摘要:

SUMMARYOphiobolus gramini‐scan spread through the soil only along the roots of its host plants. A distinction can thus be made between two phases in the activity of the fungus, a parasitic or ascendant phase, in which the fungus is actively increasing on the roots, and a pseudo‐saprophytic or declining phase, in which the fungus is merely persisting in dead host tissue. In the declining phase, the disappearance of the fungus from the soil must be hastened by the action of the soil saprophytes in actually decomposing its mycelium. Certain soil conditions, which at one time increase the activity of the fungus on the roots of its host, may at another time hasten the disappearance of the resting mycelium from a fallow soil.The rate of growth ofOphiobolus graminisalong the roots of wheat seedlings has been found to vary widely with soil conditions, and growth may even be inhibited altogether. The best growth of all is made in sand; growth in soil increases both with improvement in aeration, and with rise inpH value; it is thus best in light and open soils, and in alkaline soils. In the case of neutral and alkaline soils, growth may be improved by steaming.A hypothesis has been put forward whereby the rate of growth of the fungus along the roots is related to the concentration of carbon dioxide in the microclimate of the root zone, along which the fungal hyphae are growing. Carbon dioxide is produced by the respiration of the host root, the hyphae ofOphiobolus,and the soil microflora; variation in the concentration of carbon dioxide in the root zone will depend on the rate of diffusion of the gas away from the root. This will be most rapid, on the one hand, in light and open soils favouring rapid physical diffusion, and, on the other, in alkaline soils, which can act chemically as carbon dioxide acceptors. These are just the soil conditions which make for most rapid growth of the fungus along the roots.Growth ofOphiobolus graminisalong the roots is also most rapid under just those soil conditions known to favour the occurrence of the take‐all disease in the field, viz. loose and open soils, soils of light texture, and alkaline soils. This well‐established action of soil conditions upon the prevalence of the disease in the field is thus considered to operate directly through the fungus, rather than indirectly through the resistance, yet to be demonstrated, of the hos

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1936.tb06120.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

摘要:

SUMMARYA leaf spot disease of cherry laurel is described. The infected areas eventually become occluded and fall out, leaving irregular holes in the foliage. The disease is caused byTrochila Laurocerasi(Desm.) Fr., the imperfect stage of which is proved to beGloeosporium‐phacidiellumGrove. Infection takes place on the young leaves, most commonly through wounds, and a moist atmosphere is essential for the development and spread of the disease. Control can be effected by spraying with colloidal sulphur during spring and early summer, and by cutting back the bushes only in the autumn, not at short intervals during the summer as is frequently the practice.The writer wishes to acknowledge her indebtedness to Dr G. H. Pethybridge for valuable suggestions during the course of this work, also to Dr C. E. Foister for the photographs reproduced on PL XXX

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1936.tb06121.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

摘要:

SUMMARY1Black‐stem disease of lucerne, which may result in a serious loss of herbage, is recorded in this country for the first time.2The disease first appears on the young shoots early in spring. It is characterized by large, irregular, brownish or blackish lesions on the leaves, petioles and stems. Severe attack of the stems may involve the formation of “cankers” and may lead to wilting and death of the shoots.3The cause of the disease is a species ofAscochytawhich has been determined asA. imperfectaPeck. The dimensions of the spores and the percentage of uniseptate spores in the pycnidia are extremely variable. Some field collections and cultures of the fungus possess only “phomoid” (i.e. unicellular) spores.4The characteristics of the fungus in culture are described. It has been compared with cultures ofAscochyta imperfectaPeck andPhoma MedicaginisMalbr.&Roum. from North America. All the American cultures agree with the fungus isolated from black‐stem disease of lucerne in Britain. It is concluded that the fungus which has been referred to asP. MedicaginisMalbr.&Bourn, in the United States is synonymous withAscochyta imperfectaPeck. This opinion is substantiated by the formation of identical types of lesions on lucerne by the cultures sent from North America and by the British fungus in simultaneous inoculation experiments.5Herbarium material ofPhoma MedicaginisandAscochyta imperfecta,including type material of the latter, sent from the United States has been compared with British material of the black‐stem disease of lucerne. It is concluded that the fungus in all these collections is the same, viz.A. imperfectaPeck.6Under artificial conditionsA. imperfectacan also infectMedicago lupulinaandTrifoUum pratense,but it has not been found on these hosts in the field.7Ascochyta imperfectaoverwinters by means of pycnidia in dead lucerne stems.8The black‐stem disease of lucerne can be held in check by early cutting of the first c

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1936.tb06122.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

摘要:

SUMMARY1This investigation deals with an attempt to determine the value of seed tuber disinfection as a method for controlling common scab(Actinomyces scabies(Thaxt.) Güss.) of the potato crop when tubers affected with the disease are used for planting.2A résumé is given of previous work by other investigators dealing with the control of this disease.3Under Northern Ireland conditions it has been found that a satisfactory control of the disease may be obtained by the disinfection of afEected seed tubers before planting providing that a sufficient interval has elapsed between the growing of successive potato crops in the same land. After a 6‐year interval, which is normal in Northern Ireland farm practice, satisfactory control was obtained in all cases, and it is suggested that a 4‐year interval would probably be sufficient to ensure satisfactory results. Although good control has been obtained after the lapse of shorter intervals, such is not always the case, and the method cannot be relied upon with certainty. No control was obtained where no interval elapsed between the taking of successive potato crops.4Solutions of mercuric chloride, formaldehyde, copper sulphate, Burgundy mixture and proprietary organic mercury compounds employed in various ways were used in these experiments. The most satisfactory method for the farmer's use was found to consist of the instantaneous dipping of the tubers in solutions of proprietary organic mercurials.5The results obtained indicate that in some cases the planting of very slightly afEected seed in land which has not carried potatoes for many years may result in a high incidence of the disease in the resultant crop.6A slight depression in growth was sometimes observed to result from the planting of disinfected tubers, and this was particularly noticeable in the case of the variety Majestic. After a period of from 10 to 12 weeks it disappeared and the crop grew out normally. In some cases tuber disinfection stimulated the growth of the plants. Some of the results obtained suggest an increase in tuber yield due to disinfection of the seed tubers, but the experiments were not laid down in such a way as to permit a statistical analysis of the yields bein

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1936.tb06123.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

摘要:

SUMMARY1Strains of a bacterium causing fasciation of sweet peas have been isolated from galls onNicotiana glutinosa,asparagus,Heuchera sanguineaandGladiolusin addition to the host plants reported in a previous paper. These four new strains all produced fasciation on inoculation into sweet‐pea seedlings.2Histological examination of sweet‐pea seedlings 2–11 weeks after inoculation showed that abnormal growth occurred in the hypocotyl region. In certain areas bacterial zoogloea formed a film on the outside of the tissue, and some penetration of bacteria into the epidermal cells, and in later stages into the intercellular spaces, was observed.3Reisolation tests confirmed the evidence from the microscopical examination, that the pathogen is mainly confined to the exterior of the tissue.4A comparison is made between the action of the sweet‐pea organism andBad. tumefaciensin causing abnormal plant

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1936.tb06124.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

摘要:

SUMMARYAbout 12 hours after a leaf ofNicotiana glutinosais inoculated with ancuba mosaic disease a band of necrotic material begins to form within the cell wall, usually between the lower epidermis and the spongy parenchyma. This band extends both laterally and towards the upper side of the leaf. At the same time, nuclear division is observed in the spongy parenchyma cells, but karyokinesis is not followed by cell division. As the necrotic mesh work extends the cells within it die and dry out. After about 3 days, the lesion consists of a meshwork of this necrotic material. The cells are all dead and the virus is isolated within the necrotic area, all interchange between the infected and healthy parts of the leaf having been prevented.I am indebted to Fraulein Lina Cunow for assistance in making the preparations used in this study.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1936.tb06125.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

摘要:

SUMMARYA.Tomato spotted wilt virus (All tests made with suspensions buffered at pH.7)1The concentration of active virus units in suspensions of tomato spotted wilt virus stored at 0oC. in a buffer solution of JJH 7 was maintained without loss for 11 hours by excluding free oxygen.2A significant fall in the concentration of active virus units occurred in suspensions treated as in (1) but through which air was bubbled.3At room temperatures the virus underwent fairly rapid inactiva‐tion even in the absence of free oxygen, although the presence of oxygen hastened the inactivation. The rate of inactivation in the absence of oxygen varied from time to time, and it is concluded that this inactivation was due to the presence in the infective juice of some oxidized substance which is usually present in only small but variable amounts, and that it is reduced by those substances (see (4) below) which arrest anaerobic inactivation.4Certain substances added in the reduced form which yield suspensions with anEhvalue of +0–1 volt or less atpH7 arrested the normal anerobic inactivation of the virus. The remarkable preservative action of cystein is discussed.5The virus was rapidly inactivatedin vitroby 0–001Msolutions of oxidizing agents which induced in the suspensions a potential greater than + 0–2 volt atpH 7. With the exception of methylene blue, oxidizing agents which gave a suspension with anEhvalue below +0–1 volt atpH7 did not inactivate the virus.6The reducing agents referred to in (4) protected the virus against inactivation when exposed to air. This protective effect was not permanent but prolonged the activity of inocula for many hours beyond that of the controls.7The effect on the virus of a number of other substances was also examined. Those having greatest interest are:(a)KCN, which in 0–01Msolution protected the virus both against anaerobic and‐ aerobic inactivation. Its probable mode of action is discussed on the bases of experiments reported,(b)HgCl2, which in 0.001Msolution caused instantaneous inactivation of the virus, (c) Cathecol, quinol and phenol alone inactivated the virus in the presence of air, but did not do so if Na2SO3was also present. It is concluded that secondary oxidation products caused the inactivation observed.8Attempts to reactivate virus which had been inactivated by exposure to air or by means of HgCl2were unsuccessful.9It has been shown that the inactivating effects observed are due to an action on the

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1936.tb06126.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

摘要:

SUMMARYFour representatives of the genusHolcocnemeKon. occur more or less commonly in Britain.H. caeruleocarpaHtg. breeds onSalixandPopulus.It oviposits in pocket‐shaped incisions in the leaves, and the eggs have an incubation period of 8–9 days. The young larvae are dark with the head black, older larvae are green with the head brown. A typical body segment has six annulets with dorsal setae on the second and fourth and the caudal segment has prominent cylindrical pseudocerci rounded at the apex. Females have five and males have four larval stadia, and pupation takes place in dark brown cocoons in the soil. There are two or three generations during the year, and the insects pass the winter in the cocoons. Parthenogenetic reproduction produces males.Holcocneme lucidaPanz. breeds on species ofPrunusand lays its eggs in shallow incisions along the veins on the under surface of the leaves. The incubation period is 7–10 days. The larvae are yellowish green with the head brown. A typical body segment has six annulets of which the second and fourth are setiferous; the caudal segment bears prominent pseudocerci that are broader at the apex than at the base. Females have five larval stadia and males four. Pupation takes place in brown cocoons in the soil. The species is univoltine and parthenogenesis is arrhenotokous.Holcocneme crassaFall, is widely distributed in Britain and has been recorded as breeding onSalix, PopulusandRumex.The larvae are green with the head greenish brown and the annulation of the body segments is similar to that ofHolcocneme caeruleocarpa.The setae are longer and rather denser than those ofH. caeruleocarpaand the pseudocerci are acuminate.The biology ofH. erichsoniHtg. is described from the published accounts of MacDougall, Hewitt and Mangan. The females oviposit in the young shoots of larch; the larvae are greyish green, and though the annulation of the body segments is somewhat similar to that ofH. lucida,the caudal segment has no pseudocerci and the arrangement of the setae differs from that of the other larvae described here. Females have six larval stadia. The tough brown cocoons are constructed at the surface of the soil. In Britain the species is thelytokous and parthenogenetic reproduction produces females.The differences in the biology of the species and in the form and structure of their larval stages, together with differences in the structure of the adults and the nature of parthenogenesis suggest that the limits of the genusHolcocnemeKon. may not yet be adequately defined.I am greatly indebted to Mr Benson for specimens ofHolcocneme crassa;to Mrs Mary Miles, M.Sc, for assistance in the rearing of the larvae, and to Mr Morris Cohen, M.Sc, for help in the preparation of the text‐

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1936.tb06127.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

摘要:

SUMMARYExperiments are described on the resistance to heat ofE. kühniellain all its stages.Witheggsexposed to 45oC. (113oF.) and 47oC. (116‐5oF.) it is seen that:1One‐day‐old eggs are more resistant than older ones.2Eggs are more resistant to heat at low than at high humidities.3Eggs appear to be able to cool themselves at low humidities in a high temperature by the evaporation of water.4After heating, eggs can regain water they have lost if they are kept in a moist atmosphere.5After heating at low humidities, there is a bigger survival if the eggs are kept in a moist atmosphere than if they are kept in a dry atmosphere.6There is great variation in stock direct from a mill. Eggs from different pairs of moths may have widely different degrees of resistance.7Stock which has been inbred in the insectaries for twelve generations, shows less variation in resistance than stock direct from a mill.Larvaeare much less resistant than eggs. Newly hatched larvae and all larvae until they are full grown have about the same resistance. Last‐stage larvae are far more resistant than other larvae.Pupaeare more resistant than feeding larvae.Adultsare the most susceptible stage to heat. At low humidities the females are more resistant than the males.Experiments on all stages in undisturbed cultures show that a temperature of 45–46oC, maintained for 3 hours, kills all stages.This work was carried out under the direction of Prof. J. W. Munro, to whom I am grateful for his constant encouragement. I have to thank Mr G. V. B. Herford for his help in devising and constructing the apparatus and reading through the typescript, and I am also indebted to Dr 0. W. Richards for his helpful advice on many occasions, and to Mrs Richards who kindly supplied me with a highly inbred strain ofE. kühniella.Lastly I thank Dr G. Fraenkel for many important suggestions, especially those contained in the

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1936.tb06128.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY

摘要:

SUMMARYAs the result of studies onOscinella fritduring the years pro to 1928, it was considered that an attempt might be made to solve economic problem presented by this fly by hybridization of oats, i a resistant variety as one parent.The technique adopted is described and the experimental data show that resistance to attack is an inheritable character (or complex characters), although difficult of precise measurement. Further, shown that agricultural quality and resistance to attack are not in patible.Wet weather conditions during the flight of the fly have a marked effect in limiting the extent of damage to the crop.It is suggested that varietal differences in extent of attack ma due to varietal differences in crude fibre production or depositio silica, both tending to increase the larval difficulties and there for resistance of the plant.I have great pleasure in acknowledging the readiness with w Dr Hunter of the School of Agriculture, Cambridge, has given me benefit of his experience; also, the valuable criticism which Mr J. C. F. Fryer, of the Ministry of Agriculture Pathological Laboratory, Har‐penden, has always placed freely at my disposa

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1936.tb06129.x

出版商:Blackwell Publishing Ltd    

年代:1936

数据来源: WILEY