bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of Geostatistical and Neighbor Analyses to Data from Plant Breeding Trials
Authors: Wu Tianxia , Mather Diane E. , Dutilleul Pierre
Published: July 2010

In plant breeding trials and other experiments with many treatments, there may be spatial effects due to large‐scale trends and small‐scale autocorrelation. Geostatisticai analysis may be used to investigate the extent of spatially structured variation. When spatial structure is present, neighbor analysis can be superior to classical analysis of variance (ANOVA). The objectives of this study were to assess the validity and efficiency of neighbor analysis and to investigate the extent of spatially structured variation in cereal breeding trials. Three neighbor analysis methods (the Papadakis procedure, the iterated Papadakis method, and the first differences with errors in variables [FD‐EV]) were applied to data from uniformity trials and to data from a set of 361 cereal breeding trials. The iterated Papadakis method consistently underestimated the variance, producing tests with highly inflated Type I error rates. Thus, its relative efficiency could not be estimated correctly. Geostatistical analysis indicated that spatially structured variation was frequently present in the cereal breeding trials, and that first differencing was effective in removing it. The FD‐EV analysis consistently improved the accuracy and precision of the estimation of entry effects compared with classical analysis of variance and Papadakis analysis. Efficiency relative to classical analysis of variance averaged 152% for FD‐EV and 116% for the Papadakis procedure. Considering both validity and efficiency, FD‐EV was the best method. In the presence of spatially structured variation, FD‐EV can improve the interpretation of data from field trials. In the absence of spatial structure, FD‐EV causes no loss of efficiency.
Inheritance of Pod Type, Stem Color, and Dwarf Growth Habit in Medicago polymorpha
Authors: Haan R. L. , Barnes D. K.
Published: July 2010

Identification of marker traits in annual Medicago species (medics) would assist plant breeders in cultivar development. The objective of this research was to determine the inheritance of pod type, stem color, and dwarf growth habit in Medicago polymorpha L., a diploid species. Progeny from each of three crosses were evaluated in the F1, F2, and F3 generations. Results indicate that pod type was controlled by a single gene with a dominant allele for spiny pods. We propose the gene symbol Sp1 for the pod type trait. Stem color also was controlled by a single gene, with a dominant allele for red stems. We propose Rs1 as the gene symbol for this trait. The dwarf trait was not present in the parents or the F1 generation, but was observed in the F2 generation of one of the crosses. Dwarf plants had much shorter stems, internodes, and leaf petioles than normal plants, and they also had smaller, puckered leaves. The trait appeared to be controlled by two genes with partial recessive epistasis. We propose the gene symbols Dwl and Dw2 for this trait. Results indicated that the genes for pod type and stem color segregated independently and were not linked.
Molecular Mapping of a Male‐Sterile Gene in Soybean
Authors: Jin W. , Palmer R. G. , Horner H. T. , Shoemaker R. C.
Published: July 2010

A newly identified genie male‐sterile mutant in soybean [Glycine max (L.) Merr.] has high seed set under natural field conditions and is potentially useful in breeding programs. Meiosis is normal in the mutant line. Sterility in this mutant is caused by failure of cailose dissolution at the tetrad stage, which results in microspore abortion; however, little is known about the male‐sterile gene at the molecular level. The objective of this study was to identify molecular markers linked with the male‐sterile gene (ms) and to place the ms gene onto the soybean molecular genetic map. An F2 population of 107 individuals was constructed from a cross between the mutant msMOS (ms ms) and the cultivar Minsoy (Ms Ms). Two hundred seventy markers, including 219 RFLP and 51 SSRs, were evaluated. Of these, 102 RFLP probes and 31 SSR markers detected polymorphisms between the parents. The F2 population was screened for segregation of these polymorphic molecular markers. Analyses revealed that the male‐sterile locus, designated ‘ms’, was located on linkage group D1b of the USDA/ISU soybean molecular genetic map. The availability of linked DNA markers will facilitate the genetic analysis of this male‐sterility gene in relation to soybean breeding programs, and will be a starting point for the isolation of the ms gene by map‐based cloning.
Classifying Genetic Resources by Categorical and Continuous Variables
Authors: Franco Jorge , Crossa José , Villaseñor José , Taba Suketoshi , Eberhart Steve A.
Published: July 2010

Hierarchical and nonhierarchical clustering methods are used for classifying genetic resources. In hierarchical clustering methods, all variables (categorical and continuous) can be used to form the subpopolations (groups or clusters), but in standard nonhierarchical methods only the continuous variables are incorporated in the analysis. The Location model (LM) allows classifying individuals into homogeneous subpopulations by continuous and categorical variables. In practice, the multinomial variable of the LM that arises from the combination of all the categorical variables usually shows empty cells in some subpopulations with the consequence of not allowing estimation of cell means and within‐cell variances and covariances. The main objectives of this study were (i) to develop the Modified Location model (MLM) that allows empty cells in some subpopulations under the assumption that the means and the variance‐covariance matrices depend on a given subpopulation instead of on a specific cell, (ii) to show how to use the MLM in the context of two‐stage clustering in which the Ward method is used to form the initial groups and the MLM is applied to those groups (Ward‐MLM), and (iii) to show to apply the Ward‐MLM to three different data sets to study some of its features and to compare results with other methods. The two‐stage clustering strategy of finding initial groups by the Ward method and then improving the composition of the groups by the MLM produces compact and well‐separated groups with respect to all the variables (categorical and continuous) compared with classifications obtained with only categorical variables, with only continuous variables, and with the standard Location model.
Evaluation of Soybean Cultivars for Resistance to Sclerotinia Stem Rot in Field Environments
Authors: Kim H. S. , Sneller C. H. , Diers B. W.
Published: July 2010

Sclerotinia stem rot, caused by the fungal pathogen Sclerotinia sclerotiorum (Lib.) de Bary, has increased in importance for soybean [Glycine max (L.) Merr.] in recent years. The objectives of this research were to evaluate soybean genotypes for resistance to Sclerotinia stem rot over several field locations and compare these disease ratings with seed yields, other agronomic traits, and parentage. Eighteen soybean genotypes were evaluated for resistance to Sclerotinia stem rot and agronomic traits in six Michigan environments over 3 yr. The average disease severity index (DSI) of the 18 genotypes at a single environment ranged from 2.1 to 49.9. Mean DSI values over locations differed (P < 0.05) among the genotypes. The genotypes ‘NKS19‐ 90’, ‘Asgrow A2506’, ‘Colfax’, and ‘Corsoy 79’ had the greatest resistance to Sclerotinia stem rot. The DSI ratings of the 18 genotypes were significantly correlated between environments for only five of 15 pairs of environments. Over the six environments, a greater DSI of genotypes was significantly correlated with reduced seed yield and more plant lodging. Disease severity index was not significantly correlated with plant height at maturity, date of flowering, or date of maturity over the environments. Genotypes with parentage tracing to ‘Williams’ or ‘Asgrow A3127’ had a greater average DSI than genotypes with no parentage tracing to these cultivars. This suggests that the use of these cultivars as parents may have caused greater disease susceptibility in contemporary cultivars.
Inheritance of Fresh Seed Dormancy in Peanut
Authors: Upadhyaya H. D. , Nigam S. N.
Published: July 2010

Incorporation of seed dormancy limited duration in Spanish peanut (Arachis hypogae L. ) genotypes is required to avoid loss in pod yield and seed quality because of in situ germination in unpredictable rainfall environments. Knowledge of inheritance of fresh seed dormancy is important to peanut breeder for developing fresh seed dormant early‐maturing Spanish cultivars. This study was conducted to determine the inheritance of fresh seed dormancy using three Spanish peanut genotypes. Two dormant (ICGV 86158 and ICGV 87378) and one non‐dormant (JL 24) genotypes were crossed in all possible combinations, including reciprocals. The fresh seeds from mature pods from parents F1, F2, F3, and backcross populations were evaluated for their dormancy by germination test in the laboratory at 35 ± 2°C in the dark. Results showed that the fresh seed dormancy in these genotypes is controlled by a dominant allele of a single gene. The two dormant parents, ICGV 86158 and ICGV 87378, possess the same allele for fresh seed dormancy.
Resistance of Maize Inbreds to Pink Stem Borer
Authors: Butrón A. , Malvar R. A. , Cartea M. E. , Ordás A. , Velasco P.
Published: July 2010

The most important insect pest of maize (Zea mays L.) in southern Europe is the pink stem borer (Sesamia nonagrioides Lef.). The objective of this work was to identify sources of resistance to stem and ear damage by the pink stem borer. One hundred twenty‐one inbreds from seven germplasm groups (American, Argentine, European, Lancaster, Northern Flint, Reid, and Other), divided according to their maturity grouping (very early, early, midscason, and late), were evaluated for several years under artificial infestation at Pontevedra (northwestern Spain). Twelve traits were recorded to measure stem and ear damage. Stem and ear damage resistance traits were not correlated, therefore simultaneous selection for the two types of resistance within the same population should be carried out. Eight very early, two early, seven midseason, and four late inbreds were resistant to stem‐damage. The Reid germplasm group was more resistant to stem attack than the other groups. Therefore, the best Reid inbreds could be used to form a stem‐damage resistant Reid synthetic, which could be a source of new stem‐damage resistant varieties. Simultaneously, the best non‐Reid inbreds could be used for making a non‐Reid stem‐damage resistant synthetic. Thirteen very early, 10 early, two midseason, and three late inbreds performed better than the others against ear attack. Only seven inbreds (A509, A635, CO125, EA2024, EP39, Oh43, and PB130) were resistant to both stem and ear damage. These inbreds could be used as sources of resistance to pink stem borer in a breeding program.
Developmental Changes Associated with Divergent Selection for Rind Penetrometer Resistance in the MoSCSSS Maize Synthetic
Authors: Abedon Bruce G. , Darrah Larry L. , Tracy William F.
Published: July 2010

Rind penetrometer resistance (RPR) has been used to select indirectly for stalk lodging resistance in maize (Zea mays L.). Breeding for stalk lodging resistance would be facilitated by a better understanding of developmental mechanisms affecting RPR. Vegetative development can be divided into juvenile‐vegetative and adult‐vegetative phases. Vegetative phase change occurs when juvenile‐vegetative traits are replaced by adult‐vegetative traits. The objective of this study was to determine indirect responses in the timing of vegetative phase change and other developmental traits in nine cycles of S0 phenotypic divergent selection for RPR in Missouri Second Cycle Stiff Stalk Synthetic (MoSCSSS). In the high direction of selection, vegetative phase change occurred at lower nodes while ear leaf number and total leaf number decreased. In the low direction of selection, vegetative phase change was delayed to higher nodes while ear leaf number and total leaf number increased. In both directions of selection, plant height was reduced and flowering occurred earlier. The timing of vegetative phase change may be a factor in determining the level of RPR and stalk lodging resistance. Alternatively, modifiers may exist in MoSCSSS that coordinately regulate vegetative phase change with traits, such as ear leaf number, that are directly affected by selection for RPR.
Effect of Temperature and Water Deficit on Water‐Use Efficiency, Carbon Isotope Discrimination, and Specific Leaf Area in Peanut
Authors: Craufurd P. Q. , Wheeler T. R. , Ellis R. H. , Summerfield R. J. , Williams J. H.
Published: July 2010

Carbon isotope discrimination (Δ) and specific leaf area (SLA) have been shown to be correlated with water‐use efficiency (WUE) of peanut (Arachis hypogaea L.) and SLA has been proposed as an indirect selection criterion for Δ and WUE. The effect of high temperature and water deficit on WUE, Δ, and SLA, and relations between them, was investigated in controlled environments. Five Spanish (A. hypogaea ssp. fastigiata) and three Virginia (A. hypogaea ssp. hypogaea, botanical type) lines were grown at mean temperatures of 27 and 34°C and at 50 and 100% available soil water (ASW) from first flowering to maturity, and WUE, Δ and SLA measured at maturity. Virginia genotypes had higher total dry matter, water use and WUE(P ≤ 0.01), but were more sensitive to high temperature (P ≤ 0.01) than Spanish genotypes. Water deficit reduced water use and SLA, and increased WUE. The only water deficit × temperature interaction (P < 0.05) was for Δ, where water deficit reduced the value of Δ at 27° but not at 34°C. High temperature had no effect on water use, but decreased WUE and increased SLA. Across all water deficit and temperature treatments (n = 32), WUE was correlated with Δ (r = ‐0.78, P < 0.001) and SLA (r = ‐0.70, P 0. 001), an SLA correlated with Δ (r = 0.75, P < 0.001) with no difference associated with botanical type. Temperature and water deficit had significant (P ≤ 0.05) effects on the intercept, but not the slope of these relations. The results support the view that SLA can be used as an indirect selection criterion for Δ and WUE in genotypic selection.
Comparison of Measurement Methods of Osmotic Adjustment in Rice Cultivars
Authors: Babu R. Chandra , Pathan M. Safiullah , Blum A. , Nguyen Henry T.
Published: July 2010

Osmotic adjustmen(OA)is a major component of drought resistance. Four different methods for measuring OA in plants are in general use, but there is no information on the comparative performance of these methods. Two similar experiments were designed to evaluate the four methods for measuring OA in diverse indica and japonica cultivars of rice (Oryza sativa L.) subjected to a drying cycle in large pots in the greenhouse. The four methods were:(i) derivation of OA from regressions of leaf relative water content (RWC) on leaf osmotic potential(OP);(ii) estimation of OA from OP of stressed plants calculated to rehydrated state; (iii) estimation of OA from OP of stressed plants that have been rehydrated; and( iv) estimation (from data used in Metho 1) of OA capacity by the sustained RWC at given OP of −3.5 MPa. Method 1 was a priori considered as the best estimate. Under relatively mild atmospherci conditions and a slow development of water deficit (first experiment), mean OA over cultivars was 0.89, 0.51, and 0.72MPa by Methods 1, 2, and 3, respectively. Mean RWC at −3.5 MPa was 6 9.3%. Significant(P ≤ 0.05) variation in OA among cultivars was observed by all methods, up to a four‐fold difference in OA among cultivars (0.35≤1.51 MPa) by Method 1. Simple correlation for OA across 12 cultivars with Method 1 was significantly higher for Method 3(r = 0.76; P = 0.04) and Method 4 (r = 0.87; P < 0.01) than for Method 2(r = 0.54; P0.07). OA by Method 4 was better correlated with Method 3(r 0.80;P < 0.01)than with Method 2(r = 0.67;P = 0.02).The coefficient of variation (CV) as a measure of error was greater for Method 1 (47%)and Method 2 (31%)than for Method 3 (21%) or 4 (24%). Both Methods 2 and 3 were less demanding on labor and plant materials than Methods 1 and 4. The results support the use of Method 3 (the “rehydration method”) as a faster and an economical replacement for Method 1.
Nondestructive Screening for Oleic and Linoleic Acid in Single Sunflower Achenes by Near‐Infrared Reflectance Spectroscopy
Authors: Velasco Leonardo , Pérez‐Vich Begoña , Fernández‐Martínez José M.
Published: July 2010

Current breeding programs dealing with the modification of oleic and linoleic acid concentrations in sunflower (Helianthus annuus L.) require large numbers for chromatographic analyses of half seeds. The objective of this research was to study the potential of nearinfrared reflectance spectroscopy (NIRS) to estimate the oleic and linoleic acid concentrations of intact single sunflower achenes. Spectra from intact achenes were collected with a specially designed adapter and a standard monochromator instrument. Calibration equations for oleic and linoleic acid were developed from a calibration set including 465 intact achenes with a large range of variation for both fatty acids and were validated with an external set of 100 intact achenes. The coefficient of determination between NIRS and gas‐liquid chromatography (GLC) was 0.88 for both fatty acids in external validation, demonstrating the high reliability of NIRS to predict oleic and linoleic acid concentrations of intact, single sunflower achenes. The calibration equation for oleic acid was used to evaluate two F2 populations segregating for this fatty acid, which were further analyzed by GLC. The use of NIRS predictions permitted the discrimination of the majority of the high oleic acid achenes (>700 g kg−1), demonstrating the use of NIRS for selecting sunflower achenes with specific oleic and linoleic acid concentrations.
Genetic Similarities among Winter Wheat Cultivars Determined on the Basis of RFLPs, AFLPs, and SSRs and Their Use for Predicting Progeny Variance
Authors: Bohn Martin , Utz H. Friedrich , Melchinger Albrecht 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 (i) assessed the level of genetic diversity among German and Austrian winter wheat (Triticum aestivum L.) cultivars using 117 restriction fragment length polymorphism (RFLP) probes, 16 amplified fragment length polymorphism (AFLP) primer combinations, and 21 simple sequence repeat (SSR) primer pairs, (ii) investigated the correlation between coancestry (f) and genetic similarity (GS) estimated from molecular markers, and (iii) evaluated the use of f and GS for predicting the genetic variance (σ2g) within sets of 22 F4n (n = 7 or 8) lines derived from 30 crosses between these winter wheat cultivars. The average polymorphic information content (PIC) for polymorphic bands was not significantly different between the three marker systems (0.30 ≤ PIC ≤ 0.33), whereas the marker index was low for RFLPs and SSRs but high for AFLPs. Estimates of f between all 55 cultivar combinations ranged from 0.01 to 0.53.
‐values varied between 0.52 and 0.89 for RFLPs, between 0.40 and 0.83 for AFLPs, and between 0.16 and 0.91 for SSRs. The Mantel Z test statistic revealed no common pattern between the four dendrograms obtained by cluster analyses. Significant (P < 0.05) correlations among f̂,
‐RFLP,
‐AFLP, and
‐SSR were detected only for related parent combinations (f̂≥ 0.10). For all seven traits analyzed, estimates of σ2g were not significantly associated with any measure of GS between parents. On the basis of these results, we recommend AFLPs for fingerprinting wheat cultivars. However, predicting the progeny variance (σ2g) remains an unsolved problem.
Verifications of a Quantitative Trait Locus Affecting Agronomic Traits in Two‐Row Barley
Authors: Spaner D. , Rossnagel B. G. , Legge W. G. , Scoles G. J. , Eckstein P. E. , Penner G. A. , Tinker N. A. , Briggs K. G. , Falk D. E. , Afele J. C. , Hayes P. M. , Mather D. E.
Published: July 2010

Quantitative trait loci (QTL) affecting agronomic traits have been mapped in barley (Hordeum vulgare L.), but there have been few experimental verifications of the presence and effect of individual QTL. Here, we report on verification of a QTL on the “plus” arm of chromosome 7(5H) of barley. This QTL, affecting grain yield, plant height, maturity, and lodging severity, had been mapped in the two row barley cross ‘Harrington’/‘TR306’, on the basis of evaluation of 145 doubled haploid lines in 30 field experiments. We used molecular marker genotypes to select 47 lines from among 410 Harrington/TR306 lines that had not been used in the original mapping experiment. Comparisons among groups of lines with contrasting marker genotypes on chromosome 7 (5H) confirmed that a QTL on the “plus” arm of that chromosome affects grain yield, plant height, and lodging severity. The presence of TR306 alleles at this QTL contributed to small increases in grain yield and plant height, and reduced lodging severity. The results of this study confirmed the presence of a QTL affecting several agronomic traits, but also demonstrated that the effect of individual QTL may be small and may vary among environments.
A Two‐Stage, Three‐Way Method for Classifying Genetic Resources in multiple Environments
Authors: Franco Jorge , Crossa José , Villaseñor José , Castillo Alberto , Taba Suketoshi , Eberhart Steve A.
Published: July 2010

Cluster analysis is commonly used when gene bank accessions are evaluated in different environments and several continuous and categorical attributes are measured. The objectives of this study were (i) to develop a two‐stage classification strategy for three‐way data (accession × attribute × environment) using the Modified Location Model (MLM) with categorical and continuous variables and (ii) assess this approach for classifying observations of one simulated data set (with known structure) and two experimental data sets consisting of multi‐attribute, multi‐site field trials of Caribbean and Cónico accessions of maize (Zea mays L.). Clusters were compared including and excluding the categorical variables. Results from the simulated data showed good recovery of the group structure and a balanced effect of both categorical and continuous variables on the classification. The two‐stage, three‐way MLM method formed well‐defined groups of accessions and characterized them based on the continuous as well as the categorical variables. As expected, groups formed using only continuous variables showed no clear response patterns concerning the categorical variables; however, those formed using both types of variables had clear response patterns with respect to each type. Furthermore, groups of Caribbean accessions showed dear association with geographical origin. The MLM model should be useful for classifying genetic resources evaluated in multi‐environment trials into homogeneous groups with the objective of forming core subsets. When a large number of categorical variables are combined across environments, the MLM may not improve the initial classification obtained from hierarchical clustering strategy.
Effects of Insect Tripping on Seed Yield of Common Bean
Authors: Ibarra‐Perez F. J. , Barnhart D. , Ehdaie B. , Knio K. M. , Waines J. G.
Published: July 2010

Insect tripping might enhance seed production in common bean (Phaseolus vulgaris L.). The effect of flower visits by insects on seed production was studied during 3 yr, 1992 to 1994, in Riverside, CA, using four cultivars with different growth habits: Linden, Pindak, PI 164778, and Ferry Morse 53 (FM 53). Each year, a factorial experiment in a randomized complete block design with four replicates was used. Each cultivar was grown under three treatments: (i) exposed to open visitation by all insects, (ii) in insect‐proof cages, and (iii) in cages with bumblebees. All pods produced by bean plants were collected and counted, and seed yield was determined. Year‐to‐year variation had signiticant impact on cultivar performance and treatment effects. The bean lines were significantly different for seed yield. The treatment effects were not consistent across years. The old cultivar FM 53 and line PI 164778 had no clear trend for seed yield response to insect visits across years, whereas Linden and Pindak showed a more defined and positive response to visits. Seed yield of Linden was similar in the open visitation and caged‐with‐bumblebees treatments but was significantly higher than that of caged plants, by 13% in 1992 and by 35% in 1994. Pindak showed a 9% increase in seed yield when plants were visited by insects in the open or in caged treatments compared with caged plants in 1992. The results indicate that cultivars such as Linden and Pindak, which behave as determinate plants, may respond to bumblebee tripping by increasing seed yield.
Selection of Castor for Divergent Concentrations of Ricin and Ricinus communis Agglutinin
Authors: Pinkerton Scott D. , Rolfe Rial , Auld Dick L. , Ghetie Victor , Lauterbach Brenda F.
Published: July 2010

One of the most limiting factors in the production and processing of castor (Ricinus communis L.) is the presence of ricin and Ricinus communis agglutinin (RCA) in the endosperm. These highly toxic proteins create potential health hazards that have limited castor production in the USA, The objectives of this research were to develop a rapid assay to quantify ricin + RCA concentration in whole and partial seed of castor; to screen the USDA castor germplasm collection for ricin + RCA concentration; and to determine the inheritance of ricin + RCA in segregating populations of castor. A radial immunodiffusion (RID) assay based on ricin specific antibodies was shown to be highly repeatable in estimating the relative ricin + RCA concentrations of 18 castor accessions (rs = 0.98**). This assay could be used on whole seed or a small portion of the endosperm removed distal to the caruncle to maintain seed viability. The ricin + RCA concentration of 263 accessions from the USDA castor collections ranged from 1.9 to 16.0 mg g−1. Two accessions, PI 257 654 and PI 258 368, with low ricin + RCA concentrations were crossed with the commercial cultivar Hale. Three F3 seed from each F2 plant of six segregating populations were evaluated for ricin + RCA concentration. Individual plants of the six F2 populations and seed of the six F3 populations had an extremely wide range and significantly differed in ricin + RCA concentration. F3 plants with low and high levels of ricin + RCA were selected.
RFLP Markers Associated with High Grain Protein from Triticum turgidum L. var. dicoccoides Introgressed into Hard Red Spring Wheat
Authors: Mesfin Asfaw , Frohberg Richard C. , Anderson James A.
Published: July 2010

Increased grain protein is desirable for many bread and pasta products. Because of its importance to end‐use quality and human nutrition, this trait has been widely studied. This study was conducted to (i) identify genomic regions associated with high grain protein concentration (GPC) inherited from Triticum turgidum L. var. dicoccoides in three hard red spring wheat recombinant inbred (RI) populations (ND683/‘Bergen’, ‘Glupro’/‘Keene’, and Glupro/Bergen); (ii) examine the effects of genetic background and environment on these genes; and (iii) determine the genetic size of the Triticum turgidum L. var. dicoccoides chromosomal segment introgressed into hard red spring wheat genotypes. The F5‐derived RI lines were grown at five environments for the ND683/Bergen population and at three environments for the other two populations. The range of GPC in the ND6S3/Bergen, Glupro/Keene, and Glupro/Bergen population was 142 to 179,149 to 182, and 139 to 183 g kg−1, respectively. The four parental genotypes were surveyed for polymorphisms with 96 low copy DNA clones located on group 5 and 6 chromosomes. A single region associated with high GPC was detected with five RFLP markers (Xcdo365, Xmwg79, Xbcdl02, Xbcd357, and Xcdol380) located near the centromere on chromosome 6B. One of the markers (Xcdo365) identified a 6.5‐kb restriction fragment in Triticum turgidum var. L. dicoccoides, Glupro, ND645, and ND683. Hence, this fragment is in coupling linkage to high GPC gene(s). This marker explained 21 to 35% of the phenotypic variation in GPC in the three populations. The DNA marker in this region might be used to rapidly introgress this gene for high GPC into other wheat germplasm.
Capturing Heterosis in Forage Crop Cultivar Development
Authors: Brummer E. Charles
Published: July 2010

Despite the widespread use of hybrid cultivars in many crop species, most forage crop cultivars are synthetic populations that do not express maximum heterosis for important agronomic traits such as yield. Several aspects of these crops, including severe inbreeding depression, perfect flowers, and polyploidy, limit the ability to produce conventional single‐ or double‐cross hybrids, but the viable alternative of developing semihybrid populations has been relatively unexplored. Both theoretical and empirical evidence support the notion that hybrids, developed by crossing divergent populations, can outyield the better performing parental population. A method to produce semihybrids is discussed, necessitating the development and maintenance of heterotic groups within a species. Progeny formed by crossing populations are semihybrids because in a cross of two populations, 1/2 of the progeny result from interpopulation crosses and 1/2 from intrapopulation crosses. Expected genotype proportions are presented for several scenarios to show the feasibility of using semihybrids to capture partial heterotic gains. Development of pure hybrids is more problematic but could be realized by using transgenic selectable markers, such as herbicide resistances, to rogue nonhybrid plants in production fields. Molecular markers may aid in the development of the heterotic groups and in choosing parents to be crossed. Potential heterotic groups in several forage species are suggested. By requiring attention to germplasm resources, this method will also be useful for broadening and improving the genetic bases of most cultivated forage crops.
Selecting Soybean Cultivars for Dual Resistance to Soybean Cyst Nematode and Sudden Death Syndrome Using Two DNA Markers
Authors: Prabhu R. R. , Njiti V. N. , Bell‐Johnson B. , Johnson J. E. , Schmidt M. E. , Klein J. H. , Lightfoot D. A.
Published: July 2010

DNA markers for genes conditioning resistance to soybean [Glycine max (L.) Merr.] root infection by [Fusarium solani (Mart.) Sacc. f. sp. glycine (Burk.)] (Rfs1), sudden death syndrome (SDS), and soybean cyst nematode (SCN; Heterodera glycines Ichinohe; Rhg4 and rhg1) were previously identified in ‘Essex’ × ‘Forrest’. This study tests the effectiveness of those markers in selecting for disease resistance among recombinant inbred lines from ‘Flyer’ × ‘Hartwig’. A total of 535 among 739 lines were scored by two markers, providing four genotypes. A stratified random sample of 50 lines was evaluated for SDS by F. solani root infection severity at two locations and SCN race 3 index of parasitism in the greenhouse. Selection with BLT65 identified 281 among 671 lines with the genomic region that underlies Rhg4‐derived SCN resistance. Selection with Satt038 identified 230 among 613 lines containing the genomic region that underlies resistance to SDS (rfs1) and rhg1 ‐derived SCN resistance. A total of 93 out of 535 lines had genomic regions that underlie resistance to both SDS and SCN in Essex × Forrest. Segregation of both markers was not random (P ≤ 0.05). Infection severity means for genotypes with the Hartwig allele at Satt038 (28–29%) were lower (P = 0.0001, R2 = 28%) than with the Flyer allele (31–42%); irrespective of maturity group. BLT65 was not associated with infection severity. Mean SCN index of parasitism was lower (P ≤ 0.05) only for genotypes carrying the Hartwig allele at both Satt038 and BLT65. Therefore, alleles conferring resistance to SDS and SCN in Essex × Forrest are transferable to other populations.
Theoritical Inbreeding at Selectively Neutral Loci in Unparental Mass Selection and Recurrent Selection with Polycrossing of Selected Plants
Authors: Han L. X. , Casler M. D.
Published: July 2010

Inbreeding depression is of great concern to breeders of crosspollinated plant species, especially if the breeders intend to release synthetics or open‐pollinated cultivars. Estimation of inbreeding coefficients of cycles from recurrent selection helps planning a recurrent selection program or utilizing a population derived from recurrent selection. In this paper, we derived the formulas to estimate the inbreeding coefficient of any cycle at one locus for uniparental mass selection and for recurrent selection with polycrossing of selected plants, under the assumption that the locus is selectively neutral. For uniparental mass selection, the inbreeding coefficient of Cycle i is determined mainly by the number of plants selected in Cycle i ‐ 2, while the total number of plants in Cycles i ‐ 1 and i ‐ 2 and the number of seeds contributed to the seed bag by each selected plant in Cycle i ‐ 2 also have some effects. For recurrent selection with polycrossing of selected plants, the inbreeding coefficient of Cycle i is determined mainly by the number of plants selected in Cycle i ‐ 1 while the number of plants selected in Cycle i ‐ 2 and the number of seeds contributed to the seed bag by each selected plant in Cycle i ‐ 2 also have some effects. To make an inference regarding the use of cycles from uniparental mass selecting or to compare the efficacy of uniparental mass selection with recurrent selection that includes intercrossing or polycrossing of selected plants or lines, one should use the seed derived from one generation of open pollination in isolation for uniparental mass selection.
Genetic Analyses of Agronomic Traits Controlled by Wheat Chromosome 3A
Authors: Shah M. M. , Baenziger P. S. , Yen Y. , Gill K. S. , Moreno‐Sevilla B. , Haliloglu K.
Published: July 2010

Previous studies with chromosome substitution lines between hard red winter wheat (Triticum aestivum L.) cultivars Cheyenne (CNN) and Wichita (WI) identified genes on chromosome 3A of WI which affect grain yield, yield components, grain volume weight, plant height, and anthesis date. This study was conducted to determine if the trait variation caused by chromosome 3A could be explained by major or minor gene segregation and if these genes are pleiotropic, linked, or independent on the chromosome. A population of recombinant inbred chromosome lines for chromosome 3A (RICLs‐3A), developed between CNN and a chromosome substitution line CNN(WI3A), was evaluated in multi‐location field trials in 3 yr. Our results indicate significant differences (P ≤ 0.05) between parental lines and among RICLs for grain yield, 1000‐kernel weight, plant height, and anthesis date, but not for kernel number per spike, spike number per square meter, and grain volume weight. A 1:1 genetic ratio for anthesis date suggested the presence of a single segregating locus controlling the trait. None of the other agronomic traits could be separated into unequivocal groups and hence, major genes were not detected. This indicates that the traits were controlled either by several genes or few genes with enough environmental influence, or both, to obscure their effects. Significant correlations and possible crossover products between anthesis date, plant height, and 1000‐kernel weight suggest that these traits were controlled either by linked gene(s) or by pleiotropic genes with additional genes affecting one of the traits.
Gain from Two Cycles of Divergent Selection for Root Morphology in Alfalfa
Authors: Lamb J. F. S. , Barnes D. K. , Henjum K. I.
Published: July 2010

Alfalfa (Medicago sativa L.) has been identified for use in phytoremediation. Phytoremediation is defined as the use of green plants to remove or contain environmental contaminants. Alteration of root morphology would increase the degradative efficiency of alfalfa for phytoremediation. Root morphology traits in alfalfa are heritable, but are strongly influenced by dormancy and geographic origin. Our objective was to create alfalfa source germplasms that differ in root morphology within the same genetic background. Four experimental alfalfa germplasms differing in dormancy and genetic origin were evaluated after two cycles of divergent selection for root morphology traits. Two sources were selected for few vs. many lateral roots and the other two sources were selected for few vs. many fibrous roots followed by one subsequent cycle of selection for few vs. many lateral roots. These divergent populations were evaluated using two fertilizer rates (0 and 200 kg N ha−1) and were established twice at each of two locations. Plants from one experiment at each location were dug at the end of the establishment year and from the second experiment at the end of the first production year. All plants were evaluated for number of lateral roots, fibrous root mass, taproot diameter, plant count per plot, and plot root weight. Two cycles of divergent selection for root morphology traits in all four source germplasms produced alfalfa populations that differed in root morphology. Realized heritabilities from all germplasm sources ranged from 21 to 48% for fibrous root mass and from 11 to 43% for lateral root number. Response to selection varied among the four source germplasms and indicated that the choice of parent germplasm will be a factor for success in producing alfalfa populations that differ in root morphology within a single genetic source.
Selection for Drought Tolerance Increases Maize Yields across a Range of Nitrogen Levels
Authors: Bänziger M. , Edmeades G. O. , Lafitte H. R.
Published: July 2010

It is not known whether selection for improved tolerance to a specific abiotic stress leads to correlated changes in performance under other stresses. Drought and N deficiency are important constraints to production in the tropics. We examined the effect of selection for drought tolerance on performance of tropical maize (Zea mays L.) under a range of N levels. Original and advanced selections of four populations, improved for tolerance to midseason drought for two to eight recurrent selection cycles each, were evaluated in two experiments under severe N stress, one experiment under medium N stress, and two well‐fertilized experiments. Nitrogen accumulated in the aboveground biomass at maturity averaged 52, 63, 105, 151, and 163 kg N ha−1 in the five experiments, and grain yields of 3.0, 2.9, 5.2, 6.0, and 6.5 Mg ha−1 were obtained. Selection for tolerance to midseason drought stress increased grain yields by an average of 86 kg ha−1 yr−1 with nonsignificantly larger gains under severe N stress (100 kg ha−1 yr−1). Drought‐tolerant selections had increased biomass and N accumulation at maturity, the changes being largest under severe N stress. Additionally, drought‐tolerant selection cycles were associated with delayed leaf senescence and an increased or unchanged N harvest index, indicating that leaf N was used more efficiently for grain production. Selection for tolerance to midseason drought stress appears to increase grain yield across a range of N stress levels and may lead to morphological and physiological changes that are of particular advantage under N stress.
Linkage between the Centromere and a Gene Producing Nucleocytoplasmic Compatibility in Durum Wheat
Authors: Maan S. S. , Joppa L. R. , Kianian S. F.
Published: July 2010

Species cytoplasm specific (scs) genes on chromosome 1A) (1Ascs) derived from Triticum timopheevii Zhuk. and chromosome 1D) (1Dscs) derived from common wheat improve compatibility between the durum wheat (T. turgidum L. var. durum) nucleus and Aegilops longissima S. & M. (lo) cytoplasm. The (lo) scs durum lines thus produced are male sterile and when crossed with durum produce viable plump seeds carrying scs and inviable shriveled seeds without scs. Objectives of the present study were to determine centromere‐scs linkage distances and viability and transmission of female gametes carrying one or both scs genes. The (lo) scs durum heterozygous for 1A/1Ascs was crossed with the Langdon (LDN) durum disomic substitution line 1Dscs(1A) in which the 1A chromosome pair is substituted by a 1Dscs pair. Two types of 1A + 1D double monosomic F1s were recovered, (lo) durum 13″ + 1′1Ascs + 1′1Dscs, and (lo) durum 13″ + 1′1A + 1′1Dscs, which were confirmed in progeny tests with normal durum. For centromere mapping, these lines were crossed with LDN double diteiosomic 1A (LDN dDt 1A; 2n = 30; 13″ + t″1AS + t″1AL) and progeny examined for meiotic chromosomec onstitution. No telocentric trict1ALscs arising from recombination with 1Ascs was detected, indicating that scs is tightly finked to the centromere on chromosome 1A. To determine the transmission of female gametes carrying one or both scs genes, (lo) durum 13″ + 1′1Ascs + 1′1Dscs was crossed with LDN dDt 1A and control durum. The functional female gametes carried one or both scs genes. Crosses of (lo) durum 13″ + 1′1A + 1′1Dscs to LDN dDt 1A produced several plants with a T1AL.1DL translocation chromosome. The formation of this chromosome was coupled with strong selection for the scs gene on 1DL.
Recessive, Day Length‐Insensitive Earliness to Synchronize Flowering of Pearl Millet Hybrid Parents
Authors: Bidinger F. R. , Hash C. T. , Jayachandran R. , Rao M. N. V. Ratnaji
Published: July 2010

The availability of recessive genes for early flowering‐day length insensitivity offers an opportunity to synchronize the flowering of late‐flowering or day length‐sensitive parents with that of early‐flowering parents without necessarily affecting the flowering of their hybrids, provided that the earlier parent does not carry the same recessive allele. This study evaluated the hypothesis that incorporating the recessive e1 allele for early flowering‐day length insensitivity into a late‐flowering, photoperiod‐sensitive pollinator in pearl millet [Pennisetum glaucum (L.) R. Br.] would synchronize its flowering and improve seed production with earlier‐flowering female parents, without affecting the time to flowering or the performance of the resulting hybrids. An e1/e1 isoline of the late‐flowering pollinator ICMP85 410, produced by six backcrosses, flowered 16 d earlier under natural day lengths at Patancheru, India, (17°N) and 19 d earlier under extended day lengths (equivalent to 29°N) than its near isogenic E1/E1 counterpart. As a consequence, it successfully produced hybrid seed when sown simultaneously with early, male‐sterile line 843A, whereas the late isoline failed under the same conditions. The E1/e1 versions of eight near‐isogenic hybrids (on a range of eight E1/E1 male‐steriles) flowered an average of 3 d earlier than their E1/E1 counterparts in 2 yr of tests under both natural and extended day length conditions at the same location. This earlier flowering had small effects on hybrid yield components, consistent with known effects of earliness in the crop, but did not affect grain yield. The results indicate that the e1 allele is a powerful tool for exploiting heterosis between early‐ and late‐flowering parents in pearl millet, which is otherwise difficult to realize without complicated seed production practices.
Free‐Air CO2 Enrichment Effects on Apex Dimensional Growth of Spring Wheat
Authors: Li Aiguo , Wall Gerard W. , Trent Anthony , Hou Yuesheng
Published: July 2010

Although primordium initiation in wheat (Triticum aestivum L.) has been extensively researched, a complete description of the growth dynamics of the apex at elevated CO2 concentrations is lacking. This study determined the rates of main stem and tiller apical elongation and widening in plants grown under two levels of CO2 concentration. Spring wheat was grown at the University of Arizona's Maricopa Agricultural Center at elevated (550 μmol mol−1) or ambient (370 μmol mol−1) CO2 concentrations. Individual plant samples were collected at different developmental stages and dissected. After dissection, the lengths and widths of the apices of the main stem (MS), coleoptile tiller (TO), primary tillers (T1, T2, and T3), and secondary tillers (T00, T01, T02, T10, Tll, and T12) were measured with a stage micrometer. Apex dimensions were fitted to an exponential model. Elevated CO2 increased the apex lengths of T2 at the double ridge stage, and of T3 and T10 at the double ridge and the terminal spikelet stages, and the apex widths of T2 at double ridge stage, and of T2, T3, T10, and Tll at the flag leaf appearance stage. Combining these results with a parallel study, the longer apices did not have more spikelet primordia, but wider apices had more floret primordia. Elevated CO2 changed apex elongation or widening patterns within a plant by enhancing elongation or widening rates of the MS, and laterformed tillers. Earlier‐formed tillers were less responsive to elevated CO2 levels. This information will be used in modeling wheat apical development and grain production in the elevated atmospheric CO2 environments of the future.
Light Environment, Nitrogen Content, and Carbon Balance of Basal Leaves of Sunflower Canopies
Authors: Rousseaux M. C. , Hall A. J. , Sánhez R. A.
Published: July 2010

A good association between leaf N and photosynthetic photon flux density (PPFD) canopy distribution profiles has often been found. However, it is not clear whether N export from basal leaves anticipates the reduction in basal leaf PPFD that occurs as the canopy develops; our first objective was to examine this issue. We documented the dynamics of the light environment and specific leaf nitrogen (Nf) for target leaves at a single level of insertion under sunflower (Helianthus annuus L.) canopies grown at 0.47, 1.18, and 4.76 plants m−2 and contrasted observed Nf with the estimated value of Nf required to maximize net carbon exchange (NCE) for the actual PPFD impinging on target leaves. The second objective of this work was to define the relationships between Nf and PPFD and between Nf and the spectral composition of light impinging on basal leaves. Paired (red and farred) photodiode sensors placed on the adaxial leaf surface were used to document light quality dynamics of basal leaves. Measured Nf was greater than or similar to that required to maximize NCE for 79% of the observations made between achievement of maximum target leaf area and senescence of these leaves. Nf showed a strong association with both red/far‐red ratio of light impinging on target leaves and PPFD, but the association was stronger for the former variable. We conclude that N export from basal leaves does not precede PPFD reduction and that the red/far‐red ratio is a better predictor of Nf gradients within the canopy than PPFD.