Synergistic damage by interactions between Ditylenchus dipsaci and Rhizoctonia solani (AG 2-2IIIB) on sugar beet

The aim of this study was to investigate interactions between Ditylenchus dipsaci and Rhizoctonia solani. Both pathogens are known to cause problems in the primary sugar beet production areas in Germany. Furthermore, the organisms' ecological niches in the soil and on the beet overlap. Hence, it is probable that these parasites interact and have a deleterious synergistic impact on sugar beet production. The stem and bulb nematode, D. dipsaci, is a migratory endoparasite that penetrates the sugar beet seedling during the spring when temperatures are low. The main symptoms include distorted, bloated petioles and leaves. The fungus causing Rhizoctonia crown and root rot, R. solani, enters the plant at the beet-leaf transition zone. Synergistic damage was obtained when both organisms occurred on the same plant. Hyperspectral leaf reflectance data was used to calculate a vegetation index, the Normalised Difference Vegetation Index (NDVI), which could successfully be used to discriminate between growth reduction caused by R. solani and by dual inoculation (disease complex). High correlations were observed between ratings of disease symptoms and the vegetation index over a time series of seven weeks.