EFFECT OF OCTANOIC-ACID ON ETHYLENE-MEDIATED FLOWER INDUCTION IN DUTCH IRIS

Treatment of Dutch iris (Iris x hollandica Hoog. cv. 'Sapphire Beauty' ) bulbs with ethylene prior to precooling stimulated flowering in bulb s of various sizes. In large sized bulbs exposure to ethylene followed by precooling resulted in 100% flowering over a five months period af ter planting. Flowering in control bulbs which were not treated with e thylene prior to precooling was limited to 67% during the same five mo nths period. In medium sized bulbs flowering in the ethylene treatment was 90% compared to 75% in the control. However, the biggest stimulat ion of flowering by ethylene was found in small sized bulbs (from 16 t o 56%). Application of octanoic acid for a short time period prior to exposure to ethylene stimulated flowering in all bulb sizes. After fiv e months the final percentage flowering in large and medium sized bulb s of the octanoic acid plus ethylene treatment did not differ from tha t of the ethylene only treatment. However, the initial rate of floweri ng was higher in the former treatment. In small bulbs the percentage f lowering was much higher in the octanoic acid plus ethylene treatment than in the ethylene only treatment. The results of this study indicat e that, just as in certain flowers, fruit and seeds, treatment with oc tanoic acid stimulates ethylene sensitivity in Dutch iris bulbs. The s ensitivity of untreated bulbs to ethylene was highest in large bulbs a nd lowest in small bulbs. This correlated well with the endogenous oct anoic acid content of the bulbs. Octanoic acid levels were highest in large bulbs and lowest in small Bulbs. It appears that the endogenous levels of octanoic acid in the bulbs is determined prior to the onset of dormancy.