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The leaf rust resistance gene Lr51 is located within a segment of Triticum speltoides Taush chromosome 1S, translocated to the long arm of chromosome 1B of bread wheat (Triticum aestivum L.). In this study, Helguera et al. (728–734) determined the genetic length of the translocated 1S segment, developed a PCR marker for Lr51, and used this marker to generate isogenic lines for this gene. Lr51 is resistant to the current predominant races of leaf rust in the U.S. and will be a useful tool to protect wheat against the highly variable and dynamic leaf rust pathogen Puccinia triticina Eriks.
Maize Stay-Green and Nitrogen Supply
Subedi and Ma (740–747) in an experiment under controlled greenhouse conditions determined growth, N uptake, and partitioning patterns of three contrasting maize (Zea mays L.) hybrids. Pot-grown plants were subjected to five N treatments supplied and withheld at various growth stages. The Leafy hybrid had a greater number of leaves and total plant dry matter, while kernel yield was similar to that of the other two hybrids. There were no differences in total N uptake and partitioning among the hybrids studied across all five N treatments. For all hybrids, N supply was more critical before silking than thereafter; limited N supply until V8 or from V8 reduced ear size, kernel yield, and N uptake. The stay-green hybrid remained green until physiological maturity only when there was a continuous N supply in the growing medium.
QTLs for Slow Rusting
Slow rusting is considered a crucial component of durable resistance because of its insensitivity to frequent race changes of leaf rust fungus Puccinia triticina Eriks. Xu et al. (758–765) characterized slow leaf-rusting resistance from wheat (Triticum aestivum L.) cultivar CI 13227 by using molecular markers. Three QTLs were found to be consistently associated with several disease reaction parameters. Microsatellite markers closely associated with two of the three QTLs on chromosomes 2B and 7BL have potential to be used in marker-assisted selection for durable leaf rust resistance in wheat.
Seed Shattering Inheritance in Buckwheat
Resistance to seed shattering has become one of the major concerns in breeding self-pollinated buckwheat derived from interspecific hybridization between cultivated common buckwheat (Fagopyrum esculentum Moench) and a wild species F. homotropicum Ohnishi with the shattering character. Wang et al. (693–697) studied inheritance of seed shattering using progeny analysis of the F1, F2, and F3 generations of interspecific hybrids between these two species. The segregation patterns supported the control of seed shattering by at least three genes. This study provides the first information on shattering inheritance to enable the development of self-pollinated buckwheat with resistance to seed shattering.
Switchgrass Biofuel Quality Traits
Switchgrass (Panicum virgatum L.) biofuel quality traits are poorly characterized for southern regions. Cassida et al. (682–692) evaluated fuel quality traits and component yields of four groups of switchgrass genotypes across five latitudes in Texas, Arkansas, and Louisiana. Lignocellulose yield was greater for southern than northern ecotypes and for lowland than upland genotypes. Lowland genotypes had lower ash and nitrogen but greater moisture concentration at harvest than upland genotypes. Southern lowland switchgrass genotypes produced the best combination of combustible yield and fuel quality for this region but harvest timing also had a large impact on fuel quality.
Yield and Stand Persistence Traits of Switchgrass Genotypes
Poor adaptation of commercially available switchgrass (Panicum virgatum L.) cultivars to southern environments may result in unacceptable biomass yields. Cassida et al. (673–681) evaluated yield and stand persistence traits of four groups of switchgrass genotypes across five latitudes in Texas, Arkansas, and Louisiana. Southern ecotypes had greater yields than northern ecotypes. Lowland genotypes had greater yields and stand persistence, less lodging and disease, and were more responsive to soil moisture availability than upland genotypes. Therefore, southern lowland genotypes of switchgrass produced optimum biomass yields and stand persistence for this region, and breeding efforts are needed to supplement the one currently available commercial cultivar of this type.
Partial Resistance to Sunflower chlorotic mottle virus
Sunflower chlorotic mottling is an emerging virus disease that has been detected in commercial hybrids and wild sunflower in Argentina. Lenardon et al. (735–739) screened 232 sunflower (Helianthus annuus L.) lines for resistance to Sunflower chlorotic mottle virus (SuCMoV) by artificial inoculation under greenhouse conditions. Only three lines (L33, L74, and L52) showed a partial resistance, L33 the most resistant. Segregation data from an artificially inoculated F2 population indicated the presence of a single dominant resistance gene, designated Rcmo-1. This gene was mapped on linkage group 14 between markers MS0022 (5 cM) and ORS-307
Gummy Stem Blight Resistance in Watermelon
Disease resistance is a major goal for watermelon breeders. Gummy stem blight, caused by Didymella bryoniae (Auersw.) Rehm, is one of the most destructive diseases of watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai]. Gusmini et al. (582–588) screened the entire USDA-ARS watermelon germplasm collection to identify sources of genetic resistance to gummy stem blight. The authors measured resistance in field and greenhouse tests in North Carolina in replicated experiments, repeated over time for four years. Highly resistant PI accessions were identified and retested to confirm resistance. In addition, a set of highly susceptible PI accessions was classified for use as checks or low parents in future genetic studies.
Heritability of Waterlogging Tolerance in Wheat
Tolerance of wheat (Triticum aestivum L.) to waterlogging is related to many quantitative traits that are under a strong environmental influence. Collaku and Harrison (722–727) used Restricted Maximum Likelihood (REML) method to estimate genetic variance components. In contrast to traditional methods, REML in a mixed model approach has no limitation on the mating design and accounts for the relationship among families. The highest heritability estimates under waterlogging stress were found for kernel weight (0.47), chlorophyll content (0.37) and tiller number (0.31). Selection criteria for waterlogging tolerance in wheat were discussed based on expected improvement from correlated response and selection indices."
Fertilization of Managed Urban Landscapes
Fertilization of managed urban landscapes with phosphorus (P) and potassium (K), essential plant nutrients, increases the potential for off-site transport of P and K and inadvertent ecological consequences. To test the hypothesis that a mixed-species landscape model of largely native plants would reduce P and K leaching compared to conventional turfgrass, Erickson et al. (546–552) conducted a long-term field experiment that measured P and K leaching data from these two contrasting landscape models. Cumulative leaching losses of P (105 vs. 61 kg P ha–1) and K (630 vs. 424 kg K ha–1) were greater on the mixed-species model, which was attributed to differing establishment conditions and differing responses to precipitation after fertilization. Regardless of landscape model, leaching losses of P and K were high enough to raise concern over ecological consequences.
Sorghum Kernel Growth Patterns within the Panicle
The influence of panicle position on sorghum [Sorghum bicolor (L.) Moench] kernel growth is poorly understood. Gambín and Borrás (553–561) measured kernel weight, kernel water content, and kernel volume at two positions (apical and basal) for a wide range of genotypes throughout the grain-filling period. Apical kernels always showed a higher kernel growth rate but a shorter duration of grain filling than basal kernels. These differences were associated to changes in the maximum water content and in the kernel desiccation pattern. Kernel water relations previously described in other crops could not be generalized for sorghum kernels when the different panicle positions were considered.
Biopharmaceutical and Bioindustrial Proteins from Plants
Production systems for biotechnology products have included many different organisms but until recently have not included plants. Howard (468–472) used maize (Zea mays L.) to demonstrate how plants may offer advantages over other production systems for nonfood or nonfeed products. The first highly purified protein products have now been developed using transgenic maize. In addition, other potential products such as orally delivered vaccines have also shown efficacy when administered to animals. This represents a new use for transgenic plants beyond crop improvement and the enabling of new products that cannot be produced effectively in other systems.
Salt Stress Signaling and Salt Tolerance
Molecular tools such as gene disruption and transgenic approaches significantly enhanced our understanding of salt tolerance of higher plants. A calcium sensor protein SOS3 perceives (Chinnusamy et al., 437–448) salt stress-induced cytosolic calcium signals and activates a Ser/Thr protein kinase SOS2. Activated-SOS2 regulates sodium efflux from cytosol and sequestration into the vacuole by activating Na+/H+ antiporters of plasma membrane and tonoplast, respectively. Plant cells employ osmoprotectants, LEA-type proteins, and antioxidant defense to stress damage prevention and repair processes. Transgenic manipulations of SOS (active SOS2 and Na+/H+ antiporters) and the CBF transcriptome may help in improving crop salt tolerance.
Temperature Effects on Phyllochron in Cool-Season Grasses
In controlled environments, Bartholomew and Williams (529–534) evaluated the use of accumulated temperature values to indicate the progress of leaf appearance in cool-season grass species. Leaf appearance in Italian ryegrass (Lolium multiflorum Lam.), tall fescue (Festuca arundinacea Schreb), and tall wheatgrass [Elytrigia elongata (Host) Nevski] showed a close linear relationship with accumulated temperature, within a temperature regime, but the interval between appearance of successive leaves (phyllochron) was increased by increased average daily temperature. The phyllochron was also increased by exposures to below-freezing temperatures. The effects of variation in mean daily temperature and of plant exposure to below-freezing temperature on phyllochron should be considered if accumulated temperature is used to predict development stage of cool season grasses in the field.
Toxic-Endophyte Contamination in Tall Fescue
The fungal endophyte Neotyphodium coenophialum Morgan-Jones and Gams is abundant in tall fescue (Festuca arundinacea Schreb.) and attempts to eradicate endophyte from pastures (to alleviate its detrimental effects on livestock) are frequently offset by recontaminated volunteer seed. To test whether nontoxic-endophyte infected tall fescue swards were more resistant to reinvasion by volunteer tall fescue and its associated toxic endophyte than endophyte-free tall fescue swards. Barker et al. (616–625) inoculated endophyte-free and nontoxic-endophyte tall fescue and measured the resultant endophyte levels for 2 yr. They found higher than expected levels of endophyte in only the endophyte-free pastures and concluded that, where mechanisms for contamination exist, endophyte-free tall fescue stands can be readily contaminated by volunteer tall fescue and its toxic endophyte, but nontoxic-endophyte tall fescue is less susceptible to contamination by volunteer tall fescue.
Crested Wheatgrass Bred for Turf
Growing population and limited water resources necessitates reduced use of irrigation on western U.S. landscapes. Hanks et al. (524–528) evaluated the genetic variation in turf quality of a "turf-type" crested wheatgrass [Agropyron cristatum (L.) Gaertn.] population when grown under reduced-maintenance conditions. The evaluation revealed large broad-sense heritabilities for turf quality and other important turf traits within this population. Low-maintenance turf that is aesthetically acceptable would help turf managers limit irrigation on landscape areas.
Ancestral Soybean Lines and Viral Resistance
Soybean [Glycine max (L.) Merr.] viruses can adversely affect soybean production. More than 40 viruses infect soybean, yet resistance has been reported for only a few. The cultivated soybean varieties grown in the USA have a narrow genetic base, with six ancestors contributing 60% of the genes in current cultivars. Wang et al. (639–644) evaluated 52 ancestral soybean lines for resistance to Bean pod mottle virus (BPMV), Soybean mosaic virus (SMV) strains G1 and G5, Tobacco ringspot virus (TRSV), and Tobacco streak virus (TSV). Results showed that seven ancestors were resistant to SMV-G1, 16 ancestors were resistant to SMV-G5, only one ancestor, ‘Tanner’, was resistant to TSV, and all 52 ancestors tested were susceptible to BPMV and TRSV.
High Density, Low N, and Drought Effects on Yield
Worldwide, tropical maize (Zea mays L.) is exposed to low-N conditions and varying plant population density. A set of secondary traits was assessed by Monneveux et al. (535–545) in elite CIMMYT open-pollinated varieties, inbred lines, and hybrids under optimal, high plant population density, and low-N conditions. Association was observed under low-N conditions between grain yield and anthesis–silking interval, delayed senescence, and ear/tassel weight ratio. Under all conditions, final grain number depended more on abortion rate than on the total number of ovules at anthesis, and under low-N stress, grain yield was significantly negatively correlated with abortion rate.
DNA Fingerprinting of Bermudagrass
During the past two decades, the number of seeded-type bermudagrass [Cynodon dactylon (L.) Pers.] cultivars emerging onto the market has dramatically increased. Yerramsetty et al. (772–777) used DNA amplification fingerprinting to examine the genetic diversity among 17 current commercial seeded cultivars. The findings indicated that 13 out of 17 commercial cultivars tested were genetically closely related, suggesting the need to enhance genetic diversity in seeded-type bermudagrass cultivars.
Ergot Alkaloid Analysis by NIR Spectroscopy
Ergot alkaloids are toxins found in fungal-infected plants, such as tall fescue (Festuca arundinacea Schreb.), which is the most prevalent pasture grass in the eastern USA. Research was conducted by Roberts et al. (778–783) to quantify these toxins by near-infrared (NIR) spectroscopy, a nonchemical procedure used in routine analysis of forage quality. The NIR procedure successfully predicted ergot alkaloids in nearly all types of tall fescue samples. The NIR prediction equations can be added to equation profiles of standard analysis, thereby permitting rapid and accurate estimation of ergot alkaloids in toxic tall fescue breeding, production, and management studies.
Sheath Blight Resistance QTLs In Rice
Two prior studies, utilizing early generation (F2 and F3) rice (Oryza sativa L.) progeny, reported the chromosomal location of 12 quantitative trait loci (QTLs) putatively associated with rice sheath blight (SB) resistance. Unfortunately, poor agreement between the loci mapped in these independent studies left all the SB-QTLs unconfirmed, and researchers were understandably reluctant to pursue gene-tag development and marker-assisted selection for them. The objective of the present study by Pinson et al. (503–510) was to more accurately map SB-QTLs by collecting disease-rating data from a set of recombinant inbred lines (RILs) that, due to increased replication and plot size, would be more reliable than the phenotypic data used in the earlier mapping efforts. The RIL data confirm the chromosome location and genetic effect of six of the previously reported SB-QTLs and putatively identified nine additional QTLs.
Field Reaction to Sclerotinia Blight among Transgenic Peanut Lines
Peanut (Arachis hypogaea L.) is susceptible to many diseases. One of the major diseases affecting peanut production in the southwestern USA is Sclerotinia blight, caused by the fungus Sclerotinia minor Jagger. Transgenic peanut lines possessing fungal resistance genes offer an alternative to traditional resistance and fungicide application in managing fungal diseases. Transgenic peanut lines containing antifungal genes were evaluated for their reaction to Sclerotinia blight in field plots for 3 yr by Chenault et al. (511–515). During the 3-yr period, average disease incidence for the most resistant lines 188, Southwest Runner, 416, 540, and 654 was 0.0, 1.0, 10.0, 14.0, and 16.0%, respectively. ‘Okrun’ was most susceptible with an average disease incidence of 58.0%. All other lines had varying degrees of resistance, but averaged at least 15.5% less disease than Okrun during the 3-yr period. Transgenic peanut lines with partial resistance to Sclerotinia blight were identified which may be useful in traditional breeding programs for fungal resistance.
N Source and Rate Effects on Buffalograss Forage Production
Buffalograss [Buchloë dactyloides (Nutt.) Engelm.] is capable of producing high forage yield when fertilized with N and irrigated. Springer et al. (668–672) determined the effects of applying solid cattle (Bos spp.) manure, liquid swine (Sus spp.) effluent, or commercial fertilizer (urea) at three application rates (0, 120, or 240 kg N ha–1) on the yield, plant canopy height, and nutritive value (crude protein, CP; and in vitro organic matter digestibility, IVOMD) of buffalograss forage grown with irrigation during a 4-yr period. For all N sources, yield, canopy height, and CP increased as N rate increased during each of the 3 yr following establishment. As the buffalograss stand aged, the yield, canopy height, and nutritive value of forage declined. The long-term effects of applying livestock manure to soils in relation to nutrient loading and water quality were not addressed in this study.
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