O'Neill, T.M., Department of Plant Pathology, Volcani Center, P.O. Box 6, Bet-Dagan 50250, Israel, ADAS Horticulture, Brooklands Avenue, Cambridge CB2 2BL, United Kingdom
Niv, A., Department of Plant Pathology, Volcani Center, P.O. Box 6, Bet-Dagan 50250, Israel
Elad, Y., Department of Plant Pathology, Volcani Center, P.O. Box 6, Bet-Dagan 50250, Israel
Shtienberg, D., Department of Plant Pathology, Volcani Center, P.O. Box 6, Bet-Dagan 50250, Israel

The effectiveness of Trichoderma harzianum in suppression of tomato stem rot caused by Botrytis cinerea was examined on tomato stem pieces and on whole plants. Ten days after simultanous inoculation with B. cinerea and T. harzianum, the incidence of infected stem pieces was reduced by 62-84%, the severity of infection by 68-71% and the intensity of sporulation by 87%. Seventeen days after inoculation of wounds on whole plants, the incidence of stem rot was reduced by 50 and 33% at 15 and 26 °C, respectively, and the incidence of rot at leaf scar sites on the main stem was reduced by 60 and 50%, respectively. Simultanous inoculation and pre-inoculation with T. harzianum gave good control of B. cinerea (50 and 90% disease reduction, 10 days after inoculation). The rate of rotting was not reduced by the biocontrol agent once infection was established. However, sporulation by B. cinerea was specifically reduced on these rotting stem pieces. Temperature had a greater effect than vapour pressure deficit (VPD) on the efficacy of biocontrol. Suppression of B. cinerea incidence by T harzianum on stem pieces was significant at 10°C and higher temperatures up to 26°C. Control of infection was significantly lower at a VPD of 1.3 kPa (60% reduction), than at VPD < 1.06 kPa (90-100% control). Reductions in the severity of stem rotting and the sporulation intensity of grey mould were generally not affected by VPD in the range 0.59-1.06 kPa. Survival of T. harzianum on stems was affected by both temperature and VPD and was greatest at 10 °C at a low VPD and at 26 °C at a high VPD.