WATER STRESS MODIFIES INTRASPECIFIC INTERFERENCE BETWEEN RUST (PUCCINIA LAGENOPHORAE COOKE)‐INFECTED AND HEALTHY GROUNDSEL (SENECIO VULGARIS L.)

Abstract

SUMMARYPopulations of groundsel {Senecio vulgaris L.) were grown in the field in bottomless containers which allowed roots to penetrate freely into the natural soil profile. The 36 plants within each population (equivalent to 1250 vcC"^) were either all inoculated with the rust Puccinia lagenophorae Cooke, all rust free, or were a 1:1 mixture of the two. Rain was excluded from all populations by small shelters. Half the populations were subjected to mild drought, whilst remaining populations were well-watered. Rust significantly reduced shoot dry weights, especially in droughted populations. The frequency distributions of shoot dry weight showed significant inequality (were strongly skewed) in all treatments and populations. Inequality of the frequency distribution of shoot dry weight was increased in rusted populations because infection increased the proportion of suppressed individuals. Again the effect of rust was most pronounced under conditions of drought and particularly in mixture. Rust significantly lowered mean shoot water potential {xj/) in dry monocultures and in both wet and dry mixtures. Values of \J/ at harvest in suppressed, rusted individuals in mixtures were often highly negative. Compared with dry monocultures, water stress in mixtures was ameliorated in the healthy, but exaggerated in the rusted, components. The more negative values of ij/ in rusted populations were the result of changes in frequency distributions as well as in mean values. Under dry conditions status in the dry weight hierarchy was closely correlated with xjf. These changes are interpreted as refiecting the reduced ability of the root systems of rusted plants to compete for limited water.The competitive ability of control over rusted groundsel, as measured by relative crowding coefficient {K^^), was 1 09 under well-watered conditions but increased to 1-51 under drought. In both well-watered and droughted populations, the greater impact of rust on the population hierarchy of mixtures was refiected in the inverse relationship between the status of sub-classes, based on shoot weight and class K^^^. It is concluded that water stress probably plays a crucial role in determining the impact of rust on mixed populations in the field.

EVOLUTIONARYECOLOGY OFPLANTDISEASES INNATURALECOSYSTEMS

“…Rust infection directly affected the competitive ability of the host beyond the effects of infection on plant growth. Similar effects of rust infection have been found for intraspecific competition, including between infected and noninfected groundsel (175) and between susceptible and resistant skeletonweed (Chondrilla juncea, Asteraceae) (51). Research of this sort is sorely needed outside of agroecosystems.…”

“…Specialist pathogens like rusts can affect the competitive interactions between susceptible and nonsusceptible plant species or genotypes. Paul & Ayres found that inoculation of groundsel (Senecio vulgaris, Asteraceae) with the rust Puccinia lagenophorae significantly reduced groundsel growth, and reduced the competitive ability of groundsel with both lettuce (Lactuca sativa) (175) and the co-occurring weed petty spurge (Euphorbia peplus, Euphorbiaceae) (174). Rust infection directly affected the competitive ability of the host beyond the effects of infection on plant growth.…”

Interactions among weed, insect, and common rust treatments in sweet corn

“…include host plants in well-watered conditions (Paul and Ayres 1987) and soils low in nitrogen (Paul 1989).…”

Crown rust affects plant performance and interference ability of Italian ryegrass in the post‐epidemic generation

“…(1984). The method has particular value in separating and describing the magnitude of intra‐ and inter‐specific interference and has been used extensively in previous studies examining the impact of pathogens on plant interference (Paul and Ayres, 1987a,b; Paul, 1989). The magnitude of intra‐specific interference was determined as the relative monoculture response ( R m ): where Y p is the total projected yield in the absence of interference (calculated from the initial slope of the yield density curve) and Y m is the measured monoculture yield.…”