Population dynamics of the annual plant Senecio vulgaris in ruderal and agricultural habitats

Low genetic differentiation among seasonal cohorts inSenecio vulgarisas revealed by amplified fragment length polymorphism analysis

“…Assuming that seasonal specialization of cohorts is absent, we expect selection to favour high phenotypic plasticity enabling plants to survive and reproduce under a wide range of environmental conditions (van Tienderen 1991), including dry and warm conditions in summer and wet and cool conditions in spring and autumn. Indeed, in an earlier study with S. vulgaris we found that populations from agricultural habitats, which are characterized by temporally variable inputs of nutrients due to fertilizer application, exhibited higher plasticity in response to fertilization compared with populations from ruderal habitats, in which nutrient supply is more stable over time (Leiss & Müller‐Schärer 2001; Steinger et al . 2002).…”

“…Seasonal genetic differentiation would have been expected if there is heritable variation in the timing of germination leading to asynchronous periods of flowering among seasonal races and therefore very low levels of gene flow. For example, in S. vulgaris , some seeds germinate in autumn and overwinter as juvenile plants, whereas others germinate in spring (Leiss & Müller‐Schärer 2001). Autumn cohorts may have a head start and flower already in early spring, while spring cohorts may delay flowering until summer.…”

“…Studies on the population dynamics of common groundsel, S. vulgaris , have demonstrated that in temperate climates population density shows important fluctuations over the year with densities being highest in late spring, mid‐summer and late autumn (Vack 1992). In Switzerland, Leiss & Müller‐Schärer (2001) observed three such distinct cohorts of flowering plants. It can be asked whether each cohort of S. vulgaris simply arises from seeds shed by the previous generation, or whether seasonal genetic differentiation may occur resulting from genetically based variation in the timing of germination.…”

“…In this respect, knowledge of the amount and distribution of genetic variation in S. vulgaris populations is important because it affects biocontrol success by influencing disease development and spread of the pathogen, on the one hand (short‐term effect), and the development of resistance to the pathogen, on the other hand (long‐term effect). Studies of the genetic structure of S. vulgaris populations have so far concentrated on the spatial aspect in relation to habitat type and population size (Leiss & Müller‐Schärer 2001; Müller‐Schärer & Fischer 2001; Steinger et al . 2002) whereas little attention has been given to temporal variation within sites.…”

Modeling the impact of a biocontrol agent, Puccinia lagenophorae, on interactions between a crop, Daucus carota, and a weed, Senecio vulgaris

“…The fungus survives as mycelium within plants of S. vulgaris over winter, aecidiospores are produced within the aecidia in spring, and these aecidiospores spread to other parts of the infected plants or other plants within a population. The mortality rate of P. lagenophorae over winter is very high and, in general, no or only a few infected S. vulgaris plants are present to serve as inoculum sources for a P. lagenophorae epidemic within a S. vulgaris population in spring (Frantzen and Mü ller-Schärer, 1999;Leiss and Mü ller-Schärer, 2001;Paul and Ayres, 1986). Increasing the number of infected plants, i.e., the number of inoculum sources, within a S. vulgaris population in spring is one way to induce and stimulate P. lagenophorae epidemics controlling S. vulgaris.…”