Cercosporella herpotrichoides Fron on Gramineous Hosts in Ireland

Abstract

CLIMATIC factors are known to affect greatly the prevalence of cereal eyespot caused by Cercosporella herpotrichoides, leading to great variation in disease intensity in different seasons. The work of Sprague¹ shows that susceptibility of various gramineous species is a function of the environment; many grasses became infected in near optimum greenhouse conditions, whereas only a few species were found to be naturally infected during an intensive 7-year search in the north-western United States. These included Bromus and Agropyron species. Agropyron repens, however, was uninfected in the field though susceptible in the greenhouse. The very pronounced climatic effect on disease incidence and on the host range of the causal agent is shown by the prevalence of eyespot on spring-sown cereals in Scotland compared with the drier parts of southern England², and on oat crops in the humid conditions prevalent in Ireland³. There are few records of the natural occurrence of Cercosporella herpotrichoides on grasses in Europe, but in Holland the organism was isolated from Alopecurus myosuroides, Poa pratensis and Apera spica-venti⁴. Hosts found in Finland included Festuca and Poa species as well as Alopecurus pratensis and Agropyron repens⁵, while an isolate was obtained from Agrostis stolonifera at Rothamsted⁶.