Quick, Watson, the blots!

Abstract

Graminicolous Claviceps spp. other than C. purpurea are tribe-specific in their host ranges, whereas C. purpurea (including C. microcephala) is recorded from grasses belonging to at least seventeen tribes. On the assumption that significant differences in conidial size and shape are indicative of speciation taking place within C. purpurea, a comparative study has been made of i o i honeydew samples from thirty-one species of British grasses belonging to twenty-eight genera and thirteen tribes.Samples showed considerable variation in size and shape of conidia but, after applying Bartlett's test for homogeneity of variance, it is claimed that independent samples collected from different specimens of the same host could reasonably have come from the same population. By contrast, spore populations from different hosts are shown by the analysis of variance and covariance to differ significantly in both sizeand shape. The results of atransplant experiment, in which conidia were grown in culture from slices of sclerotia with a known size of honeydew conidia, indicate these differences to be primarily under genetic control. Conidial populations from different hosts may therefore be divided into groups by applying Duncan's multiple-range test. The groups are considered sufficiently distinct to provide morphological evidence for host restriction in C. purpurea. It is noteworthy that a close similarity exists between the species-composition of these groups and the ‘biologic forms’ proposed by Stäger from cross-inoculation experiments.