摘要:

In the present studies onPlasmodiophora BrassicaeWor., attention was focussed principally on the development of the zoosporangium and the formation and discharge of the zoospores.Resting spores, released from thoroughly clubbed tissue by the action of bacteria and fungi, germinated well in tap water at room temperature in 1 to 10 days. Germination was hastened by exposure to frost.The zoospores from the resting spores are biflagellate and heterokont, and vary in size. When such a zoospore comes in contact with root hairs or epidermal root cells of cruciferous seedlings, it settles down as an amoeba and penetrates the cell wall to form a young thallus within the host cell. The thallus may or may not become considerably enlarged before the protoplasm undergoes cleavage and an irregular cluster of zoosporangia is formed. Each zoosporangium contains four to eight zoospores, which, at maturity, are discharged from the root hair if free moisture is present; otherwise the fungal protoplasm disintegrates. At ordinary field temperatures, from four to six days are required from infection of the host to the discharge of zoospores from the zoosporangium. Discharge takes place through small openings at the point of contact of the zoosporangia with the cell wall of the root hair. These zoospores when discharged are not more than one-half the average diameter of the zoospores from germinating resting spores.Controlled temperature, studies have shown that temperatures most favourable for the growth of the host are also most favourable for infection. The optimum temperature for infection was about 70° F., the minimum between 54° and 57° F., and the maximum above 92° F. Only two to two and one-half days were needed for the process.

ISSN:1923-4287    

DOI:10.1139/cjr44c-012

出版商:NRC Research Press    

年代:1944

数据来源: NRC

摘要:

Under the experimental procedure used in these researches it was found that wheat, when kept at 25 °C. in atmospheres of relative humidities between approximately 92 and 100%, showed a continuously accelerating rate of carbon dioxide output. This acceleration of rate increased as the relative humidity of the surrounding air was increased and was more pronounced in wheat from which the germs had been removed than in undamaged wheat. Where unlimited absorption of water and germination of the wheat are prevented, the carbon dioxide production by the grain is due almost entirely to the respiration of micro-organisms that infect it.

ISSN:1923-4287    

DOI:10.1139/cjr44c-013

出版商:NRC Research Press    

年代:1944

数据来源: NRC

摘要:

The results of field tests with random lots of potato tubers showing phloem necrosis of similar type are summarized. The vines from tubers of five of these developed typical leaf-roll symptoms, but those of three others showed no sign of leaf roll, or other symptoms that suggested a virus as the causal agent. The net necrosis in one of the latter samples was known to result from vine infestation ofParatrioza cockerelliSulc, and in this case the stock returned to full vigour during the second season. It was further confirmed that once the vines show definite symptoms of leaf roll, the phloem elements of their tubers henceforth do not exhibit necrosis.The tissue contiguous to the necrotic phloem elements in the affected tubers was uniformly fluorescent, but the unaffected portion of such tubers, as well as non-necrotic tubers from positive leaf-roll plants, reacted negatively to ultraviolet light.

ISSN:1923-4287    

DOI:10.1139/cjr44c-014

出版商:NRC Research Press    

年代:1944

数据来源: NRC

摘要:

not available

ISSN:1923-4287    

DOI:10.1139/cjr44c-015

出版商:NRC Research Press    

年代:1944

数据来源: NRC

摘要:

Three species ofStemphylium, which have been isolated from agricultural seeds, are described and illustrated:S.botryosumWallr.,S.sarcinaeforme(Cav.) Wilts., andS.consortiale(Thüm.) n. comb.S.sarcinaeformehas been found only on seeds of red clover; the other two species occur on a wide variety of seeds. The perfect stage ofS.botryosumisPleospora herbarum(Pers.) Rabenh. but the perfect stages of the other two species are unknown.

ISSN:1923-4287    

DOI:10.1139/cjr44c-016

出版商:NRC Research Press    

年代:1944

数据来源: NRC