On Heterodera schachtii, with special reference to the Oat race in Britain.

Extract

In August 1933, Mr. W. Usher, Assistant Agricultural Organiser for Shropshire, called the writer's attention to a partial failure of spring oats at Montford Bridge, Shrewsbury. The Advisors in Agricultural Chemistry and Mycology for the West Midland Province had previously inspected the crop and had failed to find evidence of any manurial deficiency or fungal attack likely to be responsible for the failure. A careful examination of the roots of unthrifty plants by the writer, however, showed that they were heavily attacked by Heterodera schachtii in all stages of development. Further observations revealed that although the cysts of this eelworm were present on the oats over the whole field, very little disease was apparent on the plants except on those growing in certain “sick” areas. The plants in these affected patches were very much stunted, with small ears and shrivelled grain, the foliage was pale in colour and the lower leaves in most cases dead, the roots were excessively branched and rather heavily infested with H. schachtii. It would appear that the infection by the eelworm in the present instance is one of long-standing since cereal crops, particularly oats, had been almost a complete failure for some years in these “sick” areas. It is also significant that the infested areas which were of varying size had in recent years, according to the farmer, greatly increased in extent and that with each successive oat crop new affected patches had made their appearance. In view of this apparent old-standing infection, a special search was made for the presence of H. schachtii on cereal crops in other fields in the neighbourhood. It soon became evident in the course of this preliminary search that H. schachtii was already well established on several farms in the district and that besides oats, wheat and barley were also subject to infestation. The investigation was continued the following year when all cases of failing cereal and other cultivated crops reported in Shropshire were examined. In addition, a thorough examination was also made of the roots of apparently healthy looking crops in the immediate neighbourhood of those failing ones that were found infested with H. schachtii. Later in this paper the general field observations made during this investigation are described, together with an account of some cultural experiments that were carried out with a view of determining whether the race of H. schachtii found parasitic on cereals in Shropshire is capable of attacking other plant species of economic importance and whether this race is distinct from those commonly found in the County on potatoes and peas, respectively.