The Impact of a Pathogen (Puccinia Lagenophorae) on Populations of Groundsel (Senecio Vulgaris) Overwintering in the Field: II. Reproduction

Publisher Website
Google Scholar
Abstract
(1) Reproduction during the spring was studied in monocultures of groundsel (Senecio vulgaris L.) overwintered in the field. In the autumn, populations had been either inoculated with a fungal pathogen (Puccinia lagenophorae), which caused rust disease, or left as controls. The effects of rust infection were examined in relation to status within a hierarchical population (assessed by sub-classes buds on shoot dry weights). (2) In control populations, the first capitulum beads were produced in late February. The onset of flowering became progressively delayed as status within the hierarchy declined. In all sub-classes of the population, rust infection during the previous autumn delayed flowering in the spring by 1-2 weeks. (3) The percentage of plants within a sub-class that were reproductive (bore buds or capitula) in March and April declined as status in the hierarchy decreased. In classes of comparable status, fewer plants flowered in inoculated than in control populations. (4) In April, sub-classes with low mean dry weights in both populations produced fewer buds and mature capitula. The number of florets per capitulum were also decreased in lower status classes. Rust inhibited all measured components of reproduction in all classes. (5) During May, many large control plants senesced and their reproductive output declined. Thus, most sub-classes of control populations produced a similar number of florets. In contrast, vegetative growth in inoculated populations continued and all measures of reproduction were far greater in the class of highest status than in any other. There was a seven-fold increase in the contribution of this class to floret production (70%) relative to its frequency in the original population. In control populations, there was no more than a two-fold difference between floret production and frequency in the parent population. (6) Infection resulted in no significant change in the percentage of florets that developed into seed or in the viability of seed. (7) Over the duration of this experiment, the potential seed production of control populations (calculated from capitulum production, florets per capitulum and percentage seed set) was > 460,000 seeds m-2. Populations that had been rust-infected in the autumn potentially produced 183,000 seeds m-2, a reduction of > 60% compared with controls.