A guide to methods of isolation and preservation of Pythium is pr~vid~d.A key to the 27 species of Pythium so far record~ from New Zealand IS.glven. The following species are described and illustrated:

Sixteen species of pythium, two atypical species, and nine heterothallic isolates of rythium were tested for their ability to infect the roots of tomato seedlings in a laboratory «,say. Isolatcs 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: (i) Highly pathogenic-Po acanthicum, P. debaryanum, P. irregulare, P. spinosum, P. splendens, P. ultimum, P. (7) ultimum;. ii)Moderately pathogenic--P. ajertile, P. aqua tile, P. middletonii, P. monospermum; (iii) Mildly pathogenic-Po anandrum, P. (heterothallic isolates) Nos 1 and 4, P. torulosum; ~iv)

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