bluuebunny/crossref_metadata_2025 huggingface dataset:
Mitochondrial DNA Polymorphism in Male‐Sterile and Fertile Cytoplasms of Pearl Millet
Authors: Smith Rex L. , Chowdhury M. K. U.
Published: July 2010

Cytoplasmic male sterility (CMS) is used extensively in the production of pearl millet [Pennisetum glaucum (L.) R. Br.] commercial F1 hybrids. Although several male‐sterile cytoplasms are available in pearl millet, most of them are not stable enough for commercial use; therefore, additional male‐sterile cytoplasms are being sought. The traditional method of classifying male‐sterile cytoplasms using restorer gene responses is slow and cumbersome. This research was conducted to evaluate mitochondrial DNA restriction endonuclease fragment patterns for classifying cytoplasmic male‐sterile and fertile cytoplasms, to define restriction fragment patterns capable of distinguishing the cytoplasms, and to evaluate the relative effectiveness of restriction fragment and hybridization patterns, using maize mitochondrial gene probes to distinguish the cytoplasms. BamHI restriction patterns differentiated the male‐sterile cytoplasms, S‐Am, S‐A1, S‐A3, but grouped together S‐A2 and the five male‐sterile mutants derived from F‐B2. Those patterns also differentiated fertile F‐B2, but failed to differentiate F‐B1 and F‐B3. The CMS mutant, S‐M7, had a unique SmaI restriction pattern differentiating it from S‐A2 and the other four CMS mutants, and verifying its mutant origin. Hybridization patterns, using maize mitochondrial gene probes, differentiated the cytoplasms much the same as did the restriction patterns. Both restriction and hybridization patterns are of value in classifying the cytoplasms. Unique restriction fragments and patterns capable of differentiating the various cytoplasms were identified.
Relationship between Orchardgrass Seed Production in Indiana and Oregon
Authors: Stratton S. D. , Ohm H. W.
Published: July 2010

Orchardgrass, Dactylis glomerata L., is an important forage species in the eastern USA, but nearly all commercial seed is produced in Oregon. The objectives of this study were to: (i) determine relationships among Orchardgrass seed yield traits, and (ii) examine the feasibility of selection in Indiana for improved seed yield in Oregon. Twenty‐four Orchardgrass parents and their polycross progenies were randomly selected from a reference population, and established as spaced plants at Battle Ground and Buck Creek, IN, and Salem, OR for evaluation of seed yield and associated traits. Progenies were also established as seeded rows at all locations for seed yield evaluation. In the space‐planted study, genotypic variation was found for panicle number, seed yield, and yield per panicle in Indiana, and Oregon. Phenotypic correlations indicated that panicle number (r = 0.46–0.77) and yield per panicle (r = 0.17–0.66) were associated with seed yield. Genotypic ✕ location interactions between Indiana and Oregon were significant (P < 0.05) for panicle number, seed yield, and yield per panicle. Phenotypic and genetic correlations were low for seed yield per plant, (r = –0.19 to 0.55), panicle number per plant (r = 0.06–0.54), and seed yield per panicle (r = −0.08 to 0.68) in comparisons between Indiana and Oregon. Heritability values on a plot basis (h2 = −1.19 to 0.37) and parent‐progeny correlations (r = −0.32 to 0.12) for seed yield were low at all locations. Genotypic variation for seed yield was detected only in Oregon among seeded progeny rows. Phenotypic (r = −0.35 and 0.51) and genetic (near zero) correlations for seed yield between Indiana and Oregon seeded progeny rows were low. Low phenotypic and genetic correlations for seed yield between Indiana and Oregon, and significant genotype ✕ location interactions indicated that it would be difficult to improve Oregon seed yield through selection in Indiana within this population. The low heritability values indicated that it is necessary to practice selection of families rather than individual plants to improve seed yield.
Identification of Sources of Resistance to Common Root Rot in Wheat‐Alien Amphiploid and Chromosome Substitution Lines
Authors: Conner Robert L. , Whelan D. P. , MacDonald Malcolm
Published: July 2010

Current hard red spring wheat (Triticum aestivum L. em Thell.) cultivars have only a moderate level of resistance to common root rot caused by Cochliobolus sativus (Ito and Knrib.) Dreschl. ex Dastar. The objective of this study was to determine if wheat‐alien amphiploid and chromosome substitution lines derived from Aegilops squarrosa L. and Agropyron species could be used as new sources of root rot resistance. A series of greenhouse studies established that Agrotana, a wheat‐A. trichophorum amphiploid, carried resistance to common root rot. Tests of the chromosome substitution series for the D genome in the winter wheat cultivar Winalta by chromosomes 1 to 7 of Ae. squarrosa demonstrated that the substitutions had no consistent effect on disease severity. Similarly, substitutions of chromosomes 4D, 5D, and 6D of Winalta by homoeologons chromosomes from A. elongatum and chromosome 4B for chromosome 4 from A. intermedium had no effect on root rot severity. Isolations from the subcrown internodeshowed that Agrotana had a significantly lower percentage of plants infected with C. sativus than did other exotic lines and common wheat cultivars, suggesting that it might have a different resistance mechanism against common root rot.
Anatomy of Seed Dispersal Mechanisms in High and Low Seed Shattering Cultivars of Orchardgrass
Authors: Piccirilli Marco , Falcinelli Mario
Published: July 2010

In orchardgrass (Dactylis glomerata L.), seed shattering is a common feature that can be a serious economic problem. To obtain information for breeding improvement programs in seed retention, the mechanism that leads to seed shattering in orchardgrass was histologically determined in two cultivars, Hallmark and Marta, chosen for their different shattering levels. Two abscission layers were identified in both cultivars at the first stage of floral development. A primary abscission layer was located in the rachilla supporting the fertile floret; a secondary layer extended across the pedicel near thebase of the glumes. In Hallmark, seed shattering may occur from the soft dough stage onward because of the disintegration of the cells in the primary layer. In this cultivar the secondary layer remains intact. In Marta, the disintegration of cells in the primary layer gradually occurs over a longer period and seed shattering begins about 30 d after Hallmark and lasts until autumn. In both cultivars the deterioration process observed in the primary layer was probably the consequence of the action of one or more hydrolytic enzymes. During autumn, spikelet dispersion in Martalso occurs because of breakage of the secondary layer. The rupture of this layer was assumed to be mechanical because there was no evidence of cell disintegration.
Temperature Effect on Leaf Emergence and Phyllochron in Wheat and Barley
Authors: Cao Weixing , Moss Dale N.
Published: July 2010

An understanding of the effect of environment on leaf emergence is necessary for modeling crop canopy growth. This study was to determine the effect of controlled temperature on leaf emergence rate and phyllochron in four winter wheat (Triticum aestivum L.) and four spring barley (Hordeum vulgare L.) genotypes. Nine experiments were conducted in growth chambers at constant temperatures between 7.5 to 25 °C. The number of leaves per culm was recorded daily from seedling emergence until the fourth leaf was mature. At a given temperature, the emergence of new leaves was a linear function of time for all genotypes, with R2 values not less than 0.95. The slopes of the linear regressions, which are the leaf emergence rates (leaves/day), however, differed among genotypes and among temperatures within genotypes. For all genotypes, the leaf emergence rates increased parabolically with increasing temperature until an optimum temperature was reached and then declined. These responses could be described with quadratic polynomials with R2 values greater than 0.96 for all genotypes. As temperature increased, the phyllochron (degree‐days/leaf) increased exponentially. The relationships between phyllochron and temperature fit exponential equations with R2 0.97 or greater for all genotypes. The phyllochron ranged among the eight genotypes from 57.2 ± 5.2 degree‐days at 7.5 °C to 116.2 ± 7.1 degree‐days at 25 °C. These results suggest that the temperature effect must be considered in modeling phyllochron in wheat and barley.
Canopy Photosynthesis and its Association with Seed Yield in Advanced Generations of a Soybean Cross
Authors: Ashley D. A. , Boerma H. R.
Published: July 2010

Canopy‐apparent photosynthesis (CAP) of soybean, Glycine max (L.) Merr., plants during reproductive development differs among genotypes, is a heritable trait, and is positively associated with seed yield. These responses collectively imply a potential for yield improvement through selection for enhanced CAP. This research was undertaken to: (i) determine if the CAP response patterns of F4 lines remain relatively stable in F6 lines, (ii) determine the association CAP to yield and growth characteristics in F6 lines, and (iii) identify F6 lines with similar maturity and divergent CAP. The experiments were conducted over a 2‐yr period at Athens, GA under field conditions. A l‐min measurement of CAP was made near mid‐day in all plots for three times during reproductive development by use of a closed system and ambient conditions. Other measurements included plant height, stages of plant development, seed wt., length of seed‐fill period, and seed yield. The upper 50% of the F4 lines averaged 11% higher in CAP than the lower 50%. The F6 lines derived from the high CAP F4 lines were 6% (0.9 μmol CO2 m−2 s−1) higher in CAP than F6 lines from the low F4 lines. There was an association between CAP of F4 lines and the mean of the F6 lines derived from them (r = 0.64; P < 0.I). A positive association was found between CAP and seed yield (r = 0.28 to 0.66). Pairs of F6 lines with divergent CAP rates but similar maturity were identified. Results support previous findings that CAP during reproductive development is positively associated with seed yield in determinate soybean genotypes.
Selection for Seed Yield in Inter‐Gene Pool Crosses of Common Bean
Authors: Singh Shree P. , Cajiao Cesar , Gutiérrez J. Ariel , Garcia James , Pastor‐Corrales Marcial A. , Morales Francisco J.
Published: July 2010

The need to maximize yield of common bean (Phaseolus vulgaris L.) without increasing production costs is increasing in most countries. High‐yielding cultivars tolerant to production constraints are needed. Our objectives, therefore, were to: (i) determine the effects of input levels on selection for seed yield, (ii) compare the relative yield gains in crosses among gene pools, and (iii) study yield stability of selected lines. Six inter‐gene pool crosses of Middle and South American common bean were used. Visual mass selection for seed yield in individual plants was practiced in the F2 and F3 generations. In the F4, single plants were harvested. From F5 to F8, selection was based on plot yields. The six highest‐yielding lines from each cross and each environment were compared with five high yielding parents and four checks at high‐ and low‐input levels over 3 yr (1984–1986). Differences among years, crosses, and lines within crosses were observed for all traits. Under low input, there was a 31% reduction in yield and 7% reduction in seed weight, but maturity was accelerated. Differential anthracnose (Colletotrichum lindemuthianum) pressures did not affect the levels of resistance of selected lines. Selection was effective in both environments, but the two groups of selected lines did not differ in mean yield. Crosses within small‐seeded Middle American (SSMA) and between SSMA and large‐seeded Andean American gene pools did not produce lines yielding more than the highest yielding parent or check. Only lines selected from two higher yielding crosses between small‐ and medium‐seeded gene pools of Middle America outyielded the best parent and check cultivar.
Bidirectional Selection for Birdsfoot Trefoil‐Compatibility Traits in Orchardgrass
Authors: Short K. E. , Carlson I. T.
Published: July 2010

Perennial grass‐legume mixtures are important in forage production, but little effort has been devoted to breeding either the grass or legume component for increased compatibility in mixtures. The objective of this research was to study response to selection for birds‐foot trefoil (Lotus corniculatus L.)‐compatibility traits in orchard‐grass (Dactylis glomerata L.). Six Cycle‐1 populations were developed by bidirectional selection in Iowa 79‐OGP‐DT for maturity, spring canopy height, and a compatibility index incorporating spring vigor, spring canopy height, growth habit, and tiller number. Significant direct and correlated responses were obtained from bidirectional selection for each trait or combination of traits. Selection for late maturity, short spring canopy height, and a low compatibility index value always increased days to anthesis and decreased spring canopy height, erectness of growth, tiller number, and dry‐matter yield in a space‐planted test, with the converse occurring from selection in the opposite direction. The three populations derived from selection for a low compatibility index value, short canopy height, and late maturity yielded less forage than their respective divergent populations in a space‐planted test, in dense monoculture stands, and in mixtures with birds‐foot trefoil. The lower‐yielding populations permitted significantly more birdsfoot trefoil production than the higher‐yielding populations in mixtures. This research indicates that it is possible to increase the compatibility of orchardgrass with birdsfoot trefoil by selecting among spaced plants for decreased spring canopy height, decreased tiller number, and delayed maturity.
Heterosis and Combining Ability in Hybrids Derived from Oilseed Rape Cultivars and Inbred Lines
Authors: Brandle J. E. , McVetty P. B. E.
Published: July 2010

Basic genetic information needed to develop hybrid oilseed rape (Brassica napus spp. oleifera) cultivars has not been previously reported. Since recent work had shown oilseed rape cultivars to be genetically heterogeneous, inbred line derived hybrids were compared to cultivar derived hybrids to determine if there were differences among inbred lines in terms of their performance in hybrid combination. For inbred line derived hybrids, midparent was compared to general combining ability as a means of predicting hybrid yield. Three inbred lines, from each of three source cultivars, were crossed using a factorial mating design and the resultant hybrids were field evaluated in three environments. The inbred lines, source cultivars, and cultivar hybrids were included as checks. Yields of inbred line derived hybrids were compared to their respective cultivar derived hybrids and some inbred line crosses were found to be significantly (P < 0.05) higher and others significantly (P < 0.05) lower yielding. There were also differences in general combining ability (GCA) effects among inbred lines. This result indicates the presence of variability in breeding values among cultivar derived inbred lines and that hybrid oilseed rape breeding programs should be based on inbred line crosses, rather than cultivar crosses. General combining ability (GCA) was significant (P < 0.01) and accounted for 88% of the cross sums of squares, while specific combining ability (SCA) was nonsignificant (P > 0.05) indicating that additive genetic effects predominantly influence the expression of yield. Regression of midparent on observed hybrid yield was significant (P < 0.01), with an r2 of 0.37. Regression of expected hybrid yield, based on parental GCA, on observed hybrid yield was also significant (P < 0.01), but with an r2 of 0.88. Therefore, GCA was more effective than midparent for describing hybrid yield. There was, however, a positive relationship between midparent and hybrid yield indicating that despite the somewhat low r2, midparent may still be a useful guide for the selection of parents for testing in hybrid combination.
Characterization and Inheritance of Dwarfing Genes of Pigeonpea
Authors: Saxena K. B. , Githiri S. M. , Singh Laxman , Kimani P. M.
Published: July 2010

Pigeonpea [Cajanus cajan (L.) Millsp.] cultivars have excessive vegetative growth and are not amenable to efficient crop management practices such as foliar insecticide application and mechanized field production. This study was conducted at the ICRISAT Center in India to characterize three easily distinguishable dwarf pigeonpea phenotypes (D6, PD1, and PBNA) with respect to some morphological traits and to study the inheritance patterns for dwarfing genes. Six crosses involving the dwarf lines and tall cultivars were studied. In 1986, the parents, F1, and F2 generations were grown and in the following year, testcrosses and F3 progenies were evaluated along with their respective parents. Each population was phenotypically classified relative to parental type as tall or dwarf. The chi‐square analyses showed that the dwarf phenotype in each of the three lines was controlled by a single recessive gene in homozygous state. The D6 and PD1 lines had similar alleles (t3t3) whereas PBNA had a different allele (th3th3) for dwarfness, which was recessive to the D6/PD1 allele, thus constituting a multiple allelic series.
Yield and Yield Component Response of Eight Potato Genotypes to Water Stress
Authors: Lynch D. R. , Tai G. C. C.
Published: July 2010

The differential tolerance to moisture stress among potato (Solanum tuberosum L.) genotypes may be associated with differences in sensitivity during the ontogeny of yield development. This study was undertaken to determine the effect of a wide range of moisture stresses on the yield and components of yield of eight genotypes (‘Acadia Russet’, ‘Bintje’, ‘Jemseg’, ‘Kennebec’, ‘Raritan’, ‘Russet Burbank’, ‘Sable’, and ’Shepody’). The genotypes were subjected to three levels of soil moisture tension in 1983 (−30, −60, and −90 kPa) and four in 1984 (−30, −60, −90, and −120 kPa) at Vauxhall, Alberta on a Cavendish sandy loam (Brown Chernozemic) (fine‐loamy, mixed, frigid Ultic Haploxeralf). A mathematical model based on the method of path analysis was used to study the relationship between the components of yield and the overall response of the final tuber yield to moisture stress. Moisture stress treatments caused marked (P < 0.01) reductions in marketable yield, tuber number per stem and average tuber weight. Mainstem number was not affected. The genotypes ✕ stress interaction was significant (P < 0.05) in an analysis of variation (ANOVA) carried out over 2 yr. While analysis of the yield data using the model demonstrated that in general genotypes are very sensitive to moisture stress at both tuber initiation and at the tuber sizing growth stages, the greatest variability amongst genotypes in response to stress occurred at tuber sizing. Shepody, Russet Burbank, and Sable showed a strong sensitivity to stress in the tuber initiation phase while Jemseg, Acadia Russet, and Kennebec were more sensitive at tuber sizing. The study demonstrates differences in the structure of the response of the genotypes to moisture stress, measured in terms of the components of tuber yield, and indicates the importance of this information to ensure efficient moisture management.
Seasonal and Species Variation in Baseline Functions for Determining Crop Water Stress Indices in Turfgrass
Authors: Horst G. L. , O'Toole J. C. , Faver K. L.
Published: July 2010

Empirically based relationships between canopy minus air temperature (Tc–Ta) regressed on vapor pressure deficit (VPD) have been described as measures of crop water stress indices (CWSI) and indicators for irrigation scheduling. This study was conducted to determine seasonal and turfgrass species variation in empirical‐baseline functions. Empirical and energy‐balance CWSI functions also were compared to determine which was the most accurate estimate of CWSI over the range of turfgrass species and conditions studied. Field experiments were conducted to compare CWSI relationships derived during different climatic seasons and four different turfgrass species: buffalograss, Buchloë dactyloides (Nutt.) Engelm. cv. Texoka; common bermudagrass, Cynodon dactylon (L.) Pers. cv. Arizona common; St. Augustinegrass Stenotaphrum secundatum (Walter) Kuntze cv. Raleigh; and, tall fescue Festuca arundinacea Schreber cv. Falcon. Data were collected in midsummer of 1986 and late summer of 1987 from plots irrigated with a linear‐gradient irrigation system. The CWSI relationships were calculated from the two lowest canopy temperatures in each plot during 7 July to 1 Aug. 1986 and 30 Aug. to 11 Sept. 1987. Differences between CWSI baseline functions from 1986 and 1987 for common bermudagrass, buffalograss, and tall fescue were highly significant (P < 0.01). Mean values of net radiation, VPD, and wind speed also were significantly different (P < 0.01) for the seasons. Vapor pressure deficit usually accounted for more than 50% of the variability in Tc–Ta across seasons and turfgrass species. Using the energy‐balance method to calculate CWSI and comparing these values with empirical calculated CWSI values reduced the portion of index differences that were greater than 0.1.
Shoot Growth, Dark Respiration, and Nonstructural Carbohydrates of Contrasting Alfalfa Genotypes
Authors: Hendershot K. L. , Volenec J. J.
Published: July 2010

The physiological processes associated with genetic differences in shoot elongation rate (SER) and leaf area expansion rate (LAER) of alfalfa (Medicago sativa L.) are poorly understood. Our objective was to examine the relationships among SER, LAER, and the concentration and utilization of nonstructural carbohydrates in roots and meristematic shoot tissues of alfalfa. Two genotypes selected for contrasting SER were sampled after 7 d of herbage regrowth in 15‐h photoperiods. Remaining plants were placed in continuous darkness and sampled periodically during the next 144 h (Exp. 1) or 33 h (Exp. 2) of regrowth. In Exp. 1, LAER, concentrations total nonstructural carbohydrate (TNC), and dark respiration rates (RD) of expanding leaves decreased during the first 48 h of regrowth in continuous darkness. In Exp. 2, LAER declined to 40% of mid‐photoperiod values after 17 h of continuous darkness, while RD of expanding leaves declined to 75% of mid‐photoperiod rates. Concentrations of TNC in expanding leaves declined by Hour 17 of darkness to 19% of mid‐photoperiod concentrations, reflecting trends in RD and especially LAER. In expanding leaves, TNC concentrations greater than 28 g kg−1 dry wt. were necessary for maximum LAER and RD to occur. Averaged over experiments, root TNC concentrations were 185 g kg−1 dry wt. during the initial 17 h of continuous darkness and did not decline significantly. Although roots contained high concentrations of TNC, LAER decreased rapidly within 17 h of continuous darkness. This indicates that expanding leaves may rely upon sources of carbohydrate other than that in roots for growth under C‐limited conditions.
Response of Dry Matter Accumulation in Maize to Temperature: II. Leaf Photosynthesis
Authors: Tollenaar M.
Published: July 2010

The response of single‐leaf photosynthetic rate to temperature may be different from the response of canopy photosynthetic rate to temperature. This study was undertaken to assess the influence of the temperature response of single‐leaf photosynthesis on dry matter accumulation of maize (Zea mays L.) canopies. Maize was grown in controlled‐environment growth cabinets at a photosynthetic photon flux density (PPFD) of 650 μmol m−2 s−1 under five constant day/night temperature regimes (15, 19, 23, 27, 31 °C) and five differential day/night temperature regimes (15/3,19/7,23/11,27/15, 31/19 °C). Leaf photosynthetic rates were measured at the 12‐leaf stage at PPFDs ranging from 0 to 2500 μmol m−2 s−1 and growth analysis was performed from planting to the 12‐leaf stage. Leaf photosynthetic rate increased linearly from 15 to 27 °C and the magnitude of the response was larger at high than at low PPFD. The Q10 for specific growth rate (SGR) in the range 11 to 31 °C was 1.93 from the 4‐ to the 12‐leaf stage (r2 = 0.89, n = 36). Leaf photosynthetic rate at 650 μmol m−2 s−1 (P650) was highly correlated with SGR across temperature regimes (r2 = 0.72, n = 60). The association between P650 and SGR could be attributed, in part, to the high correlation (r2 = 0.80, n = 60) between P650 and net assimilation rate (NAR). Leaf area ratio (LAR) contributed to the variation in SGR due to temperature and LAR was positively correlated with P650, particularly in the range 19 to 27 °C. The rate of increase of SGR from 19 to 27 °C was 32% higher than the increase of P650 over the same temperature range. Results of this study show that the temperature response of NAR of young maize canopies is similar to the temperature response of leaf photosynthetic rate, but the closeness of the relationship between NAR and P650 varied with phase of development and temperature range employed in the comparison.
Performance and Stability of Indeterminate and Determinate Soybean in Short‐Season Environments
Authors: Ablett G. R. , Beversdorf W. D. , Dirks V. A.
Published: July 2010

In the traditional indeterminate (IND) soybean‐growing areas of North America, lodging in soybean [Glycine max (L.) Merr.] during the pod‐filling stages of reproductive growth can cause significant yield reductions. Maturity Group (MG) II to III determinate (DET) cultivars have recently been developed that combine excellent lodging resistance with high yield potential. This study was initiated to evaluate the performance and stability of DET soybeans in MG I to II growing areas. Fifteen IND and 15 DET lines from each of three crosses were evaluated in the F6 and F7 generations for four environments in narrow rows. In each environment, the IND lines, on average, were higher yielding, taller, had greater bottom pod heights, and were more susceptible to lodging than the DET lines. In one cross, the DETs and INDs had equivalent seed yields, whereas, in two crosses the INDs significantly outyielded the DETs, illustrating that certain genetic backgrounds favor the DET stem type. The genotype‐grouping technique identified high‐yielding stable DET lines, however, within each cross most of the lines in that category had an IND stem type. The overall results suggest that breeding for high‐yielding stable DET lines is possible in short‐season environments, but that the frequency of such lines in a population may be lower than the frequency of IND lines. Since yield of the DET stem type was generally positively associated with plant height and maturity, the stringent use of these selection criteria in early generations may provide a relatively simple way of increasing the frequency of favorable DET genotypes.
Selection for Resistance to Macrophomina phaseolina and Fusarium moniliforme in Sorghum
Authors: Bramel‐Cox P. J. , Claflin L. E.
Published: July 2010

Lodging of grain sorghum, Sorghum bicolor (L.) Moench, can be a serious problem under certain environmental conditions. Lodging at either the base of the panicle or stalk is often attributed to a complex of stalk‐rotting organisms. The two most prevalent are Macrophomina phaseolina (Tassi) G. Goid, the causal agent of charcoal rot, and Fusarium moniliforme Sheldon, the causal agent of fusarium root and stalk rots. The field study reported here evaluated the predicted gain from selection in a random‐mated population of grain sorghum for resistance to these two stalk‐rotting organisms. The experiment consisted of 150 random half‐sib families from a random‐mated population, KP8B, which were evaluated in a 2‐yr study at McCune, KS. The families were artificially inoculated with both organisms using a toothpick inoculation technique and were rated for stalk disintegration on a scale of 1 (resistant) to 6 (very susceptible). The families differed significantly for M. phaseolina and F. moniliforme resistance in each year, but the effect of years and the interaction with years were significant. The predicted gain from selection indicated that improvement could be made in this population for resistance to these organisms either directly or indirectly with selection for green leaf retention, but the level of postflowering stress would need to be severe enough to ensure the development of the disease.
Photoperiod and Light Quality Effects on Cowpea Floral Development at High Temperatures
Authors: Mutters R. G. , Hall A. E. , Patel P. N.
Published: July 2010

High temperatures in tropical and subtropical zones often have detrimental effects on plants. Plants in these zones experience differences in daylength that could influence sensitivity to heat. Contrasting genotypes of cowpea, Vigna unguiculata (L.) Walp., were grown under fluorescent plus incandescent (F) or metal halide plus incandescent (MH) lamps at different daylengths (11, 12, 13, 14, or 16 h) to determine whether the sensitivity of floral development to high night temperatures is influenced by light quality and photoperiod. Floral bud development was suppressed in heat‐sensitive genotype (CB5) at a 14‐h photoperiod under MH, while a 16‐h photoperiod was required to elicit a similar response under F. Spectral analysis showed five times more ultraviolet‐A light (UV‐A) (315‐400 rim) in MH than in F, but F supplemented with UV‐A light did not elicit the same suppression of floral bud development as MH. The reproductive response to long days with hot nights (30 °C) was closer to that of field‐grown plants under MH than under F. Percent pod set of two sensitive genotypes (CB5 and 7964) subjected to high temperatures (33/30 °C day/night) was higher (23 and 19%) at an ll‐h photoperiod than at a 14‐h photoperiod (5%) under F. No pod set occurred in an ll‐h photoperiod with red light (R) during the night. Substantial pod set (41%) was observed a 14‐h photoperiod was followed by far‐red light (FR). The effect was reversed when FR was immediately followed by R. Apparently, pod set at high nightemperatures in heat‐sensitive, day‐neutral cowpea is dependent on photoperiod through a mechanism involving phytochrome.
Responses of Tall and Hard Fescue to Deficit Irrigation
Authors: Fry Jack D. , Butler Jack D.
Published: July 2010

Tall fescue (Festuca arundinacea Schreb.) and hard fescue (Festuca longifolia Thuill.) are used extensively for turf in cool and transition zone regions. Information on irrigation requirements of these species is limited, however. Field studies were conducted to determine responses of ‘Rebel’ tall fescue and ‘Reliant’ hard fescue to deficit irrigation and irrigation frequency. Turf growing on a Satanta sandy clay loam soil (Fine loamy mixed, mesic Aridic Argiustoll) was irrigated at 50, 75, or 100% of potential evapotranspiration (ETp, i.e., turf water use when soil moisture is not limiting) on 2‐, 4‐, 7‐, or 14‐d intervals. Small weighing lysimeters adjacent to plot areas were used to obtain ETp rates. Both species performed best when irrigated every 2 or 4 d at 75 or 100% ETp. Tall fescue exhibited exceptional drought resistance. When watered every 2 d, irrigation at 50% ETp resulted in only small reductions in tall fescue visual quality. Hard fescue performed poorly under the same irrigation regime. Increased water conservation in semiarid regions may result if tall fescue is used more extensively and irrigated at 50% ETp every 2 d or 75% ETp every 2 to 7 d.
Forage Quality of Alfalfa as Affected by Potato Leafhopper Feeding
Authors: Hutchins Scott H. , Buxton Dwayne R. , Pedigo Larry P.
Published: July 2010

The potato leafhopper (PLH), Empoasca fabae (Harris), is a major pest of alfalfa, Medicago sativa L., in the north central USA, yet little information exists regarding its effects on forage quality. Three field trials were conducted in 1984 and 1985 to determine the consequence of PLH feeding on chemical composition and nutritional quality of alfalfa stem and leaf components. A factorial arrangement of four densities of PLH adults (0, 50, 100, and 200 m−2) and two infestation periods (1 and 14 d after first harvest) was replicated four times in a randomized complete‐block design. Weekly plant samples were collected for assays of in vitro digestibility, neutral‐detergent fiber (NDF), and crude protein. Total herbage digestibility did not differ among plots. Digestibility of the stem component was actually enhanced (up to 3.0% change) by severe PLH feeding. The leaf component also was slightly higher in digestibility (up to 2.2% change) under extreme PLH‐induced stress. Total herbage NDF concentration was largely unaffected at harvest by levels of PLH‐induced injury. Leaf protein concentration was reduced (about 8.2% change) in most infested plots but stem protein concentration was maintained or enhanced (up to 9.1% change) with increasing levels of PLH‐induced injury. Comparisons of chlorotic vs. nonchlorotic leaves suggested that visible symptoms of PLH feeding did not necessarily indicate differences in chemical composition of the herbage. The small effects of PLH feeding on total herbage forage quality indicate that PLH control programs should be based primarily on the likelihood of reductions in biomass or nutrient yield, rather than the likelihood of reduced forage quality.
Tassel Culture of Elite Inbreds of Maize
Authors: Pareddy D. R. , Petolino J. F.
Published: July 2010

Tassel culture of maize (Zea mays L.) to obtain normal development has significant potential for both basic and applied research studies. However, potential use of this technique for genetic manipulations has been limited by genotype specificity. This study was conducted to screen 15 commercially used inbreds for tassel culture response and to determine conditions satisfactory for successful tassel culture of each genotype. Immature tassel meristems were cultured on different media. Different concentrations of sucrose (0.2– 0.3 M) were required for different genotypes. However, Murashige and Skoog medium with 0.1 μM kinetin and casein hydrolysate (30 mg L−1) was suitable for most of the genotypes. Tassels of Oh43 derivatives were responsive to culture, while B73 and Mo17 were more recalcitrant. The cultured tassels of the inbreds A619, A632, H99, LH38, Pa91 and U94 produced mature, trinucleate pollen. Thus, the tassel culture technique can be used across a broad range of elite maize germplasm.
Solution Effects on the Thermostability of Bean Chloroplast Thylakoids
Authors: Al‐Khatib Kassim , Wiest Steven C.
Published: July 2010

Knowledge of the physicochemical nature of the strains imposed by heat stress on biological membranes requires a definition of other stresses that impose similar strains. To that end, this paper defines several solution properties that alter the effects of heat on isolated chloroplast thylakoid membranes. Isolated bean (Phaseolus vulgaris L.) ‘Oregon 1604’ thylakoids in various milieus were exposed to 25 or 45 °C, and the repercussion(s) of heat were determined. Raffinose (0.4–0.5 M) was slightly more thermostabilizing than 2 M sucrose as evidenced by an amelioration of the: (i) heat‐induced decline electron transport, (ii) heat‐induced alteration in the susceptibility of thylakoid polypeptides to trypsin digestion, and (iii) heat‐induced decline in the maximum fluorescence transient measured at 685 rim. Equimolar glucose + fructose appeared to be equivalent in effectiveness to sucrose. Solutions with a pH of 5.5 or below and 7.0 or above appeared to increase the susceptibility of thylakoid electron transport to heat. Thermoprotection of electron transport to heat was afforded by aspartate at pH 6 and glutamate at pH 7. Dimethylsulfoxide and ethylene glycol appeared to provide some thermostability at concentrations tested (1 M and 100 mL/L, respectively). Urea appeared to mimic heat‐induced injury. Exposure of thylakoids to 45 °C for 2 min appeared to cause the same degree of impairment as ca. 0.8 M urea, while exposure for 4 min appeared to cause the same as ca. 0.9 M urea. Finally, low concentrations (0.05‐0.1 M) of mercaptoethanol appeared to exacerbate heat‐induced thylakoid malfunction.
Photosynthetic Responses to Heat Stress in Common Bean Genotypes Differing in Heat Acclimation Potential
Authors: Chaisompongpan Nawarat , Li Paul H. , Davis David W. , Markhart Albert H.
Published: July 2010

Photosynthesis is one of the most heat‐sensitive processes in plants. The common bean (Phaseolus vulgaris L.) is notoriously sensitive to heat. The objectives of this study were to determine the photosynthetic activities of six common bean genotypes under heat stress and whether these activities correspond with the genotypes' ranking in purported heat acclimation potential (HAP). The HAP is defined as the change in leaf heat tolerance, based on plasmalemma thermostability measured by electrolyte leakage, at the prefloral growth stage of plants after acclimation at 37 °C day/night for 24 h. Photosynthetic response to short‐term heat stress (5 min at 42 or 45 °C) was expressed by O2 evolution and chlorophyll fluorescence. Without heat acclimation, heat stress at 42 °C decreased O2 evolution in the six genotypes from 50 to more than 95%, compared with the controls, and heat stress at 45 °C almost totally inhibited O2 evolution in all genotypes. Heat stress had less effect on peak fluorescence level than on O2, evolution. Heat acclimation slightly reduced O2, evolution, compared with nonacclimated controls. In heat‐acclimated plants, heat stress at 42 °C had no effect on O2 evolution, whereas stress at 45 °C significantly reduced O2 evolution. Changes in levels of peak fluorescence under heat stress in heat‐acclimated plants showed patterns similar to changes in O2 evolution. Photosynthetic responses to heat stress did not totally correspond with the ranking of HAPs of the six genotypes obtained by conductivity test. Full recovery of O2 evolution from heat injury at 42 °C for 5 min occurred within 4 h in GNUI 59, whereas O2 evolution rates were still lower than the controls after 6 h in the other genotypes. The recovery of chlorophyll fluorescence was slower than that of O2 evolution.
Variability in Leaf Characteristics and Water Loss in the Weeping Lovegrass Complex
Authors: Tischler C. R. , Voigt P. W.
Published: July 2010

Epicuticular wax restricts water loss across the cuticle of plant leaves and is considered to aid in drought resistance. This conserving effect is roughly proportional to the amount of wax present. We measured wax levels, water loss, and leaf width and rolling characteristics of 19 lovegrasses, Eragrostis curvula (Schrad.) Nees, to determine if variation existed for these characteristics and the relationships among them. A broad range of germplasm that could be characterized as belonging to the curvula or. robusta forms of E. curvula was established in field plots in 1979. Each characteristic was studied on at least two different dates between 1980 and 1982. Epicuticular wax levels ranged from 0.212 to 0.589 g/m2, leaf width ranged from 2.2 to 5.7 mm, and water content ranged from 60 to 104 g/m2. Values for mean cumulative water loss per amount of water contained in detached leaf sections ranged from 71 to 218 g/kg, while rate of water loss per amount of water contained ranged from 1.93 to 4.53 g kg−1 min−1. In general, genotypes with high wax had a high leaf water content, low water loss, and a low rate of water loss. The amount of epicuticular wax appeared responsible for some of the reduced cuticular transpiration. High water content per unit leaf area was associated with a low rate of leaf rolling. The interaction between wax and leaf rolling (which reduces effective leaf area) and leaf water content tended to prevent an unequivocal determination of the influence of varying wax levels on leaf water loss. Germplasm with a narrower genetic base and a wide range in leaf wax would be useful to more precisely characterize the relationship between leaf wax and leaf water loss in E. curvula.
Ozone Effects on Agricultural Crops: Statistical Methodologies and Estimated Dose‐Response Relationships
Authors: Lesser Virginia M. , Rawlings J. O. , Spruill S. E. , Somerville M. C.
Published: July 2010

The National Crop Loss Assessment Network (NCLAN) began in 1980 to coordinate research on the impact of ozone (O3) on agricultural crops. During a 7‐yr period, the program investigated 14 crops at sites across the country in a total of 41 studies. A major objective was to develop dose‐response relationships between yield of major agricultural crop species and ozone pollution in order to estimate the economic impact of ozone pollution. This paper outlines the statistical methodologies used in combining the dose‐response information for each species over all NCLAN studies, and summarizes the ozone dose‐response relationships obtained. Differences in experimental designs, treatment combinations, and levels of ozone across studies invalidated the conventional analysis of variance approach to combining information across studies. Regression analyses, with weighted least squares and transformations as needed, were used. Dose‐response relationships between yield and ozone were quantified with the nonlinear Weibull response equation and with confidence interval estimates of percentage yield losses. Significant yield losses from ozone were found for 13 of 14 crops studied. The nature of the yield response to ozone differed among crops with soybean [Glycine max (L.) Merr.] being the most sensitive and showing a nearly linear response. Losses from ozone at 0.06 μL L−1 compared with 0.025 μL L−1 were estimated as high as 20%. The impact of ozone was shown to be affected by level of moisture stress but not by SO2.
Digestibility and Cell‐Wall Components of Alfalfa Following Selection for Divergent Herbage Lignin Concentration
Authors: Kephart Kevin D. , Buxton D. R. , Hill R. R.
Published: July 2010

Breeding schemes to improve alfalfa (Medicago sativa L.) forage quality based on total herbage chemical composition can result in altered morphology. Additionally, cell‐wall composition of plant parts also may be altered. This study investigated the effects of divergent selection for lignin concentration in total herbage of alfalfa on concentration of cell‐wall components and digestibility of stems. Two groups of alfalfa previously derived from herbage‐based selection were studied. Group 1 consisted of six two‐parent Syn‐2 lines randomly selected from ‘Saranac‐AR’ for high (HL) or low (LL) acid‐detergent lignin (ADL) concentration in the total herbage. Group 2 had 11 HL and 13 LL lines produced from crossing pairs of parents of the Group 1 lines. Neutral‐detergent fiber (NDF) concentration in stem bases was 4 and 3% greater in HL lines than in LL lines in Group 1 and 2, respectively. Likewise, herbage NDF concentration was 8% greater in HL than in LL lines of Group 1 and 4% greater in Group 2. There were no differences between divergent lines in NDF concentration of stem tops. Lignin concentration in cell walls of Group 1 was 8 and 6% greater in LL lines than in HL lines in stem tops and stem bases, respectively. In Group 2, the LL lines had 2% greater cell‐wall lignin concentration than HL lines in both stem fractions. Total‐herbage NDF concentration correlated more closely with leaf‐to‐stem ratio of entire plants (r = − 0.96 and −0.78 for Group 1 and 2, respectively) than with stem length and maturity. Thus, herbage‐based selection for improved nutritive quality of alfalfa results in complex changes in stem cellwall component concentrations in addition to large morphological changes.
COTMAP, a Technique for Evaluating Structure and Yield of Cotton Plants
Authors: Bourland F. M. , Watson C. E.
Published: July 2010

Analysis of the structure and fruiting behavior of cotton, Gossypium hirsutum L., is complicated by its indeterminate growth habit and size variation among individual plants. We present COTMAP, a technique in which the primary fruiting sites (first and second sympodial positions) are individually mapped and fruit on remaining sites are considered collectively. Yield variables calculated by COTMAP include total bolls, boll distribution, and boll retention in prime fruiting sites. Plant structure variables include node of first fruiting branch, number of monopodia, number of sympodia, number of effective sympodia, number of sympodia with at least two flowering positions, total number of main axis nodes, plant height, and average internode length. Data from three tests of mepiquat chloride (N,N‐dimethyl‐piperidinium chloride) on cotton are used to illustrate the mapping technique. The COTMAP technique has been used to distinguish variation in structural characteristics and fruiting pattern of cotton plants associated with genetic differences, growth regulators, and insect damage.
Irrigation Effects on Plant Water Relations and Productivity of Thompson Seedless Grapevines
Authors: Grimes D. W. , Williams L. E.
Published: July 2010

An optimum irrigation management strategy requires information on the yield loss associated with quantified field water deficits and the ability to assess the adequacy of irrigation intensity during the growing season. This study was conducted to develop a water‐production function for grape (Vitis vinifera L.) and to establish plantbased water‐status measurement techniques and critical values that assess irrigation regime adequacy. Field studies were conducted for 3 yr with ‘Thompson Seedless’ grapevine on Panoche clay loam (fine‐loamy, mixed [calcareous], thermic Typic Torriorthent) and Hanford sandy loam (coarse‐loamy, mixed, nonacid, thermic Typic Xerorthent) in the San Joaquin Valley of California. Differential irrigation quantities were supplied in several increments ranging from 40 to 120% of the expected nonstressed crop evapotranspiration (ETcrop). Midday measurements of leaf water potential (ΨL), water stress index (CWSI), and stomatal conductance (g1) closely associated with imposed water deficits and the resulting grape yields. All plant‐based water‐status‐reflecting measurements were highly correlated. Grape yields followed declining water availability essentially linearly over the range of available data. A 50% reduction in ETcrop resulted in a 26% yield loss. Irrigation intensities that resulted in ΨL > −0.9 MPa, CWSI < 0.2, and gs > 0.008 m s−1 maintained high grape productivity. These results can be used to profit‐maximize irrigation water as a production input.
Selection of Stable Cultivars Using a Safety‐First Rule
Authors: Eskridge Kent M.
Published: July 2010

The presence of genotype by environment interaction is of major concern to plant breeders, since large interactions can reduce gains from selection and complicate identification of superior cultivars. Numerous statistics have been proposed to characterize stability of cultivars, yet none of these methods explicitly indicate how stability may be combined with mean yield in choosing superior cultivars. It is assumed that the plant breeder prefers a cultivar with a small probability of low yield. Using a decision‐theory concept known as safety‐first to model such behavior, an index incorporating mean yield and stability is developed for each of four different definitions of stability. Data from an international experimental maize (Zea mays L.) yield trial are used to illustrate the application of these indices when genotype by environment interaction is present. It is concluded that safety‐first selection indices can be useful to plant breeders when genotype by environment interaction is large and poor yield has severely adverse consequences.