Volatile organic compounds in watermelon (Citrullus lanatus) grafted onto 21 local and two commercial bottle gourd (Lagenaria siceraria) rootstocks

Volatile organic compounds (VOCs) are responsible for flavour development in watermelon (Citrullus lanatus). The objective of this study was to investigate the rootstock effects of 21 local bottle gourd [Lagenaria siceraria (Molina) Standl.] accessions collected from the Mediterranean region (Turkey) on the concentrations of VOCs in watermelon over 2 years. The watermelon cultivar 'Crimson Tide' was used as the scion and two commercial bottle gourd rootstocks were also used for comparison. The VOCs in each rootstock-scion combination were analysed using static headspace (SHS) and gas chromatography-mass spectrometry (GC-MS). A total of 24 VOCs were identified in watermelon fruit, including 11 aldehydes, seven alcohols, four ketones, one heterocyclic compound, and one acid. Acetaldehyde (25.9 - 39.5% of the total peak areas), propanal (5.0 - 8.3%), 2-propanone (2.5 - 4.9%), pentanal (2.1 - 3.6%), hexenal (14.5 - 22.6%), (E)-2-hexenal (0.4 - 2.3%), 6-methyl-5-hepten-2-one (10.0 - 19.05%), nonanal (1.6 - 4.4%), (Z)-6-nonenal (4.0 - 9.8%), (E)-2-nonenal (0.6 - 2.0%), (E,Z)-2,6-nonadienal (2.1 - 3.7%), (Z)-6-nonenol (1.0 - 3.2%), and (E,Z)-3,6-nonadienol (1.0 - 3.7%) were the most abundant VOCs found in all watermelon scions. There was no significant effect (P >= 0.05) of rootstock on the concentrations of acetaldehyde, propanal, pentanal, heptanal, ethanol, 1-pentanol, 2-propanone, 2-pentyl furan, or acetic acid. Propanal, 2-propanone, and acetic acid were identified as VOCs in watermelon for the first time. Hexanal, (Z)-6-nonanal, and 6-methyl-5-hepten-2-one concentrations were strongly affected by rootstock. The results showed that the local bottle gourd accessions 07-06 and 31-09, in particular, were the most promising genotypes in terms of producing favourable VOCs. Except for the local bottle gourd accessions 33-35, 01-17, and 07-04, the other 18 gourds accessions had high potential as rootstocks for breeding programmes in watermelon with regard to desirable VOC concentrations. Rootstock 31-09 should be considered for commercial production in terms of improved disease resistance, fruit yield, and fruit quality.