摘要:

SUMMARYCrowdingMegour a viciae(Buckton) on bean plants affects both the nymphs and adults. Crowded nymphs show a low mortality, develop more rapidly to produce light adults after a series of synchronized moults: isolated nymphs show a high initial mortality, develop more slowly to heavier adults, the duration of nymphal stages being extremely variable, with no synchronization of moulting. Development is discussed in terms of both weight gain and linear growth rate.Crowding does not affect adult mortality but it does reduce the rate at which nymphs are produced. The significance of these findings in relation to the formation and maintenance of the aphid colony is considered, and possible controlling factors are discussed.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb02943.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYSclerotia ofBotrytis tulipae(Lib) Lind. buried in field soil germinated mainly in winter and early spring to produce conidiophores and conidia and then decayed. Except when buried very late in the year sclerotia germinated and decayed in the season following burial.In the laboratory, sclerotia from pure culture germinated in two ways. On sterile water‐agar they formed colourless mycelium but no conidiophores; the rate of germination was greatest at 25 d̀C. On unsterile filter paper and on soil they produced mainly conidiophores and conidia; the rate of germination was greatest at 5 d̀C and was enhanced by previous cold treatment. It was unaffected by soil‐moisture or pH.Primary infections of tulips arose from sclerotia placed in the soil but only when they were close to the shoot tip or developing stem. It is suggested that, because of their limited survival, soil‐borne sclerotia are of importance only when tulips are planted in annual suc

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb02944.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYThe following results were obtained when fifty‐seven bulk and crate‐stored commercial seed potato stocks from the East of Scotland were examined in 1966‐8 for contamination by pectolyticErwiniaspp. (1) Most tubers of all the cultivars and stocks examined, irrespective of whether they were obtained from blackleg‐infected or blackleg‐free crops, were contaminated withE. carotovora; (2) some 80% of theErwiniaisolates obtained were identified as var.atroseptica, the rest being var.carotovora; (3) the organisms survived in and on tubers for 6–7 months of bulk storage over the winter and up to planting time the following spring; (4) contrary to what is generally thought, the high incidence of contamination of all stocks, while suggesting that the seed itself is the major source ofE. carotovorafor the growing crop, emphasizes that other factors affect manifestation of blackleg in the field and soft r

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb02945.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYCocoa necrosis virus (CNV) was transmitted by sap inoculation to twelve of twenty‐one species tested. It was propagated and assayed inPhaseolus vulgaris. Sap fromP. vulgariswas infective after dilution to 10‐3but not 10‐4, after 10 min at 60 d̀C but not 65 d̀C, and after 4 but not 7 days at 20–24 d̀C. Lyophilized sap fromP. vulgariswas infective after 2 yearsin vacuo.Virus was prepared by extracting infected leaves ofP. vulgariswith 0.1 M phosphate (pH 7.5) containing 0.05 M ethylene diamine tetra‐acetate and 0.02 M thioglycollate. After clarification withn‐butanol, virus was purified by precipitation with polyethylene glycol and several cycles of differential centrifugation. Such preparations were very infective and contained numerous particles, 24–26 nm in diameter with a hexagonal profile, which sedimented as two components with sedimentation coefficients (Sd̀20,w) of 101Sand 129S. The absorption spectra of both components with maximum and minimum absorption at 259 and 240 nm respectively were typical of nucleoproteins (101Scomponent, A 260/280 = 1.63; A 260/240 = 1.40:129Scomponent, A260/280 = 1.78; A260/240 = 1.58) and indicated nucleic acid contents ofca.35% for the 129Scomponent andca.20% for the 101Scomponent; values calculated from the sedimentation coefficients were 41 and 30% respectively. Only the 129Scomponent seemed to be infective and was not more so when mixed with 101Scomponent. Both components contained a single protein subunit weighingca.60000 daltons.Under certain conditions sap fractionated without butanol gave virus preparations containing empty protein shells (54S) and small spherical particles (20–30S)ca.12 nm diameter.CNV is a serotype of tomato blackring virus and is distantly related to Hungarian chrome mosaic virus.The cryptogram of CNV is */

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb02946.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYElectron microscopy of infectedD. stramoniumcells showed that the virus particles occurred in the cytoplasm. Particles were mostly bacilliform and measured 297 ± 18 times 64 ± 4 nm. In negatively stained leaf homogenates, particles were mostly disrupted; intact particles measured 267 ± 20 times 69 ± 6 nm. In brussels‐sprout cells containing BNYV and CIMV, BNYV particles were rarely found compared with those of CIMV, and they occurred within and near CIMV inclusion bodies. BNYV particles were also found in extracts of virus‐carryingBrevicoryne brassicae.Broccoli necrotic yellows (BNYV) and cauliflower mosaic (CIMV) viruses occurred together in naturally infected Brussels sprout plants, which showed conspicuous symptoms, and in cauliflower. BNYV was transmitted to and maintained inDatura stramoniumandHyoscyamus niger. It was partially purified fromD. stramonium. Using these preparations, from which inhibitor had been removed, BNYV was manually transmitted to cauliflower, causing mild symptoms, and to Brussels sprout, causing a symptomless infection. BNYV also infectedSinapis albabut not cabbage, lettuce,Sonchus oleraceusorPlantago major. BNYV was transmitted byBrevicoryne brassicaebut not byMyzus persicae, Hyperomyzus lactucaeorAleyrodes pro

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb02947.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYTobacco yellow vein, a disease found in Malawi, is caused by a combination of two viruses transmitted in the persistent manner by aphids. One component, tobacco yellow vein virus (TYVV) is manually transmissible, but aphids transmit it only from plants also containing the other (assistor) component, which is not manually transmissible. Aphids also transmit TYVV from plants containing either of two other assistor viruses ‐ tobacco vein‐distorting and groundnut rosette assistor. A virulent isolate of TYVV infectedSoja max, Arachis hypogaeaand several solanaceous species. It infected plants already containing tobacco mottle or groundnut rosette viruses but not those containing a mild isolate of T

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb02948.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYThe rate of deposition of 20–30 μm diameter particles, including spores and pollen grains, on plant and other surfaces, is determined, first, by the frequency at which particles strike the surfaces and, secondly, by the proportion retained on the surface rather than rebounding into the airstream.Spores and pollen grains tagged with a radioactive marker were used to show that the impaction efficiency on leaves and stems depends very much on whether or not the surfaces are sticky or moist. If they are, the rate of deposition may approach that predicted aerodynamically. If the plant surfaces are dry, there is saltation of some spores and the effective rate of deposition is greatly reduc

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb02949.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SUMMARYIn 1967 and 1968 plots of sugar beet in two identically grown crops were shaded for successive four week periods starting on 13 June, 18 July and 22 August, and the growth of the plants compared with that on unshaded plots. At the beginning of each period in 1967 some shaded and unshaded plants received additional nitrogen, and in 1968 plants continuously shaded from June to September were compared with unshaded plants irrigated to equalize their water losses with those of the shaded plants.The weather in 1967 was sunny and dry and that in 1968 dull and wet, but the yields of dry matter, and particularly of sugar, of the unshaded crop in the 2 years were similar because, although net assimilation rate (E) was greater in 1967 than 1968, mean leaf area index (L) in 1968 was almost double that in the 1967 crop. Shading decreased the incoming radiation by 56%; it decreasedEproportionally in 1967, increasingLslightly, but it decreased bothE(by 44%) andLin 1968. The weights of dry matter and sugar in the roots of the shaded crop were consistently smaller at the end of shading and at final harvest in October in both years, and their weights, but not those of the tops or the whole plant, at final harvest over all shading treatments in both years were proportional to the amount of radiation received by the crop between June and September. Although shading greatly decreased the supply of photosynthate to the roots, it did not change the sugar content percentage of dry matter, except in the early stages of growth when the sugar content was rapidly increasing. Sugar content percentage of fresh weight of the roots was consistently decreased by shading, wholly because water content was increased relative to dry matter. Therefore the sugar yield of shaded plants was less because the dry weights of the roots were less, not because the partition of photosynthate between sugar storage and root growth changed.There appears to be a mechanism within the root operating over a wide range of photosynthate supply that maintains a nearly constant proportion of sucrose to non‐sugar, contrary to the hypothesis that sugar stored in the roots is photosynthate in excess of what can be used in growth of the plant. However, in the extreme condition of continuous shading which drastically decreased the dry weights of all parts of the plant, sugar percentage of dry matter in the roots was decreased, but only from 80 to 70%.In 1967 extra nitrogen applied at the start of shading increasedLand the dry weight of the tops in all periods, but had no effect on the dry weight of roots. Because 1968 was a wet year the irrigation treatment had no effect onEorLexcept for a slight increase inLduring the first period; it had no effect on plant dry weight. Both irrigation and additional nitrogen decreased the sugar content percentage of fresh weight of the roots only by altering their water content; sugar percentage of dry matter was unaffected. None of these changes persisted until the final harvest in Octobe

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb02950.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb02951.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1972.tb02952.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY