bluuebunny/crossref_metadata_2025 huggingface dataset:
Resistance‐Susceptibility of Maize Genotypes to Artificial Infestations by Twospotted Spider Mites
Authors: Kamali K. , Dicke F. F. , Guthrie W. D.
Published: July 2010

Twospotted spider mites, Tetranychus urticae K., are pests of maize, Zea mays L., in some areas of the USA. Resistant genotypes are needed to reduce plant damage caused by this pest. Two laboratory and three field experiments were conducted in 1986 to determine the resistance‐susceptibility of maize genotypes to an artificial infestation by the twospotted spider mite. Inbred line 41:25046 was highly resistant to the twospotted spider mite in both laboratory and field tests. This inbred exhibited a high degree of antibiosis against the mite; few mites survived, and little leaf damage resulted from the artificial infestation. This inbred also is highly resistant to the European corn borer, Ostrinia nubilalis Hiibner, and has been used as a nonrecurrent parent to develop several genotypes of maize resistant to this pest. Our data show that 41:25048 also could be used to develop genotypes of maize resistant to twospotted spider mites. Nine other genotypes had intermediate or susceptible reactions to twospotted spider mites, with Mol7 being the most susceptible.
Maturity Effect on Yield and Quality of Spring Harvested Orchardgrass Forage
Authors: Berg Clyde C. , Hill R. R.
Published: July 2010

Orchardgrass (Dactylis glomerata L.) forage quality declines rapidly as plants mature. First harvest forage of 48 clones from ‘Pennlate’ orchardgrass was evaluated for yield and forage quality parameters. The objective of the experiment was to determine variability for rates of change in these parameters as the forage matured. Forage harvested un four dates (25 May, 1, 7, and 14 June) for 3 was analyzed for crude protein (CP), in vitro dry matter disappearance (IVDMD), neutral detergent fiber (NDF), acid detergent fiber (ADF), and lignin using infrared reflectance analysis techniques. Forage yield and maturity at harvest time were recorded. Significant date ✕ clone interactions were observed for all traits, but mean squares for clones were generally 10 or more times larger than for interactions. Clones that made large contributions to the date ✕ clone interaction typically had low yields and smaller than average declines in quality, or greater than average yields with greater than average declines in quality as the season progressed. No clone exhibited the desired interaction of high forage yield and a slower than average decline in forage quality, and genetic analysis suggested that development of such populations would be extremely difficult.
Characterization of Canopy Photosynthesis of Chlorophyll‐Deficient Soybean Isolines
Authors: Pettigrew W. T. , Hesketh J. D. , Peters D. B. , Woolley J. T.
Published: July 2010

The chlorophyll‐deficient, near‐isogenic lines of the soybean [Glycine max (L.) Merr.j genotype ‘Clark’, Clark y9 and Clark y11, have similar photosynthetic CO2‐exchange rates (CER) per unit leaf area as the wild‐type at full sun photosynthetic photon flux densities (PPFD). We hypothesized that, because of increased leaf reflectance and transmittance in such lines, more PPFD may penetrate the canopy, causing an increase in canopy CER. A 2‐yr field study on a Flanagan silt loam (Aquic Argiudoll) was undertaken to compare canopy CERs of the chlorophyll‐deficient isolines and the normal pigmented wild‐type. Canopy CER measurements were taken throughout the majority of the daylight period for several days in both growing seasons. For an 11‐d period in 1986, average CER values for Clark y9 were 14% higher than for Clark and during early pod fill average CER values for Clark y11 were 28% higher than for Clark in 1987. The canopy extinction coefficients for Clark y9 and Clark were not found to differ significantly. Clark and Clark y, were similar in maturity, but Clark y11 was on average 9 d earlier, which could have been a factor contributing to its higher CER. These results indicate that chlorophyll‐deficient isolines can, at times, photosynthetically out‐perform the wild‐type, possibly because of increased PPFD penetration into the canopy.
Allelopathic Effects of Wheat Straw on Cotton Germination, Emergence, and Yield
Authors: Hicks S. K. , Wendt C. W. , Gannaway J. R. , Baker R. B.
Published: July 2010

Because of recently enacted conservation compliance legislation, reduced and no‐till farming systems in which crop residues are left on the soil surface are becoming more important in areas where soils are highly erodible. On the southern high plains of Texas, many producers are planting cotton (Gossypium hirsutum L.) into wheat straw (Triticum aestivum L.). This study was conducted to determine the allelopathic potential of wheat residues on cotton germination, emergence, seedling growth, and lint yield. Laboratory bioassays revealed that cotton seedling development was inhibited by aqueous extracts of wheat straw. Cotton cultivars were screened for the ability to tolerate the inhibitive effects of wheat straw in laboratory bioassays and greenhouse pot studies. Tolerant ‘Paymaster 404’ and intolerant ‘Acala A246’ were identified and used in field experiments that were conducted in 1986 and 1987 to determine the influence of wheat stubble residues on their emergence and yield. Major reductions in emergence only occurred when above ground residues were present in the seedbed. Emergence was reduced by an average of 9% for Paymaster 404 and 21% for Acala A246 when wheat stubble residues were present in the seedbed. The allelopathic effect of wheat stubble indirectly influenced lint yield by affecting population densities. The negative effect of wheat stubble on cotton stand establishment can apparently be overcome by; limiting the amount of above ground residues that are incorporated into the seedbed during planting, increasing the seeding rates, and planting tolerant cultivars.
Association of Restriction Fragment Length Polymorphisms among Maize Inbreds with Agronomic Performance of Their Crosses
Authors: Lee M. , Godshalk E. B. , Lamkey K. R. , Woodman W. W.
Published: July 2010

Restriction fragment length polymorphisms (RFLPs) have been suggested as molecular markers to facilitate improvement of agronomic traits in maize (Zea mays L.). The objective of this study was to evaluate the utility of RFLP data in elucidating heterotic patterns among maize lines. Eight maize inbred lines and their 28 singlecross hybrids werevaluated for grain yield at two Iowa locations in each of 2 yr in a randomized‐complete block design. The diallel mating design permitted estimation of general and specific combining ability effects. Restriction fragment length polymorphism analysis of inbred lines included five restriction enzymes and five eDNA and 28 genomic clones distributed over the maize genome. Restriction fragment length polymorphism patterns of crosses were predicted from analysis of the inbred parents. Genetic distances between inbred lines were estimated as modified Rogers' distance (MRD). Grain yield and specific combining ability were significantly correlated with MRD for six of the 10 chromosomes. Dispersion of inbred lines and hybrids for RFLP allele frequencies was generally consistent with expectations based on known pedigrees. Results from this study suggest RFLP analysis as a potential alternative to field testing when attempting to assign maize inbred lines to heterotic groups.
Agronomic Comparisons Between Rht1 and Rht2 Semidwarf Genes in Winter Wheat
Authors: Allan R. E.
Published: July 2010

The Rhtl and Rht2 semidwarf genes have been the most extensively exploited factors for reducing height of wheat (Triticum aestivum L.). These genes have been used singly to develop hundreds of modern wheat cultivars. Information is limited on their relative breeding value. This study measured the effects of the Rht1 vs. the Rht2 gene on grain yield, grain yield components, lodging, crown placement, and stand establishment. Near isogenic lines of the four possible genotypes (Rht1Rhtlrht2rht2, rht1rht1Rht2Rht2, Rht1Rht1Rht2Rht2, rht1rht1rht2rht2) of four or five winter wheat populations representing three genetic backgrounds were tested in 15 trials conducted during 1976 to 1978 at several diverse environments in Washington. Compared to their rht1rht1rht2rht2 sibs, Rht1Rht1rht2rht2 and rht1rht1Rht2Rht2 isolines had similar average grain yield increases of 16% while the average increase of Rht1Rht1Rht2Rht2 isolines was only 2%. Mean differences in grain yield, grains spike−1, grain weight, crown placement, and lodging percentage were not significant (P > 0.05) between Rht1Rht1rht2rht2 and rht1rht1Rht2Rht2 isolines among or across populations. When averaged across populations, mean plant heights of rht1rht1Rht2Rht2 isolines were 2% shorter (P < 0.05) than Rht1Rht1rht2rht2 sibs. Generally, means for grain volume weight, emergence rate, and final stand of Rht1Rht1rht2rht2 isolines exceeded those of rht1rht1Rht2Rht2 isolines. These differences were not due to pleiotropic effects of the two genes because population ✕ Rht1 vs. Rht2 loci interactions occurred for each trait. From a breeding standpoint, use of Rht1 is warranted because it generally had less adverse effect on grain volume weight and stand establishment than Rht2.
Androgenetic vs. Gynogenetic Doubled Haploids of Tobacco
Authors: Wernsman E. A. , Matzinger D. F. , Rufty Rebeca C.
Published: July 2010

Cultivar development by doubled haploid (DH) methods employing in vitro anther culture has not been highly successful in tobacco, Nicotiana tabacum L., because of the low yielding ability of DH lines. The objective of this study was to compare DH lines developed from androgenetic and gynogenetic haploid sporophytes from the same parental plants. Single plants from ‘Ky10’, ‘Ky15’, and ‘Kyl7’ were self‐pollinated, crossed with pollen of N. africana Merx. and Buttler, and immature buds were anther cultured. Haploid sporophytes arising from embryo sac nuclei and vegetative nuclei of pollen were chromosome doubled and self‐pollinated. Ten random androgenetic DH lines (ADHs), 10 random gynogenetic DH lines (MDHs), and selfed progenies of the parental plant were assigned to a set, or cultivar family, and grown in three replications in each set in two environments. Data were collected for eight characters. Sixteen second cycle MDH lines were produced from one random first cycle line, Ky 10 MDH 1, and compared with the original Ky 10 parent, a first cycle MDH line composite, and Ky 10 MDH 1. The ADH and MDH lines were significantly different for all characters measured. The MDH lines were agronomically superior to ADH lines and more closely resembled the cultivars. The ADHs and MDHs yielded 79.9% and 91.5%, respectively, of the cultivars. A second cycle of MDH line production resulted in no further yield reduction. A model of heterozygosity and inbreeding depression in the parental cultivars could explain the results for yield of the MDH lines; it would not account for differences between ADH and MDH lines.
Method to Evaluate Pollen Viability of Upland Cotton: Tests with Chromosome Translocations
Authors: Gwyn J. Jefferson , Stelly David M.
Published: July 2010

Cytogenetically induced semisterility can provide a useful phenotype to facilitate many sorts of genetic and cytogenetic manipulations that otherwise require meiotic analyses. Most chromatin deficiencies are not pollen‐transmissible in Upland cotton (Gossypium hirsutum L.) due to reduced viability. A quick and reliable technique for the assessment of cotton pollen fertility has not been established. A modified fluorochrome reaction (FCR) method, using fluorescein diacetate, was evaluated for application as a pollen viability/fertility indicator by scoring fluorescence of pollen from normal and reciprocal chromosome translocation cytotypes grown in greenhouse and field environments. Analyzed materials included 44 different true‐breeding translocation homozygotes, respective F1 heterozygotes, and three different cytogenetically analyzed BC1F1 families. Translocation heterozygotes consistently produced higher frequencies (12.3–38.8%) of less intensely fluorescing pollen grains than homozygotes (0.4–6.4%) or normals (0.4–4.0%). Results were concordant with cytogenetic expectations and meiotic analyses, indicating that these and perhaps other cytogenetically aberrant types of cotton can be discerned phenotypically on the basis of percent pollen viability, thereby facilitating their detection and use as cytogenetic tools.
Ten Cycles of Full‐Sib Selection in Maize
Authors: Stromberg L. D. , Compton W. A.
Published: July 2010

Full‐sib selection is one method of intrapopulation improvement used in maize (Zea mays L.). This study was conducted to evaluate the progress from 10 cycles of full‐sib recurrent selection in the Nebraska Krug open‐pollinated maize population. A 2‐yr full‐sib selection cycle was applied to the Krug population beginning in 1966. The selection criterion was a multiplicative selection index consisting of yield (adjusted to 155 g kg−l moisture), proportion of standing plants, and proportion of plants without dropped ears. Based on field evaluations across nine seasons, the selection index increased 0.17 Mg ha−l cycle−1 (4.4% cycle−1), yield increased 0.07 Mg ha−l cycle−l (1.2% cycle−l), the proportion of standing plants increased 2.8% cycle−l, and the proportion of plants without dropped ears increased 0.1% cycle−l. Grain moisture at harvest decreased 3.0 g kg−l cycle−1 (0.3% cycle−1). Changes in plant traits other than those involved in the selection index were also measured. The multiplicative selection index was successful in increasing the yield on standing plants when applied to a full‐sib breeding system. Data indicate that yield on standing plants has continued to increase through the tenth cycle of selection.
Reproductive Efficiency of 14 Virginia‐Type Peanut Cultivars
Authors: Coffelt T. A. , Seaton M. L. , VanScoyoc S. W.
Published: July 2010

The reproductive efficiency (RE) of most peanut (Arachis hypogaea L.) cultivars has not been studied and methods for estimating RE have not been consistent. The objective of this study was to determine the changes in RE of 14 Virginia‐type peanut cultivars due to breeding efforts since 1944. The cultivars varied in release date, maturity, growth habit, and development breeding method. Field experiments were conducted at the Tidewater Agricultural Experiment Station, Suffolk, VA on two‐row plots 0.9 m wide by 6.1 m long. Plantings were made on 16 May 1983 on an Eunola loamy fine sand (fine‐loamy, siliceous, thermic Aquic Hapludult) and on 10 May 1984 on a Nansemond fine sandy loam (coarse‐loamy, siliceous, thermic Aquic Hapludult). Two randomly chosen plants were selected from each cultivar from each of four replicates for evaluation. Five methods of estimating reproductive efficiency (REM) were used: REM 1 = harvest index or (mature pod dry weight) (plant dry weight)−; REM 2 = (mature pod total) (flower total)−; REM 3 = (pod total) (flower total)−; REM 4 = (peg total + pod total) (flower total)−; and REM 5 = (mature seed total) (flower total ✕ 2)✕. Results indicated that earlier maturing cultivars had a greater RE than later maturing cultivars, erect cultivars had a greater RE than spreading cultivars, and RE was not affected by breeding method. Newer cultivars had a higher RE as estimated by REM 1 than older cultivars, but not as estimated by REM 2, 3, 4, and 5. The higher yield of most newer cultivars appeared to be related more to total flower production than to RE. Future increases for yield might best be accomplished by developing cultivars with combinations of high RE, harvest index, and total flower count.
Sugar Composition and Freezing Tolerance in Barley Crowns at Varying Carbohydrate Levels
Authors: Livingston D. P. , Olien C. R. , Freed R. D.
Published: July 2010

During hardening, carbohydrate content in winter cereals is affected by light intensity, which in turn affects freezing survival. To determine whether total carbohydrate content affects composition of individual sugars and whether particular composition is related to freezing tolerance, three barley (Hordeum vulgare L.) cultivars, differing in carbohydrate composition and in response to a controlled freezing test, were hardened under six light levels. At each level, total crown sugars were measured by water/ethanol extraction and high‐pressure liquid chromatogrphy and at four light levels plants were freeze tested. Carbohydrate composition changed depending on total carbohydrate content, and maximum freezing resistance was not found at the maximum simple sugar level. In addition, the relationship between kill temperature and total carbohydrate was different for the three cultivars. A simple relationship between carbohydrate composition and freezing tolerance was not found, but results suggest that the three cultivars may allocate total carbohydrate differently for cryoprotection.
Potassium Influence on Susceptibility of Bermudagrass to Helminthosporium cynodontis Toxin
Authors: Richardson M. D. , Croughan S. S.
Published: July 2010

Inadequate K fertilization of bermudagrass, Cynodon dactylon (L.) Pers., can lead to stand loss and increased disease symptoms. This study was conducted to determine the relationship between fungal leaf spot (Helminthosporium cynodontis Marig.) susceptibility and K status of hybrid bermudagrass ‘Grazer’ and ‘Tifton 78’ bermudagrass were grown in washed sand under six K fertilization rates (10, 30, 70, 100, 200, and 400 mg kg−1) in a greenhouse. Plants were clipped three times at 28‐d intervals and the K concentration in the tissue was determined. Prior to the final clipping, 4 mL of culture filtrate containing toxin (CFT) produced by H. cynodontis was sprayed in a fine mist on each plant. Plants were rated for disease severity according to leaf spot coverage after approximately 36 h. A curvilinear relationship was observed between disease severity and tissue K concentration. Leaf spotting increased when tissue K levels decreased below about 25 g/kg. Tifton 78 was more resistant than Grazer to CFT. Tifton 78 maintained higher tissue K levels at all fertilization rates due to lower biomass production and comparable amounts of K removed. Varietal differences should be considered when determining proper K fertilization rates from tissue analysis.
Modified Half‐Sib and Phenotypic Recurrent Selection for Resistance to Powdery Mildew in Winter Wheat
Authors: Abdalla A. H. , Coffman W. R. , Sorrells M. E. , Bergstrom G. C.
Published: July 2010

Specific resistance to powdery mildew of wheat (Triticum aestivum L.), incited by Erysiphe graminis f. sp. tritici, has been associated with several major genes that are relatively easy to select in segregating populations. Nonspecific resistance is more difficult to select because of genetic and nongenetic factors that lower heritability. The objectives of this study were to: (i) determine the effectiveness of recurrent selection for accumulating genes for nonspecific resistance to powdery mildew in two winter wheat populations, and (ii) examine the effect of changes in the level of resistance on other components of resistance. Two winter wheat populations (designated Early and Elite) carrying a dominant male sterile gene were subjected to two cycles of recurrent selection for powdery mildew resistance using phenotypic recurrent selection and modified half‐sib family selection. Ten‐day‐old seedlings were inoculated in the greenhouse with a spore suspension consisting of equal amounts of four isolates possessing combined virulence that overcame all known powdery mildew resistance genes except Pm3b and Pm8. Beginning 7 d after inoculation, area under the disease progress carve (AUDPC) was determined four times at 4‐d intervals and used select individuals for the next cycle. The mean AUDPC on the primary leaves of S1 families and the realized gains after two cycles of selection indicated that the Elite population averaged 46% gain over the two selection methods compared to 35% gain for the Early population. Over two cycles, half sib selection gains of 40 and 53% were realized in the Early and Elite population, respectively, while phenotypic recurrent selection reduced AUDPC 30% in the Early population and 40% in the Elite population. For both populations, selection for low AUDPC resulted in significantly decreased final disease severity ratings, colony number, and cumulative sporulation capacity. Duration of the incubation period was significantly increased only with two cycles of half‐sib selection for AUDPC. A high correlation between AUDPC and the final disease severity rating indicated that the breeder could select for nonspecific resistance using a final disease severity rating provided the test materials are all inoculated simultaneously.
Feasibility of Mass Selection in Pearl Millet
Authors: Rattunde H. F. , Singh Pheru , Witcombe J. R.
Published: July 2010

Mass selection is a technique widely used in both population and pedigree breeding of pearl millet, Pennisetum glaucum (L.) R. Br. To determine the feasibility of mass selecting for 19 agronomic traits of pearl millet, we (i) estimated trait heritabilities on both a single‐plant and a progeny‐mean basis and (ii) observed responses of S1 progenies to divergent selection on parental S0 plants. Fourteen hundred and forty S0 spaced plants from each of three pearl millet composites were self‐pollinated and evaluated for 19 traits at Patancheru, India on a Udic Rhodostalf soil. Random samples of 289 S1 progenies from each S0 population were evaluated for these same traits in triple‐lattice experiments at the same location. Heritabilities estimated on a progeny‐mean basis were all significantly (P < 0.01) larger than zero. Heritabilities estimated on a single‐plant basis were highest for traits such as panicle length (0.64), plant height (0.58), and seed weight (0.52); they were intermediate straw yield (0.40); and they were lowest for grain yield (0.29), threshing ratio (0.24), and harvest index (0.23), averaged across composites. Divergent selection of the highest and lowest decile of S0 plants identified S1 progenies with significantly (P < 0.05) increased and decreased means, respectively, for panicle and seed characteristics in all composites and for grain yield in two of the composites. Selection for increased efficiency of dry matter partitioning, however, was ineffective. The observed heritability values suggest that mass selection of pearl millet can be effective for all traits examined, with the rate of gain being proportional to the magnitude of those values.
Identification of New Sources of Resistance to Root‐knot Nematodes in Phaseolus
Authors: Omwega C. O. , Thomason I. J. , Roberts P. A. , Waines J. G.
Published: July 2010

Resistance to root‐knot nematode, Meloidogyne incognita (Kofoid and white) Chitwood, has been identified and incorporated into commercial cultivars of common bean, Phaseolus vulgaris L. However, the effective use of host resistance as a management tactic against root‐knot nematodes attacking common bean requires identification and incorporation of resistance to other economically important root‐knot nematodes, namely M.javanica (Treub) Chitwood, M. arenaria and M. hapla. Fifty‐four common bean and 64 tepary bean, P. acutifolius A. Gray, lines were screened for resistance to root‐knot nematodes under greenhouse and growth chamber conditions. In the greenhouse, the plants were grown in pots filled with loamy sand and, in the growth chamber, the plants were grown in growth pouches. Bean plants in the greehouse were inoculated with 5000 nematode eggs and evaluated for nematode reproduction (eggs) 6 wk after inoculation. In the growth chamber, plants were inoculated with 1000 second‐stage juveniles and evaluated for egg numbers 4 wk after inoculation. Common bean lines PI 165426 and Alabama no. 1 were found to be resistant to M. incognita Race 2, 3 and 4 but were susceptible to M. incognita Race 1 and to M. arenaria. Breeding lines A252, A315, A328, A443 and A445 were resistant to M. javanica and M. incognita Race 1. Resistance in the A lines was found to be derived from two common bean landraces, G1805 and G2618. The resistance was also effective against M. arenaria. The tepary bean accession PI 310606 was found to have good resistance to all nematode isolates tested. We postulate that resistance derived from G1805 and G2618 may be under different genetic control than that in PI 165426 and Alabama no. 1.
Path Analyses for Percent Fiber, and Cane and Sugar Yield in Sugarcane
Authors: Kang M. S. , Sosa O. , Miller J. D.
Published: July 2010

Path coefficient analysis is an excellent technique for measuring the direct and indirect effects of interrelated components of a complex trait. Although percent fiber in sugarcane(Saccharum spp.) is an important factor from the standpoint of milling efficiency, its effect on tons per hectare of cane( THC) has not been investigated. A knowledge of the effects of components of percent fiber and of the contribution of percent fiber to THC would be useful in deciding on selection criteria for improving THC. This study of plant‐cane and first‐ratoon crops from two locations was conducted to: (i) evaluate the direct and indirect effects of rind puncture resistance(measured by a rind penetrometer), percent juice extraction, and percent moisture retained by fiber (bagasse) on percent fiber, and( ii) determine the direct and indirect effects of percent fiber, stalk weight, and stalk number on THC. The direct effect of rind puncture resistance on percent fiber was positive( 0.1925), and those of percent juice extraction and percent moisture retained by bagasse were negative (−0.4729 and −0.7275, respectively). The coefficient of genetic variation (CGV) for rind puncture resistance was higher( 14.4%) than the CGVs for percent juice extraction and percent moisture of bagasse (2.6% and 3.7%, respectively). Reasonably rapid progress in reducing percent fiber would be made by selecting for softer stalks. The direct effect of percent fiber (0.024) on THC was negligible in relation to the direct effects of stalk weight(0.478) and stalk number (0.841). Cane yield would be increased by placing the greatest emphasis on stalk number, and next on stalk weight. Percent fiber was the least important component of THC. THC was the most important component of tons per hectare of sugar (THS), followed by sugar concentration. Percent fiber was the least important component of THS.
Nitrate Inhibition of Nodulation and Nitrogen Fixation by Supernodulating Nitrate‐Tolerant Symbiosis Mutants of Soybean
Authors: Eskew David L. , Kapuya Juma , Danso Seth K. A.
Published: July 2010

Several soybean [Glycine max (L.) Merr.] mutants that form a greater number of nodules (supernodulation) and display a nitrate tolerant symbiosis (nts) phenotype when grown in sand with continuous additions of NO−3 have recently been isolated. Greenhouse experiments were conducted to compare three of the nts mutants (nts 382, nts 1007, and nts 1116) to the parent cultivar Bragg, when grown in soil (3 kg) with a single addition of either 7.5, 150, 300, or 450 mg NO−3−N (KNO3) at planting. Estimated % N derived from the atmosphere (% Ndfa, 15N dilution) was significantly higher (P = 0.05) for nts 382 than for Bragg at the 7.5 mg NO−3−N level at the V5 and R3 growth stages, but 150 mg NO−3−N greatly reduced nodulation and % Ndfa in both of these genotypes. All four genotypes were compared at R7. Percent Ndfa was significantly higher for the nts mutants (72% average) than for Bragg (65%) at the 7.5 mg NO−3−N level. Nodule number was reduced (53% average) for the nts mutants at the1 150 mg NO−3−N level, but there was no reduction for Bragg. At the 300 mg NO−3−N level, nts 1007 showed a greater tolerance, 49 % Ndfa, than nts 382 and nts 1116, 31 and 28 % Ndfa, respectively (Bragg not determined). At the 450 mg NO−3−N level, nodulation was almost completely inhibited in all genotypes. Nitrate reductase activity was found in the shoots and roots of all genotypes. The results clearly indicate that the nts mutants were still sensitive to NO−3 and suggest that these are not mutations in the NO−3 response mechanism per se. Nitrogen fixation by nts 382 was greater than by Bragg early in growth, but only a slight advantage was maintained at physiological maturity.
Proline Content of the Anthers and Pollen of Heat‐Tolerant and Heat‐Sensitive Cowpea Subjected to Different Temperatures
Authors: Mutters R. G. , Ferreira L. G. R. , Hall A. E.
Published: July 2010

High temperatures cause reductions in grain yield of cowpea [(Vigna unguiculata (L.) Walp.] that are associated with low pollen viability and pod set. Preliminary controlled environment studies showed differences in proline accumulation in anthers and pollen of heat‐tolerant and heat‐sensitive genotypes under hot and optimal temperatures, but insufficient tissue was available to establish if the differences were significant. The objective was to determine whether heat injury under field conditions is associated with specific patterns of proline accumulation in leaves and reproductive tissue using heat‐sensitive an heat‐tolerant cowpea genotypes. Under moderate and hot temperatures, proline was the most abundant free amino acid in the anthers of both heat‐sensitive and heat‐tolerant cowpea genotypes. No differences in leaf proline concentrations were observed. Under hot conditions, proline levels in anthers decreased faster as pollen matured in heat‐tolerant genotypes as compared with heat‐sensitive genotypes. At pollen maturity, heat‐sensitive genotypes contained more proline in anthers and had lower levels in pollen than the heat‐tolerant genotypes under hot conditions but similar levels under more optimal temperatures. The results suggest that heat injury during floral development of sensitive cowpea genotypes may be due to inhibition of proline translocation from anther walls to pollen.
Genetics of Resistance to Reniform Nematode in Upland Cotton
Authors: Muhammad Noor , Jones Jack E.
Published: July 2010

Reniform nematode (RN), (Rotylenchulus reniformis Linford and Oliveira) is an economically important pest of upland cotton (Gossypium hirsutum L.). Sources of resistance to RN have been identified, but inheritance of resistance has not been studied previously. Four cotton lines [La RN‐910, Auburn (Aub) 612‐RNR, M 019‐ RNR, and ‘Deltapine 41’ (Dp 41)] were selected as parents for genetic study of resistance to RN reproduction. Deitapine 41 (susceptible) was crossed to each of the three lines previously reported as resistant. Means of P1, P2, F1, F2, BC1P1, and BC1P2 generations in the three crosses were analyzed by the generation mean analysis procedure to estimate gene effects. Seedlings grown in the greenhouse were individually inoculated at the first true leaf stage with 2000 RN juveniles. After an average growth period of 43 d in the winter and 32 d in the summer, the entire root system of each plant was harvested, and RN eggs were extracted and counted. Significant (p < 0.05) differences among generations and nondiscrete frequency distributions in segregating populations indicated that RN resistance in two of three crosses (La RN‐910 ✕ Dp 41 and Aub 612‐ RNR ✕ Dp 41) was under genetic control and inherited in a quantitative manner. No pattern was observed for the significance of additive and dominance gene effects, but significant (P < 0.05) epistatic gene effects occurred in most cases. The occurrence of transgressive segregation for susceptibility and epistatic gene effects suggest that resistance to RN in these cotton lines was controlled by two or more pairs of genes. Advancing generations to F4 or F5, while maintaining genetic variability prior to selection, may improve selection efficiency by reducing nonadditive gene effects for RN resistance. High coefficients of variation and general lack of additive gene effects suggest that future genetic and breeding studies for RN resistance may be enhanced by reducing environmental effects and exploring other sources of resistance.
Phosphine Fumigation Influence on Rice Seed Germination and Vigor
Authors: Krishnasamy V. , Seshu D. V.
Published: July 2010

Fumigation of seeds is one of the quarantine precautions directed against the international spread of pests. Seed treatment should ward off the pests without hampering seed germination and vigor. A study was conducted to evaluate the effect of fumigation with phosphine at different doses, exposure times, and seed moisture contents, and after the seed has been treated with fungicides on seed germination and seedling vigor in rice (Oryza sativa L.). The fumigated seed was evaluated for germination and vigor, initially and after 90 d of storage. At the normal recommended dose of 3 g m−3, fumigation did not affect germination or vigor. At 6 g m−3, vigor decreased. The effect became more perceptible after 90 d of storage. Long exposure time (6 d) showed deleterious effects. Entry differences were not significant under any of the treatments with respect to germination percentage, shoot length, root length, and seedling dry weight. However, such differences were evident in the degree of seed leaching as measured by the electrical conductivity of the leachates, and dehydrogenase activity, when seed was fumigated with a higher dose (6 g m−3) of phosphine and evaluated after 90 d of storage. There were no interaction effects between fungicidal treatment with Benlate [methyl l‐(butylcarbamoyl)‐2‐benzimi dazole carbamate] or Dithane M‐45 (zinc ion and manganese ethylene bisdithio carbamate) and fumigation on seed germination and vigor.
Field Drought Tolerance of a Soybean Plant Introduction
Authors: Sloane Richard J. , Patterson Robert P. , Carter Thomas E.
Published: July 2010

Rainfall is seldom sufficient to meet the evaporative and transpirational demands of a soybean crop [Glycine max (L.) Merr.] in the southeastern USA. Development of new drought‐tolerant cultivars would thus seem an effective way in which to address the problem of moisture stress. Unfortunately, few drought‐tolerant genotypes have been identified for use as breeding stock. The objective of this study was to compare the relative droughtolerance of plant introduction PI 416937, a visually slow‐wilting accession, with that of ‘Forrest’, a popular cultivar of similar maturity. Leaf water potential (Ψw), solute potential (Ψs), and relative water content (RWC) these genotypes were measured under two levels of soil water adjustment (well‐watered and water‐stressed at early pod‐fill) during 2 yr in the field (on a Varina loamy sand, a clayey, kaolinitic, thermic Plinthic Paleudult). Although water stress reduced Ψw equally for both genotypes, PI 416937 maintained lower levels of Ψs and. higher levels of pressure potential and RWC than Forrest. A comparison of the relationship between RWC and Ψs for the two genotypes indicated that the PI may accumulate more solutes in leaf tissue under stress than Forrest. That is, at a normalized leaf pressure potential of zero, the Ψs of the PI was estimated to be 0.3 MPa lower than that of Forrest. Seed yields of Forrest and the unadapted PI were comparable under stress. However, stress reduced the yield of Forrest by more than half while reducing yield of the PI by only a third. The superior turgor maintenance and competitive yielding ability of the unadapted PI under stress indicated that the PI may be an important source of drought tolerance for breeding programs.
Nitrogen Compositional Changes in Xylem Exudate and Leaves of Burley Tobacco
Authors: MacKown C. T. , Sutton T. G. , Bush L. P.
Published: July 2010

Leaf nitrate accumulation occurs when nitrate transport to the leaf exceeds the assimilation rate of the leaf. Observed differences in leaf nitrate concentrations of hurley tobacco (Nicotiana tabacum L.) cultivars may be associated with differences in xylem exudate nitrate. Field studies during 2 yr compared xylem exudate and leaf N composition of low (LN) and high (HN) leaf nitrate‐accumulating cultivars. In both years the LN, ‘KY15’, and the HN, ‘KY16’, were used; in the second year the HN, ‘Casey’, was added. The tobacco cultivars (main plots) were grown near Lexington, KY on a Maury silt loam (fine, mixed, mesic, Typic Paleudalf). Plants were sampled (subplots) beginning at the onset of linear growth and continuing until harvest. Leaf lamina nitrate averaged for three leaf positions and over all sampling dates was 287 and 455 mmol kg−1 for KY15 and KY16, respectively, in 1986 and 393, 551, and 580 mmol kg‐1 for KY15, and KY16, and Casey, respectively, in 1987. Differences in lamina nitrate were not due to differences in tissue dry weight. Within each year, total N concentration of xylem exudate for each cultivar was relatively constant, even though nitrate decreased and reduced N increased over time. Average xylem exudate nitrate concentrations of the HN cultivars were 16 and 13% greater than KY15, while average lamina nitrate concentrations of the HN cultivars were 59 and 44% greater than KY15 in 1986 and 1987, respectively. Assuming similar transpiration rates among the cultivars, differences in leaf nitrate levels appear to be related primarily to leaf nitrate assimilation and only partly to cultivar differences in xylem exudate N composition.
Changes During Early Soybean Seed and Axes Deterioration: I. Seed Quality and Mitochondrial Respiration
Authors: Ferguson J. M. , TeKrony D. M. , Egli D. B.
Published: July 2010

Understanding the cause of soybean [Glycine max (L.) Merr.] seed deterioration during storage will assist in the development of accurate laboratory tests to evaluate seed vigor. This study was designed to investigate the changes that occur in mitochondria! respiration during the early stages of soybean seed deterioration. High‐quality seed lots of ‘Desoto’ and ‘Union’ soybean were stored at 25 °C and 115 g kg‐1 seed moisture. Seed quality (germination and vigor) and conductivity of leachate from embryonic axes were measured at monthly intervals during storage. Mitochondrial State 3 (ST 3) respiration rates and respiratory control ratios (RCR) were measured from excised axes of samples after 24 h of imbibition. Germination remained high for seeds of both cultivars throughout storage; however, seed vigor (as measured by accelerated aging) declined significantly after 7 and 10 months for Union and Desoto, respectively. Conductivity of the leachate from excised axes for both cultivars increased early during storage prior to detectable changes in whole seed vigor. State 3 respiration rates of mitochondria from axes decreased throughout storage and RCR values declined after 2 months for Union and after 4 months for Desoto. Decreases in ST 3 respiration rates and RCR in both cultivars preceded measurable declines in whole‐seed vigor and correlated with increases in the conductivity of axes leachate.
Diallel Analysis of Callus Induction and Green‐Plant Regeneration in Rice Anther Culture
Authors: Quimio C. A. , Zapata F. J.
Published: July 2010

Low efficiencies of callus induction and green‐plant regeneration have limited the application of anther culture in breeding programs. This study was conducted to determine the inheritance of callus induction and plant regeneration in rice (Oryza sativa L.) anther culture. Sixteen genotypes derived from a four‐parent diallel mating set of two Japonica cultivars (Taipei 309 and Taipei 177) and two indica cultivars (IR36 and Basmati 370) were evaluated for their callus induction and plant regeneration abilities. For callus induction, the effects of genotype and genotype ✕ medium interaction were significant (P < 0.05). Similarly, genotype and abscisic acid (ABA) level were found to be significant (P < 0.05) for green‐plant production. The japonica cultivars generally had a higher percent callus induction and plant regeneration, and number of calli producing green plants than did the indica cultivars. Similar modes of inheritance were observed for both characters. Combining ability analysis demonstrated the predominance of additive gene effects in the control of both characters with the japonica cultivars having higher combining ability for green‐plant regeneration. Reciprocal effects were not significant (P > 0.05), suggesting the absence of maternal control on the characters. Further analysis showed gene action to be partially dominant with high response being highly recessive and controlled by a few genes. There were no indications of inter‐allelic interaction.
Digestion Kinetics and Cell Wall Composition of Brown Midrib Sorghum ✕ Sudangrass Morphological Components
Authors: Fritz J. O. , Moore K. J. , Jaster E. H.
Published: July 2010

Microbial degradation of plant fiber is an important factor limiting the utilization of forages by ruminant animals. The objectives of this study were to determine the composition and rate and extent of digestion of cell walls of normal and brown midrib (bmr) genotypes of two sorghum ✕ sudangrass [Sorghum bicolor( L.) Moench] hybrids and to assess the relationship between cell wall composition and digestibility. Plants, harvested at three stages of maturity, were separated into leaf blade, leaf sheaths, and stems and analyzed for fiber constituents, structural carbohydrates, and, alkali‐labile phenolic composition. Fiber digestion kinetics were determined utilizing in vitro batch cultures. Brown midrib genotype were lower (P < 0.05) in neutral detergent fiber(NDF) and acid detergent lignin concentrations than normal genotypes. Leaf components had a greater (P< 0.05) NDF concentration than stems; however, leaf cell walls were much less lignified than stem cell walls. There were no differences between genotypes (P > 0.05) in neutral sugar composition or in the xylose to arabinose(X:A) ratio. Morphological components varied in the concentration of all neutral sugars, except mannose, and in the X:A ratio. Brown midrib genotypes had a significantly lower trans‐p‐coumaric acid concentration and a p‐coumaric acid to ferulic acid ratio than normal genotypes. There was no difference (P>0.05) between genotypes in the rate of NDF digestion, which averaged 0.0413 and 0.0.95 h‐1 for bmr and normal genotypes, respectively; however, bmr genotypes. had a greater (P<.05)72 h extent of NDF digestion when compared to normal genotypes. The results of this study indicate that the p‐couramic acid concentration and the linear xylan content are important factors limiting the rate and extent of cell wall digestion.
Environmental Factors and Plant Phenotype Affect Alfalfa Floret
Authors: Knapp E. E. , Teuber L. R.
Published: July 2010

Extent of floret tripping influences alfalfa (Medicago sativa L.) seed yields. Our objectives were to determine if environmental factors influenced ease of tripping and if clones differing in ease‐of‐tripping phenotype affected the frequency of floret tripping in the field. Experiments were conducted in the field, in growth chambers, and in the greenhouse to determine the effect of time of day, temperature, relative humidity, and soil moisture on ease of tripping. Frequency of tripping and seed yield were evaluated on easy‐ and hard‐to‐trip clones in the field at Davis, CA. Florets on the hard‐to‐trip clones were easier to trip midday than early morning. Time of day did not affect ease of tripping of the easy‐to‐trip clones. Shifting temperature from 18 to 32 °C resulted in easier‐to‐trip florets than when temperature was shifted from 32 to 18 °C (P ≤ 0.05). Relative humidity did not influence ease of tripping. Florets tended to be easier to trip (P ≤ 0.07) under high soil moisture conditions. In the field, a greater percentage of florets was tripped on the easy‐to‐ trip phenotype (52.0%) than on the hard‐to‐trip phenotype (22.6%) (P ≤ 0.01). Manipulating ease of tripping through selection and breeding should be more successful than management of environmental factors influencing ease of tripping. Development of cultivars with florets that trip easily may increase alfalfa seed yield.
Sensitivity of Pollination to Water Deficits at Anthesis in Upland Rice
Authors: Ekanayake I. J. , Steponkus P. L. , De Datta S. K.
Published: July 2010

Rice (Oryza sativa L.) subjected to water deficit during anthesis shows pollination abnormalities resulting in low grain yields. To understand the mechanism of stress‐induced poor grain filling in relation to disturbed pollination, upland‐adapted cultivars were grown under controlled conditions. A 7‐day irrigation‐withholding period (Exp. 1) induced −1.7 and −2.0 MPa flag leaf water potentials (Ψ) in ‘Kinandang Patong’ and 63–83, respectively. A stress protocol for 7 d at anthesis achieved stress intensities of −0.4, −0.8, −1.1, −1.4, −1.7, −2.0, −2.3, −2.5, and −2.8 MPa in 63–83 and IRAT13 (Exp. 2). On the last day of the water‐deficit stress period, anther dehiscence of spikelets, pollen shedding, viability, germination, and spikelet sterility (at plant maturity) were measured. In each upland cultivar tested, low Ψ reduced pollen shedding capacity and germination. Dehiscence of anthers correlated with flag leaf Ψ (R2 = 0.944** [significant at P = 0.01] [IRAT13] and 0.987** [63–83]). Up to a stress intensity of Ψ1.4 MPa, more than 80% of anthers dehisced. Below −2.0 MPa, more than 60% of pollen grains did not dehisce. Pollen shed, total pollen per spikelet, and spikelets with more than 20 pollen were all directly related to Ψ. Pollen germination in vivo and germination per spikelet correlated linearly with water stress intensity. Significant deleterious effects on pollen viability at low water potentials were noted. All measured pollination traits accounted significantly for increases in unfilled spikelets at severe stress intensities. Thus, to ensure pollination success and spikelet fertility, responses of upland rice genotypes to a water deficit at anthesis could be evaluated using anther dehiscence, pollen shedding, and pollen germination in controlled conditions.
Agrobacterium tumefaciens Susceptibility and Plant Regeneration of 10 Soybean Genotypes in Maturity Groups 00 to II
Authors: Delzer B. W. , Somers D. A. , Orf J. H.
Published: July 2010

Agrobacterium‐mediated transformation of soybean [Glycine max (L.) Merr.] plants is affected by the susceptibility of genotypes to specific Agrobacterium strains and by the ability to regenerate plants from transformed cells of those genotypes. The objectives of this study were to: (i) determine susceptibility of cotyledons from 10 Maturity Group 00 to II soybean genotypes to strains C58, A208, and A281 of A. tumefaciens and, (ii) determine the frequency of plant regeneration from tissue cultures of the same soybean genotypes. Cotyledons from 1‐d‐old axenic seedlings of the 10 genotypes and ‘Peking,’ a highly susceptible Maturity Group IV cuitivar, were excised, wounded, and inoculated with the A. tumefaciens strains. The relative frequency of tumor formation, an indicator of susceptibility, was greatest for strains C58 and A208 on all soybean genotypes tested. The soybean genotypes Peking and PI 180529 were most susceptible. The same genotypes were evaluated from shoot organogenic tissue culture initiation from the cotyledonary node and plant regeneration via adventitiou shoot formation. The genotypes producing the highest frequency of mature plants during 30 weeks after culture initiation were Experimental Line HHP, ‘Evans’, PI 445799, ‘Hodgson 78’, ‘Corsoy 79’, and PI 180529. These may be useful genotypes for whole plant transformation studies.