Blind‐seed disease of rye‐grass (Phialea temulenta Prill. & Delacr.)

A short account of the present state of knowledge regarding the disease is given. Methods for the examination of seed samples for the estimation of infection with Phialea temulenta are described; the most suitable is the examination of each seed microscopically after the removal of one or both glumes, for the presence of macroconidia. The causal organism was isolated by germinating macroconidia and ascospores and also from mycelium within the seed. Its growth on media confirmed previous indications that Pullularia pullulans was not the parasite responsible for the disease. Growth in culture is slow, and the production of numerous mucilage‐cove red macroconidia, the formation of which was observed, gives a slimy appearance to the culture on most media. The fungus and its life history are described. Inoculation experiments carried out in 1940 and 1941 proved the pathogenicity of Phialea temulenta and the saprophytic nature of Pullularia pullulans. Italian rye‐grass, commercial perennial rye‐grass and two strains of pedigree perennial rye‐grass were all found to be susceptible to attack when inoculated at flowering time with either macroconidia or ascospores. Using commercial perennial rye‐grass the amount of infection was very much reduced when inoculations were carried out after flowering had ceased. The correlation coefficient between percentage infection and germination was calculated from the results of inoculation experiments carried out in 1941 and for samples of pedigree perennial rye‐grass (S24) seed received for examination in 1940, 1942 and 1943. In all cases there was a highly significant, negative correlation indicating that infection with Phialea temulenta resulted in reduced germination. The fungus has been isolated from Festuca ovina L., Agrostis canina L., A. palustris Huds., Poa pratensis L., Holcus lanatus L. and Cynosurus cristatus L., while Festuca elatior L. and Poa trivialis L. were successfully inoculated in 1943 using macrospores of the fungus. The control of the disease by the breeding of resistant strains and by crop management is discussed. There is little possibility of Phialea temulenta being viable in the seed if an over‐year sample is sown. In field experiments hot‐water treatment of the seed prevented the production of apothecia, but infection occurred owing to the dispersal of ascospores from other plots. A later experiment indicated that the disease is widespread in pastures, waste ground and hedgerows so that the sowing of disease‐free seed will not guarantee a resultant healthy seed crop. It has been shown that contaminated and diseased seed may be freed from infection by hot‐water treatment, whereas the use of organo‐mercury disinfectants applied dry or by the short wet method were only partially effective. Treatment with hot water for 15 min. at 50d̀ C. following a 4 hr. pre‐immersion in tepid water, or for 30 min. at 50d̀ C. without pre‐immersion provided complete control, and the germination of the seed was in no case impaired when it was thoroughly dried immediately after treatment.