A number of studies have been made to describe the development of TPD in recent years. The results emerged out from the studies are inconclusive to prove whether they are the real cause for TPD or consequence of TPD. However, it was already proved experimentally that excessive application of ethylene stimulant and overexploitation could induce more TPD incidence in Hevea population. Therefore it was hypothesised that the endogenous ethylene produced in the tapping panel of trees may be responsible for the formation of stress-induced changes in the trees. The intrinsic differences in the ethylene production capacity or tissue sensitivity to ethylene can induce TPD. The intrinsic differences/sensitivity of ethylene between different trees within a clone could explain the random nature of TPD occurrence and its apparent spread from one panel to another in a given tree upon tapping, which triggers ethylene production.
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