PERFORMANCE OF FOUR TRIPLOID WATERMELON CULTIVARS GRAFTED ONTO FIVE ROOTSTOCK GENOTYPES: YIELD AND FRUIT QUALITY UNDER COMMERCIAL GROWING CONDITIONS

Use of grafted watermelons in the USA has potential as an alternative to methyl bromide fumigation and to mitigate effects of soil-borne diseases, but commercial growers will not adopt the technology until economies of production are determined based upon horticultural performance of grafted plants. Grafted watermelon transplants were compared to ungrafted plants under commercial growing conditions in southern Florida, USA. Transplants were planted February 2006 in single-row plots, 18.3 m long by 2.7 m wide, using bare ground culture and seepage irrigation. The experimental design was a randomized complete block with three replications and a factorial arrangement of scion ('Tri-X 313', 'Palomar', 'Petite Perfection', and 'Precious Petite') and rootstock (none, BN111, BN911, 'Emphasis', J008, and 'Ojakkyo'). Plant population was 3586 and 2391 plants/ha for ungrafted and grafted plants, respectively. Grafting increased days to maturity 4 to 6 days for 'Tri-X 313' and 'Palomar' and 7 to 9 days for 'Petite Perfection' and 'Precious Petite'. There were no differences among treatments for yield (no./ha and t·ha^-1) but plant population for grafted plants was 30% less than ungrafted, indicating greater productivity per plant for grafted compared to ungrafted plants. Average fruit weight was not affected, though trends indicated that grafted plants produced larger fruits. Total soluble solids content (TSS) was high for all treatments, but TSS for 'Tri-X 313' and 'Palomar' on BN911 was lower than any other scion/rootstock combination. Flesh firmness increased for all scions on BN111, BN911 and 'Ojakkyo', and additionally, for 'Petite Perfection' and 'Precious Petite' on J008. Grafting did not affect color or hollowheart ratings, though ungrafted plants appeared to exhibit more hollowheart than grafted plants. Ratings of number of hard seed coats and true seed increased only for 'Tri-X 313' and 'Palomar' on J008. Overall, most scion/rootstock combinations performed equal to or better than ungrafted plants, especially for flesh firmness.