Characterisation of Pythium Species Associated with Damping-Off of Vegetable Seedlings in Market Gardens of Lagos and Ogun States, South West Nigeria

Damping-off of vegetable seedlings caused by Pythium species is a persistent problem in market garden nurseries supplying transplants to urban and peri-urban vegetable growers in Lagos and Ogun States. The taxonomic composition of Pythium species responsible for damping-off in this high-value production system has not been characterised using phylogenetic methods, limiting the specificity of management recommendations. This study characterised Pythium isolates from damping-off affected nurseries across 30 market garden sites in Lagos and Ogun States, targeting tomato, pepper, amaranth, and cabbage. Morphological characterisation of oogonia, antheridia, and sporangia was supplemented by molecular identification using internal transcribed spacer and cox2 gene sequencing. Phylogenetic analysis using maximum likelihood trees placed isolates in eight Pythium species, with P. aphanidermatum and P. irregulare as the most frequently isolated taxa, collectively accounting for 67 percent of recovered isolates. P. myriotylum, P. ultimum, and four additional species each contributed less than 15 percent. Host preference analysis revealed that P. aphanidermatum dominated on tomato and pepper, while P. ultimum was disproportionately represented on cabbage damping-off cases. Species diversity was significantly higher in wet-season nurseries compared to dry-season irrigated nurseries, suggesting seasonal community turnover. This multi-species characterisation provides a species-resolved framework for evaluating fungicide and biocontrol efficacy across Pythium assemblages relevant to South West Nigerian market gardening conditions and represents the first such dataset for the region. Keywords: Pythium, damping-off, vegetable seedlings, market gardens, South West Nigeria.