It is also the source of primary infections in newly established plantations. The distribution of infected vegetative planting material of cassava from diseased plantations has been the main means of disseminating the CBB bacterium over long distances into Africa and Asia. ![]() Once one cassava plant is infected, the whole crop is put at risk to infection from plant-to-plant transmission through several means, including rain-splash, insect damage, picking off young shoots as a vegetable, and contaminated cultivation tools. In this way, the pathogen invades younger tissues such as developing leaves and seeds, disrupting water flow and thus causing the characteristic wilt of the leaves and young shoots. Once inside its host, the bacterium dissolves barriers to the plant’s vascular system and begins a systemic infection, moving through the plant in the xylem. the picking of young shoots for use as a vegetable, or damage while weeding).ģ. Pseudoteraptus devastans has been implicated in the spread of the disease in cassava in Africa) and human activity (e.g. The CBB bacterium enters its host plants through leaf pores (stomata) and through wounds in leaves and stems. It survives poorly in the soil but can survive on the surfaces of weeds and in insect feces. In moist conditions, it has been shown to survive for up to thirty months without new host tissue. The CBB bacterium remains viable for many months in diseased plant tissues (e.g.the planting stakes and in the seeds), and in the gummy exudate from stems and leaves. How does the CBB pathogen survive in nature? No symptoms of CBB have been recorded on or in cassava roots.ġ. The bacterium lies dormant in the seed embryo, with dormancy breaking shortly after the There have been reports that seeds from CBB diseased plants that carry a high load of the pathogen are sometimes deformed and necrotic, but the consensus is that CBB infected seeds are asymptomatic carriers and that there are no diagnostic symptoms of CBB on cassava seeds. The vascular bundles of infected petioles and stems are also necrotic, appearing as brown or black bands. The lesions enlarge and eventually coalesce along the veins or edges of the leaf, killing the leaf. The earliest symptoms visible on cassava leaves are dark-greenish water-soaked areas limited by the leaf veins and which show gummy exudation on the water-soaked areas (Photo CBB 8). The first sign of the disease is wilting and dying of leaves (Photo CBB 1 & 2). The leaf wilting is accompanied by a viscous amber to orange coloured exudation from the leaf stalks (petioles) and young stems (Photos CBB 3 - 5). As the disease progresses the diseased shoots die so that the plants show the characteristic “dieback” symptoms, with bare leafless stems pointing upward (Photo CBB 6). When large numbers of adjacent plants exhibit the dieback symptoms, the crop appears as a forest of leafless stems which gives rise to the name in French of “la maladie des cierges” or candle disease (Photo CBB 7). in Zaire in the early 1970s, the losses due to CBB were estimated at 75% of its tuber yield and almost all of its protein-rich leaf yield every year for several years, causing severe malnutrition and even starvation.in parts of Uganda in the late 1970s yield losses caused by CBB were as high as 100%.in Nigeria in 1973, one year after the disease was first reported in the country, yield losses due to CBB were estimated at 75%.The disease was particularly damaging in Africa in the 1970s when the pathogen was first identified in the Continent, e.g.:. ![]() CBB can be devastating, causing total crop loss, and among the diseases which afflict cassava worldwide, CBB is regarded as causing the greatest yield losses. ![]() How important is cassava bacterial blight?Ĭassava bacterial blight (CBB) is regarded as one of the most limiting diseases of cassava production.
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