EXTENT OF DISEASE IN POPULATIONS OF HETERODERA, WITH SPECIAL REFERENCE TO H HETERODERA-SCHACHTII

Analysis was made of the extent of disease in 112 populations of Heterodera schachtii, comprising 88 populations of cysts obtained from soil samples and 24 populations of females and cysts taken from host roots. Overall, some 14% of full cysts taken from soil were diseased, although much variation was found. About half of the cysts were substantially and half partially diseased. Where beet monoculture had long been practised, overall disease was approximately doubled. Less than 50% of diseased cysts were parasitised by recognised egg pathogens and nearly the same proportion showed symptoms of lysis, coagulation or decay, the causes of which could not be ascertained. The remainder contained unexamined or miscellaneous fungi and a few showed oily degeneration. Disease in 10 populations of cysts from roots was higher than in cysts from soil. In females from roots it was especially variable, for most diseased females were invaded by one or two specific fungal pathogens in whose absence all were healthy. Examination of six populations of Heterodera avenae indicated the extent and nature of disease was not dissimilar from that in H. schachtii. The pathogens, which were all fungi, and the disease symptoms of uncertain origin found in cysts and females of H. schachtii are briefly summarised. Copyright © 1979, Wiley Blackwell. All rights reserved