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Plano de Gestão Ambiental e Social - Centro Regional de Liderança da Mandioca: Malanje-Angola

Plano de Gestão de Resíduos - Centro Regional de Liderança da Mandioca: Malanje-Angola

Plano de Gestão de Água - Centro Regional de Liderança da Mandioca: Malanje-Angola

Estudo de Impacto Ambiental e Social - Centro Regional de Liderança da Mandioca: Malanje-Angola

Plano de Gestão da Biodiversidade - Centro Regional de Liderança da Mandioca: Malanje-Angola

An increasing multitude of insect pests and pathogens is targeting indigenous trees of natural forests, agroforestry systems, and exotic trees in planted forests in Africa. This is raising major concerns for a continent already challenged by adaptations to climate change, as it threatens a vital resource for food security of rural commu‐ nities, economic growth, and ecosystem conservation. The accidental introduction through trade of non‐native species in particular is accelerating, and it adds to the damage to tree‐based landscapes by native pests and diseases. Old‐time and new invaders heavily impact planted forests of exotic eucalypts, pines, and acacias, and are spreading quickly across African regions. But many non‐native pathogens are re‐ cently found affecting important indigenous trees. We describe the threat to African trees by providing an overview of highly relevant insect pests and diseases of indig‐ enous and exotic trees in Africa, and discuss implications for management and future research. The implementation of an integrated and globally coordinated approach based on improved biosecurity, biological control, and tree resistance would con‐ tribute to mitigate the potentially devastating impact of these invasions on African natural resources.

Africa: a new frontier for tree invaders?

Bemisia tabaci is an important vector of cassava brown streak viruses and cassava mosaic begomoviruses, the causal agents of cassava brown streak disease and cassava mosaic disease (CMD), respectively. A study was carried out to determine the genetic variability of B. tabaci associated with cassava and the occurrence of CMD in Zambia in 2013 and 2015. Phylogenetic analysis showed the presence of only the sub-Saharan Africa 1 (SSA1) genetic group in Zambia. The SSA1 population had three population subgroups (SGs): SSA1-SG1, SSA1-SG2 and SSA1-SG3. All three SSA1 population subgroups occurred in Western Province. However, only SSA1-SG3 occurred in Eastern Province, while only SSA1-SG1 occurred in North Western and Luapula Provinces. Adult B. tabaci were most abundant in Western Province in 2013 (11.1/plant) and 2015 (10.8/plant), and least abundant (0.2/plant) in Northern Province in both 2013 and 2015. CMD was prevalent in all seven provinces surveyed, with the highest incidence recorded in Lusaka Province in both 2013 (78%) and 2015 (83.6%), and the lowest in Northern Province in both 2013 (26.6%) and 2015 (29.3%). Although SSA1-SG1 occurred at greater abundances than the other subgroups, there was no direct association demonstrated between whitefly subgroup and incidence of CMD. Establishing which B. tabaci genetic groups and populations are associated with CMD and their distribution in the country is a key factor in guiding the development of CMD control strategies for cassava-dependent households.

Cassava (Manihot esculenta) is an important food crop across subSaharan Africa, where production is severely inhibited by two viral diseases, cassava mosaic disease (CMD) and cassava brown streak disease (CBSD), both propagated by a whitefly vector and via human-mediated movement of infected cassava stems. There is limited information on growers’ behavior related to movement of planting material, as well as growers’ perception and awareness of cassava diseases, despite the importance of these factors for disease control. This study surveyed a total of 96 cassava subsistence growers and their fields across five provinces in Zambia between 2015 and 2017 to address these knowledge gaps. CMD symptoms were observed in 81.6% of the fields, with an average incidence of 52% across the infected fields. No CBSD symptoms were observed. Most growers used planting materials from their own (94%) or nearby (<10 km) fields of family and friends, although several large transactions. over longer distances (10 to 350 km) occurred with friends (15 transactions), markets (1), middlemen (5), and nongovernmental organizations (6). Information related to cassava diseases and certified clean (diseasefree) seed reached only 48% of growers. The most frequent sources of information related to cassava diseases included nearby friends, family, and neighbors, while extension workers were the most highly preferred source of information. These data provide a benchmark on which to plan management approaches to controlling CMD and CBSD, which should include clean propagation material, increasing growers’ awareness of the diseases, and increasing information provided to farmers (specifically disease symptom recognition and disease management options).

Africa produces over half of global cassava; however, the continent’s average yield is below the potential yields achieved under experimental conditions. Many factors contributing to low yield  include lack of quality varieties, poor soils, limited access to capital, competition for labour, as well  as pests and diseases. Plant diseases are the major biotic constraints to cassava production and have  caused considerable food insecurity in Africa. Although there has been some level of disease  management which has contributed to the increase in cassava production, the two viral diseases:  cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) still claim between 30- 16 40% and upto 70%, respectively of Africa’s cassava harvest. Given the importance of the two  diseases in Africa, we review the expansion of CBSD and CMD; impacts of the two diseases on food  security and how they can be managed. We provide insights in the spread of the two diseases,  management efforts, and future directions