A TEST ON THE TREATMENT OF ALSTROEMERIA STEMS WITH GIBBERELLIC ACID
Therefore, a treatment with GA3 after cutting was made compulsory to the growers.
The GA3 taken up by the stem mainly goes into the green leaves, and, if there is a preference, into the leaves of the whorl. Also 50% of the GA3 is detectable as GA3 48 h after the treatment (Hibma, unpublished results).
Therefore a quality control test on the treatment with GA3 could be based on the detection of GA3 in the leaves of the whorl. As the test has to be cheap, quick and easy to performe in large quantities, a competitive ELISA with a commercially obtained IgM was developed (Franssen et al., 1992). The ELISA has a sensitivity of 0.25 – 5 pmol/well. Before assaying the samples in ELISA, a short purification step is necessary (Franssen et al., 1992). Thereafter the purified samples were diluted 160 times and tested.
Pressed sap from leaves of untreated stems contained an amount of GA3 below the detection limit of ELISA. If the stems were treated with GA3, and at least 1 ml was taken up by the stem, GA3 could be detected: at least 0.5 pmol/well was determined.
A treatment with silver thiosulphate (STS), to protect the flowers from ethylene, preceding the treatment with GA3 showed similar results. If the stems were only treated with STS no GA3 could be detected. If the stems were treated with STS and subsequently with GA3, at least 0.5 pmol/well was found.
Experiments were performed in October, January and April. When stems were treated with GA3 in these months, the leaves of the lowest whorl showed amounts of at least 0.5 pmol/well GA3.
This indicates that during the whole year a standard of, at least, 0.5 pmol/well GA3 at a dilution of 160 times of the pressed plant sap can be used to determine whether Alstroemeria stems had been treated with GA3.
To test this hypothesis, 40 samples from the auctions were assayed. Untreated or only STS-treated samples were put in at random, and were all detected as 'untreated' (20%). 52% Of the other samples (80%) contained 0.5 pmol/well or more GA3 and 28% contained less than 0.5 pmol/well, but had a detectable amount of GA3. The test seems well applicable for horticultural purposes to control whether Alstroemeria stems have been treated with GA3 after cutting.