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Plant Grafting as a Tool to Help Reduce the Need for Soil Fumigation with Methyl Bromide
Expanding the use of resistant rootstocks, in combination with Integrated Pest Management (IPM) practices, may help to reduce the need for soil fumigation with methyl bromide for many crops. Grafting currently is used in commercial agricultural production to achieve higher yielding field and greenhouse crops, repair damaged sections of a plant, increase temperature or salinity tolerance, produce higher yielding varieties (including dwarf varieties), and extend the duration of economical harvest time. Research is being conducted to identify disease resistant germplasm for a variety of crops that currently receive methyl bromide treatments at planting. It is believed that germplasm with resistant traits may be useful for grafting, as well as the development of new cultivars. Specifically, with regard to reducing the need for soil fumigation, the primary use of grafting will be to increase disease and nematode resistance through the use of select rootstock with known resistance to soilborne pests.
Commercialization of cultivars with resistance to diseases caused by nematodes (e.g., Meloidogyne incognita) and fungi (e.g., Fusarium oxysporum) has been achieved by screening various plant species to identify traits of potentially resistant stocks that may be useful for grafting, and through breeding programs. In addition, field trials have been conducted to assess whether identified germplasm increases the ability of crops to withstand soil infestation as well as whether the crop performance will be commercially acceptable (i.e., yield, compatibility, anchorage). Finally, commercialization has been advanced through cooperation with nurseries and growers to determine the factors affecting commercial adoption of new rootstocks. Current research efforts to develop additional resistant germplasm for use in grafting for many of the crops currently treated with methyl bromide may lead to an increased ability to minimize or prevent yield losses from soil pest pressure (Ledbetter 1996b, Ledbetter 1996a, McKenry and Kretsch 1995, Lee 1994).
Grafting Techniques and Applications
Plant grafting is a propagation technique whereby two portions of plant which have similar organic texture are joined in such a manner so as to continue their development as a single plant. There are many methods of grafting plants, each involving the joining of the leaf-bearing part (scion) of one plant with the rootstock of another. Grafting methods include such techniques as apical-wedge grafting, whip-and-tongue grafting, splice grafting, flat grafting, saddle grafting, bud grafting, hole insertion grafting, tongue approach grafting, and cleft grafting.
Grafting can be used for nursery, orchard, vineyard, and vegetable crops. The technique can be particularly useful when there is a specific infestation problem that can be controlled with available rootstocks, and in situations where disease problems arise after the orchard or vineyard has already been established (McKenry 1995). In general, grafting is a technology that is readily accessible to commercial suppliers of nursery and vegetable transplants, can be easily taught to field technicians, and has a relatively low cost (Ledbetter 1996b, Rodriguez-Kabana 1995). To enhance the use of grafting, commercial nurseries and growers will need continued access to new resistant germplasm for field testing and commercial trials. In addition, mechanized grafting approaches are being developed that rely on small portable machines that can perform the basic cutting and joining procedures (Maynard 1996).
Currently, grafted plants are widely used in the United States for a variety of orchard and vineyard crops (e.g., apples, grapes). Other countries also have experience with grafting techniques. For example, in Japan, where land use is intensive and the availability of new farmland is scarce, almost 95 percent of the watermelons (Citrullus lamanis), Oriental melons (Cucumis melo var. makuwa), greenhouse cucumbers (Cucumis sativus), and solanaceous crops are grafted before being transplanted to the field or greenhouse. In 1992, Japan cultivated almost 24,000 hectares of grafted watermelon seedlings in the field, and over 3,000 hectares in the greenhouse. Most of the Oriental melons are grafted to squash rootstocks (Curcurbita spp.). Watermelons and cucumbers are grafted with either gourd stocks (Lagernaria siceraria or C. ficifolia) or mixed hybrids (e.g., C. maxima x C. moschata) (Lee 1994).
Research, Development, and Use of Resistant Rootstocks
The following research programs and commercial
applications further demonstrate the potential for
commercial use of grafting as a means to reduce soil
fumigation with methyl bromide:
- At the U.S. Department of Agriculture/Agricultural Research Service (USDA/ARS) Horticultural Crops Research Laboratory in Fresno, California, over 200 Prunus accessions were screened for resistance traits that showed promise for grafting. Germplasm with resistance to root lesion nematodes (Pratylenchus vulnus) were identified. To determine the acceptability of these rootstocks for commercial production, several additional factors are being considered, including rootstock performance in the nursery (e.g., vigor, tree anchorage, water use efficiency, and fruit production) and graft compatibility between the rootstock and the fruit bearing portion of the tree (Ledbetter 1996).
- At the USDA/ARS in Davis, California, researchers are evaluating clones, selections, and hybrids of various germplasm to identify superior resistance to Phytophthora spp. for walnut. Scientists have determined that chinese wingnut is highly resistant to Phytophthora affecting walnuts in California. Additional research is being conducted to evaluate graft compatibility and potential for hybridization of Chinese wingnut with English walnut (Anonymous1996).
- At the USDA/ARS in Byron, Georgia, researchers are investigating rootstock resistance to nematodes, including the ring and root-knot nematodes (Criconemella xenoplax and Meloidogyne spp.), that frequently cause yield losses in peach orchards. To combat diseases caused by these pests and to help reduce reliance on soil fumigation with methyl bromide, researchers have identified a resistant rootstock that has performed well in research and commercial field trials. Results indicate that the efficacy (in terms of tree survival) of the Guardian rootstock on non-fumigated plots was comparable to results on fumigated plots grown with the currently available rootstocks (e.g., Lovell and Nemaguard) (Nyczepir 1995).
- At the University of California, Davis, Dr. H. Andrew Walker and Dr. Jeffrey Granett have evaluated grape rootstocks for resistance to phylloxera in research and commercial settings. The insect pest Phylloxera vastratix feeds on grape roots, is quite prolific, and, once established, can rapidly destroy a vineyard. The primary method of controlling this insect in vineyards is through the use of resistant rootstocks (Bentley et al. 1996). As a result, numerous rootstocks with proven resistance to phylloxera have been developed and are widely used commercially (Walker and Butzke 1997, Wolpert et al. 1992, Walker 1997). According to Walker (1997), "almost all phylloxera resistant rootstocks are composed of Vitis berlandieri, V. riparia and V. rupestris in various combinations. The primary stocks in California are 5C, 110R, 3309C, 101-14Mgt, 1103P, and Freedom. In addition, there are about ten more in general use. Rootstocks are selected based upon the soils, climate and viticultural needs of a particular area."
- Between 1982 and 1991, Dr. Alberto Gomez conducted several extensive grafting studies on melon plants for the University of Valencia in Spain. The studies showed that, for melon plants, grafting will produce a larger yield and enable plants to live longer. These results were based upon a study prepared in 1982, using Roget melons grafted over Curcurbita moschata, and on a study in 1984 that evaluated the performance of Tetsukabuto grafted over Just melons. The yield increases achieved through grafting ranged from 30 to 35 percent. Additionally, Dr. Gomez prepared a study to demonstrate the benefits of grafting for watermelons. In 1982, he found that watermelons can be grafted to have a superior resistance to Fusarium oxysporum niveau (Gomez 1992).
Costs
Table 1 presents a cost comparison for grafting and standard methyl bromide fumigation for vegetable, orchard, and vineyard crops. The grafting cost estimates are for activities conducted by nurseries to prepare transplant stock for sale to growers. Typically, grafting is performed by agricultural technicians that can process up to 1,000 grafts per day, therefore, the relative impact on the price of the transplant to the grower is small (Ledbetter 1996b). The majority of the costs to nurseries would be to conduct research and development activities after the completion of university research trials. As shown in Table 1, the costs for grafting orchard and vineyard rootstocks is less than the cost of fumigation with methyl bromide. This suggests that grafting technology can be an economical technology to help reduce the need for methyl bromide fumigation for these crops. Costs of grafting for vegetable crops is more expensive than fumigation, however, vegetable grafting costs are expected to decrease as the mechanized grafting technology becomes increasingly commercialized (Maynard 1996).
| Crop | Grafting | MeBr Fumigation |
|---|---|---|
| Vegetables | 1.80 - 2.28 | 0.41 - 0.92 |
| Orchard | 0.05 - 0.06 | 1.79 - 6.07 |
| Vineyard | 1.75 | 2.14 - 3.33 |
Sources: Gomez 1992, Ledbetter 1996b, Anonymous 1993, Anonymous 1992.
References
- Anonymous. De-bugging the wine industry. Oregon Business 1992, 15(6), 12.
- Anonymous. Methyl Bromide Alternatives; United States Department of Agriculture: Beltsville, MD, Vol. 2, No. 4, 1996.
- Anonymous. Sample Costs to Produce Organic Wine Grapes in the North Coast; United States Department of Agriculture. Cooperative Extension Service. University of California: Davis, CA, 1993.
- Bentley, W.J.; Smith, R.; Zalom, F.; Granett, J. Grape pest management guidelines. Internet: http://www.ipm.ucdavis.edu, 1996.
- Gomez, A. Ph.D. Thesis, Polytechnic University of Valencia, 1992.
- Ledbetter, C.; Peterson, S. Presented at the 1996 Annual International Conference on Methyl Bromide Alternatives and Emissions Reductions, November 1996a, Orlando, FL; paper 31.
- Ledbetter, C. United States Department of Agriculture, Agricultural Research Service, Fresno, CA, personal communication, 1996b.
- Lee, J. Cultivation of grafted vegetables I. Current status, grafting methods, and benefits. HortScience 1994, 29(4), 235-239.
- Maynard, D., Gulf Coast Research and Education Center, University of Florida, Bradenton, FL, personal communication, 1996.
- McKenry, M.; Kretsch, J. Presented at the 1995 Annual International Conference on Methyl Bromide Alternatives and Emissions Reductions, November 1995, San Diego, CA; paper 32.
- Nyczepir, A.P.; Beckman, T.G.; Bertrand, P.F. Presented at the 1995 Annual International Conference on Methyl Bromide Alternatives and Emissions Reductions, November 1995, San Diego, CA; paper 105.
- Rodriguez-Kabana, R., Department of Plant Pathology, Auburn University, Auburn, Alabama, personal communication, 1995.
- Walker, M.A; Butzke, C. "The grape rootstock breeding program at UC Davis." Internet: http://wineserver.ucdavis.edu, 1997b.
- Walker, M.A., Department of Viticulture and Enology, University of California, Davis, CA, personal communication, 1997a.
- Wolpert, J.A.; Walker, M.A.; Weber, E. Presented at the Rootstock Seminar - A Worldwide Perspective, Reno, NV, June 1992; American Society for Enology and Viticulture.
Please note that this publication discusses specific proprietary products and pest control methods. Some of these alternatives are now commercially available, while others are in an advanced stage of development. In all cases, the information presented does not constitute a recommendation or an endorsement of these products or methods by the Environmental Protection Agency (EPA) or other involved parties. Neither should the absence of an item or pest control method necessarily be interpreted as EPA disapproval.
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