POST‐POLLINATION PHENOMENA IN ORCHID FLOWERS

S ummary NAA, in concentrations exceeding 0.01 μg/flower, initiates post‐pollination phenomena in Cymbidium (Orchidaceae) flowers similar to those brought on by pollination. These include stigmatic closure, swelling and loss of curvature of the column, wilting of the perianth, deformation of the calli, and anthocyanin production. Applications of relatively high concentrations of GA 3 induce post‐pollination effects which, except for anthocyanin production, are less intense than those brought about by auxin. Kinetin does not induce post‐pollination phenomena, but in concentrations of 10 μg and 100 μg/flower causes slight stigmatic closure, and in some combinations with NAA it inhibits wilting. Stigmatic closure, loss of column curvature and changes in calli, all of them NAA induced, cannot be prevented by simultaneous applications of kinetin, GA 3 or ABA. Some combinations of NAA and GA 3 lowered anthocyanin content relative to separate treatments with either hormone. Flowers treated with GA 3 plus kinetin wilted slightly in most cases, but columns did not swell and retained their curvature; calli did not develop colour and anthocyanin content was generally equal to that of flowers given only kinetin. GA 3 and ABA when applied together brought on symtoms which were similar to those caused by ABA only but anthocyanin content was lower than in flowers treated with either hormone alone. This is also true for ABA‐kinetin mixtures, but intensities of the effects are different and, with certain concentration ratios, stigmatic closure occurs. The phenomena are discussed relative to fruit‐set, seed formation, anthocyanin production, senescence, orchid biology and the possible mode of action of each hormone.