摘要:

SUMMARYMycoplasma‐like bodies were found by electron microscopy of sections of sieve tubes, both from shoots and roots of potato(Solanum tuberosum)plants affected by Scottish witches' broom disease and from graft‐inoculated tomato shoots. The bodies were bounded by a unit membrane, contained ribosome‐like material and mostly measured 200–800 nm in diameter. Most were oval in cross‐section but some had lobes or slender protrusions. Some of the bodies were found in the mouths of si

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb02831.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYIn the glasshouse, adult, apterousMyzus persicae(Sulz.) andAphis fabaeScop, settled better and deposited more larvae on sucrose‐sprayed sugar‐beet plants than on water‐sprayed plants.M. persicaesettled badly and deposited few larvae on plants that were kept in the dark before or after infestation. The effects of darkness on aphids were reduced by spraying the host plants with 10% solutions of sucrose before infestation.ViruliferousM. persicaetransmitted beet yellows virus (BYV) and beet mild yellowing virus (BMYV) less efficiently to dark‐treated plants than to those grown in normal daylight. Spraying sugar beet with sucrose before inoculation with viruliferousM. persicaeincreased the proportion of successful BYV transmissions but only when the plants were dark‐treated. The effects of sucrose and darkness on settling and larviposition of aphids and on virus transmission may be related to changes in the concentration of carbohydrates, particularly sugars, in t

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb02832.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYNew records are presented of bacterial diseases affecting the following weed plants:Heliotropium sudanicum, Rhynchosia memnonia, Vigna radiata, V. pubigera, Euphorbia acalyphoidesandPhyllanthus niruri.Bacterial leaf blight of pigeon pea(Cajanus cajan)caused byXanthomonas phaseolif.cajaniis reported for the first time from the Sudan. The causal bacteria, all of which belong to the genusXanthomonas, are compared with related pathogens. The differences between these bacteria are considered of little diagnostic value. Pathogenically, they can be separated into three groups: (i) theHeliotropiumpathogen; (ii) the bacteria affecting leguminous plants; and (iii) the bacteria affecting species of the family Euphorbiaceae. Because of the diversity in opinion on speciation in the genusXanthomonas, two alternative proposals are put forward. In the first,Xanthomonasis considered a monotypic genus withX. campestrisas the sole species. The pathogens reported in this work from previously unrecorded hosts, which proved to differ in pathogenicity from established ones, are considered to be newformae speciales.These areX. campestrisf.sp.heliotropiifromH. sudanicum, X. campestrisf.sp.rhynchosiaefromR. memnonia, X. campestrisf.sp.vigna‐radiataefromV. radiata, X. campestrisf.sp.euphorbiaefromE. acalyphoidesandX. campestrisf.sp.phyllanthiifromP. niruri.The organism fromV. pubigerais accordingly identified asX. campestrisf.sp.vignicola.Other bacteria used for comparison are also reduced to ff.sp. ofX. campestris.The other proposal is to lump together pathogens with overlapping host ranges in a single species that comprises a number of ff.sp. differing in pathogenicity. Thus the bacteria from leguminous plants are all considered to belong toX. phaseolias previously suggested by Sabet. New ff.sp. are created for the pathogens fromR. memnonia (X. phaseolif.sp.rhynchosiae), andV. radiata (X. phaseolif.sp.vigna‐radiatae). The organism fromV. pubigerais identified in this case asX. phaseolif.sp.vignicola.The bacteria from members of the Euphorbiaceae are considered to belong toX. ricinion priority grounds.X. cassavaeandX. poinsettiaecolawhich have been used for comparison are reduced to the ff.sp.X. ricinif.sp.cassavaeandf.sp. poinsettiaecolarespectively. Two new ff.sp. are created: forE. acalyphoidespathogen,X. ricinif.sp.euphorbiaeand forP. niruripathogen,X. ricinif.sp.phyllanthii.The creation of a new species (X. heliotropiisp.nov.) is proposed for theHeliotropiumpathogen.The present study shows that many weed plants may be affected with new bacterial strains that can also infect cultivated cr

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb02833.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYThe suggestion that organic amendment of soil controls scab by reducing insoluble soil manganese to soluble forms toxic toStreptomyces scabieswas investigated in pot and field experiments by assessing numbers of manganese‐reducing micro‐organisms in soil.Dried grass meal (2 tons/acre) gave significant control of scab but increases in soluble manganese were insufficient to account for this control. Populations of micro‐organisms in soil increased after adding grass meal but decreased again by the time tubers were initiated and scab infection began. The results suggest that manganese reduction could affect scab if soil contained easily reducible manganese, because dried grass meal increased the numbers of manganese‐reducing micro‐

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb02834.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARY‘Early‐dying’ disease was examined in potato plants (King Edward) with varying numbers of main stems and lateral stems. Infection withVerticilliumaffected neither the number of main stems produced nor the stem number/ lateral number/yield inter‐relationships, but did slightly reduce lateral development. The host growth pattern, however, markedly influenced the severity of disease: infected plants with a single main stem or a few, compared with those having many main stems, showed delayed symptom expression and also produced many laterals which further reduced disease severity and increased longevity. Thus yield reductions as a result of infection are likely to be smaller in single‐stemmed plants showing considerable lateral development than in those plants with many main stems and few or no

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb02835.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYThree strains ofVerticillium albo‐atrumcausing severe wilt of tomato (T), progressive (Hp) and fluctuating (HF) wilt of hop, were inoculated through the roots of four tomato cultivars at different inoculum concentrations. Symptoms were assessed visually 42 days after inoculation, and quantitatively on the change in total leaf area compared with controls. Distribution of mycelium and tyloses was determined by sections at 2 cm intervals of root, stem and petiole.Cultivars Loran Blood and Moscow showed resistance to disease expression at all levels of inoculum concentration with the T strain. Bonny Best and Potentate were both susceptible to this strain, but whereas in Potentate, disease severity increased from mild to severe with increase in inoculum concentration, Bonny Best was severely diseased at the lowest level of inoculum. All cultivars showed some susceptibility to the HP and HF strains; the ‘resistance’ of Loran Blood and Moscow was no longer apparent and Bonny Best was most severely affected. The relative susceptibilities to the strains wereHF Bonney Best>Loran Blood>Potentate>Moscow,HP Bonny Best>Loran Blood, Moscow>Potentate,T Bonny Best>Potentate>Loran Blood, Moscow.In general, vascular colonization was less in the cultivars Loran Blood and Moscow with all three fungal strains at io5propagules/ml level of inoculum, but this was not always correlated with an increase in disease severity. With the exception of the host‐pathogen combinations Bonny Best/T, Bonny Best/HF, Potentate/T and Moscow/T, increasing the inoculum concentration to 107propagules/ml increased disease severity but had little or no effect of increasing vascular colonization. In Bonny Best/T, Bonny Best/HF and Potentate/T vascular colonization was reduced with the higher level of inoculum. Moscow showed complete resistance to symptom expression and little vascular colonization with the T strain at 105prop./ml. At 107prop./ml resistance was maintained but there was very extensive growth of mycelium in the vessels.Tylosis resulted from an interaction of host, fungal strain and the level of inoculum and was not always correlated with the degree of vascular colonization. Contrary to previous reports the resistant varieties Loran Blood and Moscow developed acute disease symptoms after inoculation with HP and HF and these were associated with a high level of tylosis rather than mycelial growth. Tylosis and disease severity but not mycelial growth increased with higher levels of inoculum.The results suggested that susceptibility toVerticilliumwilt was a complex response depending on host cultivar, fungal strain and the initial inoculum concentration. In some cultivar‐pathogen combinations susceptibility was directly proportional to the amount of mycelium present in the vessels, while in others a physiological resistance mechanism independent of the degree of colonization appeared to operate. In a third category, increased disease development rather than resistance was associated with high levels o

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb02836.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYEffects ofSphaerotheca fuligineawere deduced from experiments in which cucumber foliage, exposed to naturally occurring inocula, was fungicidally sprayed. Yields increased as the incidence of mildew decreased but the relation was sometimes affected by differing amounts of phytotoxicity.The fungitoxicity and phytotoxicity of a range of chemicals applied as high‐volume sprays, fumigants or soil drenches, were tested. Non‐phytotoxic concentrations of some fungicides adequately protected cucumber foliage from subsequent attack but were often insufficient to eradicate established infections, the increased amounts needed for this being phytotoxic. Powdery mildew was controlled more effectively when drazoxolon and quinomethionate were applied as sprays with 0·1 and 0·02% a.i. respectively, than when used as fumigants at 2–4 and 1·3 g/28·3 m3(= 1000 ft3).Sprays of drazoxolon (0·1% a.i.) increased yields from 7·0 to 11·2 kg/ plant during 8 weeks picking and in another experiment weights of fruit were increased by applying quinomethionate (0·02% a.i.) from 10·8 to 52·2 kg/plot of four plants. In the former experiment appreciable amounts of phytotoxicity and infection were tolerated before yields decreased but, in the latter, yields were inversely proportional to numbers of dead leaves which were directly related to the incidence of mildew. Spraying with quinomethionate, or drazoxolon plus tetradifon (0·012% a.i.) increased numbers of female flowers from 59·5 in the mildewed controls to 93·0 and 142·8 per plant respectively, and of these 17·6, 32·8 and 16·2 % subsequently produced marketable cucumbers.In addition to decreasing yields, severeS. fuligineainfestations were associated with increased numbers of misshapen cucumbers.Increasing sulphur concentrations from 0·5 to 1·0g/28·3m3during nightly fumigations significantly decreased mildew incidence and increased(a)yields from 35·8 to 52·9 kg during 5 weeks picking, and(b)the proportion of high‐quality cucumbers from 49 to 63 %. Similar trends occurred in another trial where sulphur concentrations were increased from 0·75 to 1·0 g/28·3 m3, but comparisons with fortnightly sprays of 0·1% drazoxolon suggest that these sulphur

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb02837.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYThe onion white rot pathogenSclerotium cepivorumwas cultured on agar media containing 2% malt extract and one of the antifungal antibiotics, endomycin, griseofulvin, venturicidin and cycloheximide at concentrations that reduced but did not prevent growth of mycelium. When onion seeds or agar discs impregnated with diffusates from onion bulbs were placed on the antibiotic media, radial growth of the fungus was greatly increased, and there was a profuse development of aerial mycelium. Gaseous diffusates from onion tissue and from impregnated agar discs were also effective. On the antibiotic media, tomato, cabbage and radish seeds did not stimulate the growth ofS. cepivorumand the onion exudates did not stimulate the growth of four other fungi. This and other evidence is considered to show that the stimulation of growth ofS. cepivorumwas not caused by any direct effect on the antibiotics but by a tolerance of the fungus to them, which was specifically induced by an exudate from its host plant. The phenomenon may be related to the reported reversal by onion extracts of the inhibitory effects of soil mycostasis on germination of sclerotia of the fungus.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb02838.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYIsolates fromC. purpureasclerotia occurring naturally onPhragmites communisusually sporulated vigorously on the culture medium employed, and their failure to produce alkaloidin vitrowas associated with a thin white growth form. Such isolates also failed to produce sclerotia on the host plants tested. A variant having a plectenchymatic morphologyin vitroand producing a thick pigmented non‐sporulating growth form yielded alkaloid (up to approximately 300μg/ml mainly δ8–9 and δ9–10 lysergic acids and chanoclavine) in surface or submerged culture and developed typical ergot sclerotia (containing 0·2‐0·4% alkaloid, mainly ergotoxine and ergotamine)in vivo.Improved alkaloid yieldin vitrowas obtained from a strain reselected after passing through a parasitic phase.Aetiological aspects of theP. communisergot a

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb02839.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY

摘要:

SUMMARYSouth American leaf blight caused byDothidella uleioccurs only in tropical America, on both indigenous and cultivatedHeveaspp. The conidium (Fusicladium macrosporum) is a 1‐septate, dry, air‐borne spore about 40 × 7 μ, occurring on the abaxial surface of dry leaves in dense, powdery, olive‐green masses, and with one or both cells collapsed. The conidia adhere to the surface of water droplets, becoming turgid, and are disseminated in splash droplets.A Hirst volumetric trap, placed within a prepared source in north‐west Trinidad, showed a diurnal periodicity of conidial production, with a maximum at 10.00 h and minima at night or in the early morning. On rainless days there was also a minor peak at 20.00 h. Transient increases occurred after rain, most of which fell around noon. On wet days almost equal numbers of conidia were dispersed between 10.00 and 12.00 h. Large increases occurred in 87% of all rain showers between 09.00 and 13.00 h. After 13.00 h fewer rain showers caused such increases; the lowest (36%) was between 21.00 and 01.00 h. Twice as many were trapped on sunny days (>9 h sun) at 09.00 h when there was full sunshine, compared with overcast days (<5 h sun). A more clearly defined morning maximum occurred on relatively windy days, compared with calmer ones.Conidial sporulation became very low, or ceased, where rain fell below a mean of 3–4 mm per day for at least 20 days. Abundant sporulation occurred with a daily rainfall about twice this amount. The results support the belief that ifDothidella uleiappeared in Malaysia its spread would be rapid and its effec

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1969.tb02840.x

出版商:Blackwell Publishing Ltd    

年代:1969

数据来源: WILEY