ISHS Acta Horticulturae 463: VIII International Symposium on Plant Bioregulation in Fruit Production
CHANGES IN IAA AND ABA LEVELS AND IAA TRANSPORT OF PROLIFERATION-DISEASED APPLE TREES |
| Authors: | M. Hegele, F. Bangerth |
| Keywords: | Auxin transport inhibitor, flavanoids, Golden Delicious, phytoplasmas, Polyvinylpyrrolidone, small fruits, witches'-broom |
| Abstract:
Apple Proliferation Disease is caused by phytoplasmas. The disease is widespread in Europe and is responsible for great losses in both fruit quality and tree viability. At present, aside from removing infected plants and controlling the leafhoppers, which are presumed to be the major vectors, there is no defense against the disease. Proliferated shoots, called “witches'-brooms”, and extremely small fruits are the most obvious symptoms. Because IAA is involved in the release of buds from dormancy as well as in the growth of shoots, and because both IAA and ABA are known to influence fruit growth, changes in these two plant hormones appeared to be most likely. Therefore, we compared the transport of 3H-IAA, also the export of endogenous IAA and the levels of free IAA and ABA in various organs and phloem sap of infected and non-infected “Golden Delicious” trees, using plants of varying ages, grafted on different rootstocks. The results showed that the 3H-IAA transport, and therefore the export of endogenous IAA, had been reduced in nearly all examined infected tissues. The most obvious IAA transport inhibition was detected in the tips of “witches'-broom” shoots, which could explain the loss in apical dominance. At the same time, samples of diseased trees showed a higher content of phenolic compounds. When they were bound to PVP (Polyvinylpyrrolidone), the IAA export could be increased. These findings implicated an increased formation of natural auxin transport inhibitors, probably flavanoids, in proliferation-diseased apple trees. Fruits of infected trees contained significantly less extractable free IAA and more ABA than those of healthy plants, which could account for the reduction of fruit size in infected apple trees. | |
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