摘要:

In sucrose‐nitrate liquid mediaBotrytis cinereawas able to grow from spores when the media contained captan at concentrations up to three‐quarters of the saturation value. Because of this, and the low water solubility of the fungicide (<1 p.p.m.) all attempts to produce resistant strains were made with agar media.Spores did not germinate when applied as a suspension in water to the surface of a sucrose‐nitrate agar containing 500 p.p.m. captan; about 1% germinated when the concentration was 250 p.p.m. Similar results were obtained when an agar extracted with water and pyridine was used. There was some growth from spores on agar containing 250 p.p.m. captan; this always started at the edge of the agar.Resistant strains were produced when disks were transferred from cultures growing on agar containing low concentrations of captan to agar containing higher concentrations. By repeating this process over a period of months a strain was produced eventually which grew slowly but continuously, and sporulated on agar containing 250,000 p.p.m. captan. However, the very low solubility of the fungicide made it difficult to assess quantitatively the degree of adaptation. Although agar disk inocula from resistant strains retained their resistance on transfer to captan agar, inocula consisting of suspensions of spores only, or of hyphae and spores, were no more resistant than the parent strain. The resistant strain retained the first type of resistance after it had been grown on fungicide‐free media for four periods of 2 weeks.Spores from the resistant strain were more resistant than spores from the parent strain in germination tests with drops on glass slides; a concentration of 0·6 p.p.m. captan prevented germination of parent spores, but one or two spores out of a total of some 4000 spores of the resistant strain germinated at concentrations of 100 p.p.m. This type of resistance, transmissible by spores, was reduced when the resistant strain was grown on fungicide‐free agar.Spores from resistant strains had a very low viability, although they were produced normally and were normal in size and appearance; when obtained directly from a culture on a captan medium only 2% germinated whereas in similar conditions there was 100% germination of parent spores. Viability was increased to 13% after one transfer on a fungicide‐free medium but was no more than 52% after four transfers.Preliminary attempts to obtain strains ofVenturia inaequalisresistant to captan were unsuccessful.The significance of the results obtained

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb02518.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

The concentrations of thiram preventing germination of spores ofBotrytis cinereain drops of a 1% solution of sucrose, and on the surface of a sucrose‐nitrate agar have been determined. Thiram had much less effect on germination in the agar medium, even when a purified agar was used. There was no growth on sucrose‐nitrate agar if the concentration of thiram exceeded 31 p.p.m. Attempts to obtain strains able to grow at higher concentrations were unsuccessful.Similar results were obtained with ziram, nabam and zineb.Ferbam also was more effective in preventing spore germination in spore drops than on agar media; this effect was obtained with ordinary and with purified agar.On a sucrose‐nitrate agar generally there was no growth if the concentration of ferbam exceeded 125 p.p.m., but in one of forty‐eight plates containing 250 p.p.m. ferbam, five slowly growing colonies were produced, and from these colonies arose mycelium which grew and sporulated rapidly on 500 p.p.m. ferbam agar. Agar disk inocula were transferred from these cultures to agar containing higher concentrations of ferbam and in this way, and by repeating the process, a strain was obtained which grew slowly but continuously, and sporulated on agar containing 5000 p.p.m. ferbam. However, the poor solubility of this fungicide made it difficult to assess quantitatively the degree of adaptation.A proportion of the spores from this strain germinated in drops containing about twice the concentration of ferbam which prevented germination of parent spores.The resistance of the mycelium of the resistant strain was not lost after repeated subculture on fungicide‐free agar. The resistant strain was as susceptible as the parent strain to thiram, ziram, nabam and zineb.Attempts to obtain strains ofVenturia inaequalisresistant to thiram, ferbam, ziram and zineb were uns

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb02519.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

The fungal populations of soil and of the rhizosphere of tomatoes in steamed, fallowed and unsteamed plots were compared. Steaming greatly reduced the numbers of fungi in the soil, but fallowing had little effect. Soil bacteria were greatly reduced by steaming but increased to the level in the unsteamed plots after heavy watering. Outer rhizosphere fungal populations in unsteamed plots in July were larger than in the steamed plots, but by October this difference had disappeared, although roots in the unsteamed soil showed the greater development of disease.Root surface counts indicated that the populations on actively growing roots in July in steamed and unsteamed plots reached similar levels, and there was a slight fall in numbers in both types of plot in October. Fungal infection of roots increased noticeably in unsteamed plots between July and October, although root surface numbers showed a decrease.Of the fungal species isolatedColletotrichum atramentariumshowed a distribution between soil and root surface which suggested that it was a root inhabiting fungus.Cephalosporiumspp. were also found on the root surface and in roots, especially those from steamed soil.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb02520.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

In southern New South Wales the resumption of ley land for wheat growing has been accompanied by an increase in take‐all (Ophiobolus graminis) and Fusarium root rot (Fusarium culmorum). No such increase has been observed in foot and root rots of wheat caused byHelminthosporium sativum and Curvularia ramosa.It is shown experimentally that these differences are related to the relative capacity of the causal fungi to persist in wheat straw buried in each of two unsterilized soils which, because of past cultural treatments, differed in their organic carbon and total nitrogen content. While the saprophytic survival ofO. graminisandF. culmorumwas promoted by high soil fertility that ofH. sativumwas markedly depressed. The survival ofC. ramosawas little affected by soil fertility.F. culmorum, H. sativumandC. ramosaeach remained viable under the soil conditions best suited to their survival in one‐third to one‐half of the test straws for 2 years butO. graminiswas not recovered after the 52nd week of sam

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb02521.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

An account is given of experiments designed to study the effect of inorganic manures, both singly and in combination, soil moisture and available inoculum on the development of root disease in glasshouse soils.Growth ofRhizoctonia solaniKuhn in sterilized soil was increased by applications of balanced fertilizer, by moderate doses of potassium and by the highest rate of phosphates applied. It was decreased by the higher applications of nitrogen and the highest rate of potassium. In unsterilized soil growth was poor in all treatments.Fresh weights of lettuce seedlings were increased by moderate applications of balanced fertilizer but decreased by the higher levels of this and of the individual ingredients. Most disease was found in the balanced (basic) and nitrogen series: potassium and phosphatic amendments had comparatively little effect.Mycelium ofR. solanigrew best, and produced most disease, in the relatively drier soils. It was found to need a minimum supply of nutriment (food base) to establish itself in soil but high concentrations of inoculum reduced pathogenicity. Its survival in artificially inoculated soils was shown to be little affected by soil fertility.A description is given of a method to demonstrate the persistence and rate of spread of a parasite under relatively natural conditions.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb02522.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

The bacterial disease of castor in the Sudan has been reinvestigated. Typically the disease symptoms are brown or black, round or angular lesions on leaves; occasionally the thin succulent branches are attacked, but not the vascular tissue.The bacterium responsible for the disease was previously thought to bePseudomonas solanacearumE.F.Sm. but comparative studies show that the Sudan species differs in pathogenicity and physiology fromP. solanacearum.It closely resemblesXanthomonas ricinicola(Elliott) Dowson (=Bacterium riciniYoshi and Takimoto) in characters, host range and pathogenic effects. In culture on solid media the growth ofX. ricinicolais typically yellow, while that of the Sudan species is dirty white; but this difference is not considered sufficient to justify the establishment of a new species.The author proposes the specific namericinioriginally adopted by Archibald (1927) and Yoshi&Takimoto (1928), for the species ofXanthomonascausing the leaf blight disease of castor, and considers that the causal organism in the Sudan is an atypical strain of this species.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb02523.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

The water loss per unit leaf area of tomato plants was decreased after inoculation withVerticillium albo‐atrum.When diseased plants began to wilt water loss temporarily increased, but then rapidly decreased to become less than that of healthy plants grown under conditions of adequate or restricted water supply.The transpiration of excised leaves from plants grown with a restricted water supply was reduced, but not so severely as that of comparable leaves from infected plants. Water loss from leaves on infected plants was reduced irrespective of any blocking of the petiolar xylem.The rate of water loss from turgid leaf disks on mannitol solutions, and the rate of water uptake of leaf disks on water was similar for disks cut from wilting or turgid leaves of diseased plants or healthy plants grown with an adequate or restricted water supply.Disease or poor water supply reduced leaf growth but had no effect on the rate of leaf initiation. Although the density of stomata was higher on leaves of diseased plants the stomatal area was less than on healthy plants.The resistance to water flow in diseased stems was high and was correlated with vessel blockage. About half the blocked vessels contained hyphae. The severity and localization of symptoms in inoculated plants growing on susceptible or resistant rootstocks was directly related to the extent of invasion by the pathogen and to vessel blockage.Experiments on the wilting activity of cell‐free filtrates from cultures of the pathogenin vitroindicated that it produced a stable substance, not an enzyme, that caused wilting in cut shoots by blocking the end of the stem. It is suggested that an increasing internal water shortage causes major symptoms of dise

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb02524.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

Whereas the spinach strain of cucumber mosaic virus fails to multiply and cause symptoms in tobacco plants kept above 30° C., the yellow strain infects at 36° C. and causes more severe symptoms than at 20° C. Increasing the temperature up to 28° C. increases the initial rate at which the spinach strain multiplies, but the virus later reaches much higher concentrations in leaves at lower temperatures, presumably because it is rapidly inactivated at 28° C. Exposing inoculated plants to 36° C. for 6 hr. decreases the number of infections by the spinach strain when the exposure starts within 6 hr. of inoculation, but not afterwards.Pancreatic ribonuclease inhibits infections by strains of cucumber mosaic virus; inhibition is greatest when the enzyme is present in the inoculum, and when applied to inoculated leaves its effect decreases rapidly with increasing time after inoculation.Infection by and the multiplication of strains of cucumber mosaic virus in tobacco are only slightly affected by thiouracil and greatly by azaguanine, whereas strains of tobacco mosaic virus are inhibited much more by thiouracil than by azaguanine. Like tobacco mosaic virus, cucumber mosaic virus multiplies more when inoculated leaves are floated in nutrient solutions than in water, but unlike tobacco mosaic virus, its multiplication is not inhibited by thiouracil more in nutrient solutions than in

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb02525.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

Three mechanically transmissible viruses were isolated from a diseasedSolanum jasminoidesplant obtained from India. One is a strain of potato virusY, which in some potato varieties produces symptoms resembling those caused by potato virusC, but unlike potato virusCit is readily transmitted byMyzus persicae.The second, named tobacco wilt virus, is also transmitted byM. persicaebut much less readily, whereas the third, named datura necrosis virus, is not. All three have a wide host range, but neither tobacco wilt nor datura necrosis viruses infects potato plants. All three have long flexuous particles and similar general properties.Simultaneous infection with datura necrosis virus usually decreases the concentration reached by potato virusYin tobacco plants but not inNicotiana glutinosa.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb02526.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY

摘要:

The reactions of fifteen plant species in families related to the Caryophyllaceae (Hutchinson's classification) when mechanically inoculated with sixty‐eight isolates of fifty‐two plant viruses are described. No general relationship could be detected between susceptibility to particular viruses and taxonomic relationships of the host plants. Some of the species were susceptible to many more viruses than were others.Chenopodium amaranticolor, Gomphrena globosaandTetragonia expansawere hosts for many viruses and their reactions make them suitable as standard test plants.Amaranthus caudatus, Celosia argentea, Beta vulgarisandSpinacia oleraceahad limited use in diagnostic or quantitative work.Dianthus barbatusandPrimula malacoideswere convenient plants for maintaining stock cultures of some viruses.Phytolacca americana, Stellaria media, Fagopyrum esculentumandPlantago lanceolatahad little use, andPortulaca oleraceaandLythrum salicariawere useless as test plants.All fifteen species contained inhibitors of infection; these did not prevent infection on the fifteen species, but many did so in Solanaceous and Leguminous plants.Systemic invasion in some hosts depended on such factors as temperature, virus concentration in the inoculum, virus strain and type of local lesion.Strains of one virus often had different host ranges or caused different kinds of symptoms, while similar symptoms were sometimes caused by different viruses. But some viruses that caused similar symptoms on several of the test plants also shared other properties. Host‐range studies can be used to separate similar viruses or virus strains, and can suggest similarities between viruses for further study. But host‐range studies are unlikely to provide a useful basis for a natural classification of

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1959.tb02527.x

出版商:Blackwell Publishing Ltd    

年代:1959

数据来源: WILEY