Temporal spread of wheat dwarf virus and mature plant resistance in winter wheat

Wheat dwarf is a potentially severe disease of winter wheat. The causal agent is wheat dwarf virus (WDV), a geminivirus transmitted by the leafhopper Psammotettix alienus. Field surveys of WDV incidence and vector occurrence were conducted for 4 years in winter wheat fields in central Sweden. The objective was to estimate the extent of primary spread of WDV in autumn, by adult leafhoppers migrating into the fields, and the secondary spread in the following early summer, by the progeny of the immigrants. We also related the rate of virus spread in early summer to the phenological development of the vector and the host plant. Furthermore, the development of mature plant resistance was assessed by inoculating winter wheat plants in various growth stages with infectious leafhoppers. Field survey data indicate that the rate of primary infections did not exceed 5%, and that infection rates increased to up to 50% during the summer. Infection rates ceased to increase as the crops reached the end of stem elongation, and virus transmission experiments showed that plants became resistant to infection at growth stage DC 31 (first node detectable). (C) 2003 Elsevier Ltd. All rights reserved.