Evaluation of grafting for processing tomato production in California’s Central Valley

Abstract

The benefit of grafting for California processing tomato production in the lower Sacramento Valley was evaluated in commercial tomato fields, one each year from 2016 to 2017. The investigation focused on fruit yield and quality from rootstocks grafted onto popular cultivars. Treatments included 3 rootstocks (Maxifort, Multifort and DRO 138TX) and 3 scions (‘H 8504’, ‘DRI 319’ and ‘HM 3887’) plus each of the non-grafted scions as controls. In year 2, ‘N 6428’ replaced ‘H 8504’. Grafts were done by hand, at Growers Transplanting, Inc., coastal facility in Salinas, California. Rootstocks and scions were grown and later healed in 230-cell trays (~28 cc cell volume) within their commercial greenhouses in Salinas. The grafted plants were finished in their Central Valley greenhouse ahead of field planting. Within the field, seedlings were transplanted with the grower’s ‘finger-style’ Mechanical Transplanter® as per norm. The trial design was a randomized complete block with 4 replications. Plots were a single plant line on a 1.5-m centered bed for 30 m. Planting depth was 10 cm or more below the bed top without concern for the depth of the graft union which was buried. Emergence of wild rootstock shoots (which were removed) was minimal in year 1 and none in year 2. Irrigation was only with buried drip at a depth of 25 cm. Harvest was performed mechanically using the grower’s harvester and crew. Yields increased, on average, 10% in 2016 and 19% in 2017. Scion choice made a difference in yield outcome, but rootstock choice did not. Brix performance was related to scion, but not to rootstock. Factorial interaction did not occur between scion and rootstock for yield or Brix in either year, although grafting reduced Brix in 2017. Grafting for processing tomato production was not economically attractive without substantially higher yield gain, lower cost of grafting and/or reduced planting rate. The test will be conducted in the upper San Joaquin Valley from 2018 through 2020.