Biological control of Botrytis cinerea on tomato plants by the use of epiphytic yeasts Candida guilliermondii strains 101 and US 7 and Candida oleophila strain I-182: I. in vivo studies I.D. Saligkarias, a F.T. Gravanis, b and H.A.S. Epton a, * a School of Biological Sciences, 1.800 Stopford Building, The University of Manchester, Oxford Road, Manchester M13 9PT, UK b Technological and Educational Institution of Larissa, Department of Plant Production, Larissa 41110, Greece Received 7 September 2001; accepted 21 May 2002 Abstract Candida guilliermondii (strains 101 and US 7) and C. oleophila (strain I-182) were screened for biocontrol activity (BA) against Botrytis cinerea, both in vitro and in a bioassay, using stem portions and atomized aqueous pathogen suspensions. Yeast C. guilliermondii strains 101 and US 7 significantly reduced disease incidence, when applied simultaneously with the pathogen, whereas C. oleophila strain I-182 and isolated epiphytic yeasts had no BA against B. cinerea. When tomato stem portions were inoculated with yeasts (strains 101 and US 7) 24 h before pathogen challenge, the BA significantly improved. Addition of exogenous nutrients significantly reduced BA of both yeast strains, indicating that nutrient competition may be involved in their mode of action. In vivo application of both C. oleophila (strain I-182) and C. guilliermondii (strains 101 and US 7) gave significant control of B. cinerea, even though strain I-182 had been ineffective in the stem assay. These results suggest that yeasts selected for the biocontrol of postharvest diseases have the potential to control diseases of whole plants. Ó 2002 Elsevier Science (USA). All rights reserved. Keywords: Candida oleophila; Candida guilliermondii; Botrytis cinerea; Lycopersicon esculentum; Gray mold; Biological control 1. Introduction Botrytis cinerea Pers.:Fr is an important pathogen of tomato plants, causing stem rot of long-term tomato growing indoors. The pathogen gains access through leaf wounds caused by cultivation practices (O’Neill et al., 1997; Peng et al., 1996; Verhoeff, 1967) and in- fection is favored by high humidity and low temperature (Eden et al., 1996; Morgan, 1984; Morgan, 1985; Nicot and Allex, 1991). Recent studies (O’Neill et al., 1997) suggest that infection and sporulation occur at temper- atures between 5 and 26 °C, with disease development most rapid at 15 °C. These conditions are ideal for spore germination and subsequent infection and are generally the outcome of energy saving regimes to reduce costs during the winter. Chemical control has become increasingly difficult due to the development of resistant strains (Locke and Fletcher, 1988; Rewal et al., 1991; Rosslenbroich and Stuebler, 2000; Yourman and Jeffers, 1999) as well as the increased concern of consumers towards pesticide use. Natural epiphytic yeasts have demonstrated promising biocontrol activity against several posthar- vest pathogens including B. cinerea (Arras, 1996; Cheah et al., 1996; Lima et al., 1997; Lurie et al., 1995; McGuire, 1994; McLaughlin et al., 1992; Schena et al., 1999), but relatively little effort has been focussed on the biological control of preharvest diseases. Recent studies have given evidence that the epiphytic yeasts Candida sake, Galactomyces geotrichum, Trichosporon pullulans, Candida pulcherrina, and Aurobasidium pullulans can colonize tomato plant wounds and con- trol B. cinerea (Cook et al., 1997b; Dik et al., 1999). Earlier work has also given evidence of remarkable biocontrol activity by yeasts when applied to tomato leaves (Elad et al., 1994). The present study was undertaken as part of a screening program to evaluate the biocontrol activity of C. oleophila (strain I-182) and C. guilliermondii (strains Biological Control 25 (2002) 143–150 www.academicpress.com * Corresponding author. Fax: +44 161 275 5586. E-mail address: harry.epton@man.ac.uk (H.A.S. Epton). 1049-9644/02/$ - see front matter Ó 2002 Elsevier Science (USA). All rights reserved. PII:S1049-9644(02)00051-8