Differential response and sensitivity to exogenous ethylene of cut flowers of two Vanda hybrids – ‘Sansai Blue’ vs. ‘Kanun Blue’

Vanda is one of the most important orchids for cut flower production in Thailand. Due to their various types of flowers with beautiful shapes and colors, the Thai Vanda orchids are very demanded in the flower market. Two Vanda hybrids ‘Sansai Blue’ (SB) (V. ‘Crimson Glory’ × V. coerulea) and ‘Kanun Blue’ (KB) (V. coerulea × V. ‘Rinnachai’) with big delicate blue shade florets were examined for their response and sensitivity to exogenous ethylene. Both hybrids were exposed to ethylene treatment (10 μL L-1 for 24 h), which resulted in fast floret bleaching, expressed in reduced anthocyanin content during vase life. Different derivatives of anthocyanins were found in both hybrids, but all of them were rapidly degraded in response to ethylene treatment. This reduction was suggested to result from increase in the ethylene-induced peroxidase (POD) enzyme activity. However, the Vanda KB hybrid showed a significantly more severe response to ethylene in color bleaching than that of the Vanda SB hybrid. In addition, in response to the ethylene treatment, the petals of the KB florets showed necrosis already at the end of the treatment, which became worse with time, and was followed by severe floret abscission. These symptoms were not observed in the SB flowers. As a result, ethylene shortened the vase life duration of the KB flowers by 50% compared to the control, and by only 14% in SB flowers. Untreated KB florets had higher respiration rates than SB florets, which were rather constant throughout the vase period. Ethylene treatment increased the respiration rates in both Vanda orchids during 9-12 days of vase life, with higher rates observed in the KB hybrid. In conclusion, the results obtained with the various parameters of anthocyanin content and composition, POD activity and respiration rates show that the KB flowers are much more sensitive to ethylene than the SB flowers, although a very low amount of endogenous ethylene production could be detected in both untreated and ethylene-treated Vanda orchids.