Effect of calcium propionate dip and spray applications on botrytis blight of ornamental plants

The use of conventional fungicides to control botrytis blight of ornamentals caused by Botrytis cinerea has its limitations due to increasing resistance to site-specific fungicides. Calcium propionate (CaP) has suppressive action against this disease and resistance in B. cinerea to CaP has not been reported. This study evaluated the efficacy of postharvest dip applications of 0.1% CaP (pH 6.0) to control botrytis blight in four cut rose (Rosa ×hybrida) cultivars and analyzed gene expression of CaP-treated rose petals. CaP reduced botrytis blight symptoms in rose ‘Alive’ but not in ‘Freedom’, ‘Momentum’, and ‘Orange Crush’, and no change in gene expression in ‘Orange Crush’ was detected following CaP treatment. Aerial spray applications at 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% CaP made twice a week for 5 weeks caused minimal phytotoxicity damage to calendula (Calendula officinalis), carnation (Dianthus sp), dahlia (Dahlia sp), pansy (Viola ×wittrockiana), and snapdragon (Antirrhinum majus) leaves; however, CaP spray applications generated residues at all CaP concentrations in all species except for dahlia where no residue was observed. The results suggest that CaP will suppress botrytis blight in some but not all rose cultivars and establish a reference for phytotoxicity symptoms and visible CaP residues on ornamental plants.