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Extension Spotlight

Using grafted plants can benefit tomato and melon growers significantly. It is also clear that grafted vegetable plants can be prepared on farm and by hand in small-medium quantities. To obtain the benefits of grafted plants, they must be prepared properly. This Extension Spotlight outlines major steps in hand grafting. Other resources on the topic are available here. The availability of grafted tomato, melon, cucumber and other crop plants for purchase will increase with time as automated and semi-automated approaches improve.
 
Grafting is organ transplantation. As such, steps must be taken to ensure that the union of the rootstock (with its specialized root system) and scion (which produces marketable fruit) is complete and effective in every way for the grower.
 
First, the rootstock (RS) and scion (S) must be genetically compatible. New rootstock and scion varieties are available each year. Most commercial rootstocks should be compatible with most commercial fruit-producing (scion) varieties. That said, new RS-S combinations should be tested on a small-scale before being attempted on larger scales. The success of an attempted graft is usually evident in 7-10 days. Also, research-based information and experience from growers and others in the industry will help steer rootstock and scion selection.

Rootstock selection is usually driven by growers aiming to overcome specific challenges including soilborne disease, low soil moisture or fertility stress, salt stress, and/or temperature stress. Like scion varieties, rootstock varieties have been bred to have specific characteristics. Individual RS varieties may be effective at countering one or more of these problems but it is best to review RS options carefully. The root systems of nearly all RS varieties are more vigorous than the root systems of standard scions; therefore, grafting may improve crop performance even when growing conditions are generally good.

Second, the stem diameters of the rootstock and scion seedlings must be similar and correct. Stem diameters being similar is critical for two reasons. Similar stem diameters are easier to align during grafting. And, more important, similar stem diameters allow the grafted plant’s vasculature (xylem, phloem) and cambium (growing ring) to stitch properly, assuring strong, unrestricted movement of all substances form roots to shoots and vice versa throughout the life of the grafted plant. Stem diameters being correct is important because seedlings can be too small or too large to graft. In our experience, tomato seedlings should have a stem diameter of approximately 3mm (a little more than 0.1 inch) at grafting.

Finally, newly grafted plants must be allowed to heal in carefully controlled conditions. The actual graft (surgery) may require less than one minute but the healing period may last up to three weeks. During that time, temperatures around the grafted plant should remain 77- 86°F (for tomato), the relative humidity should remain around 95% and the light level should not exceed more than 75% of normal sunlight (approximately 50% for the first week after grafting is best). Grafters often achieve these conditions with the use of simple open-framed structures covered with plastic and shade cloth. We have also found that a flooded capillary mat beneath grafted plants gives them both the little water they need and adds humidity to the air in the healing chamber. The VPSL attempts to prevent liquid water from ever coming in contact with grafted plants while they are in the healing chamber – therefore, we use no hoses or large droplet vaporizers.

Lab Happenings

 
The VPSL is currently focused on a range of research projects in the areas of vegetable grafting, fertility management and quality. It also continues to contribute to the domestication and commercialization of Taraxacum kok-saghyz (TKS), a plant known for its production of natural rubber and inulin, and to the development of superior potato varieties.

Grafting studies are underway in open field, high tunnel and controlled environment settings and in conventional and organic production systems. Studies involving tomato, pepper, watermelon and cantaloupe are located at the OARDC and on area farms. The goal of this work is to maximize the performance of grafted plants from preparation through harvest. This work is supported in part by the USDA-NIFA Specialty Crops Research Initiative.

A new statewide effort to document the status of vegetable soils based on soil test results is underway. The VPSL is working with Ohio vegetable growers to compile a database of soil test results that will guide future research and extension activities. This work is supported in part by the Ohio Vegetable and Small Fruit Research and Development Program. Contact the VPSL for more information. Also ask about our participation in collaborative efforts to develop algae-based biofertilizers and to evaluate other commercial natural products reported to enhance vegetable crop growth and yield.

Brix is among the most commonly measured characteristics of fruits and vegetables. However, the optimal use of Brix values is rarely obvious. In 2012, the VPSL developed four fact sheets regarding Brix values (i.e., tips for obtaining and using them). It continues to study relationships between vegetable crop management and Brix, as one step in enhancing overall crop quality.  

North America has a huge and growing appetite for natural rubber and inulin. TKS has the potential to supply both feedstocks, limiting the amounts that are currently imported. Therefore, commercial production and processing of TKS in Ohio and large tracts of the northern U.S. would strengthen on- and off-farm business there. With its PENRA partners, the VPSL continues to develop TKS germplasm and to develop seeding methods that maximize TKS stand establishment. Seed harvest in 2013 is nearly complete and root harvest is approaching quickly. Where TKS is not yet a commercial crop, potato is an enormously important one throughout the Eastern U.S. The VPSL is cooperating with potato breeding programs in ME, NY, NC and the USDA in the evaluation of more than 100 varieties and pre-commercial lines.

Extension activities are also important to the VPSL. Recently, it has contributed to tours of commercial and research farms, delivered production workshops, addressed individual grower questions, participated in industry roundtables, initiated the development of fall-winter programs, and authored publications. We are particularly pleased that Version 2 of our Vegetable Grafting Guide will be released soon. The new guide contains new sections and updated content throughout. The release of the new guide will be announced here.