摘要:

Cylindrocarpon Ehrenbergiappears to be one of the most important pathogenic fungi associated with early spring injury of roots of alfalfa and sweet clover in Alberta. It occurs in virgin and cultivated soils. It produces distinctive symptoms, and is highly pathogenic in the early spring, but less virulent during the growing season. It can invade unwounded roots through lenticels or the basal tissues of branch roots, or by direct penetration. It is also pathogenic on roots ofTrifoliumspp. This species has not been previously reported on the legume forage crops, and very little is known concerning its parasitism on other plants.On the roots of alfalfa and sweet cloverC.obtusisporumis slightly to moderately pathogenic,C.radicicolais very weakly pathogenic, andC.olidumis non-pathogenic. These species occur infrequently on diseased roots, and usually in association withC.Ehrenbergi.C.radicicolahas been reported as an important root parasite of other plants.Isolates ofC.Ehrenbergidiffer in degree of pathogenicity, and there is some evidence of host specialization. They also differ markedly in morphological and cultural characteristics, which, however, do not appear to be correlated with their parasitic abilities. The temperature range for growth ofC.Ehrenbergiin pure culture is from − 2° to 32 °C., but different isolates do not have the same optima. Isolates with an optimum at about 19 °C. caused the most damage in the early spring, while one which grew best at 24 °C. proved the most virulent during summer. The optimum hydrogen ion concentration for growth ofC.Ehrenbergivaries with the medium employed. Growth and spore germination studies indicate that the iso-electric point for the fungus lies at approximately pH 5.1.Most of the commonly grown varieties of alfalfa and sweet clover are susceptible to attack byC.Ehrenbergi, but resistant species likeMedicago falcatamay prove valuable as plant breeding material. Apparently cereal crops are not attacked by the pathogen, therefore they should be grown for several years in severely infested fields.

ISSN:1923-4287    

DOI:10.1139/cjr37c-031

出版商:NRC Research Press    

年代:1937

数据来源: NRC

摘要:

The effect of high temperatures on the development of stem rust and leaf rust on wheat seedlings and stem rust and crown rust on oats seedlings was studied in greenhouse experiments. The experimental results show that, for temperatures above the optimum for rust development, the higher the temperature the less vigorous the pustule development. Physiologic races that at ordinary temperatures produce a "4" type of infection tend to develop a "3" type or an "x" type at higher temperatures. At still higher temperatures the infection type becomes "2" or "1" or even merely necrotic flecks. Physiologic races of the same rust differ in their sensitiveness to temperature. In stem rust of wheat, races that had been inbred by repeated selfings for two or more generations, showed greater sensitiveness to temperature than races collected in the field. Leaf rust of wheat and crown rust of oats were less tolerant of high temperatures than stem rust of wheat.

ISSN:1923-4287    

DOI:10.1139/cjr37c-032

出版商:NRC Research Press    

年代:1937

数据来源: NRC

摘要:

The application of heteroauxin in lanoline (1 mg. of heteroauxin per gm. of lanoline) to the distal end of disbudded cuttings of leader shoots of balsam poplar, stimulated cambial activity for a distance of 1.0–1.5 in. below the point of application. Marked stimulation of local cambial activity, in relation to a bridged ring some considerable distance below the point of application of the heteroauxin, was also obtained. The response at the wound was distinct and separate from the response in the region of application of the heteroauxin, since in the intervening distance no cambial activity had occurred. The experiments were carried out during the winter months, so that the cambium was dormant in material as it came from the field. Cambial activity subsequent to treatment was estimated in terms of xylem formation. The structural features of this new xylem are described and discussed, with particular reference to the question as to whether heteroauxin stimulates cell division only in the cambium or, in addition, is active in differentiation of typical xylem elements.

ISSN:1923-4287    

DOI:10.1139/cjr37c-033

出版商:NRC Research Press    

年代:1937

数据来源: NRC

摘要:

Of 15 chemicals applied to perennial weeds over the same range of dosages, only five appear to possess a useful toxicity as judged by the number of living plants 12 months after treatment. The effective chemicals can be classified into three groups according to their toxicity, (i) sodium chlorate; (ii) barium chlorate and arsenic pentoxide; and (iii) ammonium thiocyanate and sodium arsenite. The relative toxicity of these three groups of chemicals, judged from the certainly lethal dosage, appears to fall in the proportions of 1:1.5:> 2.

ISSN:1923-4287    

DOI:10.1139/cjr37c-034

出版商:NRC Research Press    

年代:1937

数据来源: NRC