摘要:

SUMMARYAn isolate ofVerticillium albo‐atrum, highly pathogenic to tomato plants, secreted polygalacturonase (PG) on a variety of synthetic media. Particularly active filtrates were obtained from cultures on media containing mineral salts, casamino acids and pectin or polypectate. Pectates were degraded more rapidly than pectin. None of the filtrates had high cellulase or pectinesterase activity; the most active were from cultures with carboxymethyl cellulose or pectin as carbon sources.The fungus made little growth in exudates from xylem sap unless carbon sources were added, and then culture filtrates had appreciable PG and cellulase activity but very little pectinesterase activity. Saps from susceptible and resistant varieties gave similar results.The fungus was also grown on a synthetic sap based upon an analysis of xylem exudate. Results similar to those for xylem sap were obtained.Filtrates from cultures on dead stems of both varieties had little pectinesterase activity and a definite but relatively low PG and cellulase activity.Extracts from diseased plants had no PG or cellulase activity but had a considerably higher pectinesterase activity on fresh and dry weight bases. Exudates from xylem of diseased plants had no PG or cellulase activity but had a low pectinesterase activity which was slightly higher than that from healthy plants.The effects of different culture filtrates on cuttings is described. Filtrates with high PG activity produced some of the symptoms found in naturally diseased plants.Solutions of pectin, polypectate and carboxymethyl cellulose caused cuttings to wilt in very low concentrations; much higher concentrations were needed after solutions of these substances had been degraded by PG or cellulas

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1961.tb03597.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

SUMMARYThe resistance to potato blight (Phytophthora infestans(Mont.) de Bary) of the haulms of four potato varieties, Up to Date (UD), King Edward (KE), Majestic (MJ) and Arran Viking (AV) was assessed in the field from 1956 to 1959. Although these varieties are reputed to differ appreciably in resistance, the differences measured were smaller than expected and significant in only two seasons. They were shown better by measurements on individual leaves than by assessing effects on whole plots. The greater resistance of AV and MJ, compared with UD and KE, was correlated with a slower increase of blight at the start of an attack rather than with differences in the rate of haulm destruction when the attack was well advanced. However, there was some evidence that leaves of KE died most rapidly and leaves of AV most slowly after infection.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1961.tb03598.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

SUMMARYIn liquid culturesCercosporella herpotrichoidesutilized both organic and inorganic sources of nitrogen and showed an absolute requirement for thiamin. On nutrient agar and through sterilized straw,C. herpotrichoidesgrew more slowly than other facultative fungal parasites of cereal roots and stem‐bases.The competitive saprophytic ability ofC. herpotrichoideswas found to be very limited. The observation that saprophytic colonization of straw tissue byOphiobolus graminisdeclined as invasion progressed inwards was confirmed and found to occur also withC. herpotrichoidesandHelminthosporium sativumbut not withFusarium culmorum.It is concluded thatC. herpotrichoidesexhibits a low competitive saprophytic ability and is therefore unlikely to colonize straw in the soi

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1961.tb03599.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

SUMMARYThe saprophytic survival ofCercosporella herpotrichoidesin naturally infected and artificially infested wheat straw has been investigated. Test pieces of straw containing the fungus were buried both in unsterilized soil in laboratory containers and in the field. Survival of the fungus was assessed by its ability to produce viable and infective spores on the surface of the recovered pieces of straw when incubated in a moist chamber. It was found thatC. herpotrichoidessurvived, virtually undiminished in vitality, in straw buried for 3 years, the maximum period tested. Straw colonized byC. herpotrichoideswas observed to decompose more slowly in the soil than did uninoculated straw; this suggests a mechanism wherebyC. herpotrichoidesmay be enabled to survive for such long periods in the presence of competitors.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1961.tb03600.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

SUMMARYObservations and experiments were made on silvering disease of red beet during the period 1952–59. The disease is most prevalent on seed crops of the variety Cheltenham Green Top, but also affects other cultivars ofBeta vulgaris, often only mildly. The causal organism isCorynebacterium betaesp.nov. which can be found in the tap‐roots, stems and leaves of systemically affected plants causing veinal or uniform silvering of the leaves followed by wilting and death of the plant. External leaf infection gives rise to silvered lesions on the laminae or leaf margins.About 1% of the seeds from infected plants contain the pathogen and these seeds give rise to plants showing systemic symptoms. The bacteria spread from such plants in the seedling bed during the autumn and winter, probably entering other plants through their leaf edges. Such spread can occur to distances of at least 50 yards, and the planted out seed crop may be up to 75% infected. The disease is readily transmitted on knives which have cut infected roots.Seed treatment with streptomycin or erythromycin (200–400 g/ml.) gives almost complete control of the disease. Mercurial dusts are less effective but have been found of some value in pra

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1961.tb03601.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

SUMMARYThe chrysanthemum eelworm moved in sand and in a clay soil at much the same rate as other eelworm species so far studied. Leaf washing and soil examination in infested chrysanthemum plots showed that the eelworm never spread laterally through the soil or from leaf to leaf more than to the second row of plants from the source of infestation, a maximum distance of about 30 in. At Rothamsted and in the National Chrysanthemum Society's variety trial the number of infested varieties increased greatly in September, during periods of heavy mists. Experiments with isolated leaves, artificially infested and kept under either dry or humid conditions suggested that eelworms were more active in humid conditions. They invaded isolated leaves within 15–30 min. In pot experiments, eelworms added to soil invaded chrysanthemum plants inducing symptoms in 18 days: 26 days after such inoculations no eelworms could be detected in the soil. Few eelworms persisted in fallow soil in pots after 32 days. No eelworms were found after the end of November in soil taken from an infested field plot at intervals between August 1959 to January 1960. Attempts to infest plants with eelworms from stored soil taken from highly infested plots failed. Examination of stools during the winter showed that many eelworms were present in the green tissues. It is concluded that infestation from eelworms which persist over the winter in soil is slight and that the main source of the pest is the chrysanthemum stoo

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1961.tb03602.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

摘要:

SUMMARYIn stained sections of eelworm‐infested chrysanthemum leaves the earliest effect of the attack is the appearance of a brown substance inside the leaf cells; this browning extends and ultimately reaches the leaf epidermis. The number of chloroplasts dwindles, the cell walls break down and large spaces appear in the leaf. Finally the leaf shrinks, the epidermis disintegrates and the brown substance is found on all the cell walls. The collenchyma around the main veins, where it reaches the upper and lower epidermis, does not break down until the final stage of attack.Cuttings of thirteen chrysanthemum varieties, each artificially infested with about 110 eelworms, showed leaf blotches, stunting, blindness, browning of the stem and leaf petiole, leaf distortion, leaf scars or feeding areas and puffy, blistered and puckered leaves. Infested cuttings with severe symptoms may produce side‐shoots or breaks which seem healthy but become badly infested later in the season when the plants are wetted by rain or prolonged mists. The eelworms often failed to penetrate further than the substomatal space in the youngest leaves. All the symptoms listed above, except leaf blotches, probably result from ectoparasitic feeding by the eelw

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1961.tb03603.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1961.tb03604.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1961.tb03606.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1961.tb03607.x

出版商:Blackwell Publishing Ltd    

年代:1961

数据来源: WILEY