The pathology of our native larch, Larix laricina (Du Roi) Koch, has never been carefully investigated in the province of Quebec. One of the explanations of this apparent lack of interest in diseases of this tree species is the very important infestation by the larch sawfly (Pristiphora Erichsonii Htg.), which, at the beginning of the present century, greatly reduced the best stands of larch in Northeast America. Usually the Eastern larch, commonly called tamarack, provides a hard, heavy and non-porous wood of high technical value. Its resistance to decay outweighs any other conifer of Eastern and Central Canada (2).

A major objective of the Agricultural Sciences is the utilization of' natural resources in such a manner that the effects of factors which reduce the yields of products useful to man, will be minimized. Although nematodes, as parasites of vertebrates and plants, have been recognized as significant factors in reducing agricultural production, they are themselves victims of a number of parasitic organisms. Struggle for existence is universal among living organisms regardless of their biological level, and this competitive relationship between nematodes and other organisms in their environments is by no means unique. Fungi, that prey upon or parasitize microscopic animals, are usually referred to as predacious fungi.

In recent years agricultural scientists have become aware of the fact that plant parasitic nematodes have been a serious world problem by depriving farmers of higher yields and greater returns from their crops. It is impossible to assess their economic importance even roughly, for in many parts of the world they have still to be sought, but it is probably safe to say that every country or every crop is troubled by nematodes. Nematodes of the species ‘Aphelenchus avenae’ Bastian, 1865 are of widespread occurrence in soil and in dead or dying plant parts that have been in or on the soil, yet their significance in relation to plant diseases and their role in the soil community remains uncertain.

The production of horticultural crops, although it accounts for only 6.8 per cent of the total agricultural revenue of Quebec, is one of the most dynamic sections of the agricultural industry in this Province (39). The total area in vegetables grown for commercial purposes was estimated at 70,360 acres in 1962, compared to 66,690 in 1961 and 63,660 acres in 1960. Estimates of the farm value of production were 13.7 million dollars for 1962, compared with 13.2 million in 1961 and 12.6 million in 1960. Potatoes, as field crops, are grown on 90,200 acres in Quebec (29.1 per cent of the total acreage for potatoes in Canada), with an annual production of 8,833,000 bushels. Strawberries, as small fruit crops, were cultivated on 2,840 acres in 1962, with a production of 6,490,000 lbs. (Private communication with Dr. Jean David, Department of Horticulture, Macdonald College, McGill University).

Among the physiological features of the infected plant, the pathological increase in respiration is a striking one. This altered rate of respiration, usually measured in terms of oxygen uptake, starts before symptoms of disease appear, rises gradually to a maximum as the disease develops, and declines rapidly as death is approached. These observations on abnormal rate of gas exchange indicate that the enzyme-catalysed processes resulting in oxygen absorption are accelerated in the host tissue as a result of infection. A natural question is then, what enzymes are involved in this acceleration. Among the great variety of enzymes that could possibly be involved, cytochrome oxidase can be regarded as an important one, as it functions as terminal oxidase in the phosphorylating electron transport system of the mitochondria.

The toxigenic theory of plant disease explains the occurrence of pathological disturbances in advance of the invading pathogen as the effect of a toxin produced in the course of host-pathogen interaction. A considerable amount of work has been done on such diseases, which are called toxemia; however much of it is still a matter of controversy. Much more research must be done on this subject before many of the concepts involved can be accepted. At present, there is need for studies to show that pathogens can produce the same toxins both in axenic culture and in infection, and that injection with toxins can reproduce the physiological disturbances and the symptoms characteristic of the disease.

L'emploi de substances'herbicides pour le désherbage chimique des cultures connaît depuis quelque 15 ans une montée fantastique qui représente un aspect intéressant pour l'économie agricole. Chaque année, un grand nombre de composés sont le sujet d'études intensives en vue de leur emploi possible comme herbicides. Il y a environ 3 ans, un dérivé de l'urée, le linuron, a été mis à la disposition des chercheurs intéressés aux problèmes du désherbage chimique des cultures. Les résultats ont été des plus satisfaisants, du fait que ce composé offrait de grandes possibilités en traitement de préémergence. [...]

Atmospherical environmental factors have long been known to affect rust development on green plants. Environmental conditions subsequent to infection usually have more effect than conditions prior to infection. Moisture, temperature, and light have been shown to be most significant of the atmospheric factors. [...]

Corynebacterium sepedonicum (Spiekermann and Kothoff), Skaptason and Burkholder, is the causal agent or bacterial ring rot of potatoes. Histological observations have invariably revealed that it primarily inhabits the water conducting vessels of the potato. [...]

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