A contribution to the study of african cassava mosaïc disease

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A contribution to the study of african cassava mosaïc disease

  • Jean Dubern


A contribution to the study of african cassava mosaïc disease 13 2 - A~CONTRIBUTION TO THE STUDY OF AFRICAN CASSAVA MOSAJÇ lli~~A~~ Jean Dubern, Virologist ORSTOM, Abidjan, Ivory Coast The vnrious reports so for published on the Cassava Mosn~c Disease have been conc~rnGd with symptomatology, epidemiology, trans- mission by Aleyrodidae, varietal selection and treatment by heat. No paper has given sufficicnt information on the nature of the agent (s) responsible for the disease. This is the subject of this paper. The study of transmission wns undertaken. No attempt at trans- mitting the disease by mechanic21 means was successful. On the other hand the attempts to transmit the diso3se by dodder (Cuscutasubinclusa~ were successful. The present study is based on trans- mission from a single cassava variety. This variety, Agba Baoulé, is particularly susceptible to tho disease: mosoic, deformation, and stunted growth reminiscent of the symptoms of "witches'broom" (Fig. 1). The disoased cassava plants of this varicty were obtainod by cuttings. Seeds plnnted in insect-proof shelters, provided disease- froe seedlings which wero used when they were 6 to 10 weeks old. Young stems of dodder were deposited at the axil of hoalthy seedlings. The experimental procedure is as follows : The stems of Cuscuta subinclusa that had grown on diseased cass~va plants for three weeks, while still intertwined on these plants, were hung on the stems of the healthy plants and left for three weeks. They were then detatched from the plants. Six to eight weoks aftor cont~ct with dodder that hod developed on the diseosed cassova, a yellowing was obscrved on Vinca rosea, Petunia violacoea, Capsicum frute- scens and Capsicum annum. Control plants that had been in contact with healthy dodder, though showing chlorotic symptoms due to the parasitic effect of the dodder, showed no yellowing and quickly regained normal appoarance once the parasite wos cut away. Four to six weeks later the new leaves that appeare

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