Evaluation of grafting for processing tomato production in California's Central Valley
The benefit of grafting for California processing tomato production in the lower Sacramento Valley was evaluated in commercial fields. Results from 2016 to 17 were reported at a 2018 ISHS symposium. Two trials were conducted in 2018, which added depth to the evaluation. The investigation focused on fruit yield and quality of popular cultivars grafted onto rootstocks. Treatments primarily included three rootstocks (Maxifort, Multifort and DRO 138TX and later FusaPro, two experimental rootstocks and a non-disclosed entry) and four scions (H 8504, DRI 319, N 6428 and HM 3887, although not all together) plus each of the non-grafted scion as controls. Grafting was performed at commercial greenhouses. At the fields, seedlings were mechanically transplanted per grower norms. Planting depth was about 10 cm below the bed top which buried the graft union. The trial design was a randomized complete block with four replications. Plots were on 1.5-m centered beds and up to 30.5 m long, mostly as a single plant line. Emergence of shoots from rootstocks was minimal. Irrigation was via buried drip tape at a depth of 25 cm. Harvest was mechanical. Grafting increased yields on average by 10% in 2016, 19% in 2017, and 29 and 8% in the 2018 trials. Scion selection made a difference in yield outcome but rootstock selection was not significant. However in 2018, no yield advantage occurred with a non-disclosed and two experimental rootstocks. Brix performance was mostly related to scion, and in some instances with rootstocks. No interaction (unique combination) occurred between scion and rootstock for yield or Brix in any year. Grafting for processing tomato production is not economically attractive without substantial yield improvement, lower cost for grafted plants or reduced planting density. Testing will continue in the upper San Joaquin Valley in 2019 and 2020 including an evaluation of lower planting density.
Miyao, G., Aegerter, B. and Wang, Z. (2021). Evaluation of grafting for processing tomato production in California's Central Valley. Acta Hortic. 1302, 57-64
scion, rootstock, yield response, transplant seedlings, commercial field