A detailed survey of the geographical distri~ution of the potato eelworm disease in the central and south regions of Chile is presented. This disease is produced by Heterodera marioni.
From this survey it is concluded that the mast infested areas are found in the central region. From there heavy infestation extends southward to the Province of Cautin.
Provinces of Osorno, Llanquihue and Chiloe, the most important seed producing region, are practically free from the disease with the exception oí three small sections in Rupanco, Puerto Octay and Frutillar.
The absence of the nematode was noticed in all the determinations made in Chiloe and adjacents islands. If this condition prevail in the rest of the Province of Chiloe, it isa very important factor for the production of certified potato seed.
The purpose of this survey was to know the exact distribution of the nematode to take proper measures against the recent outbreak of the disease in Rupanco, Frutillar and Puerto Octay.
Neither the prohibition against cultivation of contaminated soils in the south, nor the prohibition against transportation of tubers to other regions is advisable because the disease is already widely spread in the central region.
The most appropriate remedy, already adopted by the Department, is the production and selection of potato varieties with genetic resistance.
The result obtained in the testing for eelworn reaction with introduced and chilean potato varieties and seedlings are given in detail.
The test of reaction was made in as soil heavy infested with the nematode. Its infestation was evident because of having diseased tubers during previous seasons.
The test consisted of plots containing 4 plants of each variety with two replications each year. Each tuber was planted at a distance of 0.60 m. in the row and 1 m. between rows. Every other row was planted with the susceptible check variety, in this case, the standard "Corahila larga".

1 Ingeniero Agronómo, Jefe de la Sección Plantas Industriales y Hortícolas, Departamento de Investigaciones Agrícolas, Ministerio de Agricultura