European Journal of Plant Pathology 104: 753–763, 1998. © 1998 Kluwer Academic Publishers. Printed in the Netherlands. 753 Significance of leaf infection by Botrytis cinerea in stem rotting of tomatoes grown in non-heated greenhouses D. Shtienberg, Y. Elad, Ariela Niv, Y. Nitzani and B. Kirshner Department of Plant Pathology, ARO, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel Accepted 8 July 1998 Key words: cultural control, Integrated Pest Management, Lycopersicon esculentum, sanitation Abstract The most serious symptom of Botrytis cinerea in tomatoes grown in greenhouses is stem rotting. Lesions on the stem may result from direct infection or from progression of the rot along infected leaves, until infection approaches the stem. In a set of experiments conducted in commercial greenhouses, an experimental greenhouse and growth chambers, the significance of the two types of stem infections was studied. In non-heated greenhouses most of the stem lesions originated from progression of the pathogen along infected petioles. The rate at which B. cinerea had progressed on infected petioles was 0.3–0.5 cm/day, an average of ca. 6 weeks was needed for a leaf infection to approach the stem. Application of Trichoderma harzianum T39 extended this time by 1–2 weeks and application of chemical fungicides by 3 weeks. Influence of the environment on the progression of B. cinerea along infected petioles was then determined. Within range of 5–30 ◦ C, the higher the temperature, the more rapid was the rate of disease progression. The fungus progressed more rapidly on tomato petioles incubated at high vapour pressure deficit (VPD) rather than at low VPD. The source-sink relationship of the plant governed the rate of B. cinerea progression along the petioles as well: it was more rapid when the source was restricted (by shading) and slower when the sink was restricted (by removal of flowers and small fruits). The possibility that sanitation of infected leaflets would reduce the incidence of stem rotting was examined in two experiments. In plots not treated with a fungicide, the sanitation treatment substantially decreased the incidence of stem lesions and this treatment was as effective as weekly application of chemical fungicides. Introduction Botrytis cinerea Pers.: Fr., the causal agent of grey mould, attacks flowers, fruits, leaves and stems of tomato plants grown in greenhouses. The relative im- portance of the various symptoms is governed by the environmental conditions and by the cultural prac- tices: in non-heated or partially heated greenhouses, the pathogen infects primarily leaves, but lesions on the stems are also apparent. In heated greenhouses, the occurrence of leaf and fruit infections is limited but infections on stems are common. Stem rotting caused by B. cinerea has become an increasing problem in long season (up to 8-11 months) tomato crops (Elad and Shtienberg, 1995) and it is often the reason why a crop is finished earlier than planned (Chastagner et al., 1977; Elad et al., 1992; Jarvis, 1989, 1992; O’Neill, 1994; Yunis et al., 1990). Stem rotting may be devasta- ting: for example, in an experiment conducted recently in a commercial greenhouse in Israel under a natural epidemic of B. cinerea, 72% of untreated plants died prematurely from stem rotting (Shtienberg and Elad, 1997). Stem rotting may develop from two distinct sources: (i) direct infection of the stems, usually on wounds that are created during pruning of lower leaves or side branches; and (ii) subsequent progression of the pathogen from an infected leaflet along the peti- ole, until it approaches the stem (Verhoeff, 1968). Excessive heating and ventilation limits canopy wet- ness and reduces the intensity of grey mould on leaves, flowers and fruits (Morgan, 1985; Winspear et al., 1970), but is generally less effective in preventing stem infections. Consequently, growers apply fungi- ejpp787.tex; 9/11/1998; 15:55; p.1 MENNEN/SCHRIKS:DISK/CP: Pips Nr.:184414; Ordernr.:236356-mc (ejppkap:bio2fam) v.1.1