Pythiumspecies in market gardens and their pathogenicity to fourteen vegetable crops

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Abstract
Seedlings of 14 major vegetable crops showing symptoms of damping-off or ill-thrift were collected from 85 North Island [New Zealand] market gardens during autumn and spring 1973. Of 4070 specimens 18% yielded isolates of Pythium. These included 9 spp. of Pythium, 1 atypical species and many heterothallic forms. P. coloratum Vaartaja was recorded for the 1st time in New Zealand. A single isolate of each species of Pythium and 1 heterothallic form were tested for their ability to infect germinating seed and seedlings of the same 14 crops in inocualted soil. On the basis of virulence and host range, the Pythium isolates were classified as highly pathogenic: P. afertile Kanouse and Humphrey, P. irregulare Buisman, P. utimum Trow; moderately pathogenic P. debaryanum auct. non Hesse. P. coloratum Pythium (heterothallic form); and slightly pathogenic: P. acanthicum Drechsler, P. echinulatum Matthews, P. rostratum Butler, P. (?) rostratum, P. torulosum Coker and Patterson. Crops tested showed a wide variation in their susceptibility to infection by the 11 isolates. Germination and survival of brussels sprouts were signficantly reduced by 10 isolates; only P. ultimum significantly affected asparagus.