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Biological Control

Effect of Pathogen Inoculum, Antagonist Density, and Plant Species on Biological Control of Phytophthora and Pythium Damping-off by Bacillus subtilis Cot1 in High-Humidity Fogging Glasshouses. F. Berger, Department of Plant and Soil Science, Cruickshank Building, University of Aberdeen, Aberdeen AB9 2UD, UK, Permanent address: Institute für Pflanzenbau und Tierhygiene in den Tropen und Subtropen, Universität Göttingen, 37000 Göttingen, Germany; Hong Li(2), D. White(3), R. Frazer(4), and C. Leifert(5). (2)(3)(4)(5)Department of Plant and Soil Science, Cruickshank Building, University of Aberdeen, Aberdeen AB9 2UD, UK; (2)Permanent address: Department of Biology, Yunnan Normal University, Kunming, Yunnan 650092, PR China. Phytopathology 86:428-433. Accepted for publication 20 February 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/Phyto-86-428.

Bacillus subtilis Cot1 prevented Phytophthora and Pythium damping-off of Astilbe, Photinia, and Hemerocallis microplants and conventional Brassica seedlings under high-humidity conditions in fogging glasshouses. With Photinia, biocontrol activity was similar to that of the commercial fungicide metalaxyl when the antagonist concentration applied to roots was ≥3 × 10⁵ CFU/g root fresh weight (RFW) and fungal inoculum was ≤10² oospores per g of peat. B. subtilis Cot1 colonized the developing root system of Photinia microplants and Brassica seedlings growing in peat substrate during the 28-day in vivo acclimatization period in the fogging glasshouse. With inocula of 4 × 10⁶ and 3 × 10⁵ CFU/g RFW, spore numbers remained between 10⁵ and 10⁶ CFU/g RFW in the older sections of the root system and between 10⁴ and 10⁵ CFU on root-tip sections. B. subtilis Cot1 application slightly reduced damping-off on Daphne plants. Poor persistence on Daphne roots and suppression of B. subtilis Cot1 by spent media of Daphne tissue cultures suggests that poor biocontrol activity was due to the release of inhibitory compounds by Daphne roots.