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(1) Monocultures and mixtures of Senecio vulgaris (groundsel) and Euphorbia peplus (petty spurge) were grown in 4-litre tubs at a range of population densities and proportions in mixtures and in the presence or absence of the S. vulgaris-specific pathogen Puccinia lagenophorae (a rust). (2) Rust-infection greatly reduced S. vulgaris dry weights, especially of the roots, both in monocultures and mixtures but the yields of both control and rusted S. vulgaris were little changed by competition from E. peplus at any planting density. E. peplus yields were greatly reduced by competition from S. vulgaris but less so in the presence of rust, especially at lower planting densities. (3) The magnitude of rust-induced reductions in the yields of S. vulgaris decreased as the proportion of E. peplus in mixtures increased. However, increases in E. peplus yields when S. vulgaris was rusted were unaffected by species proportions. (4) The inequality (skewness) of the dry weight and plant height hierarchies of S. vulgaris increased with population density and rust infection but were not changed by competition from E. peplus. However, because most E. peplus plants were severely suppressed in mixtures with S. vulgaris, hierarchies were much more unequal than in monocultures. The weight and height of the largest E. peplus plants were greater, and the proportion of very small individuals less, in mixtures with rusted S. vulgaris than with the controls. Hence, if the effects of competition were determined for plants of differing status in the population hierarchy, then it was evident that only the stronger E. peplus individuals were able to grow better when S. vulgaris was rusted. There was no interaction between infection and status on the performance of S. vulgaris in mixtures. (5) S. vulgaris, whether control or rusted, strongly outcompeted E. peplus even though the root dry weights of the latter were often substantially greater. The more rapid early growth and greater height of S. vulgaris appeared to be the primary factors determining the outcome of competition between these species under our conditions. Rust infection had little effect on the competitive ability of S. vulgaris because it reduced plant height only slightly; any reduction in the density of the canopy of rusted S. vulgaris appeared to be significant only at low planting densities. (6) The effects of rust infection on the competitive ability of its host in mixture with E. peplus are compared with the results of previous investigations involving the S. vulgaris-P. lagenophorae system and the possible implications of these results for future studies of the role of pathogens on interspecific competition are discussed.

Aims: To assess the effects of solar UV-B radiation on phyllosphere bacteria of tea leaves in relation to blister blight disease in the field. Methods and Results: The effects of UV-B radiation on the phyllosphere microbiology of tea ( Camellia sinensis) were studied in contrasting wet and dry seasons at a tropical site. Wavelength-selective filters were used to separate the effects of UV-B from those of other factors. Bacterial populations were quantified in relation to the incidence of blister blight disease. Attenuation of UV-B increased the survival of Xanthomonas sp. when populations were not water limited, and increased the incidence of blister blight, but had no effect on Corynebacterium aquaticum. Conclusions: The effects of solar UV-B on phyllosphere bacteria were substantial but depended on both species and interactions with other environmental variables. Xanthomonas sp. was more sensitive to UV-B than C. aquaticum, but this did not result in differences in population density under high radiation conditions (dry season), but only in the wet season when other factors were not limiting. Significance and Impact of the Study: The role of UV-B on leaf surface microbiology in the tropics is marked but depends on other conditions, and the contrasting UV-B responses of different organisms can be masked by other limiting factors. [ABSTRACT FROM AUTHOR]

(1) Seedlings of groundsel (Senecio vulgaris L.) were planted into tubs of soft sunk to the level of the normal soft surface at a field site in late spring. Plants in half the tubs were inoculated with rust fungus (Puccinia lagenophorae Cooke). (2) Infection inhibited the expansion of leaves and reduced plant dry weight. The pattern of partitioning of dry weight between organs was little changed. Senescence occurred earlier and more rapidly in rusted plants than in controls. (3) Cumulative production of capitula was inhibited by 43% in infected plants the number of florets per capitulum was also slightly lower in infected plants than in control plants, resulting in a 46% reduction in overall floret production. (4) Little seedling mortality occurred, but mortality of mature, flowering plants began earlier and was more rapid in inoculated populations than in controls. This greater mortality combined with the reduced growth of infected individuals resulted in substantially lower vegetative production in rusted populations. (5) Infection reduced the percentage of plants which flowered, and cumulative production of capitula was some 60% lower in infected than in healthy populations. Cumulative floret production was 64 000 m[sup -2] in control populations, but only 25 000 m[sup -2] in infected populations. (6) Responses of the summer population to rust are contrasted with the previously reported responses to rust of an over-wintering population. [ABSTRACT FROM AUTHOR]

Examines the life of the Vashons and their contribution to the United States history as nationalist, abolitionist, linguist, educator and actors in the pursuit of racial equality. How they earn the respect of the Black society; Acquaintances with known nationalists and abolitionists; Vashons' legacy.