摘要:

The bark‐split disease of plums commences with necrotic lesions in the outer bark, causing depressions on the surface; these lesions extend in area and depth, resulting in split and roughened bark, and crippling or killing trees of sensitive varieties like Cambridge Gage.The causal virus was transmitted by grafting in the dormant season, but, probably because it is localized in older tissues, it was rarely transmitted or scion‐perpetuated by summer budding.About 90% of Common Plum clonal rootstocks from East Malling Research Station's layer‐beds were found to be infected. Apparently virus‐free Common Plum was propagated by cuttings from the roots of Common Plum under normal Cambridge Gage trees.A different type of bark‐split disease developed on Shiro Plum inoculated with virus from a tree of Quetsche Précoce de Zimmer. Leaf symptoms accompanying infection with this and with the virus from Common Plum were similar.Bark‐split disease is compared and contrasted with diamond canker of French Prune in California, and features that distinguish bark‐split from bacterial canker

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1957.tb00404.x

出版商:Blackwell Publishing Ltd    

年代:1957

数据来源: WILEY

摘要:

The virus causing phyllody (virescence) in clover flowers was transferred byCuscuta subinclusatoFragaria vescaandDuchesnia indicaplants which then produced symptoms of strawberry green‐petal disease.The jassidEuscelis plebejus(Fall.) in several forms, includingE. lineolatusBrullé, transmitted green‐petal virus from clover to clover, to and from a wide range of other hosts, and from but not to strawberry. Two viruses (or strains) were distinguished, one causing phyllody and the other witches' broom on clover; both were retained for more than 2 months by the vector, in which both had a latent period of about 30 days.Macrosteles viridigriseus(Edwards) also transmitted both viruses.Variation in symptoms on strawberry plants infected naturally, and experimentally through dodder, suggested that two diseases have previously been grouped under the name ‘green petal“. It is proposed to distinguish these as (a) green petal caused by the virus inducing phyllody in clover, and (b) bronze leaf wilt caused by the clover witches' bro

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1957.tb00405.x

出版商:Blackwell Publishing Ltd    

年代:1957

数据来源: WILEY

摘要:

Chrysanthemum virusBis widespread in English chrysanthemum stocks, but it appears to do little damage, for in thirty‐four varieties it caused no or very slight symptoms; the name mild mosaic is proposed for the disease.VirusBinfected ten out of eighty‐six plant species tested by mechanical inoculation and by grafting. Petunia was used as a local lesion test plant; petunias were much less susceptible to infection during the summer. In addition, some petunias showed genetical resistance at all seasons. The concentration of infective virusBin chrysanthemum sap decreased in the summer.VirusBwas transmitted by five out of six aphid species tested; aphids became infective with short acquisition feeds, and lost infectivity within 1 hr.Chrysanthemum was difficult to infect by mechanical inoculation, and the virus was not spread by leaf contact, or by knives used for taking cuttings.The thermal inactivation point of virusBis between 70 and 75°C.; the dilution end‐point varied from 1/10 to 1/1000, depending on the host plant tissue from which sap was obtained; the virus inactivated within 24 hr. at 18°C.Infective sap contained rod‐shaped particles, about 750 ± 17 mμ, not found in sap from uninfected plants. Three strains of virusBwere differentiated by their reaction on petunia; one strain prevented infection by a second.Two other, previously unrecorded, viruses were found in chrysanthemums that cause local lesions in petunia: vein mottle virus was similar in some ways to virusB, but virusBdid not protect plants against vein mottle. Vein mottle severely damaged some varieties of chrysanthemum, but caused no symptoms in others.Chrysanthemum latent virus was carried without symptoms by eleven varieties of chrysanthemum; thirteen out of twenty‐seven plant species were readily infected by mechanical inoculation. Latent virus had a dilution end‐point of 1/200 to 1/500, was inactivated after 10 min. at 70°C., or within 48 hr. at room temperature. It was not spread by the cutting knife, root contact, or by two species of aphid. It was found rarely and seems of no commercial importance in English chry

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1957.tb00406.x

出版商:Blackwell Publishing Ltd    

年代:1957

数据来源: WILEY

摘要:

Experiments during 1953–6 tested the effects of early and late planting of King Edward potatoes on the incidence of virus diseases in the tubers and the suitability of the tubers for use as seed. Plantings were made each month from April to August and tubers were lifted after 12 weeks' growth or after the haulms had died.Aphids began to colonize the early‐planted plots about mid‐June each year, but their multiplication and flying were influenced by weather and varied greatly from year to year. The May‐planted plots usually carried the most aphids. Winged aphids visited the July and August plantings, but few bred extensively though the plants were young and green. The incidence of virus diseases in the tubers was not related to the maximum aphid populations on the plants. Most of the plants that became infected became so by aphids flying from diseased potato plants in the same field, and the late‐planted plots did not escape. Crops planted in mid‐April and harvested in early July produced the fewest virus‐infected tubers.Planting in April and lifting at the end of the season produced most ware‐sized tubers. In plots lifted after 12 weeks, May or June planting produced more ware than April planting. Few or no ware‐sized tubers were produced from July or August planting, and yields of seed‐sized tubers also were poor. Most seed‐sized tubers were produced by the late‐lifted May or June plantings. The date of lifting had little effect on the total number of tubers, but the date of planting affected it greatly. Most tubers were usually set by the May plantings and the number decreased with successive plantings.Early‐lifted immature tubers were easily damaged and were difficult to store. Blighted tubers occurred only in the July or August plantings, which also suffered most from slug and cutworm damage.Infection with leaf‐roll virus reduced yield by about three‐quarters, whether the seed had been lifted early or late the previous year. Healthy or virus‐infected mature seed produced a bigger crop the next year than immature seed obtained by early lifting or late planting.Late‐planted tubers produced more main stems than those planted at the normal time, but growth of axillary shoots was reduced and total leaf area remained small, even when the p

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1957.tb00407.x

出版商:Blackwell Publishing Ltd    

年代:1957

数据来源: WILEY

摘要:

In laboratory and field experiments from 1952 to 1955, 2:3:5:6‐tetrachloro‐I‐nitrobenzene (tecnazene) delayed the development of sprouts on treated potato tubers, and 2:3:4:6‐TCNB retarded sprout development in two laboratory experiments. At the usual commercial rates of application the 2:3:4:5 isomer had no effect on sprout development and very little effect at higher rates. The crop from 2:3:5:6‐TCNB‐treated seed tubers usually contained a higher proportion of small tubers than that from untreated or 2:3:4:5‐TCNB‐treated seed. Marketable yield from 2:3:5:6‐TCNB‐treated seed was sometimes below that from untreated seed, but when this happened the yield from 2:3:4:5‐TCNB‐treated seed was higher.Both isomers produced good control of dry rot,Fusarium caeruleum(Lib.) Sacc., on five varieties of potatoes, but did not produce a commercial control on Doon Star. To achieve control, the isomers had to be present at the time of infection. There was some evidence that the development of disease symptoms was delayed in treated, infected tubers. Since 2:3:4:5‐tetrachloro‐1‐nitrobenzene has no sprout depressant action it merits further trial as a fungicida

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1957.tb00408.x

出版商:Blackwell Publishing Ltd    

年代:1957

数据来源: WILEY

摘要:

An isolate ofErwinia aroideaecaused much more rotting of potato tubers than did isolates ofPseudomonassp.,Flavobacteriumsp., andPseudomonas syringae; filtrates from cultures of each of the bacteria in potato extract had about the same macerating activity.Pseudomonassp. andP. syringae, but notErwinia aroideaeorFlavobacteriumsp., were agglutinated in three different types of potato extract at the normal pH of potato tubers.Measurements of growth by turbidity and total count methods were compared. In undisturbed potato sap,Erwinia aroideaehad grown much more after 12 hr. than hadFlavobacterimsp. andPseudomonas syringae. Erwinia aroideaealso grew more rapidly thanPseudomonassp., but in this case the difference was caused largely by a longer lag phase.The two species ofPseudomonasgrew far less rapidly in potato sap cultures shaken hourly than in undisturbed cultures.Erwinia aroideaegrew slightly more rapidly in disturbed culture. Measured by the total count method, growth ofFlavobacteriumsp. was better in undisturbed cultures, but the opposite result was obtained when growth was measured turbidimetrically.With a small inoculum, growth ofErwinia aroideaeand ofPseudomonassp. was delayed by as much as 3 days in potato sap sterilized by heat. This effect was not obtained with an inoculum twenty times bigger, with potato extract, or with sap sterilized by filtration.Potato sap reduced the macerating activity of preparations from each bacterium; oxidation of the sap had no further effect. Production of macerating enzymes byFlavobacteriumsp. andPseudomonas syringae, but not byErwinia aroideaeandPseudomonassp., was less in potato sap than in potato extract.Erwinia aroideaesecreted macerating enzymes into potato sap much more rapidly during the first 12 hr. of growth than didPseudomonassp.The activities of filtrates from cultures ofErwinia aroideaeandPseudomonassp. were higher at the pH of the culture at the time of sampling than at higher and lower values.The addition of CaCO3to media apparently increased the pH optimum for macerating activity ofErwinia aroideaeand, to a lesser extent,Pseudomonassp. preparations.There was little difference in the toxicity of preparations of similar macerating activity from cultures of the four organisms.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1957.tb00409.x

出版商:Blackwell Publishing Ltd    

年代:1957

数据来源: WILEY

摘要:

Potato tubers in the laboratory were rotted by an isolate ofErwinia aroideae, but isolates ofPseudomonassp. (probablyP. marginalis),Flavobacteriumsp., andPseudomonas syringaewere only weakly pathogenic. Differences in the amount of rotting of tubers of different varieties were not related to differences in the rates of browning of outer cells, of suberin development or of phellogen formation.Growth‐regulating substances which affected the rate at which healing occurred at the wound surface did not affect rotting when they were added to inocula ofErwinia aroideaeorPseudomonassp.Increasing the water content of tuber tissue by soaking had little effect on the rotting caused byErwinia aroideae, but greatly increased rotting by the other organisms. The rotting by each of the four organisms was increased further when the tissue was injected with water. Cell‐free filtrates from cultures of each of the four bacteria rotted soaked and injected tissue in much the same way as did the bacteria, but in normal tissue filtrates from cultures of the non‐pathogenic bacteria caused more rotting than didE. aroideaepreparations, although in maceration tests with disks cut from potato tubers they had about the same activity.The non‐pathogenic bacteria caused active rots when the outer surfaces of tubers were sealed with Vaseline; this treatment also increased rotting byE. aroideae. OnlyE. aroideaegrew to any extent anaerobically in liquid culture.E. aroideaeandPseudomonassp. rotted Vaseline‐sealed tubers more than unsealed tubers kept in a desiccator over alkaline pyrogallol.Rotting of tubers byErwinia aroideae, but not byPseudomonassp., was increased when the tubers were kept in a moisture‐saturated atmosphere.The two species ofPseudomonas, but not the other two bacteria, caused appreciable rotting at 5°C.Allowing surfaces of inoculation cavities to heal for 1–4 days before inoculation reduced the number and size of active rots caused byErwinia aroideae, but did not prevent attack. Delaying inoculation for 1 day did not affect rotting by cell‐free filtrates from cultures of this organism and ofPseudomonassp.The surface layers of tubers, peeled and exposed to the air for 2 days, did not contain readily extractable materials toxic toErwinia aroideaeorPseudomonassp.Pseudomonassp. could be made to attack the healed surface of sealed tubers, by keeping the surface moist for twelve hours after inoculation.The significance of these resu

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1957.tb00410.x

出版商:Blackwell Publishing Ltd    

年代:1957

数据来源: WILEY

摘要:

Absorption of nitrogen, phosphorus and potassium by S48 timothy plants ran parallel to dry‐weight increase, at an increasing rate until the autumn, almost completely ceasing in the winter, and increasing again in the spring.Flowering tillers accumulated nutrients until ear emergence, after which the content per tiller of all nutrients decreased until death of the tillers during the winter.Non‐flowering tillers continued to accumulate nutrients steadily throughout the whole period of the experiment.These observations are discussed in relation to the perennial habit of the pl

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1957.tb00411.x

出版商:Blackwell Publishing Ltd    

年代:1957

数据来源: WILEY

摘要:

Infection of seedling tomatoes withVerticillium albo‐atrumchecked growth but did not result immediately in leaf yellowing. Localized wilting occurred in some plants 2 weeks after the check to growth was evident. 8 weeks after inoculation, dry weights of leaf, stem and root were decreased by 72, 70, and 65% respectively.Of the growth attributes studied, leaf area was most reduced by infection and this was due to a failure of the leaves to expand rather than to a fall in the rate of leaf production. Neither water nor nitrogen appeared to be limiting factors in this respect. The water content of infected leaves was not reduced until 6 weeks after inoculation, when leaf yellowing and necrosis had also appeared. The percentage N contents of stem, root and leaf of infected plants exceeded those of the healthy controls 24 days after inoculation. N uptake was not seriously impaired until 21 days later.The photosynthetic efficiency of the green leaves of infected plants was reduced. The mean values for net assimilation rates were: Healthy 0.47 and infected 0.39 g./dm.2/week.Plants, in which two‐thirds of the root system had been killed by crushing, were placed in contact with mycelium in soil. This initial root injury did not significantly affect the growth of infected plants.The data accord with a toxin theory of damage to infected plants, but the slow development of chlorosis and wilting symptoms in the young plants suggested a greater tolerance to the toxin than is found in older pla

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1957.tb00412.x

出版商:Blackwell Publishing Ltd    

年代:1957

数据来源: WILEY

摘要:

Experiments, in which alate aphids were marked immediately after eclosion from the last nymphal instar and observed until they took flight, gave information which, together with the measured rate of moulting and a continuous record of temperature, has been used to construct theoretical daily curves for numbers flying from a bean crop. These curves have been matched against the observed curves for the same days.The differences between curves so constructed for a period of 17 days and the observed curves for the same period are of the same order and kind as the differences between two measured curves in different sites at the same time.The different types of daily flight curve can thus be accounted for in terms of the rate of production of alatae by moulting, the effect of temperature on the teneral (‘drying out’) period and the effect of low light intensity and temperature on take‐off beha

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1957.tb00413.x

出版商:Blackwell Publishing Ltd    

年代:1957

数据来源: WILEY