Quality analysis of cut Vanda ‘Sansai Blue’ orchid flowers during vase life in response to exogenous ethylene, 1-MCP and sucrose

The ‘Sansai Blue’ Vanda orchid flower is very sensitive to exogenous ethylene although the flowers produce very low amounts of endogenous ethylene. We reported previously that there is a rapid ethylene-induced anthocyanin breakdown, which occurs before the senescence processes could be detected (Khunmuang et al. 2019b). In addition, there is a possibility that at the same time, ethylene may inhibit the anthocyanin biosynthesis, which also continues during vase life. Therefore, the purpose of the present study was to understand how ethylene, the ethylene inhibitor, 1-MCP, and sucrose affect anthocyanin content and flower quality parameters during vase life. For this purpose, the cut inflorescences were exposed to air (control), ethylene, 1-MCP or sucrose, and the effects of these treatments was examined on four genes encoding for anthocyanin biosynthesis enzymes, and on various quality parameters in cut Vanda ‘Sansai Blue’ orchid flowers at the bloom stage during vase life.

The results revealed that exogenous ethylene caused petal discoloration in cut ‘Sansai Blue’ Vanda orchid flowers in accordance with their anthocyanin degradation, as well as the down-regulation of expression of genes encoding for the four anthocyanin biosynthesis enzymes. Treatments of 1-MCP alone or 1-MCP before ethylene treatment up-regulated the expression of the four genes, as compared to the control two days after treatments. This suggests that 1-MCP can prevent the effects of both endogenous and exogenous ethylene on anthocyanin biosynthesis. 1-MCP was also very effective in preventing ethylene responses in ‘Sansai Blue’ Vanda orchids by delaying the decrease in anthocyanin and sugar contents, and maintaining color appearance of flowers. Treatment with sucrose alone significantly inhibited floret discoloration, induced higher accumulation of anthocyanin and soluble sugar contents during vase life, and delayed quality parameters, as well as floret senescence throughout the vase period. However, sucrose could not overcome the effect of ethylene in enhancing anthocyanin degradation. It seems therefore, that these positive effects of sucrose may stem from its senescence-delaying effects, rather than being an anti-ethylene agent. Our findings indicate that the 1-MCP and sucrose treatments enhanced anthocyanin accumulation in the petals of cut 'Sansai Blue' Vanda orchid flowers at the bloom stage, but in different mechanisms. The present study also provides further support to the conclusion that the two processes of ethylene-induced discoloration and senescence proceed separately and independently during vase life of cut ‘Sansai Blue’ Vanda flowers.