ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07846.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

A survey of aphids and virus diseases of sugar‐beet root crops in eastern England was made between 1940 and 1948. Prior to 1943 the observations were made on fertilizer experiments; from 1943 onwards they were made on commercial fields selected for position in relation to beet and mangold seed crops. The incidence of beet yellows increased with increasing numbers ofMyzus persicae, but not ofAphis fabae.The relation withM. persicaewas sufficiently close to suggest that it is the most important, possibly the only important, vector of beet yellows virus. Beet mosaic virus also increased with increasing numbers ofM. persicae, but the relation was not close enough to exclude the possibility of other vectors.Numbers ofA. fabaeon sugar beet were slightly, but consistently, depressed by the use of salt as a fertilizer. Other fertilizers had variable effects. Neither aphids nor virus are likely to be greatly affected by fertilizers.Beet yellows is most prevalent in areas where seed crops are grown, but within these areas nearness to individual seed crops did not appear to increase its incidence.M. persicaewere more numerous on sugar beet in seed‐crop areas than elsewhere, and this alone might account for the prevalence of yellows. Beet mosaic virus is more closely associated with seed crops than is beet yellows. It is most prevalent near to seed crops within the seed‐crop

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07847.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

The growth ofPhytophthora infestanswas retarded on leaves of potato plants that had been artificially inoculated with virusXor with virusY.Using different virus strains and potato varieties, the effect of virus infection on blight development was found to be greater, the more severe the systemic virus symptoms exhibited on the infected leaves beforeP. infestansinoculation.The development of the fungus was never increased by virus infection.The reduced blight development on virus‐infected leaves is partially caused by an increase of resistance to infection. It is also suggested that virus infection alters the nutritional status of leaves to one less favourable for the development ofP. infestan

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07848.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

A severe disease affecting many plants in a crop of broad beans was found to be caused by a previously undescribed virus, provisionally named broad‐bean mottle virus. The distribution of diseased plants suggested spread by a vector, but none of the six insects tested transmitted it. The virus was transmitted to several species of leguminous plants by mechanical inoculation of sap; infectivity for some hosts seemed to be increased by propagation in these hosts.The virus has an unusual combination of properties. Its thermal inactivation point is about 95°C., whereas sap becomes non‐infective within 3 weeks at room temperature. The infection end‐point of broad‐bean sap is 1/1000, only a little higher than the precipitation titre with specific antiserum. Precipitation with antiserum occurs over a smaller range of antigen/antibody ratios than with other viruses previously studied, possibly because of its greater solubility; it is not precipitated with (NH4)2SO4until the salt concentration exceeds 75% saturation.A specific nucleoprotein, containing nucleic acid of the ribose type, can be isolated from infective broad‐bean sap in yields up to 2 g./l. Purified preparations, made by salt precipitation and ultracentrifugation, contain uniform spherical particles approximately 17 mμ in diameter. It is suggested that much of this nucleoprotein is non‐infective, but may otherwise resemble infect

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07849.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

The methods used and the results of 10 years' search for cacao resistant to swollen‐shoot disease are described. Selection among the trees surviving in farms devastated by this virus disease led to the discovery of mild virus strains which can protect trees against virulent strains.When tested by graft inoculation with virulent virus, none of the selections showed any immunity or resistance save that conferred by previous mild‐strain infection. A low degree of tolerance was found in some selections.Local selections and a range of new introductions were tested by mealybug infection, and only types from the Upper Amazon region of Ecuador were consistently resistant to infection. This genetical resistance seems to be strongest in cacao from the Nanay peninsula, near Iqui

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07850.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

A selection of Norfolk Giant raspberry is infected with a virus transmissible byAmphorophora rubiKalt. after short feeding periods on infected plants and persisting for at least 18 1/2 hr. in the aphid. This virus is identified with one which is carried without symptoms by Norfolk Giant and Baumforth's Seedling B, and causes necrosis onRubus henryiand mosaic symptoms onR. saxatilis, American black raspberryR. occidentalis(var. Cumberland) and the red raspberry varieties Chartham, Mailing Landmark and St Walfried. The virus is present in some commercial stocks of Baumforth's Seedling B, Burnetholm Seedling, and the Mailing varieties Enterprise, Notable and Promise. The name raspberry leaf mottle is proposed.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07851.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

The distinguishing characters ofAvena fatuaandA. ludovicianaare described.Pot experiments and field observations showed that most seeds ofA. fatuagerminated in spring and a few in autumn; hardly any germinated in summer or winter. Seeds ofA. ludovicianagerminated in winter only. The greatest depth of sowing from which seedlings of either species reached the surface was 9 in., but seedlings from this depth were weak and yellow when they first appeared.A. ludovicianagave more and sturdier seedlings thanA. fatuafrom 6 and 9 in. There was no evidence of induced dormancy in seeds ofA. fatuaburied at depths down to 20 in. Germination of this species was hastened by monthly cultivation of the soil. The maximum survival ofA. fatuawas 3 years in pots and slightly longer in the field; seeds ofA. ludovicianain pots survived only 2 years. The two or three seeds of each spikelet ofA. ludovicianagerminated in turn, starting with the largest, but the interval between germination of successive seeds varied.Seedlings from freshly sown seeds of both species were more vigorous than seedlings from seeds which had been buried for a year or more. Germination and subsequent growth of both species took place in soil of pH 4.5 to 7.0 approx.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07852.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

Observations in West Midlands orchards in 1947–50 on the apple varieties Cox's Orange Pippin and Laxton's Superb showed that brown rot was often associated with shallow holes in the fruit. Laboratory experiments with undamaged apples proved that earwigs (Forficula auricularia) could cause this type of injury.Bands of sacking soaked in BHC placed around trunks of Laxton's Superb trees in 1949 and 1950 trapped many earwigs; less brown rot occurred in the banded than on control trees. A survey of picked fruit in 1950 showed close correlation between degree of earwig damage and amount of brown rot.Earwig damage was appreciable in fruit from ten out of thirteen grass orchards, but was negligible in fruit from nine arable plantation

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07853.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

In experiments on the infection of bee larvae withNosema apis, the parasitic spores did not germinate and infected adults did not result. In hives of bees infected withN. apisabout 10–20% of the eggs laid did not complete their development probably because of inadequate care and feedin

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07854.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY

摘要:

The occurrence of large numbers of larvae ofTipula lateralisMeig. in watercress beds has not hitherto been recorded. Observations on commercial beds and laboratory experimental work show this species to be primarily a saprophyte feeding on rotting submerged cress leaves, though it can develop during the final instar on green cress. Populations as high as 250,000/acre do not affect cress beds adversely.There are two generations a year and probably a partial third. The life cycle can be completed in 63 days. Mating and oviposition are described, the preferred site for egg laying being on wet soil. The average number of eggs is over 500. The egg and first‐instar larva are described for the first time. There are four instars, the anal segment of the first being radically different from that of the remainder. It has been shown that pupation cannot take place under water as previously state

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1951.tb07855.x

出版商:Blackwell Publishing Ltd    

年代:1951

数据来源: WILEY