Floral flavonoids and pH in Dendrobium orchid species and hybrids

Anthocyanidins were identified in 28 Dendrobium species and hybrids selected for analysis based on colour and suitability in cut flower breeding. Flowers designated pink, red, maroon, orange, bronze, and brown in the trade were placed in RHS colour groups red-purple, purple-violet, violet on yellow, greyed-purple on yellow or yellow-orange, and brown. This colour range contained anthocyanins based on cyanidin, with peonidin occurring as a minor pigment. The colours of three blue genotypes, D. gouldii K280-6, D. biggibum 'blue', and D. Kultana 'blue', were light violet to purple by RHS standards and contained anthocyanins based on cyanidin. Peach-coloured flowers were classified as red or red-purple and included pelargonidin glycosides. Anthocyanin concentrations ranged from 0.13 to 0.18 mu moles/g FW in light lavender and peach, and up to 3.66 mu moles/g FW in brown. Combined cellular and vacuolar pH ranged narrowly from 4.67 to 5.09 among white, peach, lavender, and brown lines. Predominant copigments were flavonol glycosides based on kaempferol, quercetin, myricetin, and methylated derivatives. Flavonol aglycones and glycosylation sites differed little among two colour forms of D. gouldii and two D. Jaquelyn Thomas hybrids. Accumulation of quercetin, myricetin, and cyanidin indicated flavonoid 3' and 3',5' hydroxylation activities in several Dendrobium. Additional accumulation of isorhamnetin, syringetin, and peonidin indicated active flavonoid 3'- and 3',5'-O-methyltransferase enzymes.