Using a selective fast turn-around bioassay for population density determination of Heterodera schachtii

Abstract

In Central Europe, Heterodera schachtii is kept below threshold levels by cover-cropping with resistant crucifers and crop rotation with non-hosts. Determining population densities of H. schachtii in soil is critical when implementing resistant and tolerant sugar beet cultivars in integrated pest management (IPM) programmes. Soil extraction of the cysts followed by egg counts or extraction of the second-stage juveniles (J2) facilitated by the chemical stimulant acetox can be unsatisfactory in mixed field populations of cyst nematodes. In contrast to H. schachtii, nematodes typically present in sugar beet soils, e.g., Globodera pallida, G. rostochiensis, H. avenae, H. filipjevi, Meloidogyne hapla, M. incognita and Pratylenchus penetrans, rarely penetrated radish roots. In this bioassay, equivalents of 50 g of soil dry weight were adjusted to 10-20% moisture, seeded with Raphanus sativus cv. Saxa 3, and incubated at a day-night (16:8 h) cycle of 28/23°C for 4 days before J2 in radish roots were enumerated. In different soil types, penetration by H. schachtii reflected the inoculation levels. When inoculated with mixes of H. schachtii with H. avenae or H. filipjevi, counts of H. schachtii were similar to those in soils with H. schachtii only. When comparing three methods in three soils spiked with H. schachtii cysts, the bioassay and the extraction method were lightly impacted by the soil texture but results of the acetox method varied with texture. When implemented for field samples from Franconia, the radish bioassay and the acetox method provided results related to cyst and egg extraction data. The radish bioassay provided a quick and easy method for quantifying H. schachtii in the presence of other nematode species in a wide range of soil types. Including this assay in IPM programmes may serve as an alternative to standard methods and will improve the decision making in sustainable production systems.