Wintering of the biotrophic fungus Puccinia lagenophorae within the annualplant Senecio vulgaris: implications for biological weed control

Epidemics of the obligate biotrophic fungus Puccinia lagenophorae might be used to control populations of the annual plant, groundsel, Senecio vulgari s. Insight into the mechanisms of survival of P. lagenophorae over winter m ay help to explain the number of inoculum sources, and their strength (asse ssed by number and size of pustules), present in an S. vulgaris population in spring, indicating the probability and rate of progress of a subsequent epidemic. Results of the study indicated survival of the rust as mycelium w ithin the host over winter. Survival outside the host is unlikely, because aecidiospores lost their capacity to germinate over winter and teliospores have not been reported to be infectious. Survival of S. vulgaris plants ove r winter was reduced by rust infection in autumn. The mortality of S. vulga ris was 30-100% depending on the date of infection. All plants infected ear ly in autumn died but those infected late in autumn were more likely to sur vive. In turn, poor survival of the host impacted on the survival of P. lag enophorae over winter. Consequently, the results of the study suggest that no inoculum sources, or only a kw weak ones, are present in vulgaris popula tions in spring. This suggestion was supported by observations of an S. vul garis population at a ruderal site. Therefore, research on biological weed control should focus on increasing the negative impact of P. lagenophorae o n S. vulgaris populations while augmenting the probability of survival of t he rust over winter to start new epidemics in spring.