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   

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