The integration of technologies and principles to assess, manage, and evaluate spatial and temporal variability has enabled the site-specific application of variable rates of agrochemicals. It is referred to as precision management. This article concerns with the potential of precision management for weed control. Weeds are heterogeneously distributed and show different levels of spatial aggregation. A better understanding of weed patchiness is necessary for precision weed management. Studies reviewed in this article showed that significant reduction in the amount of herbicide can be achieved when the spatial variability of weeds is taken into account. It is often difficult, however, to obtain information on the spatial distribution of weeds with accuracy because it depends on monitoring techniques, scales of observation, and statistical methods applied. We conclude that the precision application of herbicides is one approach to managing weeds and it will be possible to achieve a drastic reduction in herbicide applications by using a combination of several different types of weed control strategies. Not only farmers with large fields but also those with small fields should have better access to information on spatial variability to make decisions for weed control.
We examined the feasibility of near-infrared (NIR) reflectance spectroscopy to estimate the contents of moisture, fat, and protein in the flours of common and tartary buckwheat harvested in 1996 and 1997. Multiple linearregression analysis for NIR spectral and chemical data was carried out. The standard error of the prediction (SEP) for the samples harvested in 1996 was 0.22% for moisture, 0.06% for fat, and 0.21% for protein, when the calibration equations obtained from the analysis of common and tartary buckwheat were used. When the same calibration equations for the buckwheat flour harvested in 1997 were used, the correlation graphs between the reference values and the calculated values were skewed and biased. However, the relative values were sufficient for the selection based on the contents of the constituents, and the bias-corrected SEPs were 0.15% for moisture, 0.10% for fat, and 0.44% for protein. We also examined the feasibility of NIR spectroscopy to estimate the total polyphenol content and 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity in the flours of common buckwheat harvested in 1998. The estimation error was acceptable for use in the selection of varieties with a higher activity. Using the NIR method, the contents of moisture, fat and protein, and physiological activity (total polyphenol content and DPPH radicalscavenging activity) in the buckwheat flours could be successfully estimated for a simple and rapid-breeding selection.
The spike of the main culm in winter wheat was examined by scanning electron microscopy from the double ridge to 6 days after the terminal spikelet stage to quantitatively evaluate the effects of shading and nitrogen supply at the spikelet phase on the numbers of spikelets and floret primordia, and the development of florets. Positional differences on a spike in grain setting at maturity were also investigated. Nitrogen supply affected neither the rate nor duration of spikelet initiation, the number of spikelets remaining unchanged. Although nitrogen supply positively affected the initiation and development of florets, it slightly reduced the grain weight per spike at maturity due to a decrease in the number of grains per spike and the reduced grain weight. These results suggested that under the field condition, nitrogen supply at the double ridge stage is too late to have a significant effect on the spikelet number, and might induce competition for nitrogen between the main culm and tillers, or induce mutual shading between plants, resulting in lighter grain weight per spike. Shading decreased the rate of spikelet initiation, resulting in a significant decrease in spikelet number. The initiation and the development of florets were also decreased by shading. Lower nonstructural carbohydrate content at the terminal spikelet stage suggested that the limited assimilate supply by shading was likely responsible for the decreases in the initiation and development of spikelets and florets.
The chloroplasts of mesophyll cells in Cyperus serotinus Rottb. (mizugayatsuri) leaves possessed well-developed stroma and granal thylakoids. In Kranz chloroplasts, many stroma thylakoids and a considerable amount of peripheral reticula were discernible. The interposed mestome cells had a thick cell wall and poor cytoplasm. The effect of DTP, the herbicidal entity of Pyrazolate, on the development of plastids in the photosynthetic cells of C. serotinus leaves was examined by TEM. Deformation of the plastids appeared under continuous light for 7 d in the plants treated with 1 mg L>-1< DTP. However, even 50 mg L>-1< DTP did not cause such damage either in the plants kept in darkness or in those exposed to light for less than 2 hr after darkness. The plastids deformed by DTP under prolonged exposure to light were very poor in the inner membrane system, but the envelopes were intact. DTP treatment in the dark allowed normal development of etioplasts, in which a central lattice was composed of numerous tubules about 40 nm in distance. Exposure to light after the dark treatment caused an extrusion of prothylakoids from a central crystalline structure of the etioplasts. The ultrastructure of nuclei and mitochondria in the DTP-treated leaves was not different from those in the untreated plants. From the above results, we draw a conclusion that DTP causes the collapse of thylakoid membranes only in light and not in darkness.
We examined the mechanism of reserve mobilization in Japanese yam seed tubers and eddo seed corms on and after sprouting. The decomposition of starch in pith parenchyma cells of Japanese yam tubers and eddo corms progressed from the region distant from vascular bundles to that adjacent to vascular bundles. In eddo corms, the starch also decomposed from the proximal to the distal region adjacent to the sprout or regenerate plant body. In the yam tubers, the decomposition process was similar in the proximal, middle and distal regions. The first step in the reserve mobilization in pith parenchyma cells was the decomposition of the amyloplast envelope. Subsequently, starch granules decomposed. In Japanese yam tubers, the envelope and starch granules started to decompose from the peripheral regions of the amyloplasts. The observation of soluble polysaccharides, which was the decomposition product of starch granules, was made possible by the quick freezing-vacuum freeze-drying method. By this method, we demonstrated that the soluble polysaccharides in the parenchyma cells decomposed and decreased in density. In addition, the mucilage in the mucilage duct started to decompose and decreased in density from the proximal to the distal part of the corm and also from the periphery to the center of the duct. It was shown that not only starch mobilization but also mucilage mobilization mainly supported sprouting and the growth of the regenerate plant body during about the first half of the vegetative stage.
One hundred and fifteen clones of Zoysia spp. collected around the coast of Taiwan were examined for the variation of salinity tolerance. Zoysia spp., native of Taiwan, showed a wide range of salinity tolerance among the clones collected from various regions. The clones from the regions with higher annual rainfall and limestone showed lower NaCl tolerance, and some of them showed 100% shoot mortality under 3% NaCl within 3 weeks. On the contrary, some clones from the regions with lower rainfall retained a few green leaves even at 7.5% NaCl for 3 weeks. A positive correlation was observed between the percentages of 100% shoot mortality in clones treated with 6% NaCl and the rainfall of the regions where the clones were collected. However, based on the same level of rainfall, the clones collected from the limestone region showed higher percentages of shoot mortality than those collected from the other regions. Using four clones including NaCl-tolerant and NaCl-sensitive, the effect of Ca on the salinity stress was further examined. Addition of CaCl2 to the nutrient solution could alleviate the leaf firing and electrolyte leakage from the leaf of Zoysia clones caused by NaCl. The geographical variation of salinity tolerance in Zoysia might be caused by the differences in the salt and calcium concentrations in soil, which were affected by rainfall and geology of their habitats.
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