and to determine if modern wheat cultivars have a lower genetic diversity than earlier cultivars (genetic erosion). No significant differences in genetic diversity were found among the large private and public breeding programs, suggesting that each of them contains a representative sample of the complete diversity of the Argentine germplasm. Significant differences were found for both SSR and AFLP only between breeding programs with large differences in number of released cultivars. No significant differences in genetic diversity were found between the group of cultivars released before 1960 and those released in each of the following three decades. Average diversity values based on SSR markers were almost identical for the four analyzed periods. Genetic diversity estimates based on AFLP data confirmed the absence of a reduction of genetic diversity with time, but significant differences (P = 0.01) were found between bread wheat cultivars released in the 1970s (PIC = 0.28) and those released in the 1980s (PIC = 0.34). These results show that the Argentine bread wheat germplasm has maintained a relatively constant level of genetic diversity during the last half century.
Comparative Effects of 1BL.1RS and 1AL.1RS on Soft Red Winter Wheat Milling and Baking Quality
Authors: McKendry Anne L. , Tague David N. , Ross Kathleen
Published: July 2010

The wheat (Triticum aestivum L.)–rye (Secale cereale L.) chromosomal translocations 1BL.1RS and 1AL.1RS are widely reported to have detrimental effects on hard wheat quality. This study was designed to investigate the impact of these translocations on soft wheat milling and baking quality where information on their effects is limited. A set of backcross‐six F2‐derived F6 near‐isolines containing either the ‘Kavkaz’‐derived 1BL.1RS or ‘Amigo’‐derived 1AL.1RS translocation were developed in five soft red winter wheat backgrounds at Columbia, MO. A randomized complete block design, replicated four times, was grown in each of three Missouri environments. Treatments were arranged as a split‐plot with genetic background as the main‐plot factor and isolines as the subplots. Both the presence of rye and the source of the translocation (1BL.1RS vs. 1AL.1RS) were significant for all traits measured. 1BL.1RS was associated with a significant reduction in softness equivalent but had no overall effect, across backgrounds, on adjusted flour yield or milling quality, while 1AL.1RS was associated with significant reductions in all three traits. Both translocations were associated with reduced baking quality due to their association with increased alkaline water‐retention capacity and reduced kernel softness. For all traits the negative effect of 1AL.1RS was more pronounced than that of 1BL.1RS. Background interaction effects were significant for both milling‐quality and baking‐quality traits, and often were large enough to offset the negative effects associated with the translocation. This suggested that breeders could develop soft red winter wheat cultivars carrying either translocation that had acceptable end‐use quality.
Photoperiod and Temperature Responses in Early‐Maturing, Near‐Isogenic Soybean Lines
Authors: Cober Elroy R. , Stewart Douglas W. , Voldeng Harvey D.
Published: July 2010

While photoperiod responses have been studied in soybean [Glycine max (L.) Merr.] isolines, identification of temperature and photo–thermal responses are lacking in early‐maturing soybean. This study was conducted to quantify photoperiod and temperature responses of early‐maturing soybean. Six ‘Harosoy’ isolines with different combinations of alleles at the E1, E3, E4, and E7 loci were grown in growth cabinets with 10‐, 12‐, 14‐, 16‐, and 20‐h photoperiods and with either 18 or 28°C constant temperature. Under the most inductive conditions (10 and 12 h, 28°C), all isolines flowered in about 26 d. Under the least inductive conditions (20 h, 28°C), there was a 50 d difference in flowering time between the early‐ and late‐flowering isolines. Interestingly, the late‐flowering isolines flowered earlier under cool than under warm temperatures. A mathematical model was developed to quantify the effects of temperature and photoperiod on days to first flower. This model related the rate of phenological development from planting to flowering to temperature, photoperiod and the interaction between temperature and photoperiod. The equation was integrated analytically, resulting in an inverse time (1/time) equation, or numerically resulting in the development of a Growing Photothermal Day (GPTD) similar to a heat unit. The model had a base temperature (5.8°C) below which the rate of phenological development was zero, a critical or base photoperiod (13.5 h) below which photoperiod had no effect, and two genetic coefficients, one of which varied with isoline. The isoline photoperiod sensitivity coefficient was linearly related to the number of dominant (late flowering, photoperiod sensitive) alleles. The model fit the observed data well (R2 = 0.96).
Improving Erucic Acid Content in Rapeseed through Biotechnology: What Can the Arabidopsis FAE1 and the Yeast SLC1‐1 Genes Contribute?1,2
Authors: Katavic Vesna , Friesen Winnie , Barton Dennis L. , Gossen Kalie K. , Giblin E.Michael , Luciw Tammy , An Jing , Zou Jitao , MacKenzie Samuel L. , Keller Wilfred A. , Males Daryl , Taylor David C.
Published: July 2010

The main goal of our research is to produce, by genetic manipulation, Brassica napus L. cultivars with higher amounts of 22:1 in their seed oil than in present Canadian high erucic acid rapeseed (HEAR) cultivars developed through traditional breeding, ideally with proportions of 22:1 approaching 80 mol% (828 g kg−1). To probe some rate‐limiting steps in the accumulation of triacylglycerols containing very long chain fatty acids (VLCFAs), particularly erucic acid (22:1), we have taken a transgenic approach, studying the effect of expressing two target genes in HEAR B. napus cv. Hero. To study the role of the elongase complex, involved in elongation of C18 fatty acid moieties to produce VLCFAs, we expressed the Arabidopsis thaliana L., fatty acid elongase 1 (FAE1) gene under the control of a seed‐specific promoter (napin), in Hero. This resulted in increased proportions of 22:1 in the seed oil, rising from 430 g kg−1 in non‐transformed controls to 480 to 530 g kg−1 22:1 in FAE1 transgenic Hero lines. The FAE1 lines exhibited higher elongase activity in vitro compared to control lines. These data suggest that the level of active condensing enzyme in the native elongase complex is somewhat rate limiting for synthesis of erucic acid and other VLCFAs in HEAR. In small scale field trials, the VLCFA and 22:1 content of FAE1 transgenic lines were superior to field‐grown control lines. We report that in field plot trials, the progeny of our best T4 B. napus cv. Hero SLC1‐1 transgenic lines clearly out‐performed controls in terms of 22:1, oil content, and yield.
Drought‐Stress Effects on Branch and Mainstem Seed Yield and Yield Components of Determinate Soybean
Authors: Frederick James R. , Camp Carl R. , Bauer Philip J.
Published: July 2010

A better understanding of how drought stress affects soybean [Glycine max (L.) Merr.] seed‐yield determination would aid in the development of improved cultivars for the southeastern Coastal Plain and better production systems aimed at ameliorating the effects of drought stress. The objective of this field study was to examine the effects of drought stress on both soybean branch vegetative growth and the distribution of seed yield and yield components between the main stem and branches. Soybean was grown on an Eunola loamy sand in 1998 and 1999 with three levels of drought‐stress treatment: (i) irrigation and no deep tillage, (ii) deep tillage but no irrigation, and (iii) no deep tillage or irrigation. Total seed yield, branch seed yield, and the percentage of total seed yield on the branches were highest with irrigation, followed by the in‐row subsoiled/no deep tillage treatment and the no irrigation/no deep tillage treatment. Drought‐stress treatment had no effect on mainstem seed yield. Branch seed number per square meter was highly correlated with branch seed yield (r = 0.994; P < 0.0001) and total seed yield (r = 0.989; P < 0.01) over both years and all levels of drought‐stress treatment. A close relationship was found between branch seed number per square meter and branch dry weight at harvest maturity (r = 0.963; P < 0.05), final branch length per square meter (r = 0.994; P < 0.05), and final branch number per square meter (r = 0.995; P < 0.05). Most branch growth occurred between initial flowering and the beginning of seed fill. Less association was found between individual seed weight and seed yield from the mainstem or branch fractions. These data indicate that drought stress occurring between initial flowering and seed fill decreases total seed yield primarily by reducing branch vegetative growth, which reduces branch seed number and branch seed yield.
Response of Perennial Ryegrass to Free‐Air CO2Enrichment (FACE) Is Related to the Dynamics of Sward Structure during Regrowth
Authors: Suter Daniel , Nösberger Josef , Lüscher Andreas
Published: July 2010

At elevated partial pressure of CO2(60 Pa pCO2), field‐grown perennial ryegrass (Lolium perenneL.) swards generally show a strong increase in photosynthesis of the youngest fully expanded leaves but a weak yield response. We investigated this discrepancy by determining the effects of elevated pCO2on the dynamics of regrowth. During the whole regrowth period, swards at elevated pCO2exhibited a greater dry mass of roots (68%), of pseudostems (34%), and of shoot necromass below cutting height (45%). During the first 4 wk of regrowth, when dry mass (DM) and the leaf area index increased strongly, elevated pCO2stimulated the yield, total DM, and leaf area by up to 46, 63, and 30%, respectively. Elevated pCO2also resulted in an increase of almost 60% in the number of tillers during this period when the transmission of photosynthetically active radiation to the tiller bases was high. Towards the end of regrowth, however, the leaf area, total DM, and yield showed no net increase; under elevated pCO2, the number of tillers decreased strongly. These results indicate that there was not a strong sink for additionally fixed C during the second half of regrowth. The gap between leaf photosynthesis and yield at elevated pCO2is suggested to be related to a loss of tillers when shading of tiller bases was strong and to a change in dry mass allocation.
A Genetic Linkage Map of Diploid Paspalum notatum
Authors: Ortiz Juan Pablo A. , Pessino Silvina C. , Bhat Vishnu , Hayward Michael D. , Quarín Camilo L.
Published: July 2010

Paspalum notatum Flugge is a subtropical grass native to South America. The most common form in the USA is P. notatum var. saurae Parodi (Pensacola bahiagrass), which is a valuable forage. Pensacola bahiagrass is a sexual diploid, while most other races of P. notatum are apomictic tetraploids. The objective of this work was the construction of a genetic linkage map of diploid P. notatum (2n = 2x = 20) that can be used as a framework for basic genetic studies as well as breeding purposes. The mapping population derived from a cross between the genotypes Q408410 and Tift9 that originated from Cayastá, Santa Fe, Argentina, and Tifton, GA, USA, respectively. Heterologous restriction fragment length polymorphism (RFLP) clones of maize (Zea mays L.), rice (Oryza sativa L.), and oat (Avena sativa L.) were used to cover the Paspalum genome uniformly in a comparative approach, while random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) markers were added to condense the linkage groups. A combined map was constructed with the markers segregating from both parental genotypes by the program JoinMap 1.4. A total of 149 marker loci were used for map construction. One hundred twelve loci were allocated to 10 linkage groups, covering a total map distance of 991 centimorgan (cM). The average distance between markers was about 9 cM. Paspalum Linkage Groups 1, 3, 4, 5, 6, 8, and 10 showed syntenic regions with maps of maize and rice. Moreover, several RFLP loci reported to be associated with apomixis in hybrids of maize‐Tripsacum and Brachiaria were located on the map. This study provides a genetic linkage map of a subtropical forage grass with both sexual and apomictic forms, which can be used for investigating simple and complex traits.
Feed‐Quality Variation in the Barley Core Collection of the USDA National Small Grains Collection
Authors: Bowman J.G.P. , Blake T.K. , Surber L.M.M. , Habernicht D.K. , Bockelman H.
Published: July 2010

Feed is an important end use of barley (Hordeum vulgare L.). Recent research has identified high starch content, low acid‐detergent fiber (ADF), low ruminal dry‐matter digestibility (DMD), and large particle size after dry rolling as desirable barley feed‐quality characteristics for beef cattle. Knowledge about the variation available may help barley breeders develop strategies for feed‐quality improvement. Our objective was to estimate the variation in feed‐quality characteristics in barley around the world. The spring barley core subcollection from the USDA‐ARS National Small Grains Collection was planted in 1995. Ruminal DMD of 1480 accessions was evaluated. Seventy‐three accessions, selected on variation in DMD, were planted in two field replications in 1996 and 1997. These 73 accessions were evaluated for starch, DMD, ADF, and particle size after dry rolling. The range in DMD was 82 to 621 g kg−1, with a mean of 398 g kg−1 (SD = 75 g kg−1). The ranges for other traits of the 73 selected accessions were 387 to 593 g kg−1 (starch); 15 to 96 g kg−1 (ADF); 187 to 510 g kg−1 (DMD); and 1118 to 1572 μm (particle size). Six‐row types had greater ADF and particle size (P < 0.001), lower starch, and DMD (P < 0.001), compared with 2‐row types. Starch was higher (P < 0.01), and ADF and DMD were lower (P < 0.01), for hulless than for hulled accessions. Substantial variation in the spring barley core collection for feed quality‐related characters could be exploited to develop barley cultivars for feed quality.
Association of Ecogeographical Variables and RAPD Marker Variation in Wild Potato Populations of the USA
Authors: del Rio A.H. , Bamberg J.B. , Huaman Z. , Salas A. , Vega S.E.
Published: July 2010

The goal of germplasm conservation in genebanks is to maximize genetic variation. Collecting explorations would be more efficient if factors that predict areas and habitats associated with greater genetic differences and diversity could be identified. Therefore, the objective of this research was to investigate whether ecogeographical variables have significant associations with patterns of genetic variation in wild potato populations. This study examined 96 wild potato populations collected from the southwestern USA. These were 43 populations ofSolanum fendleri(2n= 4x= 48) and 53 populations ofS. jamesii(2n= 2x= 24). These species represent two of the most predominant breeding systems found amongSolanumspecies: tetraploid inbreeders and diploid outcrossers, respectively. Random amplified polymorphic DNA (RAPD) markers were used to assess populations in two ways: determination of simple genetic difference between pairs of populations, and genetic diversity of a population based on the frequency of that population's RAPD markers in the whole set. Results from 2282 comparisons indicated that patterns of genetic differences were not associated with any differences in ecogeographical structure assessed. Remarkably, even geographical separation of populations, a parameter usually considered important when collecting germplasm, did not predict genetic differences very well. Latitude, longitude, and heat‐related factors significantly predicted genetic diversity inS. fendleribut not inS. jamesiiThis experiment revealed few associations between ecogeographic parameters and genetic variation in the wild. It follows, therefore, that one should collect many populations and incorporate a manageable subset into the genebank on the basis of empirical measurements of genetic diversity.
Winter Hardiness, Root Physiology, and Gene Expression in Successive Fall Dormancy Selections from ‘Mesilla’ and ‘CUF 101’ Alfalfa
Authors: Cunningham S. M. , Gana J. A. , Volenec J. J. , Teuber L. R.
Published: July 2010

Fall dormancy is positively associated with alfalfa (Medicago sativa L.) winter survival, but the physiological bases for this association are not understood. Our objective was to determine how incremental changes in fall dormancy due to genetic selection influenced autumn height and winter survival, root physiology, and expression of a cold acclimation responsive gene family. Seed from each of three cycles of selection for contrasting (greater or less) fall dormancy using ‘Mesilla’ and ‘CUF 101’ as parents were planted in rows in the field (Starks‐Fincastle, fine‐silty, mixed, mesic, Aeric Ochraqualf) in West Lafayette, IN, in May 1997 and 1998. Plant height was measured in October and roots were sampled in December. Plant survival was determined in March of the year following seeding. Fall dormancy (reduction in shoot height in October) increased in a linear manner over the three cycles of selection for both Mesilla and CUF 101. A positive linear relationship was observed between fall height and winter injury in both years. Root sugar and protein concentrations increased as fall dormancy increased in populations derived from both Mesilla and CUF 101. Expression of the cold acclimation‐responsive gene, RootCAR1, was positively associated with winter survival, and may be useful as a molecular marker for identifying winter hardy plants among semi‐dormant or nondormant alfalfa germplasm in December of the seeding year.
Phenotypic Alterations and Crop Maturity Differences in Ultra‐Narrow Row and Conventionally Spaced Cotton
Authors: Jost Philip H. , Cothren J. Tom
Published: July 2010

Ultra‐narrow row cotton (Gossypium hirsutum L.) production is considered a potential strategy for reducing production costs by shortening the growing season. A 2‐yr field study was conducted near College Station, TX, on varying soil types to document phenotypic alterations and crop maturity differences for cotton grown in 19‐, 38‐, 76‐, and 101‐cm row spacings. In the 19‐cm rows, the plant densities were 12.2, 18.8, and 40.5 plants m−2 Densities of 11.3 and 19.5 plants m−2 were established in the 38‐cm rows. In the 76‐ and 101‐cm rows, plant densities of 11.7 and 7.4 plants m−2, respectively, were evaluated. Plant height and node counts were reduced in the narrow (19 and 38 cm) row spacings in only 1 yr. The narrow row spacings at the higher plant densities consistently accumulated leaf area index more rapidly than the conventional (76 and 101 cm) row spacings. In 1998, when the study was conducted on a heavy clay soil, the higher plant densities in the 19‐ and 38‐cm row spacings tended to partition more biomass to reproductive structures and yielded more than the conventional row spacings. In 1999, the test was conducted on a lighter silty clay loam soil and yields were unaffected by the row‐spacing treatments. In 1998, the higher plant densities in the 19‐ and 38‐cm row spacings had a greater percentage of harvestable bolls at the first fruiting positions on lower nodes, a boll distribution pattern that contributed to earlier crop maturity. Narrow row spacings and high plant densities did not consistently alter fiber quality. No conclusive differences for crop growth and development could be ascertained between the medium and high plant densities in the 19‐ and 38‐cm row spacings. However, ultra‐narrow row cotton may be more advantageous to producers when grown on heavier soils that typically do not promote excessive vegetative growth.
Allelic Shifts and Quantitative Trait Loci in a Recurrent Selection Population of Oat
Authors: De Koeyer D. L. , Phillips R. L. , Stuthman D. D.
Published: July 2010

Recurrent selection to enhance grain yield of oat (Avena sativa L.) has been ongoing at the University of Minnesota since 1968. Grain yield was increased by 21.7% after seven cycles of recurrent selection. The objectives of this study were to monitor the long‐term genetic changes in this recurrent selection population using restriction fragment length polymorphisms (RFLPs). Ninety‐seven RFLP loci detected by 73 cDNA clones were used to evaluate changes in allelic frequencies during the recurrent selection process. Significant allelic shifts were detected in eight genomic regions. Four linkage groups were studied in greater detail to localize putative quantitative trait loci (QTL). In total, seven primary or major QTL regions were identified using allelic shift, correlation, and single‐factor analysis of variance (ANOVA) data. Six of these regions were associated with grain yield and one was associated with plant height. Thirty‐three other minor QTL were detected using correlation and/or ANOVA data. Multiple regression models for grain yield, heading date, and plant height indicated that associated markers accounted for 30, 38, and 27% of the phenotypic variance, respectively. Our results indicate that we have identified genomic regions containing favorable alleles selected during the recurrent selection process. Thirteen of the 40 QTL identified for the individual traits in the recurrent selection population were previously identified in the Kanota × Ogle recombinant inbred mapping population. Therefore, these QTL may be generally important in oat.
Induction of Highly Embryogenic Calli and Plant Regeneration in Upland (Gossypium hirsutum L.) and Pima (Gossypium barbadense L.) Cottons
Authors: Sakhanokho Hamidou F. , Zipf Allan , Rajasekaran Kanniah , Saha Sukumar , Sharma Govind C.
Published: July 2010

To accomplish our objective of broadening the number of regenerable cotton lines, we developed a protocol capable of producing plants through somatic embryogenesis of diverse cotton species. Callus was initiated from hypocotyl and cotyledon explants on a callus initiation medium [CIM; modified MS with 1 mg L−1 kinetin and 2 mg L−1 naphthaleneacetic acid (NAA)]. Friable embryogenic callus was periodically selected and transferred onto callus selection/maintenance medium (CS/MM) [modified MS with 0.1 mg L−1 kinetin and 0.5 mg L−1 NAA]. The selected callus was then transferred into a liquid embryo initiation medium (EIM) (modified MS medium in which NH4NO3 was removed and KNO3 amount doubled) followed by transfer to solid embryo maturation media EMMS2 (0.5 mg L−1 NAA + 0.05 mg L−1 kinetin). The liquid step not only decreased the culturing time but also increased the number of embryos per gram of cultured tissue. Germinating somatic embryos were placed on MS medium with no hormones and plantlets were acclimatized before transfer to the greenhouse. Significant numbers of somatic embryos and their derived plantlets were obtained from a commercial cultivar of G. hirsutum, Deltapine 90 and G. barbadense accession GB‐35B126 (PI‐528306). The mean embryos per gram for Deltapine 90 on EMMS2 were higher than those previously reported for Coker 312. Highly significant differences were found between the two genotypes for both embryo and plant production. To our knowledge, this is the first report of regeneration of G. barbadense through somatic embryogenesis.
Comparison of Molecular Linkage Maps and Agronomic Trait Loci between DH and RIL Populations Derived from the Same Rice Cross
Authors: He P. , Li J. Z. , Zheng X. W. , Shen L. S. , Lu C. F. , Chen Y. , Zhu L. H.
Published: July 2010

Doubled haploid (DH) and recombinant inbred line (RIL) populations are two types of permanent populations for rice (Oryza sativa L.) breeding and genetic mapping. In this study, we report the comparison of molecular maps and mapped agronomic trait loci between DH and RIL populations derived from the same rice cross, ZYQ8 (indica) × JXI7 (japonica). We investigated six agronomic traits (days to heading, plant height, number of spikelets per panicle, number of grains per panicle, 1000‐grain weight, and seed set percentage) and found that five of them did not show significant differences between the two populations. Restriction fragment length polymorphism (RFLP) and microsatellite markers were selected to construct two linkage maps of the DH and RIL populations. All the DNA markers except G39 showed the same linkage groups and orders between the two populations. The genetic distance per chromosome in the RIL population was shorter than that in the DH population, and the total genetic distance of genome in the RIL population (1465 cM) was 70.5% of that in the DH population (2079 cM). In the RIL population, 27.3% markers showed distorted segregation at P < 0.01 level, of which 90% markers favored indica alleles, while in the DH population, the skewed markers favoring indica and japonica alleles were in accordance with 1:1 ratio. Eight commonly distorted regions on chromosomes 1, 3, 4, 7, 8, 10, 11, and 12 were detected in both RIL and DH populations, of which seven skewed toward indica alleles and one toward japonica allele. Five of them were located near gametophytic gene loci (ga) and/or sterility gene loci (S). We also compared the quantitative trait locus (QTL) mapping results between the DH and RIL populations and found a number of similarities in the QTL locations between these two populations. So both RIL and DH populations are equally effective in rice breeding and genetic analysis.
Identification of Molecular Markers Associated with Adult Plant Resistance to Powdery Mildew in Common Wheat Cultivar Massey
Authors: Liu Sixin , Griffey C. A. , Maroof M. A. Saghai
Published: July 2010

Powdery mildew, caused by Blumeria graminis (DC.) E.O. Speer f. sp. tritici Em. Marchal (syn. Erysiphe graminis f. sp. tritici), is one of the major diseases of wheat (Triticum aestivum L.) worldwide. Race‐specific resistance has been extensively used in wheat breeding programs, even though it is ephemeral. Adult plant resistance (APR) to powdery mildew is more durable than race‐specific resistance. The APR to powdery mildew in winter wheat cultivar Massey has remained effective since its release in 1981. A cross was made between Massey and a powdery mildew susceptible cultivar Becker. Powdery mildew severity on F‐2 leaves (the second leaf below the flag leaf) of 180 F2:3 lines was rated under natural disease pressure in the field. Among 213 RFLP and 139 microsatellite markers surveyed, 88 (41%) and 90 (65%) markers, respectively, detected polymorphism between Becker and Massey. Bulked segregant analysis (BSA) was used to facilitate the identification of molecular markers associated with APR to powdery mildew. Three quantitative trait loci (QTLs), designated as QPm.vt‐1B, QPm.vt‐2A, and QPm.vt‐2B, were identified with interval mapping. They are located on wheat chromosomes 1B, 2A, and 2B, and, respectively, explained 17, 29, and 11% of the total variation of F2:3 lines for powdery mildew resistance. The three QTLs associated with APR to powdery mildew were derived from Massey, and displayed additive gene action. QPm.vt‐2B also fits a recessive model for APR to powdery mildew. In a multi‐QTL model, the three QTLs explained 50% of the total variation of F2:3 lines for APR to powdery mildew. The presence of the three QTLs was confirmed with 97 recombinant inbred (RI) lines, tested for APR to powdery mildew under natural powdery mildew pressure over 3 yr (F5:6–F7:8 generation). The molecular markers identified in this study have potential for use in marker‐assisted selection and pyramiding of genes for resistance to powdery mildew.
Isolation distances for minimizing out‐crossing in spring wheat
Authors: Hucl P. , Matus‐Cádiz M.
Published: July 2010

Currently recommended isolation distances of 3 or 10 m for pedigreed seed production of spring wheat (Triticum aestivum L.) may not be sufficient for cultivars with high out‐crossing (OC) rates. The detection of higher than expected OC rates in wheat has directed this research to reassess currently recommended minimum isolation distances. The objective of this study was to determine if increased isolation distances are needed for cultivars that exhibit higher than normal levels of out‐crossing. In each of 2 yr, OC rates were determined for four Canadian spring wheat cultivars at each of 15 distances (0–33 m) from a blue aleurone pollen source. Cultivars were grown in rows perpendicular to the pollinator block to the north, south, west, and east. Target rows were replicated four times within each direction. Out‐crossing in ‘Katepwa’ and ‘Biggar’ was not detected beyond 3 m. Cultivars ‘Roblin’ and ‘Oslo’ exhibited higher than normal OC at distances of up to 27 m. For Roblin and Oslo, an isolation distance of 30 m is recommended to mitigate OC‐derived off‐types in the subsequent generation of pedigreed seed.
Genetic Progress in Soybean of the U.S. Midsouth
Authors: Ustun Ali , Allen Fred L. , English Burton C.
Published: July 2010

Yield increase in crops has occurred due to plant breeding and improved production and management techniques. The amount of increase due to plant breeding in soybean in the southern USA has not been determined. The objective of this study was to evaluate the genetic improvements in soybean yield and other important agronomic traits. ‘CNS’ and ‘S‐100’ were chosen as representative ancestral lines from the 1940s. ‘Ogden’ and ‘Lee’, ‘Hill’ and ‘Essex’, and ‘TN 5‐85’, and ‘Hutcheson’ were released in early 1950s, late 1950s and early 1970s, and late 1980s, respectively. The experiments were conducted in Knoxville Experiment Station in Knoxville, TN and at the Ames Plantation near Grand Junction, TN, for 3 yr, and at the Milan Experiment Station in Milan, TN, and at the Highland Rim Station in Springfield, TN, for 2 yr. Results showed that cultivar improvement increased soybean yield 14 kg ha−1 per year. Yield increase over time was linear. This linear increase demonstrates that a yield plateau in the U.S. Midsouth has not been reached in soybean [Glycine max (L.) Merr.]. Most of the increase has come via genetically related elite by elite parent crosses. However, infusion of exotic germplasm into elite germplasm can often promote increases in yield, as in the development of Hutcheson. Current cultivars showed better yield stability and more response to favorable growing conditions than ancestral lines. Genetic improvement resulted in shorter plant height and decreased lodging. Oil content was increased until the 1980s, but then started to decrease. However, because of correlated effects, protein content started to increase after the 1980s.
Recurrent Selection for Kernel Weight in Spring Wheat
Authors: Wiersma Jochum J. , Busch Robert H. , Fulcher Gary G. , Hareland Gary A.
Published: July 2010

Increasing kernel weight has been proposed as a method to increase flour extraction in spring wheat (Triticum aestivum L.). Recurrent selection was initiated to increase kernel weight while maintaining genetic variation for the unselected traits. Our objectives were to determine (i) genetic gain for kernel weight after eight cycles of selection, (ii) the indirect effects of the selection for kernel weight on other agronomic traits, kernel morphology, milling fractions, and grain protein concentration, and (iii) the level of genetic variability among lines within selection cycles for kernel weight and unselected traits. Ten lines, selected for high kernel weight, were originally intermated to form the base population. About 20 F2 plants with the highest kernel weight were selected (∼2% of the population), and about three of their F3 progeny were intermated to form the next cycle. This procedure was repeated for eight cycles, with an average of 60 crosses per cycle. Forty random lines from each cycle were used to evaluate agronomic traits in three environments. Kernel weight increased linearly at about 4.5% cycle−1 Cycle means did not differ for plant height and grain yield, but tillers per square meter and kernels per spike decreased 2.4 and 1.6% per cycle, respectively. Spikelets per spike, kernels per spikelet, test weight, and days to heading decreased, whereas spike length increased in response to selection for kernel weight. The proportion of bran and shorts decreased, and flour extraction and grain protein concentration increased 0.58 and 0.16% cycle−1, respectively. No clear trend towards decreased genetic variance for kernel weight was observed since gain was linear over eight cycles. The observed gain from selection and heritability estimates point to kernel weight being controlled by several genes with small effects. Selection for increased kernel size in this population resulted in increased flour yield.
Quality Control in the Development of Transgenic Crop Seed Products
Authors: Mumm Rita Hogan , Walters Donald S.
Published: July 2010

In light of (i) public concern with the safety of genetically modified crops, (ii) the issue of food labeling, and (iii) governmental regulation of transgenic plants, quality control (QC) monitoring of the process of Transgenic Seed Product Development (TSPD) is essential to protecting research investments, maintaining compliance with governmental regulations, and ensuring customer satisfaction. The primary goal of QC monitoring in TSPD is to ensure the authenticity (transgenic event identity and purity) of seed materials used in product testing, in the development of regulatory data packages for governmental review, and to develop seed volumes for commercial release. Monitoring is performed to confirm the presence of the presumed transgenic event(s) and the absence of all others. Sophisticated QC strategies formulated to monitor the product development process and to maintain quality standards in the manufacturing industry can serve as a foundation in devising efficient strategies tailored to meet needs in the seed industry. A number of considerations in the design of an optimized QC monitoring plan for TSPD are discussed, including: costs vs. economic benefits of developing and commercializing nondefective products; effective timing of inspections; joint scheduling of inspections with other genetic analyses; assay methods that maximize screening efficiency, flexibility, and accuracy; sampling vs. 100% assessment of transgenic populations; the ability to bulk samples to minimize data point requirements; and the need to minimize or eliminate inspection errors. An overview of the general process of TSPD and an example QC monitoring strategy for corn (Zea mays L.) are provided.
Heritability of Heat Tolerance in Winter and Spring Wheat
Authors: Ibrahim Amir M. H. , Quick James S.
Published: July 2010

Cell membranes are the site for many biological activities of the plant and play a key role in heat‐induced damage to wheat (Triticum aestivum L.). This study evaluated the genetic variability of wheat using two assays of heat tolerance, and estimated their heritability by parent‐offspring regression, parent‐offspring correlation, and realized heritability using F3 plants and their F4 progeny means. One assay of heat tolerance was membrane thermal stability (MTS) which measures electrolyte leakage from leaf tissue after exposure to high temperature. Heat injury was also assessed by quantifying the reduction of triphenyl tetrazolium chloride (TTC) to formazan by mitochondrial dehydrogenase respiratory enzymes in heat‐stressed seedlings. Results from the two assays were highly associated (r = 0.62, n = 14, P < 0.05). Parent‐offspring regression and correlation heritability was intermediate to high (0.50–0.65) for TTC and relatively low (0.32–0.38) for MTS. Realized heritability, based on 15% selection intensity, was intermediate to high (0.49–0.64) for TTC and low to intermediate (0.27–0.47) for MTS. The high heritability of TTC warrants good progress from selection in early generations. The relatively lower heritability of MTS suggests the use of multiple replications during selection to limit environmental effects.
Predicting Progeny Means and Variances of Winter Wheat Crosses from Phenotypic Values of Their Parents
Authors: Utz H. F. , Bohn M. , Melchinger A. E.
Published: July 2010

The efficiency of breeding programs could be increased by predicting the prospects of crosses for line development before producing and testing lines derived from them. In this study, we examined the performance of F4:n (n = 7 or 8) lines randomly derived from 30 winter wheat (Triticum aestivum L.) crosses produced by a factorial mating of five high yielding with six high baking quality cultivars. Our objectives were to (i) contrast the midparent value m̂ij with ĉij for each cross and apply tests for the presence of epistasis, (ii) compare the estimates of the variance between means of crosses (σ2c) with the average segregation variance within crosses (σ2g), (iii) determine the variation in σ2gij among crosses, (iv) evaluate the use of various parameters for predicting cij, σ2gij, and Uij, and (v) briefly describe quantitative‐genetic theory for interpretation of our experimental findings. Twenty‐two lines per cross and the respective parents were evaluated in four environments for seven agronomic and quality traits. Additionally, 44 F2:4 lines per cross were tested in hills in two environments. On the basis of first‐degree statistics, parental means were good predictors of cross means, yet significant epistatic effects were observed for most traits. In agreement with quantitative‐genetic expectations, the genetic variance between σ2c was of the same size as the variance between parental means and the average σ2g of F4:n lines within crosses for all traits but sedimentation. Here, the two parental groups differed significantly in their mean, and σ2g was significantly larger than σ2c Estimation of the segregation variance (σ2gij) for individual crosses is not recommended because they (i) have a large standard error, (ii) can be assessed reliably only in advanced selfing generations, and (iii) are expected to have a minor influence on differences in the usefulness among crosses. Among all predictors investigated, only the parental means can be recommended for predicting the usefulness of crosses.
Loss of Kernel Set Due to Water Deficit and Shade in Maize
Authors: Setter Tim L. , Flannigan Brian A. , Melkonian Jeff
Published: July 2010

To advance our understanding of the underlying processes by which kernel set is regulated in maize (Zea maysL.), leaf photosynthesis, sugars, starch, abscisic acid (ABA), and cytokinin were quantified in plants subjected to water deficit and shade, imposed for 5 d at the pre‐pollination and early post‐pollination stages. Both water and light deprivation, at both stages, decreased kernel set primarily in apical ear regions. Treatments decreased leaf photosynthesis similarly; however, sugar concentrations in reproductive tissues increased in water deficit while they decreased 20 to 50% in shade. During treatments, nonstructural carbohydrate accumulation was nearly halted in both apical and basal florets at the pre‐pollination stage, whereas it was decreased to a greater extent in apical than basal endosperm/nucellus at the post‐pollination stage. Both water deficit and shade increased ABA concentrations in reproductive tissues, but only at the post‐pollination stage was ABA greater in apical than basal ear zones, thus corresponding to effects on kernel set. Treatments did not consistently alter zeatin‐like cytokinin concentrations. We conclude that photosynthate flux and ABA are components of a regulatory system by which water and light deprivation affect kernel set at the post‐pollination stage, while additional factors may underlie effects at the pre‐pollination stage.
Stratification in Switchgrass Seeds Is Reversed and Hastened by Drying
Authors: Shen Zheng‐Xing , Parrish David J. , Wolf Dale D. , Welbaum Gregory E.
Published: July 2010

Switchgrass (Panicum virgatum L.) seed dormancy is a major obstacle to successful establishment of this multi‐purpose species. We have investigated the influences of prolonged stratification, poststratification drying, restratification, and afterripening on germinability of ‘Cave‐in‐Rock’ switchgrass seeds. Germination can be increased many‐fold to ≥80% with 14 d of stratification, if the seeds are moved directly to germination without drying. However, we have found germinability (but not viability) may decrease by half or more if the stratified seeds are first dried and then rehydrated for germination testing. The reappearance of dormancy (secondary dormancy) during poststratification drying is herein called reversion During poststratification drying, dormancy reversion increased as the degree of desiccation increased. Extended stratification (for ≥42 d) prevented reversion. Afterripening also reduced the potential for reversion. Stratification and afterripening appeared to work additively to remove revertibility. Restratifying dried seeds showed that, while a drying interruption caused reversion, it also decreased the dormancy variability within a seedlot and shortened the total stratification time needed to obtain maximum germination compared with continuous stratification. Switchgrass seeds can be moved toward greater germinability by stratification, but drying following insufficient stratification can lead to dormancy reversion.
Dimensions of Diversity in Modern Spring Bread Wheat in Developing Countries from 1965
Authors: Smale M. , Reynolds M. P. , Warburton M. , Skovmand B. , Trethowan R. , Singh R. P. , Ortiz‐Monasterio I. , Crossa J.
Published: July 2010

Diverse and varied crop genetic resources are necessary (though not sufficient) for adequate food production in a rapidly changing world. Since the scientific community first raised public concern several decades ago, modern cultivars have been viewed as the cause of declining diversity in the world's crop genetic resources. This paper tests the hypothesis of increasing genetic uniformity in modern spring bread wheat (Triticum aestivum L.) cultivars from 1965, a year which marks the release of some of the first modern semidwarf cultivars carrying Rht1 and Rht2 genes in the developing world. Results from previously published studies are summarized. Preliminary molecular analyses, and new analyses of cultivar numbers, areas, ages, and genealogies are presented. An estimated 77% of the spring bread wheat area in the developing world today is sown to CIMMYT‐related wheats, but this does not imply that they are genetically uniform. The hypothesis of increasing genetic uniformity is tested by assessing changes in the diversity of leading progenitors over three decades, in terms of several dimensions of diversity. Latent dimensions include genetic distance and genealogies. Apparent dimensions include performance with respect to yield potential, maintenance and stability across management (input use), and growing environments. The data are not consistent with the view that the genetic diversity of modern semidwarf wheat grown in the developing world has decreased over time. Moreover, since national programs in developing countries cross CIMMYT lines with their own materials before releasing them, the genetic diversity in their cultivars is at least as great as that present among CIMMYT lines.
Combining Cytoplasmic Male Sterility and Xenia Increases Grain Yield of Maize Hybrids
Authors: Weingartner Urs , Kaeser Olivier , Long Muhua , Stamp Peter
Published: July 2010

Male sterility is documented in many plant species. When a plant is male‐sterile, an open pollination by a genetically diverse pollinator is possible. This study investigates the combined effects of nonrestored cytoplasmic male sterility (CMS) and xenia (cross‐pollination) on the grain yield of seven European flint × dent single‐cross maize (Zea mays L.) hybrids. Open pollinated field experiments were conducted in six environments in Switzerland in 1998 and 1999; the design was a split‐plot. The effect of CMS on grain yield was statistically significant (P < 0.05). Three CMS hybrids in nonrestored T‐cytoplasm, pollinated by their male‐fertile isogenic counterparts, had a higher grain yield (+7.4%) than their male‐fertile isogenic counterparts. The higher grain yield was due to a greater number of kernels per square meter (KN). The average increase in grain yield due to xenia was 2.6%. The effects of pollinator hybrids on grain yield, kernel weight (KW), and KN were statistically significant (P < 0.001), whereas the pollinator × environment and pollinator × CMS hybrid interactions were not significant. Thus, the general pollinator ability (GPA) of the pollinator hybrids differed significantly and consistently. Averaged across the six environments, the three CMS hybrids, pollinated by five nonisogenic hybrids, outyielded their male‐fertile, isogenically pollinated counterparts by 2.1, 9.3, and 15.8%, respectively. The best combination of a CMS hybrid and a nonisogenic pollinator hybrid increased grain yield by 21.4% compared with the male‐fertile isogenic counterpart of the CMS hybrid. Therefore, the plus‐hybrid system (CMS hybrids grown in mixtures with male‐fertile nonisogenic pollinator hybrids) combines the grain yield advantages brought about by CMS and xenia.