摘要:

In water culture experiments, tobacco plants of Hicks variety were supplied with factorial combinations of high and low concentrations of nitrogen, phosphorus and potassium. Incidence of powdery mildew and growth and chemical composition of infected and healthy plants were compared.There was more disease when all elements were supplied at the higher of two concentrations, but the increase in infection was less than the increase in growth. Plants grown in media containing a low ratio of potassium to nitrogen produced the least susceptible leaves; their disease indices were up to 30 times less than those of plants that received the full nutrient treatment. Potassium‐deficient leaves had thinner cell walls, larger water content, smaller sugar and potassium contents, and greater amino nitrogen and magnesium contents, compared with those of plants grown in any of the other media. The possible relation between these characteristics and susceptibility toErysiphe cichoracearumDC. are discusse

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01194.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYIn 1961 an epidemic attack byAlternaria porrioccurred on irrigated onions at Baringo in the Rift Valley, Kenya. Two distinct lesion types appeared: (1) typical purple or brown blotches; (2) white, irregular spots or flecks. These were present in varying proportion, depending on the duration of conditions favourable to infection, and subsequent relative humidity. High R.H. favoured the development of purple blotches; low R.H. for prolonged periods after infection usually resulted in white flecking only. These flecks were often sterile, making diagnosis difficult.Germination, appressorial and lesion formation displayed a broad optimum temperature (21–30° C). Resistance to the disease shown by a number of American hybrid onions was governed by cuticle thickness; this resistance was reduced by wounding—such as is associated with sand‐storm blast—or by incubation after infection for prolonged periods at high R.H.Two fungicides, mancozeb and dicloran, effectively controlled the disease in t

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01195.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYStudies of the relationship between the viability ofSeptoriaon celery seed and the ability of the seed to give rise to infected plants have enabled the effectiveness of various fungicides against celery blight to be readily assessed by tests of treated seed. Seed of differing degrees of infectivity was obtained by storage over a period of 14 months or by various seed disinfection treatments.The germination of spores derived from infected seeds was determined by streaking them on agar and the viability of the ‘total’ fungus (spores and mycelium within the seed) was assessed by inserting seeds into slits in celery petioles. The ability of the seed to give rise to infected seedlings was determined by sowing the seed on compost in seed boxes and retaining glass covers on the boxes for 14 days after seedling emergence.Using the three tests concurrently on stored seed it was shown that the decline in the viability of the ‘total’ fungus was similar to that of the spores and was reflected in the decline in seedling infection. It was thus concluded that tests of the viability of spores from infected seed would indicate the ability of such seed to give rise to infected seedlings and that spore germination tests could be used for assessments of the effectiveness of seed treatments.By this means it was shown that soaking diseased seeds in 0·2% thiram suspension for 24 hr. at 30° C. eliminated

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01196.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYStorage of Cox's Orange Pippin apples in 5% CO2+ 3% O2or 0% CO2+ 3% O2at 3·3° C. reduced rotting byGloeosporiumspp., as compared with storage in air. 5% CO2+ 16% O2was less effective and reduced rotting on fewer occasions. In some years no reduction of rotting was obtained by storage in these gas mixtures. Retardation of rotting was sometimes achieved during the early part of the storage period by treatments which did not control rotting over the whole period. Production of pectolytic enzymes was reduced by incubation in these atmospheric conditions; the effect onG. albumwas greater than onG. perennan

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01197.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYField assessments of copper fungicides used to control coffee leaf rust have indicated an effective life of a few weeks, whereas residues can be determined chemically on the leaves for several months. The studies reported in this paper were designed to study this discrepancy.The amounts of copper which were dissolved by three aqueous solvents from deposits of a cuprous oxide formulation, a copper oxychloride and Bordeaux mixture were determined at various intervals after spraying; as also were the amounts of copper physically removed.The levels of rust infection in the field following single spray applications, which had undergone various periods of natural weathering before the infection period, were recorded.No evidence of chemical deterioration was derived from the aqueous solvent studies but the data on physical weathering indicated that the initial loss of deposit was rapid and suggested that natural weathering could result in the fungicide deposit becoming insufficient to give disease control. Some evidence on the form of the loss of copper from the different fungicide deposits was obtained.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01198.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYWhen conidial spores ofVenturia inaequalis(Cooke) Wint. were germinated on glass, in distilled water only, very little variation was found, but addition of copper sulphate produced a marked variation, particularly between slides.An examination of the standard cleaning technique showed its inadequacy to produce a chemically clean surface, but the introduction of a cleaning method based on permanganic acid led to a very marked decrease of the total variation.When copper sulphate was applied as a deposit, with various wetting agents, to slides cleaned by this method, there was no appreciable reduction in the variation. When the wetting agent was applied with the spore suspension, however, a marked reduction was obtained, but the total variation was further reduced to an acceptable level only when the toxicant was applied in the nutrient solution in which the spores were suspended.A modification of a commercial inverted microscope, to facilitate counting, is described.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01199.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYThe germination of conidia ofErysiphe betae, E. graminis, E. horridula, E. martii, Oidium begoniae, anOidiumsp. fromCrepis taraxacifoliaandUncinula necatorwas studied on dry uncoated glass slides and on dry slides with the following coatings: cellulose acetate (C.A.); the polyvinyl acetate derivative Gelva 7; nitrocellulose (collodion); and ethyl cellulose. Slides dusted with conidia were incubated at 21±1° C. in a saturated atmosphere in the dark. Germination over 85% and as high as 96±4% was obtained on slides coated with C.A. or Gelva 7. The germination on slides coated with collodion was lower and abnormal, the germ‐tubes growing away from the substrate.The possibility of studying the toxicity of chemicals towards conidia of powdery mildew fungi by incorporating them into a C.A. layer used as a coating for glass slides was examined. ‘Dinocap’, a captan analogue and members of a homologous series ofn‐alkyl fatty acids were used, with conidia ofE. betae, E. horridula, E. martiiandO. begoniaeas test organisms. The results obtained demonstrated the potentialities of

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01200.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYConidial germination in sixteen nematode‐trapping Hyphomycete species in amended and unamended soil was studied. On the basis of the pattern of germination the fungi could be divided into two ecological groups: a sensitive group where conidia or germlings quickly gave rise to trapping organs and an insensitive group in which little trap formation occurred. The significance of this in relation to biological control of plant‐parasitic nematodes is discus

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01201.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYThe relationship between the time and temperature necessary for killingDitylenchus dipsaciin hot water suggests that the cause of death at 48° is different from that below 46° C. The ability of nematodes, which survived one hot‐water treatment, to recover their resistance so as to survive a second hot‐water treatment and yet to show a susceptibility to storage temperatures which are not lethal to untreated nematodes, supports the view that there are at least two causes of death after heat treatment.Acclimatization increases the heat resistance of the nematodes and would cause failure of hot‐water treatment as a control measure against bulb eelworm. Storage at temperatures of 25–30° C. after hot‐water treatment increases the proportion of dead nematodes and, if applied to bulbs, might improve control. The effects of such temperatures before and after hot‐water treatment are not due to heat shock following the sudden rise or drop

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01202.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY

摘要:

SUMMARYA field cropped with potatoes in the 1st and 6th years and with non‐host crops in the 2nd to the 5th years was divided into plots for D‐D injection, each at 400 lb./acre. Before the final potato crop, untreated plots showed a 50% mean annual decline of the population of potato‐root eelworm. Single injections in different years left populations not materially different. With repeated injections there was a progressive decrease in the proportion of nematodes killed. However, injections for 4 or 5 consecutive years decreased the populations by spring of the 6th year enough to affect them after the final host crop was grown. Under this crop, all populations increased to about the same e

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1964.tb01203.x

出版商:Blackwell Publishing Ltd    

年代:1964

数据来源: WILEY