| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Turfgrass is managed as a perennial ecosystem, with a goal of sustained uniformity. Chemical weed control has been studied intensively, while turfgrass cultural alternatives to herbicides have been infrequently studied (Busey, 1899–1911). Data on the effect of mowing, fertilization, irrigation, cultivation, planting, and turfgrass selection on weeds must be expanded before integrated pest management (IPM) can apply to weeds in turfgrass. There is consensus on a few cultural factors influencing weeds in cool-season turfgrasses, such as taller mowing height and higher rates of N fertilization reducing the crabgrass population. Adapted turfgrasses that are genetically resistant to biotic and environmental stresses can sometimes be managed without herbicides, especially if they are well established. Research is needed on the role of canopy density and light gaps in weed germination, seed bank dynamics, and weed dispersal to develop long-term strategies for cultural management.
Intrinsic Value and Integrity of Plants
The natural approach of organic agriculture involves ecological and ethical principles. It includes an appreciation for the integrity of plants, which refers to their inherent nature, wholeness, completeness, species-specific characteristics, and being in balance with their environment. To instrumentalize this concept, Lammerts van Bueren et al. (1922–1929) evaluated integrity with criteria derived from the integrity of life, plant-specific integrity, genotypic integrity, and phenotypic integrity. The results were applied to evaluate existing breeding and propagation techniques. In vitro techniques and techniques that engineer at the DNA level were found to be incompatible with the integrity of crops, with the exception of use of DNA markers.
Survey of U.S. Land-Grant Universities for Plant Breeding Training
Wehner and Guner (1938–1944) conducted a survey to identify land-grant universities in the USA having plant breeding programs involved in graduate student training. A total of 51 departments had plant breeding programs, and they awarded 409 (53%) Ph.D. and 361 (47%) M.S. degrees in 1995 to 2000. Of those, 362 (47%) graduates were domestic and 408 (53%) were international. Universities with an average of seven or more graduates per year were University of Wisconsin-Madison, North Carolina State University, University of Nebraska-Lincoln, Cornell University, University of Minnesota-St. Paul, Iowa State University, and Texas A&M University.
Allelic Diversity Changes in Oat Cultivars
Concern has often been expressed that modern plant breeding techniques reduce crop genetic diversity, but this concern gained little support from recent molecular studies of genetic diversity of several crop species. Fu et al. (1989–1995) applied the simple sequence repeat technique to assay 96 Canadian oat (Avena sativa L.) cultivars released from 1886 to 2001 and found the first, clear-cut molecular evidence for the negative impacts of oat breeding on genetic diversity. Apparently, allelic diversity at particular loci, rather than the genome-wide diversity, is sensitive to breeding practices. Thus, the need for more attention to oat germplasm conservation is warranted.
Soybean Genes lf2 and Pd2 Are Linked
Genetic linkage determines the coinheritance of genes. In this study, Devine (2028–2030) found that the lf2 gene, which controls whether soybean [Glycine max (L.) Merr.] has seven-leaflet leaves or the usual three, was linked to another gene, Pd2, which controls the degree of pubescence on leaves and stems. Pubescence inhibits predation by leafhopper insects. The lf2 gene may be important in regulating the amount of plant leaf material. When soybean is used for forage, the amount of leaf material affects forage quality. Knowledge of the linkage of these genes will help breeders to estimate the number of progeny needed to couple or decouple these genes in breeding new cultivars.
Selection Index for Spring Wheat Traits
Resistance to Helminthosporium leaf blight (HLB), a serious disease of wheat (Triticum aestivum L.) in South Asia, is considered to be positively correlated with late maturity and low kernel weight, posing a problem to improve them simultaneously. Sharma and Duveiller (2031–2036) used resistance, maturity, and kernel weight in a selection index (Is) in four wheat crosses. The results suggested that selection for HLB-resistant wheat lines with high grain yield and kernel weight was possible with this Is. The method did not significantly penalize the crop for maturity and plant height, two important agronomic traits for wheat.
Nondormant Alfalfa Chromosomes
Alfalfa [Medicago sativa ssp. sativa (L.) L. & L.] (2n = 4x = 32) chromosomes are very small (2–3 µm in length), and are almost symmetrical; thus, it is very difficult to identify individual chromosomes and make comparisons among germplasm sources based on karyotypic analysis. Bauchan et al. (2037–2042) utilized C-banding techniques, computerized image analysis, and cluster analysis of C-banding patterns to discriminate among chromosomes from four historically distinct nondormant alfalfa germplasm sources (African, Chilean, Indian, and Peruvian). Abundant variability in the number and location of constitutive heterochromatic DNA (C-band) was noted among chromosomes; however, this variability was not sufficient to preclude recognition of homologous chromosomes when the four karyotypes were compared with a reference African karyotype. Cluster analysis based on all eight alfalfa genome chromosomes showed no clear distinction among the nondormant alfalfa populations. However, the mean number of heterochromatic bands in the Indian germplasm was significantly fewer than in the other three germplasm sources.
Divergent Selection for Resistance to Maize Weevil
Maize weevils (Sitophilus zeamais Motschulsky) cause serious losses for farmers who store maize (Zea mays L.) on-farm in the tropics. Dhiwayo and Pixley (2043–2049) applied divergent selection for weevil resistance for six maize populations with unreplicated S1, unreplicated S2, and replicated S2 lines. Grain samples were infested with weevils and then incubated in a laboratory. Synthetics were formed among the most resistant 10% and the most susceptible 10% of 
100 lines for each maize population. Replicated S2 selection was successful for both populations where it was applied, S1 unreplicated selection succeeded for two of the six populations, while S2 unreplicated selection was not successful.
Water Stress-Induced Acceleration of Senescence in Soybean
Continuous water stress during seed filling accelerates leaf senescence, shortens the seed filling period, and reduces yield in most grain crops. Since short periods of stress are more likely in many humid environments were grain crops are grown, Brevedan and Egli (2083–2088) stressed soybean [Glycine max (L.) Merrill] plants for short periods (3–13 d) during seed filling. Water stress-induced acceleration of senescence could not be stopped by eliminating the stress after a short period. Short periods of water stress during seed filling may, therefore, have larger than expected effects on yield.
Productivity of Old and Modern Durum Wheats
Genetic variability for leaf net photosynthesis rate (An) and its relation to productivity in durum wheat (Triticum turgidum L. var. durum) are not well defined. Koç et al. (2089–2098) compared old and modem cultivars in terms of productivity and An in field experiments. Old cultivars were late, tall, and inefficient in dry matter distribution. Although An of nonsenescent leaves was greater in old cultivars than in modem cultivars, they showed no superiority in grain yield. High An was associated with high mesophyll conductance. Besides preanthesis dry matter distribution, total flag leaf photosynthesis and duration appear to be causal factors in determining yield, especially under drought.
Rice Cold Tolerance
Rice (Oryza sativa L.) is sensitive to chilling injury, yet in temperate regions rice is planted as soon as temperatures rise above the minimum required for seed germination. Cold spells and chilling night temperatures retard rice growth and chilling damage to rice plants is common. Kuk et al. (2109–2117) determined if cold tolerance could be induced in rice by cold acclimation. They also quantified some physiological responses to chilling, including antioxidative enzyme activity, to determine mechanisms of chilling tolerance. Both cold-acclimated and nonacclimated plants showed physiological damage from chilling temperature, but cold-acclimated plants recovered from chilling injury, whereas nonacclimated plants did not. Cold temperature induced the total activities of antioxidant enzymes. Catalase and ascorbate peroxidase were the principal antioxidant enzymes that showed elevated activity in both rice leaves and roots in response to cold stress. Cold tolerance in rice can be achieved by cold acclimation.
African Marigold Petals
African marigold (Tagetes erecta L.) petals are commercially valuable as a natural source of lutein pigments to color egg yolks orange and poultry skin yellow. Bosma et al. (2118–2124) found that ‘E-1236’ was the top producer of five cultivars tested, consistently producing high pigment yields of 20.7 to 22.0 kg ha-1 over both years tested when flowers were hand harvested. For simulated mechanical harvesting, transplanted ‘Orange Lady’ plants performed best, producing the highest pigment yield (10.6 kg ha-1). Transplanted plants produced higher amounts for all yield parameters than did direct-seeded plants for 3 yr. Supplemental nitrogen application did not increase pigment yield.
Plant Density and Yield of Gamagrass
Much is known about the effects of fertilization and harvest frequency on the yield of eastern gamagrass [Tripsacum dactyloides (L.) L.]; however, information on the effects of plant density is lacking. Springer et al. (2206–2211) reported on the effects of plant population density on the dry-matter yield, vegetative shoot density, and basal area of plant crowns of irrigated eastern gamagrass. In young stands, higher plant densities generally produce higher dry-matter yields compared with 3-yr-old or older stands. At Woodward, OK, the highest sustained forage yields were obtained with a density of 4.8 plants m-2. Planting recommendations for eastern gamagrass were developed primarily for seed production to accommodate seed production equipment. Narrower row spacings, however, may facilitate pasture establishment while increasing forage production early in the life of the stand.
Early Maturing Pigeonpea in the Southern Great Plains
Forage-based livestock production is a significant component of the agricultural economy throughout the southern U.S. Great Plains. However, forage production is limited for efficient livestock production during late August through October because the grasses and other forage plants which grow in the region are not productive and have a low quality during these months. Rao et al. (2212–2217) evaluated two early maturing pigeonpea lines in Oklahoma to determine whether they have the potential to provide high-quality forage during those months or could be used to produce again. Both cultivars produced acceptable quantities of forage with high protein content late in the summer, relative to other forage plants. Grain yield varied with summer rainfall amounts, but were as high as 5 Mg ha-1 when drought conditions did not exist. These or similar pigeonpea cultivars can be grown in the region to fill the late summer forage deficit period, or could be grown for production of grain which can be used as a protein source for livestock.
Evaluation of Switchgrass Agronomic and Biofuel Traits
Switchgrass (Panicum virgatum L.) is a widely adapted crop potentially useful as a feedstock for bioenergy production. Casler and Boe (2226–2233) evaluated six switchgrass cultivars of diverse origins for agronomic and biofuel traits. The optimal harvest date for biomass yield and long-term survival was late summer or early autumn. Broadly adapted, broadly unadapted, and specifically adapted germplasm of switchgrass were identified. It should be possible, through selection and breeding, to develop switchgrass germplasm with increased availability of fermentable sugars and decreased unfermentable and/or incombustible residues.
Related articles in Crop Science:
| ||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Agronomy Journal | Vadose Zone Journal | |||
| Journal of Natural Resources and Life Sciences Education |
Soil Science Society of America Journal | ||||
| Journal of Plant Registrations | Journal of Environmental Quality |
The Plant Genome | |||
