1Research Station for Floriculture and Glasshouse Vegetables, 2670 AA Naaldwijk, The Netherlands; 2ARO Volcani Center, Department of Plant Pathology, Bet-Dagan 50250, Israel

Background and objectives
Botrytis cinerea is one of the major airborne pathogens in ornamentals grown in greenhouses. B. cinerea on cut flowers is a problem during the pre-harvest period, but even more so during the post-harvest stage. In spite of intensive control efforts and the timely sorting out of infected flowers at the growers', flowers of Dutch and Israeli origin are regularly found to be infected with B. cinerea at auction. Fungicides do not provide adequate control of B. cinerea on these flowers. Moreover, fungicide residues are undesirable in cut flowers. The objective of the work was to develop biological control based on saprophytic microorganisms that will reduce infection of petals with B. cinerea and that will be at least as good as chemical fungicides.

Materials and methods
Roses were harvested and inoculated with a spore suspension of B. cinerea. After 24 h, antagonists were applied and the flowers were subjected to a certain combination of temperature and RH for 24 h. Then, climatic conditions were put to an RH of 100%. After 1-3 days, lesions on the petals were counted or infected leaf area was assessed. A set of yeast and bacterial isolates was tested under a range of climatic conditions.

Results and conclusions
In general, disease was most severe at 20-25C and decreased with a decrease in temperature. Both at high and low vapour pressure deficits (VPD), bacterial isolates performed better at temperatures between 2 and 10C than at higher temperatures. The efficacy of yeast isolates was also good at low temperatures, but the effect at high temperatures was variable for some strains. Most of the bacterial and yeast isolates were more effective at low than at high VPD, but some strains were also highly effective at high VPD. Most isolates were more effective at high VPD in combination with low temperature than in combination with high temperature. Research will continue with the isolates that were effective at high VPD and at low temperatures. Efficacy may be further enhanced by combining the microorganisms with various salts. In our opinion, several isolates show good perspectives for biological control of B. cinerea in roses. This will reduce the input of chemical fungicides and the dependence of the growers on these fungicides.