The goal of the project is to understand the suitability of different scions when grafted onto commonly used watermelon rootstocks in California. This scion variety trial was conducted in 2024 within a commercial watermelon field near Stockton, California. Six different scions (Captivation, Fascination, Citation, Embasy, Melody, and Summer Breeze), categorized by horticultural characteristics such as maturity, fruit size, and color, were grafted onto three widely used watermelon rootstocks in California (Camelforce, Cobalt, and Carolina Strongback). The three rootstocks are grouped into interspecific hybrid squash (Cucurbita maxima x Cucurbita moschata) and Citron (Citrullus amarus). The field experiment was arranged as a randomized block design including eighteen treatments replicated three times. Each plot was 60 ft long and contained 10 triploids and 3 grafted pollenizers (Sentinel). The field was mechanically transplanted on May 14, 2024. In-season plot maintenance included vine separation multiple times to ease data collection and harvest. Canopy coverage was measured using a handheld crop sensor starting at 10 days after transplanting and thereafter at an approximate interval of two weeks for a total of eight measurements. With the help of farm crew, three harvests were conducted on August 5, 12, and 26. Total yields from each harvest and fruit quality taken from the first harvest were recorded and compared among the rootstock-scion combinations. For quality assessment, fruit length and width were measured by yardstick. Fruit flesh firmness was measured using a fruit penetrometer at the spots 1/3 and 2/3 distance from the blossom end after a melon was cut in half. Rind thickness at the blossom and stem ends were measured with a caliper. Sugar content (⁰Brix) was measured by scooping the center flesh of each half and reading the results through a portable reflectometer. Canopy coverage showed no significant differences among the treatments. For yield, four out of six scions (Fascination, Citation, Embasy, and Melody) produced the highest total yield (ton/acre and no/acre) when they were grafted onto Camelforce, while Captivation and Summer Breeze resulted in higher total yield when grafted with Carolina Strongback. A notable difference was observed in fruit quality for ⁰Brix and firmness that Carolina Strongback produced the lowest firmness and highest ⁰Brix when grafted with all six scions. These results provide a helpful advantage for growers in California who are considering grafting in their production. Continuous assessments will be conducted to further aid in the understanding of field performances from different rootstock-scion combinations.
