Evidence from ascospores for host restriction in Claviceps purpurea

Abstract

On the assumption that there may be significant differences in the length of ascospores of Claviceps purpurea from different hosts, and that such differences are primarily under genetic control, a comparative study was made of 85 samples of ascospores obtained from ergots that had been collected from 28 species of British grasses belonging to 24 genera and 10 tribes. Because it is shown that different samples of ascospores from the same hosts could reasonably represent parts of the same population, it is possible to separate populations of ascospores obtained from different hosts into groups by using Duncan's multiple range test. On the basis of the mean length of their ascospores, the population means for 17 different grasses, covering 16 different genera, may be divided at a probability level of 005% into three groups. One group (with ascospores averaging > 100 μm long) includes the strains of C. purpurea infecting Triticum aestivum, Glyceria fluitans and Brachypodium sylvaticum , a second group (with ascospores averaging 79–91 μm long) contains the strains infecting all the other grasses included in the test except Deschampsia caespitosa , which is the only member of a third group (with ascospores averaging C. purpurea infecting the four abovementioned grasses are host-restricted. This conclusion is discussed in relation to the results of cross-inoculation experiments, and alkaloid analyses of ergot sclerotia, carried out by other workers.