Swelling and rottenness of squash rootstock in grafted watermelon

In recent decades, grafting watermelon onto squash rootstock has become a common practice worldwide, primarily to combat soil-borne diseases.
In addition, the strong vigor of the squash rootstock was found to have a positive effect on the watermelon yield.
However, a new problem has emerged in recent years – rotting at the graft union between watermelon and squash.
When infection levels are high, this issue can significantly reduce the watermelon yield biomass.
Moreover, a survey indicates that this phenomenon is more prevalent in areas when the crop is exposed to high relative humidity.
Pathogen isolation efforts did not detect a specific major pathogen that can fully explain the phenomenon.
Instead, the pathogens that were found in the infection area are considered as a secondary pathogens that can only infect a weak tissue.
Field trials have further shown that the occurrence of the phenomenon is related to the scion-rootstock pairing.
Specifically, the rotten grafting was observed only in specific rootstock-scion combinations.
When either the rootstock or the scion was replaced with watermelon (rootstock) or other watermelon accession (scion), the phenomenon did not occur.
These findings suggest that the root cause of the issue is more likely to be physiological rather than epidemiological.
Future research will focus on understanding the physiological factors that contribute to the formatting of this graft rot.

IX International Symposium on Seed, Transplant and Stand Establishment of Horticultural Crops and III International Symposium on Vegetable Grafting

A. Cochavi, A. Koren, O. Frenkel

graft tissue rot, microclimate-related stress, physiological incompatibility, scion-rootstock interaction, watermelon grafting

https://doi.org/10.17660/ActaHortic.2026.1453.5