Soil Nematodes of Brassica rapa: Influence of Temperature and pH

Abstract

An investigation of the soil nematodes associated with Brassica rapa and the effects of temperature and pH on their populations was carried out. The nematodes recovered were categorized into three ecologically functional groups; Nitrogen Releasing Nematodes (NRN, bacterial- and fungal- feeders), Plant-Parasitic Nematodes (PPN), and Pest Suppressor Nematodes (PSN, Carnivorous or predatory (Ca) and Omnivorous (Om), nematodes). While over 67% of the NRN were bacterial feeding nematodes (Ba 2 ), dominated by Plectus and Acrobeloides; over 65% of the PPN were contributed by the Pl 3 nematodes dominated by Helicotylenchus mucronatus and Rotylenchus buxophilus ; and the PSN were dominated (over 63%) by the omnivores (Om 4 ; Mesodorylaimus and Dorylaimus). Populations of all the nematode categories recovered fluctuated significantly (P < 0.01) during the sampling period. All the nematode groups were similarly weakly negatively correlated with pH and temperature. Approximately 1000 H. mucronatus nematodes/100 mL of soil was recorded. This is 10x the value for which the management of PPN is recommended. The entire soil nematode food web structure was represented in the nematodes recovered, all groups of nematodes responded similarly to environmental changes, all groups of nematodes tended to be acidophilic and thermophobic, and the PPN could potentially be a threat for profitable B. rapa production.