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971.
Genetic diversity and mixed infections of begomoviruses infecting tomato, pepper and cucurbit crops in Nicaragua 总被引:1,自引:0,他引:1
M. Ala-Poikela E. Svensson ‡ A. Rojas T. Horko L. Paulin J. P. T. Valkonen A. Kvarnheden † 《Plant pathology》2005,54(4):448-459
Begomoviruses were detected in Nicaraguan fields of tomato ( Lycopersicon esculentum ) and adjacently growing plants of pepper ( Capsicum annuum ), chilli pepper ( C . baccatum ), cushaw ( Cucurbita argyrosperma ) and Mexican fireplant ( Euphorbia heterophylla ) using polymerase chain reaction (PCR) and universal begomovirus primers. All tomato and Mexican fireplant plants showing symptoms were infected with begomoviruses, while only 30–46% of the pepper, chilli pepper and cushaw plants showing symptoms tested virus-positive. No begomoviruses were found in potato. The virus species were provisionally identified by sequencing 533 bp of the viral coat protein gene ( AV1 ). Tomato severe leaf curl virus (ToSLCV), Tomato leaf curl Sinaloa virus (ToLCSinV) and Pepper golden mosaic virus (PepGMV) were found to infect both tomato and pepper. A new provisional species designated Tomato leaf curl Las Playitas virus (ToLCLPV) was detected in a tomato plant. Squash yellow mottle virus (SYMoV) and PepGMV were found in cucurbits, the latter for the first time in this host. Euphorbia mosaic virus (EuMV) was detected in Mexican fireplant. Sequencing of a larger number of PCR-amplified clones from selected plants revealed intraspecific viral sequence variability, and also multiple begomovirus infections which could represent up to three species in a single tomato or cushaw plant. Phylogenetic grouping of virus sequences did not correlate with the host of origin. 相似文献
972.
G. Alexandre-Pires T. Gilot D. Pais M. Correia J. A. Esperança Pina 《Anatomia, histologia, embryologia》2005,34(S1):2-3
Leishmaniases are a globally widespread group of parasitic diseases from the group of anthropozoonoses. They are caused by an intracellular protozoan parasite that causes a wide spectrum of diseases in humans and dogs worldwide. In fact, the dog is considered one of the most important reservoir. The spleen is one of the several haematopoietic and immunocompetent organs involved. As this organ is a blood filter, the authors looked for the expression of this infection over the microvascular environment and modifications of the spleen cell population related to immunological responses to this parasitic condition.
Tools: Scanning electronic microscopy over intact tissue and corrosion casts, transmission electronic microscopy, histology and immunohistochemistry (MAC 387 and CD3).
Results: Our results show three important modifications concerning the microvascular architecture of the spleen when compared to the normal pattern. A striking scarcity of the sinusoidal system sheath that surrounds the central arteries of the white pulp, a huge development of pulp venules and veins, differentiation of typical features of high endothelial venular cells.
Remarks: According to our results it seems that independent of the virulence of the parasite involved and the kind of immunity prevalent in a particular host, the spleen develops blood dynamic conditions that allows a sluggish blood flow so that cells involved in immunological processes can proliferate and differentiate and it also contributes to the trapping of lymphocytes to the area through the differentiation of typical characteristics of HEV endothelial cells. 相似文献
Tools: Scanning electronic microscopy over intact tissue and corrosion casts, transmission electronic microscopy, histology and immunohistochemistry (MAC 387 and CD3).
Results: Our results show three important modifications concerning the microvascular architecture of the spleen when compared to the normal pattern. A striking scarcity of the sinusoidal system sheath that surrounds the central arteries of the white pulp, a huge development of pulp venules and veins, differentiation of typical features of high endothelial venular cells.
Remarks: According to our results it seems that independent of the virulence of the parasite involved and the kind of immunity prevalent in a particular host, the spleen develops blood dynamic conditions that allows a sluggish blood flow so that cells involved in immunological processes can proliferate and differentiate and it also contributes to the trapping of lymphocytes to the area through the differentiation of typical characteristics of HEV endothelial cells. 相似文献
973.
T Vanholder JLMR Leroy J Dewulf L Duchateau M Coryn A de Kruif G Opsomer 《Reproduction in domestic animals》2005,40(5):460-467
The present study aimed to investigate the pathogenesis of cystic ovarian disease (COD) in high-yielding dairy cows postpartum (pp). Hormonal and metabolic profiles during the first 3 weeks pp as well as during the final week prior to ovulation/cyst formation, were compared between dairy cows that developed either an ovulatory follicle (OV) or a cyst (CYST) < day 60 pp. Thirty-four lactations of 28 high-yielding (9500 kg/305 days) Holstein-Friesian dairy cows were studied. Ovaries of cows were scanned twice a week from day 10 pp on, until ovulation/cyst formation. Milk yield data, body condition scores and blood samples, for determination of oestradiol-17beta, insulin, beta-OH-butyrate and non-esterified fatty acids, were collected simultaneously. Milk samples for progesterone analysis were collected daily. Four lactations were excluded from further analysis because of irregular pp ovarian cyclicity, excluding COD. Eight lactations (26.7%) developed a cyst, while 22 lactations ovulated < days 60 pp. Ovulation and cyst formation occurred at similar times pp. Metabolic and hormonal profiles did not differ between CYST and OV lactations during the first 3 weeks pp. In the final week prior to cyst formation/ovulation, insulin concentrations were lower in CYST than in OV lactations while no differences were observed for any of the other parameters tested. In two lactations, cyst formation was preceded by suprabasal progesterone and increased oestradiol-17beta concentrations. These results suggest that cyst formation in high-yielding dairy cows pp is associated with lower insulin levels but not with other distinct hormonal and metabolic alterations. However from this study, we cannot exclude the involvement of subtle hormonal and metabolic changes in the pathogenesis of ovarian cysts. Suprabasal progesterone, and altered oestradiol-17beta concentrations, seem to play a minor role in cyst formation. 相似文献
974.
Jo?o A T Pigatto José L Laus Jaime M Santos Cristine Cerva Luciana S Cunha Valéria Ruoppolo Paulo S M Barros 《Journal of zoo and wildlife medicine》2005,36(4):702-705
The corneal endothelium is essential for the maintenance of the corneal transparency. The aim of this study was to examine the morphology of the endothelial surface and perform morphometric analysis of the normal corneal endothelial cells of the Magellanic penguin (Spheniscus magellanicus) using scanning electron microscopy. The present work demonstrates that the corneal endothelium of the Magellanic penguin is similar to those described in other vertebrates. 相似文献
975.
Stems of Chenopodium album . and Sinapis arvensis . and leaves of Lolium perenne . were cut with a CO2 laser or with a pair of scissors. Treatments were carried out on greenhouse-grown pot plants at three different growth stages and at two heights. Plant dry matter was measured 2 to 5 weeks after treatment. The relationship between dry weight and laser energy was analysed using a non-linear dose–response regression model. The regression parameters differed significantly between the weed species. At all growth stages and heights S. arvensis was more difficult to cut with a CO2 laser than C. album . When stems were cut below the meristems, 0.9 and 2.3 J mm−1 of CO2 laser energy dose was sufficient to reduce by 90% the biomass of C. album and S. arvensis respectively. Regrowth appeared when dicotyledonous plant stems were cut above meristems, indicating that it is important to cut close to the soil surface to obtain a significant effect. When cutting L. perenne plants with 2-true leaves at a height of 2 cm from the soil surface with a laser, the biomass decreased significantly compared with plants cut by scissors, indicating a delay in regrowth. This delay was not observed for the dicotyledonous plants nor for the other growth stages of L. perenne . 相似文献
976.
Studies were carried out to optimize production of nucleopolyhedrovirus of American bollworm,Helicoverpa armigera (Hübner), by treating larvae individually with an inoculum dose that allowed maximal larval growth and also gave the highest
occlusion bodies (OB) yield/larva. The maximum virus yield of 12.2x 109 OB/larva was obtained when 6-day-old larvae were fed individually with a dose of 1 x 103 OB. Topical spiracular treatment of larvae as old as 8 days with 10 μ of 2x 107 OB ml-1 gave the highest yield, of 15.2x 109 OB from 13-day-old larvae, of 12.8x 108 OB from prepupae and of 1.49x 108 OB from pupae at the time of their death. These studies showed that dietary inoculum is the best route for 6-day-old larvae
and topical spiracular treatment is the best for 8-day-old larvae. 相似文献
977.
W. G. D. Fernando A. K. Watson T. C. Paulitz 《European journal of plant pathology / European Foundation for Plant Pathology》1996,102(1):1-7
Colletotrichum coccodes is currently being investigated as a mycoherbicide against the weed velvetleaf (Abutilon theophrasti). Two isolates ofPseudomonas spp. (Ps2 and Ps5) reduced the percentage of germ tubes and increased appressorial formation ofC. coccodes on detached leaves of velvetleaf. A study was conducted to see whether this effect could be attributed to competition for nutrients or iron betweenC. coccodes andPseudomonas spp. Ps2 and Ps5 had no effect on early spore germination, but reduced the percentage of germ tubes at 24 and 30 h, compared to the nontreated control. This reduction was diminished by the addition of nutrients but not Fe3+. Ps2 and Ps5 stimulated the formation of dark-coloured appressoria without germ tubes (AWGT), but this stimulation was diminished by the addition of nutrients or Fe3+. Germ tube branching at 30 h was also inhibited by the bacteria, but was not diminished by the addition of nutrients or iron. EDTA stimulated conidial germination at 10 h, which was reduced by the addition of Fe3+. However, EDTA did not stimulate the formation of appressoria (AWGT). These results suggest that the reduction in the percentage of germ tubes and the increase in the percentage of appressoria induced by the bacteria may be due to the competition for carbon or nitrogen. Iron competition may also be involved in the stimulation of appressorial formation, but not in the reduction in germ tube percentage and branching. Phylloplane bacteria may compete for carbon, nitrogen and iron, limiting the saprophytic phase of the pathogen on the phylloplane and accelerating the development of the parasitic phase. This may enhance the field efficacy ofC. coccodes as a biocontrol agent against velvetleaf. 相似文献
978.
The role of peroxidase in the resistance of sunflower against Orobanche cumana in Russia 总被引:1,自引:0,他引:1
We present the results of a histochemical study comparing seedlings of races C and D of Orobanche cumana Wallr. (syn. O. cernua Loefl.) attacking sunflower (Helianthus annuus L.) in southern Russia. Three groups of O. cumana seedlings were distinguished according to the peroxidase content of the cells in the radicles: (1) those with neither extracellular nor intracellubr peroxidase and whose radicles have a smooth apex (these were classified as non-infective): (2) those with a high peroxidase content of the nuclei and the cytoplasm layer adjacent to the cell wall, as well as excretion of peroxidase from the apex of the radicles: (3) those with a similarly high peroxidase activity in the parasite cells, but without extracellular excretion. The apices of the radicles of the last two groups are swollen. It is suggested that these belong to O. cumana races C and D respectively. The extracellular peroxidase in O. cumana race C reacts with phenolic compounds, which are lignin precursors of the host, resulting in host resistance due to the formation of lignin layers in sunflowers possessing the Or3 gene for resistance. The absence of extracellular peroxidase in O. cumana race D prevents lignin formation and enables the parasite to attach to the host vascular system. Comparison of these data with the information on the earlier O. cumana races A and B, and older sunflower cultivars, points to a crucial role of peroxidase in the process of breeding new sunflower cultivars and the evolution of new O. cumana races. 相似文献
979.
第1次利用电子显微镜对核盘菌在亚麻叶片上侵染致病的微观过程进行深入细致的观察。结果表明,该菌在侵入叶表面之前可能产生某些酶类物质来软化溶解亚麻叶表面角质层,以帮助该菌对叶表面的侵入。本文还对菌丝和子囊孢子侵染过程的异同进行了比较。 相似文献
980.