Bacterial blight of cassava (Manihot esculenta Crantz) was first recorded from Africa in 1973. This report is concerned with the distribution, epidemiology and ecology of the disease in Africa and the characteristics of the causal agent, Xanthomonas campestris (Pammel 1895) Dowson 1939 pv. manihotis (Arthaud-Berthet and Bondar 1915) Dye 1978.
In terms of cultural characters and physiological reactions, twenty-one isolates of X. campestris pv. manihotis from Africa, Asia, South America and Mauritius were similar to one another and to other xanthomonads of the species X. campestris (Pammel 1895) Dowson 1939. Isolates from Africa could be differentiated from other isolates of X. campestris pv. manihotis by phage typing, using three newly-described phages. There were differences in aggressiveness amongst nine isolates from West Africa but no evidence of pathological specialization amongst the isolates.
The presence of the disease was confirmed in Ghana, Togo, Benin, Nigeria, Cameroon, Zaire, Kenya and Tanzania. It was more prevalent in the savanna and forest/savanna transition zones than in the forest. Experiments showed that epiphytotics could be established from a few diseased plants in the first two zones but not in the last.
A leaf-infiltration technique was devised to assay the presence of the pathogen in various infection sources. It survived the dry season on leaves, in infected stems and in plant debris. Numbers surviving in debris decreased sharply as substrates became moist, in both field and laboratory experiments. An epiphytic phase on leaves was shown to be part of the disease cycle of bacterial blight of cassava. A potential for seed transmission of the pathogen was demonstrated and curative treatments for infested seed investigated.