Shaul, O., Department of Plant Pathology, ARO, The Volcani Center, Bet Dagan, 50250, Israel, Kennedy-Leigh Center of Horticultural Research, Faculty of Agriculture, The Hebrew University of Jerusalem, P.O. Box 12, 76100 Rehovot, Israel
Elad, Y., Department of Plant Pathology, ARO, The Volcani Center, Bet Dagan, 50250, Israel
Zieslin, N., Kennedy-Leigh Center of Horticultural Research, Faculty of Agriculture, The Hebrew University of Jerusalem, P.O. Box 12, 76100 Rehovot, Israel

Symptoms of Botrytis blight in petals of harvested rose flowers inoculated after harvest with suspensions of Botrytis cinerea conidia become visible after five-seven days. The development of Botrytis blight was significantly suppressed in detached petals of cvs. Mercedes and Sonata treated for 24 h with a 20 mg l-1 solution of GA3. Botrytis was suppressed to a lesser extent in petals of cvs. Celica and Ilseta, with no effect recorded in cvs. Golden Times and Madelon. To obtain a similar level of suppression in intact flower buds to that obtained in detached petals, a postharvest spray of GA3, with a concentration of 346 mg l-1 (1 mM) was required. Soon after harvest, the inner petals of cv. Mercedes were more sensitive to B. cinerea than the outer petals, whereas the converse was observed when petals were removed from buds maintained for five days in a vase. Neither spore germination, germ-tube elongation nor the linear growth of the fungus mycelium were affected by gibberellin. Use of GA3 for control of Botrytis blight in rose flowers as an alternative to environmentally-hostile fungicides is proposed. © 1995.