Inoculum potential and host range of Polymyxa betae and beet necrotic yellow vein furovirus1

Abstract

The inoculum potential of Polymyxa betae and BNYVV was studied from 52 random samples of Belgian soils and 10 samples from other European countries, by culture of bait plants in tubes under controlled conditions on serial dilutions of the soils in sterile sand. P. betae was detected in all samples within the range of 0.01 to 27.1 infection units per g of soil. BNYVV was detected by ELISA on root extracts of bait plants grown on three Belgian soil samples. All the tested samples from rhizomania‐infested areas in France, FRG, the Netherlands, Switzerland and Austria, were found to be infested by BNYVV by this technique. For BNYVV survey, the plant bait technique appears more reliable than the analysis of rootlets collected in the field and observation of external symptoms in case of low BNYVV infestations or non‐expression because of unfavourable environmental conditions. P. betae isolates from various origins heavily infected Beta spp. but only moderately spinach. Chenopodium album was slightly infected by 2 of the 7 isolates, C. murale by 4 of them.