Effects of different rootstocks on aroma volatile compounds and carotenoid content of melon fruits.

Grafting plants on resistant rootstocks is an effective tool for controlling soil borne diseases and represents a common practice in land-intensive melon cultivation. Although it is known that type of rootstock alters both yield and quality attributes of the fruit, the horticultural industry has traditionally focused only on yield. The increasing consumer attention for high quality vegetable crops make it indispensable to carefully select rootstocks/scion combinations able to ensure also an high quality fruits. In this regards the research aimed to evaluate the effects of grafting on melon volatile aroma compounds and carotenoid content that are quality parameters rarely investigated till now in grafted melon. Five Cucurbita maxima × Cucurbita moschata hybrids (namely Polifemo, AS10, RS841, P360 and ELSI) and two genotypes of melon (Energia and Sting), selected for their disease resistance, were tested as rootstocks for melon cv Proteo under greenhouse conditions. All the used rootstocks exhibited a good affinity with the scion, with Polifemo showing, in the early harvest, a productivity higher than control (about 60 %) and a significant increase in fruit number. As regards the volatile compounds, the content of key aroma esters ethyl 2-methylbutanoate and ethyl butanoate resulted lower in most of the grafted samples (20-55 % and 63-95 % less than control, respectively), except in sample from Proteo/Sting grafting combination. The aroma of melons grafted on pumpkin hybrid and on Energia rootstocks resulted more similar to the control. The use of pumpkin hybrids rootstocks determined an improvement of qualitative and quantitative carotenoid profile for the presence of lutein (5.5-13.7 mg kg-1 of fresh weight) in fruit samples from Elsi, P360, RS841 and AS10 grafting combinations and the higher amount of β-carotene (about eight fold more than control) and α-carotene (about 56 % more than control) in P360 sample, whereas the melon genotype rootstocks determined a decrease in the amount of β-carotene (about 55 % less than control). In conclusion, the Cucurbita rootstocks resulted acceptable for melon cv. Proteo, both for productivity and quality of fruits, whereas Sting rootstock caused a reduction in fruit quality parameters.