摘要:

Exposing both surfaces of leaves systemically infected with cabbage black ring spot virus (CBRSV) or henbane mosaic virus to ultra‐violet radiation decreases the infectivity of expressed sap to about one‐fifth. As irradiation probably inactivates virus mainly in the epidermis, which occupies about one‐quarter the volume of the leaves, these viruses seem to occur at much higher concentrations in sap from the epidermis than in sap from other cells. By contrast, tobacco mosaic virus seems not to occur predominantly in the epidermis.CBRSV and henbane mosaic virus are normally transmitted most frequently by previously fasted aphids that feed for only short periods on infected leaves, but aphids treated like this transmit rarely from leaves that have been exposed to ultraviolet radiation. Irradiation has relatively little effect on the proportion of aphids that transmit after long infection feedings. Fasting seems to increase transmission by increasing the probability that aphids will imbibe sap from the epidermis of leaves they newly colonize. With longer periods on infected leaves, the ability of fasted aphids to transmit probably decreases because they then feed from deeper cells and their stylets contain sap with less virus. Only virus contained in the stylets seems to be transmitted, not virus taken into the stomach. About half the transmissions of henbane mosaic virus by aphids that have colonized tobacco leaves for hours may be caused by insects that temporarily cease feeding on the phloem and newly penetrate the epidermis.Irradiating infected leaves affected the transmission of sugar‐beet mosaic virus in the same way as that of henbane mosaic virus, but had little effect on the transmission of beet yellows virus, whose vectors become more likely to transmit the longer they feed on infected

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1954.tb01116.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

Four sap‐transmissible viruses were isolated from cultivated Solanaceae in Trinidad: (1) tobacco mosaic virus, from tobacco, tomato and sweet pepper; (2) cucumber mosaic virus, from tobacco and petunia; (3) ‘pepper vein‐banding virus’, probably related to pepper mosaic viruses in Puerto Rico and Brazil, from peppers and tobacco; (4) ‘egg‐plant mosaic virus’, possibly related to the tobacco ring‐spot virus, from egg‐plant and tomato. Pepper vein‐banding virus causes leaf‐crinkling and vein‐banding inPhysalis floridana, petunia, variousNicotianaspp. and most peppers; the Large Bell Hot pepper is killed; tomato and egg‐plant are immune. Egg‐plant mosaic virus produces mosaic, ring‐spotting, or both, on different solanaceous species. It also gives local and systemic ring‐spotting onChenopodium hybridumand necrotic local lesions on the primary leaves of cowpea (var. Black‐eye); cucumber is a symptomless carrier. Only cucumber mosaic virus was found naturally infecting non‐solanaceous hosts, cucumber and certain common wild plants.The thermal inactivation point of pepper vein‐banding virus is 62° C, its dilution end‐point 2×10‐5and its longevityin vitro6 day s at 23–30° C.; corresponding values for egg‐plant mosaic virus are 78° C., 10‐6and over 3 weeks.Aphisgossypiitransmits cucumber mosaic and pepper vein‐banding, but not egg‐plant mosaic, of whichEpitrixsp. is an occasional vector. Tobacco mosaic, as elsewh

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1954.tb01117.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

Homogenates of the thoracic nervous system ofLocusta migratoria migratoriodesare able to hydrolyse acetylcholine (ACh) ando‐nitrophenylacetate (NPA), and this hydrolysis can be inhibited by tetraethylpyrophosphate (TEPP) at approximately the same molar concentration for both substrates. It is possible that one acetyl‐esterase is responsible for the breakdown of the two substances, and there is no reason to assume the existence of a specific acetylcholinesterase. In normal horse serum, on the other hand, the pseudocholinesterase is quite distinct from the enzyme responsible for the breakdown of NPA.In an attempt to correlate the inhibition of the locust nerve cord acetylesterase with toxic activity to insects and mice, four chlorinated diethyl‐phenylphosphates were tested as contact poisons against a number of insects and by injection against locusts and mice, and also asin vitroinhibitors of locust nerve cord acetylesterase and horse‐serum pseudocholinesterase. The chemicals were the 2‐chloro‐, 4‐chloro, 2:4‐dichloro‐ and 2:4:5‐trichloro‐ analogues of diethyl‐phenylphosphate.Good correlation exists between theirin vitroactivity against the nerve‐cord acetylesterase and their contact activity to aphids, but not between the former and injection toxicity to locusts. No correlation could be established between the inhibition of horse‐serum cholinesterase and injection toxicity to mice. It is thought likely that the inhibition of nerve‐cord acetylesterase is of greater importance in aphids than in other insects, where the toxic action of the phosphoric esters is at least partly concerned with other vital processes, and that a detoxication mechanism in the mammal breaks down some of the phos

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1954.tb01118.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

Four compounds—bisdimethylaminophosphonous anhydride(schradan), bis(dimethylamino)fluorophosphine oxide (dimefox), diethyl paranitrophenyl phosphate (paraoxon) and sodium fluoroacetate (acetate)—have been tested against the mustard beetle,Phaedon cochleariaeFab. When the four compounds are compared by a direct contact technique in which insects can also imbibe some of the test solutions, or the insects are caged with foliage which has been dipped and then dried, the order of toxicity to adults and larvae was found to be Paraoxon>acetate ≏ dimefox>schradan.The paraoxon is very much more toxic than the other compounds. In all cases the adults are more resistant than the larvae.When the insecticides are applied systemically the order of toxicity changes to Paraoxon>dimefox>acetate ≏ schradan because the acetate causes the plants to wilt and less of it is absorbed. Both paraoxon and dimefox give complete kills of adultPhaedonwhich is the most resistant stage, at practical concentrations.When the insecticides were applied to the outer leaves and translocated to the inner untreated leaves an effect was observed with the dimefox and paraoxon after numerous application, but with a single application very inconsistent results were obtained.It is concluded that schradan and the acetate are ineffective systemically againstPhaedon.The dimefox and paraoxon are very effective, but because of their high mammalian toxicity they would require very careful handling in p

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1954.tb01119.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

Laboratory techniques are described for the estimation of the stomach poison, direct and residual film contact poison and fumigant poison effects of chemicals to adult worker honey‐bees.The toxicity of eleven chemicals used in plant protection has been investigated by these methods. The order of effectiveness as stomach and contact poisons was: parathion, TEPP, γ‐BHC, dieldrin, aldrin, chlordane,o,o‐diethyl‐o‐ethylmercaptoethyl thiophosphate (constituent of Systox), bisdimethylamino fluorophosphine oxide, toxaphene and the sodium salts of 2:4‐D and MCPA: as residual films, dieldrin, aldrin, γ‐BHC, parathion, chlordane, ando,o‐diethyl‐o‐ethylmercapto‐ethyl thiophosphate (constituent of Systox); toxaphene, TEPP and bisdimethylamino fluorophosphine oxide had no measurable effect; as fumigants, dieldrin, γ‐BHC, aldrin, parathion, and chlordane; the remainde

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1954.tb01120.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

Conditions affecting the production of gliotoxin by a strain ofTrichoderma viride, known to produce this antibiotic in synthetic culture media, were studied in two types of soil, a highly acid, sandy podsol from Wareham Heath and a less acid garden soil. High yields of an antibiotic substance, which results from bioassays showed to be similar to gliotoxin, were obtained from both inoculated soils when autoclaved and supplemented with organic material. The autoclaved soils behaved differently when unsupplemented; Wareham soil supported production of the antibiotic but little or none was produced in the garden soil. No antibiotic activity could be demonstrated in soil which had not been inoculated withT. viride.Acidification of unsupplemented garden soil by addition of sulphuric acid had a favourable effect on production of the antibiotic, but raising the pH of Wareham soil by addition of calcium hydroxide also increased the yield. These effects, therefore, cannot be due simply to the change in pH of the soil.The beneficial effect of autoclaving the soil on production of the antibiotic assumed to be gliotoxin was analysed and separated into three distinct effects, elimination of the microflora, increase in availability of nitrogen compounds and increase in available carbon compounds. The last effect was considered to be of greatest significance.The antibiotic was produced in normal Wareham soil if supplemented with additional carbon compounds, but not in garden soil unless this had also been acidified before inoculation. A chromatographic method of bioassay used in the later work gave more substantial evidence that the antibiotic produced in the soil was, in fact, gliotoxin.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1954.tb01121.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

The effectiveness of fungicides for the control ofPlasmodtophora brassicaeWoron. in pot tests under controlled conditions is influenced by spore load, duration of storage of spores prior to inoculation, time of year and temperature. Many fungicides are less effective in soil which has been heavily treated with calcium hydroxide than in unlimed soil or in soil treated with calcium carbonate. In general, fungicides are less efficient when very heavy attacks of the disease occur. If experiments are made under comparable conditions consistent conclusions can be obtained.A schedule of testing is recommended, and it is suggested that fungicides found to be satisfactory in a preliminary test should be subjected to a detailed test. The proposed method of evaluation of a fungicide is to compare its efficacy with that of a standard treatment under comparable conditions. For comparative purposes the efficiency of a fungicide is measured by the percentage number of diseased plants occurring in treated soil and also by the disease index.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1954.tb01122.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

Blastomyces luteushas been shown to be antagonistic in culture to bothVerticillium albo‐atrumandV. dahliaeover a wide range of temperature and irrespective of the pH value of the medium. WhenB. luteusis grown on Dox's and potato‐dextrose solutions it produces an exudate which, added to agar media, has an inhibiting effect upon the growth of these two species ofVerticillium.The effectiveness of this inhibiting material is slightly reduced by boiling for 15 min.When ‘spent’ Dox's liquid medium, which has supported the growth ofB. luteus, is injected into tomato and antirrhinum seedlings inoculated withVerticilliumno control of the disease is effected, but whenB. luteusmycelium is added to soil infected withVerticillium, marked reduction in the incidence of disease results when the antagonistic organism and the pathogens have co‐existed in the soil a sufficient length of time for the exudate of the former to be effective upon the development of t

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1954.tb01123.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

The influence of varying levels of iron and substrate pH on the uptake of nickel and the intensity of toxicity symptoms in oat plants have been investigated using sand‐and water‐culture techniques.Nickel‐toxicity symptoms (both necrosis and chlorosis) are less severe when the concentration of iron in the nutrient solution is high. The reduction in degree of necrosis is related to a reduced content of nickel in the leaf blades, whilst that of chlorosis is related to the Ni/Fe ratio in the leaf blades—an internal antagonism being indicated in the latter case.A reciprocal relationship exists between the nickel and iron contents of the leaf blades; the nickel content is materially reduced by high concentrations of iron in the nutrient solution, and the iron content by nickel, the former being the more pronounced effect.Uptake of nickel increases with increasing pH for a constant iron level in the substrate, although the degree of necrotic symptoms is similar over pH range 4–7. Iron uptake is reduced by both nickel and increasing pH and results in chlorosis at pH values of 5·5 and above.For a constant level of iron supply the phosphate content of the stem extracts is higher the greater the degree of nickel toxicity; the phosphorus status of the plant may be a factor in producing nickel toxicity but if so, it has to be considered in relation to oth

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1954.tb01124.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY

摘要:

Strains A and B ofMonochaetia unicornisproduced cankers following inoculation intoCupressus arizonica, C. benthami, C. lusitanica, C. macrocarpa, C. sempervirens, C. torulosa, Cupressocyparis leylandii, Chamaecyparis lawsoniana, Juniperus proceraandThuja orientalis.Strain D was parasitic only onJuniperus procera.Monochaetta unicornisgrew well on agar media prepared from bark and sapwood extracts ofCupressusspecies andJuniperus procerabut only slowly onPodocarpus graciliorbark agar.Test trees of five species ofCupressus, grown commercially in East Africa, were alternated with artificially inoculated trees ofC. macrocarpain field plots. The subsequent development of natural infections in trees of the test species confirmed field observations thatC. macrocarpawas the most susceptible.Plots (each of 340 trees) of the five species were inoculated with mycelium. In 4 months, the most extensive cankers had developed inC. benthami, and this species also had the largest number of active cankers and the most rapid height growth. When examined again 4 months later,C. macrocarpahad the most extensive cankers and 60% of them were still active as compared with 20% inC. lusitanicaand 6% inC. benthami.Delayed inoculation following wounding confirmed these results and in the dry season the number of successful infections was always highest inC. macrocarpa.Periderm was formed in the bark and sapwood of theCupressusspecies in response to wounding, the process being slower inC. macrocarpaandC. torulosathan in other species. Secondary growth was most rapid inC. macrocarpa.It is suggested that rapid height growth coupled with rapid secondary growth in this host favour the growth of the pathogen rather than the host reaction, andC. macrocarpais consequently very susceptible. During the rains the fungus develops as rapidly in species having a slower secondary growth rate but in the ensuing dry season such infections dry out and the cankers are occluded.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1954.tb01125.x

出版商:Blackwell Publishing Ltd    

年代:1954

数据来源: WILEY