ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06766.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

A method is described for estimating the relative numbers ofPlasmodiophora brassicaespores germinating in different soils, by counting infected root hairs. Cabbage seedlings are grown for 1 week at 25d̀C. in glass tumblers of the infected soils; after washing out, the tap roots are stained in 1% aceto‐carmine and a count is made of the number of root hairs containing zoosporangia ofP. brassicae, along 2 cm. of root. It is shown that by this method it is possible to study, for example, the action of different bases in inhibiting root‐hair infection; the main inhibiting factor was found to be soil alkalinity, however produced. Other factors were found to influence infection in lesser degree; thus the number of infected root hairs was reduced in soils receivingN/10 sodium and potassium chlorides in place of distilled water. Root‐hair infection was also inhibited by low soil‐moisture

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06767.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

Some fifty isolates of moulds, mainlyAspergillusspp. andPenicilliumspp., were tested for their reaction to sulphanilamide, sulphonamide E.O.S., sulphapyridine, sulphamezathine, sulphaguanidine, propamidine and phenamidine.The moulds showed a high degree of specificity in their reaction to the drug concentrations:Aspergillusspp. were more susceptible to the drugs than werePenicilliumspp. Most of the species included in theAspergillus glaucusgroup were inhibited by concentrations of 1/8000 (125 p.p.m.) of sulphanilamide, sulphonamide E.O.S. or propamidine. Similar concentrations of sulphapyridine, sulphamezathine, sulphaguanidine and phenamidine had only a slight inhibitory effect on mould development.A. versicolorandA. sydowishowed very similar reactions to the drug concentrations, which is in keeping with their relationship on morphological grounds. In general,Penicilliumspp. were not affected by small concentrations (1/2000 or less) of the drugs and were only partially inhibited by higher concentrations (up to 1/125) of sulphonamide E.O.S. Propamidine was more effective against certainPenicilliumspp. though not all were susceptible. Some of the moulds were slightly stimulated by small concentrations of the drugs. No difference in the fungistatic effect of sulphonamide E.O.S. was apparent at different pH levels between 4 and 8.Different strains of the same species sometimes showed different degrees of resistance or susceptibility to the drug concentrations. This was particularly noted for strains ofAspergillus ruber, two of which showed marked resistance to propamidine when incorporated in beer‐wort agar while four other strains of the same species were susceptible to the drug when incorporated in this medium. The two resistant strains, however, were susceptible to propamidine when incorporated in the synthetic Czapek‐Dox medium.4 p.p.m. ofp‐aminobenzoic acid was found to annul the fungistatic action of sulphonamide E.O.S. at concentrations of 250 p.p.m. The addition ofp‐aminobenzoic acid to a synthetic medium incorporating propamidine did not annul the inhibitory action of th

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06768.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

A detailed histological study was made of the necrotic areas induced in the stem of a resistant and a susceptible variety of plum as the result of artificial inoculations ofPs. mors‐prunorumWormald. The pathogen was found to penetrate the tissues intercellularly, causing plasmolysis of cell contents, followed by disintegration of cell walls, and gradual invasion of the bacteria. The seasonal progress of infection was followed, the maximum cankers caused by winter inoculations in the susceptible host appearing in spring. Limitation of necrosis occurs in summer, generally accompanied by the production of new tissue composed of xylem elements. Viable bacteria were isolated in autumn from those cankers in which the area of necrosis had extended into the wood cylinder beyond the limiting periderm. The difference in the nature of the injury to the tissues of the resistant trees is quantitative rather than qualitative. The significance of the apparently more efficient host mechanism of periderm production in this variety is considered. Lesions similar in histological aspect were obtained as the result of the injection of cell‐free filtrates of cultures of the causal organ

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06769.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

A technique for introducing 2‐3 c.c. liquid into the bark of plum trees is described. Parallel injections with dyestuff throughout the spring failed to afford a reliable index of the invasive powers of the various test fluids introduced in this manner.A susceptible variety of plum (Giant Prune) showed greater injury by cell‐free filtrates ofPs. morsprunorumthan did a resistant variety (Warwickshire Drooper), which showed negligible injury. The greatest injuries were caused by filtrates of cultures 5 weeks old, and over, especially when concentrated.Of other bacteria testedPs. prunicola, Ps. syringaestrains,Syringa3, Ap. No. 1, Ap. No. 2, andBact. pruni, yielded damaging filtrates, whereasPs. syringae, strains pear 6 and 7,Ps. tabaci, Ps. fluorescens, Ps. marginalis, Ps. phaseolicola, Ps. tumefaciens, Ps. pisi and Ps. cerasifailed to do so.Some evidence is advanced for the view that the deleterious activity ofPs. mors‐prunorummay be due in part to an endotoxin of protein nature obtainable from the dried bacterial cells by acetic acid extra

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06770.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

Observations at periodic intervals on marked plants in strawberry plantations in south Devon showed that the maximum appearance of crinkle symptoms occurs in June and July, in which months rogumg and inspections should be completed. The data suggest that infection in summer by apterous aphides passing on to neighbouring plants is probably the principal cause of spread.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06771.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

The sheep tick is practically confined to the rough hill‐grazings in Britain where the chief domestic hosts are sheep and cattle. The practical difficulties of treating sheep, lambs and cattle are outlined. Sheep with lamb‐at‐foot, and suckling Galloway and Kyloe cows unused to handling, are the biggest problems.Research on anti‐tick materials having been done chiefly by commercial firms, public knowledge is very scanty. Thirty‐nine experimental and commercial anti‐tick preparations were tested on sheep, lambs and cattle.A sheep dip must be safe, easily mixed, have lasting effect, be capable of dealing with all or most of the ecto‐parasites present and reasonably cheap. So far no experimental dip has surpassed a commercial product comprised of sodium arsenite, ground derris root, cresols and woolfat. In the case of the female, tick, with 30 sec. immersion this dip kills all ticks attached at time of dipping and keeps sheep free of ticks for 7‐10 days, while reinfestation is not complete until 3—4 weeks after dipping. Derris is chiefly responsible for duration of residual effect in this dip. Unlike arsenic, derris kills a proportion of ticks before they can attach and thus lessens tick‐worry and the chances of disease transmission. The dip has no ill‐effects on sheep.The present method of assessment by tick counting does not quite show the full lethal effect of dips. No improvement in the method seems possible.Changes in the bath fluid and in residual protection for sheep were studied at different stages of normal dippings (c.200‐300 sheep) in spring. Herdwick ewes and Black‐faced yearlings each finally carry away about 1/2 gal. (2.28 l.) of dip fluid in their fleeces. A large quantity of foreign solid matter is added to the bath by sheep as dipping progresses; arsenic content remains unchanged while derris is somewhat reduced. The ground derris root particles are thought to be trapped in the meshes of the fleece as excess dip fluid runs back to the bath. Surface tension increases from about 48 to 50 dynes/cm. Residual protection for sheep against ticks lessens as dipping progresses, probably due to progressive reduction of derris in the bath. On the average, provided each sheep gets its share, the dip could furnish each sheep with not more than 0.08 oz. (2.27 g.) ground derris root, 0.18 oz. (5.10 g.) arsenic (as As2O2), and woolgrease at the rate of 10‐17% (0.64‐1.12 oz. or 18.14‐31.75 g.) of the weight naturally present in the fleece (6.40 oz. or 181.44 g.). The dip is effective against all ecto‐parasites except blowfly larvae.Light smearing with vaseline or woolgrease kills attached female ticks within 24 hr. 16% of female ticks on Cheviot yearlings in spring are attached in long‐woolled areas. For this and other practical reasons, sprays and smears are useless for sheep. A derris‐Fuller's earth dust is as effective against ticks as the dip described above but is difficult to disperse in woolled areas. The chief drawback with derris dust, however, is that at certain times it can blind half the sheep. For sheep, the dip is superior to any known dust.Young lambs cannot be dipped: they must be treated on the pasture by methods described. Derris‐Fuller's earth dust is superior to a derris smear, giving protection of a similar order to the dip on sheep. Among thousands of lambs dusted, very much less than 1 % had their eyes affected.Cattle can be treated in stalls by washing or dusting, if used to handling; if not (with the exception of suckling Galloway and Kyloe cows), they can be jetted in stocks. Of several derris dusts, washes and jetting fluids, the best is one containing derris, soap and water. This gives protection of the same order as that with dip on sheep.The derris materials described are the best yet produced for anti‐tick treatment of stock. Cube (Lonchocarpus) root of similar rotenone content to derris root gives similar results to derris in the dip for sheep, dust for lambs and wash for cattle.Attempts have been made to reduce tick populations on grazings by serial anti‐tick treatment of stock. The maximum serial interval possible with derris‐containing materials is 2‐3 weeks. Because lambing prevents dipping for about 6 weeks, this permits about 50 % of the female ticks to escape and breed on the normal sheep farm in spring. The serial interval, i.e. residual protective duration of anti‐tick materials, requires to be lengthened to 5‐6 weeks to prevent this escape. The research work necessary to show whether or how the duration of

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06772.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

A simple procedure for evaluation of the effectiveness of different louse‐killing substances is described. Factors likely to influence the results are discussed, and it is shown to what extent differences in age, mode of application and interaction of carriers are able to influence the insecticidal effect. A number of substances was tested by the methods described and their potency against lice determined by comparison of the minimum time of exposure necessary to give 100% kil

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06773.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

The wireworm survey in the Eastern Counties revealed many cases where the observed wireworm damage failed to correspond with the estimated field population. A possible explanation for this was the inaccuracy of counts made by picking wireworms out of the soil samples by hand. Tests showed that such methods recovered an extremely variable proportion of the wireworms in the‐ samples and, on the average, only two‐fifths of the larvae were obtained. A modified form of the washing and flotation technique used by Salt&Hollick (1944) was introduced for large‐scale work and is described. By this method, ten samples of soil (4 in. diam. and 6 in. deep) bulked together are examined at a time and can be dealt with at the rate of 13 samples per man per hour with an efficiency of 95‐100% in the extraction of wireworms. The populations estimated on 600 fields sampled between December 1942 and May 1943 have thrown more light on the size and composition of the wireworm population in grass and arable fields. Inspection of the crop results on fields tested by the washing process showed a much closer relationship between wireworm population and wireworm damage than had been obtained by the hand‐sorting method in the prev

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06774.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

The fly (Pegomyia betaeCurtis) was studied in its ecological and phenological aspects in central Nottinghamshire, and experiments on the lines of Continental workers, using sodium fluoride and molasses spray, were carried out.It is shown that some pupae from the second generation‐ fail to emerge in the late summer but emerge in the spring of the following year, rather earlier than the pupae resulting from the third generation. The flies resulting from this early emergence are less fertile than those appearing later.Methods of control discussed include cultural, biological and chemical means. Delayed drilling (not before mid‐May) helps to avoid the attack of the first generation. A rapid increase in number of parasites was observed and resulted in the annihilation of a large population of the fly. Treatment with molasses/sodium fluoride bait spray gave promise of cont

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06775.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY