BOTRYOSPHAERIA CANKER AND DIEBACK A THREAT TO DOMESTICATION OF BAOBAB (ADANSONIA DIGITATA L.) AND MARULA (SCLEROCARYA BIRREA A. RICH.) IN AGROFORESTRY SYSTEMS IN KENYA
Keywords:Adansonia digitata, agroforestry, Botryosphaeriaceae, Sclerocarya birrea, tree cankers
Cultivation of indigenous fruit trees such as baobab (Adansonia digitata) and marula (Sclerocarya birrea) play a pivotal role in providing key nutrients and income for smallholders and enhancing diversification of agroforestry systems in the drylands of Sub-Saharan Africa. Tree decline associated with stem cankers and canopy dieback is increasingly being observed negatively impacting on baobab and marula in domestication trials and farms in Kenya, but little is known about the disease occurrence and associated pathogens. Evaluation was done on disease incidence and severity in the field, isolation and characterization of fungi in family Botryosphaeriaceae was done with comparisons of DNA sequences (ITS and Tef 1-? gene). Pathogenicity of selected isolates was undertaken on baobab, marula and additional agroforestry trees; Vachelia xanthophloea and Calodendrum capense. Nine taxa belonging to genera Lasiodiplodia, Neofusicoccum and Dothiorella were identified co-occurring in both symptomatic and asymptomatic plant material. Seedlings inoculated with isolates L. pseudotheobromae, L. theobromae and N. parvum showed similar symptoms but with various degrees of pathogenicity. These findings confirm that Botryosphaeria spp., occur as endophytes and act as disease agents, with the potential to infect a wide range of trees in Eastern Africa. Further investigation of ecology and impact of this potential threat to agroforestry systems in the African drylands, need to be carried out in order to develop mitigation strategies. Further their occurrence as endophytes may complicate disease management since they may be exchanged with healthy looking materials. This implies that testing of all germplasm is important to ensure that stakeholders receive disease free materials.
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