The Submergence of the Graft Union Causes the Death of Grafted Mango Trees (Mangifera indica L.) under Flooding

Abstract

The risk of flooding has increased as a result of climate change inspired by global warming. In this study, the difference in tolerance to flooding between grafted trees and seedlings was investigated in mango trees (Mangifera indica L.). Two levels of flooding treatment were established, in addition to a non-treated control. One was “30-flood,” in which trees were submerged up to 30 cm from the soil surface, and another was “10-flood,” in which trees were submerged up to 10 cm from the soil surface. Grafted trees treated with the 30-flood were submerged up to 5 cm above the graft union. Only the grafted trees in the 30-flood treatment began to decrease Fv/Fm and the root sugar content during treatment, then died after the completion of treatment. In grafted trees and seedlings alike, both flooding treatments also reduced root vigor, as determined by triphenyl tetrazolium chloride reduction tests and root starch content. However, root vigor and root starch content in grafted trees treated with the 10-flood as well as seedlings treated with both 10- and 30-flood recovered within two months after the completion of treatment, so that no significant differences were detected between the control. These results suggest that the submergence of the graft union into water causes the decline in photosynthesis of the scion first and the death of the grafted trees as a result.