摘要:

Two series of experiments are described: in one, the hatching of half and whole cysts is compared, in some cases after they have been subjected to tryptic digestion; in the second series, the hatching of free eggs is considered.Total emergence from halved cysts was very much greater than that from intact cysts. Emergence from trypsin‐treated halved cysts was greater than emergence from control halved cysts, suggesting that the enzyme affects the egg shell or the larva inside; it is possible, however, that the enzyme also affects the cyst wall, for treated whole cysts shrink more rapidly and to a greater extent when exposed to air.Total emergence from trypsin‐treated whole cysts did not differ significantly from that of untreated whole cysts, unlike previous findings (Ellenby, 1946 a); however, emergence began sooner from these cysts. Halving the cysts also resulted in earlier emergence, the biggest effect being produced by a combination of both trypsin and subsequent halving.The variability shown by the intact cysts was considerably greater than that shown by the halved cysts; halving the cysts reduced the coefficient of variation from 0·55 for whole untreated cysts, to 0·19 for untreated halved cysts, and to 0·13 for trypsin‐treated halved cysts. Apparently some of the variability in emergence, like the limitation of total emergence, is bound up with the nature of the cyst as a more or less closed system.In two experiments the hatching of eggs freed from half‐cysts was compared with that of eggs in their fellow intact halves. In one experiment there was no difference; in the other it was possible to show that a higher proportion of free eggs hatched. Evidently factors limiting hatching may operate among eggs in a mass, even though they are no longer completely enclosed

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1956.tb06843.x

出版商:Blackwell Publishing Ltd    

年代:1956

数据来源: WILEY

摘要:

Twenty‐five varieties of potato in common commercial cultivation were found to be susceptible to tuber attack by potato‐derived populations ofDitylenchus destructorunder field and pot experimental conditions. Stunting and leaf deformation may also be caused by the eelworms but appear less consistently. A race ofD. destructorfrom mushroom spawn had almost no effect on potatoes. Various races ofD. dipsacican reproduce in the shoot tissue of potato, sometimes causing damage. One population of this stem eelworm produced lesions on the tub

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1956.tb06844.x

出版商:Blackwell Publishing Ltd    

年代:1956

数据来源: WILEY

摘要:

Experiments on specially constructed microplots were undertaken to overcome some of the difficulties associated with population studies using field plots. In these microplots Cruciferae caused greater increases in beet‐eelworm populations than Chenopodiaceae when the initial population was low and greater decreases when it was high. Non‐hosts and inefficient hosts caused reductions of the same order as host plants in the same families.When sugar beet was grown at varying initial populations, the final population tended to rise to a ‘ceiling’ which varied with soil and season. The ‘ceiling’ effect is also observed in the field and in pot tests, and may be used as a measure of the efficiency of different host plants or, if the same host plant is grown, as a measure of the effect of different soils and seasons. A linear relationship exists between the logarithm of the initial eelworm population and the yield of roots and tops.Eelworm attack upon sugar beet renders the plants incapable of profiting from favourable growing conditions and reduces the size of the plants without affecting the sugar content of the roots. Within certain limits, the final eelworm population is independent of yield or plant density. Cruciferae are far less susceptible to injury by root invasion than the cultivated varieties ofBeta vulgaris.It is suggested that host efficiency in raising and supporting eelworm populations and susceptibility to injury are distinct and independent attributes of host plants. Decay of populations in land under fallow or non‐host crops in non‐host families is approximately 20, 40 and 50% per annum for cysts, cysts with contents, and eggs respectively, and appears to be largely independent of initial population level. The average egg content of cysts with contents falls from 177 eggs/cyst in the first winter after the cultivation of a host crop to 131, 118 and 114 in the second, third and fourth respectively. Thein vitrohatch from beet‐eelworm cysts is affected by previous cropping. Low hatches are sometimes obtained in the winter and spring after the cultivation of host crops, especially where there has been considerable increase. A period of maturation appears to be necessary before eggs are fully sensitive to hatching stimuli.The implications of the microplot results are briefly discussed. Population increase appears to be limited by intraspecific competition rather than by specific enemies. The development and decline of infestations follows a course similar to that in other pests but, because of lack of mobility, the time factor is greatly extended. The differential effects of soil, season and host crop render set rotations ineffective as a measure of control once land has become generally infested. At this stage a system of advice based on soil samp

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1956.tb06845.x

出版商:Blackwell Publishing Ltd    

年代:1956

数据来源: WILEY

摘要:

Moisture content, pore size, depth and oxygen consumption in the soil, which influence soil aeration, have been studied in relation to larval emergence from cysts of the beet eelworm. Experiments show that the rate of larval emergence increases with aeration. In studies of larval emergence in the field emphasis should be laid on soil structure rather than on a mechanical analysis. Those factors associated with good soil tilth favour high rates of larval emergence.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1956.tb06846.x

出版商:Blackwell Publishing Ltd    

年代:1956

数据来源: WILEY

摘要:

Observations have been made on the infestation by aphids of winter lettuce at Imperial College Field Station, Slough, for the seasons 1947–8 and 1949–54. The effects of transplanting and of the use of insecticides have been studied.Plants drilled in September where they were to mature were ready for cutting a little earlier than those transplanted in November, but in years when aphids were numerous the drilled lettuces were heavily infested and very few of them hearted.The infestation of young crops varied from year to year; in some winters it fell to a low level, in others it increased rapidly and persisted with serious effect on the crop. In some years lettuce mosaic virus was also prevalent. The dominant aphid species wasNusonovia ribis‐nigri(Mosley).An early and persistent attack, even in the absence of virus disease, much reduced the number of hearted plants and their average weight. A late attack by winged aphids in early spring sometimes spoilt fully hearted lettuces.Dipping the plants in nicotine solution at the time of transplanting in November reduced aphid infestation; dusting with benzene hexachloride proved more effective.If transplanting was delayed until February or March a relatively clean crop could be produced by insecticide treatment, but losses from fungal disease were usually

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1956.tb06847.x

出版商:Blackwell Publishing Ltd    

年代:1956

数据来源: WILEY

摘要:

The variance of groups of traps sampling the blowfly populations of areas of different degrees of complexity is examined from data for three representative types of pasture—semi‐arable, reclaimed peat bog, and upland sheepwalk.For mean catches of under twenty flies the coefficient of variation was less for limited areas of homogeneous vegetational cover than for larger areas and greater diversity of vegetation; at intermediate mean levels the difference was negligible, hut it reappeared at mean levels of 40 and upwards.Throughout the range of catches examined the variance was much greater than the mean. For very low catches even the standard deviation exceeded the mean, and at no level of mean was it less than 40%.Even for uniform areas such as association fragments the high variance made results with less than six traps difficult to interpret, and ten or more traps are advised.Two methods of comparative sampling of populations are discussed—stratification of the area to be sampled into subunits of relatively uniform vegetational or edaphic facies, and random distribution of the traps over the whole area. For the mean catches by these methods standard regression lines are suggested, from which variance estimates may be made when comparing observed means. Both regressions consist of two straight lines, the lower in each case having a steeper slope. The lines are:Sections S.D. =x̄+ 1 and 0·5x̄+7.Subsection blocks S.D. = 0·8x̄+ 1

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1956.tb06848.x

出版商:Blackwell Publishing Ltd    

年代:1956

数据来源: WILEY

摘要:

Variations in the application rates of chalk and superphosphate and the omission of all the fertilisers had no visible effect on the incidence of wilt caused by any of the five Verticillium species.he literature dealing with the influence of soil conditions upon the Verticillium wilt of a wide range of host plants is reviewed. It is shown that the species V. alboatrum, V. dahliae, V. nigrescens, V. nubilum and V. tricorpus vary inter se in their pathogenicity to Antirrhinum majus, and that their infectivity may be influenced by soil treatments. Thus, in pot cultures, the incidence of antirrhinum wilt induced by Verticillium dahliae and V. nigrescens was reduced by increasing sulphate of potash or ammonium sulphate; or by decreasing soil moisture. Very wet soil and heavy dressings of hoof‐and‐horn were the only conditions under which V. nubilunt and V. tricorpus induced wilt symptoms. Z7. albo‐atrunt was the most virulent species tested; none of the soil treatments decreased its pathogen

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1956.tb06849.x

出版商:Blackwell Publishing Ltd    

年代:1956

数据来源: WILEY

摘要:

The extent of rotting of commercially stored Cox's Orange Pippin apples byGloeosporiumspecies has been severe in recent years. G.perennanshas been found to be mainly responsible.Tree infections of this fungus have usually been found to be prevalent in the orchards on farms where storage losses of fruit have occurred, and conidia ofG. perennanshave been found on cankers at all seasons during the year. Winter as well as summer pruning cuts have been found to become infected. Detached leaves of Cox's Orange Pippin have been successfully inoculated withG. perennansin the laboratory and the fungus has also been found on dead detached leaves in the orchard after picking time. Considerable variations have been found in the susceptibility to rotting of samples of different varieties of apple and samples of Cox's Orange Pippin apples from different orchards. Periodic loading of fruit with spores after picking has shown that resistance declines with length of storage. Wide variation in the time at which rotting commences in commercially stored samples has been observed. A series of inoculations on picked and unpicked immature fruit has shown that the apple loses its resistance to attack on picking. Lenticels which are impermeable to gaseous exchange have been shown to be resistant to penetration by the fungus. Temperature affects the development of lenticel rotting byG. perennans, infection being most rapid at temperatures of about 20°. Rotting can occur at 0°

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1956.tb06850.x

出版商:Blackwell Publishing Ltd    

年代:1956

数据来源: WILEY

摘要:

Cotton seedlings raised under glass from seed pre‐soaked in a water suspension ofXanthomonas malvacearum, and watered by sub‐irrigation only, developed atypical dull green flaccid areas extending from the periphery of the cotyledons. Later symptoms that variably developed were: vascular discoloration, not necessarily continuous, in the petioles of affected cotyledons, in the hypocotyl, and in parts of the plant above the cotyledonary node; premature withering of cotyledons; dull green flaccid areas in true leaves, not necessarily the lowest, later turning brown and drying, with usually a chlorotic margin; parenchymatous attack in stems, petioles and leaves. Evidence is adduced, from the progression of symptoms and from associations between them, and from isolations of the pathogen from various parts of the plant at different stages, that the course of this type of infection is primarily vascular, progressing from the edges of cotyledons into the hypocotyl and thence upwards in vascular tissues. Thence the infection may break out at any time into parenchymatous tissues, leading to the more characteristic forms of the disease, of greater or less severity according to the susceptibility of the parenchyma at the time of its invasion. Similar symptoms have been observed in field plantings, and it is suggested that vascular infection is of greater and wider significance in the epidemiology of bacterial blight than has hitherto been commonly accep

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1956.tb06851.x

出版商:Blackwell Publishing Ltd    

年代:1956

数据来源: WILEY

摘要:

Nine derivatives of pentachlorophenol have been prepared and tested for fungistatic activity against the mycelia ofBotrytis fabae, Sclerotinia laxaandStereum purpureumand for phytotoxicity towards tomato, apple and plum. The most fungitoxic of these compounds was the acetyl ester. Its phytotoxicity, although much less than that of pentachlorophenol itself, nevertheless precludes its effective use as an eradicant fungicide on foliage.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1956.tb06852.x

出版商:Blackwell Publishing Ltd    

年代:1956

数据来源: WILEY