Indexing melon physiological decline to fruit quality and vine morphometric parameters

- We examined non-pathological decline in grafted melon.
- Negative rootstock effect on scion dry weight may constitute an index of incompatibility.
- Internodal attenuation and lower mesocarp firmness reflect susceptibility to decline.
- Earliness of harvest maturity possibly relates to ethylene-mediated stress and decline.

While grafting cucurbits has become essential in the management of soil borne diseases and for improving performance under conditions of abiotic stress, commercial melon grafting has been curbed by the incidence of non-pathological decline, usually expressed right before harvest and attributed to physiological scion-rootstock incompatibility. The current study investigated the potential indexing of physiological incompatibility to plant performance, vine morphometric parameters and fruit physicochemical characteristics. Graft combinations sensitive to physiological incompatibility (scions: melon cvs. Elario, Polynica and Raymond; rootstocks: interspecific hybrids 'TZ148', 'N101', 'Carnivore' and '30900') were grown between February and May in a disease-free soil environment. Results indicate that plant collapse shortly before harvest is a onetime event that does not necessarily reflect on the performance of the asymptomatic, surviving plants. However, a negative rootstock effect on scion dry weight was indicative of rootstock-scion combinations subject to incompatibility and prone to decline. The attenuation of the 1st internode's diameter relative to the hypocotyl's ('Elario' 29.1%; 'Raymond' 41.5%; 'Polynica' 44.0%) and the loss of mesocarp firmness reflected the categorical sensitivity of the scions to physiological decline. No systematic pattern was identified connecting fruit soluble carbohydrate (fructose, glucose and sucrose) content to physiological incompatibility and plant decline. However, earliness of harvest maturity, pronounced in sensitive climacteric scions 'Polynica' and 'Raymond', may relate to ethylene-mediated comprehensive acceleration of ripening stressing rootstock-scion synergy to collapse.