Soil chemical properties influence abundance of nematode trophic groups and Ralstonia solanacearum in high tunnel tomato production

Background: Plant parasitic nematodes (PPNs) and bacterial wilt (Ralstonia solanacearum) are serious soil-borne pests in tomato (Solanum lycopersicon L) production in high tunnels. This study was undertaken to determine effects of soil chemical properties on their abundance. Method: Soil samples were collected from 32 high tunnels in the sub-counties: Gatundu North, Gatundu South, Juja, Thika, Ruiru and Kiambu, Kenya, from January to November 2016. Nematodes genera, R. solanacearum and soil chemical properties were evaluated from composite soil samples collected from the high tunnels. Results: The soil pH and N, P, K, Ca, Mg, Na and Cu varied across sub-counties. Twenty-four nematode genera including 14 PPNs, 5 bacterivores, 3 fungivores and 2 predators were recovered from soil samples. The genera Meloidogyne, Alaimus, Aporcelaimus and Mononchus were the most abundant PPNs, bacterivores, fungivores and predators, respectively, and differed across sub-counties. The abundance of Meloidogyne spp. and R. solanacearum was higher in Gatundu North than in the other sub-counties. There was a strong, positive correlation between Meloidogyne spp. (second stage juveniles counts) population and R. solanacearum (cfu∙mL-1) with soil N and P, and a weak negative correlation with soil pH, EC, Zn and Cu. Fungal feeders exhibited a strong negative correlation with soil pH and Ca; predators, bacterial feeders, and PPNs had similar correlations with N, P and Ca, respectively. Conclusion: Soil chemical properties affect abundance of beneficial and phytoparasitic nematodes and R. solanacearum, which varies with location.