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141.
142.
F. E. Manzer D. C. Merriam R. H. Storch G. W. Simpson 《American Journal of Potato Research》1982,59(7):337-349
The Green Mountain cultivar was used in field tests to determine the effects of inoculating potato plants at various times with the potato leafroll virus (PLRV) on development of internal necrosis of tuber tissue. Viruliferous apterae of the green peach aphid,Myzus persicae (Sulz.), were placed on each stem in all hills to be inoculated in each 3.0 m single-row plot. Planting and inoculation dates were varied in all field experiments and, in one, several vine-killing dates were also included. All harvested tubers were stored for approximately four months at 10°C to enhance development of internal necrosis prior to examination. Similar but smaller greenhouse studies involving both apterous and alate green peach aphids were also conducted using Green Mountain, Irish Cobbler, and Russet Burbank cultivars. All results showed that as inoculation was delayed relative to plant development, more net necrosis (NN) occurred. Conversely, when plants were inoculated early, stem-end browning (SEB) rather than NN predominated. A high percentage of naturally occurring SEB tubers (cv. Russet Burbank) were found by ELISA to contain PLRV. Plants produced by these tubers only rarely developed leafroll symptoms. These findings suggest a previously unsuspected causal relationship between SEB and PLRV. Implications of this apparent relationship on the epidemiology of potato leafroll in Maine are discussed. 相似文献
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Daniel R. Kidd Megan H. Ryan Timothy D. Colmer Richard J. Simpson 《Grass and Forage Science》2021,76(1):57-71
Serradella (Ornithopus) species are high‐quality pasture legumes that originate from the Mediterranean basin and have been increasingly used in southern Australian temperate grazing systems. They are generally regarded as tolerant of soils with low pH and, by inference, elemental toxicities such as aluminium (Al). No studies have examined the effect of high Al concentrations on the growth of French serradella (Ornithopus sativus Brot.) or newly developed cultivars of yellow serradella (O. compressus L.). Several cultivars/accessions of each species were grown in low ionic‐strength nutrient solutions at pHCa 4.5 containing a range of Al concentrations. Their susceptibility to root growth inhibition by Al was benchmarked against reference species ranging from Al‐sensitive to Al‐tolerant. Most serradella cultivars had moderate‐to‐high Al tolerance in solution culture but one yellow and two French serradella cultivars ranked alongside the Al‐sensitive reference species. A subset of cultivars and reference species were then grown in an Al‐toxic soil to test the validity of the solution culture results; these cultivars spanned the apparent range in Al sensitivity/tolerance indicated by the solution culture experiment. Variation in the relative root length achieved in Al‐toxic solution culture explained ~59% of the variation in the relative root length achieved in the acidic Al‐toxic soil. This result supports the conclusion that Al tolerance varies among serradella and that some cultivars may not thrive in soils with pHCa < 4.5 and elevated extractable Al concentrations. 相似文献
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The production of nitrous oxide by soils was studied over short periods at a range of moisture contents up to field capacity with a highly-sensitive gas Chromatographic method.Nitrous oxide (N2O) was emitted from all soils studied at all soil moisture contents, which ranged from air dry to field capacity. The rate of emission increased with increasing moisture content and with increasing temperature up to 37°C.The evolution of N2O was not due to displacement of soil air during wetting. It was inhibited by HgCl2 and toluene, and was prevented by formaldehyde and autoclaving. Thus it appeared to be due to microbiological processes.The results of experiments with nitrification and denitrification inhibitors suggest that a considerable part of the N2O was produced by the oxidation of ammonia. Production by denitrification of nitrate cannot be ruled out. The relative importance of these two mechanisms probably depends on the moisture and oxygen content of the soil.It is concluded that the microbial production of N2O is continuous in soil at all moisture contents. The process at low moisture contents constitutes an important component in the cycle which maintains the N2O concentration in the atmosphere. 相似文献
147.
Ammonia losses to the atmosphere from a grass-clover pasture were measured by a combined chemical-micrometeorological technique. Losses from the pasture when grazed were quite considerable (~13g N ha?1 h?1) but when ungrazed they were comparatively small (2 g N ha?1 h?1).Measurements within the canopy of the ungrazed pasture at maturity indicated a large production of NH3 near the ground surface and almost complete absorption of it by the plant cover. The amounts of NH3 absorbed appeared to be too large for stomatal uptake alone.This closed NH3 cycle has important consequences for the field assessment of N2 fixation and gaseous N losses. 相似文献
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149.
Infection of pigs and cattle with bovine viral diarrhoea virus on a farm in England. 总被引:6,自引:0,他引:6
Deaths within a litter of sucking pigs led to a suspicion of hog cholera, but pestiviruses isolated from both dead and live piglets appeared to be bovine viral diarrhoea virus. Persistent viraemia with bovine viral diarrhoea virus was demonstrated in living littermates and also in a bought-in calf, housed in a nearby pen on the same farm. Only two of the littermates survived, both of which had been virus negative and seropositive from the outset of testing. Porcine and bovine virus isolates grew well in calf testicular cells and were neutralised equally by sera collected at the farm from cattle and pigs. However, a comparison by means of their reactivity to monoclonal antibodies showed that they were similar but not identical, and only the porcine isolates grew well in a porcine kidney cell line. 相似文献
150.