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High-yielding rice (Oryza sativa L.) cultivars were developed under high N inputs. Hasegawa (921–926) compared five temperate high-yielding rice cultivars with nine other cultivars, seven of which were bred under low N inputs. At a reduced N rate (40 kg N ha-1), Hasegawa found that high-yielding cultivars Akichikara, Fukuhibiki, Habataki, Hokuriku 153, and Xin Ging Ai 1 surpassed others not only in grain yield but also in aboveground dry matter, harvest index, N utilization efficiency, and sink capacity. Consequently, high-yielding rice cultivars have the potential for alternative cropping systems, in which external inputs and adverse environmental effects should be minimized.
Glyphosate and Water Stress Effects in Glyphosate Resistant Cotton
Both water stress and the herbicide glyphosate applied to glyphosate-resistant (GR) cotton (Gossypium hirsutum L.) can cause loss of young bolls from the plant. Pline et al. (879–885) studied effects of water stress and glyphosate treatments on fruiting and carbohydrate levels in GR and conventional cotton varieties grown in a greenhouse. In general, GR plants treated with glyphosate at the four-leaf stage over-the-top and at the eight-leaf stage directed on the stem had fewer first-position bolls after 0 and 1 d of water stress than nontreated GR and conventional plants. All plants subjected to 2 and 3 d of water stress had fewer bolls and squares than plants with 0 and 1 d of water stress. Leaf carbohydrate and boll sucrose, glucose, and starch content did not differ after glyphosate treatments but did so in response to water deprivation. Differences in carbohydrate profiles of young bolls and leaves from glyphosate-treated and water-stressed cotton plants suggest that water stress and glyphosate treatments may promote fruit loss through different mechanisms in the plant.
Common Bean Nutrition in Cultivated vs. Wild Form
In common bean (Phaseolus vulgaris L.), some nutritional traits are lower in the cultivated form as compared with the wild counterpart. To assess the feasibility of wild bean as the potential source of desirable traits, a study was performed by Guzmán-Maldonado et al. (1029–1035) to identify quantitative trait loci (QTL) associated with seed mass, Ca, Fe, Zn, and tannin content in bean seed. Amplified fragment length polymorphism markers were scored in 120 F2:3 segregating individuals derived from a cross between cultivated ‘Bayo Baranda’ and a wild common bean accession. Putative QTL were significantly associated with seed mass, Ca, Fe, Zn, and tannin content in the seed.
Forage Yield of Brown-Midrib Sudangrass
Brown-midrib genes increase digestibility due to reduced and altered lignification in sudangrass, Sorghum bicolor subsp. drummondii (Nees ex Steud.) de Wet & Harlan. Brown-midrib lines are known to be low in forage yield potential, but this reduction in forage yield has not been previously quantified. Casler et al. (782–789) showed that improved nutritional value of brown-midrib sudangrass offsets losses in forage yield for first harvest, but not for second harvest. The brown-midrib phenotype of sudangrass appears to be associated with environmentally sensitive genes in some genetic backgrounds, suggesting that forage yield losses associated with the brown-midrib trait may be reduced in warmer and longer growing seasons.
Developing Germplasm for Nonthermal Management Systems of Kentucky Bluegrass
Air quality issues are making field burning of Kentucky bluegrass (Poa pratensis L.) residue to stimulate seed production untenable. Johnson et al. (1091–1099) investigated yield, yield components, and turf quality on a diverse set of 45 Kentucky bluegrass entries under three different residue treatments. Unburned treatments generally yielded less than burned treatments as expected, but for six of the 15 highest yielding entries, burned and residue-removed treatments did not differ significantly. Turf quality was negatively correlated with seeds per panicle but not with panicles per meter, suggesting that increasing yield through panicles per meter would have minimal impact on turf quality. Sufficient variation for seed production appears available for developing germplasm for nonthermal management systems.
Exposure Duration and Freeze Damage to Bermudagrasses
Bermudagrasses, Cynodon sp., are susceptible to winter injury in the transition zone for warm- and cool-season turfgrasses. Anderson et al. (973–977) used laboratory-based methodology to characterize the relative freeze tolerance of recently released and standard cultivars and determined the effects of extended exposure duration on survival. Significant cultivar differences in freeze tolerance were identified. In a second set of experiments, acclimated plants were held at constant, subfreezing temperatures for various periods of time. Freeze damage to turf bermudagrasses increased as exposure duration increased.
Gene Effects on Dormancy in Rice Seed
Seed dormancy is generally stronger in weedy than in cultivated rice. Gu et al. (835–843) evaluated the effects of seed tissue components on dormancy and investigated the inheritance of the trait in selected weedy strains. Germinating seeds, caryopses, caryopses with pericarp/testa removed, and excised embryos revealed seed dormancy is imposed by the maternal tissues hull, or both hull and pericarp/testa. A high heritability for and major gene effects on hull- or pericarp/testa-imposed dormancy was detected in weedy strain-derived F2 populations. Authors conclude weedy rice provides ideal gene donors to elucidate mechanisms of dormancy and to improve resistance to preharvest sprouting.
Properties of Stockpiled Tall Fescue
Many livestock producers use stockpiled tall fescue (Festuca arundinacea Schreb.) to extend the grazing season into winter. Kallenbach et al. (1001–1005) determined the herbage mass, nutritive value, and ergovaline (toxin) concentration of stockpiled tall fescue when infected with a native endophyte (K31 E+), a nontoxic endophyte (HiMag NTE), and with no endophyte (HiMag E-). Herbage mass and nutritive value was equal for all entries at each of four winter harvests. Neither HiMag E- nor HiMag NTE contained ergovaline, but K31 E+ had substantial levels of ergovaline in early winter. The absence of ergovaline in HiMag E- and HiMag NTE suggest that livestock producers could eliminate winter toxicosis problems by stockpiling these forages.
Photosynthetic Rate and N Concentration
The vertical distribution of N within a canopy can influence whole canopy photosynthesis. Changes in N distribution with development or fertility could, therefore, influence the relationship between N status arid canopy radiation use efficiency (RUE). Milroy and Bange (904–913) studied photosynthetic rate and N concentration (specific leaf nitrogen, SLN) of cotton (Gossypium hirsutum L.) leaves in two field experiments in which the rate of N application was varied. A framework that scales from leaf photosynthesis to RUE was then used to explore the impact of N and light dynamics on RUE of cotton canopies. There appeared to be little impact of the ontogenetic changes in light extinction coefficient and vertical gradients of SLN within the canopy on RUE. For crop simulation purposes, this simplifies the process of modulating RUE in growth models.
Stability in Tetraploid x Diploid Potatoes
Internal heat necrosis (IHN) can be a severe physiological disorder of potato tubers produced in the mid-Atlantic states. Currently, there are no commercial potato cultivars that possess both high specific gravity (SG) and resistance to IHN. Our purposes (790–796) were to evaluate tetraploid potatoes derived from closely related diploid species for SG and resistance to IHN. Several of these hybrid clones possessed high SG and resistance to IHN. These will be valuable breeding materials to develop new potato cultivars with both high SG and resistance to IHN for the mid-Atlantic states.
Chickpea Genetic Diversity
To ameliorate the lack of genetic diversity in cultivated chickpea (Cicer arietinum L.), breeders are looking to the wild relatives. Currently, the world collection of annual wild Cicer species is spread across nine genebanks, and is comprised of a mixture of original accessions (one to 34 per species) and a larger number of selections made from the originally collected material. Berger et al. (1076–1090) consolidate the world collection of annual wild Cicer species and compare the habitat characteristics of ex situ collections with those potentially available according to local floras. The results indicate that only a small proportion of the diversity available in wild populations is present in ex situ collections, and therefore targeted collection missions based on ecogeographic principles are imperative.
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