The haustorial host-parasite interface in rust-infected bean leaves after high-pressure freezing     

G. M. Knauf  K. Welter  M. Müller  K. Mendgen   《Physiological and Molecular Plant Pathology》1989,34(6)

The haustorial fine structure of the bean rust fungus, Uromyces appendiculatus var. appendiculatus, was studied within the cells of its host, Phaseolus vulgaris. Results were obtained after high-pressure freezing and subsequent freeze-substitution or freeze-fracturing. Good preservation of leaf tissue after freeze-substitution needed cryoprotection with 8% methanol. For freeze-fracturing, no chemical treatment was applied. In addition to the organelles which are generally found in fungi after cryo-fixation, tubular-vesicular complexes were found in the cytoplasm. Both techniques revealed an extrahaustorial matrix of even width, surrounding the haustorial body. The extrahaustorial membrane was not undulated, and the side facing the plant cytoplasm was lined with a delicate fringe of well-stained material. The extrahaustorial membrane was nearly devoid of intramembrane particles. The host plasma membrane in infected tissue, especially the protoplasmic face, had fewer intramembrane particles than those in uninfected tissue. The haustorial plasma membrane contained many intramembrane particles.  相似文献   

Morphological Basis of Resistance in Cotton to the WhiteflyBemisia Tabaci     

N. S. Butter  B. K. Vir 《Phytoparasitica》1989,17(4):251-261

The morphological basis of resistance to the whiteflyBemisia tabaci Genn. (Aleyrodidae: Hemiptera) was studied. The plant characters examined were leaf area, thickness of leaf lamina, hair density, hair length, angle of insertion of leaf hair, and density of gossypol glands. Hair density and leaf thickness were positively correlated with the population ofB. tabaci, and a positive correlation was obtained between the adult whitefly population and gossypol glands on stem internodes. Cotton genotype USA-22 (sparsely hairy) was found to be more tolerant toB. tabaci than was genotype USA-13 (velvety hairy). The use of thinner and glabrous leaved cotton varieties is suggested to minimize the whitefly menace in cotton.  相似文献   

Effects of temperature,relative humidity and age of conidia on the incidence of spotting on gerbera flowers caused by Botrytis cinerea     

J. Salinas  D. C. M. Glandorf  F. D. Picavet  K. Verhoeff 《European journal of plant pathology / European Foundation for Plant Pathology》1989,95(1):51-64

In recent years, spotting of ray florets of gerbera flowers has become an important problem. This type of small necrotic lesions may occur before, but especially shortly after harvesting the flowers.Botrytis cinerea was easily isolated from such lesions. Inoculation withB. cinerea only gave typical necrotic lesions, when dry conidia were dusted on the flowers with a short period of high rh after inoculation. At 18–25 °C a high rh for at least 5 hours was necessary. Rotting of ray florets and receptacles byB. cinerea occurred when inoculated flowers were kept wet for a few days. Spots consist of one to several necrotic, usually epidermal cells. A single conidium could give rise to a necrotic lesion after germination. Germination of conidia and lesion formation occurred between 4 and 25 °C; at 30 °C, germination and lesion formation did not occur. Between 18 and 25 °C, many lesions became visible within 1 day after inoculation; at 4 °C it took 2 to 3 days before lesions could be seen. If kept dry, conidia ofB. cinerea remained ungerminated on ray florets of gerbera flowers and could be removed from the ray florets. Within 1 day at high rh, germination occurred and lesions were produced. Conidia ofB. cinerea, stored dry, were able to survive much longer than the lifetime of a gerbera flower. Even after storage at room temperature for up to 14 months, some conidia were able to germinate in vitro and on ray florets and induce the formation of lesions. Addition of gerbera pollen diffusate stimulated germination and lesion formation.  相似文献   

Investigations concerning soil-borne viruses in sugarbeet in Sweden1     

K. LINDSTEN 《EPPO Bulletin》1989,19(3):531-537

Some experiments with soil-borne beet viruses in cement tubes in a wire netting enclosure are described. It is confirmed that rhizomania (virus + vector) originating from German soil can survive and cause rhizomania in Sweden. Antisera produced in 1987 to one German BNYVV isolate and to one Swedish soil-borne beet virus isolate, 86-109, which is distinct from BNYVV, were used to check ELISA reactions in the tube beets. Positive ELISA was obtained not only for BNYVV but also for the 86-109 virus from tubes with German inoculum. Beets from tubes with Swedish inoculum reacted only against 86-109 antiserum. In 1988-09, ELISA of 118 sugarbeet plants from Öland and 73 from Skåne, collected in 42 different fields with spots resembling rhizomania, showed no or weak reactions against 86-109 antiserum, in contrast to plants collected in 1987. However, after transplanting the field plants into a warm glasshouse and using bait plants it was shown in ELISA and in transmission to Chenopodium quinoa that many of the bait plants became infected with the 86-109 and ‘related viruses’ but not with BNYVV. Viruses of the 86-109 type seem to be common both in Sweden and elsewhere but may escape detection, especially in mixed infections with BNYVV.  相似文献   

Biological control by Trichoderma harzianum of damping-off of lettuce caused by Rhizoctonia solani1     

M. WILSON  E. K. CRAWFORD  R. CAMPBELL 《EPPO Bulletin》1988,18(1):83-89

Ten isolates of Trichoderma harzianum were tested for their ability to control lettuce seedling damping-off caused by introduced Rhizoctonia solani. T. harzianum isolates TRC 9 and 28 both reduced damping-off. Dual culture experiments were used to select isolates for the study of antibiotic production and mycoparasitism. T. harzianum isolate TRC 12 produced volatile and non-volatile antibiotics, whilst TRC 33 produced only non-volatile antibiotics. T. harzianum isolates 018-2/Y and TRC 9,15 and 28 mycoparasitized R. solani by coiling around and lysing the host hyphae. It appeared that mycoparasitism was more important than antibiosis in the biological control of damping-off.  相似文献   

Chemotherapy of experimental toxoplasmosis with special reference to robenidine     

S K Bakhtari  J Jíra 《Folia parasitologica》1988,35(3):193-198

Robenidine as an anticoccidial agent alone (in doses of 50 and 100 mg/kg) or in association with two other antiprotozoal compounds--pyrimethamine and sulfadoxine (in doses of 2.5 and 250 mg/kg, respectively) were tested in the treatment of chronically infected mice with an avirulent cyst-forming HF strain of Toxoplasma gondii. The efficacy of the used drugs was evaluated by the cysts number in the brains of treated mice versus control group, antibody level and viability of survived cysts by the consecutive infection of mice. According to these criteria none of the tested drugs alone or combined exhibited to be able to produce an effective cure of cyst-stage of toxoplasmosis in experimental mice.  相似文献   

Importance of the proportion of grassy weeds within legume crops in the perpetuation of Gaeumannomyces graminis var. tritici     

P. J. COTTERILL  K. SIVASITHAMPARAM 《Plant pathology》1988,37(3):337-343

Various grass species susceptible to infection by Gaeumannomyces graminis var. tritici were mixed-sown into a legume crop in order to assess their influence on density of inoculum and take-all disease in a subsequent crop of wheat.
In a pot experiment take-all inoculum increased ( P < 0.001) in all treatments containing a proportion (from 20 to 100%, in increments of 20%) of grass in subterranean clover. In a plot trial, most severe take-all occurred in the 20% legume/80% grass stands and least in the 100% legume and 80% legume/20% grass stands. Total grain weight was highest ( P <0.1) after the 100% legume stands. There was no difference in severity of take-all after pure stands of medic, subterranean clover and lupin, but there was more severe take-all after the grass-infested medic stands than after those of subterranean clover ( P < 0.1) or lupin ( P < 0.05). No significant differences ( P > 0.1) in yield occurred in wheat following any of the legumes or mixed stands.  相似文献   

Persistence and binding of DDT and gamma-HCH in a sandy loam soil under field conditions in Delhi,India     

Thomas Samuel  Hari C. Agarwal  Madathil K. K. Pillai 《Pest management science》1988,22(1):1-15

Persistence and binding capacity of [¹⁴C]p, p′-DDT and [¹⁴C]y-HCH were studied for one year in a sandy loam soil of Delhi, India, after surface treatment during monsoon, winter and summer seasons under field conditions. Both DDT and HCH dissipated more rapidly under the Indian subtropical climate than reported for temperate regions. In all three seasons, both insecticides dissipated most rapidly during the initial 60 days. However, in the final six months there was very little change in the residue levels. After one year, the final soil burden of DDT varied from 33 to 36% and of HCH from 14 to 15% of the initial concentrations in the different experiments. HCH bound more with the soil as, out of the total residues present after one year, more than 75% of HCH was in bound form compared with only 24% of DDT. The observed time for 50% initial dissipation of DDT ranged from 60 to 120 days, while in the case of HCH it varied from 30 to 45 days. However, the rate of loss of residues which persisted for more than 6 months was equivalent to a half-life of between 500 and 10000 days for DDT, and between 700 and 2000 days for HCH, thus illustrating the very long persistence of aged residues. Since degradation of both insecticides was apparently minimal, the data indicate that dissipation of DDT and HCH was largely due to volatilisation.  相似文献   

Persistence of hexachlorocyclohexane isomers and carbofuran applied to surface and sub-surface layers of a flooded soil     

Soudamini Panda  M. Sharmila  K. Ramanand  D. Panda  N. Sethunathan 《Pest management science》1988,23(3):199-207

The persistence of carbofuran (2, 3-dihydro-2, 2-dimethylbenzofuran-7-yl methylcarbamate) and the β- and γ-isomers of HCH (hexachlorocyclohexane) applied to surface (oxidised) and sub-surface (reduced) layers of a flooded soil was studied using radiolabelled insecticides. In one experiment, these compounds were placed in the surface (2–5 mm) and sub-surface (10–15 cm) layers of 10-day flooded soil columns. HCH isomers were unstable under flooded soil conditions irrespective of their placement, but disappeared slightly faster when applied to the sub-surface layer, possibly due to the more reduced conditions prevailing. In contrast, sub-surface-applied carbofuran was more stable than surface-applied carbofuran. The decreased stability of surface-applied carbofuran may be due to a relatively higher pH in the surface layer and in the flood water which was in immediate contact with the surface layer. In another experiment, surface and sub-surface soil samples were collected from a rice field which had been flooded for 30 days. These soils were then again flooded under laboratory conditions prior to addition of carbofuran and β-HCH. Upon submergence, both surface and sub-surface soil samples attained almost equally reduced conditions. In flooded surface soil samples, more rapid degradation not only of carbofuran but also of β-HCH occurred, compared with similarly incubated sub-surface soil samples.  相似文献   

Association of double-stranded RNA with whitefly-mediated silvering in squash     

N. BHARATHAN  W. R. GRAVES  K. R. NARAYANAN  D. J. SCHUSTER†  H. H. BRYAN  R. T. McMILLAN JR 《Plant pathology》1990,39(3):530-538

A disorder of unknown aetiology appearing as silvering on squash (Cucurbita pepo) leaves has become prevalent in south Florida. Typical symptoms, observed after 2 weeks of exposure to adults of Bemisia tabaci , the sweet potato whitefly (SPWF) include vein clearing followed by silvering of whole leaves. Fruits from affected plants are blanched or streaked longitudinally. The silverleaf syndrome was not mechanically transmissible when crude extracts of symptomatic leaves were used as inoculum. Two sizes of double-stranded RNA (dsRNA) of c. 4.6 and 4.2 kilobase pairs (kbp) were consistently observed in leaf extracts of caged, whitefly-infested, symptomatic plants. In contrast, caged plants not exposed to whiteflies showed no symptoms and contained no detectable dsRN A. In addition, squash plants exposed to SPWF colonies from California neither developed silverleaf symptoms nor contained any dsRNA. Double-stranded RNA could also be readily detected in whitefly-infested yellow summer squash and zucchini from the field. However, asymptomatic eggplant and watermelon infested with SPWF from nearby fields did not contain detectable dsRNA. Dot-spot hybridization assays using an RNA-specific probe detected homologous sequences in both adults and nymphs of SPWF that induced silverleaf symptoms but not in adults and nymphs of SPWF that could not induce silverleaf symptoms. These results, along with the non-endogenous nature of the detected dsRNA suggest that the dsRNA is or is associated with the causal agent of whitefly-mediated leaf silvering in squash.  相似文献