An Enrichment Method to Estimate Potential Seedling Disease Caused by Low Densities ofPythium ultimumInocula in Soils

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Abstract
Inoculum densities of P. ultimum of .apprx. 25 propagules (sporangia and ripened oospores) or less per gram of soil can initiate significant seedling disease of alfalfa [Medicago sativa] or cotton [Gossypium hirsutum] when environmental conditions are favorable. However, inoculum densities of P. ultimum are frequently too low to measure directly. Therefore, low densities of inocula were magnified by amending soils with dried cotton leaf fragments (1 mm2) and measuring population enhancement. A direct correlation was found between final inoculum density and disease severity measured in soils before amendment. This enrichment technique may be used to estimate the inoculum potential of P. ultimum in greenhouse or field soils.

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