bluuebunny/crossref_metadata_2025_split huggingface dataset:
FACTORS AFFECTING THE SURVIVAL OF PLASMODIO‐PHORA BRASSICAE WOR. IN THE SOIL AND ITS ASSESSMENT BY A HOST TEST
Authors: MACFARLANE I. 
Published: February 2008

The activity of Plasmodiophora brassicae Wor. in the soil was measured simultaneously by counts of root‐hair infection on cabbage seedlings and percentage clubbing of older plants. A linear relation was found between the logarithms of the mean number of root‐hair infections per seedling and the logarithms of the spore concentration in the inoculum. It was found that a high proportion of clubbed plants could be associated with very low average numbers of root‐hair infections on seedlings. The percentage of clubbed plants can be used for assessing quantitatively the infestation of soil by P. brassicae but only at lower levels of infestation than can counts of root‐hair infections. An effect of early application and higher levels of nutrients in increasing clubroot indicates that the nutrient status of the soil is also important, but it is not clear whether this is due to increased club growth or to a direct effect on the fungus.Experiments on the survival of resting spores showed that, in a wet acid soil, there was a rapid decline in numbers of infections to a low and nearly constant level with increasing time from inoculation. This decline could be considerably delayed by alkaline or dry soil conditions or by the addition to the soil of mustard oil (allyl isothiocyanate). This fall in activity is ascribed to spontaneous germination of resting spores, germination being prevented or delayed by such conditions as alkalinity, low soil moisture or the presence of inhibitors.In an attempt to cause biological stimulation of resting‐spore germination by growing short‐term catch crops in infested soil (re‐infestation of the soil from diseased crucifers being prevented), there were fewer infections on test cabbage seedlings after crucifers or ryegrass had been grown than after a number of other non‐crucifers. In fallow soil, a similar reduction was, however, caused by adding nutrients alone.It was confirmed that P. brassicae can infect the root hairs of a number of non‐crucifers and form zoosporangia and zoospores, but no other stages of the fungus have been seen in those plants.Possible improvement of the sampling design in experiments using the root‐hair infection‐count method is briefly discussed.
SOME EFFECTS OF NITROGEN NUTRITION ON THE MORPHOLOGY AND ANATOMY OF MARROW‐STEM KALE
Authors: ARNEY S. E. 
Published: February 2008

Marrow‐stem kale plants grown on plots receiving frequent additions of sulphate of ammonia showed a 40% increase in length of internode and a 25% increase in number of nodes per plant, and the leaf size was increased by between 50 and 70% over plants in plots receiving no N fertilizer. Leaves of kale continue to increase in area until they turn yellow, and the high N leaves showed a greater rate of increase in area at every stage in the life of the leaf.Various features of leaf structure, such as stomatal index, and thickness of palisade and mesophyll, were unaffected by N treatment. The size of the epidermal cells of the leaves was very variable, and although the high N leaves showed a 12% increase in area per epidermal cell over the low N leaves, this difference is not statistically significant. The increased area of the high N leaves can therefore be attributed mainly to increased cell division during the life of the leaf. Only a very slight increase in rate of cell division is necessary to produce the observed effect.The greater leaf area of the high N plants can be attributed mainly to increased size of individual leaves, but there was also a significantly greater number of living functional leaves per plant on the high N plants; at 23 weeks from sowing the high N plants had an average of 13.4 living leaves, while the low N plants had only 11.7 living leaves per plant.There was an appreciable degree of N succulence in the high N kale leaves, which showed a 2% greater moisture content than the low N leaves.A seasonal drift in epidermal cell size, palisade thickness, and total leaf thickness, is shown to be fully significant, statistically. Marked variations in stomatal frequency are barely significant at the 5% level.
STUDIES ON THE APHID TRANSMISSION OF A STRAIN OF HENBANE MOSAIC VIRUS
Authors: BRADLEY R. H. E. 
Published: February 2008

A virus causing a wilt of Datura stramonium was identified as a strain of henbane mosaic virus. It causes necrotic local lesions in Nicotiana rustica, and local lesions are demonstrable in tobacco by staining with iodine. Some of the factors affecting its transmission by Myzus persicae (Sulz.) were studied quantitatively using these lesions.Infective aphids differed little in their ability to cause infection, and usually produced two or three lesions. The duration of the feeding puncture did not affect the number of infections and had little effect on the percentage of aphids becoming infective. Transmissible virus did not seem to be continually imbibed while aphids fed on infected plants, and there were indications that it was acquired immediately before aphids withdrew their stylets from the leaf. Aphids became infective when allowed to make feeding punctures into epidermis stripped from infected leaves. M. persicae transmitted during feeding punctures as brief as 5–10 sec; the probability of single feeding punctures resulting in infection reached a maximum with those lasting from 20 to 30 sec, during which the stylets did not penetrate as far as the centre of the epidermal cell and little or no saliva appeared to be ejected. M. persicae did not transmit the virus when its stylets were artificially wetted with infective sap.Periods of darkness before inoculation with datura wilt virus increased the susceptibility of Nicotiana rustica to infection by rubbing, but not to infection by aphids.
THE CHEMICAL CONTROL OF WATER WEEDS IN THE GEZIRA AREA OF THE SUDAN
Authors: JONES K. WILSON , ANDREWS F. W. 
Published: February 2008

Chlorophenoxyacetate weed‐killers have been tested for the control of aquatic weeds in the canals of the Sudan Gezira. Using water in tanks, it was shown that 10 parts per million of sodium 2‐methyl‐4‐chlorophenoxyacetate (Methoxone) or of sodium 2:4‐dichlorophenoxyacetate (Fernoxone) would kill most of the angiospermous water‐weeds found in the Gezira area.Small‐scale field experiments, using channels of known water capacity, have shown that not only leaves and stems but also seeds and underground rhizomes were killed in treated stagnant water, provided that the weed‐killers were applied as dusts. The water remained toxic to crop plants for approximately 7 weeks after treatment.In a large‐scale experiment in 1950, treating normal irrigation canals, temporary weed clearance was attained, re‐infestation was delayed, and one major canal, 4.5 km. long, remained weed‐free 12 months after treatment.
DRY‐ROT DISEASE OF THE POTATO
Authors: BOYD A. E. W. 
Published: February 2008

A laboratory method is described in which a modified hypodermic syringe is used to inoculate potato tubers with Fusarium 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.
SOME EFFECTS OF HIGH TEMPERATURE ON THE SUSCEPTIBILITY OF PLANTS TO INFECTION WITH VIRUSES
Authors: KASSANIS B. 
Published: February 2008

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 and died in a day.
SOIL SAMPLING FOR WHEAT‐BLOSSOM MIDGES
Authors: GOLIGHTLY W. H. 
Published: February 2008

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 of Sitodiplosis mosellana Géhin 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 of S. mosellana remain 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 50,000 Contarinia tritici Kirby 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 midges.
THE CHANGING NUMBERS OF APHIS FABAE SCOP., FLYING AT CROP LEVEL, IN RELATION TO CURRENT WEATHER AND TO THE POPULATION ON THE CROP
Authors: JOHNSON C. G. 
Published: February 2008

Aphis fabae Scop, flying over bean crops in the summer usually show a double peak of aerial density during the day; scarcely any flight occurs at night. The first peak is thought to be composed mainly of alatae moulted since the previous evening and the decline of the peak to their depletion as they fly away from the crop. The second peak is probably composed mainly of alatae moulted during the same day. Lack of flight at night is due partly to low temperature, partly to lack of alatae old enough to fly and probably also to low light intensity.Contrary to expectation changes in aerial density from hour to hour are only very weakly correlated with weather factors, especially wind‐speed. The total numbers in each of the two peaks do show a low but significant correlation with both wind‐speed and temperature in one case, but even then only a relatively small amount of the variation in aerial numbers is associated with weather changes. Other factors, particularly rapid changes in the numbers of alatae on the crop caused by moulting, accumulation before flight and depletion by flight evidently obscure changes due simply to varying flight behaviour. Thus because of large populations on the crop, it is possible to have quite large numbers in the air even when the weather is relatively unfavourable for flight.In addition to these observations, the relation between total numbers caught at different wind‐speeds shows that most of the migration occurred in winds when the aphids could have had no control over the general direction of flight. The current view that most migration takes place only in calm weather can therefore no longer be held.
THE USE OF TETRA‐ AND PENTA‐CHLORONITRO‐BENZENES IN THE CONTROL OF BOTRYTIS DISEASE AND RHIZOCTONIA ATTACK OF LETTUCE
Authors: LAST F. T. 
Published: February 2008

Botrytis disease in the ‘spring’ lettuce crop was controlled by six talc dusts containing s, 10 or 20 % of tetra‐ or penta‐chloronitrobenzene. All the dusts increased equally the final stand in the frames, but the number of seedlings with stem lesions decreased with increasing concentrations of both compounds. At similar concentrations the tetra‐ was more effective than the penta‐compound. The percentage survival in the field was increased by the dust treatments. The 20% dust of the penta‐ was only as effective as the 5% dust of the tetra‐compound.The dusts affected the leaves, stunted the seedlings and delayed hearting. At similar concentrations the tetra‐ was more harmful than the penta‐compound. The 5 % dust of the tetra‐ was less damaging than the 20% dust of the penta‐compound.The spread of Rhizoctonia solani was reduced by incorporating the dusts with soil. Again, the 5% tetra‐ dust was as effective as the penta‐ dust at 20%. At 12·5 g. of dust per 20 kg. of soil, none of the dusts retarded the rate of emergence of lettuce seedlings but the highest concentration of the tetra‐ series reduced the number emerging.Foliage applications of two dusts, 5% tetra‐ and 20% penta‐ dusts, controlled the spread of R. solani.
OBSERVATIONS ON APPLE CANKER
Authors: CROWDY S. H. 
Published: February 2008

Field observations on leaf‐scar canker of apple confirm its importance in the southwest of England: on a heavily infected tree more than 5% of the current year's growth may be damaged. Leaf scars may become infected by spores of Nectria galligena which are sucked into the tracheids of a freshly exposed scar where they develop in a relatively protected environment. These freshly exposed scars become much less susceptible to infection after approximately one hour.Infections established in leaf scars may develop immediately into cankers or they may be confined by a suberized or gum barrier. Mycelium from some of these confined lesions may spread into the surrounding healthy tissue through growth cracks when the buds develop. The lesions extend throughout the winter and spring; usually the scars earliest inoculated are the first to show cankers. It seems possible that infections of this type might be controlled by eradicant sprays applied just before leaf‐fall.
SCAB, CANKER, AND BRANCH BLISTER OF APPLE AT EAST MALLING IN RELATION TO NUTRITIONAL TREATMENT OF THE HOST
Authors: MOORE M. H. , BENNETT MARGERY 
Published: February 2008

On the sandy loam at East Mailing, moderate annual dressings of inorganic sources of nitrogen and potash exerted no consistent influence on the incidence of apple scab, even when the dressings were continued over an eleven‐year period on established trees of four different varieties on M.IX rootstock. Likewise, no influence of such dressings continued over five seasons was shown on the incidence of apple canker on the rootstock M.VIII, which was grown under conditions favourable for severe infection.There was evidence from early observations that grassing‐down to excess can reduce the incidence of scab, but only at the expense of nitrogen starvation in the trees. Short‐term mixed leys had no such effect.The incidence of branch blister, a functional disease associated with adverse soil conditions and retarded vigour, was greatly reduced in the variety Cox's Orange Pippin by potash manuring, and was further influenced by the rootstock.
STUDIES IN THE BACTERIAL DIE‐BACK AND CANKER DISEASE OF POPLAR
Authors: SABET K. A. , DOWSON W. J. 
Published: February 2008

The bacterial die‐back and canker of poplar is characterized by dark necrotic areas in the leaves, die‐back accompanied by cracks in the bark of 1–4‐year‐old branches, and by cankers on the trunk and branches of different ages. The cankers may be ‘closed’ or ‘open’ and when moist exude slime containing bacteria.The disease is caused by Pseudomonas syringae f. sp. populea, a new forma specialis closely resembling Ps. syringae in bacteriological characters but differing from it in parasitism. The association of the slime with the bacteria is essential for the production of typical lesions.Inoculations with the pathogen alone, or in association with other organisms produce atypical symptoms.The bacteria attack the cortical parenchyma and occasionally invade the xylem vessels.
A STUDY OF THE EPIDEMIOLOGY OF CLUB‐ROOT DISEASE OF BRASSICAE
Authors: COLHOUN JOHN 
Published: February 2008

The epidemiology of club‐root disease of cabbages has been studied by growing plants in naturally and artificially contaminated soils under varying conditions of moisture, temperature, spore load, soil reaction and lime content.The disease can occur in both acid and alkaline soils. By attention to the interaction of factors influencing infection the presence or absence of an attack, as well as its extent and severity, can be predetermined.In acid soils, very favourable conditions for the incidence of the disease are a moisture content equal to about 70 % of the maximum water‐holding capacity and a mean air temperature of 18–23° C. Fluctuations in soil moisture at high levels provide as favourable conditions for infection as a high constant moisture. The level of spore load (within the limits of 103 to 2.5 × 107 spores per g. of soil) does not influence the number of diseased plants in acid soils when favourable conditions for an attack and for good growth of the host are provided. Under less favourable conditions spore load does exercise an effect.The disease occurred in both naturally and artificially contaminated soils showing a pH of 7.8 at planting time; in the former, the pH was adjusted to 7.8 by liming in the field over a period of years, and in the latter by treatment with pure calcium hydroxide shortly before planting. In alkaline soils infection is favoured by high moisture content, high temperature and high spore load. Satisfactory conditions for infection are provided, as in acid soils, at a moisture content of 70% of the maximum water‐holding capacity, it being immaterial whether this level is constantly maintained or fluctuating at high levels. No diseased plants occurred when the soil moisture fluctuated or remained constant at low levels. Severe attacks occurred in alkaline soils when the air temperature fluctuated between points much higher and lower than the mean temperature of 23° C. It is suggested that the optimum temperature for infection is higher than 23° C. In alkaline soils at moisture contents and temperatures favourable for infection a heavy attack can develop only in the presence of a high spore load.In general, it was found that the conditions which were most favourable for the incidence of the disease also favoured the intensity of its development.No substantial differences in the incidence of the disease in different soils were found, but more plants contracted club root in the lighter soils when conditions were less favourable for infection.The results obtained suggest that while liming in the field may control the disease if the spore load is low, even very heavy applications of lime may not be effective if the soil is heavily contaminated and soil moisture and temperature do not operate as limiting factors.
OBSERVATIONS ON THE UPTAKE AND TRANSLOCATION OF FIVE ACTINOMYCETE ANTIBIOTICS BY CUCUMBER SEEDLINGS
Authors: PRAMER D. 
Published: February 2008

The uptake and translocation of five actinomycete antibiotics by cucumber seedlings has been investigated by qualitative and quantitative techniques.Chloromycetin and streptomycin were absorbed from nutrient solution by the root system of cucumber seedlings and translocated to the leaves. The streptomycin concentration of leaf tissue increased with time to a level above that in the nutrient solution, whereas the chloromycetin concentration tended to remain constant at a level below that in the nutrient environment. Chloromycetin and streptomycin were identified in the leaf tissue of treated seedlings by paper chromatography.No convincing evidence of uptake and translocation of aureomycin, neomycin or terramycin was obtained.
DEPOSITION OF AIR‐BORNE LYCOPODIUM SPORES ON PLANE SURFACES
Authors: GREGORY P. H. , STEDMAN O. J. 
Published: February 2008

The deposition of Lycopodium spores on sticky surface traps, including vertical and horizontal microscope slides and Petri dishes as used in routine aerobiological survey, was studied in a small wind tunnel at wind speeds from approximately 0.5–9.5 m./sec.Deposition results from several processes acting singly or in combination. The pattern of deposit on a microscope slide orientated at angles varying from o to 90° to the wind, with gravity either positive, neutral or negative, indicates that, except on a surface parallel to the wind at the lowest wind speed, sedimentation under gravity plays a minor part in deposition on plane surfaces. As the wind speed is increased the deposit is decreased because of ‘edge shadow’. At the highest wind speed the deposit is as large on the lower as on the upper surface of the horizontal slide, which suggests deposition by turbulence. Deposition by impaction against a vertical strip increases with wind speed, and efficiencies observed are lower than for cylinders of the same diameter. The deposit on slides inclined at angles of 45° or less to the wind direction is increased by impaction of an ‘edge drift’. The interaction of these various deposition processes on mean deposition at different angles and wind speeds gives a series of curves with a maximum at 90° at 9.5 m./sec. and with minima at 0, 90 and 180° at wind speeds lower than 9.5 m./sec. At these lower wind speeds there are two maxima in the range 20–70° and 135–150° respectively.Deposits on Petri dishes show rim effects differing at different wind speeds. These can be eliminated by sinking the dish below a flat surface.Blow‐off from non‐sticky surfaces is least at about 45°, and greatest at 0°.Spore concentration in air is difficult to estimate from the deposits on planesurface traps, because horizontal traps under‐record at medium wind speeds, and because vertical traps are very sensitive to changes in wind speed. Power‐operated suction traps are to be preferred when data on spore concentrations are required.