Performance of interspecific Cucurbita rootstocks compared to their parental lines

- Commercial cucurbits are commonly grafted onto interspecific Cucurbita hybrid rootstocks.
- The paradigm is that hybrid rootstocks pose high vigor, better yields and high-level resistance.
- The superiority of the hybrid over its parents is not conclusive and varies among crosses and traits.

Commercial cucurbits are commonly grafted onto interspecific Cucurbita hybrid rootstocks. The unproven paradigm is that hybrid rootstocks are more vigorous, resulting in better yields and high-level resistance. The objective of this study was to test the above hypothesis by comparing the performance of parental lines to that of derived F1 hybrids as non-grafted Cucurbita accessions and as grafted melons, in experiments conducted in the greenhouse and in the field. The response to biotic stress was evaluated in with Rhizoctonia solani inoculated non-grafted Cucurbita parents and hybrids. In four out of the five hybrid-parent sets evaluated, susceptibility of the hybrid to R. solani was reduced or comparable to that of the parents. Grafted melon performance, expressed by plant development index, physiological wilt incidence and fruit yield, was evaluated in the field and in the greenhouse. Three hybrids out of the five tested in the field exhibited lower physiological wilt incidence than their parents. In three parent-hybrid sets, the male parent exhibited the worst rootstock performance and in one case, the male parent exhibited the lowest wilting. Fruit yield of grafted melons was highly correlated to wilt incidence. According to our results, the superiority of the hybrid over its parents and the benefit of the interspecific Cucurbita rootstock are not conclusive and varies among crosses and traits. The pathological, horticultural and economic benefits of this approach should therefore be further tested and reconsidered.