Cassava Bacterial Blight: A Devastating Disease of Cassava

Abstract

Cassava (Manihot esculenta Crantz) with its long life cycle is affected by several diseases of which cassava bacterial blight (CBB) is the major bacterial disease in the cassava belt worldwide. The epidemiological and ecological investigations undertaken on the disease showed that the causal agent, the bacterium Xanthomonas axonopodis pv. manihotis (Xam), possesses several means for survival and dissemination that may play an important role as inoculum sources for the infection when favorable conditions occur, and the subsequent damage of the plant causing severe yield losses. In fact, Xam survives epiphytically on some weeds occurring in and around cassava fields without developing blight symptoms. Investigating the survival period over the seasons, a longer survival exceeding 5 months has been observed in non-decayed cassava debris. Also, some insects in cassava field like the variegated grasshopper (Zonocerus variegatus) vehicles the pathogen for some time. Over seasons Xam also survives often latently, in cassava stems which are then used for establishing new plantations. In regional disease surveys across ecozones in West Africa, no zone of preference has been found. Though, comparing the development of the disease and the damages caused in yield loss trials in two agro-eco-zones over 2 years, CBB was more pronounced and caused higher yield and biomass losses in the forest savannah transition zone than in the dry savannah where symptom development was positively correlated with the rainfall patterns. The detailed knowledge of the epidemiology, disease development, survival and dissemination, of the reaction of cassava varieties towards CBB such as physiological resistance mechanisms, identification of genetic resistance (QTL) and the background of observed field resistance as well as of the influence of planting time and cropping pattern allows to recommend integrated management measures such as sanitation, intercropping, removal of diseased leaves, management of planting dates according to ecozone, soil amendments, use of resistant genotypes.

A novel seed treatment-based multiplication approach for cassava planting material

“…These include cassava common mosaic virus, cassava frogskin disease and cassava root rot disease [10]. In East Africa, cassava mosaic disease, cassava brown streak disease and cassava bacterial blight are a major cause of seed degeneration and yield loss [11,12,13,14]. The presence of these pests and diseases leads to average yields of around 8.3-11.2 tons per hectare in East Africa, which is roughly a third of what is believed to be the crop's potential in this region [15].…”

Assessment of Three Cassava Varieties Responses to Cassava Bacterial Blight (Cbb) in the Seven Agro-Ecological Zones of C?te D?ivoire During a Survey in 2017.

“…It could be explained by the fact that the pathogen achieved its complete cycle. In fact, according to Fanou et al (2018), Xpm goes through a survival stage during the dry season for the establishment of the primary inoculum and a parasitic stage during the rainy season where the disease symptoms occur. In Côte d'Ivoire, the AEZ6 has two seasons, a six months dry season and a six months rainy season.…”

“…manihotis (Xpm), (Constantin et al 2016). Losses of fresh roots, planting material, low accumulation of starch in edible roots and leaves which affect the availability of leafy vegetables for humans and reduces cash income in communities where cassava leaves are sold, have also been observed and can be high under favourable environmental conditions (Fanou et al, 2018). CBB is present in countries where cassava is produced, but its incidence and severity are variable (Fanou et al, 2017;Fanou et al, 2018).…”

“…Losses of fresh roots, planting material, low accumulation of starch in edible roots and leaves which affect the availability of leafy vegetables for humans and reduces cash income in communities where cassava leaves are sold, have also been observed and can be high under favourable environmental conditions (Fanou et al, 2018). CBB is present in countries where cassava is produced, but its incidence and severity are variable (Fanou et al, 2017;Fanou et al, 2018). The characteristic symptoms of the disease are the wilting of leaves, blighting, angular leaf lesions and stem cankers, stem and leaf exudates production and dieback of stems (Jorge et al, 2001).…”

Effect of Intercropping on the Development of Cassava Bacterial Blight

“…manihotis (Xam) (Vauterin et al, 1995 ;Fanou et al, 2018). It is one of the major diseases affecting cassava (Lozano & Booth, 1974;Rubio et al, 2017).…”