Different scion/rootstock combinations influence the yield and quality of grafted watermelon fruits

The experiment was conducted in a greenhouse, on the Experimental Field of the Biotechnical Faculty in Ljubljana, Slovenia, from April to September 2011. Two watermelon cultivars 'Crimson sweet' and 'Tex' (mini watermelon) were grafted onto three rootstocks: 'DFCT', 'RS 841' (Cucurbita pepo × Cucurbita moschata) and 'Friend' F₁ (Lagenaria siceraria), self-grafted plants were used as a control. The experiment was designed in 3 repetitions, each repetition included 3 plants. On 19^th of September, all fruits were harvested, counted and weighed and 3 fruits per repetition were randomly chosen for morphometrical measurements. Grafted plants had significantly higher yield with both cultivars. The highest yielding combinations in decreasing order were 'Crimson sweet'/'Friend' (23.7 kg plant^-1), 'Crimson sweet'/'DFCT' (18.5 kg plant^-1) and 'Crimson sweet'/'RS 841' (14.7 kg plant^-1). The lowest yield had self-grafted plants of 'Crimson sweet' (7.3 kg plant^-1). Mini watermelon had the highest yield at grafted plants 'Tex'/'RS 841' (8.9 kg plant^-1), followed by 'Tex'/'Friend' (5.7 kg plant^-1) 'Tex'/'DFCT' (3.6 kg plant^-1). Grafting also influenced some morphological characteristics of watermelon fruits: grafted plants had significantly bigger and heavier fruits compared to self-grafted plants; at both cultivars higher rind thickness (on average 17.1 mm) at fruits from grafted plants was found, compared to fruits from self-grafted plants (14.8 mm). Grafting had significant impact on fruit ripeness at mini watermelon 'Tex', but not at 'Crimson sweet'. Fruits from grafts 'Tex'/'Friend' and 'Tex'/'RS 841' had significantly higher amount of unripe seeds (87%) compared to fruits from self-grafted plants (3%) and from grafts 'Tex'/'DFCT' rootstock (20%).