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   

Susceptibility of Mastomys natalensis to Brugia malayi following pretreatment with antifilarials     

K Tyagi  P K Murthy  A B Sen 《Folia parasitologica》1990,37(3):261-265

Mastomys natalensis pretreated with diethylcarbamazine (DEC), levamisole or centperazine were exposed to the standard inoculum of infective larvae of Brugia malayi. Percentage 'take' of infection, duration of prepatent period, course of microfilaraemia and number of adult worms recovered were compared with those of untreated infected Mastomys (control). DEC and centperazine did not alter the 'take' (DEC/centperazine: 100%; control: 88.24%) and the average prepatent period (DEC: 105.44 days; centperazine: 105.18 days, control: 109.20 days). In levamisole pretreated animals on the other hand, the 'take' was much lower (68.18%) with extended prepatent period (125.87 days). However, unlike centperazine and control, the course of microfilaraemia was identical in DEC and levamisole pretreated animals. The average adult worm recovery was significantly high in centperazine pretreated animals being 14.09 as against 8.12, 7.46 and 8.42 in DEC, levamisole pretreated and control animals, respectively.  相似文献   

Detection of tomato spotted wilt virus and transmission by Frankliniella occidentalis in France   总被引：1，自引：1，他引：1  

G. MARCHOUX  K. GÉBRÉ-SELASSIE  M. VILLEVIEILLE 《Plant pathology》1991,40(3):347-351

Tomato spotted wilt virus (TSWV) was isolated from pepper, tomato, eggplant, broad bean, lettuce, basil, chrysanthemum, aster, New Guinea impatiens, anemone and gloxinia plants. Virus identification was based on host range, vector transmission, serology and electron microscopy. TSWV was readily detected by ELISA in naturally or artificially infected cultivated or weed plants. The virus was also detected in individual F. occidentalis thrips. The spread of TSWV in vegetable and ornamental plants in greenhouses and/or in the open is related to the close relationship of the virus with the vector.  相似文献   

Phenotypic instability of flusilazole sensitivity in Venturia inaequalis   总被引：2，自引：0，他引：2  

W. KÖLLER  F. D. SMITH  K. L. REYNOLDS 《Plant pathology》1991,40(4):608-611

Sensitivities of 16 monoconidial isolates of Venturia inaequalis to the sterol demethylation inhibitor flusilazole were found to be stable, when cultures which had been successively transferred to inhibitor-free nutrient agar and maintained at 20 C were retested 6 months after isolation. In contrast, with storage of these isolates at 2 C for 7 additional months, phenotypic sensitivities were subject to change. A high degree of phenotypic instability was also observed for 77 representative strains which had been subcultured for 10 months. In both cases, the majority of strains became more sensitive to flusilazole. The frequency and magnitude of these changes were most pronounced for strains with moderate levels of resistance. More than 70% of the strains investigated were collected from wild-type populations, suggesting that the reversion of resistant strains was not related to a process of unstable adaptation but to a high degree of plasticity in the genetic control of sensitivities to sterol demethylation inhibitors.  相似文献   

Quick decline of macadamia trees: association with Xylaria arbuscula     

W. H. KO  R. K. KUNIMOTO 《Plant pathology》1991,40(4):643-644

Some macadamia trees in a commercial orchard on the island of Hawaii showing symptoms of quick decline had club-shaped fruiting bodies of Xylaria arbuscula on the trunk. X arbuscula was consistently isolated from diseased wood and was shown to kill branches of healthy macadamia trees on inoculation. Trunk infection by this pathogen leading to girdling resulted in a more rapid decline than would be expected with root infection by soil-borne pathogens.  相似文献   

Weed size hierarchies in Denmark     

P. K. JENSEN 《Weed Research》1991,31(1):1-7

In 962 field trials in different crops, the size of a number of weed species was investigated. The weeds were ranked according to their size on a single occasion. The ranks of the species were examined relative to two weed species, Viola arvensis and Matricaria inodora. The ranking was, however, independent of which of the two species were used as standard. The correlation between the rankings with Viola arvensis as standard, and the rankings with Matricaria inodora as standard were r= 0-93 for spring sown crops, and r= 0.84 for autumn sown crops. Sinapis arvensis was the largest weed species in spring sown crops, with a weight of 14.5 times that of Viola arvensis, followed by Brassica napus, Galeopsis spp., Thlaspi arvense and Amsinckia spp. Viola arvensis. Veronica spp. and Lamium spp. were the smallest weed species in spring sown crops. Galium aparine was the largest species in autumn sown crops, whereas spring germinating species such as Polygonum spp. were among the smallest. The ranks of Viola arvensis, Myosotis arvensis, Lapsana communis, Matricaria inodora and Lamium spp. were almost identical in spring sown crops and in autumn sown crops.  相似文献   

Selection of sorghum (Sorghum bicolor (L.) Moench) varieties resistant to the parasitic weed Striga hermonthica (Del.) Benth     

A. OLIVIER  K. V. RAMAIAH  G. D. LEROUX 《Weed Research》1991,31(4):219-225

Pot and field experiments were performed in Burkina Faso in 1987 and 1988 to evaluate the resistance of selected ‘low-stimulant’ sorghum (Sorghum bicolor (L.) Moench) varieties to the parasitic weed (Striga hermonthica (Del.) Benth. In a pot experiment, the variety IS-7777 supported the lowest number and had the latest emergence of Striga, compared with the other varieties tested. The varieties IS-14825, IS-6961, IS-7739, IS-14928 and IS-14975 also had signifi cantly lower numbers of emerged Striga per pot than the resistant control Framida. The resist ance of IS-7777 was confirmed in field experi ments, as was that of IS-7739, IS-6961 and IS-14928. However, the yield potential of these poorly adapted varieties was low in Striga-infested fields. The varieties IS-14975, IS–14825 and Seguetana Niarabougou exhibited a low susceptibility associated with a grain yield equivalent to that of the other varieties in farm fields infested by Striga. As Seguetana is already grown by Sahelian farmers, its use could be recommended in the absence of resistant varieties adapted to Sahelian agroclimatic conditions. The exceptionally high level of restance exhibited by IS-7777 could be exploited in studies on the genetics and mechanisms of resistance of the host plant to the parasite, as well as in sorghum improvement programmes.  相似文献   

Pectate lyases of Erwinia chrysanthemi: Pel E-like polypeptides and pelE homologous sequences in strains isolated from different plants     

K. K. Thurn  F. Barras  Y. Kegoya-Yoshino  A. K. Chatterjee 《Physiological and Molecular Plant Pathology》1987,31(3)

Pel E, one of the four major pectate lyases produced by Erwinia chrysanthemi (Echr) strain EC16, was purified to homogeneity and was found to have an apparent molecular weight of 47 500 and a pI of 10. Antibodies produced against this preparation inhibited Pel E activity, but did not affect Pel A, Pel B or Pel C activities. Immunotitration revealed that Pel E accounted for a major fraction of the total extracellular Pel activity ranging from 40–60% in culture and potato tuber tissue. Isoelectric focusing of the extracellular Pels produced by various Echr strains indicated that while the Pel profiles of strains isolated from various hosts were different, the profiles of strains isolated from the same host were very similar. A significant proportion (ranging from 39 to 74%) of the Pel activity of these strains was inhibited by the anti-Pel E antibodies. DNA hybridization under stringent conditions indicated the presence of pelE homologous sequences in the genomes of E. chrysanthemi strains. We conclude that a Pel E-like enzyme occurs in all E. chrysanthemi strains examined.  相似文献   

Pyrethroid insecticides derived from 2,2-dimethyl-3-(3-phenoxybenzyloxy)propanal     

Axel Svendsen  Lars-Erik K. Pedersen 《Pest management science》1987,18(3):169-178

Fourteen oxime ethers and eleven other unsaturated compounds derived from 2,2-dimethyl-3-(3-phenoxybenzyloxy)propanal were synthesised and their insecticidal activity against Musca domestica, Locusta migratoria, Dysdercus cingulatus, Aedes aegypti, Plutella xylostella, Drosophila melanogaster, Tetranychus urticae and Spodoptera littoralis tested. Structural variations including chain length, branching and unsaturation of the oxime ether O-alkyl group and substituent exchange at the carbon-carbon double bond of the unsaturated compounds were made in order to examine the structure-activity relationship. All biological activities were compared with the activity of the ether pyrethroid MTI-500.  相似文献   

Accumulation of malathion residues in grain stored on malathion-treated wood surfaces     

G. W. K. Mensah 《Pest management science》1987,20(3):161-166

Laboratory studies were conducted to determine whether insecticides applied to storage structures are able to move past a single layer of grain kernels to give adequate control of stored-grain insects. The extent of uptake of insecticides was assessed on three layers of wheat in contact with wood surfaces treated with malathion 836 g litre^?1 e.c. at 1–0 g a.i. m^?2 using chemical and biological methods at predetermined time intervals. There was a progressive uptake of malathion beyond the layer directly in contact with the treated surfaces and the uptake depended on the duration of storage. After 8 weeks a sufficient amount of malathion accumulated on the top layer of grain kernels to cause 100% mortality of adult Tribolium castaneum (Herbst).  相似文献