Suppressing black anther symptoms in orchid inflorescences by fungicides

摘要

The efficacy of synthetic fungicides and bio-fungicides for suppression of black anther symptom development, caused by CoIIetotrichum gloeosporioides on harvested orchid inflorescences [Dendrobium 'Big White Jumbo') was studied. Four synthetic fungicides (500 ppm of carbendazim, chlorothalonil, prochloraz and 200 ppm of sodium hypochlorite) and two bio-fungicides (10 mL L1 Bioextract and 1 mL L1 Mycoderma) were used to investigate their efficacy against mycelia growth of CoIIetotrichum gloeosporioides (in vitro test), and the selected fungicides were used to suppress the disease symptom development on harvested orchid inflorescences (in vivo test). Results of the in vitro test revealed that Prochloraz had the greatest inhibitory effect on mycelial growth (100%), followed by bioextract (69.23%), chlorothalonil (46.83%), carbendazim (13.97%) and sodium hypochlorite (1.15%) respectively, while mycoderma (0%) was not inhibitory. For the in vivo test, the inflorescences of naturally infected orchid werecut and immersed for 5 min in solutions of the selected synthetic fungicides and bio-fungicides prepared at the same concentrations as those used for the in vitro test. Orchid inflorescences immersed in tap water were used as controls. The treated samples were then dried under ambient condition, placed in tubes with vase solution and kept for 4 days at 13°C to simulate as the air shipment. All treated cut-orchid inflorescences were subsequently transferred to 25±2°C and kept for 6 days in distilledwater to investigate disease development and quality during display. Black anther disease symptoms gradually increased throughout vase life. Immersing orchid inflorescences in prochloraz was the best treatment for suppressing black anther disease symptomdevelopment followed by chlorothalonil and bioextract, respectively. Furthermore, prochloraz did not exhibit any negative side effects on petal color (Chroma, C° value), could delay flower drop and promoted water up take significantly as compared to the control. These results simply that pre-treatment with prochloraz can suppress black anther disease and improve the quality of orchid inflorescences during shipping and display.