1. 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 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?

2. 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% BS
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 ~ 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
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.