摘要:

Following the appearance of the Cladosporium blight of sweet pea in Ontario in 1945, a study of the causal organism and the disease was carried out. As a result of this study the nameCladosporium albumDowson has been retained for the organism in preference toErostrotheca multiformisMartin and Charles, orHyalodendron album(Dows.) Diddens. Temperature and humidity studies have indicated that the parasite and the disease develop most rapidly at 25 °C., and that high humidity is necessary for infection and for fruiting on the leaf. Penetration is stomatal, without appressoria, and occurred 10 times as often into leaves with 'open' as into leaves with 'closed' stomata. Evidence thatC.albummay show a positive hydrotropism was obtained. Frequency of penetration increased with an increasing gradient around the stomata, and this was interpreted as evidence that hydrotropism is a factor in penetration. Host range studies and a comparison of frequency of penetration into an immune and a susceptible species showed frequent penetrations into the immune species but no appreciable development in any but sweet pea.

ISSN:1923-4287    

DOI:10.1139/cjr47c-014

出版商:NRC Research Press    

年代:1947

数据来源: NRC

摘要:

A number of pathogenic fungi were isolated from blighted brome grass and crested wheat grass seedlings grown in Saskatchewan and Ontario soils. The parasitism of one of the widely distributed and commonly occurring of these,Fusarium culmorum(W. G. Sm.) Sacc, was studied in more detail.One per cent ofF.culmorumsand–cornmeal inoculum caused more blight of brome grass seedlings in sterilized soil than did 6% in unsterilized soil. The development ofF.culmorumin sterilized soil was optimum at 25 °C. and declined rapidly with rising and more slowly with falling temperatures. Seedling blight was severe in sterilized soil at all temperatures from 10° to 35 °C., but was significantly more severe near the optimum for the fungus provided the soil was not infested too heavily. In unsterilized soil, however, both the development ofF.culmorumand the incidence of seedling blight were much greater at 10 to 20 °C. than at 25 °C. and higher, whereas other soil fungi and bacteria were more numerous at 25° C. and above than at the lower temperatures.An infusion of unsterilized soil, a suspension of miscellaneous soil bacteria, and a mixture of 75 soil fungi suppressed the development ofF.culmorumin sterilized soil, and also caused reductions in seedling blight. Of 136 soil fungi tested, only three reduced fusarial blight in sterilized soil. These antagonistic fungi included isolates ofAcremonium,Gliocladium fimbnatumGilman and Abbott, andPhialophora. Their ability to reduce disease incidence was not consistently correlated with the production of toxic filtrates, or the inhibition ofF.culmorumin culture or in the soil but it was related to the effect they had on the development ofF.culmorumin the environment in the immediate vicinity of the germinating seeds. This zone within which the germinating seed induces a characteristic change in the microbiological balance is designated as the 'spermatosphere'.Disease incidence varied among different unsterilized field soils uniformly infested withF.culmorumand in these experiments was more severe in clay than in the soils of lighter texture. There was no consistent correlation between the suppression of blight and the numbers of fungi, bacteria, or actmomycetes in the different soils, but there was a correlation with the numbers of bacteria in the spermatosphere.

ISSN:1923-4287    

DOI:10.1139/cjr47c-015

出版商:NRC Research Press    

年代:1947

数据来源: NRC

摘要:

Polyporus obtususBerk, is a heartwood decaying fungus that attacks several American species of broadleaved trees, principally oaks. It has a wide geographical range, but tends to occur in localized concentrations within which it causes great destruction, while elsewhere it is rarely found. On account of its peculiar distribution,P.obtususis not well known, and the published references to it are comparatively few. A local concentration of this disease, the only one known in Canada, occurs at the Petawawa Forest Experiment Station, Ont. Here, oak trees from 0.8 to 4.8 in. in diameter were being attacked. The resulting white rot continues to advance into the sapwood, ultimately causing death of the tree. The large, cream-coloured, bracket-like sporophores are borne on the diseased trees in great abundance in some seasons, and are comparatively scarce in others.

ISSN:1923-4287    

DOI:10.1139/cjr47c-016

出版商:NRC Research Press    

年代:1947

数据来源: NRC