Prioritizing nematode species likely to be introduced and threaten agriculture, biodiversity, and forestry in Zambia: A Horizon Scanning Approach

Abstract Introduction of invasive alien species through intentional or unintentional human mediated activities has caused enormous loss of income to economies, affected livelihoods and degraded biodiversity. This has necessitated forward planning through horizon scanning coupled with risk assessment to identify, prioritise, and prevent introduction of alien species that may become invasive (quarantine pests). CABI has developed the Horizon Scanning Tool that utilises information in the CABI compendia to identify pests not yet reported as present in the area at risk. When applied to Zambia, the tool identified 199 candidate nematode species not reported as present in Zambia. The list was refined to focus on species affecting Zambia’s important value chains resulting in a final subset of 130 species that were assessed using agreed guidelines. The possible highest and lowest overall risk scores expected were 250 and 2 respectively however, the highest recorded was 140 for Pratylenchus penetrans , P. thornei , and Rotylenchulus reniformis and the lowest 3, for Peltamigratus luci . A minimum overall risk score of 54 suggested as the cut-off was attained by a proportion of 45% (n = 58) species. The majority (54%, n = 70) of the nematode species were likely to be introduced via the contaminant or stowaway pathways while 41% (n = 53) and 5% (n = 7) solely as contaminants and stowaways respectively. Twenty-one (16%) of the nematode species vectored pathogenic organisms, one bacterium ( Rathayibacter toxicus ) and 11 viruses. Among the viruses vectored, five recorded overall risk scores above 54 and included Tomato ringspot virus (105), Tobacco rattle virus (90), Pea early-browning virus (72), Tomato black ring virus (70), and Arabis mosaic virus (60). One of the viruses, Tobacco ringspot virus was not assessed because it was already reported as present in Zambia. The information from this assessment will guide a number of interventions aimed at preventing the introduction of nematode species that may become invasive or prevent the spread of already introduced species.