2017 ASHS Annual Conference

Rootstock regrowth can prevent effective healing of grafted vegetable seedlings and outcompete the scion for light, space, and nutrients later in production. Rootstock regrowth is especially problematic for watermelon (Citrullus lanatus) because the crop is most commonly grafted using methods where meristematic tissue remains on the rootstock. The objective of this study was to test whether sucrose solution [0% (water control), 1%, 2%, and 3%] applied as a drench to rootstock seedlings prior to grafting would increase the survival of watermelon grafted using the splice method where both rootstock cotyledons were removed in order to eliminate meristem tissue and rootstock regrowth. Starch accumulation in rootstock seedlings was highest for plants that received 3% sucrose solution (71%), followed by plants that received 2% sucrose solution (52%), 1% sucrose solution (29%), and water (6%). Survival (%) of splice grafted watermelon seedlings 21 d after grafting was greatest for plants that received 2% and 3% sucrose solution (89 and 82%, respectively), followed by plants that received 1% sucrose solution (78%), and was lowest for plants that received water (58%). There was a significant interaction due to repeat for both starch accumulation and grafted transplant survival; however, environmental conditions were similar for both repeats: the daily average temperature was 23ºC, the RH was 64-67%, and the daily average light intensity was 224-243 µmolm^-2s^-1. Further, while the vapor pressure deficit from 1 to 6 pm was 2.49 kPa for repeat 1 and 1.42 kPa for repeat 2, plant survival was greater in repeat 1 than repeat 2. These results indicate that drench applications of sucrose solution to rootstock seedlings prior to grafting can increase grafting success when both cotyledons are removed from the rootstock prior to grafting, but further research is needed to optimize the environmental conditions for survival of grafted plants.