Pathogenicity ofPythiumspp. to seeds and seedling roots

Abstract

Abstract Sixteen species of Pythium, two atypical species, and nine heterothallic isolates of Pythium were tested for their ability to infect the roots of tomato seedlings in a laboratory assay. Isolates of the same species, with the exception of P. megalacanthum, were also tested in a glasshouse trial for capacity to cause damping-off of germinating seeds and seedlings of tomato cv. ‘Potentate’, pea cv. ‘Victory Freezer’, and Ipomoea violacea L. cv. ‘Heavenly Blue’. According to their capacity to infect seeds or seedling roots in soil, the Pythium spp. tested were classified as follows: 1. Highly pathogenic—P. acanthicum, P. debaryanum, P. irregulare, P. spinosum, P. splendens, P. ultimum, P. (?) ultimum;2. Moderately pathogenic—P. afertile, P. aquatile, P. middletonii, P. monospermum;3. Mildly pathogenic—P. anandrum, P. (heterothallic isolates) Nos 1 and 4, P. torulosum; 4. Not pathogenic—P. echinulatum, P. inflatum, P. rostratum, P. (?) rostratum Pathogenicity of the Pythium spp. tested was similar on tomato seedlings in the laboratory assay and germinating tomato seeds in soil.