Fungoid pests of cultivated plants / by M.C. Cooke.

  • Mordecai Cubitt Cooke
Date:
1906
Catalogue details

Licence: In copyright

Credit: Fungoid pests of cultivated plants / by M.C. Cooke. Source: Wellcome Collection.

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    conidia must be destroyed in the autumn to prevent their extension to healthy plants; and the destruction of all rotting dtbris must be carried out during the winter, so as to extirpate all the concealed resting spores, and thus prevent the infection of seedlings in the spring. 1'iom these details it will be evident that plants once attacked by cndophytal parasites are in themselves hopeless. No external application can destroy organisms which it cannot reach, or, if they could be destroyed, no manipulation can replace the disorganised tissues. Hence, then, all ellorts should be directed towards the destruction of the conidia and resting spores, in order to stamp out the disease at its source and prevent the future infection of healthy plants. The application of spray- ing to plants apparently without disease would be done as a preventive, in older to destroy at once any germs which might be brought into con- tact with the foliage ; and the destruction of all infected material would limit the local sources of infection. With an intelligent appreciation of the objects which have to be attained, the cultivator may accomplish a great deal in the way of prevention, even though he may be helpless to effect a cure. It will be seen how much of this depends upon an accurate diagnosis of the disease. There are many other forms of endophytal parasites, and the life-history of some of these is still obscure. In the majority of them only a conidial fructification is yet known, and the internal tissues do not appear to be so absorbed and destroyed as in the case of the “ rot moulds ” ; but in such black moulds as the “ Apple and Pear scab ” the mycelium appears to be perennial, and produces a fresh crop of conidia each successive year. There is some evidence that this disease is deep-seated and hereditary, and if so it is doubtful whether any amount of external application will result in a perfect cure. The genus Glieosporium includes many species which are very destructive, but often they seem to be localised, and the mycelium may not pass internally to other parts. This can only be ascertained by closer investigation. The little pustules on the leaves, and the fruits, are seated beneath the cuticle, where a cushion or stroma of compacted mycelium produces conidia, but without any enclosing mem- brane or perithecium. When the conidia are matured the cuticle is ruptured, and the spores escape to the surface, in many cases adhering in a somewhat gelatinous mass, which oozes out in the form of tendrils. In such cases it is evident that the application of some fungicide capable of destroying the vitality of the conidia will be of service in preventing the spread of the disease (PL 1. fig. 9). A large and important group of endophytes is that known as the Uredines, of which the common and disastrous “ Wheat rust ” or “ Wheat mildew ” is a familiar example. In the first instance, the host-plant pro- duces upon its leaves, in the spring, clusters of little cups, partly embedded in the substance of the leaf, which is usually thickened and discoloured. These little cups constitute the “cluster cups,” or jecidium form; the margin is usually white and fringed, and the interior filled with orange subglobose spores, termed tecidiospores, produced in chains, but soon falling apart (PI. I. fig. 21). The tecidiospores will germinate when mature and produce a thread of mycelium, which is capable also of producing secondary spores (fig. 1). Smaller bodies are also to be found in company,
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