This brochure discusses the production and potential advantages of using grafted tomatoes for the California fresh market tomato industry, and presents data from one of the first public field trials in the state.   Potential benefits of grafted tomato plants: Increased economic returns. Rootstock “vigor” drives higher yields relative to non-grafted plants. The economic break-even point varies with cost of grafting and fluctuations in tomato market value. Resistance to soil pathogens. Grafted tomato plants with resistant rootstocks can produce high yields in pathogen-infested fields. For example, Maxifort is resistant to corky root rot, Fusarium crown & root rot, and nematodes. Reduced pesticide use (including fumigants). Resistant rootstocks may allow the elimination or reduction of certain pesticides. Tolerance to abiotic stress. Rootstock vigor may improve production under saline or drought-stressed conditions. The 2016 trials evaluated grafted plants under conditions typical for California fresh market tomato field production.   Producing the plants using the “clip” method: Step 1: Cut rootstock and scion stems at 45° angles Step 2: Attach plastic clip, and place cut ends of scion and rootstock together, aligning the 45° angles of the stems Step 3: Hold plants in “healing chamber” with high humidity for ~1 week, in the greenhouse for several more weeks, and then transplant in the field. California fresh market tomato industry: $350 million per year Merced and San Joaquin among top counties Tomatoes: A major soil fumigant user in CA Unique varieties not grown anywhere else Potential use of grafted tomatoes for the CA fresh market industry only now being studied   What are grafted tomatoes? High-yielding scion variety grafted onto “vigorous”, soil pathogen-resistant rootstock Many of ~50 commercial rootstock varieties listed at http://www.vegetablegrafting.org are resistant to several different soil pathogens, such as corky root rot and nematodes. Due to scion/rootstock interactions, “graft incompatibility” may reduce the performance (i.e., yield) of specific variety combinations The only way to know if two varieties will improve performance when grafted together is by trial-and-error Their extensive adoption in the fresh market tomato industries of Europe and Asia, suggests their benefits can be realized in commercial production systems.   For example, Spain uses ~50-70 million grafted plants annually (~40% of commercial tomato production). Can grafted plants improve the profitability of California’s fresh market tomato industry, and reduce soil pesticide use?

Quick Guide to Grafted Tomatoes Our commercial field trials in San Joaquin and Merced counties, California, 2016. Quick Guide to Grafted Tomatoes First Edition   Included 3 scion varieties, each tested non-grafted and grafted onto 3 rootstocks (listed below). See the Growers’ Guide to Grafted Tomatoes for additional experimental details. Table 1. Yield data from our 2016 California field trialsx   Marketable yield (25-lb boxes/A)v SCION San Joaquin Merced Combined ROOTSTOCK Yield % diffw  %diff % diff BOBCAT MAXIFORT 2240 a 60% 2512 -7% 2376 16% DR0138TX 1902 abc 36% 2655 -1% 2279 12% BS01543756 1697 21% 3206 19% 2452 20% NON-GRAFTED 1402 bc 2687 2045 HM1794 2224 ab 17% 2893 -16% 2559 -4% 2124 2615 -24% 2370 -11% 1904 3428 2666 1766 3671 7% 2781 2% DIXIE RED 2002 31% 3569 -8% 2786 3% 1967 28% 2158 -44% 2063 1944 27% 3675 -5% 2810 4% 1533 3864 2699 GALILEA 1715 23% 2284 -9% 2000 1414 1% 2099 -17% 1757 -10% 1399 2516 1958 1282 c 2525 0% -3% San Joaquin trial Almost all grafted combinations had higher yields than the corresponding non-grafted variety. Yield increases reached up to 60% for grafted combination Bobcat/Maxifort. Merced trial For many treatments, yields were ~1.5-2.0 times the yields at San Joaquin. Grafted plants often gave yields similar to or lower than the non-grafted plants. Combined results from both counties Bobcat yield increases: 12-20% Grafting advantages for others unclear Many studies have found best yield response to grafting with sub-optimal growing conditions. Results from San Joaquin may reflect this effect. Additional trials to be conducted in 2017 and 2018.   Michael Grieneisen1, Brenna Aegerter2, Scott Stoddard3, Minghua Zhang1 1Department of Land, Air & Water Resources, University of California, Davis 2University of California Cooperative Extension, San Joaquin County 3University of California Cooperative Extension, Merced County v Marketable yield excludes culls and undersize fruit. w Percentage difference in yield of grafted plants compared to the non-grafted controls. x The Growers’ Guide to Grafted Tomatoes includes tables with additional data and a more detailed economic analysis of using grafted versus non-grafted plants. Economic considerations Economic benefits of grafted plants depend on grafted plant costs and crop value. Bottom line: The top yield increase in the combined data above (20%) is expected to increase a grower’s total net returns only when grafted plants are $0.40 each or less and the value of the tomato crop of ~$9 or more per 25-lb box (see Growers’ Guide to Grafted Tomatoes for a more detailed analysis). Acknowledgements We would like to thank Growers Transplanting Inc. (Salinas, CA) for their assistance in producing the grafted plants, and our grower-cooperators Live Oak Farms and Pacific Triple-E. A more detailed version of this brochure is online: Growers’ Guide to Grafted Tomatoes http://agis.ucdavis.edu/Research/tomato/GrowersGuide.docx Note: The Department of Pesticide Regulation (DPR) provided partial funding for this project but does not necessarily agree with any opinion expressed, nor endorse any commercial product or trade name mentioned.