Detection and characterisation of bean yellow mosaic virus in corms of Gladiolus grandiflorus

Bean yellow mosaic virus (BYMV) could not be detected in corms of infected gladioli unless they were cut 6–60 days before testing. Detection after cutting was time- and temperature-dependent, was restricted to the cut area, and varied among cultivars. Virus could be recovered from uncut corms after storage for over 2 yr at 6 ^oC. BYMV in corms could be detected by enzyme-linked immunosorbent assay and by immunosorbent electron microscopy with antisera against a gladiolus isolate purified from gladiolus leaves or corms. It could not be detected in corms with antiserum against a lupin isolate which readily detected BYMV in gladiolus leaves. Protein subunits of corm-BYMV banded in SDS-PAGE as a single 31 000 dalton polypeptide, while leaf-BYMV produced a major 34 000 and several smaller polypeptides. Both major polypeptides retained the different serological properties of their source virions but their peptide maps indicated a common origin. It is suggested that the smaller polypeptide from corm-BYMV is a stable cleavage product of the intact leaf-BYMV coat subunits. Corm-BYMV, although lacking some of the antigenic properties of leaf-BYMV, was still infective.     

Disturbance, interspecific interaction and diversity in metapopulations

Metapopulation diversity patterns depend on the relations among the timescales of local biological interactions (predation, competition), the rates of dispersal among local populations and the patterns of disturbance. We investigate these relationships using a family of simple non-linear Markov chain models. We consider three models for interspecific competition; if the species are identified with early and late successional species, the models describe the facilitation, inhibition and tolerance models of ecological succession. By adding a third competing species we also compare transitive competitive hierarchies and intransitive competitive networks. Finally, we examine the effects of predation in mediating coexistence among competing prey species. In each model we find circumstances in which biotic or abiotic disturbance can increase both local and regional diversity, but those circumstances depend on the various timescales in the model in ways that arc neither obvious nor trivial.