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Maize (Zea mays L.) germplasm available at CIMMYT for resistance to the maize weevil (Sitophilus zeamais Motsch.) was used to investigate the biochemical and biophysical basis for resistance. García-Lara et al. (44:1546–1552) investigated weevil resistance with phenolic acid content, hydroxyproline-rich glycoproteins, grain hardness, and physical properties of the pericarp. Cell wall cross-linking components could contribute to resistance by fortification of the pericarp cell wall and contribute to grain hardness. This structurally based mechanism should be considered in the development of hybrids and varieties where storage pests are prevalent.
Sugarcane Yields in High Water Tables
Sugarcane (Saccharum spp.) in the Everglades Agricultural Area (EAA) increasingly is exposed to periodic floods and undesirably high water tables. In a 2-yr study using lysimeters filled with organic soil common to the EAA, Glaz et al. (44:1633–1641) tested leaf photosynthesis, transpiration, and stomatal conductance of two sugarcane genotypes exposed to four 21-d cycles of 7-d flooding followed by drainage for 14 d to depths of 16, 33, or 50 cm. A fourth water treatment was a constant water-table depth of 50 cm. High water table and floods usually did not reduce, and sometimes enhanced, sugarcane leaf CO2 exchange rates. These results help explain previously reported results of favorable sugarcane yields in high water tables.
Peanut Genetic Diversity
An understanding of the amount and distribution of genetic variation within and among peanut (Arachis hypogaea L.) varieties will assist in the efficient conservation and use of peanut germplasm. Ferguson et al. (44:1847–1854) assessed genetic diversity in six peanut botanical varieties and among three continents of origin, using 12 microsatellite loci. Eighty-nine alleles were scored. Maximum differentiation was observed among continents within varieties for three varieties. Nei's unbiased estimate of gene diversity revealed very similar levels of diversity within botanical varieties. Landraces from South America had the highest diversity, and possessed 90% of alleles, compared with Africa (63%) and Asia (67%). Patterns of diversity are explained in terms of dispersal from a center of origin and diversity, and observed adaptation.
Nonflowering Orchardgrass Trait
Orchardgrass (Dactylis glomerata L.) is a valuable pasture species in much of temperate humid North America. However, profuse and early flowering in spring creates management problems for graziers and reduces intake of livestock in a management-intensive rotational grazing system. Casler et al. (44:1601–1607) demonstrated that nonflowering orchardgrass populations have plants with a wide range of expression of this trait, ranging from slight expression (sparse-flowering in one year) to highly stable (stable nonflowering across years). The nonflowering trait appears to be controlled by genes that are temperature sensitive—colder winters promoted more reliable and stable expression of the nonflowering trait. Nonflowering populations had adequate panicle production in a seed production environment, suggesting that commercial seed production of nonflowering orchardgrass is possible.
Corn Stover Lignin Concentration of Non-Bt and Bt Commercial Hybrid Pairs
Corn (Zea mays L.) hybrids incorporating the Bt transgene have occasionally been reported to contain more lignin than nontransgenic hybrids, suggesting that forage quality of silage from Bt hybrids might be compromised. Jung and Sheaffer (44:1781–1789) determined lignin concentration of corn stover by three methods of analysis for six non-Bt/Bt commercial hybrid pairs grown in a replicated trial at four locations in Minnesota. Presence of the Bt transgene had no effect on lignin concentration or any other forage quality trait. Producers can expect Bt corn hybrids to be of similar forage quality as non-Bt hybrids of similar genetic background.
Turfgrass Response to Potassium Fertilization
Turfgrass response to K fertilization has been inconsistent. In this study, Fitzpatrick and Guillard (44:1721–1728) determined the effects of varying K and N fertilization rates on Kentucky bluegrass (Poa pratensis L.) clipping dry matter yield, quality, tissue K concentration, apparent N recovery, and N use efficiency. There were no positive effects of K fertilization on clipping yields or quality, even though the initial soil extractable K levels tested low. Increasing the K rate for all but the highest N rate, however, increased apparent N recovery and use efficiency. This effect was more pronounced as the N rate decreased. Tissue K concentrations increased with initial K rates, but not at the highest K rates. There was no relationship between tissue K concentrations and clipping yields or quality, suggesting that adequate K was being supplied without fertilization at this site to meet Kentucky bluegrass needs. Nonexchangeable K levels were high in the sandy loam soil, possibly supplying an additional source of K for bluegrass during the growing season. These results suggest that extractable K values alone may not adequately predict K availability to Kentucky bluegrass in this soil.
Buckwheat Interspecific Hybridization, Isozyme Patterns, and Cytology
Chen et al. (44:1511–1518) studied the interspecific hybridization, GOT (glutamate oxaloacetate transaminase) isozyme patterns, and cytology of 11 accessions of eight species belonging to the big-achene group of genus Fagopyrum Moench. Following normal pollination, it is suggested that there are no reproductional isolations among F. esculentum, F. esculentum var. homotropicum, and F. esculentum subsp. ancestrale. The results of GOT isozyme supported the hypothesis that F. megaspartanium (genome M) and F. pilus (genome P) are the ancestral species of common buckwheat (genome E) and tartary buckwheat (genome T), respectively. The cytological analyses showed that tetraploid F. cymosum and F. giganteum are all allotetraploid species with two different size genomes. The two genomes of F. giganteum were designated M and T, and those of F. cymosum X and P.
Turfgrass Seed Weight and Germination
In this study, Larsen and Andreasen (44:1710–1720) described the relationship between seed weight and germination in the turfgrass species slender creeping red fescue (Festuca rubra L. subsp. litoralis Vasey), perennial ryegrass (Lolium perenne L.), and Kentucky bluegrass (Poa pratensis L.). Seed lots were graded into nine seed weight fractions, and a sample from each fraction was germinated at two temperature regimes. For all species and both temperature regimes, germination percentage increased, and mean germination time decreased with increasing 1000-seed weight. When combining data from the two temperatures, we found that mean germination thermal time decreased with increasing 1000-seed weight, that is, light seeds of all three species required more degree days for germination than heavy seeds.
Soil-Conserving Crop Production System
Delineation of the benefit derived from either surface or subsoil tillage is important for the advancement of soil-conserving crop production systems in the Coastal Plain. Soils of the experimental plots initially possessed different surface residue and organic matter characteristics because they had received in-row subsoiling with either surface-disking tillage or no surface tillage for the previous 18 consecutive years. Hunt et al. (44:1673–1681) split the plots into subsoiled and no subsoiled. The experiment was conducted during one of the driest 5-yr periods of the last half century. Surface no-till and the associated accumulation of organic matter could only somewhat compensate for the need to subsoil. With or without surface tillage, paratill subsoiling was very beneficial for corn (Zea mays L.) and wheat (Triticum aestivum L.) yields.
DNA Markers for Three Rice Blast Resistance Genes
Most molecular markers found to be linked to rice blast resistance genes are not amenable for marker-aided selection of resistance. The goal of Fjellstrom et al. (44:1790–1798) was to develop PCR-based molecular markers tightly linked to three rice blast resistance genes, Pi-b, Pi-k, and Pi-ta2. Microsatellite markers were identified that closely flank all three blast resistance genes, two microsatellite markers that (independently) co-segregate with the Pi-b and Pi-k genes, and one dominant marker based on the published Pi-b gene sequence that co-segregates with the Pi-b gene. These markers should enable the efficient selection and stacking of these genes for the development of broad-based blast resistant rice cultivars.
Cultivated Barley ß-Amylase Types
ß-Amylase is the most important enzyme for brewing beer, and the landraces of the crop is a treasury of genetic diversity. Zhang et al. (44:1608–1614) investigated ß-amylase types of 8270, a worldwide collection of cultivated barley (Hordeum vulgare L.) accessions by analyzing the thermostability and isoelectoric focusing (IEF) patterns. By combining the thermostability and IEF pattern, 14 types constituted of five common and nine rare types including ß-amylase-less and super thermotolerant mutants were detected. ß-Amylase types showed a clear geographical differentiation reflecting the phylogenetical differentiation of the barley: nearly 90% of East Asian accessions were the high-thermostable type but 97% of Ethiopian accessions were the low-thermostable type.
Semiarid Conditions and Mulched Wheat
Sustainable production of food grains to meet increasing demands for grain products in semiarid northwest China has been a challenge to agriculture. Niu et al. (44:1682–1688) used plastic mulches as a means to improve soil water conservation in a study where they quantified the seasonal and spatial patterns of root growth in spring wheat (Triticum aestivum L.) grown with and without plastic mulches. Under semiarid conditions, mulched wheat produced 22% more root weight, 23% more seeds per plant, 5% heavier seed weight, and 28% greater grain yield than unmulched wheat.
Reciprocal Recurrent Selection in Maize
Reciprocal recurrent selection (RRS) in maize (Zea mays L.) is used to develop populations with superior combining ability when crossed with one another. It is usually assumed that these populations must be genetically diverse for RRS to be effective. Butruille et al. (44:1527–1534) evaluated six cycles of RRS for grain yield starting with two randomly derived subpopulations of the open-pollinated maize population Golden Glow to determine whether genetic distinctiveness between paired populations is necessary for RRS to succeed. While the conventional view is that combining ability patterns in maize are based on pre-existing genetic relationships among populations, an alternative notion arises from this study. Combining ability groups in maize can readily be developed de novo by breeding, and that genetic divergence follows, either by genetic drift or selection for complementary gene interactions.
Buffalograss Quality, Color, and Clipping Yield
Research supporting management recommendations for turf-type buffalograss [Buchloë dactyloides (Nutt.) Engelm.] is lacking. Frank et al. (44:1615–1621) planted four buffalograss cultivars in Nebraska, Kansas, and Utah to determine nitrogen rate and mowing height effects on buffalograss quality, color, and clipping yield. Regardless of cultivar, the 98 kg N ha–1 rate sustained quality, color, and density over the 3-yr evaluation period. The general mowing height recommendation for turf-type buffalograss is 5.0 to 7.5 cm. Contrary to past views, this research proves that buffalograss will respond favorably to fertilizer applications.
Specific Bean Rust Resistance
Park et al. (44:1799–1807) utilized bulked segregant analysis to identify RAPD markers linked to Ur-6 for specific rust resistance in an F2 population from the bean (Phaseolus vulgaris L.) cross Olathe x Nebr.#1 sel.27. The gene was flanked by two coupling-phase markers OBC06.300 and OAG15.300 at 1.3 and 2.0 cM. SCAR marker SOBC06.308 was developed on the basis of a specific primer pair. The RAPD and SCAR markers were present in pinto beans having Ur-6. We also confirm the Ur-6 location on linkage group 11 of the P. vulgaris map.
Barley Radiation-Use Efficiency
Information on barley (Hordeum vulgare L.) radiation-use efficiency (e) is scarce. Kemanian et al. (44:1662–1672) report values of e for two cultivars and planting rates of spring barley in different environments. They measured values ranging from 0.9 to 1.2 g biomass MJ–1 solar radiation, with no cultivar or planting rate effects. Their results, as well as information compiled from the literature, suggest that the unstressed e for barley (and wheat, Triticum aestivum L.) is negatively associated with the daytime vapor pressure deficit of the air (D). The maximum values previously reported for barley and wheat of around 1.6 g MJ–1, would only be attainable in low D environments. The influence of D should be considered in the interpretation and use of measured values of radiation-use efficiency.
Seaweed Extract and Humic Acid Contain Cytokinins
Drought continues to be a major limiting factor for creeping bentgrass (Agrostis palustris Huds. A.) quality and persistence on golf courses. Zhang and Ervin (44:1737–1745) treated creeping bentgrass with seaweed extract (SWE) and humic acid (HA), alone or in combination, and maintained in a greenhouse at approximately field capacity (–0.01 MPa) or allowed to dry until near the permanent wilting point (–1.5 MPa). Unashed samples of SWE and HA contained 66 µg g–1 and 57 µg g–1 zeatin riboside, respectively, while ashed samples contained no detectable cytokinins as determined by ELISA. The combination of HA+SWE enhanced root mass (21–68%), and foliar 
-tocopherol (110%) and ZR (38%) contents. This is the first known report indicating that these natural products contain cytokinins and that their application resulted in increased endogenous cytokinin levels, possibly leading to improved creeping bentgrass drought resistance.
Bean Angular Leaf Spot Resistance
Angular leaf spot (ALS), caused by Phaeoisariopsis griseola (Sacc.) Ferr., is the most important fungal disease of common bean (Phaseolus vulgaris L.) in Latin America and in Africa, where annual yield losses are estimated at 19%. Mahuku et al. (44:1817–1824) found that a Guatemalan landrace, G10474, was immune to 95% of 456 isolates under greenhouse conditions. A single dominant gene conditioned resistance to pathotype 63-63. Three AFLP markers cosegregated with the resistance gene in coupling phase, and one, E-ACA/M-CTT330, was converted to a codominant SCAR at 5 cM from the resistance gene. This marker can serve to introgress the G10474 resistance gene into common bean of the Andean gene pool.
Optimizes Maize Kernel Production
Achieving the optimum seed yield per unit land area in maize (Zea mays L.) hybrid seed production often is based on limited information about male pollen shed and practical experience synchronizing male and female inbred flowering. Fonseca et al. (44:1696–1709) developed a simple mechanistic model to simulate and optimize kernel production in seed production fields on the basis of the flowering dynamics of male and female inbreds. Simulated kernel numbers were closely correlated with measured values (r2 = 0.98) in six commercial seed fields where harvested kernel number varied from 8.4 to 23.1 million per female hectare. The model is useful for optimizing kernel production for an established inbred pair or for defining initial management protocols for new combinations of inbreds.
Somatic Embryogenesis Following Transformation of Soybean Cotyledons
Transformation of somatic embryos of soybean [Glycine max (L.) Merr.] using Agrobacterium-mediated transfer has been limited to a few cultivars. In the report by Ko et al. (44:1825–1831), soybean cultivars representing a wide range of maturity groups (MG 00–MG VIII) have been screened for their embryogenic and transformation potentials. Among 15 cultivars, 13 produced transformed somatic embryos under hygromycin selection. Moreover, this paper reports on observed phenotypic differences of immature cotyledonary explants that are associated with genotypic variability for embryogenic response.
Maize Grain Yield and the Stability of Harvest Index
Grain yield and the stability of harvest index are greater in newer than in older Argentinean maize (Zea mays L.) hybrids. Using as a framework the relationship between kernel number per plant and plant growth rate during the period bracketing silking, Echarte et al. (44:1654–1661) demonstrated that the greater kernel set per unit plant growth rate in newer vs. older hybrids was related to (i) a lower threshold of plant growth rate for kernel set and (ii) a greater potential kernel number at high availability of resources per plant. They also report that genetic yield improvement in maize is attributable, in part, to increased partitioning of dry matter to the ear during the critical period bracketing silking.
Integration of QTL Analysis into Breeding Strategies
Integration of QTL analysis into breeding strategies has been proposed to increase the power and accuracy of QTL detection. Cervantes-Martinez and Brown (44:1572–1583) developed a specific scheme for QTL analysis in sets of F1 breeding populations of outbred plant species, such as cocoa (Theobroma cacao L.), with a high degree of accuracy. Theoretical assumptions indicate that the method is more appropriate for outbred plant species that are highly heterozygous and have phenotypic traits that show few interlocus interaction effects.
Nutritive Value of Alley-Cropped Orchardgrass Herbage
Physiological responses may differ for grasses grown in agroforestry and conventional microsites. Burner and Belesky (44:1776–1780) compared diurnal change of herbage nutritive value for orchardgrass (Dactylis glomerata L.) grown without shade and in alleys of loblolly pine (Pinus taeda L.) and shortleaf pine (P. echinata Mill.). Herbage in agroforestry plots had more crude protein and digestibility, but less yield and nonstructural carbohydrates than the conventional plots. Except for total nonstructural carbohydrates, which varied diurnally in conventional but not in agroforestry plots, herbage nutritive value was temporally stable in disparate environments.
New Russian Wheat Aphid Biotype in Colorado
Host plant resistance has proven to be an effective control strategy to reduce the economic impact of Russian wheat aphid [RWA; Diuraphis noxia (Mordvilko)] infestation in wheat (Triticum aestivum L.). An isolate of RWA collected in the spring of 2003 from southeastern Colorado was used by Haley et al. (44:1589–1592) in greenhouse seedling screening tests with a collection of RWA-susceptible and RWA-resistant cultivars and germplasm accessions. The responses observed showed that this isolate has a different virulence pattern than the original RWA isolate and that all RWA-resistant wheat cultivars currently available are susceptible to this isolate. Breeding efforts for RWA resistance in wheat will depend on rapid identification of germplasm resistant to this new biotype and transfer of this resistance to adapted germplasm.
Sunflower Resistance to Sclerotinia
Sunflower (Helianthus annuus L.) hybrids with genetic resistance to Sclerotinia head rot, caused by Sclerotinia sclerotiorum (Lib.) de Bary, are necessary to reduce yield losses caused by this disease. General and specific combining ability for resistance of inbred lines in hybrid combinations were estimated by Van Becelaere and Miller (44:1542–1545). Thirty-six hybrids produced by crossing six female and six male lines were planted in four environments and inoculated with a suspension of ascospores. Additive gene effects were relatively more important than nonadditive gene effects in the phenotypic expression of resistance. Selection could start at the inbred line development stage, although hybrids should also be tested since nonadditive gene effects were significant in the individual environments.
Growth Regulators and In Vitro Plant Regeneration in Wheat
Although durum or macaroni wheat (Triticum turgidum L.) is an important cereal crop worldwide, work on its improvement using modern biotechnology is limited. Standardizing a reliable in vitro regeneration protocol is a prerequisite for application of transgenic technology. Satyavathi et al. (44:1839–1846) studied the effect of three growth regulators (2,4-D, picloram, and dicamba) on callus induction and plantlet regeneration in four commercial durum cultivars: Ben, Maier, Munich, and Lebsock. Dicamba proved the best for inducing compact callus and plantlet regeneration across the four cultivars. Maier gave the highest plantlet regeneration on a 2.0-mg L–1 dicamba medium. These results will facilitate genetic transformation work with durum wheat.
Interactive Effects of N on Maize Yield and Grain Composition
Cereal grain yield and grain protein concentration both respond positively to supplemental N, yet often exhibit a negative genetic relationship. Uribelarrea et al. (44:1593–1600) investigated the effects of N supply on grain yield and composition in corn (Zea mays L.) hybrids highly divergent for grain protein, using the Illinois Protein Strains crossed to an elite tester. They found strong genetic control of grain composition that was modulated by N and that yield responses to N were primarily due to increased kernel number. The results suggest improving sink capacity of high-protein genotypes may lead to high-yielding hybrids with enhanced grain protein.
Mapping As You Go
Recent advances in molecular genetics have led to an enthusiasm for using marker-assisted selection (MAS) to improve the performance of traits in plant breeding. To date, this approach has been relatively ineffective for complex traits controlled by many genes that are under the influence of epistasis and gene x environment interaction effects. The Mapping As You Go (MAYG) approach investigated by Podlich et al. (44:1560–1571) is a mapping-MAS strategy to accommodate the presence of epistasis and gene-by-environment interaction by implementing MAS such that the estimated values of QTL alleles can evolve as the current germplasm evolves over cycles of selection. The MAYG method operates by cyclically reestimating the value of QTL alleles each time a new set of germplasm is created during the breeding process. Computer simulation was used to investigate the effectiveness of the MAYG approach applied to complex traits. The results indicated that greater levels of response were achieved when estimates were revised frequently compared with situations where estimates were revised infrequently or not at all.
Spider Mite Resistant Maize Inbred Lines
Seven mite-resistant maize (Zea mays L.) lines were evaluated by Bynum et al. (44:1535–1541) for resistance and combining ability in a Griffing's Method 2 diallel mating design. Total mite densities, total damage ratings (TDRs), mite per damage ratio, and a seasonal damage ratio (SDR) sampling criteria provided good methods for analyzing the environment x genotype interaction. Broad-sense heritability estimates showed that >90% of the TDR and SDR were associated with genotypic effects. Overall resistance was better when tolerant lines were part of the cross. General combing ability for reducing mite damage was highest for two mite tolerant lines.
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