**1. Introduction**

Grafting has become globally entrenched as an imperative and sustainable tool for overcoming biotic and abiotic stresses confronting vegetable crops [1]. Watermelon (*Citrullus lanatus* (Thunb) Matsum and Nakai) in particular is the crop that has known the widest application of grafting onto rootstocks resistant to soilborne pathogens or resilient to salinity, water stress, nutrient stress, heat stress, organic pollutants, alkalinity, acidity and contamination of soils by heavy metals [2–4]. Grafting may thus facilitate cultivation of watermelon and other vegetable fruit crops in previously non-arable land and contribute toward global food security. Notwithstanding the importance of grafting for managing biotic and abiotic stress conditions, fruit quality and composition is also modulated by scion–rootstock interaction although it has received comparatively far less attention than the phytoprotection and physiology aspects of crop production [5]. The potential of exploiting wild genetic resources for

stress-tolerant rootstocks compatible to commercial scions can be a faster route to trait stacking than breeding; moreover, it may bypass undesirable pleiotropic effects on fruit quality traits that befall breeding based on selection of desirable qualitative traits [6]. Toward this end, analytical information is essential on how rootstock–scion interaction under field conditions may impact physical, chemical, bioactive and sensory components of fruit quality. In this respect, it is important to examine how different scion types (e.g., diploid vs. triploid or mini vs. large fruited) may interact with different rootstock types (e.g., interspecific vs. gourd) to configure crop performance and fruit quality.

Changes in fruit physicochemical composition and morphometric characteristics also inevitably bear an impact on the postharvest performance of watermelon, which has received little attention to date [1,7]. Yet fruit quality along the horticultural supply chain and ultimately at the customer end is largely influenced by postharvest handling and storage practices. Watermelon is a non-climacteric fruit with a cultivar-dependent but overall brief shelf-life of less than three weeks at 10–15 ◦C [8]. Previous work on rootstock-mediated watermelon postharvest performance is limited, but has established that grafting effects on the physicochemical composition of watermelon fruit extend to the postharvest period [1,9]. It is therefore critical to understand how different rootstock types may interact with different scion types to configure postharvest changes in sensory, compositional and functional quality traits that ultimately define shelf-life.

Accordingly, the current work examined how rootstocks TZ148 and Festival, which represent the two major classes of exploited rootstocks—interspecific hybrids (*Cucurbita maxima* (Duchesne) × *C. moschata* (Duchesne ex Poir)) and gourd (*Lagenaria siceraria* L.), respectively—interacted with two mini triploid (Extazy and Petite), two mini diploid (Vivlos and Esmeralda) and one large-fruited diploid scion cultivar (Pegasus) to impact crop performance and fruit morphometric characteristics. Moreover, fruit sensory quality traits (pulp colorimetry, firmness, sweetness index), chemical composition (fructose, glucose, sucrose) and bioactive components (lycopene and citrulline) were examined at harvest and following postharvest storage at 25 ◦C for 10 days. The current work constitutes a contribution toward understanding rootstock–scion relations and how they mediate crop performance, fruit quality and postharvest behavior of watermelon.
