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81.
82.
Y. J. Huang C. Toscano-Underwood B. D. L. Fitt † X. J. Hu A. M. Hall 《Plant pathology》2003,52(2):245-255
Ascospores of both A-group and B-group Leptosphaeria maculans germinated at temperatures from 5 to 20°C on leaves of oilseed rape. Germination of ascospores of both groups started 2 h after inoculation and percentage germination reached its maximum about 14 h after inoculation at all temperatures. Both the percentage of A-/B-group ascospores that had germinated after 24 h incubation and germ tube length increased with increasing temperature from 5 to 20°C. Germ tubes from B-group ascospores were longer than those from A-group ascospores at all temperatures, with the greatest difference at 20°C. Hyphae from ascospores of both groups penetrated the leaves predominantly through stomata, at temperatures from 5 to 20°C. A-group ascospores produced highly branched hyphae that grew tortuously, whereas B-group ascospores produced long, straight hyphae. The percentage of germinated ascospores that penetrated stomata increased with increasing temperature from 5 to 20°C and was greater for A-group than for B-group L. maculans after 40 h incubation. 相似文献
83.
Eiko E. Kuramae Alexandre L. Buzeto Maisa B. Ciampi Nilton L. Souza 《European journal of plant pathology / European Foundation for Plant Pathology》2003,109(4):391-395
Fungi isolated in Brazil, from lettuce, broccoli, spinach, melon and tomato, were identified as Rhizoctonia solani. All lettuce isolates anastomosed with both AG 1-IA and IB subgroups and all isolates from broccoli, spinach, melon and tomato anastomosed with AG 4 subgroup HG-I, as well as with subgroups HG-II and HG-III. DNA sequence analyses of ribosomal internal transcribed spacers showed that isolates from lettuce were AG 1-IB, isolates from tomato and melon were AG 4 HG-I, and isolates from broccoli and spinach were AG 4 HG-III. The tomato isolates caused stem rot symptoms, the spinach, broccoli and melon isolates caused hypocotyl and root rot symptoms on the respective host plants and the lettuce isolates caused bottom rot. This is the first report on the occurrence in Brazil of R. solani AG 4 HG-I in tomato and melon, of AG 4 HG-III in broccoli and spinach and of AG 1-IB in lettuce. 相似文献
84.
植物苯丙氨酸解氨酶基因的表达调控与研究展望 总被引:43,自引:0,他引:43
苯丙氨酸解氨酶(phenylalanineammonia-lyase,PAL,EC4.3.1.5)是催化苯丙烷代谢途径第一步反应的酶,也是这个途径的关键酶,对植物有非常重要的生理意义。根据有关文献综述了植物PAL的分布与定位、酶学性质,总结了生长发育、钝化因子与调节因子、末端产物等内部因素及光、温、机械损伤与生长调节剂等外部因素对PAL的调控作用,得出外部因子是在转录水平上对酶活性实施调控的结论,并运用酶学和分子生物学方面的知识阐述了其调控机理。还着重阐述了PAL酶在果树上的研究现状与进展,并对其今后的研究及在果树上的应用进行了展望。 相似文献
85.
G. DAHAL 《Integrated Pest Management Reviews》1997,2(3):139-159
Research on insect pests (including leafhoppers and planthoppers) in Nepal was initiated in 1956 by the Entomology Division and Plant Protection Units of the Department of Agriculture. More systematic work began after the establishment of a Rice Improvement Programme in 1972. Because of poor documentation and publication of research findings, it is difficult to assess the research efforts and achievements to date. The available research reports are mostly published in the proceedings of national seminars/workshops. They are used here to assess the current status of research on the occurrence and damage caused, distribution and composition, relative abundance, biology and management through chemicals. Much of past research has focused on insect surveys by light traps and sweep nets and the evaluation of insecticides and, since early 1990, some research on rice green leafhoppers (Nephotettix virescens and Nephotettix nigropictus) has begun to determine their relative abundance and population characteristics in relation to their potential as vectors of rice viruses. The challenges to pest management in general and some suggestions for future research needs are discussed, based on the present standing of agricultural research in the country 相似文献
86.
87.
Anthropogenic influences on potential fire spread in a pyrogenic ecosystem of Florida, USA 总被引:1,自引:1,他引:1
Fire has historically been an important ecological factor maintaining southeastern U.S. vegetation. Humans have altered natural
fire regimes by fragmenting fuels, introducing exotic species, and suppressing fires. Little is known about how these alterations
specifically affect spatial fire extent and pattern. We applied historic (1920 and 1943) and current (1990) GIS fuels maps
and the FARSITE fire spread model to quantify the differences between historic and current fire spread distributions. We held
all fire modeling variables (wind speed and direction, cloud cover, precipitation, humidity, air temperature, fuel moistures,
ignition source and location) constant with exception of the fuel models representing different time periods. Model simulations
suggest that fires during the early 1900's burned freely across the landscape, while current fires are much smaller, restricted
by anthropogenic influences. Fire extent declined linearly with patch density, and there was a quadratic relationship between
fire extent and percent landscape covered by anthropogenic features. We found that as little as 10 percent anthropogenic landcover
caused a 50 percent decline in fire extent. Most landscapes (conservation or non-conservation areas) are now influenced by
anthropogenic features which disrupt spatial fire behavior disproportionately to their actual size. These results suggest
that land managers using fire to restore or maintain natural ecosystem function in pyrogenic systems will have to compensate
for anthropogenic influences in their burn planning.
This revised version was published online in May 2005 with corrections to the Cover Date.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
88.
Maurice Keith R. Welch Joan M. Brown Christopher P. Latham Roger Earl 《Landscape Ecology》2004,19(6):603-620
The Pocono mesic till barrens (PMTB) are a unique assemblage of fire-maintained shrub communities that support numerous rare species. Historically these barrens covered a large area in the vicinity of Long Pond, Pennsylvania, USA. However, due largely to regional fire suppression instituted in the early 1960s, over 70% of the area covered by barrens succeeded to fire-intolerant forest that does not support the rare species. We investigated the influence of forest proximity on barrens succession across three geomorphic types during periods of high fire frequency and fire suppression, testing the hypothesis that forest processes such as seed rain, shading, and detrital enrichment of soils enhances barrens succession through a contagion effect. Evidence of a forest contagion effect should be shown by increased rates of barrens succession with increasing proximity to the nearest forest edge. In order to detect a forest contagion effect, barrens persistence and barrens succession were modeled in proximity zones of 0-50 m, 50-100 m, 100-200 m, and greater than 200 m from the nearest forest edge. We used existing GIS data layers for fire, geomorphology, and vegetation distribution in 1938, 1963, and 1992. The layers were modified and overlain using ArcView software to determine persistence and succession rates for each unique combination of layers in each proximity zone from 1938 to 1963 (pre-fire suppression) and 1963 to 1992 (post-fire suppression). ANCOVA results indicate that proximity to the nearest forest edge significantly affected barrens persistence rates in both time periods, but succession rates were significantly affected in 1938 to 1963 only. Twenty-eight percent of the 1938 barrens succeeded to forest by 1963; 56% of the 1963 barrens became forest by 1992. Results support previous findings that barrens persistence is enhanced by increased fire frequency, and that barrens persist longer where they overlie flat glacial till than on other geomorphology types. 相似文献
89.
AIM: This study was designed to investigate the secretion of VEGF and its receptor (flt-1 or flk-1/KDR) protein by cultured bovine thoracic aortic endothelial cells treated with various insulin concentrations. METHODS: Endothelial cells was isolated from bovine thoracic aorta, and cultured in serum-free medium, then incubated with different insulin concentrations (30 mU/L, 300 mU/L, 3 000 mU/L). The level of VEGF and its receptor (flt-1 or flk-1/KDR) protein were detected by immunohistochemical staining. RESULTS: As compared with no insulin group, the expression of VEGF protein in low insulin concentration (30 mU/L and 300 mU/L) groups were significantly increased (P<0.01). The expression of VEGF protein in high insulin concentration (3 000 mU/L) group was significantly decreased (P<0.05). Howerer, no difference of the expression of VEGF receptor (flt-1 or flk-1/KDR) protein among all groups (P>0.05) was observed. CONCLUSION: Low concentration insulin up-regulates the VEGF protein expression while high concentration insulin down-regulates the VEGF protein expression in bovine thoracic aortic endothelial cells, but insulin had no directly effect on the VEGF receptor (flt-1 or flk-1/KDR) protein expression in bovine thoracic aortic endothelial cells. 相似文献
90.
对捕食线虫性真菌——少孢节丛孢菌A1分离株(Arthrobotrys oligospora A1)的18S rDNA基因序列进行了研究。结果表明:其18S rDNA全基因序列为1769bp,在进化树上与同种国外分离株A.oligospora var oligospora 1最为接近,同源性为94.7%。这与二者都具有捕食性结构—菌网的特点相一致。证实捕食线虫性真菌的捕食性结构与捕食线虫性真菌种系发生有关。从少孢节丛孢菌3个分离菌株(Arthrobotrys oligospora A1、A.oligospora 1、A.oligospora2)的进化树及同源性来看。不同国家地区的丛孢菌属(Arthrobotrys)分离株确实存在差异。 相似文献