2019 ASHS Annual Conference

Grafting watermelon with suitable rootstock can be effective to control biotic and/or abiotic stresses that significantly impact production in the Pacific Northwest region of the United States. Despite well-established benefits, growers have been slow to adopt watermelon grafting on a large scale, partially because of the high cost of grafted transplants produced by commonly used grafting methods and partially due to some reports showing reduced fruit quality. When using grafted watermelon plants, regardless of grafting method, harvest timing needs to be re-evaluated for traditional harvest indicators (e.g., dry leaflet and tendril attached to the fruit pedicel) as fruit from grafted plants can be slightly immature, resulting in undesirable fruit quality. Furthermore, grafted rootstock can affect the timing of male and female flowering of watermelon, thereby affecting fruit maturity and harvest dates. Thus, it is difficult to harvest ripe fruit from grafted and non-grafted plants concurrently, leading to conflicting reports regarding the quality of grafted watermelon. Splice grafting is the fastest and most efficient grafting method, and solanaceous crops are grafted exclusively using this method. Research at Washington State University has shown that splice grafting can be successful for watermelon grafting with 60-90% survival in the greenhouse. Now research is needed to evaluate field survival of splice-grafted watermelon transplants and impacts of this grafting method on crop development. The objectives of this trial are to 1) evaluate the survival of splice-grafted watermelon in both the greenhouse and field; 2) measure the effect of grafting method on flowering date; and 3) establish harvest indicators to be used by growers in the area and test their effect on fruit quality. The experimental trial is located at the Oregon State University, Hermiston Agricultural Research and Extension Center and designed as a random complete block with six replications. Two commercial interspecific hybrid squash rootstocks cvs. Tetsukubato and Super Shintosa, with two grafting methods, the splice method and the one-cotyledon method are being evaluated with scion cv. Secretariat. This study will help develop field performance attributes and harvest indices of watermelons grafted using both methods. Measurements will ascertain field survival and plant health parameters, as well as flowering time, indicators of harvest time, and internal fruit quality affected by grafting with both methods. Results will be presented for our field trial conducted in summer 2019, thus pre-harvest measures will be discussed, such as plant survival and health, and flower initiation data.