摘要:

Strawberry plants, variety Premier, were grown in naturally-infected root rot soil in which consecutive "crops" of several agricultural plants had been turned under, and in other lots of the same soil that had been steam sterilized or fertilized with barnyard manure. On examination of their roots it was found that the incidence and severity of root rot were closely correlated with soil treatment. Plants grown in sterilized soil remained free from disease as did those of the soybean series until the third season when they were slightly affected. Plants in the manure, corn, red clover, timothy, and untreated soil series all became diseased, the severity of attack increasing in the respective series in the order named.Although roots of the various cover crops were found to contain representatives of several different genera of fungi, a specific fungus was dominant in each as was the nematode,Pratylenchus pratensis, in timothy and clover. This build-up of specific organismsappearedto be correlated with the incidence and severity of the disease in the roots of the strawberry plants that followed in the respective series.However, in strawberry plants grown in the variously treated soils, fungal infection was negligible and, on the whole, not related to that of the preceding cover crop. An exception to this was the heavy infection by the mycorrhizal fungus (Rhizophagussp.?), following timothy and corn, but a lack of correlation, in many cases, between the presence of the fungus and discoloured and necrotic tissue indicated that other agencies might be responsible for the injury. In timothy and red clover treated soils, nematodes, particularlyPratylenchus pratensis, might have been an important factor.Fewer bacteria were found adjacent to roots of healthy plants than to those of diseased ones. Qualitative differentiation on the basis of nutritional requirements indicated a striking relationship between the incidence of certain groups of bacterial isolates and the severity of disease attack. The equilibrium between presumably "harmful" bacteria and the innocuous, normally occurring rhizosphere types is designated the Bacterial Balance Index. There are marked differences in the microbiological equilibria of the different soil series; increased severity of root rot is associated with a fall in the Bacterial Balance Index.

ISSN:1923-4287    

DOI:10.1139/cjr41c-023

出版商:NRC Research Press    

年代:1941

数据来源: NRC

摘要:

Soybean and red clover, grown as cover crops and incorporated into strawberry root rot soil, showed a marked difference in ability to control the disease on variety Premier. Soybean caused a striking reduction in the incidence of root rot and a drastic shift in the bacterial equilibrium of the soil. Red clover had little effect on the severity of the disease or the general microflora of the soil.A study of "rhizosphere effects" reveals that the characteristic differences between theresultantbacterial equilibrium of the soils in which the two leguminous plants were grown, could not be attributed to influences exerted by the latter in the living state. However, the bacterial types favouredduring decompositionin experimental cultures of tissues of red clover and of soybean, each inoculated with root rot soil, were identical with those isolated from root rot soil with which red clover and soybean, respectively, had been incorporated. In contrast to the putrefactive decomposition of red clover, soybeans apparently underwent a carbohydrate breakdown that could be reproduced essentially in culture by the substitution of glucose for soybean tissues. Beneficial changes in the bacteriology of actual root rot soils could be induced by the decomposition of pure carbohydrate in place of soybean. The favourable alteration in the bacterial equilibrium was accompanied by a corresponding modification of the fungous flora such that potentially pathogenic forms were replaced by presumably innocuous ones. These carbohydrate treated soils were capable of producing strawberry plants with well developed healthy root systems. The ability of soybean to control strawberry root rot therefore seems to depend primarily on a carbohydrate type of breakdown in diseased soil, causing a highly favourable shift in the microbiological equilibrium. The decomposition of red clover, on the other hand, did not under the same conditions induce these salutary effects.

ISSN:1923-4287    

DOI:10.1139/cjr41c-024

出版商:NRC Research Press    

年代:1941

数据来源: NRC

摘要:

Marquis wheat treated with a series of talc dusts containing indolylacetic acid, potassium naphthylacetate, potassium nitrate, and ethyl mercuric bromide was grown in soil in the greenhouse. Potassium naphthylacetate increased the final germination count 2.6% while indolylacetic treatments failed to affect germination or early growth. Neither of these growth stimulating chemicals interacted with potassium nitrate or ethyl mercuric bromide. Ethyl mercuric bromide retarded the germination rate but increased the final germination count. Potassium nitrate in conjunction with the organic mercurial disinfectant reduced final germination and the air-dry weight of young plants. On the average, dust treatments reduced the rate of germination but increased the air-dry weight of stems.

ISSN:1923-4287    

DOI:10.1139/cjr41c-025

出版商:NRC Research Press    

年代:1941

数据来源: NRC

摘要:

It is pointed out that size data from over 50 tomato crosses are explained by the assumption of the geometric action of size factors but not by a simple additive theory.The fact that theF1results fitted such a theory was pointed out in a previous paper when the theory was proposed. The analysis is here extended to theF2generation and to cell size measurements.The use of the geometric scale introduces regularity into the otherwise unpredictableF2segregations, and they become amenable to a simple logarithmic scheme. Analysis by such a scheme indicates that differences in cell number or ovary size are caused by the segregation of three to five pairs of major genes, whereas mature cell size differences seem to be brought about by the segregation of at least twice as many factors.Final weight is thus the resultant of the proportionate action of the following factors:—1. The number of mitotic divisions in the pre-anthesis period and therefore the number of cells at anthesis.2. The cell expansion after anthesis.3. Fruit shape, locule number, and other size-modifying effects.

ISSN:1923-4287    

DOI:10.1139/cjr41c-026

出版商:NRC Research Press    

年代:1941

数据来源: NRC