Validation of extraction methods for diagnosis of the stem and bulb nematode Ditylenchus dipsaci

The stem and bulb nematode, Ditylenchus dipsaci (Kuhn) Filipjev, is a serious threat to many important crops worldwide, including garlic. For this crop, effective detection methods are essential to discard infected seed cloves and avoid contaminated fields. This study compared the efficacy of different extraction methods for soil and garlic tissues infested with this nematode. The Baermann pan, Baermann funnel and sugar flotation were compared on four types of soil (sand, loam, silty clay and muck soil) previously inoculated with D. dipsaci. There was no significant difference between the Baermann methods which recovered an average of 57.2% of the D. dipsaci from soil. The sugar flotation only captured 20.8% of the D. dipsaci added to the soil. Slight variations were observed between soil types, especially when using the Baermann methods to extract nematodes from silty clay or loam. The two Baermann methods were also compared to a sonication technique for the extraction of D. dipsaci from garlic stems, leaves and bulbs. The Baermann methods showed greater sensitivity at low population density while the sonication allowed the recovery of more D. dipsaci at high density. Overall, this study confirmed the validity of the Baermann pan and funnel methods for the extraction of D. dipsaci from soil and garlic tissues. The sugar flotation and sonication procedures yielded significantly less D. dipsaci or had a poorer sensitivity and were not considered adapted for the diagnosis of this species from soil or garlic tissues.