. Fungous les maladies des plantes : avec des chapitres sur la physiologie, les méthodes de culture et de technique . Les champignons dans l'agriculture. 3i8 FUNGOUS LES MALADIES DES PLANTES se propage à la tige et les feuilles. Entrée de la tubercules est acquise, par conséquent, en règle générale, à travers les tiges sur lesquelles ils sont supportés. Le système vasculaire de la plante hôte est décoloré, bien que souvent les tubercules ne sont pas grièvement blessés à l'extérieur jusqu'à ce qu'elles sont recueillies. Dans l'entreposage, toutefois, le champignon progresse rapidement, qui noircit l'anneau vasculaire. À ce stade, la maladie est seulement apparu dans les tubercules en les coupant à crosswis

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. Fungous diseases of plants : with chapters on physiology, culture methods and technique . Fungi in agriculture. 3i8 FUNGOUS DISEASES OF PLANTS spreads to the stem and leaves. Entrance to the tubers is gained, therefore, as a rule, through the stems upon which they are borne. The vascular system of the host plant is discolored, al- though frequently the tubers are not seriously injured externally until after they are gathered. In storage, however, the fungus progresses rapidly, blackening the vascular ring. At this stage the disease is only made apparent in the tubers by cutting them crosswise; still it may be so serious as to render them unavailable for table purposes. Later on there may be considerable drying of the tubers, or soft rots due to secondary organisms may ensue. The fungus. The mycelium produces micro- conidiaand macro- conidia (Fig. 150) abundantly in arti- ficial cultures, also some chlamydo- spores. On boiled potatoes small greenish sclerotia are developed, but no ascogenous stage has thus far been connected with this species. Control. This fungus lives apparently -for a considerable time in the soil, and a rotation of crops is essential whenever it be- comes of serious importance. Again, the use of pure seed only should be allowed. If necessary, inspect by cutting a large num- ber of the tubers which are to be used for this purpose. All diseased and discarded tubers should be burned and not returned to the land. Seed tubers which may have come in contact with conidia should be treated as for potato scab. The sleepy disease of tomatoes which has been attributed to Fusarium Lycopersici Sacc. may also be produced by the fungus above described, although this point has not been demonstrated experimentally.. Fig. 150. Fusarium oxysporum: Mycelium, Conidia, and chlamydospore. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not

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