Chapters 47.2

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Introduction

Grafting is a horticultural technique that holds much promise for farmers around the world. To graft, a branch of a tree or shoot of a plant is cut (“scion”) and joined onto a decapitated rootstock (“rootstock”). In a successful graft, the vascular tissues of the scion and rootstock will fuse together. With trees or perennials, a primary benefit of grafting is that it permits rapid propagation of a shoot that has desirable characteristics (e.g. desirable fruits) by taking advantage of an already established root system. Grafting allows mixing and matching of traits from different cultivars (e.g. rootstock that is disease resistant to a shoot that bears desirable fruits). Grafting can usually only take place between two plants of the same genetic family. For instance, successful grafting can occur between plants of the Solanaceae family which includes tomatoes, eggplants, potatoes and tobacco (Kudo, 2007). Remarkably, grafts can be successful not only within the same species (e.g. tomato with tomato) but also between species (e.g. tomato with eggplant).

One of the main reasons that a plant would be grafted would be out of a desire to maintain certain characteristics of a plant, such as in a fruit tree that would otherwise produce asexually. The offspring of an apple tree, for instance, are not very likely to mimic the parent in terms of flavor, texture. By grafting a branch of the tree with the desired fruit onto a rootstock, the fruit of the resultant tree will be highly similar to those of the parent, and allow for predictable cultivation of specific ‘varieties’ at a large scale.

Grafting is an effective way to not only replicate traits that are culinary, but also agricultural traits such as drought tolerance, cold tolerance, and salinity tolerance, amongst others. For example, rootstock of a plant may have good tolerance to the cold, but may produce less fruit than another variety. When the ‘scion’ of the highly productive plant is placed on the ‘rootstock’ of the cold hardy plant, the plant will often survive and become both cold tolerant and highly productive (Mudge, 2009).

Grafting allows for individual fruit farmers to respond to market changes faster than if they were to plant a young tree, since fruit will be produced quicker from the combination of mature rootstock and scion than from a younger tree (Hart, 2005). Consequently, there remains a stronger possibility that this individual will have access to larger markets and higher asking prices for in-demand fruits and vegetables.

Some trees, such as the Baobob tree from the Sahel countries of Africa, are grafted quite easily, with success rates ranging from 80-95% (Maranz, 2008). However, this is not consistent across all species, and does not account for the ‘learning curve’ in practicing proper technique. Maranz (2008) notes that ‘exotic’ varieties of Baobob (those from other Sahel countries) have superior nutritional benefits, and determines that grafting represents an interesting possibility for developing a market for the new varieties, since the local variety has far superior basal diameter, tree height, and resistance to termites. Assah (2011) details the possibility of an emerging market for three novel Alanblackia species in Africa for its nutritive, medicinal, cosmetic, and detergent properties. These species could be grafted onto locally available rootstock for local production to take place. Mudge (2009) details the grafting of Ceara rubber tree onto a cassava rootstock, for the purpose of invigorating the rootstock. The resulting yield of cassava tubers was increased by 30-100% depending on the combination of species.

Critical analysis

Grafting at a large scale is labour intensive, and does require some training. The success rate of grafting is highly variable depending on species; research should be performed on the specific species to determine average success rates, or a test plot should be initiated (Mudge, 2009). There is an ongoing debate about the possibility of the transference of genetic material from scion to rootstock and how this affects the ‘heritage’ of traditional varieties (Mudge, 2009).

Practical tips

The University of Minnesota has a comprehensive manual on grafting, including timing, species selection, and materials needed.

The University of Arizona publishes free ‘how-to’ videos on vegetable grafting. While limited to tomatoes, curcubits and eggplants, many of the principles remain the same.

Usefull Images

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References

Asaah, E., Tchoundjeu, Z., Ngahane, W., Tsobeng, A., Kouodiekong, L., Jamnadass, R., & Simons, A. (2011). Allanblackia floribunda: A new oil tree crop for africa: Amenability to grafting. New Forests, 41(3), 389-398. Hart, T., & Burgess, R. (2005). Grafting keeps farmer in the export market. Appropriate Technology, 32(3), 13-14. Retrieved from http://search.proquest.com/docview/200037126?accountid=11233 Kudo, & Harada, T. (2007). A graft-transmissible RNA from tomato rootstock changes leaf morphology of potato scion. HortScience : A Publication of the American Society for Horticultural Science., 42(2), 225-226. Maranz, S., Niang, A., Kalinganire, A., Konaté, D., & Kaya, B. (2008). Potential to harness superior nutritional qualities of exotic baobabs if local adaptation can be conferred through grafting. Agroforestry Systems, 72(3), 231-239. Mudge, K., Janick, J., Scofield, S., & Goldschmidt, E. E. (2009). A history of grafting. Horticultural Reviews.,437-493.