bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Water Deficit during Grain Filling on the Pattern of Maize Kernel Growth and Development1
Authors: Ouattar S. , Jones R. J. , Crookston R. K.
Published: July 2010

There are distinct phases of grain development in maize (Zea mays L.). Little has been reported on the relative effects of water deficits during the different phases of maize kernel development. Since endosperm cell number is important in determining sink capacity or strength, a water deficit during the lag phase may affect kernel development differently than one during the linear phase dominated by starch deposition. The objective of this research was to determine the effect of short‐ and long‐term water deficit, imposed during different phases of grain filling, on the pattern of maize kernel growth. We conducted two separate experiments. In the first, a short‐term (10 day) water deficit was imposed during endosperm cell division (the lag phase) or during the period of rapid starch deposition (the linear‐filling phase). In the second, a water deficit was initiated during the same phases, but extended until maturity. Plants were grown outdoors in Rabat, Morocco, in large pots arranged to achieve a stand density of 50 000 plants/ha. Short‐term water deficit during the lag phase resulted in a significant but transient delay in the accumulation of kernel dry mass. However, recovery from this delay was such that overall rate and duration of kernel growth were not affected. Similarly, short‐term water deficit during the linear‐filling phase had no effect on the rate or duration of kernel growth. When the long‐term water deficit treatment was initiated during the lag phase, kernel growth rate was not affected for approximately 24 days. Grain filling then terminated prematurely, resulting in a significant decrease in the duration of the grain‐filling period, and a 50% decrease in final kernel weight. When long‐term stress was imposed during the linear‐filling phase, kernel growth was not affected for 20 days, but then terminated abruptly, resulting in an 8‐day decrease in the grain‐filling period. Final kernel weight was not significantly decreased, however. Our results show that kernel growth is more sensitive to water deficits during endosperm cell division than during the period of rapid starch deposition. The higher sensitivity to water deficits during the lag phase was not a consequence of either a lack of carbohydrate availability to the grain, or an inhibition of starch synthesis, but was apparently due to an inhibition of endosperm cell division and the subsequent establishment of kernel sink capacity.
Effect of Drought on Water Relations of Developing Maize Kernels1
Authors: Ouattar S. , Jones R. J. , Crookston R. K. , Kajeiou M.
Published: July 2010

Although considerable information exists concerning the effect of drought on the water relations of maize (Zea mays L.) leaves, little has been published about the water relations of maize grain, or on how the process of grain filling is affected by a limited water supply. We had previously observed that the maize plant sustained normal rates of kernel growth for long periods in spite of severe water deficit during grain filling. The objective of this study was to investigate the nature of that response. Plants were grown outdoors in Rabat, Morocco, in large pots. Severe water deficit was imposed during either early or mid grain filling, and was maintained until maturity in each case. Grain water status (water potential, osmotic potential, and turgor pressure) was independent of whole‐plant water status, particularly leaf status. Photosynthesis decreased as judged by leaf water potential, diffusive resistance, leaf senescence, and total plant dry weight. Kernel growth was relatively unaffected by a water deficit that completely inhibited net photosynthate production. Kernel growth was maintained by a remobilization of stored assimilates from nongrain parts to the grain. The main source of assimilates was the stem as judged by dry weight loss and soluble sugar content. The maintenance of a high stalk moisture content in spite of severe leaf dehydration may have facilitated translocation from the stalk to the grain.
Carbon Dioxide Exchange and Total Nonstructural Carbohydrate in Soft White Winter Wheat Cultivars and Snow Mold Resistant Introductions1
Authors: Kiyomoto Richard K.
Published: July 2010

Experiments were conducted to investigate the relationship between snow mold resistance in winter wheat (Triticum aestivum L.) and levels of total nonstructural carbohydrates (TNC) in tissues and to test the hypothesis that TNC concentrations and resistance could be explained by increased photosynthesis or slower respiration. As a group, snow mold resistant introductions depleted TNC from tissues at a slower rate than susceptible or locally adapted soft white winter wheat cultivars. Leaves lost the greatest proportion of TNC during 20 days in darkness, whereas stem and crown TNC first declined rapidly and then declined slowly after 10 days. The pattern of TNC depletion was similar in all accessions, thus TNC translocation between tissues may play a role in resistance only when concentrations become low, and does not support the idea that TNC translocation is linked to early expression of leaf senescence observed in snow mold resistant introductions. Photosynthesis was measured on plant canopies and leaves in the tillering stage, and on flag leaves during anthesis. In all cases the cultivars as a group had the highest net photosynthesis with the exception of snow mold resistant introduction PI 181268, which ranked high for net photosynthesis in all experiments. Respiration of leaves in the dark showed a significant correlation (r = ‐0.71) with snow mold resistance. The correlation was negative because greater resistance was assigned a lower numerical score. Thus, the high TNC of snow mold resistant tissues cannot be attributed to slower dark respiration of leaf tissue. The selection pressures that gave rise to snow mold resistant plants have altered their TNC metabolism during overwintering, but the mechanism was not explained by changes in CO2 exchange of leaf tissue.
Nitrogen Transfer from Forage Legumes to Grass in a Systematic Planting Design1
Authors: Brophy Laura S. , Heichel G. H. , Russelle M. P.
Published: July 2010

Alfalfa (Medicago sativa L.) is the most important forage legume in the USA, but N transfer from this or other perennial forage species to companion grasses growing in a mixed sward is poorly understood. Furthermore, interplant distances and legume/grass ratios have seldom been controlled in studies of N transfer from legumes to non‐legumes. The objectives of this field study were: (i) to determine the amount of N transferred from alfalfa and birdsfoot trefoil (Lotus corniculatus L.) to reed canarygrass (Phalaris arundinacea L.); (ii) to define conditions of distance and species ratio under which N transfer occurs; (iii) to compare the two legumes for N transfer; and (iv) to determine the effect of grass proximity on legume N2 fixation. Legumes were interplanted with grass in single‐species rows within 1‐m2 plots on a Typic Hapludoll soil labeled with 15N. Analysis of herbage showed significantly lower 15N concentration in grass near legumes than in grass grown alone, and significantly lower 15N concentration in legumes near grass than legumes in monoculture. Calculations using isotope dilution methods showed that grass derived a maximum of 68% of its N from alfalfa and 79% from trefoil. This N represented 13% of the N2 fixed by trefoil and 17% of that fixed by alfalfa. The results indicated that N transfer occurred over a distance of 20 cm with maximum N transfer in areas of high legume/grass ratio. At third harvest, N derived from symbiosis was significantly higher (95% in alfalfa, 92% in trefoil) for legumes grown in mixture with grass than for legumes grown in monoculture (86% in alfalfa, 80% in trefoil). These results indicate that significant N transfer occurred, and that the amount of N transferred was dependent on interspecies distance and legume/grass ratio.
A Hybrid Seed Production Method Based on Synthesis of Novel Linkages between Marker and Male‐Sterile Genes1
Authors: Jorgensen Richard A.
Published: July 2010

Mendelian male‐sterile genes are rarely used in hybrid seed production because pure stands of male‐sterile plants are difficult to obtain. We describe here a general method for hybrid seed production whereby linkage is synthesized between a male‐sterile gene and a marker gene through genetic transformation. Such linkage permits the production of nearly pure stands of male‐sterile plants. The method should be applicable in any plant species in which markers can be introduced into approximately random genomic locations. It is shown that the Agrobacterium transformation system can be used to synthesize tight, novel linkages between markers and male‐sterile genes in tomato (Lycopersicon esculentum Mill.). In addition, a marker gene is identified that is potentially suitable for use in the proposed hybrid production system in several crops. This marker, IaaH, determines a dominant chemical sensitivity phenotype which, if linked in coupling phase with a male‐sterile gene, should allow chemical removal of fertiles from a population segregating for male sterility/fertility and chemical resistance/sensitivity.
Allelic and Nonallelic Interactions of af, st, and tlw Genes in Pea1
Authors: Cardi T. , Frusciante L. , Monti L. M.
Published: July 2010

Interaction effects between alleles at one locus with other loci and with environments influence degrees of dominance and F1 hybrid performance. To evaluate the effect of interactions among alleles, eight near‐isogenic lines of pea (Pisum sativum L.) with the eight combinations of genes at the af, st, and tlw loci were self‐fertilized and intercrossed in a half‐diallel design. Plants were grown at Portici, Italy, in a randomized complete block design with three replications; results were compared with a similar experiment at Norwich, UK. The af gene was partially dominant for number of fertile nodes, number of pods and seeds, and yield per plant. The three genotypes ranked in order: AfAf > Afaf > afar for each of these traits. The st gene was partially dominant for stipule weight, but Stst heterozygotes exceeded both the homozygous StSt and stst genotypes in both yield and yield components. The recessive homozygotes were the least productive genotypes for all but one character. The tlw gene affected only leaf weight and number of basal branches, and showed overdominance for the latter trait. Since heterozygotes are morphologically very similar to dominant homozygotes, the mutant alleles studied can show pleiotropic effects also when the leaf phenotype does not vary or it varies slightly. Allelic interactions at one locus were influenced by the allelic state of the other two loci for number of fertile nodes and pods per plant, node of first flower, leaf weight, and number of pods at the first flowering node. The degree of dominance at the Af and St loci for plant yield varied with environment.
Identification of Single Genes Controlling Resistance to Stem Canker in Soybean1
Authors: Kilen T. C. , Hartwig E. E.
Published: July 2010

Stem canker [caused by Diaporthe phaseolorum (Cke, & Ell.) Sacc. var. caulivora Athow & Cald.] is a serious disease of soybean [Glycine max (L.) Merr.] in many areas of the USA. Two major dominant alleles for resistance have been found in ‘Tracy‐M’, each of which conditions complete resistance. However, soybean lines possessing one or the other dominant allele in the homozygous state have not been identified. This has impeded progress in identifying and using other sources of resistance. The objective of this study was to identify lines having one or the other pair of dominant alleles for resistance in Tracy‐M. Crosses were made between Tracy‐M and a very susceptible breeding line, J77‐339. Two selections from that cross were identified as being dominant homozygous for one or the other locus. These were crossed with each other and crossed with J77‐339. Disease reactions in the field and greenhouse confirmed that the two selections possessed homozygous resistance alleles at different loci. The gene symbols Rdc1 and Rdc2 have been assigned.
Independent Inheritance of Genes Conditioning Resistance to Phytophthora Root Rot from Diploid and Tetraploid Alfalfa1
Authors: Havey M. J. , Maxwell D. P. , Irwin J. A. G.
Published: July 2010

Phytophthora root rot, caused by Phytophthora megasperma Drechs. f. sp. medicaginis Kuan and Erwin (Pmm), is a major cause of decline of established alfalfa (Medicago sativa L.). Three different inheritance modes for resistance to Pmm have been proposed and independently inherited resistances could be combined into a single alfalfa population. The objective of this study was to determine if genetic factors conditioning resistance to Pmm from diploid (2n = 2x = 16) and tetraploid (2n = 4x = 32) alfalfa are independently inherited. Resistance to Pmm was transferred from the 4x alfalfa plant M193 to the 2x level by use of triploid‐bridge crosses, and the inheritance of resistance in the derived diploids DDR‐850, DDR‐ 1049, DDR‐ 1051, and DDR‐1070 was studied. Each derived diploid was crossed as the female and male parent with susceptible 2x plants. Progeny were grown in the greenhouse in pots containing a peat:sand mix and inoculated at 8 weeks with a chopped mycelial suspension of Pmm. Resistance in DDR‐850 and DDR‐1049 was conditioned by a dominant allele at both of two independently segregating complementary loci, Pm1 and Pm2. Resistance in DDR‐1051 and DDR‐1070 was conditioned by a dominant allele at either of two independently segregating loci, Pm5 and Pm6. Plants DDR‐850 and DDR‐1051 were each crossed as the female parent with each of five 2x Medicago falcata L. plants resistant to Pmm. Testcross segregations revealed that the Pm3 and Pm4 loci from M. falcata are inherited independently of at least one and maybe both of the Pml and Pm2 loci from DDR‐850 and independently of at least one and maybe both of the Pm5 and Pm6 loci from DDR‐1051. This paper is the first known example of successful transfer of disease resistance from 4x to 2x alfalfa, combination of genes conditioning disease resistance from diverse sources, and completion of inheritance studies at the 2x level.
Seasonal Variation in Leaf Hydrocyanic Acid Potential of Low‐ and High‐Dhurrin Sorghums1
Authors: Haskins F. A. , Gorz H. J. , Johnson B. E.
Published: July 2010

The KS8 and N32 sorghum [Sorghum bicolor (L.) Moench] lines are low and high, respectively, in the hydrocyanic acid potential (HCN‐p) of mature leaves. Thisd difference is conditioned primarily by a single pair of alleles. The main objective of his study was to determine, at various staes of plant growth and various times during the growing season, the HCN‐p of upper leaves and tillers of field‐grown plants of these two parental lines and of two low‐HCN‐p F3 lines derived from crosses between KS8 and N32. The four entries were grown in a randomized complete block design with three replications in 1985. Samples of leaf tissue were dried, ground, and extracted, and cyanide in the extracts was assayed colorimetrically. Using a mean HCN‐p level of 500 mg kg−1 dry wt to separate safe from unsafe sorghum forage, all samples of KS8 mature leaves and tillers would be considered safe, and all N32 samples would be considred potentially dangerous. Values for most of the samples of the F3 lines fell within the safe range, but some samples of young regrowth exceeded the 500 mg kg−1 limit. Regressions of HCN‐p on height for upper leaves of main stems and of tillers indicated a significant negative relationship for all entries except for leaves from the amin stems of KS8. However, the relationship was not close enough to support the use of plant or tiller height as a reliable indicator of HCN‐p. Levels of HCN‐p also were determined for mature leaves and young regrowth of hybrids involving KS8, N32, and ‘Redlan’ sorghums as seed parents and NP25, ‘Piper’, and ‘Greenleaf’ sudangrasses [S. sudanense (Piper) Stapf] as pollinators. Results indicated that for minimizing the risk of cyanide poisoning, KS8 would be the seed parent of choice, and NP25 and Piper would be the preferred pollinators.
Genetic Variation for Rate of Cell Wall Digestion and Related Traits in First Cut Smooth Bromegrass1
Authors: Casler M. D. , Talbert H. , Formey A. K. , Ehlke N. J. , Reich J. M.
Published: July 2010

Genetic improvement and an increased understanding of forage quality as it relates to ruminant nutrition will depend upon identification of appropriate selection criteria. The objectives of this study were to investigate genetic variation for rate of cell wall digestion and the length of the initial digestion lag phase (lag time) in smooth bromegrass (Bromus inermis Leyss.) and to relate variability for these traits to chemical composition. Eighteen clones were grown at Arilington, WI, and sampled in 1982 and 1984. Forage samples were analyzed for cell wall constituents and in vitro cell wall digestibility (IVCWD) after 6, 12, 24, 48, and 72 h of incubation. Rate of cell wall digestion and lag time were computed from the log‐linear regressions of potentially digestible cell wall remaining on incubation time. Five regression models were used, based on various combinations of incubation times, to evaluate the influence of each incubation time on the rate and lag estimates. clones differed significantly for all traits evaluated. Cloanl variation for rate of cell wall digestion and lag time could only be detected when data from the 48‐h incubation time was excluded from the regression models. The low repeatability of 2‐yr clone means (0.35 for rate and 0.26 for lag time) and the low or moderate interyear rank correlations (0.19 for rate and 0.52 for lag time) suggest that replicated genotypic selection will be necessary for successful genetic improvement of these traits. Both rate and lag time were positively correlated wih in vitro dry matter and cell wall digestibility. Lag time appeared to be influenced by the concentration of cellulose and lignin, whereas variation in rate of cell wall digestion appeared to be a function of other plant factors.
Segregation for Resistance to Aflatoxin Contamination among Seeds on an Ear of Hybrid Maize1
Authors: Widstrom N. W. , McMillian W. W. , Wilson D. M.
Published: July 2010

Consistent differences among maize (Zea mays L.) genotypes for resistance to Aspergillus flavus Link ex Ft. infection and aflatoxin contamination have been difficult to demonstrate. Populations derived from visibly classified segregating kernels, obtained from a single fungus‐infected hybrid ear, were tested for aflatoxin contamination amounts. The objectives were to look for hypothesized differences in contamination between the two selected populations derived from kernels related no less closely than half sibs, and to determine if the differences between these two populations were consistent when samples were inoculated with A. flavus in the field and laboratory. The population (MAS:gk), expected to be resistant based on the fungus‐free appearance of kernels selected from the original ear, had significantly less aflatoxin contamination than its counterpart (MAS:pw,nf) in three of four field experiments and two of three laboratory experiments. The seven replicated experiments were conducted during a 5‐yr period, and contamination of MAS:pw,nf exceeded that of MAS:gk in all seven trials. The probability of this occurring as hypothesized, when two populations are in fact equal in resistance, is <0.01. The variation in kernel phenotype on which the initial selections were made has since disappeared, and the populations resulting from sib‐poilination do not differ in their resistance to insects nor in several other traits measured thus far. The populations MAS:gk and MAS:pw,nf offer a unique opportunity for genetic improvement for resistance to aflatoxin through selection and for investigating the mechanisms of resistance.
Ploidy Effects on Protein, in Vitro Dry Matter Disappearance, and Potassium/(Calcium + Magnesium) Equivalent Ratio in Tall Fescue Forage1
Authors: Kasperbauer M. J. , Karlen D. L. , Burton H. R.
Published: July 2010

Use of higher ploidy levels to improve concentrations of protein and digestible matter in forage grass might adversely affect other plant characteristics. Tall fescue (Festuca arundinacea Schreb.) lines with 21, 42, or 84 chromosomes were used in a greenhouse study to evaluate the effects of pioidy level on forage in vitro dry matter disappearance (IVDMD), crude protein, K, Ca, and Mg concentrations, and the K/(Ca + Mg) ratio (calculated on equivalent bas is). Protein and IVDMD increased with higher ploidy. The K/(Ca Mg) equivalent ratios were 1.35, 1.48, and 1.61 for the 21‐, 42‐, and 84‐chromosome lines, respectively. This increase in ratio with increase in ploidy occurred because K concentrations (primarily in cell contents) increased more than Ca and Mg concentrations. Although all ratios obtained in the 25°C greenhouse were below the critical value of 2.2 that is associated with increased occurrence of grass tetany, the study suggests that increasing the pioidy level of forage grass may increase its protein and IVDMD concentrations, but may also increase its K/(Ca + Mg) ratio and the potential to induce grass tetany under some field environments.
Apomixis: Its Identification and Use in Plant Breeding1
Authors: Hanna W. W. , Bashaw E. C.
Published: July 2010

Apomixis, an asexual method of reproduction through the seed, provides unique opportunities for developing superior cultivars in the future. Apomixis occurs at low levels in some cultivated species and can be found in closely related species of many cultivated crops.The purposes of this paper are to help plant breeders and geneticists recognize apomixis and to show how it can be used in plant improvement. Transfer of apomixis to important crops would make possible development of true‐breeding hybrids and commercial production of hybrids without a need for cytoplasmic male sterility and high cost, labor‐intensive processes. Obligately apomictic hybrids would breed true regardless of heterozygosity. It could also provide an efficient method for incorporating genes into new genotypes. Superior obligate apomictic genotypes would be ready for performance testing without a need for progeny testing to determine genetic stability. The commercial hybrid production process would be simplified with apomictic hybrids. Several apomixis mechanisms have been shown to be genetically controlled and therefore subject to genetic manipulation in plant breeding programs. Characteristics such as: (i) uniform progenies from heterozygous F1 or open‐pollinated parents, (ii) maternal types in crosses, (iii) high seed set in unstable genotypes, and (iv) multiple ovules and seedings per ovule are indicators of apomixis that should be investigated.
Effects of Selection Parameters on Effective Population Sizes for Mass Selection1
Authors: Wells W. C. , Roose M. L. , Guzy M. R.
Published: July 2010

In a random mating population of constant size, the effective population size (Ne) is a function of the number of parents (n) and the variance of their gamete contributions (Vk). The objective of this study was to conduct a computer simulation of mass selection of maternal and paternal parents in order to determine the effects of n, selection intensity (i), and heritability (H2) on Vk. The computer simulation consisted of four independent runs of 10 consecutive repetitions of simulated mass selection at n = 20, 40, and 80, i = 1/40 and 4/40, and h2 = 0.0 − 1.0/0.1. The mean Vk increased linearly as h2 increased from 0.0 to 1.0, resulting in a decrease in the ratio Ne/n from 0.984 to 0.577 for i = 1/40, and from 0.986 to 0.741 for i = 4/40. The effect of n on Vk was small. The results of this study indicate that equating Ne with n will lead to a substantial underestimation of the cumulative effects of random drift and inbreeding depression when mass selection is carried out for a moderately or highly heritable trait.
Sucrose Metabolism in the Primary Culm of Sweet Sorghum During Development1
Authors: Lingle Sarah E.
Published: July 2010

Sweet sorghum (Sorghum bicolor (L.) Moench] accumulates large amounts of sugar in culm parenchyma after anthesis, but the biochemical basis of this accumulation is not understood. This study was to identify the enzymes responsible for the pattern of sucrose accumulation in sweet sorghum. Sugars and four enzymes of sucrose metabolism were extracted from whole primary culms and individual internodes of primary culms of ‘Rio’ sweet sorghum at intervals during reproductive development. In whole culms, sucrose concentration increased seven‐fold between the boot and mid‐grain filling stages. This increase was accompanied by a decline in soluble acid invertase (pH optimum 5.0) and sucrose synthase activities. Soluble neutral invertase (pH optimum 7.0) activity was evident throughout, although its activity declined between soft dough and physiological maturity. Very low activity (<13 μmole·kg−1 FW·s−1) of sucrosephosphate synthase was also detected throughout development. At the flag leaf stage, the two uppermost internodes were still elongating. These internodes had the highest activities of acid and neutral invertase and sucrose synthase, and virtually no accumulation of sucrose. In succeeding growth stages, sucrose accumulated most rapidly in internodes below the top two. At anthesis, the top six internodes had similar activities, on a fresh weight basis, of all enzymes assayed. The onset of sucrose accumulation in sweet sorghum was associated with the onset of the reproductive phase of growth and the decrease in acid invertase activity, but sucrose concentration was not correlated with the activity of any enzyme. In this regard, sweet sorghum appears to be biochemically different from sugarcane (Saccharum spp.).
Plant Density Effects on Main Culm and Tiller Development of Grain Sorghum1
Authors: Gerik T. J. , Neely C. L.
Published: July 2010

The development of tillers represent as an important yield compensation mechanism for many cereals. A 2‐yr irrigated field study was conducted at Temple, TX, on a Houston Black clay (fine, montmorillonitic, thermic Udic Pellusterts) using two recently developed low tillering sorghum hybrids [Sorghum bicolor (L.) Moench], ATx623 ✕ RTx430 and ATx378 ✕ RTx430, to compare tiller phenological development to that of the main culm, and determine the impact of tillering on crop phenology and grain yield. Planting dates and plant densities were varied to determine the elasticity of tillering for these hybrids. Tillering occurred early in ontogeny and tillers originated from the axillary buds on the basal nodes on the main calm. Tillers extended the flowering interval from 7 to 10 days, depending upon year and planting date, but variability among the tiller and main culm flowering dates resulted in numerous instances when flowering by tillers and main culms occurred simultaneously. On average, four more leaves were produced on main culms than on tillers. Environments with cool temperatures/short daylength and high temperatures/long daylength retarded tiller development. Tillers had little effect on grain yield when plant densities were ≥ 12.5 plants m−2. A precipitous decline in number of grain forming tillers was found at densities >2.5 plants mm−2. This suggests that sorghum tillering maybe controlled by a biophysical mechanism similar to the light‐mediated tillering control reported for wheat (Triticum aestivium L.) and deserves further study.
Growth and Environment Effects on Anatomy and Quality of Temperate and Subtropical Forage Grasses1
Authors: da Silva J. H. S. , Johnson W. L. , Burns J. C. , Anderson C. E.
Published: July 2010

The constituents determining the nutritive value of forage plants can be altered by short‐ and long‐term environmental changes. The objective of this study was to associate environmental effects on plant morphology and anatomy with cell‐wall composition and in vitro true digestibility (IVTD) and cell wall disappearance (IVCWD) of three grasses. ‘Kentucky 31’ tall fescue (Festuca arundinacea Schreb.), flaccidgrass (Pennisetum flaccidum Griseb.), and ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.] were grown in a one‐third perlite and two‐thirds gravel media in controlled environment chambers with 18/14, 22/18, 26/22, or 30/26°C day/night temperatures (T) at either a 9‐ or 12‐h light period (LP). Successive harvests were taken at 1.5, 3, 4.5, or 6 weeks. Dry matter (DM) yield was highest at 22/18°for tall fescue (TF), but increased linearly with T for both subtropical species. The ratio of stem (plus sheath) DM to leaf blade DM (SLR) was positively associated with total yield in all grasses and increased T resulted in higher SLR for flaccidgrass (FG) and Coastal bermudagrass (CB). Cell‐wall constituents in TF increased with age and with T only to 26/22°C, whereas the age and T effects occurred for the subtropical species throughout the ranges studied. Only the bundle sheath area in TF stems (plus sheath) and the ratio of leaf thickness to average bundle diameter in FG was positively influenced (P ≤ 0.01) by either T or LP. Quality measurements were negatively related to the ratio of leaf thickness to vascular bundle diameter in FG and to the schlerenchymatous sheath areas in TF stems. An index computed for leaf degradability was related to CB IVCWD (r = 0.66**, significant at the 0.01 probability level) and for stem degradability was related to both IVTD and IVCWD for TF (r = 0.46** and 0.63**) and FG (r = 0.50** and 0.46**).
Relative Winter Forage Quality of Selected Bermudagrass Cultivars1
Authors: Taliaferro C. M. , Coleman S. W. , Claypool P. L.
Published: July 2010

Bermudagrass [Cynodon dactylon (L.) Pers.] forage is often stockpiled or accumulated in situ for use during winter. Very little information is available on the quality of such forage as affected by cultivar or age. This study reports results of two experiments conducted to: (i) determine relative quality of stockpiled forage of selected bermudagrass cultivars as indicated by in vitro dry matter disappearance (IVDMD) and crude protein (CP) concentrations, and (ii) monitor dormant season patterns of change in IVDMD and CP. Three cultivars (Alicia, Hardie, and Midland), two locations, and four sampling dates in the winter of 1975–1976 were included in Experiment 1. In Experiment 2, three cultivars (Hardie, Midland, and Tifton 44) were evaluated at six locations on four sampling dates in the winter of 1981–1982. Sampling in each experiment began in mid November and continued at 30‐day intervals through mid‐February. Hardie usually had higher IVDMD than the other cultivars throughout the sampling period in both experiments. There was no difference among cultivars in CP concentration in either experiment. The trend in change of both the IVDMD and CP concentrations through the winter was a decrease, but the changes were not linear, generally being best described by cubic equations. No consistent differences among cultivars in rate of change in either IVDMD or CP were found. None of the cultivars maintained high enough IVDMD levels through winter to supply minimum energy requirements for dry pregnant mature cows. Except at Mangum in Experiment 1, all cultivars maintained high enough CP levels to meet the minimum requirements of dry pregnant beef cows.
Bidirectional Selection in Alfalfa for Activity of Nodule Nitrogen and Carbon‐Assimilating Enzymes
Authors: Beck D. L. , Barnes D. K. , Vance C. P.
Published: July 2010

The nodule enzymes phosphoenolpyruvate carboxylase (PEPC) and glutamate synthase (GOGAT) are important in the assimilation of symbiotically fixed N2 in alfalfa (Medicago sativa L.). The objectives of this study were: (i) to determine the response to one cycle of bidirectional selection for nodule PEPC and GOGAT activities within six alfalfa germplasms, and (ii) to determine the effect of selection for nodule enzyme activity on other traits previously found to be associated with increased N2 fixation and on the associations among those traits. Four subpopulations (SPO, SP1, SP2H, and SP2L) were obtained for each of the six germplasms. The SP1 subpopulation for each germplasm was derived from the unselected base SPO subpopulation by sequential selection for seedling vigor, increased shoot, nodule, and root mass, and high acetylene‐reduction activity (ARA). The SP2H and SP2L were developed by intercrossing plants selected from the SP1 for high and low nodule enzyme activity, respectively. Plants from the SPO, SP1, SP2H, and SP2L subpopulations of the six germplasms were evaluated simultaneously in the glasshouse for PEPC and GOGAT activities, ARA, nodule mass and soluble protein concentration, shoot and root dry weights, and N concentration in the shoots and roots. Selection for traits to form the SP1 subpopulation was effective in increasing ARA, nodule mass, and shoot and root dry weight above the SPO. Averaged over the six germplasms, the SP1 subpopulation had about 5 and 7% greater PEPC and GOGAT activities, respectively, than did the SPO. Bidirectional selection for nodule enzyme activity resulted in the PEPC and GOGAT activities of the SP2H subpopulations being 20 and 18%, respectively, greater than those of the SP2L. The SP2H subpopulation had greater nodule soluble protein and root N concentrations than did the SP2L. The ARA, nodule mass, root dry weight, and shoot N concentration traits were not affected by selection for enzyme activity, but selection for low nodule enzyme activity reduced shoot dry weight. This study demonstrated that it was possible to concurrently select for two enzyme activities involved in N and C assimilation in the same plant organ.
Application of Multistage Selection Indices to Crop Improvement
Authors: Godshalk E. B. , Timothy D. H. , Burns J. C.
Published: July 2010

Index selection to improve agronomic crop traits has generally been restricted to one‐stage indices. Multistage selection has been confined to tree and animal breeding. This study was undertaken to compare predicted one‐stage index genetic gains with two‐ and threestage gains when attempting to improve switchgrass (Panicum virgatum L.) forage quality and yield. These indices were compared within the context of two selection methods (mass and modified earto‐ row selection) and four levels of replicates (4, 6, 8, and 12). A total of 33 switchgrass haif‐sib families were evaluated for initial growth dry weight, in vitro dry matter disappearance (IVDMD), and N concentration, and for IVDMD of regrowth sampled in July (IVDMD1) and again in August (IVDMD2). One‐stage index lection consisted of selecting all five traits simultaneously. In twostage selection, initial growth traits were selected in the first stage and regrowth traits were selected in the second stage. In three‐stage selection, the first, second, and third stage traits were initial growth traits, regrowth IVDMD1, and regrowth IVDMD2, respectively. Predicted genetic gains of two‐ and three‐stage indices were generally higher than one‐stage index gains over the range of replicates and over the two selection methods. This indicates that breeding program costs could be reduced by decreasing the number of individuals evaluated following the first stage of selection. More consideration by breeders should be given to multistage selection as an alternative to one‐stage index selection.
Dinitrogen Fixation Estimates in Alfalfa‐Ryegrass Swards Using Different Nitrogen‐15 Labeling Methods
Authors: Danso S. K. A. , Hardarson G. , Zapata F.
Published: July 2010

The amount of 15N‐labeled fertilizer and the method by which it is added to soil may influence the estimates of N2 fixed (Ndfa) in perennial forage stands. A 2‐yr field experiment was conducted to compare the estimates of N2 fixed in an alfalfa (Medicago sativa L.)‐ryegrass (Lolium perenne L.) sward, using two N rates, different methods of introducing JSN into soil, and 15N uptake from previous applications (residual 15N). During the 2 yr, alfalfa derived about 210 kg N/ha or 88% of its N from atmospheric N2. Pure as well as mixed sward ryegrass reference crops estimated similar % Ndfa in alfalfa. All of the three approaches by which 5 kg N/ha of 15Nlabeled fertilizer was applied to soil resulted in similar % Ndfa at each harvest, in contrast to the application of 45 kg N/ha, which frequently resulted in significantly lower estimates of % Ndfa. Labeling soil with 5 kg N/ha before each regrowth consistently gave higher % Ndfa than when 15N uptake was from residual 15N in soil, but these reached significant levels only at one or both of the secondyear harvests (depending on the reference crop). Even then, these differences were of little agronomic significance because total N2 fixed was similar for all methods. The consecutive addition of small amounts of 15N at frequent intervals therefore appears to he satisfactory for N2 fixation measurements in perennial pastures.
Ontogenetic Changes in the Respiration Coefficients of Grain Sorghum
Authors: Stahl Randal S. , McCree J.
Published: July 2010

The daily carbon balance of a plant is determined by the gross input of C, the efficiency of new biomass, and the maintenance requirement of existing biomass. According to models of C utilization in plants, the synthesis efficiency (or yield of growth, Y8) should depend on the nature of the product being synthesized, while the maintenance requirement per unit biomass (m) should depend mainly on the concentration and turnoverate of the protein in existing biomass. Values of Y8 and m were determined throughout the ontogeny of grain sorghum [Sorghum bicolor (L.) Moench]. Individual plants were grown and tested under controlled environment conditions (30°C, high light). Carbon balance determinations were made from 28 to 100 d after emergence. The value of Y8 was found to increase from 0.70 g C.g C−1 to 0.78 g C.g C−1, while m decreased from 24 mg C.g C−1.d−1 for young plants to 6 mg C.g C−1. d−1 for mature plants. It is suggested that the changes in Yg reflect changes in the composition of the end products of biosynthesis. Protein concentration was found to decrease with age. The efficiency of synthesis of proteins is less than that of the carbohydrates that make up the bulk of plant tissue. A decrease in protein synthesis could therefore explain the increase in Y8. The decrease in m after anthesis was much greater than the decrease in protein concentration. It therefore seems likely that a large fraction of the protein in the plants during grain filling was structural or storage protein that was not being rapidly turned over.
Canopy Photosynthesis and Seed‐Fill Duration in Recently Developed Soybean Cultivars and selected Plant Introductions
Authors: Boerma H. R. , Ashley D. A.
Published: July 2010

Canopy photosynthesis and seed‐fill period have been shown to be positively related to seed yield in soybean [Glycine max (L.) Merr.]. The present study was undertaken to identify recently developed cultivars (RC) and plant introductions (PI) with high canopy‐apparent photosynthesis (CAP) or long seed‐fill period and to determine the relationship of these traits to seed yield in these genetically diverse genotypes. Twenty genotypes in Maturity Groups (MG) VI, and VII were grown on an Appling course sandy loam soil (Typic Haplndult, clayey, kaolinitic, thermic) near Athens, GA, for 2 yr. The genotypes consisted of seven RC, seven PI, which had been previously identified as having high seed yield, three high photosynthetic cultivars (HPC), and three low photosynthetic cultivars (LPC). Five CAP measurements were taken during the reproductive stage of development. When averaged over maturity groups, the RC were 5% higher in CAP than the LPC and 13% higher than the PI. The RC and HPC had 4 to 5 days longer seed‐fill period than PI or LPC. The RC averaged 12% higher in seed yield then the LPC and 6% higher than PI. In MG V, PI157440 and the RC ‘Deltapine 345’ had CAP rates higher than the LPC ‘Dare’ and equal to the HPC ‘Forrest’. In MG VII, ‘GaSoy 17’ had a CAP rate above the HPC ‘Bragg’. Partial correlation coefficients with the effect of maturity removed were positive between seed yield and CAP (r = 0.63), seed‐fill period (r = 0.54), and the product of CAP and seed‐fill period (r = 0.78). These results indicate that high photosynthetic capacity and long seed‐fill period were associated with high seed yield in this diverse group of genotypes.
Photosynthesis and Water Vapor Exchange of Pigeonpea Leaves in Response to Water Deficit and Recovery
Authors: Lopez Francis B. , Setter Tim L. , McDavid Charles R.
Published: July 2010

Pigeonpea [Cajanus cajan (L.) Millsp.; cv. UW‐10], a crop being developed for use in low‐rainfall environments, was studied during development of water stress and recovery after rewatering to determine the treatment effects on photosynthesis and leaf diffusive conductance. Plants were grown in a greenhouse and leaf gas exchange was measured at various photosynthetic photon flux densities during an 8‐d period of water stress development and during an 18‐d period of recovery following rewatering. Predawn total water potential (ψw) declined by 1.0 MPa after 8 d of withholding water, whereas the pressure component of water potential (ψp) remained positive due a decrease in the solute component of water potential (ψp) from −1.2 to −1.7 MPa. During stress development, decreases in leaf diffusive conductance (gL) occurred earlier than decreases in photosynthetic CO2 exchange rate (CER), indicating that a water conservation mechanism was induced. Differences in gL between unwatered and control plants were first detected at 5 d after withholding water. Differences in CER between control and unwatered plants were not detected until Day 8 of the treatment. As a result of these CER and gL changes, the CO2 concentration in the intercellular air space (Ci) decreased during the period from 5 to 8 d after withholding water. After rewatering, CER and gL slowly recovered over an 18‐d period. It is concluded that pigeonpea responds to water stress by partially limiting the rate of water loss and maintaining a low CER, and it responds to rewatering by slowly recovering CER and gL.
Telocentric Mapping in Wheat of the Gene Lr32 for Resistance to Leaf Rust
Authors: Kerber E. R.
Published: July 2010

Lr32, a gene for resistance to leaf rust (Puccinia recondite Rob. ex. Desm.) previously transferred to hexaploid wheat (Triticum aestivum L.) from Triticum tauschii (Coss.) Schmal. and known to be associated with chromosome 3D, was located on the short arm of this chromosome, 26.8 ± 4.0 crossover units from the centromere. Male transmission of telocentric 3DS in competition with complete 3D was 23.2%.
Isolation of Trisomics from Crosses of Diploid, Triploid, and Tetraploid Red Clover
Authors: Taylor Norman L. , Chen Kuey
Published: July 2010

The objectives of this study were to examine the fertility of crosses of various ploidies, to determine the chromosome numbers of progenies from these crosses, and to produce a complete series of primary trisomics in red clover. The ultimate goal is to use the primary trisomics for mapping of genes in this agriculturally important species. Seed set from 2x‐3x, 3x‐2x, 3x‐3x, 3x‐4x, and 4x‐3x crosses of red clover (Trifolium pratense L.) averaged 9.4, 7.4, 6.3, 2.4 and 5.3% respectively. Chromosome numbers produced were 2n = 14, 15, 16, 21, 26 and 28. About one half of the progenies were diploid (2n 14), about one third trisomic (2n = 15), about 6% putative double trisomics (2n = 16), and about 4% had higher numbers. All classes of crosses, except those involving tetraploids, produced trisomics. The 3x‐2x crosses produced higher percentages of trisomics, double trisomics and higher numbers than did 2x‐3x crosses indicating greater female than male transmission of the extra chromosomes. Triploids used in these crosses contained either 21 or 22 chromosomes. The use of 21 chromosome triploids produced higher fertility than did 22 chromosome triploids. In 3x‐2x crosses, 22 chromosome parents produced more double trisomics (15.9%) than did the 21 chromosome parents (6.1%). From a total of 37 trisomic plants, all seven of the possible primary trisomes of the red clover genome were tentatively isolated. Morphological differences were not associated with the different trisomics.
Effect of Plant Height and Flowering Date on Seed Yield of Determinate Soybean
Authors: Maw Sun Lin , Nelson Randall L.
Published: July 2010

An experiment was conducted to study the value of plant height and time of flowering in improving yield of determinate soybean [Glycine max (L.) Merr.) grown in the northern USA. Eight crosses were made among 10 determinate plant introductions. Twenty F2 families representing four plant types: tall, early flowering; tall, late flowering; short, early flowering; and short, late flowering were identified in the F3 generation for each of Maturity Groups I, II, and III. They were yield tested in 1985 and 1986 in a Flanagan silt loam (Aquic Argiudoll) at Urbana, IL. Seed yield was significantly affected by time of flowering in all three groups. Early flowering families outyielded the late‐flowering families by 7, 28, and 14% in Groups I, II, and HI, respectively. The short, early‐flowering type had the highest mean yield and highest yielding individual families for all three Maturity Groups. The highest yielding F2 families were taller than currently grown determinate cultivars and yielded approximately 80% of ‘Gnome’ and ‘Hobbit’. These data indicate that time of flowering is relatively more important than plant height in determining seed yield of determinate soybean in Maturity Groups I through III.
Sl Family Recurrent Selection in Autogamous Crops Based on Dominant Genetic Male‐Sterility
Authors: Knapp S. J. , Cox T. S.
Published: July 2010

Recessive genetic male‐sterility has been widely used to facilitate crossing in recurrent selection programs in autogamous crop species. Dominant genetic male‐sterility, on the other hand, has not been widely used. Mass and half‐sib family selection schemes have been described for the dominant male‐sterile program. Our objective was to describe S1 family recurrent selection schemes and expected selection responses for the dominant male‐sterile program. There is no mechanism for intermating selected S1 families in a dominant male‐sterile program, other than manual emasculation and pollination, because S1 families are completely fertile. We proposed various S1 family recurrent selection schemes where intermating is done between selected S1 families and a male‐sterile allele source as a means for overcoming this problem. These schemes include S1 family recurrent selection using the reference population as the male‐sterile allele source and combined S1 and half‐sib or S1 and full‐sib family recurrent selection using half‐sib or full‐sib families, respectively, as the male‐sterile allele source. Expected selection responses were described for selection of the same or different traits in different family types for combined family type selection schemes. The strengths of S1 family selection in a dominant genetic male‐sterile program are that complete S1 family fertility eliminates the problem of male‐sterile phenotype pleiotropy and selection response per year is often greater for S1 compared to mass or half‐sib family recurrent selection. The weakness of S1 family selection in a dominant compared to a recessive male‐sterile program is that expected selection response is less than that for S1 family selection in allogamous species where intermating is done strictly between S1 selected families.