摘要:

Three synthetic growth‐regulating substances, α‐(2‐naphthoxy)‐, α‐(2:4‐dichloro‐phenoxy)‐ and α‐(2:4:5‐trichlorophenoxy)‐propionic acids, have been resolved into their (+)‐ and (‐)‐forms. The physiological activity of these isomers and of the racemic compounds has been investigated using the pea curvature andAvenacylinder test methods of assessment.The (+)‐isomers in each case displayed high activity in both tests, whereas that exhibited by the (‐)‐isomers was negligible. The racemic compounds showed intermediate activity.The mode of action of aryloxyalkylcarboxylic acids is discussed in the light of the results presented. These considerations suggest the possibility that the activity of the (+)‐isomers might be antagonized by the presence of the corresponding inactive enantiomorphs. Our experiments show tha

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1952.tb01012.x

出版商:Blackwell Publishing Ltd    

年代:1952

数据来源: WILEY

摘要:

Alternaric acid, a metabolic product of some strains ofAlternaria solani, is highly phytotoxic. If introduced into the vascular system of cut shoots of tomato or potato, it travels upwards and causes necrotic lesions of the stem, petioles and leaf blades, very similar in appearance to the lesions appearing in some phases of natural attack byA. solani.Alternaric acid also produces similar lesions on plants outside the host‐range ofA. solani.Associated with the production of visible lesions is a disturbance of the water‐balance of shoots. Transpiration is increased and, in spite of a simultaneous but smaller increase in water uptake, this eventually leads to complete desiccation of the shoots. A strain ofA. solaniknown to produce alternaric acid in synthetic culture media produces a substance with similar biological properties when inoculated into tomato fruits. Since other workers have shown that some of the symptoms ofA. solaniattack are toxigenically induced, it is tempting to suggest that alternaric acid is the toxin concerned. On the other hand, there is no correlation between virulence of strains ofA. solaniand their ability to produce alternaric acid in synthetic culture media or in tomato fruits. Some highly virulent strains produce little or no alternaric acid under any conditions tested. There is some evidence that other toxins beside alternaric acid are produced byA. solani, not necessarily in the same proportions by all stra

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1952.tb01013.x

出版商:Blackwell Publishing Ltd    

年代:1952

数据来源: WILEY

摘要:

A laboratory method is described in which a modified hypodermic syringe is used to inoculate potato tubers withFusarium caeruleum.This injection method gives consistent results and permits reliable assessments of factors such as varietal susceptibility.The occurrence of arrested lesions is noted.Suspensions of very high spore concentration or of spores already germinated did not greatly increase the amount of dry rot above that given by the standard too spores per inoculation, provided that spore germination was adequate.The size of tuber and site of inoculation were found to have a considerable effect upon the results of inoculation experiments, large tubers being more susceptible than small ones and the heel end being more susceptible than the rose end. The necessity for uniformity of material used in inoculation experiments is emphasized.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1952.tb01014.x

出版商:Blackwell Publishing Ltd    

年代:1952

数据来源: WILEY

摘要:

The standard dry‐rot inoculation technique was employed to demonstrate variation in susceptibility in a number of commercial potato varieties over the whole storage season. Susceptibility is lowest at about normal lifting time and gradually rises. Different rates of seasonal progress in susceptibility between varieties were observed.A very high peak of susceptibility occurs in immature tubers in the post‐flowering period of plant growth, which, in the variety Doon Star, is in the latter part of August. This is followed by a sudden decrease which reaches a minimum when the haulm is dead. This susceptibility is not due to thinness of skin of the immature tubers but to physiological or chemical changes in the tubers.Some differences in susceptibility were also observed in different stocks of the same variety, possibly due to soil conditions, but when samples of these stocks were grown on the same soil no clear differences were found in the overall susceptibility, although variations occurred at different sampling da

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1952.tb01015.x

出版商:Blackwell Publishing Ltd    

年代:1952

数据来源: WILEY

摘要:

By combining the results of the standard laboratory injection test and a riddle‐abrasion method of inoculation, both carried out at different periods of the year, a susceptibility index for a number of commercial potato varieties grown on the same soil was obtained, using the variety Catriona as a standard. None of the varieties tested was immune from the disease.The reactions of certain varieties were found to differ in both tests and in a few, e.g. Golden Wonder, this is believed to be caused by differences between ‘physiological’ susceptibility, i.e. that of the tuber flesh, and ‘mechanical’ susceptibility, i.e. where liability to abrasion is also involved.A method for assessing skin abrasion is described.The rate of development of rotting was found in some cases to be independent of the final susceptibil

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1952.tb01016.x

出版商:Blackwell Publishing Ltd    

年代:1952

数据来源: WILEY

摘要:

The standard injection method of inoculation was used in conjunction with the riddle‐abrasion method, at three periods during the storage season, to determine the effect of storage of potatoes of three varieties at three temperatures or ranges of temperature upon their subsequent susceptibility toFusarium caeruleum.Susceptibility was greatly increased by increase in storage temperature. Low‐temperature storage (39°F.) before inoculation decreased susceptibility. If, however, such storage immediately followed inoculation, although little or no signs of rotting were obvious after 6 weeks, when these tubers were replaced for a further 6 weeks at the normal temperature of incubation (60°F.) the amount of rotting was enhanced.Some practical consequences of these facts are disc

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1952.tb01017.x

出版商:Blackwell Publishing Ltd    

年代:1952

数据来源: WILEY

摘要:

When plants were kept at 36°C. for some time before inoculation, their susceptibility to infection by five mechanically transmissible viruses was greatly increased. When kept at 36° after inoculation, fewer local lesions were produced than at lower temperatures, but the effects of the post‐inoculation treatment differed with different viruses. Tomato spotted wilt and tobacco mosaic viruses multiply in plants at 36°, and the post‐inoculation treatment reduced the local lesions they caused to numbers that varied between 10 and 90% of the control; these two viruses also have large thermal coefficients of heat inactivation. By contrast, tobacco necrosis, tomato bushy stunt and cucumber mosaic viruses, were much affected by post‐inoculation treatment, lesion formation being completely prevented by exposure to 36° for a day or more. These three viruses appear not to multiply in plants at 36°, and although they have high thermal inactivation points, they have small temperature coefficients of thermal inactivation.The extent to which lesion formation was affected by pre‐ or post‐inoculation exposure of plants to 36° depended not only on the length of the treatment, but also on the physiological condition of the plants.The symptoms of infected plants changed considerably if kept at 36°. At 36°Nicotiana glutinosa, inoculated with tobacco mosaic virus, gave chlorotic local lesions instead of necrotic ones, and became systemically infected. When systemically infected plants were brought to ordinary glasshouse temperature, the infected tissues all collapsed

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1952.tb01018.x

出版商:Blackwell Publishing Ltd    

年代:1952

数据来源: WILEY

摘要:

Contarinia triticiemerges the same year as the larvae are in the wheat ears and up to 3 years later. Its parasites emerge up to 2 years after the larvae are in the wheat ears, but never the same year. This indicates that the supernumerary generation ofC. triticithat occurs on couch grass in August and September may be expected to be free from parasites and so constitutes a dangerous source of replenishment of the pest.Emergence ofSitodiplosis mosellanacan take place after the larvae have been in the soil up to twelve winters. Most of any one year's larvae do not necessarily emerge as midges after one winter, although usually this is so. Any one year's flight is probably a composite one derived from several previous generations of this one‐generation‐a‐year gall

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1952.tb01019.x

出版商:Blackwell Publishing Ltd    

年代:1952

数据来源: WILEY

摘要:

Fully fed larvae of the wheat‐blossom midges need moist conditions in order to descend from the ears to the soil. A dry spell coinciding with the fully fed stage therefore causes an accumulation of larvae, which subsequently leave the ears in a body when rain comes. Conversely, in wet weather each larva leaves the wheat as soon as it finishes feeding, and, since all the eggs are not laid on the same day, the descent will then be a gradual process.A method is described of taking small samples of wheat ears at frequent intervals, thus facilitating the determination of the correct date on which to take the main sample for the assessment of infestation by the two wheat‐blossom mid

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1952.tb01020.x

出版商:Blackwell Publishing Ltd    

年代:1952

数据来源: WILEY

摘要:

A method of assessing the population of wheat‐blossom midges by the recovery of the cocoons from soil is described.In the dry summer of 1947, considerable numbers of larvae ofSitodiplosis mosellanaGéhin were still in the ears at the time of harvesting. Burning the straw immediately after combining may considerably reduce the numbers of midges.The majority of the larvae are found in the top 3 in. of the soil although a considerable number may be found from 3 to 6 in. Headland infestations may be lighter than the rest of the field.Cocoons ofS. mosellanaremain viable in the soil for several years, and 150,000 per acre were recovered in February 1951 from a field which had not had a wheat crop since 1944. At the same time 50,000Contarinia triticiKirby cocoons per acre were found in a field which was last under wheat in 1947.Viable pupae were successfully obtained by soil sampling, and the pupation in the soil and subsequent emergence of the midges can be followed. Thus it is possible also to estimate the numbers of midges that will emerge.Progress has been made towards predicting outbreaks of these two midg

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1952.tb01021.x

出版商:Blackwell Publishing Ltd    

年代:1952

数据来源: WILEY