bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimating Turfgrass Evapotranspiration Using Atmometers and the Penman‐Monteith Model
Authors: Qian Y. L. , Fry J. D. , Wiest S. C. , Upham W. S.
Published: July 2010

Information is lacking on the precision of atmometers and empirical models used to estimate turfgrass evapotranspiration (ET). Experiments were conducted to evaluate the precision of black Bellani plates, a class A evaporation pan, and the Penman‐Monteith empirical model for estimating ET of ‘Mustang’ tall rescue (Festuca arundinacea Schreb.), ‘Meyer’ zoysiagrass (Zoysia japonica Steud.), ‘Prairie’ buffalograss [Buchloe dactyloides (Nutt.) Engelm.], and ‘Midlawn’ bermudagrass [Cynodon dactylon (L.) Pers. × transvaalensis Burtt‐Davy] under well‐watered conditions. Tall rescue was mowed once weekly at 6.5 cm, and warm‐season grasses were mowed at 4.5 cm twice weekly. Diurnal ET was measured between June and September in 1993 and 1994 using weighing lysimeters and the water balance method. Evaporation from atmometers was measured during the hour that turfgrass ET was determined, and Penman‐Monteith‐estimated ET was calculated for the same time period. Black Bellani plate evaporation was correlated most closely with measured turf ET (R2 = 0.73), followed by class A pan evaporation (R2 = 0.67), and Penman‐Monteith‐estimated ET (R2 = 0.60). Ranking of grasses for mean daily ET was tall fescue (6.8 mm d−1) > zoysiagrass (5.6 mm d−1) > buffalograss (5.1 mm d−1) = bermudagrass (5.0 mm d−1). The black Bellani plate provides the most precise estimate of turfgrass ET under well‐watered conditions.
Organization of RFLP Diversity among Inbred Lines of Maize Representing the Most Significant Heterotic Groups
Authors: Dubreuil P. , Dufour P. , Krejci E. , Causse M. , de Vienne D. , Gallais A. , Charcosset A.
Published: July 2010

One hundred‐sixteen inbred lines of maize (Zea mays L.) from significant heterotic groups (i.e., European flint, Lancaster Sure Crop, Minnesota 13, and Reid Yellow Dent) and miscellaneous origins were assayed for restriction fragment length polymorphism (RFLP). Our goals were to investigate (i) genetic variability and its structure among and within heterotic groups and (ii) the use of RFLP markers to assign miscellaneous lines to heterotic groups by means of probes selected for locus specificity, clear patterns, and reproducibility. Among the 63 single copy probe‐enzyme combinations used, 372 variants were scored with a mean of 5.9 variants per combination. Principal component and cluster analyses performed on lines from established heterotic groups clearly separated flint lines from dent lines. Loci that contributed the most to the genetic differentiation between European flint and northern U.S. dent lines were determined. Within U.S. germplasm, classification showed an association of inbreds that closely matched associations based on pedigree relationships. Correlation between pedigree distance and molecular Rogers' distance was significant (r = 0.77, P < 0.001). Based on these results, classification by molecular distance was convenient (i) for identifying heterotic groups and (ii) for assigning origins to unknown or broadly based inbreds. This information should prove useful for choosing (i) combinations of inbreds to be evaluated in hybrid trials and (ii) parents for breeding programs.
New Resistance to Virulent Root‐Knot Nematodes Linked to the Rk Locus of Cowpea
Authors: Roberts P. A. , Matthews W. C. , Ehlers J. D.
Published: July 2010

Screening of cowpea [Vigna unguiculata (L.) Walp.] germplasm for additional resistance to the root‐knot nematodes, Meloidogyne incognita (Kofoid and White) Chitwood and M. javanica (Treub) Chitwood, revealed an accession (IT84S‐2049) from Africa with resistance to diverse populations of both root‐knot species. The resistance was effective against nematode isolates that are virulent to the resistance gene Rk present in commercial cowpea cultivars, in addition to isolates of gene Rk‐avirulent populations. This study was conducted to elucidate the inheritance of a newly identified, highly effective source of resistance, and to determine its relationship to gene Rk in existing cultivars. Egg mass production on root systems of plants in growth pouches was used to assess susceptibility‐resistance of F1, F2, F3, BC1F1, BC1F2, and TC1 populations generated from crosses of IT84S‐2049 with California Blackeye no. 3 (CB3, susceptible), CB5, or CB46 (both possessing Rk). Segregation of resistance to gene Rk‐virulent M. incognita in progenies from IT84S‐2049 × CB3 showed that resistance in IT84S‐2049 is governed by one dominant nuclear gene. No susceptible recombinants were found among 1206 F2 and 1144 TC1 progeny from IT84S‐2049 × CB5 or CB46 and inoculated with Rk‐avirulent M. incognita (used to detect both resistance phenotypes). Resistance in IT84S‐2049 is conferred by an additional dominant allele of the Rk locus, or by another gene locus very tightly linked to Rk within 0.17 map units. We propose the symbol Rk2 to designate this new resistance factor in IT84S‐2049. Thus, Rk may be a complex nematode resistance locus, analogous to those reported for other plant pathogen‐host combinations.
Optimal Replication in Selection Experiments
Authors: Gauch H. G. , Zobel R. W.
Published: July 2010

The efficiency and selection gain of yield trial experiments is affected by experimental design. A larger number of genotypes, G, increases the chances of including markedly superior genotypes, and a larger number of replications, R, reduces errors and thereby increases the chances of correctly identifying truly superior material. But assuming that cost rises approximately as the number of plots GR, containing research cost imposes a tradeoff between G and R. This paper gives tables specifying the number of replications that optimizes selection of genotypes with the highest true yields. It also quantifies the impact of suboptimal choices. Even with an optimal level of replication, the value of a selection experiment rises logarithmically with the number of plots and hence the cost. Since benefits from more data follow this severe law of diminishing returns, statistical strategies for decreasing errors and improving selections are quite important.
Evaluation of Bread Wheat Germplasm for Resistance to Bacterial Streak
Authors: Tillman B. L. , Harrison S. A. , Clark C. A. , Milus E. A. , Russin J. S.
Published: July 2010

Bacterial streak caused by Xanthomonas campestris pv. translucens (J.J.&R.) Dye (Xct) reduces grain yield of wheat (Triticum aestivum L. em. Thell) by as much as 40%. Resistant cultivars offer the best control in the absence of effective bactericides. However, few resistant genotypes have been identified for use in breeding programs. Five thousand bread wheat accessions from the USDA National Small Grains Collection were inoculated with Xct and evaluated for resistance to bacterial streak in the field during 1992. On the basis of agronomic characteristics and bacterial streak severity, a total of 428 accessions was selected for continued testing. These accessions were inoculated with Xct and evaluated in replicated hill plots in the field during 1993 and 1994. Accessions were also evaluated for water‐soaking (WS) reaction to Xct in growth chambers using a seedling syringe inoculation method. Average bacterial streak severity (BSS) during 1993 and 1994 was negatively correlated with heading day (HD) (r = −0.55;P< 0.001). To reduce the maturity effect, accessions with HD >106 were dropped and the remaining accessions were grouped into the HD classes: ≤84, 85 to 89, 90 to 94, 95 to 99, and ≥100. Selection was practiced within a HD class based on the following criteria: (i) BSS ≤ 10% in each year, (ii) if HD ≤ 94, then maximum average BSS ≤10%, (iii) if HD 95–99, then maximum average BSS ≤ 9%, and (iv) if HD ≥ 100, then maximum average BSS ≤ 7%. Twenty‐six resistant accessions are recommended for the southern USA. Two controls, Terral 101 and GA 22 triticale (X. triticosecale Wittmack), also met these criteria with 6% average BSS. BSS and WS were not positively correlated, suggesting that the WS reaction to Xct from the syringe inoculation test may have limited usefulness. Field screening was effective in identifying resistance, but reaction of genotypes was confounded by relative maturity and genotype × environment (G×E) interactions.
Phosphorus Distribution and Remobilization in Bean Plants as Influenced by Phosphorus Nutrition
Authors: Snapp Sieglinde S. , Lynch Jonathan P.
Published: July 2010

Remobilization of P from vegetative tissues can be an important source of grain P in common bean(Phaseolus vulgaris L.). Yet, data on the extent of remobilization of P from roots is scarce.We measured P remobilization from roots and leaves and examined the influence of P nutrition on remobilization patterns and tissue longevity. A split‐root system was used to expose a portion of the root system (compartment roots) to low‐P treatments independently from those imposed on the main root system. Phosphorus content of retained leaves, abscised leaves, stems, pods, seeds, and roots were observed overtime. Leaf remobilization supplied over half of the pod plus seed P. Flux analysis suggested that leaf remobilization occurred aerlier in low‐P than it did in high‐P plants. Root P content of compartment roots did not decrease with ontogeny. We compared remobilization patterns of root P in low‐P and high‐P plants in a short‐term experiment using 32P applied to roots grown in either low‐P or high‐P compartments. Compartment roots retained over 80% of absorbed 32P almost all cases. Thee exception was roots of high‐P plants growin in a high‐P compartment, which retained only 20% of absorbed 32P. Together these results indicate common bean roots retain P when soil P levels are low. This behavior is in contrast to that of leaves and stems which remobilize P to the grain at both low and high levels soil P fertility.
Teosinte Cytoplasmic Genomes: I. Performance of Maize Inbreds with Teosinte Cytoplasms
Authors: Edwards Jode W. , Allen James O. , Coors James G.
Published: July 2010

Cytoplasmic variation in maize (Zea mays L.) is known to influence qualitative phenotypes such as male sterility and teosinte‐cytoplasm‐associated miniature. Cytoplasmic influences on quantitative characters such as grain yield have been difficult to document. The objective of this research was to study effects of diverse teosinte cytoplasmic genomes on quantitative agronomic characters in two maize inbreds. Ten diverse cytoplasms derived from three subspecies of Z. mays and one Z. perennis cytoplasm were substituted for the cytoplasms of inbreds A619 and W23 by at least six generations of backcrossing. Inbreds with teosinte cytoplasms were compared with A619 and W23 in a replicated field trial in three environments. Five of the 11 cytoplasms had quantitative influences. Three of these five cytoplasms decreased yield, with one of the cytoplasms reducing yield of the A619 nuclear genotype by 1.07 Mg ha−1 or 20%. Many effects were specific to either the A619 or W23 nuclear background indicating that teosinte cytoplasmic genomes interacted with maize nuclear genomes. Cytoplasmic effects tended to be small and unfavorable in the context of a maize breeding program.
Host Genetic Variation in the Early Nodulation and Dinitrogen Fixation of Soybean
Authors: Pazdernik D. L. , Graham P. H. , Vance C. P. , Orf J. H.
Published: July 2010

Soybeans [Glycine max (L.) Merr.] grown on soils low in N can exhibit N deficiency during early plant development. Improved early N2 fixation may alleviate this problem. Our objectives were to (i) examine genetic variation in early nodulation and N2 fixation of soybean, and (ii) identify traits useful in breeding for early nodulation and N2 fixation in this crop. Eighty‐six soybean lines showed considerable genetic variation in efficiency and speed of nodulation with Bradyrhizobium japonicum strain USDA 110. Eighteen lines were then reevaluated for nodulation efficiency with the B. japonicum strains USDA 123, UMR 161, and NA 6407 for differences in nodule number 5 to 12 d after inoculation (DAI) and for differences in plant dry weight, nodule fresh weight, acetylene reduction activity (ARA), nodule enzyme activity, leghemoglobin concentration, and nodule soluble protein concentration (SOLP) 10 to 17 DAI. The 86 lines differed in percentage roots nodulated (PRN; 26–93%) and number of nodules above the root tip mark (NARTM; 0.3–3.0), and in uppermost nodule position (− 17.5 to 19.5 mm). For the 18 lines that were reevaluated, mean PRN and NARTM values were greater for USDA 123 than for USDA 110 (65.1 vs. 57.9%; 1.4 vs. 1.0, respectively). For these lines, correlation analyses showed that PRN correlated with nodule number at 5 (r = 0.69**) but not 12 DAI, while nodule number 12 DAI correlated positively with nodule fresh weight, ARA, enzyme activity, and SOLP 17 DAI. Plant dry weight, nodule fresh weight, and nodule SOLP assayed at 17 DAI are suggested as traits for use in a breeding program to improve early nodulation and N2 fixation in soybean.
Chromosome Number and Nuclear DNA Content of Several Switchgrass Populations
Authors: Hopkins Andrew A. , Taliaferro Charles M. , Murphy Christopher D. , Christian D'Ann
Published: July 2010

Information regarding ploidy level of switchgrass (Panicum virgatum L.) is needed for use of populations in breeding programs and for maintenance of germplasm. Our objectives were to determine chromosome number and variation in DNA content of several switchgrass populations and to examine the usefulness of flow cytometry techniques for estimating ploidy level in switchgrass. Chromosome numbers were determined by means of light microscopy; laser flow cytometry was used to determine nuclear DNA content. Only octaploid plants were found within ‘Blackwell’, ‘Pathfinder’, ‘Cave‐in‐Rock’, and ‘Trailblazer’, all of which were previously reported to be hexaploid populations. Average nuclear DNA contents, with ranges in parentheses, were 3.1 (2.7–3.2) pg for verified tetraploid populations and 5.2 (4.8–5.8) pg for verified octaploid populations. Flow cytometry techniques were useful in discriminating between 4x and 8x plants; ploidy level of plants estimated to be 6x may need to be verified with actual chromosome counts.
Multiple Trait Selection in a Recurrent Selection Population in Oat (Avena sativa L.)
Authors: Dolan D. J. , Stuthman D. D. , Kolb F. L. , Hewings A. D.
Published: July 2010

Single trait selection is often utilized to maximize genetic gain in recurrent selection systems. However, traits negatively correlated to the primary trait can deteriorate with single trait selection. Multiple trait selection can be used to prevent or correct correlated trait deficiencies. Our objective was to compare the effectiveness of several multiple trait selection schemes with selection for grain yield alone. Five multiple‐trait selection schemes were evaluated for their effect on total genotypic worth and individual trait responses in an “opened” oat (Avena sativa L.) recurrent selection population. Grain yield, days‐to‐heading, plant height, and reaction to barley yellow dwarf virus (BYD) were studied in several environments. The phenotypic correlations with yield were 0.44 and 0.60 for heading date and plant height, respectively. There was no association between yield and BYD. A restricted index, a Smith index, a modified base index, a multiplicative index, and independent culling were evaluated and compared with selection for yield alone. The restricted and Smith selection indices, when compared with selection for yield alone, selected genotypes with improved heading date, plant height, and BYD with only negligible decreases in yield. Greater correction for heading date and plant height was achieved with the modified base index, the multiplicative index and independent culling, but yield decreased accordingly. Realized gains in total worth for the restricted index were 15% above, and the Smith index 14% above, the gain realized by selection for yield alone. Restricted and Smith index selection were effective at preventing secondary traits from deteriorating through selection for grain yield.
Water Status and Leaf Area Production in Water‐ and Nitrogen‐Stressed Cotton
Authors: Fernáandez C. J. , McInnes K. J. , Cothren J. T.
Published: July 2010

The combined effects of water and N deficits on leaf area production and water relations in cotton (Gossypium hirsutum L.) have not been investigated thoroughly. A study was conducted to evaluate the responses of leaf area production and water relations in cotton plants exposed to water and N deficits during the preflowering stage. Two N treatments‐nutrient solution with 12 mM of N (N‐supplied) and N‐free nutrient solution (N‐starved)‐were applied to plants when the third true leaf was visible. Two irrigation treatments‐daily irrigation (well watered) and no irrigation (water stressed)‐were superimposed on each N treatment once the plants were moved into the test chambers when they reached a leaf area of 0.050 ± 0.002 m2. Leaf area and leaf water and osmotic potentials were measured at the end of each day‐time period. Under well‐watered conditions, leaf turgor potential in N‐starved plants was about 0.3 kJ kg−1 lower than in N‐supplied plants. When plants were exposed to water deficits, the decline of leaf water potential relative to soil water content was greater in N‐starved plants than in N‐supplied plants. Nitrogen deficiency delayed and decreased the magnitude of osmotic potential adjustment and, therefore, reduced the capacity of leaves to maintain turgor. Water and N deficits decreased whole‐plant cumulative leaf area about 50 and 40%, respectively, through decreased daily production of mainstem and branch leaves and decreased final area of individual mainstem and branch leaves. Nitrogen deficiency induced a higher sensitivity of leaf growth inhibition to water deficits.
Contribution of Leaf Expansion, Rate of Leaf Appearance, and Stolon Branching to Growth of Plant Leaf Area under Water Deficit in White Clover
Authors: Belaygue Christine , Wery Jacques , Cowan Alexander , Tardieu Francois
Published: July 2010

Response of white clover (Trifolium repens L.) leaf area to water deficit depends on three processes: individual leaf expansion, phytomer production, and stolon branching. We have evaluated these processes in five clones under a wide range of conditions. Four experiments of 60 to 120 d duration were conducted: two in a growth chamber, one in a greenhouse, and one outdoors. Water supply was managed in such a way that predawn leaf water potential and day‐time leaf relative water content (RWC) were maintained at constant values during deficit periods of 20 to 68 d. This was achieved by growing plants either in soil columns with irrigation controlled by tensiometers, or in vermiculite, on top of foam columns with a controlled level of water inside the foam. Leaf appearance rate (LAR) and leaf initiation rate remained constant with time at a given RWC, but decreased with decreases in RWC. A reduction in individual leaf area (LA) was observed in all leaves which experienced water deficit during part of the expansion period. Stolon branching decreased considerably with relatively mild deficits. Similar relationships between relative reductions in RWC (compared with control plants), and relative reductions in LA, LAR and stolon number were observed in all experiments. Short deficits (1–2 wk) caused a 20 to 30% reduction in stolon number and individual LA but no change in leaf number per stolon. Longer deficits with mild, intermediate, or severe intensities caused major reductions in stolon number, individual leaf area, and number of leaves per stolon, respectively, with respect to the reduction in plant leaf area. In addition to individual leaf area, phytomer production and stolon branching make major contributions to drought‐induced reductions in leaf area depending upon the type of water deficit.
Bermudagrass Carbohydrate Levels as Influenced by Potassium Fertilization and Cultivar
Authors: Miller Grady L. , Dickens Ray
Published: July 2010

Stored nonstructural carbohydrates are a primary source of reserve energy in vegetative organs of warm‐season grasses. Research is needed concerning the influence of potassium on carbohydrate levels in turfgrasses. Four K rates ranging from 24 to 390 kg ha−1 per growing month were applied twice monthly from 1992 to 1994 to ‘Tifdwarf’ and ‘Tifway’ bermudagrasses [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt Davy] field grown on Uchee loamy sand (loamy, siliceous, thermic Arenic Hapluduit) and sand‐peat (9:1 by volume) dium. Root + rhizome and shoot + stolon samples were evaluated monthly for total non‐structural carbohydrate (TNC) concentrations by means of near infrared reflectance spectroscopy. TNC concentrations varied among cultivars, plant parts, and time of year. Tifdwarf produced 30% greater root + rhizome TNC concentration and 55% greater shoot + stolon concentration than Tifway. Higher K rates either did not influence or reduced root + rhizome TNC concentrations compared to low K rates. Correlation analysis indicated that root + rhizome yields and TNC concentrations were negatively influenced by temperature. Carbohydrate and root + rhizome yield responses suggesthere is no benefit to applying K at rates beyond those that provide sufficient K levels for normal growth.
Genetic Mapping of Quantitative Trait Loci in Maize in Stress and Nonstress Environments: I. Grain Yield and Yield Components
Authors: Veldboom Lance R. , Lee Michael
Published: July 2010

The utility of restriction fragment length polymorphisms (RFLPs) in detecting quantitative trait loci (QTL) in maize (Zea mays L.) populations has been established. Conflicting results have been reported on the ability to consistently detect the same QTL across environments. Grain yield is considered to be highly polygenic and strongly influenced by the environment. QTL mapping studies conducted in contrasting environments might increase our understanding genotype × environment interactions and improve selection response in maize breeding. Our objectives were to compare the QTL for grain yield and yield components detected in two diverse environments in an elite, adapted maize population and to investigate the relationship among the genetic factors controlling these traits. A population of 150 F2:3 lines was produced from the cross of elite inbreds Mo17 and H99. The lines per se were evaluated for 2 yr at the same location. The first year had relatively average growing conditions, but the second year with cool, wet growing conditions provided a stress environment. Grain yield and yield components were measured on replicated progeny each year. By using a linkage map of 111 loci, QTL determinations were made in the two environments and in the mean of the two environments. About 50% of all QTL detected across environments were detected in both enviromnents. These QTL were consistent in the magnitude of their effects and parental contribution. Determinations of QTL in the mean of the two environments were most informative in that 74% of all QTL and 82% of the QTL detected in each of the individual environments were identified in the mean environment. Most QTL identified regions associated with two or more yield components in a manner consistent with correlations among traits and parents phenotypes.
Genetic Mapping of Agronomic Traits Using Recombinant Inbred Lines of Soybean
Authors: Mansur L. M. , Orf J. H. , Chase K. , Jarvik T. , Cregan P. B. , Lark K. G.
Published: July 2010

Many agronomic traits of interest to plant breeders are quantitative. Recombinant inbred (RI) lines are particularly useful in genetic mapping studies of quantitative traits. A recombinant inbred population was derived from the Glycine max (L.) Merr. parents ‘Minsoy’ and ‘Noir 1’. This soybean population was used to investigate the genetic basis of several agronomic traits: days to flower (Rl), days to maturity (R8), reproductive period (RS‐R1), plant height, lodging score, height divided by lodging (the ability of tall plants to stand upright), seed protein content, seed oil content, seed size, yield, seed number, yield divided by height (the yield from short plants), leaf width, leaf length, and leaf area. In this RI population, transgressive segregation was observed for all of these traits. As expected, height and lodging were correlated, as were height and maturity; height and maturity with yield; and leaf length and width with leaf area. Height divided by lodging and yield divided by height showed little correlation with other traits, indicating that these traits measured new plant phenotypes. A genetic map was constructed for this population, with restriction fragment length polymorphism markers, simple sequence repeat markers and classical markers. Approximately 2000 cM of linkage was defined. The data were used to identify quantitative trait loci (QTLs) by linking quantitative phenotypes to qualitative genetic markers. for many traits, a few QTLs accounted for a large proportion of the variation observed. QTLs for most of the traits were associated with three linkage groups, often with the same genetic locus within the linkage group. At the level of resolution of the genetic map for this population, it was not possible to determine whether these QTLs have pleiotrophic effects or are clusters of separate, tightly linked genes. The data suggest that separation of QTLs for different traits (such as maturity or lodging and yield) may be difficult, but that this RI population will be useful in resolving questions concerning marker assisted selection of quantitative traits.
Meloidogyne arenaria Development in Three Clover Populations
Authors: Call N. M. , Quesenberry K. H. , Dunn R. A.
Published: July 2010

Root‐knot nematodes (RKN; Meloidogyne spp.) limit productivity of red clover (Trifolium pratense L.) in southeastern USA. Root‐knot nematodes damage root systems affecting water and nutrient uptake and predispose plants to other soil‐borne pathogens. Penetration and development of M. arenaria (Neal) Chitwood Race 1 on three clover populations differing in resistance levels were evaluated in two greenhouse experiments conducted in two years (1993 to 1995). The RKN susceptible cultivar Kenstar red clover, a red clover breeding selection designated FLMR6 with moderate RKN resistance, and a highly RKN resistant species T. stoioniferum Muhlenberg, running buffalo clover (RBC), were grown in Cone‐tainers (Stuewe and Sons, Inc., Corvallis, OR) and inoculated with 450 M. arenaria Race 1 second‐stage juveniles (J2) 21 after se ed germination. Numbers of J2, J3‐J 4 (thi rd‐stage or fourth‐stage juvenile nematodes), and adults at 1, 2, 4, 8, 16, 24, 36, 48, 60, 80 (Exp. 2), and 120 (Exp. days aft er inoculation (DAI) were measured. Fecundity was characterized by counting number of egg masses and total number of eggs per plant at 80 and 120 DAI. Kenstar had more J2 in roots at 4, 36, 48, 60, 80, and 120 DAI than FLMR6 or RBC. At 48 DAI, more J3‐J4 were found in Kenstar than in FLMR6 or RBC. Fewer adults were found in FLMR6 and RBC than in Kenstar at 36, 48, 60, 80, and 120 DAI. At 120 DAI, adult numbers in FLMR6 and RBC were 2.4 and 0.2%, respectively, of the number in Kenstar. Number of egg masses and total number of eggs per plant on Kenstar were greater than on FLMR6 and RBC. The reduced fecundity of M. arenaria on the FLMR6 red clover breeding selection suggests this population should be evaluated for use in rotations with RKN susceptible crops.
Eliminating Duplicates in Germplasm Collections: A White Clover Example
Authors: Greene S. L. , Pederson G. A.
Published: July 2010

One area that is often given low priority in the management of many germplasm collections is the elimination of duplicate and genetically redundant accessions. The purpose of this communication is to (i) describe a simple and effective procedure used in the National Plant Germplasm System white clover (Trifolium repens L.) collection for identifying and eliminating duplicate cultivar accessions, and (ii) discuss the potential gain in management efficiency that results from eliminating duplicates. The Germplasm Resources Information Network and plant inventory books were reviewed to ensure accessions were properly identified and to detect suspected duplicates. Additional historical documentation (plant introduction station card catalogs, acquisition logs, correspondence, and reports) were reviewed to characterize suspect duplicate accessions. Morphological data was obtained to supplement historical information. The white clover collection had 42 cultivars that occurred more than once in the collection, involving 133 of 626 accessions. Based on our review, 35 accessions were retained with no change, 39 accessions were bulked into 16 new accessions, and 59 accessions were designated as inactive, resulting in a net reduction of 82 accessions (13% of total collection). This results in savings of $41 000 ($500 cage−1) in regeneration costs alone. Eliminating duplicates is an effective method of reducing germplasm maintenance costs without losing valuable genetic resources.
Leaching and Mass Balance of 15N‐Labeled Urea Applied to a Kentucky Bluegrass Turf
Authors: Miltner E. D. , Branham B. E. , Paul E. A. , Rieke P. E.
Published: July 2010

The fate of urea applied to Kentucky bluegrass (Poa pratensis L.) turf was studied over a 2‐yr period using a combination of intact monolith lysimeters and small plots. Soil type was a Marlette fine sandy loam (fine‐loamy, mixed mesic Glossoboric Hapludalfs). Urea was applied at a rate of 196 kg N ha−1 yr−1 in five equal applications of 39.2 kg N ha−1, using two application schedules. Treatments were fertilized at approximately 38‐d intervals with the “Spring” treatment fertilized from late April through late September and the “Fall” treatment from early June through early November. In 1991 only, the April and November applications used 15N‐labeled urea (LFN). For the Spring treatment, 31% of LFN was recovered from thatch at 18 DAT. This value remained constant for the next year, then gradually declined to 20% after 2 yr. Only 8% of the LFN was recovered from soil at 18 DAT and increased to only 20% 2 yr after application. Approximately 35% of the LFN was harvested in clippings over 2 yr. Through May 1993 (748 DAT), LFN in leachate totaled 0.18% of the amount applied. For the Fall treatment, 62% of the LFN was recovered from thatch at 18 DAT. This value declined to 35% by the following June. LFN in soil increased from 12% to25% over 2 yr. Approximately 38% of the LFN was harvested in clippings over 2 yr. Total leachate LFN recovery was 0.23% over the 2‐yr period. Total recovery of LFN was 64 and 81% for the Spring and Fall treatments, respectively, suggesting volatile losses of N. Whether the N was applied in the spring or late fall, rapid uptake and immobilization of the LFN resulted. A maximum of 25% of applied LFN was recovered in the soil from either application timing at any time over the 2 yr of the experiment. A well‐maintained turf intercepts and immobilizes LFN quickly making leaching an unlikely avenue of N loss from a turf system.
Association of Elevated Palmitate Content with Agronomic and Seed Traits of Soybean
Authors: Hartmann Richard B. , Fehr Walter R. , Welke Grace A. , Hammond Earl G. , Duvick Daniel N. , Cianzio Silvia R.
Published: July 2010

Soybean [Glycine max (L.) Merr.] genotypes with elevated palmitate content in the seed oil have been developed for food and industrial applications. The objective of the study was to determine the association of elevated palmitate with agronomic and seed traits of soybean. Two high‐yielding cultivars with normal palmitate content of ≈110 g kg−1 were crossed to lines with the genotype fap2‐b fap2‐b fap4 fap4 that had an elevated palmitate content of ≈250 g kg−1. From each of the two segregating populations, 27 F3‐derived lines with elevated palmitate content and 27 with normal palmitate content were selected for replicated testing at two locations in Iowa in 1993 and 1994. The elevated palmitate lines had significantly reduced yield; later maturity; reduced lodging; elevated height; reduced seed weight, protein, oil, stearate, oleate, and linoleate; and elevated palmitate and linoleate than the normal‐palmitate lines. The magnitude of the negative association between elevated palmitate and seed yield was different between the crosses, which indicated that multiple high‐yielding parents with normal palmitate should be considered for developing cultivars with the fap2‐b fap2‐b fap4 fap4 genotype. The distributions for oil content of the elevated‐ and normal‐palmitate lines did not overlap; therefore, the oil content of cultivars with elevated palmitate is likely to be less than that of normal cultivars. The magnitude of the differences between the elevated‐ and normal‐palmitate lines for the other characteristics was not sufficient to preclude the development of acceptable cultivars with the fap2‐b fap2‐b fap4 fap4 genotype.
Brown Patch Severity in Perennial Ryegrass as Influenced by Irrigation, Fungicide, and Fertilizers
Authors: Fidanza Michael A. , Dernoeden Peter H.
Published: July 2010

Brown patch (Rhizoctonia solani Kühn) is a common and destructive disease of turfgrasses, but little information is available regarding its management by cultural practices. This 2‐yr field study assessed the influence of irrigation, and N source alone or in combination with P and K on brown patch severity. Perennial ryegrass (Lolium perenne L. cv. ‘Caravelle’) was subjected to either morning or evening irrigation. Sodium nitrate, a quickly available non‐soil reacting N source, was compared with sulfur‐coated urea (SCU), a slowly available soil acidifying N source. Fertilizer treatments were applied three (May‐September‐October) and six (March‐May‐June‐September‐October‐November) times annually, representing lower and higher N application rates, respectively. Forty‐nine kilograms N per hectare were applied on each date for a total of 147 and 294 kg N ha−1 yr−1. Plots were split with one‐half treated with iprodione [3‐(3,5‐ dichlorophenyl)‐IRN‐( 1‐methylethyl)‐2,4‐dioxo‐1‐imidazolidine‐carboxamide)](3.1 kg ai ha−1) on an extended 21‐d interval. In nonfungicide‐treated plots, brown patch severity was consistently reduced with morning irrigation when compared with evening‐irrigation. Non‐fungicide‐treated plots fertilized with SCU generally had lower blight levels than NaNO3‐treated plots, regardless of N rate. In the second year, brown patch was more severe in plots treated with the high N rate, and P (72 kg ha−1 yr−1) and K (150 kg ha−1 yr−1) reduced blight for both N‐sources in non‐fungicide‐treated plots. Sulfur‐coated urea applied at the high N rate plus P and K resulted in blight levels equivalent to or less than low N. Fungicide‐treated plots receiving the high rate of N from SCU plus P and K had the highest summer quality in both years. While low soil pH was weekly correlated (r = 0.352) with less blight, the slow N release characteristics of SCU were probably a more important factor in disease reduction than soil acidification. While brown patch severity was reduced by morning irrigation, SCU + P + K, and iprodione, an excellent level of summer turfgrass quality was not achieved using the extended fungicide application interval.
Variance Effective Population Size for Two‐Stage Sampling of Monoecious Species
Authors: Crossa José , Vencovsky Roland
Published: July 2010

During the process of collecting, storing, and regenerating germplasm, random changes in allele frequency due to sampling (genetic drift) occurs and affect the genetic representativeness of the population. Drift is quantified and predicted through the variance effective population size, Ne(v). When sampling a population, drift may occur at two stages: (i) when parents are sampled (selected) for reproduction (ii) when gametes (offspring) are subsequently sampled from these parents. Hence, Ne(v) measures should include drift due to sampling of zygotes, relative to the original population, and that due to gametic sampling, relative to the set of parents. In this paper, the variance of the number of contributed gametes, Vk and Ne(v) were derived, under a two‐stage sampling scheme for monoecious species. An alternative derivation, solely based on the theory of random sampling within finite populations, is also given for comparison with the previous result. Practical procedures involving full‐sibs (FS), half‐sibs (HS), and half‐sibs stemming from a restricted set of parents (HS') for decreasing Vk, or increasing Ne(v), for field collection of germplasm and accession regeneration are described. For germplasm collection, results showed the advantage of the HS scheme over a wide range of situations. In the HS system, collectors should take, from a random set of plants, an equal number of seeds from as many seed parents as possible. When the number of seed parent plants is small compared with the total number of plants, the FS system is always better than the HS'scheme. When the reference population is a germplasm accession, the FS is clearly superior to the HS and HS' alternatives. Under the proposed model, measures of Ne(v) require clear definition of (i) the reference population and the proportion of effective parents, (ii) the mating scheme, (iii) the number of parents and offspring sampled, and (iv) the level of female and male gametic control. The combination of these factors will determine the final Ne(v) value.
Yield Potential Progress in Short Bread Wheats in Northwest Mexico
Authors: Sayre K. D. , Rajaram S. , Fischer R. A.
Published: July 2010

Germplasm from the spring wheat (Triticum aestivum L.) breeding program at the International Center for Improvement of Maize and Wheat (CIMMYT) has had a major impact on the yield of irrigated spring wheats in most developing countries in the past 30 yr. The rate and nature of yield potential progress in this germplasm was measured comparing eight outstanding short cultivars released in northwest Mexico between 1962 and 1988. They were grown under irrigation and optimal management, including disease and lodging protection, in each of six winter growing seasons (1989–1990 to 1994–1995) at the CIANO (Centro de Investigaciones Agricolas del Noroeste) experiment station in Sonora, Mexico. There were highly significant effects of cultivar on grain yield, and, although cultivar × year interaction was significant, there were few significant crossover interactions between pairs of genotypes and years in the grain yield data set. Yield averaged across the 6 yr increased linearly from 6680 kg ha−1 for the earliest cultivar, Pitic 62, to 8475 kg ha−1 for Bacanora 88, the latest. The rate of progress against year of release was 67 kg ha−1 yr−1 (r = 0.99, P < 0.001), or 0.88% per year. Grain yield progress was correlated with kernel number per square meter (r = 0.84, P < 0.01) and harvest index (r = 0.81, P < 0.02), but not with total biomass production, kernel weight, days to anthesis, spikes per square meter, or kernels per spike. Thus linear progress in yield within short germplasm has continued at least until the late 1980s, and the yield components studied did not indicate any clear direction for future progress, apart from that suggested by the strong relationships between grain yield and harvest index and grain yield and kernels per square meter, as has been seen in most studies of yield progress in cereals.
Disease Reaction Changes from Tandem Selection for Multiple Disease Resistance in Two Maize Synthetics
Authors: Lambert R. J. , White D. G.
Published: July 2010

Future maize (Zea mays L.) productivity increases require breeding materials with high grain yield potential and multiple disease resistance. As part of an integrated program to develop breeding populations with high grain yield potential and multiple disease resistance, two maize synthetics were reciprocally recurrently selected for yield and mass selected for multiple disease resistance. The objective of this study was to determine selection response of two maize synthetics to six cycles of tandem selection for multiple leaf diseases (MLD) and multiple stalk rots (MSR). Plants were inoculated each cycle and evaluated for MLD including their causal agents; northern corn leaf blight, (NCLB) [Exserohilum turcicum (Pass.) Leonard and Suggs, Races 0 and 1], southern corn leaf blight (SCLB) [Bipolaris maydis (Nisik) Shoem.], northern corn leaf spot (NCLS) [Bipolaris zeicola (Stout) Shoem. Races 1, 2, and 3], anthracnose leaf blight [Colletrotrichum graminicola (CES) G. W. Wils.], and eyespot (Kabatiella zeae Narita and Hiratsuka). Following anthesis, plants were inoculated and evaluated for resistance to MSR including their causal agents; diplodia stalk rot (DSR) [Stenocarpella maydis (BERK) Sutton = syn. Diploidia maydis (BERK)], anthracnose stalk rot (ASR) (Colletotrichum graminicola), gibberella stalk rot (GSR) [Gibberella zeae (Shw.) Petch.], and fusarium stalk rot [Fusarium moniloforme, Shield]. In 1993 and 1994, selection cycles 0, 2, 4, and 6 of synthetics RSSSC, RBS10, and their cycle crosses were evaluated. Selection response to MLD, NCLB, SCLB, NCLS, gray leaf spot (GLS; Cercospora zeae‐maydis Tehon and Daniels), MSR, DSR, GSR, and ASR were measured in separate experiments. Decreases in leaf blight severity from Co to C6 in RSSSC was 29% for MLD, 23% for NCLB, 33% for SCLB, 28% for NCLS, and 21% for GLS. Decreases for RBS10 were 34% for MLD, 33% for NCLB, 37% for SCLB, 49% for NCLS, and 16% for GLS. Cycle crosses were usually intermediate in values for leaf blight reductions. For stalk rots, the reduction in percentage internode area discolored from C0 to C6 for RSSSC was 44% for MSR, 42% for DSR, 39% for GSR, and 18% for ASR. Reductions for RBS10 were 63% for MSR, 67% for DSR, 64% for GSR, and 63% for ASR. Selection for multiple disease resistance along with a reciprocal recurrent program for yield resulted in significant improvement in resistance to multiple and individual diseases in RSSSC, RBS10, and their crosses.
Yield Stability of Hybrid vs. Pureline Hard Winter Wheats in Regional Performance Trials
Authors: Peterson C. J. , Moffatt J. M. , Erickson J. R.
Published: July 2010

Hybrid hard winter wheats (Triticum aestivum L.) have shown superior grain yield potential in regional performance trials during the last decade. Evidence for enhanced yield stability, combined with enhanced yield potential, would facilitate wider acceptance of hybrid wheat by growers. Hybrid and pureline yield stability and environmental responsiveness were compared with the use of data from the Southern Regional Performance Nursery (SRPN), 1990 through 1995, and Agripro Standard Variety Trial (SVT), 1993 and 1994. Hybrid and pureline yields were regressed on an environmental index based on location mean yields for purelines, and response slope and deviations were calculated. Analyses were conducted separately for each nursery, as hybrid and pureline entries varied. Hybrids showed significantly higher mean yields compared with purelines and the yield advantage generally increased with increasing environmental yield potential. Average regression slope for hybrids was significantly higher (1.09–1.12) than for purelines (1.0) in the 1994 and 1995 SRPN and 1993 and 1994 SVT. Hybrid slopes were not significantly different from those for purelines in the 1990 through 1993 SRPN, where they ranged from 1.0 to 1.07. There was no crossover in yield response between hybrids and purelines at lower yield levels. Deviations from regression were of similar magnitude for hybrids and purelines. Confidence intervals for hybrid and pureline regressions generally overlapped throughout the observed yield ranges in the SRPN. In the 1993 and 1994 SVT, hybrid and pureline confidence intervals diverged as environmental yield potential increased. Compared with pureline cultivars, hybrid wheats have potential for enhanced mean yield and greater yield response to favorable environmental conditions with similar deviations from expected response.
Correlation between Molecular Marker Distance and Hybrid Performance in U.S. Southern Long Grain Rice
Authors: Maroof M. A. Saghai , Yang G. P. , Zhang Qifa , Gravois K. A.
Published: July 2010

Improving grain and milling yields of long‐grain rice (Oryza sativa L.) continues to be a major objective of southern U.S. breeding programs. The objective of this study was to determine the relationship between molecular marker polymorphism of the parents and performance of the F1 hybrids. A diallei cross was made by intermating eight lines commonly used in U.S. southern long‐grain rice breeding programs. The 28 F1 hybrids and the parents were evaluated for rough rice yield, head rice percentage, and head rice yield in replicated field trials. Very little heterosis was detected among hybrids for head rice percentage, whereas heterosis was high for rough rice yield and head rice yield. A survey for DNA polymorphisms with 82 RFLPs and 26 microsatellites revealed high levels of variation among the eight parents. A cluster analysis resolved these eight lines into indica (one line) and tropical japonica (seven lines) rice subgroups. A majority of the markers detected statistically significant effects on one or more traits by an analysis of variance. Marker F1 heterozygosity was highly correlated with rough rice yield (0.79**) and head rice yield (0.82**), and was also significantly correlated with heterosis of these two traits (0.47*, 0.58**, respectively). However, the correlations were largely attributed to the concurrence between high levels of heterozygosity and high performance in crosses between the indica variety Jasmine 85 and the remaining seven lines. Compared with the data published in previous studies, it was concluded that the level of correlations between marker distance and hybrid performance is dependent on the germplasm used.
Winter Rye Leaf Emergence and its Relationship to the Phyllochron
Authors: Gan Y. , McLeod J. G.
Published: July 2010

Winter rye (Secale cereale L.) is a high‐tillering cereal crop. Understanding the relationship between the phyllochron for mainstem leaves and that of tillers is useful in adequately describing plant development and selecting crop management strategies. This study was conducted to determine the phyllochrons of conventional height (CH) and semidwarf (SD) genotypes of winter rye and the relationship of the phyllochron of mainstem leaves to that of primary tillers. Three CH and two SD genotypes were planted in a controlled‐environment growth room. Leaf stages were determined with the Haun scale and the phyllochron calculated as the inverse of the slopes of linear regressions of Haun stage to growing degree‐days (GDD). For both CH and SD genotypes, the Haun stage increased linearly with GDD, and the phyllochron was constant in the pre‐vernalization (0 < GDD ≤ 266) and vernalization (266 < GDD ≤ 566) periods. During post‐ vernalization (566 < GDD ≤ 914), the phyllochron for the mainstem increased with GDD. Leaves on the coleoptile tiller (TO), T1 (the tiller from leaf no. 1 of the mainstem), and T2 had mean phyllochrons similar to that for the mainstem. Leaves on higher positioned tillers (T4, T5) had greater phyllochron than the earlier tillers. The higher positioned tillers also required more thermal time units to emerge than the earlier tillers. To precisely describe winter rye development using the phyllochron, one should consider that the phyllochron changes with leaf and tiller position on the culm.