Plant parasitic nematodes on soybean in expanding production areas of temperate regions
Soybean [Glycine max (L.) Merrill] is the most economically important legume in the world. One of the main yield limiting factors is plant parasitic nematodes, such as Heterodera glycines, Meloidogyne incognita or Pratylenchus brachyurus, which cause severe damage in the main production regions of soybean around the world. For Germany, soybean is still a relatively newly cultivated crop and so far, no information about the occurrence and damage potential of plant parasitic nematodes on soybean is available for this region. For a successful growth of soybean, farmers need to understand, which plant parasitic nematodes can be of risk for soybean production. Within this respect, the objective of this study was to describe the spectrum and abundance of plant parasitic nematodes occurring on soybean under temperate conditions in Germany. Data were collected from farmer fields and experimental sites throughout Germany between 2014 and 2015. Representative soil samples were taken before planting and shortly after harvest. Plant parasitic nematodes were extracted by centrifugal floatation, and identified morphologically to genus level. Selected individuals of Pratylenchus were further identified to species level based on COI gene sequences. The population dynamics of Pratylenchus penetrans and co-occurring plant parasitic nematodes on soybean cv. Merlin was studied in microplots. Finally, the impact of P. penetrans affecting nitrogen fixation by the symbiotic bacterium Bradyrhizobium japonicum was studied in greenhouse experiments. Our findings indicated that Pratylenchus is widely spread in soybean fields in Germany. Main species were P. neglectus and P. crenatus and to a lesser extent P. penetrans. In the microplot experiment, nematode multiplication was highest for P. penetrans, followed by Rotylenchus robustus and Paratylenchus projectus. Infection of soybean by P. penetrans significantly reduced nitrogen fixation as indicated by lower numbers of bacteroids and reduced concentration of ureides In conclusion, Pratylenchus spp. are considered to be the most threatening plant parasitic nematodes for soybean production under the temperate conditions of Germany.