New grafting technique eliminates tomato rootstock regrowth

With the phase-out of methyl bromide (MB) fumigation looming, researchers are seeking alternative pest management programs for both sustainable and organic vegetable production. Vegetative grafting has been proposed as a potential technique for dealing with the loss of MB and managing diseases in tomatoes under open-field conditions. Although vegetative grafting has been adopted in Asia, Europe, and Mexico, sheltering covers such as high tunnels or netting are generally used in these countries. Little information is currently available about the use of grafted plants in unprotected open-field production like those commonly used in the United States.

A study in HortScience documents a simple grafting technique and provides new protocols and procedures for that can substantially reduce rootstock suckering in field-grown tomatoes. According to author Michael G. Bausher, a Research Plant Physiologist at the United States Department of Agriculture–Agricultural Research Service (USDA–ARS), an unintended consequence of currently adopted grafting techniques for tomatoes is the propensity for rootstocks of the grafted plants to outgrow the scion. "We found a serious limitation with current grafting techniques, which resulted in recurring rootstock shoot regrowth, or suckering, from the rootstock cotyledons when left intact," Bausher explained. "Left unchecked, the regrowth of tomato rootstocks can envelop the experimental scions, which can impact the growth of field-grown tomatoes."

In the first year of the research study, Bausher's team grafted tomato cultivars 'Multifort', 'Aloha', and 'TX-301' with 'FL-47' scions using a commercial propagator. The grafted plants were planted in a field experiment and, after a specified time, the number of rootstock suckers was counted and removed; this process was repeated over five time periods. In the second year the scientists grafted all of the plants below the rootstock cotyledons. "The difference in the two years was dramatic," Bausher said.

In year one, bud regrowth from the rootstock occurred in all rootstocks measured during five different time periods over a span of 57 days; the number of plants with rootstock regrowth was as high as 84.6% for 'Multifort', 30.7% for 'Aloha', and 15.4% for 'TX-301'. In the second year, when the different grafting technique was used, no regrowth from the rootstocks was observed.

"Even when the rootstock regrowth was removed using traditional grafting methods, the rootstock sprout growth would reappear from the rootstock," the study said. "Rootstock regrowth has not been observed in subsequent field experiments since adopting the simple method of eliminating the cotyledon axillary meristems."

The new, simple grafting method holds promise as an alternative to methyl bromide for open-field tomato production throughout the world.

The complete study and abstract are available on the ASHS HortScience electronic journal web site: http://hortsci.ashspublications.org/cgi/content/abstract/46/4/596