bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Some Qualitative Genes on Soybean Performance in Late‐Planted Environments
Authors: Raymer P. L. , Bernard R. L.
Published: July 2010

Researchers have suggested that cultivars adapted specifically to double‐crop environments should be developed. Little information is available concerning what plant traits are advantageous in these environments. Sets of near‐isogenic lines (isolines) of soybean [Glycine max (L.) Merr.] can be used to evaluate specific plant traits without the confounding effects of different genetic backgrounds. Isolines in ‘Harosoy’ and ‘Clark’ genetic backgrounds that possess genes controlling maturity and stem morphology were grown in conventional and in late‐planted environments at Urbana, IL in 1980, 1981, and 1982. The isolines tested provided a wide range of maturities and stem lengths, and produced wide differences in yield at both planting dates. Gene combinations that produced maturities of 96 to I01 d in the late environment were among the highest yielding in both environments. The Dt2 S gene combination, which conditions for semideterminate stem growth and shortened internodes, significantly increased yields in both environments in the later maturing backgrounds. Isoline ✕ planting date interactions were small and nonsignificant in the combined analysis over years. Thus, the genes tested conferred no more of a yield advantage in a late‐planted environment than they did in a conventional early‐planted environment. No evidence was found that any of these traits imparted specific adaptation to late planting. However, the improved performance in both planting times imparted by Dt2 and S is of interest.
Shading Effects on Dry Matter and Nitrogen Partitioning, Kernel Number, and Yield of Maize
Authors: Reed A. J. , Singletary G. W. , Schussler J. R. , Williamson D. R. , Christy A. L.
Published: July 2010

Assimilate supply to the developing ear of maize (Zea mays L.) is an important determinant of grain yield. The objective of the current study was to determine the relative limitations of photosynthate and reduced N supply to the ear for determination of yield components, kernel number and kernel weight. Field‐grown maize plants on Dupo silt loam (Coarse‐silty over clayey, mixed, nonacid, mesic Aquic Udifluvents) were shaded during either vegetative growth, flowering, or grain fill. Control plants were not shaded. Photosynthesis was measured on plots from 9 d before flowering to grain maturity, and plants were sampled at intervals during this period for measurement of dry weight and reduced N content of plant parts of the aboveground vegetation (stover) and ear. When plants were shade during flowering, photosynthesis decreased during this period and kernel abortion increased relative to controls. However, N concentration was higher in aborting kernels than in nonaborting kernels through late flowering and early grain fill. The supply of reduced N to the ear during flowering was not a limiting factor for determination of kernel number. During grain fill, remobilization of N and dry matter from the stover of controls accounted for 46.5 and 4.7% of ear N and dry weight at maturity, respectively. Availability of newly reduced N was apparently more limiting than availability of current photosynthate for kernel dry weight accumulation. It is proposed that supply of newly reduced N to the ear may be limited by the amount of photosynthate partitioned for nitrate uptake and reduction during grain fill.
Selection Pressure on Soybean Cyst Nematode from Soybean Cropping Sequences
Authors: Young L. D. , Hartwig E. E.
Published: July 2010

It has been recommended that soybean [Glycine max (L.) Merr.] cultivars resistant to soybean cyst nematode (SCN), Heterodera glycines Ichinohe, be rotated with susceptible cultivars in order to delay or avoid development of populations capable of damaging resistant cultivars. The objective of this study was to determine if evidence for stabilizing selection of SCN populations with use of susceptible cultivars existed following 10 yr of such cropping sequences. Cropping sequences included susceptible ‘Tracy’ and race 3 resistant ‘Centennial’ grown consecutively with and without nematicide. Sequences of 2 yr of Centennial and 1 yr of Tracy, a blend of 80% Centennial and 20% Tracy, and a breeding line resistant to SCN races 3 and 4 planted consecutively were the other treatments. ‘Lee’, ‘Pickett 71’, ‘Peking’, PI 88788, and PI 90763 were grown in the greenhouse in soil from each field plot in 1985. Cyst indices (percent of cysts on a soybean line compared to number on Lee) were calculated for these race differentials. Race 3 was predominant following Tracy planted consecutively and the breeding line resistant to races 3 and 4. Race 2 was predominant in one of three treatments involving rotation with 2 yr of Centennial and 1 yr of Tracy. Cyst indices on Pickett 71 were large for cropping sequences continuing Centennial and the blend of Centennial and Tracy. Cyst indices were variable on Peking, PI 88788, and PI 90763 for sequences involving Centennial, but indices were within a standard deviation of the description for race 4. No evidence for stabilizing selection sufficient to prevent race shifts in SCN populations through use of susceptible cultivars was obtained.
An Indicator of the R6.5 Stage of Development for Indeterminate Soybean
Authors: Whiting K. R. , Crookston R. K. , Brun W. A.
Published: July 2010

The interval between the soybean [Glycine max (L.) Merr.] reproductive stages R6 and R7 represents an important phase of soybean development that includes seed fill and the initiation of whole plant senescence. The time between stages R6 and R7 has been observed to be relatively long for soybean grown in northern maturity zones. The objective of this study was to identify an indicator that signaled a point midway between stages R6 and R7 (R6.5). Six soybean cultivars representing Maturity Groups 00, 0, and 1 were grown in the field at St. Paul, MN in 1983, 1984, and 1985. Changes in seed, pod, and leaf appearance were monitored during the R6 to R7 interval. The midpoint of the interval was observed to occur when all the normal pods on the four uppermost nodes of the main stem had their pod cavities completely filled, suture‐to‐suture, with seeds. At this stage, seeds had accumulated approximately half of their final dry weight. This stage also marked the initiation of whole plant senescence, or rapid leaf yellowing. We therefore recommend the pod cavities filled trait as an indicator of stage R6.5 for indeterminate soybean cultivars grown in northern maturity zones.
Response to Four Cycles of Combined Half‐Sib and S1 Family Selection in Maize
Authors: Coors J. G.
Published: July 2010

Effective recurrent selection for intrapopulation improvement in maize (Zea mays L.) should be most effective when both inbred and noninbred progenies are evaluated. The objective of this study was to examine the effectiveness of evaluating both half‐sib (HS) and selfed (S1) families during selection to improve population per performance and inbred productivity. Four cycles of combined HS and S1 selection for increased grain yield and reduced grain moisture were completed in a narrow‐based maize population derived from inbred lines; A635, W182E, and W64A. For each cycle, both HS and S1 progenies were produced on prolific plants by selfing the bottom ear and exposing the upper ear to random pollen from the population. Half‐sib and S1 progenies were then evaluated in separate trials. Plants with superior HS and S1 progeny performance, i.e., above average yield and below average grain moisture in both trials, were selected. Half‐sib progeny were used for recombination through the first two cycles. In the third cycle, S1 progeny were recombined. Both progeny types were recombined to form two subpopulations in the fourth cycle. Over four selection cycles, yield of the population increased by 3.5% cycle−1, and grain moisture decreased by 1.5% cycle−1. Corresponding increases in yield were not detected in testcrosses with inbred lines A554 and Wl17, but cycle four testcrosses had significantly lower grain moisture than corresponding testcrosses with the initial population. The yield of bulked composites from random, selfpollinated plants increased by 20 g plant‐1 over four cycles. Broad‐sense heritability estimates were 0.34 and 0.76 for HS and S1 families, respectively, for yield, and 0.68 and 0.88 for moisture. The genetic covariance of HS and Sa progenies was compared to the variance among HS progenies for grain yield and moisture in order to estimate D1, the covariance of additive and homozygous dominance effects. A large negative value for D̂1 for yield, −309±126 g2 plant−2, indicated that simultaneous improvement of both inbred and testcross performance may be difficult. However, the magnitude of D̂1 may have been affected by linkage disequilibrium in the initial population.
Randomness of Intermating in Soybean Populations Containing Male‐Sterile Plants
Authors: St. Martin S. K. , Ehounou N. E.
Published: July 2010

The use of genetic male sterility has been proposed to facilitate intermating in soybean [Glycine max L. (Merr.)]. With many breeding procedures, failure of such insect‐mediated pollination to result in equal contributions of the parents to the gametic pool could lead to undesirable results. The objective of this experiment was to evaluate male‐sterility‐facilitated intermating in a soybean population with respect to equality of parental contribution. Isolated plantings consisting of male‐sterile maintainer line L74‐01 with eight pollen parents were made in 1981 to 1983. The parents carried marker genes so chosen that the progeny of the crosses with L74‐01 could be identified as to pollen parent. The F−1 seed harvested from L74‐01 was planted in a winter nursery and F−1 plants harvested individually. Frequencies of marker phenotypes were observed in an F−2 progeny row to identify the pollen parent of each F−1 plant. The chisquare statistic was used to test for equality of contribution to the pollen pool by all pollen donors. Statistically significant differences among pollen donors were detected in all 3 yr. Variance of family size (Vk) in hypothetical intermated population with the same distribution of gametic frequencies as those of this experiment was calculated from the observed frequencies of parents in the pollen pool. The estimates of Vk were, respectively, 1.2, 1.3, and 0.9 for the 3 yr of the study. Since these estimates were less than the value expected in a random‐mating population due to random variation of family size, inequality of gametic contributions, to the extent observed in this experiment, is probably not a serious drawback to the use of male sterility‐facilitated intermating in soybean breeding.
Leaf Nitrogen, Photosynthesis, and Crop Radiation Use Efficiency: A Review
Authors: Sinclair T. R. , Horie T.
Published: July 2010

Effects of N in crops are profound, but much understanding of crop growth responses to N is empirical. This review attempts to develop a mechanistic understanding of the effects of N on crop biomass accumulation by elucidating quantitative relationships among leaf N content, CO2 assimilation rate, and crop radiation use efficiency. Three crop species were considered: soybean (Glycine max [L.] Men.), rice (Oryza sativa L.), and maize (Zea mays L.). The correlation between leaf N content and leaf CO2 assimilation rates was high within each species, although the response functions were markedly different among species. A relationship was developed predicting crop radiation use efficiency (biomass accumulated per unit solar radiation intercepted) for each of the crops as a function of both leaf CO2 assimilation rate and leaf N content. Radiation use efficiency within each species was nearly constant at high leaf CO2 assimilation rates, but decreased appreciably at low leaf CO2 assimilation rates. At the leaf CO2 assimilation rates typical of a species, the radiation use efficiency was predicted to be about 1.2 g MJ−1 for soybean, 1.4 g MJ−1 for rice, and 1.7 g MJ−1 for maize. Simple calculations during early crop growth examined the competitive use of N for the construction of either large leaf area or high leaf N content. Maize had the greatest biomass accumulation because it had low leaf N contents that allowed the most crop leaf area growth, and it had high radiation use efficiencies. For each rate of N supply to leaves, an optimum leaf N content existed to maximize crop biomass accumulation.
Inheritance of a Mutation Influencing Chlorophyll Content and Composition in Cowpea
Authors: Kirchhoff W. R. , Hall A. E. , Roose M. L.
Published: July 2010

Chlorophyll‐deficient mutants are useful for studying the functional significance of photosystem components and the influence of chlorophyll composition on productivity. Individual mutants can exhibit changes in several characteristics, such as the contents of chlorophylls a and b, and the chlorophyll a:b ratio. It is not known which of these characteristics provides the least ambiguous classification of the mutant phenotype. Inheritance of a chlorophyll‐deficient mutation in cowpea [Vigna unguiculata (L.) Walp.] was studied by crossing the mutant to its presumed parent ‘California Blackeye No. 3’, and a genotype specifically chosen for its dark green foliage. Chlorophyll a and b content and chlorophyll a:b ratios in leaves of progeny were measured. Chlorophyll a:b ratio provided more distinct classification of progeny than chlorophyll content. Segregation of the F1, F2, and backcross generations for chlorophyll a:b ratio was consistent with the hypothesis that the mutation involves a single recessive nuclear gene.
Soybean Seedling Growth Responses to Light Reflected From Different Colored Soil Surfaces
Authors: Hunt P. G. , Kasperbauer M. J. , Matheny T. A.
Published: July 2010

Spectral balance (quality) of light influences many aspects of plant growth and development; and spectral balance of reflected light in the seedling establishment zone is affected by the color of soil surfaces, plant residues, and mulches. Soybean [Glycine max (L.) Merr.] seedlings were grown over white, red, and black surfaces in greenhouse studies. Painted insulation panels, cloth‐covered insulation panels, and different colored soils over insulation panels were used to test the effects of reflected light while minimizing root zone temperature differences. Reflected light from 400 to 800 nm was measured at 5‐nm intervals and expressed as the percentage of direct sunlight at each measured wavelength. Photosynthetically‐active light (400–700 nm) reflected from the white and black surfaces was about 40 and 5%, respectively, of that in direct sunlight. Blue light (400–500 nm) was reflected at about 40% from white and 5% from either black or red panels. Red surfaces reflected similarly to the black from 400 to 570 nm and similarly to the white from 620 to 800 nm. Soybean seedlings were grown in 1‐L containers of vermiculite mounted below the insulation panels, inoculated with Bradyrhizobium japonicum, and supplied with N‐free nutrient solution. Plants grown over white surfaces developed the shortest stems, the most lateral roots and nodules, and the smallest shoot:root dry matter ratios. The amount of blue light as well as the far‐red/red ratio in reflected light contributed to these morphogenic effects. It was concluded that the surface color of soil can substantially alter the growth and nodulation of soybean seedlings even though root zone temperatures under variou surface colors are similar.
Variation and Evaluation of Seed Shape in Soybean
Authors: Nelson Randall L. , Wang Peiying
Published: July 2010

Differences in soybean [Glycine max (L.) Merr.] seed shape are obvious but no measure of that variability has been published. The objectives of this research were to determine the consistency of seed shape and to establish and test a visual classification scheme for soybean seed shape. Such a scheme could exploit the variability of this trait to assist in the identification and classification of germplasm. Ninety‐nine germplasm accessions in Maturity Groups I to IV were selected and grown at Urbana, IL for 3 yr. Measuring 20 seeds per seed lot provided a reasonable estimate of seed shape. A description of seed shape was established using two ratios, height to length (HLR) and height to thickness (HTR). Repeatability ues for the two ratios were 0.90 or greater based on line means. Five and three categories of HLR and HTR, respectively, were established to create a binary, visual classification scheme. All seed lots were assigned a classification based on the mean of actual seed measurements and two samples from each of the 297 seed lots were visually classified. Visual observations agreed with actual measurements for the HLR and HTR for 68 and 76% of the samples, respectively. For all of the visual misclassifications for the HTR rating and 98% of the visual misclassifications for HLR rating, the differences between the visual rating and the rating determined by actual measurement were less than half of the range of a single class. The visual classification scheme proposed here is an effective means of categorizing differences in seed shape among soybean lines and could be used to describe soybean cultivars and germplasm accessions.
Kernel Breakage and Density of Normal and Opaque‐2 Maize Grain as Influenced by Irrigation and Nitrogen
Authors: Kniep K. R. , Mason S. C.
Published: July 2010

Grain quality is important to farmers, grain elevators, millers, and domestic and foreign buyers. Excessive broken kernels can reduce the grade of grain, lower the selling price farmers receive, decrease production from dry and wet milling processes, reduce artificial drying efficiency, and increase potential dust hazards. However, little attention has been focused on the influence of production practices on grain quality. This study was conducted to determine whether irrigation and soil N levels would affect the quality of maize (Zea mays L.) grain. Two water regimes and five N fertilization levels ranging from zero to 360 kg ha−1 i were applied to two normal and two opaque‐2 hybrids. The experimental site was a Sharpsburg silty clay loam (fine, montmorillinitic, mesic, Typic Argiudoll) near Mead, NE. Opaque‐2 grain was 2.4 times more susceptible to breakage, and 8% lower in density than normal grain. Irrigation increased kernel breakage susceptibility (KBS) from 13.5 to 17.9, 3.2 to 3.8, and 5.4 to 7.3% in 1985, 1986, and 1987, respectively. Increasing soil N levels decreased KBS for all hybrids. Kernel density (KD) of opaque‐2 grain was increased with irrigation but decreased with higher N levels. In contrast, KD of normal grain decreased with irrigation but increased with higher N levels. Average grain yields were 9.4, 7.3, and 5.5 Mg ha−1, with irrigation increasing yields 28, 9, and 27% over nonirrigation in 1985, 1986, and 1987, respectively. Normal hybrids averaged 5% greater yields than opaque‐2 hybrids. Yield increased quadratically with N rate within each moisture regime in each year. Results indicate production practices influence KBS and KD as well as yield, and may become important considerations in the future.
Rice Yield and Plant Yield Variability Responses to Equidistant Spacing
Authors: Counce Paul A. , Moldenhauer K. A. K. , Marx D. B.
Published: July 2010

The effect of plant population density on rice (Oryza sativa L.) yields often is confounded experimentally by other effects such as mortality and spacing uniformity. Equidistantly spaced, transplanted rice was used in this study in an effort to obtain less equivocal information on the effects of spacing on plant yield variability. The objectives of this study were (i) to determine the effects of equidistant spacing and cultivar on rice grain yield and yield components and (ii) to determine variation in and relationships among the grain yields of individual plants in the rice crop community. Randomized complete block design experiments were conducted at Keiser, AR in 1984, 1985, and 1986. ‘Lebonnet’ and ‘Lemont’ were whole‐plot treatments and equidistant spacings (51, 76, and 102 mm) were the split‐plot treatments. Plant yield, crop yield, culms/plant, kernels/panicle, and kernel weight increased as spacing increased. Lemont had more culms/plant and greater kernel weight than Lebonnet whereas Lebonnet had more kernels/panicle. Optimum equidistant spacings for crop grain yields of transplanted rice were 53 to 71 mm. Plant yield coefficients of variation (CV) were greatest at the closest spacing. Increased plant yield CV at closer spacings is consistent with a large body of research which indicates plant communities become more hierarchical and variable as plant population densities increase. It is likely that efforts to account for individual plant yield variation must incorporate the control or measurement of relevant environmental variations.
Yield Response of Corn Hybrids and Inbred Lines to Phylloplane Treatment with Mycopathogenic Fungi
Authors: Vakili N. G. , Bailey T. B.
Published: July 2010

This study was part of a larger investigation on the biological control of stalk rot of corn (Zea mays L.) through application of mycopathogenic fungi on above‐ground surface (phylloplane) of the corn plant conducted at Iowa State University, Ames, IA. The objectives were to determine if grain yield is an effective trait for testing the interaction of selected mycopathogenic fungi with corn genotypes and whether the application of mycopathogens to the corn phylloplane had an effect on yield. Seven corn hybrids and nine inbred lines were planted in a Spillville clay loam (fine‐loamy, mixed mesic Cumulic Hapludoll) with three cultural histories: oat (Avena sativa L.)‐corn‐soybean [Glycine max (L.) Merr.] rotation, continuous corn cultivation, and fumigation. Plants were treated in the phylloplane with aqueous spore suspension of mycopathogens Gliocladium roseum (Link) Bainier, Gonatobotrys simplex Corda, and Sphaeronaemella helvellae (Karsten) Seeler, and water as control. Hybrid yields were not affected by the treatments, whereas inbred yields differed significantly. Fumigation of the soil with methyl isothiocyanate resulted in a significant response by inbreds to treatment with mycopathogens, which was primarily due to G. roseum. Differences in the yields of the inbreds planted in corn‐soybean‐oat rotation were nonsignificant. Variation in the yield of the inbreds indicated that there was a highly significant interaction between inbred genotypes and mycopathogens in continuous com culture and in fumigated soils. Inbreds B73 and Va26 had the most varied responses to the mycopathogens, whereas B85 and W629A had the least. Selection and breeding of inbreds with high yield response to mycopathogens could result in genotypes that, in the presence of a compatible mycopathogen, would suppress stalk rot development and have greater yield potentials.
In Vitro Digestion Kinetics of Temperate Perennial Forage Legume and Grass Stems
Authors: Buxton D. R.
Published: July 2010

Digestion of plant cell walls (CW) in the rumen is determined part by digestion kinetics. This study was conducted to gain information regarding plant factors that affect in vitro kinetics of CW digestion. Analyses were conducted on the basal 150 mm o immature and mature stems of field‐grown cultivars of alfalfa (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.), red clover (Trifolium pratense L.), smooth bromegrass (Bromus inermis Leyss.), and orchardgrass (Dactylis glomerata L.). Stem samples were digested in rumen fluid, and data were fitted with a first‐order nonlinear model to estimate potentially digestible CW (PDCW), indigestible residue (IR), digestion rate of PDCW, and digestion lag. These parameters of digestion kinetics were related to CW constituents determined previously. Maximum size of IR was about two‐thirds of CW mass. Within legume and grass stems, IR was closely correlated with lignic noncentration (r = 0.84 and 0.94, respectively). The IR:lignin ratio, however, was 71% greater in grasses than in legumes. The IR concentration was positively related by stepwise regression to total nitrobenzene oxidation products (NBO) of core lignin, lignin concentration, p‐coumaric acid concentration, and arabinose:xylose ratio; and was negatively related to proportion rhamnose in CW neutral sugars. Digestion rate of PDCW was 50% faster in legume than in grass stems and 70% faster in immature than in mature stems. By using stepwise regression, digestion rate of PDCW was negatively related to NBO:lignin ratio, and was positively related to proportion mannose in CW neutral sugars and to the arabinose:xylose ratio. Results of this study suggest that selecting for low NBO:lignin ratio and low p‐courmaric acid concentration will reduce the inhibitory influence of lignin on digestive kinetics.
Temperature Parameters Useful for Modeling the Germination and Emergence of Pearl Millet
Authors: Carberry P. S. , Campbell L. C.
Published: July 2010

The modeling of germination and seedling emergence is required for the construction of a simulation model of pearl millet [Pennisetum americanum (L.) Leeke]. This study provides the temperature parameters necessary to model these processes. Seed of BJ104 pearl millet were germinated in incubators at six controlled temperatures (15, 20, 25, 30, 35 and 40 °C). Germination percentage and coleoptile lengths were measured over time in each temperature regime. Germination percentage at 5 d after the commencement of imbibition was not affected by temperature. Cubic polynomials described the rates of development for germination and coleoptile elongation over the temperature range of 15 to 40 °C. The relationships between rate of development for germination and the lag stage prior to linear elongation of the coleoptile and temperature were linear only between a base of 16 °C and an optimum of 35 °C. The thermal time for the growth stages from planting to 50% germination, germination to the start of linear coleoptile extension, and the duration of linear coleoptile elongation from seed depth until 50% emergence were 5.3 ± 0.4, 7.5 ± 0.4, and 0.82 ± 0.06 degree‐days (°C‐d)mm−1, respectively. It is proposed to use these parameters in a crop simulation model to predict emergence of pearl millet seedlings.
Genes for Resistance to Soybean Cyst Nematode Populations
Authors: Luedders V. D.
Published: July 2010

Relatively few soybean (Glycine max (L.) Merr.) lines have been reported to be resistant to soybean cyst nematode (CN, Heterodera glycines Ichinohe) populations and races. The criterion for resistance was relatively few cysts per plant, a phenotype of the cyst nematode‐soybean association determined by genes of both organisms. Thus the frequencies of nematode genes for avirulence influenced the phenotypes observed. The vast majority of lines are considered to be susceptible to CN, implying that they have no genes for resistance. The objective was to show that some CN susceptible soybean lines do have genes for resistance to some CN. Previously developed CN inbreds were further inbred by transferring single cysts for several CN generations. Artificial selection among inbreds resulted in fewer cysts on specific susceptible soybean lines, apparently due to increased frequencies of some CN genes for avirulence. Twelve susceptible soybean lines apparently have genes for resistance to specific CN inbreds since relatively few cysts per plant were observed. Crosses involving six of these lines produced continuous distributions of numbers of cysts on F2 plants, indicating the segregation of at least two genes for CN resistance in each cross. The possible genetic similarities of some of these lines and some CN resistant lines are discussed, including the potential linkage effects of CN genes for avirulence on the different phenotypes.
Growth and Yield Performance of Several Potato Clones Grown at Three Elevations in Hawaii. I. Plant Morphology.
Authors: Manrique L. A. , Bartholomew D. P. , Ewing E. E.
Published: July 2010

There are few data on the growth and yield of potato (Solanum tuberosum L.) genotypes in the field in tropical and subtropical environments despite interest in such work. Among other things, the data were needed to validate a potato growth model being developed for use in agriculture technology transfer in the tropics. A genotype by environment experiment was conducted on Mr. Haleakala, Maui, HI in 1985 and 1986 at elevations of 91, 282, 640, and 1097 m. The 91 and 1097 m elevations were common in both years. Mean maximum air temperatures during the experimental period for 1985 and 1986 were 29.2 and 30.3 °C at 91 m and 23.1 and 24.0 °C at 1097 m. Mean minimum air temperatures for the same period in 1985 and 1986 were 20.9 and 20.5 °C at 91 m and 14.3 and 15.0 °C at 1097 m. Differences in irradiance across the sites was small. The growth and yield of the standard temperate cultivars Desiree, Katahdin, Kennebec, and Norchip and three heat tolerant clones LT‐1, C14‐343, and C1‐884 were contrasted across the sites. Stem numbers per plant did not differ across elevations but plants were taller, internodes were longer, there were more branches per stem, and the leaf area index was greater for plants grown as the low‐elevation sites. Days to tuber initiation decreased significantly as the elevation increased. Numbers of nonmarketable tubers (diam. < 5 cm) were greater at the lowest elevation, whereas a higher percentage of marketable tubers (diam. > 5 cm) was produced at the highest elevation. Katahdin outperformed all cultivars producing relatively high yields of marketable tubers at all elevations. The heat‐tolerant clones began tuber initiation earlier than the cultivars, but early tuber formation did not result in higher yields. There was little evidence that the heat‐tolerant clones were superior to the temperate cultivars, even at the lowest elevation where temperatures were warmest.
No‐Till Alfalfa Planting in Late Winter Following Fall Vegetation Suppression with Herbicides
Authors: Wolf D. D. , Edmisten K. L. , White H. E.
Published: July 2010

Successful establishment of no‐till alfalfa (Medicago sativa L.) in spring and late summer is limited by soil moisture, weed competition, and disease. Thistudy tested an alternative planting time that partially avoids these problems. Vegetation was suppressed with fall‐applied herbicides and plantings were made in late winter (early March). Plantings were made into Typic Hapludult and Typic Fragiudult soils. All areas received 2,4‐D [(2,4‐dichlorophenoxy) acetic acid] in late August, but this could have been omitted if no broadleaf weeds had been present. A no‐herbicide treatment was included as a check. Herbicide suppression included glyphosate [N‐(phosphonomethyl) glycine] at 3.4 kg ha−1 on 1 October, paraquat (1, l′‐Dimetyl‐4, 4′‐bipyridinium ion) applied once on 1 October or 1 November at 0.56 kg ha−1, or a split paraquat application with 0.56 kg ha−1 applied 1 October and 0.28 kg ha−1 applied 15 November. Treatments were harvested three times in the year of establishment and four times in the year after seeding. Excellent seedling emergence occurred from all treatments in each year, so yield differences were due to success of weed suppression by herbicides. No‐till alfalfa planted in early March resulted in vigorous seedlings where original species in the sod were suppressed the previous fall. Vigor and productivity of plants established without herbicide was not satisfactory. Percentage alfalfa in the harvested herbage and yields in both harvest years tended to be higher for the split application of paraquathan other treatments even though this was not always significant (P ≤ 0.05). The split paraquat treatment was more consistent between sites and years than the glyphosate or single paraquat treatments. These results suggest that in environments similar to the test site (37 ° N, 80 ° W, and 600‐m elevation) high yielding alfalfa stands can be established using fall applications of a split paraquat treatment, followed by late‐winter planting with a no‐till drill.
Use of F2 Generations to Identify Inbreds with Favorable Alleles not Present in an Elite Hybrid
Authors: Zanoni Urs , Dudley J. W.
Published: July 2010

Previous theory for estimating the relative number of favorable alleles (μG*) in a donor inbred (Iw) useful for improving the parents of an elite hybrid (I1, I2) was extended from use of inbred and F1 data, to use of inbred and F2, or F1 and F2 data. To compare the three methods of evaluating donor inbreds, maize (Zea mays L.) inbreds B73 and Mo17 crossed to three inbred lines of Stiff Stalk Synthetic (B84, H100, N7A), four of Lancaster (Pa91, H102, H95, Va26), and five of unrelated origin (B77, B75, B57, B79, N152), hybrid B73 ✕ Mo17, their F2's, and the inbreds per se were evaluated at two locations in 1986. Inbreds with the lowest and highest estimates of the relative number of favorable dominant alleles (μG*) not present in B73 ✕ Mo17 were the same whether inbred and F2, F1 and F2, or inbred and F1 data were used. Rankings of donor lines with intermediate μG* values varied with the method used. These differences in ranking may have resulted from failure of assumptions such as no epistasis or differences in precision in the evaluation of inbreds, F1's and F2's. The different generations resulted in some different assessments of the relative relationship of lines (Iw) to the parents of the elite hybrid and different decisions on whether to backcross prior to selfing. When improving a parental line for grain yield, the progress for other dominant or recessive traits could be predicted.
Genetic Drift and Selection Evaluated From Recurrent Selection Programs in Maize
Authors: Helms T. C. , Hallauer A. R. , Smith O. S.
Published: July 2010

If recurrent selection methods are effective, the frequency of favorable alleles is expected to increase in the population. Random changes in gene frequency will also occur, if effective population size is small, due to the effect of sampling. In maize (Zea mays L.), where dominance gene action is positive in direction for traits such as grain yield, genetic drift results in inbreeding depression. Genetic drift is the change in gene frequency due to sampling in a finite population. Two major processes are expected to be operating to change the mean over cycles of recurrent selection in a population of finite size, selection acting to increase the mean and inbreeding depression due to genetic drift acting to decrease the mean. Estimation of the effects of genetic drift may be useful because the choice of what constitutes adequate effective population size may be altered, on the basis of empirical results. The objectives of the current study were to compare progress between reciprocal recurrent selection (RRS) and intrapopulation selection that included half‐sib (HT) and S2 (S) selection in ‘Iowa Stiff Salk Synthetic’ (BSSSC0), and to separate the effects of selection from those of genetic drift. Effects due to selection for grain yield improvement of populations on a per‐cycle basis were not significantly different between methods of recurrent selection. When advanced cycles were evaluated for grain yield in crosses with an unrelated inbred line (Mo17), improvements paralleled improvement in the populations. The improved populations crossed to an unrelated population [BSCB1(R)Cn], which was used reciprocally as the tester for BSSS(R)Cn, suggested that response to RRS in improving the population cross mean was similar to the populations improved by either HT or S methods of selection. Effects of genetic drift were significant and should be considered in long‐term selection programs. Differences among selection methods for genetic drift were not significant.
Heritability of Specific Gravity of Diploid Potato under High Temperature Growing Conditions
Authors: Haynes K. G. , Haynes F. L. , Henderson W. R.
Published: July 2010

High temperatures encountered during the growing season reduce tuber dry matter content in commercial tetraploid potato (Solanum tuberosum L.). Variability in dry matter content as measured by specific gravity was observed in a diploid hybrid population of S. tuberosum Group Phureja and S. tuberosum Group Phureja and S. tuberosum Group Stenotomum grown under high temperatures. The objective of this research was to estimate heritability of specific gravity in this diploid hybrid population under high temperature growing conditions in North Carolina. Heritability was estimated by midparent offspring regression. Parents were grown at three high‐temperature locations and offspring at eight. Analyses of variance on specific gravity for each of the eight offspring locations revealed heterogeneity of error variances, therefore data were not combined over years and locations for further analyses. Twenty‐four estimates of heritability were obtained, 16 of which were unbiased (parents and offspring were grown in different years and different locations). The average unbiased estimate of heritability was 0.28 (range −0.07 to 0.77). Four estimates were biased because parents and offspring were grown at similar locations in different years. The average of these estimates was 0.57 (range 0.51‐0.63). Two estimates were biased because parents and offspring were grown in the same year in different locations, the average of which was 0.38 (range 0.29–0.46). Two estimates were biased because parents and offspring were grown in the same year at similar locations. These averaged 0.41 (range 0.40‐0.42). Considered together, the moderate estimates of heritability suggest that it should be possible to continue to improve this population for specific gravity under high‐temperature growing conditions. There was an apparent upward bias in the heritability estimates when the parents and offspring were not grown in different years and different locations.
Tiller Phenology and Yield of Spring Wheat in a Semiarid Environment
Authors: Hucl P. , Baker R. J.
Published: July 2010

Cereal grain yields are, in part, determined by tillers formed during the plant's vegetative phase. This study was conducted to determine the extent of genotypic differences in tiller phenology and yield characteristics of individual tillers of spring wheat (Triticum aestivum L.) grown in a semiarid environment. Time to emergence, percent emergence, and survival of individual tillers were determined for 10 genetically diverse genotypes seeded into a Typic Haploborall clay loam at Saskatoon, SK on two dates (4 and 28 May) in 1983. Genotypes differed significantly for percent tiller emergence and survival. Tiller emergence was more rapid (11–12 d) for the later seeding date. Genotype differences in time of tiller emergence (2–6 d) were significant for specific tillers. Main stem Haun stage at the time of tiller emergence (MSHE) was not influenced by seeding date but varied significantly among genotypes (0.40–1.07 Haun units). At maturity, the main stem and tillers T0, Tl, T2, and T3 contributed an average of 26.0, 4.4, 21.8, 18.8, and 12.2 % to plant grain yield, respectively, at a seeding rate somewhat below that used commercially. Tillers Tl, T2, and T3 did not differ from the main stem in culm length, spikelets spike−1, or harvest index; but produced fewer, lighter kernels. Tiller grain yields, spikelets spike−1, and culm length were negatively correlated with MSHE. Days to tiller emergence was not related to mature plant traits. The ability of MSHE to detect small differences in tillering pattern among genotypes and its relationship to yield should prove useful in the study of genotype‐environmental interaction.
Indirect Effects of Recurrent Selection for Fe Efficiency in Soybean
Authors: Beeghly H. H. , Fehr W. R.
Published: July 2010

Genetic improvement for Fe efficiency was achieved in the soybean [Glycine max (L.) Merr.] population AP9 by recurrent selection. The purpose of this study was to evaluate possible indirect effects of recurrent selection for Fe efficiency on plant and seed traits. Parents of the Cycle 0 (C0) through Cycle 7 (C7) populations were evaluated in replicated tests over 2 yr on noncalcareous soil. There was a significant linear increase in yield of 1.4 g m−2 cycle−1, height of 2.6 cm cycle−1, and lodging of 0.I score cycle−1. There were significant linear decreases in seed wt. of 1.9 mg seed−1 cycle−1 and seed oil of −0.6 g kg−1 cycle−1. Seed‐filling period decreased linearly an average of −0.2 d cycle−1. There were no significant linear changes in time of maturity, seed protein percentage, length of flowering period, leaflet area, leaflet wt., or specific leaflet wt. There was a significant linear change in three of the five fatty acids in the seed oil. Palmitic and linolenic acids increased 1 g kg−1 cycle−1, and oleic acid decreased 2 g kg−1 cycle−1. There were no significant linear changes in stearic or linoleic acids. A micronutrient analysis of the seed from C1 and C7 indicated that the average content of Fe was significantly greater in C7 and that the content of P was significantly greater in C1. There were no significant differences between C1 and C7 in the micronutrients B, Na, Mn, K, Ca, Mg, Zn, or Cu. The data obtained in this study indicate that, with the possible exception of an increase in lodging, the AP9 population has not been deleteriously affected by selection for Fe efficiency.
Influence of Temperature on Expression of Resistance to Rust in Diploid Alfalfa
Authors: Skinner D. Z. , Stuteville D. L.
Published: July 2010

Some alfalfa (Medicago sativa L.) plants resistant to the rust fungus (Uromyces striatus Schroet.) in the field have proven susceptible under laboratory conditions. These differences have been attributed to environmental conditions suboptimal for rust development in the field. Our objectives were to study the effects of temperature on resistance to rust in diploid alfalfa. We used a six‐parent diallel cross to measure the inheritance of factors that influence latent period at 20, 25, and 30 °C. Infection‐type data and latent period data were highly correlated (r = 0.97, P < 0.0001). Pustules developed on 37% of all S1 and F1 plants (combined) at 20 °C, on 50% at 25 °C, and on 30% at 30 °C. However, when plants in tests completed at 20 or 30 °C were moved to 25 °C, pustules developed on additional plants until the percentages of plants with pustules were not significantly different (P > 0.05) from those of plants held continuously at 25 °C. The degree of dominance was 0.59, 0.32, and 0.98 at 20, 25, and 30 °C, respectively; thus, resistance appeared most dominant at temperatures suboptimal for disease development. These results indicated that temperature altered the genetic behavior of factors involved in alfalfa resistance to rust, and that the optimum temperature for rust development with the materials we used was about 25 °C.
Photoperiodically Sensitive Interval in Time to Flower of Soybean
Authors: Wilkerson G. G. , Jones J. W. , Boote K. J. , Buol G. S.
Published: July 2010

In order to accurately model the flowering process, it is essential to determine which environmental factors are affecting development at any point in time. The purpose of this research was to determine when different soybean [Glycine max (L.) Merr.) genotypes first become sensitive to photoperiod and how long photoperiod continues to influence the appearance of the first flower under optimal temperature conditions. Controlled‐environment experiments were conducted in which plants were switched at intervals between emergence and flowering from long‐day (22 h) to short‐day (9 h) treatments and from short‐ to long‐day treatments. AH photoperiod chambers were maintained at 26 °C both day and night. Six cultivars from six maturity groups were used: ‘Dawson’, ‘Williams’, ‘Ransom’, ‘Forrest’, ‘Davis’, and ‘Jupiter’. Two nearly isogenic breeding lines differing in response to inductive conditions were also evaluated. All cultivars tested were sensitive to photoperiod by the time the unifoliolate leaf was fully expanded. The experimental line bred for a lengthened juvenile phase exhibited apparent insensitivity to photoperiod for 11 d longer than any of the other genotypes. After flowering was induced, further inductive nights hastened flowering. for all cultivars, photoperiod during the last 6.3 to 8.7 d prior to expression of the first flower had no effect on time to first flower. Thus, for modeling purposes, the interval between emergence and first flower can be divided into four phases: (1) a purely vegetative phase (absent in most of the cultivars tested); (2) a photoperiod‐sensitive inductive phase; (3) a photoperiod‐sensitive post‐inductive phase; and (4) a photoperiod‐insensitive post‐inductive phase.
Direct and Correlated Responses to Selection for Rate and Duration of Grain Fill in Maize
Authors: Hartung R. C. , Poneleit C. G. , Cornelius P. L.
Published: July 2010

Grain filling duration and dry matter accumulation rate are associated with maize (Zea mays L.) yield potential and might be used for indirect yield selection. Additional physiological and genetic information, however, are needed to verify selection procedures and potential gains. Phenotypic recurrent selection was used to develop subpopulations for the physiological components of kernel growth: long EFPD (effective filling period duration), short EFPD, high DMAR (dry matter accumulation rate), and low DMAR. Our objectives were to measure selection progress for these yield components and to observe correlated responses. The original population (CO) and synthetics from three selection cycles (C1‐C3) were evaluated for physiological traits at one location and for agronomic traits at three locations in lattice designs. Regressions and realized heritabilities were calculated. Changes per cycle for the long and short EFPD subpopulations were +4.1 and −3.1% with heritabilities of 0.19 and 0.15, respectively. High and low DMAR selection caused changes per cycle of +4.8 and −8.0% with heritabilities of 0.20 and 0.44, respectively. Concurrent half‐sib yield selection lengthened EFPD. Long EFPD C3 yield was not different and high DMAR C3 was 13% greater than CO. Stalk lodging, harvest moisture, and plant height were affected. Kernel number per plant was influenced by DMAR but not EFPD. Although kernel wt. and number were influenced by DMAR and kernel wt. by EFPD, yield per unit area was changed only by the DMAR and half‐sib selections. Failure of the long EFPD selection, which also reduced DMAR, to increase yield per unit area was due to marginally reduced kernel size and number. Selection for long EFPD and high DMAR is possible, but improvement of yield may be dependent on concurrent control of other yield components.
Influence of Water Management on Growth and Yield of No‐till Planted Rice
Authors: Dabney S. M. , Hoff B. J.
Published: July 2010

To determine the feasibility of producing rice (Oryza sativa L.) on lands equipped with sprinkler‐irrigation systems, the productivity of flood‐irrigated rice was compared with that of rice grown under two levels of sprinkler irrigation on a Mhoon silty clay (fine mont‐morillonitic, nonacid, thermic, Vertic Haplaquept) from 1984 to 1986. Two high‐quality cultivars, ‘Labelle’ and ‘Lemont,’ were compared with ‘CICA‐8,’ one of the most productive cultivars on favored upland sites in Latin America. Soil matric potential was monitored daily with tensiometers placed at 15‐ and 30‐cm soil depths. Beginning 30 d after no‐till drill planting into a killed legume cover crop, rice was flood‐ or sprinkler‐irrigated when soil matric potential at either depth fell below −20 or −50 kPa. Each cultivar matured later and yielded less, as a result of reduced numbers of seed per panicle and reduced seed weight, when grown under sprinkler irrigation compared with flooded culture. In years without severe disease, Lemont and CICA‐8 yields were reduced 10 to 25% from the 5000 to 6700 kg ha−1 produced under flood, while Labelle yield was reduced 27 to 56%. During 1986, rotten‐neck blast (caused by Pyricularia oryzae Cav.) reduced yields of all cultivars grown under sprinkler‐irrigated conditions by 60 to 80%. Biomass production and yield differed between the two levels of sprinkler irrigation only when precipitation plus irrigation was less than potential evapotranspiration (PE). It is concluded that no level of sprinkler irrigation can completely eliminate water stress in upland rice when PE is high.