Section 11
Chapter 10,244

Biological control of Pythium damping-off and root rot of greenhouse-grown geraniums and poinsettias

Filonow, A., B.; Dole, J., M.

Proceedings of the Oklahoma Academy of Science 79: 29-32


ISSN/ISBN: 0078-4303
Accession: 010243682

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Pythium ultimum, which causes root rot and damping-off of many floricultural crops grown in Oklahoma greenhouses, produces oospores for survival and to initiate disease. Strains of Actinoplanes spp. that are hyperparasites of oospores were evaluated for their biological control of Pythium root rot of plants grown in a greenhouse. In soil-less potting mix infested with 103 oospores of P. ultimum/g mix, strains W57, W257, or 25844 of Actinoplanes spp. on clay granules applied at 5% or 0.5% w/w to the mix 5 d prior to replanting geranium or poinsettia seedlings reduced root rot severity and increased plant stand compared to nontreated plants after 6 wk. Granules of W257 applied at 5% w/w to mix 7 d prior to replanting poinsettia seedlings reduced root rot of the plants after 6 wk, whereas seedling dips in a suspension of macerated mycelium of W257 (109 colony-forming units/mL) had no effect. Strain W257 applied as granules (1% w/w) or as a root dip (8 X 108 colony-forming units/mL) 7 d after replanting poinsettia seedlings was as effective as a fungicide (metalaxyl) in reducing root rot after 9 weeks, but no treatment increased plant stand. Colonization of roots by P. ultimum was reduced by metalaxyl or W257 compared to roots from nontreated, pathogen-infested mix. Actinoplanes spp. show promise in the biological control of P. ultimum in greenhouse floricultural crops.

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