bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct and Indirect Effects of Full‐Sib Recurrent Selection for Resistance to Common Rust (Puccinia sorghi Schw.) in Three Sweet Corn Populations
Authors: Abendon B. G. , Tracy W. F.
Published: July 2010

Common rust (Puccinia sorghi Schw.) is a major pathogen of sweet corn (Zea mays L.). Recurrent selection may be useful for improving resistance to common rust. The objectives of this study were to (i) evaluate three sweet corn populations (Minn11, Minn14, NECDR) after three cycles of full‐sib recurrent selection for resistance to common rust evaluated 40 d after pollination (DAP), (ii) determine if selection increased resistance 21 DAP, and (iii) determine if selection affected agronomic traits related to plant architecture, maturity, and yield. Cycles 0 to 3 from each population were evaluated under artificial rust infestation in 1989, 1990, 1993, 1994, and 1995, and without infestation in 1994 and 1995. Percent leaf area infected declined linearly from 37.0 to 8.2% in Minn11 (R2 = 0.98) and 57.0 to 9.9% in NECDR (R2 = 0.98) evaluated 40 DAP, and from 22.5 to 7.8% in Minn11 (R2 = 0.89) and from 22.8 to 10.0% in NECDR (R2 = 0.91) evaluated 21 DAP. Population Minn14 tended to have decreased percent leaf area infected over cycles, but the response was not significant because of cycle × year interactions in each experiment. Most agronomic traits decreased linearly over cycles except for ear weight/stover weight ratio in Minn11 and NECDR, and silk delay in Minn14, which increased linearly. In general, plants tended to be more compact and flower earlier over cycles. Selection for plant type, ear weight, and flowering time should accompany selection for resistance to common rust.
Influence of Ozone Stress on Soybean Response to Carbon Dioxide Enrichment: III. Yield and Seed Quality
Authors: Heagle A. S. , Miller J. E. , Pursley W. A.
Published: July 2010

Ozone in the troposphere can cause plant stress, whereas elevated CO2 generally causes positive responses. Little is known of how these gases interact to affect plant response. Interactive effects on yield and seed quality of soybean [Glycine max (L.) Merr.] grown in 14‐L pots were measured in open‐top field chambers. Essex was tested in 1993, and Essex, Holladay, and NK 6955 were tested in 1994. Plants were exposed from emergence to maturity to four CO2 levels (ambient and 1.3,1.6, and 2.0 times ambient) and three O3 levels (0.4, 0.9, and 1.5 times ambient) in 12 combinations. Increasing O3 suppressed growth and yield, whereas CO2 enrichment stimulated growth and yield. Carbon dioxide‐induced stimulation was greater for plants stressed by O3 than for non stressed plants. For example, CO2 at 2.0 times ambient increased 2‐yr mean seed yield of Essex by 16, 24, and 81% at O2 levels of 0.4, 0.9, and 1.5 times ambient, respectively. Effects of O3 and CO2 on seed oil content were variable with numerous cultivar differences. Seed protein content was never affected. Elevated O3 suppressed oleic acid content in seeds, whereas CO2 increased it; the nature of the O3 × CO2 interaction for oleic acid was similar to that observed for most yield measures. Carbon dioxide‐induced stimulation of plants stressed by O3 was apparently caused partly by amelioration of O3 stress. Interactions between O3 and CO2 must be considered for proper interpretation of cause‐effect relationships in CO2, enrichment studies.
Physiological Response of Two Turfgrass Species to Varying Ratios of Soil Matric and Osmotic Potentials
Authors: Dean‐Knox D. E. , Devitt D. A. , Verchick L. S. , Morris R. L.
Published: July 2010

Plants grown under saline conditions can experience elevated matric and osmotic stress between irrigation events. Research was conducted to assess the physiological response of tall rescue (Festuca arundinacea Schreber ‘Monarch’) and common bermudagrass (Cynodon dactylon L. ‘Numex Sahara’) to varying combinations of soil matric (ΨM) and osmotic potentials (ΨII). Two line‐source gradient experiments were conducted, using municipal water with an electrical conductivity (EC) of 1.1 dS−1 or saline a quifer water blended with municipal water (EC of 6.0 dS m−1). Turf temperature, leaf xylem water potential (ΨL), tissue osmolality (ΨII‐TISS), yield, evapotranspiration (ETa), percent cover, turf color, and tissue ion concentrations were monitored during a 68‐d drydown period during the summer of the second year of experimentation. The total soil water potential (ΨT) was highly linear with distance from the line source with no significant difference between fresh and saline treatments within each species (bermudagrass, Adjr2 = 0.867**; tall rescue, Adjr2 = 0.810"). Significantly lower soil osmotic potentials were recorded under the saline treatment, while lower soil matric potentials were recorded under the fresh treatment for both species. Turf temperature, yield, ETa, turf color, and canopy cover responded to ΨM and ΨII in an additive fashion. The ΨL, ΨII‐TISS and tissue ion concentrations in bermudagrass and ΨII‐TISS and tissue ion concentrations in tall rescue responded in a nonadditive fashion, however. Our results suggest that water with a salinity level of 6.0 dS m−1 could be used as a supplemental irrigation source for both tall fescue and bermudagrasisf irrigation practices were designed to minimize water deficit.
Differentiation of Tall Fescue Monosomic Lines Using RFLP Markers and Double Monosomic Analysis
Authors: Eizenga G. C. , Schardl C. L. , Phillips T. D. , Sleper D. A.
Published: July 2010

Tall fescue (Festuca arundinacea Schreb., 2n =6x =42) is a major cool‐season pasture and turf grass with the genome constitution PPG1G1G2G2. Lack of aneuploid stocks hinders genetic studies in this important grass. The objective of this study was to characterize 23 fertile, embryo culture‐derived, ‘Kenwell’ tall fescue monosomic lines by means of (i) RFLP markers, (ii) double monosomic analysis, and (iii) isozyme phenotypes of F1 progeny. Standard procedures were used for RFLP chemiluminescent detection, crossing, cytogenetic analyses, and obtaining isozyme banding patterns. Using RFLP markers, we ascertained that four monosomic lines were hemizygous for a P‐genome marker and the 23 plants were placed into 17 groups based on plants having the same RFLP banding patterns. For double monosomic analysis, metaphase I chromosome pairing relationships were ascertained for 220 F1 progeny from 26 crosses among the monosomic lines. Five of the progeny were trisomic, 148 disomic, 60 monosomic, and seven had 40 chromosomes. All of the 40‐chromosome progeny were double monosomic plants, indicating the monosome carried in the parents were not the same chromosome. Isozyme phenotypes were ascertained for 203 F1 progeny from crosses for double monosomic analysis which had both 42‐ and 41‐chromosome progeny to determine if an isozyme locus mapped to the monosome from the female parent. A PGI‐2 locus most likely mapped to one monosome. Double monosomic analysis provided evidence that at least four of the 21 possible tall fescue monosomic lines were obtained.
Restriction Fragment Length Polymorphisms in Landrace Barleys from Ethiopia in Relation to Geographic, Altitude, and Agro‐Ecological Factors
Authors: Demissie Abebe , Bjørnstad Åsmund , Kleinhofs Andris
Published: July 2010

Forty‐three landrace (LR) barley (Hordeum vulgare) populations from a wide agro‐ecological range in Ethiopia were assayed for RFLPs with 31 probes distributed over all barley chromosomes. Diversity between LRs was analyzed by Nei's genetic similarity (F) and genetic distance (d) parameters. The 43 populations were represented either by one single line (Set 1) or by four to five lines in a subset of populations(Set 2). The greatest diversity between LRs was observed in Set 1. However, many populations appeared rather similar in RFLP patterns. Relationships between LRs were sharply altered by including the within LR‐diversity component (Set 2), and the average level between‐LR differentiation was reduced compared with Set 1. The within‐LR diversity was similar in magnitude to that for geographical regions. Levels of within‐LRR FLP diversity were poorly correlated with morphological and isozyme variations in the same LR or region. The results highlight the critical role of a sampling strategy that includes both within and between LR components, which is important both to large scale and core collections.
Field and Nutrient Solution Tests Measure Similar Mechanisms Controlling Iron Deficiency Chlorosis in Soybean
Authors: Lin Shun‐Fu , Baumer James S. , Ivers Drew , de Cianzo Silvia Rodriguez , Shoemaker Randy C.
Published: July 2010

Nutrient solution systems have been considered an alternative method to field evaluations for studies of iron deficiency chlorosis (IDC) and for breeding soybeans [Glycine max (L.) Merr.] with improved iron efficiency. Although rates of gain are similar for both methods, it has not been previously demonstrated that field tests and nutrient solution tests for IDC measure similar genetic mechanisms. To test this, quantitative trait loci (QTL) identified in nutrient solutions were compared with those previously identified in field studies. F2:4 lines from two populations, Pride B216 × A15 and Anoka × A7, were grown in nutrient solution and evaluated for IDC by visual scores and determinations of chlorophyll concentrations. In the Anoka × A7 population, one major gene on linkage group N, and modifying QTL on linkage groups A1 and I, that were previously mapped during field tests, also were identified in the nutrient solution test. In the Pride B216 × A15 population, one QTL previously mapped on Linkage Group I during field tests was not identified in the nutrient solution test, and a newly identified QTL was mapped on Linkage Group BI. QTL on Linkage Groups B2, G, and N were identified in both field and nutrient solution tests. We concluded that similar QTL are identified in nutrient solution and field tests and, therefore, both systems identify similar genetic mechanisms of iron uptake and/or utilization.
Germplasm Diversity among Cultivars and the NPGS Crimson Clover Collection
Authors: Steiner J. J. , Piccioni E. , Falcinelli M. , Liston A.
Published: July 2010

Crimson clover (Trifolium incarnatum L.) is a cool‐season annual forage legume. Few morphological traits are recorded to distinguish genotypes and very little is known about its genetic diversity. The objective of this research was to classify and characterize the genetic diversity in the USDA‐ARS National Plant Germplasm System (NPGS) accessions and USA and European Economic Community (EEC) cultivars. Descriptions of EEC cultivars and their breeding histories are also presented. A secondary objective was to determine if T. incarnatum vat. molinerii (Baib. ex Hornem.) Ser. should be considered a distinct species. Genomic DNA from leaves of 37 taxa was examined in 1993 by the polymerase chain reaction (PCR) using 29 random amplified polymorphic DNA (RAPD) markers. Plants grown in the greenhouse were also observed for inflorescence color and relative flowering time. Cluster analysis of pairwise means of RAPD maker distances and cultivar pedigree histories revealed similar genetic backgrounds among most cultivars. Flower color was associated with RAPD marker grouping (P ≤ 0.02) but flowering time was not (P ≤ 0.31). Bolh red vs. non‐red inflorescence color and early‐ vs. late‐flowering traits could be predicted by specific RAPD bands (95 and 93% accuracy, respectively). Analysis of internal transcribed spacer region sequences (ITS) from ribosomal DNA (rDNA) showed diverse crimson clover taxon to be more similar to one another than to var. molinerii (0.4 and 0.9% base pair differences, respectively; P ≤ 0.001). Because of the limited diversity within the current NPGS collection, additional accessions should be collected, morphologically evaluated, and genetically analyzed to broaden the genetic base of the collection. Crimson clover var. molinerii is a sister taxa of more typical crimson clover accessions but exhibits enough ITS diversity to be classified as another species.
Yield, Flowering, and Leaf Area Index of Okra‐Leaf and Normal‐Leaf Cotton Isolines
Authors: Heitholt J. J. , Meredith W. R.
Published: July 2010

Cotton (Gossypium hirsutum L.) with alternative leaf morphologies, such as the cleft‐shaped okra‐leaf types, offers production advantages such as earlier maturity. However, okra‐leaf types have not been commercially viable in the USA. The objectives of this study were to test okra‐leaf types in genetic backgrounds varying in maturity and region of adaptation and to provide growth data that might explain yield differences. Four to seven pairs of selected cotton okra‐ and normal‐leaf isolines (and check cultivars) were grown in the field in one 2‐yr (Exp. A) and two 1‐yr experiments (Exp. B and C) from 1994 to 1996 near Stoneville, MS, in row spacings of 76 and 102 cm. In Exp. A, average lint yields of okra‐leaf isolines were greater overall than normal‐leaf lines (847 vs. 749 kg ha−1), but in Exp. C, the opposite was true (1020 kg ha−1 for okra‐ vs. 1130 kg ha−1 for normal‐leaf types). No yield difference was found between leaf types in Exp. B. Yields of okra‐leaf lines were either equal to or less than those of recently released high‐yielding commercial types whose okra‐leaf isolines are not yet available. Okra‐leaf types were usually 1 to 4 d earlier in maturity than their normal‐leaf counterparts, possibly contributing to their overall yield advantage in Exp. A. When only okra‐leaf isolines were considered, Tamcot HQ95 ranked first or second highest for yield and was the earliest to mature in all three tests. In general, the row‐spacing effect and interactions with row spacing were not significant. The results indicate that the okra‐leaf trait should be considered for producing future cultivars.
Utilization of Cowpea Crop Residues to Reduce Fertilizer Nitrogen Inputs with Fall Broccoli
Authors: Schroeder Judith L. , Kahn Brian A. , Lynd J. Q.
Published: July 2010

Environmental concerns have led to renewed interest in use of sustainable green manure legume cropping systems. Field experiments were undertaken to determine whether cowpea [Vigna unguiculata L. (VValp.)] crop residues could be used to reduce fertilizer N inputs with fall broccoli [Brassica oleracea L. (Italica Group)]. Studies in 1992,1993, and 1994 involved broccoli preceded by cowpeas, with or without factorial combinations of preplant N and sidedress N from urea on the broccoli. Control broccoli plants were grown on fallowed ground and supplied with 168 kg ha−1 of N from urea. Cowpea crop residues alone did not provide sufficient N for optimum production of marketable broccoli. Marketable broccoli yields sometimes showed no significant differences between controls and cowpea residue treatments receiving only 84 kg ha−1 of fertilizer N. However, there was a tendency for increased broccoli transplant mortality in cowpea residue plots. A fourth study in 1994 indicated a negative main effect of cowpeas on broccoli stand establishment, and a complex interaction of cowpeas and trifluralin treatments on broccoli yield. Petiole N concentrations of broccoli plants with reduced fertilizer N inputs which succeeded cowpeas usually were lower than those of control plants. Soil nitrate levels at 15‐ to 30‐cm soil depths at the time of broccoli planting were consistent indicators of apparent nitrate utilization by microbial decomposition of cowpea crop residues. We were unable to demonstrate a cowpea‐broccoli succession cropping system which consistently reduced fertilizer N inputs without some type of adverse effect on the broccoli crop. Therefore, the use of cowpea crop residues to reduce fertilizer N inputs with fall broccoli is not recommended.
Effect of Temperature on Time to Panicle Initiation and Leaf Appearance in Sorghum
Authors: Craufurd Peter Q. , Qi Aiming , Ellis Richard H. , Summerfield Rodney J. , Roberts Eric H. , Mahalakshmi Vishwanathan
Published: July 2010

Leaf‐tip appearance and duration from planting to panicle initiation (PI) are important developmental processes in cereals. This study was conducted to determine the effect of air temperature on rates of leaf‐tip appearance and 1/PI for sorghum [Sorghum bicolor (L.) Moench]. Nine genotypes were grown in pots at mean temperatures of 17 to 33°C and photoperiods of 11.0 to 12.3 h d−1 in glasshouses. Leaf‐tip appearance was recorded every 3 to 5 d and PI determined by apical dissection. The optimum temperature (To) for 1/PI was between 26 and 27°C and supra‐optimal temperatures delayed PI in all genotypes. The base temperature (Tb) ranged from 6 to 10°C but only one genotype had a Tb significantly different from a common value of 8.5°C. Growing degree days (GDD) for PI among genotypes at snb‐optilnal temperatures varied from 411 to 592 (P < 0.001) above a Tb of 8.5°C. Warmer temperatures (>27°C) reduced the rate of leaftip appearance in five genotypes; in the remainingenotypes the rate of leaf appearance was effectively constant at mean temperatures between 23 and 33°C. There was no significant difference (P > 0.20) amongenotypes in the phyllochron, which was 57 GDD above a Tb of 8.5°C. The final number of leaf‐tips was constant within genotypes at mean temperatures of 18 to 30°C, but varied among genotypes from 11.8 to 17.3. In conclusion, the Tb and To for 1/PI were approximately 8.5 and 27°C and there was variation in 1/PI but not in the rate of leaf‐tip appearance among the genotypes studied.
Soybean Yield Response to Narrow Rows Is Largely due to Enhanced Early Growth
Authors: Bullock D. , Khan S. , Rayburn A.
Published: July 2010

Researchers in the southern USA have shown that the increased yield associated with narrow rows for late‐planted determinant soybean [Glycine max (L.) Merr.] is due mainly to a greater crop growth rate during vegetative and early reproductive stages which allows for an increase in the number of fertile nodes and increased number of pods per fertile node. The objective of this study was to determine if a similar explanation is applicable to the narrow‐row yield response reported with full‐season narrow‐row production of indeterminate soybean cultivars in the midwestern USA. To test this hypothesis field experiments were conducted in 1992 and 1993 on a Flanagan silty loam soil (fine, montmorillonitic, mesic, aquic, argiudoll, mollisol). Soybean was sown in row widths of 38, 76, and 114 cm and thinned to 450 000 plants per ha at VI to V2. A linear decrease with increasing row width was observed for grain yield (3497, 3250, 2920 kg/ha), number of pods per plant (93, 89, 85), plant height (99, 96, 93 cm), number of branches per plant (3.3, 3.1, 2.9), and harvest index (33, 31, 30). Crop growth rate increased with decreasing row width until about R5 after which row width had no significant affect on crop growth rate. These results support our hypothesis that the yield increase noted for narrow‐row indeterminate soybean production in the midwestern USA is due predominantly to beneficial effects experienced prior to the main grain‐fill periods in a manner similar to that reported for late‐planted narrow‐row determinate soybean production in the southern USA.
Root Anatomical, Physiological, and Morphological Responses to Drought Stress for Tall Fescue Cultivars
Authors: Huang Bingru , Fry Jack D.
Published: July 2010

Two experiments were conducted to investigate genotypic variations in morphological, anatomical, and physiological responses of roots to drought stress in tall rescue (Festuca arundinacea Schreb.). Such information would facilitate breeding programs and management practices for improving turfgrass drought resistance. Tall rescue cultivars ‘Kentucky‐31’ (forage‐type), ‘Mustang’ (turf‐type), ‘MIC18’ (dwarf, turf‐type) were examined under well‐watered or drought‐stress conditions in a greenhouse. Root systems of MIC18 were much shallower and smaller than those of Kentucky‐31 and Mustang under well‐watered conditions. After 7 d of soil drying, root dry weight was significantly lower than that of well‐watered plants for both MIC18 than Kentucky‐31. The reduction in root dry weight, relative to control plants, was greater for MIC18 than Kentucky‐31. Root water potential and turgot pressure were reduced with soil drying, leading to cortical cell shrinkage. Kentucky‐31 roots suffered less turgot loss than those of MIC18 under drying conditions. Specific root length (SRL) and root/shoot ratio increased with soil drying. Greater increases in SRL occurred for Kentucky‐31 than for MIC18. More extensive root hairs developed in plants of Kentucky‐31 and MIC18 stressed for 14 d than in well‐watered plants. Root hairs became less extensive after 28 d of drying. After 14 and 21 d of drying, Kentucky‐31 roots had significantly lower electrolyte leakage than those of MIC18. Cultivar variations in anatomical, morphological, and physiological features of roots accounted for the variability in shoot performance under drought stress noted in a previous study.
Runoff and Sediment Losses from Natural and Man‐Made Erosion Control Materials
Authors: Krenitsky E. C. , Carroll M. J. , Hill R. L. , Krouse J. M.
Published: July 2010

Man‐made erosion control materials are increasingly being used at construction sites. The performance of these materials in comparison to natural materials is largely unknown. A rainfall simulation study was designed in which four man‐made materials (wood excelsior, jute fabric, coconut fiber blanket, and coconut strand mat) and two natural materials (straw and turfgrass sod) were evaluated. The erosion control materials were evaluated on a Sassafras loamy sand (fine loamy, mixed mesic Typic Hapludult) having a 8% slope and on a Sassafras sandy clay loam (fine, silty, mixed mesic Typic Hapludult) having a 14 to 21% slope. Disturbed soil surface areas (0.76 m2 each) were covered with each material and subjected to a 96 mm hr−1 simulated rainstorm. Runoff and sediment loss rates were determined every 5 rain for 35 min after recording the time required for runoff initiation. Sod was the only material that extended the time required for runoff initiation. Runoff from all materials was less than bare soil for the first 5 rain of runoff; however, only straw, jute, and sod reduced runoff over the entire storm event. The total amount of runoff, compared with bare soil, was decreased by 61% for sod, 25% for straw, and 16% for jute. Erosion control materials reduced bare soil erosion by 80 to 99%. Of the man‐made rosion control materials, only jute reduced runoff and sediment losses at both locations. Therefore, of the materials tested, only sod, straw, and jute would be expected to effectively reduce both runoff and sediment losses
Utility of SSRs for Determining Genetic Similarities an Relationships in Maize Using an Agarose Gel System
Authors: Senior M. L. , Murphy J. P. , Goodman M. M. , Stuber C. W.
Published: July 2010

Among maize (Zea maize L.) breeders, there is a heightened awareness of the necessity for both maintaining genetic diversity for crop improvement and improving the quality of genetic resource management. Restriction fragment length polymorphisms (RFLPs) and isozymes can serve as genetic markers for estimating divergence or diversity; however, the limited number of polymorphic isozyme loci available and the labor intensive and time consuming nature of RFLPs make their use for this purpose prohibitive. Simple sequence repeats (SSRs), when resolved using agarose gels, may be a viable and costeffective alternative to RFLPs and isozymes. Ninety‐four elite maize inbred lines, representative of the genetic diversity among lines derived from the Corn Belt Dent and Southern Dent maize races, were assayed for polymorphism at 70 SSR marker loci using agarose gels. The 365 alleles identified served as raw data for estimating genetic similarities among these lines. The patterns of genetic divergence revealed by the SSR polymorphisms were consistent with known pedigrees. A cluster analysis placed the inbred lines in nine clusters that correspond to major heterotic groups or market classes for North American maize. A unique fingerprint for each inbred line could be obtained from as few as five SSR loci. The utility of polymerase chain reaction (PCR)‐based markers such as SSRs for measuring genetic diversity, for assigning lines to heterotic groups and for genetic fingerprinting equals or exceeds that of RFLP markers, a property that may prove a valuable asset for a maize breeding program.
Rhizomatous Lotus corniculatus: IV. Inheritance of Rhizomes
Authors: Nualsri C. , Beuselinck P. R.
Published: July 2010

Rhizome production has been transferred from wild germplasm of Lotus corniculatus L. (broadleafed birdsfoot trefoil) into domesticated cultivars and autogamous germplasm. The objective of this study was to determine the inheritance of rhizomes in L. corniculatus. Crosses were made between AG‐S4, an autogamous, nonrhizomatous germplasm and two rhizomatous accessions from Morocco, G31276 and G31317. Two autogamous progeny from each cross (verified as F1 hybrids by morphological, meiotic, and RAPD markers) produced F2 seed and were reciprocally backcrossed (BC). After 40 wk growth in the greenhouse, F2 and BC progeny were scored for rhizome production. Plants failing to express rhizomes in the greenhouse were transplanted to the field at Columbia, MO, and reevaluated for presence or absence of rhizomes at the end of the growing season. Segregation ratios for rhizome expression were tested for goodness‐of‐fit by the Chi‐square (✕2) test. The ratios of rhizome production in F2 and BCs to AG‐S4 fit 3:1 and 1:1 rhizomatous:nonrhizomatous ratios, indicating that rhizome presence in L. corniculatus germplasm G31276 and G31317 is controlled by a single dominant gene. The gene symbol R is proposed for rhizome expression.
Responses of Alfalfa to Stem‐Tip Inoculations with Five Isolates of Sclerotinia trifoliorum
Authors: Halimi E. S. , Rowe D. E. , Pratt R. G.
Published: July 2010

Effective breeding for economically important resistance to Sclerotinia trifoliorum Eriks in alfalfa (Medicago saliva L.) requires that the plant breeder have an understanding of any genetic basis for variability in measurements of resistance and the likelihood that selection for resistance to one isolate confers resistance to other isolates. Fifty alfalfa plants were repeatedly evaluated for their resistance to five isolates of S. trifoliorum. Tips of excised stems were inoculated with a S. trifoliorum isolate and stem necrosis was measured after 14 d. The inoculation of five stems from each of 50 plants with a single isolate was repeated five times. For the length of stem necrosis, the interaction of pathogen isolate and alfalfa plant was not significant but differences among alfalfa plants and among isolates were significant. The plants that, on average, developed larger necrotic regions did not have more or less variation in their replicated measurements of necrosis than those plants which averaged much smaller necrotic regions. The genotype of the alfalfa plant had a greater effect on the variability in replicate measurements of disease than the genotype of pathogen isolate. Resistance to different isolates were significantly correlated (r = 0.48–0.60) and selection of some plants for resistance to one isolate appeared to improve resistance to other isolates.
Enzymatic Control of Soluble Carbohydrate Accumulation in Cold‐Acclimated Crowns of Alfalfa
Authors: Castonguay Yves , Nadeau Paul
Published: July 2010

Sucrose and the raffinose family of oligosaccharides (RFO), stachyose and raffinose, accumulate in crowns of alfalfa (Medicago sativa L.) during low temperature acclimation. In vitro and in vivo evidence from the literature suggests that these sugars might have important adaptive roles in freezing tolerance. To better understand the regulation of cold‐induced accumulation of soluble sugars, we measured the activity of key regulatory enzymes involved in the metabolism of sucrose and RFO in crowns of three alfalfa cultivars of contrasting winterhardiness which had been acclimated to winter conditions. Both sucrose‐phosphate synthase (SPS) and galactinol synthase (GS) showed markedly higher activity at low temperature. There was a close relationship between the activities of SPS and GS and the levels of sucrose and RFO, respectively. A delay of approximately 2 wk was observed between the rise in GS activity and RFO accumulation. For both SPS and GS, the increase in activity occurred earlier and reached higher levels in two winter hardy cultivars than in a nonhardy cultivar. In contrast, the activity of the RFO degrading enzyme alpha‐galactosidase (α‐gal) was identical in all cultivars. The activity of sucrose synthase (SS), mainly involved in sucrose hydrolysis, decreased during fall acclimation. In cold‐acclimated alfalfa, both acid and neutral invertase activities were low and comparable in all cultivars. Our results indicate that differential accumulation of soluble sugars between alfalfa cultivars of contrasting winterhardiness is the result of differences in synthetic capacity rather than differences in hydrolytic activities.
Comparison of AFLP and Pedigree‐Based Genetic Diversity Assessment Methods Using Wheat Cultivars from the Pacific Northwest
Authors: Barrett B. A. , Kidwell K. K. , Fox P. N.
Published: July 2010

Comparing results of different genetic diversity estimation methods may be indicative of their utility as parental selection tools for plant breeders. Forty‐three spring and winter wheat lines (Tritlcum aestivum L.) from the Pacific Northwest (PNW) were used to compare pedigree and amplified fragment length polymorphism (AFLP)‐based genetic diversity estimates (GDEPED and GDEAFLP, respectively). The mean of the 903 GDEPED pairwise comparisons was 0.96, and 89% of the values were >0.90. In contrast, GDEAFLP values were normally distributed (mean = 0.54), suggesting that this diversity measure was better able to identify pairs of genotypes representing the entire range of possible GDEs. Thus, GDEAFLP may have more utility than GDEPED for identifying parental combinations with maximum allelic variation. Despite the substantially different means and distributions of the two diversity measures, a moderate rank correlation (rs = 0.42, P < 0.001) was detected between the two GDE matrices. AFLP fragments from hypomethylated portions of the genome (generated with Pst I:Mse I) were more highly associated with GDEPED than were fragments generated with the methylation insensitive combination Eco RI:Mse I (rs = 0.44 and 0.28, respectively). Pedigree and AFLP‐based GDEs detected a similar hierarchical pattern of genetic diversity among the 43 cultivars evaluated. Although GDEPED was not well suited for identifying degree of relatedness among individuals, it may be adequate for assessing overall patterns of genetic variation among regionally adapted germplasm. It remains to be determined which method, if either, provides predictive estimates of heterosis or genetic variance among progeny from specific parental combinations.
QTL Mapping in Testcrosses of Flint Lines of Maize: III. Comparison across Populations for Forage Traits
Authors: Lübberstedt Thomas , Melchinger Albrecht E. , Fähr Susanne , Klein Dietrich , Dally Andreas , Westhoff Peter
Published: July 2010

We mapped and characterized quantitative trait loci (QTL) affecting testcross performance of important forage maize (Zea mays L.) traits and investigated their consistency across different populations. Four independent populations comprising 380 F3 lines (A✕Bc), 113 F5 lines (A✕BV), 131 F4 lines (A✕CV), and 140 F4 lines (C✕DV) were produced from four elite flint inbreds (A, B, C, D) and genotyped at 89, 151, 104, and 122 RFLP marker loci, respectively. All lines were testcrossed to the same dent inbred tester and evaluated in field trials with two replications in five environments. Six traits were analyzed: dry matter yield (DMY), dry matter concentration (DMC), plant height (PHT), in vitro digestible organic matter (IVDOM), starch concentration (STC), and protein concentration (CPC) of forage. Genotypic variances (σ̂2g) were mostly significant for these traits in all populations and heritabilities generally exceeded 0.50. Between 2 and 14 QTL were detected in individual populations by composite interval mapping, which explained between 17.6 and 65.7% of the total phenotypic variance (σ̂2p). Few of the detected QTL displayed significant digenic epistatic or QTL ✕ environment interactions. Consistency of QTL positions across all four populations was greater for DMC, STC, and PHT than for DMY, IVDOM, and CPC. Across all traits' QTL, results were largely consistent among A✕BC and A✕Bv, but not among A✕Bc and A✕Cv or A✕Bc and C✕Dv. When QTL positions and substitution effects for DMY obtained in A✕BC, explaining 43% of σ̂2p, were employed for prediction of QTL positions and substitution effects in the other three populations they explained 24% of σ̂2p in A✕BV, 11% σ̂2p in A✕Cv, and 0% of σ̂2p in C✕DV. QTL results were poorly consistent among crosses within the flint heterotic pool, suggesting that prior to marker‐assisted selection, QTL mapping must be performed separately for each population.
Detection of Genes for Resistance to Common Bacterial Blight of Beans
Authors: Yu Z. H. , Stall R. E. , Vallejos C. E.
Published: July 2010

One of the most important diseases of common bean (Phaseolus vulgaris L.) in tropical and sub‐tropical regions is common bacterial blight (CBB), which is caused by Xanthomonas axonopodis pv. phaseoli (= X. campestris pv. phaseoli). Useful sources of resistance to CBB have been found in the related species P. coccineus Lam. and P. acutifolius A. Gray. Despite the complexity of their inheritance, these resistances have been introgressed into bean breeding lines. ‘XR‐235‐1‐1’ is a Mesoamerican bean breeding line that carries P. coccineus‐derived oligogenic resistance to CBB. We have analyzed the linkage relationships between 117 DNA marker loci and CBB resistance genes in a recombinant inbred family obtained between XR‐235‐1‐1 and ‘Calima’, a susceptible Andean genotype. Two genes for resistance to CBB from XR‐235‐1‐1 were detected, one linked to Bng40 in Group A, and the other to Bng139 in Group F. Surprisingly, the effect of two Calima‐derived resistance genes, linked to Bng25a and Bng154 in Group J, was also detected. Analysis of several models with these resistances pointed to the most efficient model that explained at least 40% of the variation for resistance to CBB and included the two XR‐derived resistances and the Bng154‐1inked Calima‐ derived resistance. Marker assisted selection is proposed for introgression of resistance genes into susceptible backgrounds.
Genetic Variation among Tomato Accessions from Primary and Secondary Centers of Diversity
Authors: Villand J. , Skroch P. W. , Lai T. , Hanson P. , Kuo C. G. , Nienhuis J.
Published: July 2010

The Asian Vegetable Research and Development Center (AVRDC) maintains one of the largest collections of Lycopersicon germplasm. Approximately 60% of the collection is from Old World regions; however, it is unclear whether these accessions represent unique sources of genetic variation compared with accessions from New World regions. The objective of this study was to compare the magnitude and structure of genetic variation among tomato accessions collected from Old and New World regions. Forty‐one random amplified polymorpbic DNA (RAPD) primers generated 98 polymorphic RAPD markers and were used to estimate relationships among 96 accessions collected from a wide geographic range. Genetic distances, marker frequency, and marker diversity were used to compare subpopulations of these accessions. Differences in RAPD marker frequencies indicated uniqueness of accessions from the New and Old World collections. In addition, accessions from Ecuador, Peru, and Chile had a larger magnitude of marker diversity than do Old World accessions. Comparison of sub‐populations of L. esculentum and its sub‐species, L. esculentum var. cerasiforme, indicated that the two are distinct but have similar levels of diversity. Variation among L. esculentum accessions can be obtained at a faster rate by sampling accessions from the primary center vs. other geographic regions. Yet Old World accessions complement accessions from the New World and are not simply redundant sources of variation.
Inheritance of Low Linolenic Acid Level in the Soybean Line RG10
Authors: Stijšin Duška , Luzzi Bruce M. , Ablett Gary R. , Tanner Jack W.
Published: July 2010

Relatively high linolenic acid content (80–100 g kg−1) in soybean [Glycine max (L.) Merr.] cultivars is the most important factor contributing to oxidative instability of soybean oil. Mutation breeding was used to develop soybean line RG10 with reduced linolenic acid content (<25 g kg−1). The usefulness of this line in a breeding program designed to reduce linolenic acid content would depend on the complexity of inheritance of linolenic acid level. The objective of our study was to determine the number of loci and type of gene action associated with the inheritance of reduced linolenic acid level in RG10. The F2 and F3 progenies from crosses RG10 × C1640 and RG10 × ‘Century’ segregated in trimodal fashion. On the basis of chi‐square analyses of F2 seeds and F3 families from RG10 × C1640 and F3 families from RG10 × Century cross, the observed frequency distributions significantly fit a 1:2:1 ratio. These results indicate that the low level of linolenic acid in RG10 is controlled by a mutant allele at the Fan locus. This allele shows additive gene action when combined with the fan allele from C1640 and the Fan allele from Century. The gene symbol fan‐b fan‐b was assigned for very low (<25 g kg−1) level of linolenic acid in RG10. The simple inheritance of the low level of linolenic acid makes RG10 an ideal parent in breeding programs aimed at improving oil quality in soybean.
Wheat Yield Progress Associated with Higher Stomatal Conductance and Photosynthetic Rate, and Cooler Canopies
Authors: Fischer R. A. , Rees D. , Sayre K. D. , Lu Z.‐M. , Condon A. G. , Saavedra A. Larque
Published: July 2010

Grain yields of eight representative semidwarf spring wheat (Triticum aestivum L.) cultivars released in northwest Mexico between 1962 and 1988 have increased linearly across years as measured in this region during 6 yr under favorable management and irrigation. To understand the physiological basis of this progress and possibly assist future selection for grain yield, leaf traits were determined during 3 yr in the same study. Stomatal conductance (gs), maximum photosynthetic rate (Amax, and canopy temperature depression (CTD), averaged over the 3 yr, were closely and positively correlated with progress in the 6‐yr mean yield. The correlation was greatest with gs (r = 0.94, P < 0.01). Compared with the overall yield increase of 27%, gs increased 63%, Amax increased 23%, and canopies were 0.6°C cooler. Carbon‐13 isotope discrimination was also positively associated with yield progress (r = 0.71, P < 0.05), but other leaf traits such as flag leaf area, specific leaf weight, percentage N and greeness were not, nor was crop growth rate around anthesis. The causal basis of the leaf activity interrelationships is reasonably clear, with both increased intercellular CO2 concentration and increased mesophyll activity contributing to the increase in Amax. However, causal links to the yield progress, and the accompanying increase in kernels per square meter, are not clear. It is concluded that gs and CTD should be further investigated as potential indirect selection criteria for yield.
Heritability and Phenotypic Variation of Tolerance to Phytophthora Root Rot of Soybean
Authors: Glover K. D. , Scott R. A.
Published: July 2010

The most destructive fungal disease of soybean [Glycine max (L.) Merr.] is Phytophthora root rot. The most common method of protecting soybean from Phytophthora root rot utilizes specific resistance genes, but continuous selection pressure exerted on the pathogen frequently causes resistance genes in soybean to become ineffective. Infected plants which exhibit tolerance often yield nearly as well as uninfected resistant plants and prevent the buildup of races capable of overcoming resistance genes. Experiments were initiated to obtain information concerning the genetics of tolerance to Phytophthora root rot. The objectives were to: (i) compare parent‐offspring regression, correlation, and realized heritability estimates of tolerance, (ii) compare heritability and phenotypic variation among single‐, three‐way, and double‐cross populations, and (iii) correlate non‐infected yields with tolerance and maturity. Ten F3:4 populations were screened for tolerance in the F3 and F4 generations by the inoculum layer method. Heritability estimates were low, ranging from 0.17 to −0.10 when obtained through parent‐offspring regression. These estimates were not separable from zero because of the magnitude of their standard errors. Parent‐offspring correlation estimates were larger than parent‐offspring regression estimates, and ranged from 0.43 to −0.19. Realized heritability was estimated by selecting the 20% highest and lowest tolerant lines within each population. These results were generally larger, ranging from 0.80 to −0.13, and suggested that relatively high tolerant lines may be identified through selection. The number of parents composing a population did not influence heritability or phenotypic variation within populations. Most correlations among yield, tolerance, and maturity were non‐significant. Tolerance levels within populations should not vary with maturity. The inoculum layer method may not be sensitive enough to allow accurate screening of germplasm with low tolerance levels.
Xenia Effects in Maize with Normal Endosperm: I. Importance and Stability
Authors: Bulant C. , Gallais A.
Published: July 2010

Xenia is the effect of pollen on the development and characteristics of the fruits. To reexplore its importance and consequences for grain production in maize (Zea mays L.), the effect of pollen genotype on kernel weight was studied with five white kernel lines as females and several yellow kernel lines as males in a factorial (5 × 20) and in a diallel (5 × 5) mating design. White single‐cross hybrids were also used as females. Cross‐fertilization advantage was studied in 1993, 1994, and 1995 by mixing pollen from a male and pollen from a female (i.e., autopollen). When inbred lines were used as females the average increase in kernel weight at maturity, because of cross fertilization, was 13% in 1993, 11% in 1994, and 11.5% in 1995. Female effects were the strongest; however, male and female × male interaction effects were also significant although at the limit of significance because of large environmental variation. These effects were also significant for white kernels, showing that there was a stimulation effect on the filling of kernels from self fertilization by the more active filling of kernels from cross fertilization. With single‐cross females, crossfertilization advantage was about halved. Despite genotype × year interaction, the phenomenon seems sufficiently repeatable with significant correlation among years. Results are interpreted as an early manifestation of heterosis which increases sink strength of kernels from cross fertilization.
Nondestructive Assessment of Sinapic Acid Esters in Brassica Species: I. Analysis by Near Infrared Reflectance Spectroscopy
Authors: Velasco Leonardo , Matthäus Bertrand , Möllers Christian
Published: July 2010

Sinapic acid esters (SAE) are important antinutritional compounds of the seed of rapeseed (Brassica napus L.) and related Brassica species. The objective of this work was to study the potential of near infrared reflectance spectroscopy (NIRS) to analyze SAE content intact‐seed samples of the genus Brassica. A total of 400 samples belonging to 17 species of Brassica were used to develop an initial calibration equation for this trait by using modified partial least squares regression on second derivative‐transformed and scatter‐corrected spectra. The r2 in cross validation was 0.91, and the standard error of cross validation was 1.1 g kg−1 seed (mean = 10.0). The calibration set was expanded with 187 further samples, selected for low SAE content with the initial equation, and the accuracy of the method was tested through both external and independent validation. In the first case, the analysis of samples not included but belonging to species represented in the calibration set led to an r2 of 0.92 and standard error of performance (SEP) of 1.1 g kg−1 (mean = 9.2). In the second case, the analysis of 57 samples of B. juncea (L.) Czern., not represented with any sample in the calibration, resulted in a SEP of 1.1 g kg−1 (mean = 7.3). The results demonstrated the robustness of the calibration equations to estimate SAE content in a wide range of species of the genus Brassica, even of those not used for calibration. NIRS discrimination of this trait was associated with eight spectral regions, all related to chemical absorbers in the sinapic acid molecule.
Economic Evaluation of Forage Quality Gains—Past and Future
Authors: Ford Stephen A.
Published: July 2010

Annual returns to society from agricultural research have historically been very high, generally in excess of 20%. Estimates of returns to forage researcha re likely similar in magnitudea and must also include consumer benefits, the economic value of changes in environmental impacts, spillover research benefits, and complementary on‐farm effects. The estimation of returns to improved forage quality involves more than an analysis of enterprise costs and returns and must also account for whole‐farm effects. Annuale xpenditures for forage quality research are estimated to be approximately $125 million, roughly 2% of total U.S. agricultural research. Total allocation of forage quality research expenditures to the dairy sector would cost consumers only 0.22 cents L−1 milk. This amount is also equivalent to a 10 g crude protein kg−1 increase over only 18% of all hay harvested in the USA. A whole‐farm dairy optimization model provides results of potential farm‐level impacts of improved forage quality and illustrates the complexity of determining on‐farm benefits to forage quality improvement. Forage quality attributes that limit farm profitability are identified to be crude protein, undegradable intake protein, neutral detergent fiber, and dry matter intake. Average dairy farm potential of forage quality increases exceeds $3000 annually because of expanding hay acreage in addition to improved quality. However, very high quality forage may have a negative impact on profits because of off‐farm feed purchases to provide additional fiber. Gains from improvement in forage quality will be greater as commodity prices and intensity of animal agriculture increase.