bluuebunny/crossref_metadata_2025 huggingface dataset:
Seed Dormancy and Its Alleviation in Lovegrass Hybrids
Authors: Voigt P. W. , Tischler C. R. , Poverene M. M.
Published: July 2010

Weeping lovegrass, Eragrostis curvula (Schrad.) Nees, was introduced to the Americas for soil conservation. It is a useful forage only if intensively managed. Apomictic lovegrass hybrids, developed from introductions with higher forage quality, need to be evaluated in multiple environments to determine their potential. Studies were to be established in Argentina the same year seed was produced in the USA. This could only be accomplished if seed dormancy was low. Seed of experimental strains were harvested in 1993 and 1994 at Temple, TX. Germination and/or emergence experiments were conducted in alternating light‐dark and dark environments. A mixture of 2‐chloroethanol and sodium hypochlorite (CHL) was evaluated a dormancy breaking treatment. The lovegrass hybrids studied in these experiments varied widely in germination, because of seed dormancy. This dormancy was largely dissipated after 0.75 yr of storage in a temperature‐controlled laboratory. Thus, this post‐harvest dormancy is short‐lived compared with that of ‘A‐68’ lehmann lovegrass, Eragrostis lehmanniana Nees. Absence of light during germination usually inhibited germination, but in a few genotypes it promoted germination. Seed treatment with CHL compensated for absence of light. Effects of CHL on emergence did not decrease with time, but the difference between treated and untreated seed decreased as the post‐harvest dormancy declined with seed ageing. Concerns about obtaining adequate plants for establishment of plots in South America the same year seed was harvested were valid. Treatment of seed with CHL was a rapid, easy, and effective procedure for breaking seed dormancy in E. curvula and in E. lehmanniana and for obtaining the numbers of plants required for evaluation experiments. However, CHL is toxic and should only be used for seed treatment in laboratories where human exposure to the chemical can be controlled.
Allozyme Diversity in Cultivated Crops
Authors: Hamrick J. L. , Godt M. J. W.
Published: July 2010

Estimates of genetic diversity maintained by plant species and its distribution within and among populations allows plant geneticists to predict, in a general way, the evolutionary potential of species. Single‐gene markers, particularly allozymes, have been used to measure the genetic diversity of species. In this paper, the plant allozyme literature was reviewed to compare levels of genetic variation maintained by crop and non‐crop species. Crop species (plant species intentionally cultivated by humans) have more allozyme diversity as a whole than other seed plant species, although the mean genetic diversity partitioned within populations of crop species was similar to that of other plant species. Populations of crop species were more genetically heterogeneous, an observation that was probably due to the higher proportion of crops that reproduce by self fertilization. Dicotyledonous crops have much less genetic diversity than monocotyledonous crops at the species and the population level and exhibit more inter‐population genetic differentiation. Annual and perennial crop species had similar levels of genetic diversity and partitioned genetic diversity in similar ways. Predominantly selflng crops had somewhat less genetic diversity than outcrossing or mixed‐mating species. Selflng crops exhibited more population‐to‐population variation in genetic diversity and allele frequency differences were much greater among their populations. High population‐to‐population variation in genetic diversity increases the importance of empirical data for the design of sampling protocols.
Genotype × Environment Interaction for Carbon Isotope Discrimination in Spring Wheat
Authors: Matus Alejandro , Slinkard Alfred E. , van Kessel Chris
Published: July 2010

Carbon isotope discrimination (CID) has been proposed as a parameter to indirectly select for improved transpiration efficiency (W) and grain yield in spring wheat (Triticum aestivum L.). Little information exists on the genotype ✕ environment (G ✕ E) interaction for CID in spring wheat. Therefore, to determine the magnitude of the G ✕ E interaction for CID eight spring wheat genotypes were grown at five locations in both 1992 and 1993 in Saskatchewan, Canada. In addition, we measured genetic variability for CID and the magnitude of the phenotypic correlation between grain yield and CID. Samples were collected for CID determination from leaves at flowering, mature leaves, and mature kernels. The genotype ✕ location (G ✕ L) interaction for CID traits was non‐significant. The significant genotype ✕ year (G ✕ Y) interaction for CID of mature leaves was a crossover type interaction, due to the genotype ‘Lakhish’. The crossover genotype ✕ location ✕ year (G ✕ L ✕ Y) interaction for grain yield and the significant G ✕ L ✕ Y interaction for CID of leaves at flowering was at least partially due to the erratic response of the genotypes ‘Genesis’, ‘Oslo’, ‘AC Minto’, and Lakhish. Genotypic differences for CID of leaves at flowering and CID of mature leaves were not significant. However, wheat genotypes differed in CID of kernels. The phenotypic correlations between grain yield and the three CID traits were not significant. These results suggest that among our selected sample of eight genotypes CID of leaves at flowering, CID of mature leaves, and CID of kernels could not be used to indirectly select for grain yield.
Resistance to Hessian Fly Conditioned by Genes H19 and Proposed Gene H27 of Durum Wheat Line PI422297
Authors: Ohm H. W. , Ratcliffe R. H. , Patterson F. L. , Cambron S. E.
Published: July 2010

The durum wheat (Triticum turgidum Desf.) line PI422297 has been reported to carry two genes that condition resistance to Hessian fly, Mayetiola destructor (Say) biotype L, gene HI9 and an unnamed gene that is closely associated with gene H16. It is useful to identify the effects of genes that confer host resistance in parental source lines for wheat improvement. Our objectives were to determine the effectiveness of HI9 to biotype L at several temperatures, and to determine the effectiveness of the second gene of PI422297 that is closely associated with gene HI6. In the present study, gene H19 was transferred from P1422297 to susceptible durum wheat line D6647 to separate H19 from other genes and to compare it with the other resistance gene in PI422297. Durum wheat lines homozygous for HI9 were developed by identifying segregating backcross F2 families and pedigree selection. In the F5 generation, lines homozygoufso for H19 were identified from testcrosses involving durum wheat line IN80164 (H16H16). Nearly all seedlings of the homozygous H19 lines were resistant at 19°C, only 42 to 66% were resistant at 23°C, and none were resistant at 26°C. All, 89%, and 15% of PI422297 seedlings were resistant at 19, 23, and 26°C, respectively. All seedlings of line IN80164 (H16H16) were resistant at 19 and 23°C and 84 % were resistant at 26°C. Thus, the second gene in PI422297 is not HI6, and it is tentatively designated as H27.
Rate‐Reducing Resistance to Fusarium solani f. sp. phaseoli underlies Field Resistance to Soybean Sudden Death Syndrome
Authors: Njiti V. N. , Suttner R. J. , Gray L. E. , Gibson P. T. , Lightfoot D. A.
Published: July 2010

Yield losses occur in soybean [Glycine max (L.) Merr.] because of sudden death syndrome (SDS) caused by Fusarium solani (Mart.) Saec. f. sp. phaseoli (Burk.) Snyd. & Hans, type A. Our objective was to determine whether tolerance or partial resistance to infection underlies field resistance to SDS. Seven field resistant cultivars and five susceptible cultivars were planted at two locations. Twenty taproots per cultivar were sampled every 7 to 21 d from the V0 to R8 growth stages, 8 to 121 days after planting (DAP). Six taproot sections per plant were tested for F. solani on a selective medium. Infection frequency (IF), the percentage of infected plants, and infection severity (IS), the percentage of infected root segments, were scored. Leaf symptoms were recorded and standardized to the R6 stage and the disease index (DX) was calculated. Infection was detected at the VI stage (within 15 DAP) and reached a maximum by about R1 (55–68 DAP). All cultivars were infected by F. solani. However, seasonal mean IF and mean IS were significantly lower among the resistant cultivar class. After R1, infection was also significantly lower among the resistant cultivar class within individual sampling dates. Also, DX and IF were correlated in each environment (r = 0.38 and 0.61). Therefore, in the resistant cultivars Forrest, Ripley, Jack, PI520733, ExF44, ExF59, and ExF78, late season rate‐reducing (partial) resistance decreased the DX, IF, and IS. Resistance probably extends the latent period of F. solani. Among susceptible cultivars, Essex and A5403, had reduced leaf symptoms but high IF and IS suggesting tolerance to F.solani that alleviated SDS.
Canopy Gas Exchange Response to Moisture Stress in Old and New Maize Hybrid
Authors: Nissanka S. P. , Dixon M. A. , Tollenaar M.
Published: July 2010

Grain yield improvemenotf maize (Zea mays L.) hybrids in Ontario has been associated with increased stress tolerance. Effects of shortterm water‐deficit stress on canopy gas exchange of an old and a new maize hybrid were studied. Plants of Pride 5 (old) and Pioneer 3902 (new) were grown under controlled‐environment conditions until tassel emergence and, subsequently, plants were transferred to enclosures, each containing the aboveground parts of four plants. Canopy photosynthesis, respiration, transpiration, and stem water potential were measured continuously for 7 d. Plants were either well watered or exposed to a water‐deficit stress by withholding water supply until net canopy photosynthesis declined to zero and, subsequently, plants were rehydrated. Under well‐watered conditions, the two hybrids did not differ significantly in terms of canopy photosynthesis, transpiration, and stem water potential. In contrast, hybrids responded differently to a water‐deficit stress. Cumulative canopy photosynthesis and transpiration during the drying cycle were reduced by 21 and 31%, respectively, in Pioneer 3902 and by 34 and 31%, respectively, in Pride 5. The threshold stem water potential related stomatal closure, and thus, photosynthesis and transpiration, was lower for Pioneer 3902 than for Pride 5. During the recovery day, canopy photosynthesis was 53% higher and canopy transpiration was 31% higher in Pioneer 3902 than in Pride 5. Respiration per unit CO2 fixed was lower in Pioneer 3902 than in Pride 5 in all conditions.
Seedling Emergence and Growth of Solid Matrix Primed Kentucky Bluegrass Seed
Authors: Yamamoto I. , Turgeon A. J. , Duich J. M.
Published: July 2010

Seed priming is effective in reducing the time required for germination and emergence, and for increasing final germination and/or emergence especially under sub‐optimal conditions. This study was conducted to determine whether advanced emergence due to solid matrix priming (SMP) is followed by advanced seedling growth of Kentucky bluegrass (KBG) (Poa pratensis L.) under sub‐optimal conditions (15/5°C). Coleoptile, the second and third leaf emergence, and seedling size 28 d after emergence were examined in four cultivars, which differed in their seed sizes. Distributions of coleoptile emergence over time were significantly affected by SMP, and seedlings from SMP seed emerged more rapidly and uniformly in three cultivars. Moreover, the number of days required for 50% emergence (T50) was shortened by 5 to 14 d. In contrast, the rate of second and third leaf emergence and seedling size 28 d after emergence did not differ between seedlings emerged from unprimed and SMP seed, indicating that the vegetative growth is basically determined genetically. However, SMP could subsequently enhance the mean seedling size of a population by increasing the number of seedlings that emerged rapidly. The SMP treatments could provide practical benefits on stand establishment of KBG under sub‐optimal temperatures by enhancing the mean seeding size but not by increasing the growth rate of individual seedlings.
Meloidogyne javanica Development in Three Clover Populations
Authors: Call N. M. , Quesenberry K. H. , Dunn R. A.
Published: July 2010

Root‐knot nematodes (RKN), Meloidogyne spp., cause damage to red clover (Trifolium pratense L.) which affects water and nutrient uptake and may predispose plants to other soil‐borne pathogens. Penetration and development of M. javanica (Treub) Chitwood three clover populations differing in resistance levels were evaluated in two greenhouse experiments conducted during 1994 and 1995. The RKN susceptible red clover cultivar ‘Kenstar’, a red clover breeding selection designated FLMR6 with moderate RKN resistance, and a highly RKN resistant species T. stoloniferum Mublenburg, running buffalo clover (RBC), were grown in Cone‐tainers and inoculated with 450 second‐stage juveniles (J2) 21 d after germination. Responses measured were numbers of J2, J3/J4 (third‐stage or fourth‐stage juvenile nematodes) and adults at 1, 2, 4, 8, 16, 24, 36, 48, 60, 80 (Exp. 2), and 120 (Exp. 1) days after inoculation (DAI). Fecundity was evaluated by counting number of egg‐masses and total number of eggs per plant at 80 and 120 DAI. More J2 were found in Kenstar roots than in FLMR6 and RBC roots at 4, 8, 36, 60, 80, and 120 DAI. More third or fourth stage juveniles (J3/J4) were found Kenstar and FLMR6 roots than in RBC at 16, 24, 36, 48, 60, 80, and 120 DAI, and Kenstar J3/J4 numbers were higher than FLMR6 at 60 and 120 DAI. Fewer adults were found in FLMR6 roots than in Kenstar at 36, 48, 60, 80, and 120 DAI, but adult numbers in RBC roots were signiftcantly lower than in FLMR6 at these same dates. At 80 and 120 DAI, number of egg masses and total number of eggs were greater on Kenstar roots than on FLMR6a, nd total egg numbers on RBC were lower than on FLMR6. The resistance mechanisms in FLMR6 and RBC hindered normal M. javanica development because of a combination of slower maturation to later growth stages and fewer J3/J4 maturing to adults, which produced fewer J2 for secondary infection.
Lack of Association between Fusarium Foot Rot and Head Blight Resistance in Winter Rye
Authors: Miedaner Thomas , Gang Gudrun , Reinbrecht Carsten , Geiger Hartwig H.
Published: July 2010

Foot rot and head blight caused by Fusarium culmorum (W.G. Sm.) Sacc. may lead to considerable loss of yield and grain quality in winter rye (Secale cereale L.). Breeding for resistance to the two diseases would be facilitated if the same resistance mechanisms were involved. The purpose of this study was to estimate the genetic correlation between the resistance to the two diseases in advanced winter rye breeding materials. Twenty self‐fertile inbred lines were grown at two locations in South Germany in 1992, 1993, and 1994 (six environments). Lines were arranged in three adjacent treatment blocks: no inoculation, inoculation for foot rot, and inoculation for head blight. Disease severity was rated on a 1‐to‐9 scale for foot rot and head blight. Besides the foot rot and head blight rating scale, ELISA (enzyme‐linked immunosorbent assay) was used to quantify the amount of Fusarium protein within stem issue from the foot rot treatment and relative grain weight was measured from the head blight treatment. In all but one environment, F. culmorum was re‐isolated from diseased stems at high percentages (≥90%). Disease severity was moderate for foot rot and head blight rating at all environments. Mean ELISA absorbance was 0.55 and mean relative grain weight 77.4%. Significant genotypic variation existed for all resistance traits. Broad‐sense heritabilities, calculated on an entry‐mean basis, were high for foot rot and head blight rating (h2 ≈ 0.8) and somewhat lower for ELISA absorbance and relative grain weight (h2 ≈ 0.5–0.6). No significant correlation was found between the resistances to foot rot and head blight. This was confirmed by a highly significant (P = 0.01) genotype‐plant organ interaction. Thus, resistance mechanisms most likely differ for the two diseases. Resistance selection requires separate multi‐environmental screening tests for F. culmorum foot rot and head blight.
Changes in Gene Expression in Six Alfalfa Cultivars Acclimated under Winter Hardening Conditions
Authors: Castonguay Yves , Nadeau Paul , Laberge Serge , Vézina Louis‐P.
Published: July 2010

Alfalfa (Medicago sativa L.) improvement programs would benefit from the identification of gene products closely related to winterhardiness. The expression of cold‐regulated (COR) genes was compared among six cultivars of contrasting winterhardiness by means of electrophoretic analysis of in vitro translation products. Plants were acclimated to simulated field conditions in an unheated greenhouse at a site near Quebec City during the 1992–1993 winter and were tested for their freezing tolerance and changes in gene expression. Down‐regulated translation products cumulatively showed a stronger decline in the cold hardy cvs Rambler and Apica than in the non hardy cv Moapa 69. Conversely, up‐regulated translation products progressively increased in the fall of 1992 and were cumulatively more abundant in hardy Rambler and Apica than in non hardy Moapa 69. A large degree of similarity occurred in the cold‐induced changes observed for the six cultivars with noticeable differences between the classes of hardiness. A relationship was observed between the accumulation of specific translation products in a group of low molecular weight basic peptides (LMWBP) and the hardiness potential of the cultivars. In the LMWBP group, three peptides were present in the very hardy cultivars; a single peptide was observed in the moderately hardy cultivars; and none were detected in the non hardy cultivars. The single LMWBP present in hardy Apica was not induced by water stress and was absent in leaves. Differential accumulation of COR gene products in alfalfa cultivars of contrasting winterhardiness were documented. This study indicates that determination of hardiness potential in alfalfa might be related to the differential expression of a limited number of COR genes. Future characterization of gene products that preferentially accumulate in winterhardy cuitivars will help elucidate the molecular bases of alfalfa adaptation to cold climates.
Inheritance of Crown Rust Resistance in Four Accessions of Avena sterilis L
Authors: Fox S. L. , Brown P. D. , Chong J.
Published: July 2010

Genetic resistance in common oat, Avena sativa L., provides an effective means of controlling crown rust, caused by Puccinia coronata Cda. f. sp. avenae Eriks. Four Avena sterilis L. accessions (IB 1487, IB 2402, IB 2465, and IB 3432) were selected for a genetic study based on low disease reaction to 15 isolates of crown rust and ease of hybridization to common oat. Crosses were made to determine the mode of inheritance of the resistance in each accession and to detect the linkage relationship of the resistance genes with several known crown‐rust resistance genes. The accessions were crossed to the susceptible common oat line Rodney 0, intercrossed among themselves, and crossed to six lines, each with a single gene for crown rust resistance: Pc38, Pc56, Pc58, Pc61, Pc63, and Pc68. In a greenhouse, the F2 populations were evaluated for seedling reaction after inoculation of the first leaf with crown rust isolate CR 13. Each accession had a single incompletely dominant or dominant gene conferring resistance, and genes were designated as Gene A in IB 1487, Gene B in IB 2402, Gene C in IB 2465, and Gene D in IB 3432. Gene A is allelic or closely linked to Pc56. Genes B and C are allelic or closely linked to Pc68. Having not been described previously, Gene D may be a useful addition to existing germplasm.
Combining Ability of the Stay Green Trait and Seed Moisture Content in Sunflower
Authors: Cukadar‐Olmedo B. , Miller J. F. , Hammond J. J.
Published: July 2010

Plants of sunflower (Helianthus annuus L.) which retain a green color in stems at physiological maturity are characterized as having the stay green trait. Research on inheritance of the stay green/early senescence trait may provide valuable information to plant breeders for developing new cultivars with better resistance to drought and pests, and increased standability. This study was conducted to determine the general (GCA) and specific (SCA) combining abilities of different female and male inbred lines in F1 hybrids for the stay green characteristic. The study included 36 sunflower hybrids produced by crossing six female lines to six male lines in a factorial mating design. Change in stem color was used as a criterion for the stay green characteristic with stem color analyzed by a computer program called Maps and Image Processing System. The relative magnitude of ratios of the female and male GCA components to the female and male GCA plus SCA components for the stay green trait, suggested that additive gene effects were more important than nonadditive gene effects in controlling stay green expressed among hybrid combinations. However, significant SCA effects detected at physiological maturity also implied the contribution of nonadditive effects to the variation. Nonsignificant correlation coefficient between stem color at physiological maturity and seed moisture content at harvest indicated that it is possible to develop hybrids with the stay green trait and low harvest seed moisture content. Significant but small correlation coefficients for stem color between different plant stages after anthesis suggested that selection would be most effective at physiological maturity.
Growth Analysis of Cotton Crops Infested with Spider Mites: II. Partitioning of Dry Matter
Authors: Sadras Víctor O. , Wilson Lewis J.
Published: July 2010

Foliar pests can affect reproductive allocation in plants. Depending on how spider mites (Tetranychus urticae Koch) affect dry matter partitioning in cotton (Gossypium hirsutum L.), yield losses in infested crops could be similar, greater, or lower than expected from shoot growth reduction. In this paper, we analyzed the effects of mite infestations initiated at three stages during the crop cycle on the yield, growth and dry matter partitioning of cotton. Normal‐ and okra‐leaf types, which are known to differ in their responses to mites, were compared in two experiments. Lint yield losses were significant and were greatest for the earliest mite infestations. Reduced shoot dry matter and reduced harvest index (lint yield/shoot dry matter) both contributed to these yield reductions. Yield losses were less severe in the okra‐leaf cultivar than in its normal‐leaf counterpart; this was in part due to a more favorable partitioning to key yield components in the former. In both experiments, reduced lint fraction Lg lint (g seed cotton)−1] contributed to the lower harvest index of damaged crops. Reductions in both fruit number per unit shoot dry matter and seed cotton mass per fruit also contributed to reductions in harvest index of damaged crops. Despite the observed reductions in harvest index and some of its components, allometric analysis showed that mites did not affect partitioning to reproductive organs even in the more severely infested treatments. Rather, the low harvest index of miteinfested crops was the result of small plant size. We conclude that mite effects on cotton growth and yield could be modelled by taking into account their primary effect on radiation‐use efficiency and leaf senescence. Explicit modelling of the effects of mites on dry matter partitioning may not be necessary.
Meristem Culture for Virus Elimination and Peanut Interspecific Hybrid Preservation
Authors: Morris J. B. , Dunn S. , Pinnow D. L. , Hopkins M. S. , Pittman R. N.
Published: July 2010

In 1989, more than 20% of the USDA's clonal Arachis species and their hybrids were infected with peanut mottle potyvirus (PMV) and peanut stripe potyvirus (PStV) or combinations of these viruses. PStV is a serious virus that can cause up to 20% yield reductions. PMV can also cause serious infections with up to 20% peanut (Arachis hypogaea L.) yield reductions under optimal environmental conditions. Once introduced, these viruses can spread throughout crop collections and research plots by insect vectors or routine handling of plants. This study was conducted during 1993 and 1994 in a greenhouse at Griffin, GA, to determine whether interspecific peanut hybrids derived from nodal and meristem cultures differed for in vitro morphogenesis, and if PMV and PStV could be eliminated via meristem culture from vegetatively propagated peanut accessions. Nodal segments were placed in MSB5 media containing Murashige and Skoog (MS) salts, 65 vitamins, and 20 g L−1 sucrose. Apical meristems from explants were plated on MSB5 media augmented with 1 mg L−1 each of a‐naphthalaneacetic acid (NAA) and benzylaminopurine (BAP). Explants not producing shoots were subcultured onto MSB5 media supplemented with 1 mg L−1 of BAP to induce shoot cell growth. Significant variation for shoot and root production was observed among hybrids. Regenerated plants from meristem culture were examined at the four leaflet stage by double antibody sandwich enzyme‐linked immunosorbent assay (DAS‐ELISA) for the presence of virus. PStV was not detected by DAS‐ELISA in any plants derived from meristems. However, PMV was eliminated from 50 to 100% of five hybrids, but not from the other hybrids. Meristem culture provides an efficient method of virus elimination from interspecific Arachis hybrids.
Morphological and Physiological Characteristics Associated with Tolerance to Summer Irrigation Termination in Alfalfa
Authors: Wissuwa Matthias , Smith S. E.
Published: July 2010

Deliberately withholding irrigation to alfalfa (Medicago sativa L.) during summer, a management strategy referred to as summer irrigation termination (SIT), has been suggested to conserve water in long‐season desert environments. Summer irrigation termination may reduce productivity of alfalfa stands, although such effects may be lessened if cultivars with improved tolerance to SIT could be developed. This study was conducted to identify characteristics associated with low crown mortality as the primary component of tolerance to SIT. Using such traits in selection may be superior to direct selection for post‐SIT yield, a trait potentially characterized by low heritability. Single spaced nondormant alfalfa plants were grown in a field trial in Tucson, AZ, and subjected to two SIT treatments during two years (Treatment 1, 84 d in 1994 and Treatment 2, 42 d in 1994 and 75 d in 1995). Traits evaluated prior to SIT (forage yield, stem number, plant height, leaf area, and root diameter) were not significantly associated with crown mortality. Significant but weak correlations were detected between crown mortality and days to wilting (r = −0.25*) and plant height during SIT (r = −0.29*). Accumulation of osmotically active substances, such as proline and sucrose, was not related to crown mortality. However, crown mortality was significantly correlated with concentration of total nonstructural carbohydrates (TNC) in crown tissue on Days 28 (r = − 0.57*) and 35 (r = − 0.79*) of SIT. The TNC reserves may be essential for continued respiration during periods of drought. Depletion of TNC reserves could have caused plant death in intolerant plants. Concentrations of TNC in crown tissue may represent a criterion in indirect selection for decreased crown mortality during SIT in selected environments.
DNA Markers Associated with Resistance to Javanese Root‐Knot Nematode in Soybean
Authors: Tamulonis J. P. , Luzzi B. M. , Hussey R. S. , Parrot W. A. , Boerma H. R.
Published: July 2010

Javanese root‐knot nematode [Meloidogyne javanica (Treub) Chitwood] (Mj) is a pathogen of soybean [Glycine max (L). Merr.] in the southern USA. Although breeding for root‐knot nematode resistance is an important objective in many plant breeding programs, progress in selection for nematode resistant lines is hampered by laborious screening procedures. The inheritance of resistance to Mj is quantitative and has a moderate to high heritability (0.48‐0.76). The objectives of this study were to use restriction fragment length polymorphism (RFLP) markers to identify quantitative trait loci (QTL) conditioning resistance to Mj and to determine the genomic location and the relative contribution to resistance of each QTL. Eighty‐four F2 progeny from a cross between “CNS” and a root‐knot nematode resistant soybean plant introduction, PI230977, were used to map 86 RFLP markers and three morphological traits. The 89 markers converged on 18 linkage groups spanning a total of 1053 centimorgan (cM). Sixty‐eight of the 84 F2:3 families were assayed for Mj galling in the greenhouse. Analysis of variance and interval mapping were used to identify QTL associated with galling. Two QTL with alleles derived from PI230977 conditioning resistance to Mj were identified on two Linkage Groups (LG). Marker B212‐1 on LG‐F accounted for 46% of the variation in gall number, whereas A725‐2 on LG‐D1 accounted for 13%. The additive model best fit the data, and together the two markers accounted for 54% of the variation in gall number. Marker B212‐1 is within a cluster of seven other disease resistance loci that span a 5‐ to 10‐cM region on LG‐F.
Leaf Photoassimilation and Partitioning in Stress‐Tolerant Sorghum
Authors: Sowder C. Matt , Tarpley Lee , Vietor Donald M. , Miller Frederick R.
Published: July 2010

Previous attempts to relate variation in physiological measurements of carbon and water exchange to prettowering and postflowering tolerance to water stress in Sorghum bicolor (L.) Moench have yielded inconsistent results. The objective of this research was to compare physiological indicators of sorghum photoassimilation and partitioning among a prefiowering‐tolerant line (Tx430), postflowering tolerant line (B35), and an F1 hybrid thereof. Leaf CO2 exchange and sucrose synthesis rates, carbohydrate concentrations, and 14C‐assimilate partitioning were quantified in field‐grown plants that were exposed to 14CO2 for 3 h under steady‐state labeling conditions. Leaf CO2 exchange and sucrose synthesis rates were slower, and concentrations and radio‐activity in blade starch were greater, in B35 than in Tx430 under well‐watered conditions. In addition, the postflowering‐tolerant cultivar B35 retained 70% more 14C‐assimilate in the labeled blade than did Tx430. The differences in leaf traits were associated with 33% smaller grain weights in B35 than Tx430 or the hybrid, but aerial biomass and upper stem carbohydrate concentrations at preboot and anthesis did not differ among the cultivars under well‐watered conditions. The consistency of differences between B35 and Tx430 across sampling stages suggested that metabolic and unloading processes in leaf blades, rather than limitations to assimilate unloading in growing and storage tissues, contributed to slower rates of CO2 exchange, sucrose synthesis, and 14C‐assimilate export in B35. Leaf traits and dry weights did not differ among cultivars when water stress was imposed on potted plants during preboot, anthesis, and grain filling. The lack of a relationship between leaf traits under well‐watered conditions and postflowering tolerance to water stress indicates tolerant sorghum phenotypes could be selected to avoid the relatively low rates of CO2 exchange, sucrose synthesis, and export observed for B35.
Variation in Soft Winter Wheat Characteristics Measured by the Single Kernel Characterization System
Authors: Hazen S. P. , Ward R. W.
Published: July 2010

Kernel hardness is one of the key grain attributes considered in wheat (Triticum aestivum L.) marketing in the USA. The objective of this research was to characterize the effects of cultivar, environment, and cultivar × environment interaction on kernel hardness as measured by the Single Kernel Characterization System. Kernel weight and width were also studied. Eleven soft winter wheat cultivars were grown in replicated trials in 19 environments in Michigan. All three traits were significantly (P < 0.01) affected by cultivar, environment, and cultivar × environmentin teraction. Variation for kernel hardness was large and continuous among cultivars and environments. Hhün's nonparametric stability statistic showedt hat there were no differences in ranks tability of the cultivars. Principal componenatn alysis of the cultivar × environment interaction effects showed that there were no consistent patterns of behavior for similar cultivars, locations, or seasons. The only significant and large correlation was kernel weight vs. kernel width (r = 0.89). These data suggest that one environment of testing or a composite sample of multiple environments may be sufficient to accurately rank cultivars for kernel hardness. The large magnitude of the environmental effects will make prediction of hardness of a given wheat crop difficult even when the cultivar is known.
Characterization and Inheritance of Adult Plant Stem Rust Resistance in Durum Wheat
Authors: Hare R. A.
Published: July 2010

Few durable resistance genes have provided long‐term effective control of stem rust (casual pathogen Puccinia graminis Pers. f. sp. tritici Eriks and E. Henn.), a destructive disease of wheat (Triticum ssp.). The most prominent gene, Sr2, derived from the tetraploid wheat, ‘Yaroslav Emmer’ (Triticum turgidum L.), contributes to the protection of many hexaploid cultivars worldwide. Additional durable resistance genes are necessary to reduce the reliance on the continued effectiveness of Sr2 alone, or in gene combinations. To find alternative sources of durable resistance, the adult plant reactions of four durum (T. turgidum) cultivars, ‘Glossy Huguenot’, ‘Marouani’, ‘Bansi) Strain 168’, and ‘Russian 1364‐3’ to a group of P. graminis tritici pathotypes were studied. Glossy Huguenot and Marouani displayed adult plant resistance alone, while the other cultivars were susceptible. The adult plant resistance significantly reduced the number of stem rust pustules per unit area and delayed the onset of disease, compared with susceptible controls. Genetic analysis performed on F1 plants, F2‐derived fatal. lies, and F3 plants from segregating F2‐derived families showed that adult plant resistance was determined by dominant alleles at a single locus in each parent. AH progeny from the cross of the resistant parents were adult plant resistant, suggesting that the allele is probably common to each parent. The apparent continued effectiveness of the Glossy Huguenot adult plant resistance in Australia over the past 90 yr indicates the possibility of durable resistance. When transferred to the hexaploid level the gene should provide a valuable supplement to Sr2.
Efficiency of High‐Nitrogen Selection Environments for Improving Maize for Low‐Nitrogen Target Environments
Authors: Bänziger M. , Betrán F. J. , Lafitte H. R.
Published: July 2010

Most maize (Zea mays L.) in the tropics is grown under low‐nitrogen (N) conditions, raising the need to assess efficient breeding strategies for such conditions. This study assesses the value of low‐N vs. high‐N selection environments for improving lowland tropical maize for low‐N target environments. Fourteen replicated trials grown under low (no N applied) and high (200 kg N Ha−1 applied) N at CIMMYT, México, between 1986 and 1995 were analyzed for broad‐sense heritability of grain yield, genetic correlation between grain yields under low and high N, and predicted response of grain yield under low N to selection under either low or high N. Broad‐sense heritabilities for grain yield under low N were on average 29% sm ller than under high N because of lower genotypic variances under low N. Error variances were similar at low and highN. Genetic correlations between grain yields under low and high N were generally positive. They decreased with increasing relative yield reduction under low N, indicating that specific adaptation to either low or high N became more important the more low‐N and high‐N experiments differed in grain yield. Selection under high N for performance under low N was predicted significantly less efficient than selection under low N when relative yield reduction due to N stress exceeded 43%. Maize breeding programs targeting low‐N environments in the tropics should include low‐N selection environments to maximize selection gains.
Seedling Development and Deposition of Starch and Storage Proteins in Alfalfa Roots
Authors: Kalengamaliro N. E. , Volenec J. J. , Cunningham S. M. , Joern B. C.
Published: July 2010

The physiological basis for defoliation tolerance in alfalfa (Medicago sativa L.) is associated with taproot organic reserves, including soluble sugars, starch, and vegetative storage protein (VSP). It is not known when organic reserve accumulation begins in developing seedlings or the factors that influence their deposition. The objectives of three greenhouse experiments were to determine (i) the onset starch and VSP accumulation in roots of alfalfa seedlings, (ii) if N fertilization of seedlings stimulated root VSP deposition, and (iii) seedling defoliation tolerance is associated with the presence of root organic reserves. In Exp. 1, roots and shoots of ‘Vernal’, ‘Resistar’, and ‘WL 605’ were sampled periodically beginning 19 d after planting (DAP) to determine the developmental paltern of starch and VSP deposition in roots. In Exp. 2, normal and ineffective nodulating ‘Saranac’ was grown with or without 10 mM N to determine if applied N stimulates early VSP deposition. In Exp. 3, alfalfa seedlings were completely defoliated (including cotyledons) 14, 28, 42, and 56 DAP, and shoot regrowth and seedling survival were used to measure defoliation tolerance. In all experiments, starch, soluble sugars, protein, and VSP concentrations in roots were determined. Root starch and VSP concentrations were low up to 30 DAP. Starch and VSP accumulation began by 39 DAP and coincided with declining root protein and soluble sugar concentrations. Addition of N increased herbage growth but did not stimulate early VSP deposition. In Exp. 3, ≈80% of seedlings survived complete defoliation 14, 42, and 56 DAP, while only 52% survived defoliation 28 DAP. Roots contained low starch and VSP concentrations 14 and 28 DAP. Although seedling survival 42 and 56 DAP was associated with presence of starch and VSP in seedling roots, defoliation tolerance of alfalfa seedlings 14 DAP appears to be influenced by factors other than root starch and VSP concentrations.
Super‐Optimal CO2 Reduces Seed Yield But Not Vegetative Growth in Wheat
Authors: Grotenhuis Timothy P. , Bugbee Bruce
Published: July 2010

Although terrestrial atmospheric CO2 levels will not reach 1000 μmol mol−1 (0.1%) for decades, CO2 levels in growth chambers and greenhouses routinely exceed that concentration. CO2 levels in life support systems in space can exceed 10 000 μmol mol−1 (1%). Numerous studies have examined CO2 effects up to 1000 μmol mol−1, but biochemical measurementisn dicate that the beneficial effects of CO2 can continue beyond this concentration. We studied the effects of near‐optimal (≈1200 μmol mol−1) and super‐optimal CO2 levels (2400 μmol mol−1) on yield of two cultivars of hydroponically grown wheat (Triticum aestivum L.) in 12 trials in growth chambers. Increasing CO2 from sub‐optimal to near‐optimal (350‐1200 μmol mol−1) increased vegetative growth by 25% and seed yield by 15% in both cultivars. Yield increases were primarily the result of an increased number of heads per square meter. Further elevation of CO2 to 2500 μmol mol−1 reduced seed yield by 22% (P < 0.001) in cv. Veery‐10 and by 15% (P < 0.001) in cv. USU‐ApogeeS. uper‐optimal CO2 did not decrease the number of heads per square meter, but reduced seeds per head by 10% and mass per seed by 11%. The toxic effect of CO2 was similar over a range of light levels fromh alf to full sunlight. Subsequenttr ials revealed that super‐optimal CO2 during the interval between 2 wk before and after anthesis mimickedth e effect of constant super‐optimal O2. Furthermore, near‐optimal CO2 during the same interval mimicked the effect of constant near‐optimal CO2. Nutrient concentration of leaves and heads was not affected by CO2. These results uggest that super‐optimal CO2 inhibits some process that occurs near the time of seed set resulting in decreased seed set, seed mass, and yield.
Callus Induction and High Efficiency Plant Regeneration via Somatic Embryogenesis in Paspalum
Authors: Cardona C. A. , Duncan R. R.
Published: July 2010

Paspalum vaginatum Swartz (seashore paspalum) is a warm season grass that can be used for turf, forage, erosion control, or bioremedialion. The species is a sexual diploid, but produces less than 5% viable seed, which poses problems for genetic enhancement by conventional breeding methods. The selection of somaclonal variants is one alternative methodf or genetic improvement. The objective of this study was to develop a standard tissue‐culture regeneration protocol for this species. Immaturein florescences of nine seashore paspalume cotypes were used as explants for the induction of embryogenic callus in two controlled laboratory experiments during 1993 to 1994 in Georgia. Five levels of (2,4‐dichlorophenoxy)acetic acid (2,4‐D; 0.0, 1.0, 2.0, 6.0 mg L−1) and three 6‐benzylaminopurine levels (BAP; 0.0,1.0, 2.0 mg L−1) were tested for callus induction during 1993 and four levels of 2,4‐D (2.0, 3.0, 6.0, 10.0 mg L−1) during 1994 in a factorial experiment with all treatment combinations. BAP effects were not significant for all ecotypes except Adalayd. The 2,4‐D response varied by ecotype, but all ecotypes responded to the lowest rate (1 mg L−1). significant embryogenic response was obtained in all ecotypes with 1 mg L−1 BAP in combination with 0.5 to 2.0 mg L−1 et‐naphthaleneacetic acid (NAA). HI‐1, Mauna Key, PI 299042, and K3 were highly embryogenic and PI 509021 and Adalayd were less embryogenic. High frequency plant regeneration of five ecotypes (PI 509021, HI‐1, Mauna Key, Adalayd, PI299042) was successfully achieved. The protocol from callus induction to plant regeneration for seashore paspalum has been streamlined to be effective and efficient.
Using AFLP Markers to Determine the Genomic Contribution of Parents to Populations
Authors: VanToai Tara T. , Peng Jiqing , St. Martin Steven K.
Published: July 2010

Estimates of proportions of parental contribution to germplasm populations are useful to breeders. The objective of this research was to assess the ability of amplified fragment‐length polymorphism (AFLP) markers to characterize the contributions of the original parents to later cycles of a soybean [Glycine max (L.) Merr.] population that had undergone recurrent selection. Use of four primer pairs yielded a total of 47 polymorphic bands. Estimates of parental contribution were consistent between primer pairs and between cycles and conformed to those expected based on pedigrees. Standard errors of estimates were 3 to 5%, indicating satisfactory precision. The AFLP markers should provide relatively inexpensive, precise estimates of parental contribution. This marker system may also be useful in tracking genetic changes in populations.
Performance of Doubled Haploid Populations Segregating for Linolenic Acid Levels in Spring Rapeseed
Authors: Rajcan Istvan , Kott Laima S. , Beversdorf Wallace D. , Kasha Kenneth J.
Published: July 2010

Linolenic acid (18:3) is a trienoic fatty acid known as the unstable component of canola oil contributing, upon oxidation, to undesirable odors and flavors of oil. The environmental sensitivity and complex inheritance of the trait make the breeding for lower 18:3 content difficult. A 2‐yr, two‐location study was carried out using a doubled haploid (DH) population of rapeseed lines (Brassica napus L. or Brassica rapa L.) varying for 18:3 content in order to characterize these lines agronomically and assess the magnitude of environmental variation of the 18:3 content. Correlation analyses between 18:3 and other fatty acids as well as various agronomic and quality traits were performed to determine possible correlated responses associated with breeding for low 18:3 canola. Decreasing the 18:3 content was significantly associated with later flowering and maturity, higher oil, and lower protein content but not with yield, lodging, and plant height. Orthogonal contrasts comparing the low with intermediate and high 18:3 containing DH lines showed no yield disadvantage of the low 18:3 DH lines for one location in 1 yr. Environmental influence on the 18:3 content was larger between the years than between locations in I yr. Because of environmental sensitivity and correlation between low linolenic acid content and later maturity, it may be preferable to use molecular markers linked to the low 18:3 content alleles to select for low linolenic canola at the seedling stage.
Flowering Responses of Selected Annual Bluegrass Genotypes under Different Photoperiod and Cold Treatments
Authors: Johnson Paul G. , White Donald B.
Published: July 2010

Poa annua L. turf on golf courses is often criticized for persistent flowering, even under low mowing heights. But in fact, P. annua genotypes exhibit wide variation in their flowering characteristics. This study was conducted in greenhouse and growth chamber environments during 1994 and 1995 at the University of Minnesota to test for photo‐period requirements for floral induction and development. The five P. annua genotypes studied ranged from a true annual type to strongly perennial forms. Photoperiod effects were investigated without prior cold treatment, during cold treatment, and after cold treatment requirements had been satisfied. Cold treatments were 4°C for 12 wk. The annual type (UM2283) was not responsive to cold treatments and is day‐neutral. In the absence of a cold treatment, one perennial genotype (UM234) was induced in long days (16 h), two perennials (UM42, UMl17) were induced to flower in short days (8 h), and one perennial (UM184) was not induced in either. Ninety minute night breaks during a 16‐h dark period were effective in producing the long‐day responses. Photoperiod did not affect the cold treatment response at 4°C. Floral development after 4°C cold treatment was generally favored by long days (16 h), but is genotype dependent. Photoperiodism is associated with perenniality in P. annua, and may be important in the selection pressures caused by management practices golf course environments. Selection for longer cold treatment requirements and less induction in short days (8 h) may reduce the amount of flowering a genotype would exhibit in a turf stand.