Grafting Vegetable-Crop Plants: Pros and Cons. M. Edelstein. Department of Vegetable Crops, Agricultural Research Organization, Newe Ya'ar. Research ...
Grafting Vegetable-Crop Plants: Pros and Cons M. Edelstein Department of Vegetable Crops, Agricultural Research Organization, Newe Ya’ar Research Center, Ramat Yishay, Israel Keywords: Grafting, soil-borne pathogens, salt stress, low temperature stress, fruit yield. Abstract Grafting comprises the uniting of two living plant parts so that they grow as a single plant. Grafting of vegetable plants is a common practice in Japan, Korea, and several European countries; its main purpose is to control soil-borne diseases and nematodes. In addition, grafted plants may have higher yields, improved tolerance to environmental stresses such as high boron, soil salinity, and low soil temperatures. Grafting of vegetable crops is an old practice; grafting of cucurbits was briefly described in a seventeenth century book in Korea. Grafting was first used commercially in 20th century vegetable production in Asia. Grafting of eggplants started in the 1950s, followed by grafting of cucumber and tomato around 1960 and 1970, respectively. In 2000, a total of 700 million grafted vegetable crop plants were used in Japan and Korea. There are various manual grafting methods that suit each vegetable, and recently, grafting machines have been developed to produce the huge amount of grafted plants required. In spite of its advantages, there are some problems associated with grafting. These include the additional cost, graft incompatibility that commonly appears to cause physiological disorders, and reductions in yield, fruit quality, and flower formation. Initiating or increasing the use of grafted plants should be done only after the benefits and risks of grafted seedlings have been fully understood. ADVANTAGES Resistance to Disease and Insect Pests Damage to vegetable production associated with continuous cropping has been ascribed principally to soil–borne diseases and nematodes (Takahashi, 1984). Fumigation with methyl bromide prior to planting plays an important sanitizing role in reducing this problem, but the use of methyl bromide is expected to be banned worldwide in the near future. The use of other chemicals is also limited because of environmental pollution concerns; therefore, alternative measures for disease management are needed. One of the alternatives could be the use of grafted plants. Resistance to root diseases can be induced by the rootstock. For example Fusarium was controlled by grafting in: melon (Cohen et al., 2002; Lee, 1994; Morra, 1998; Traka Mavrona et al., 2000), cucumber (Pavlou et al., 2002), watermelon (Heo, 2000), and tomato (Gindrat et al., 1977). Moreover grafted plants may be more tolerant to other diseases, such as sudden wilt in melons, caused by Monosporascus cannonballus (Edelstein et al., 1999), bacterial wilt in tomato (Tikoo et al., 1979) and eggplant (Monma et al., 1997), and verticillium wilt in tomato (Bravenboer, 1962). Damage by soil nematodes (Meloidogyne spp.) can be controlled by grafting onto resistant rootstocks. For example, tomato grafted on a resistant roostock was more resistant to nematodes than non-grafted tomato (Mian et al., 1995). Grafting can transfer resistance against the carmine spider mite (Tetranychus cinnabarinus) from Lagenaria rootstocks to Cucurbita scions (Edelstein et al., 2000). Moreover, some rootstocks can render grafted plants resistant to some viruses (Iwasaki and Inaba, 1990). Stress Tolerances Agricultural production in arid and semi-arid regions relies mainly on irrigation. Proc. VII IS on Prot. Cult. Mild Winter Climates Eds. D.J. Cantliffe, P.J. Stoffella & N. Shaw Acta Hort. 659, ISHS 2004
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However, the water resources in these regions are scarce; therefore, the use of marginal water for irrigation is increasing. These marginal waters contain relatively high salt levels and, in some cases, high boron concentrations. Moreover, fertigation can increase the salt concentration in the soil solution. Romero et al. (1997) compared the effects of salinity on two varieties of melon that were grafted onto three hybrids of squash with its effects on non-grafted melons, and found that the grafted melons were more tolerant to salinity than non-grafted ones. Romero et al. (1997) suggested that grafted plants developed various mechanisms to avoid physiological damage caused by the excessive accumulation of Cl- and Na+ in the leaves, including exclusion of Cl- and/or decrease in Cl- absorption by the roots and the replacement or substitution of total K+ by total Na+ in the foliar parts. Rootstock tolerance to salinity differs widely among plant species, e.g., Cucurbita spp. were found to be less inhibited by NaCl than L. siceraria (Matsubara, 1989). Grafted plants may also be more tolerant to low root temperatures. Okimura et al. (1996) reported that growth of tomato plants grafted onto ‘KNVF’ (L. esculentum × L. hirsutum) was excellent at low soil temperatures of 10 and 13°C, in contrast to that of non-grafted tomato plants. They also found that watermelon plants grafted onto ‘Shintosa No.1’ exhibited higher resistance to low soil temperatures than watermelon grafted on watermelon and onto wax gourd (Benicasa hispida), and that eggplants grafted onto ‘Taibyo VF’ (S. integrifolium × S. melongena) grew better at low temperatures of 18 and 21°C than non-grafted plants. It was suggested that the tolerance of rootstocks to low temperatures derives from differences in membrane lipids. These examples indicate that the grafting of plants onto cold-tolerant rootstocks could lead to normal production of the crop and minimize the damage from sub-optimal temperatures. Growth and Yields The rootstock can also greatly influence plant growth, yield and fruit quality. Shimada and Moritani (1977) reported that cucumber plants grafted onto pumpkin (Cucurbita) rootstocks produced more dry mass than self-rooted cucumber, and White (1963) found that grafted tomato plants were more vigorous and had higher yields than non-grafted ones. Grafting of watermelon onto Cucurbita enhanced the vegetative and root development of the plant, led to earlier and increased yield, and improved the fruit quality (Chouka and Jebari, 1999). In some cases, the rootstock’s vigorous root system increases the efficiency of water and nutrient absorption; it may also serve as a source of endogenous plant hormones, thus leading to increased yield in addition to controlling diseases (Lee, 1994). In fact, Leoni et al. (1990) reported an increase of 310% in the yield of Pacio melon grafted on RS841. In other melon hybrids the increase was only 50-60%. DISADVANTAGES Cost The grafted plants are more expensive because of the costs of rootstock seeds, and the labor required for the grafting and for raising the grafted seedlings. Incompatibility Garner (1979) defined graft incompatibility as failure of the scion to unite with the rootstock, failure of the grafted plant to grow in a healthy manner, or premature death following grafting. Poor rootstock-scion compatibility may result in blocking of the transport of photosynthates from scion to rootstock, as reported by Stigter (1971) for melon grafted on Cucurbita ficifolia. This can lead to yield reduction, poor fruit quality, and even plant collapse. Rootstock-scion compatibility depends on anatomical, physiological and genetic variables. Oda et al. (1993) suggested that reducing the difference in hypocotyl diameter between the cucumber scion and the squash rootstock may increase compatibility, but the numbers of vascular bundles did not affect compatibility. Traka-Mavrona et al. (2000) also reported that differences in stem diameter 236
between Cucurbita and Cucumis reduced the survival rate of grafts, but fruit yield was not affected by any rootstock. Yields of tomato plants grafted onto Datura tatula were significant lower than non-grafted tomato plants (Karmer, 1957). Fruit Quality It is known that rootstocks can affect the quality of the fruit borne by the scion. For example, some Cucurbita spp. rootstocks adversely affect the shape and taste of watermelon and melon fruits. In tomato, fruit quality was slightly lowered by grafting, relative to that non-grafted plants (Harnett, 1974). Moreover, physiological disorders can appear in fruits from grafted plants, depending on the rootstock (Matsuda and Honda, 1981). CONCLUSION Grafting of vegetable crops is practiced in many countries where land use is very intensive. Grafting a crop plant onto another cultivar or species can reduce susceptibility to soil-borne diseases, increase tolerance to salinity and low temperatures, and enhance vegetative growth and fruit yield. However, rootstocks must be carefully chosen, because they may have additional, undesirable effects on the grafted scion. In general, the benefits of using grafted plants outweigh the risks. Literature Cited Bravenboer, L. 1962. Control of soil-borne diseases in tomatoes by grafting on resistant rootstocks. Proc. 16th Int. Hort. Congr. Brussels. 1:8. Chouka, A.S. and Jebari, H. 1999. Effect of grafting on watermelon vegetative and root development, production and fruit quality. Acta Hort. 492:85-93. Cohen, R., Horev, C., Burger, Y., Shriber, S., Hershenhorn, J., Katan, J. and Edelstein, M. 2002. Horticultural and pathological aspects of fusarium wilt management using grafted melons. HortScience 37:1069-1073. Edelstein, M., Cohen, R., Shraiber, S., Pivonia, S. and Shtienberg, D. 1999. Integrated management of sudden wilt in melons caused by Monosporascus cannonballus using grafting and reduced rates of methyl bromide. Plant Dis. 83:1142-1145. Edelstein, M., Tadmor, Y., Abo-Moch, F., Karchi, Z. and Mansour, F. 2000. The potential of Lagenaria rootstock to confer resistance to the carmine spider mite, Tetranychus cinnabarinus (Acari: Tetranychidae) in Cucurbitaceae. Bull. Ent. Res. 90:113-117. Garner, R.J. 1979. Compatibility and cambial contact. p. 49-67. In: The Grafter’s Handbook. 4th ed. Oxford University Press, New York. Gindrat, D., Ducrot, V. and Caccia, R. 1977. Varietal resistance and grafting: two methods of preventive control for tomato Fusarium wilt. Revue Suisse Viticulture Arboriculture Horticulture. 9:109-114. (in French) Harnett, R.F. 1974. Resurgence of interest in grafting techniques on heated tomato crops. Grower 82:861-862. Heo, Y.C. 2000. Disease resistance of Citrullus germplasm and utilization as watermelon rootstocks Ph.D. Diss., Kyung Hee Univ., Korea. (in Korean with English summary). Iwasaki, M. and Inaba, T. 1990. Effects of different Cucurbita rootstock on incidence of viral wilt in grafted cucumber plants. Ann. Phytopathol. Soc. Japan. 56:674-676. Karmer, M. 1957. Physiological aspects of grafting solanaceous plants. Biologico 23:73-76. (in Spanish) Lee, J.M. 1994. Cultivation of grafted vegetables. I. Current status, grafting methods, and benefits. HortScience 29:235-239. Leoni, S., Grudina, R., Cadinu, M. and Carletti, M.G. 1990. The influence of four rootstocks on some melon hybrids and a cultivar in greenhouse. Acta Hortic. 287:127134. Matsubara, S. 1989. Studies on salt tolerance of vegetables. 3. Salt tolerance of rootstocks. Bull. Okayama Univ., Agric. 73:17-25. 237
Matsuda, T. and Honda, H. 1981. Studies on physiological disorder in the fruit of melon (1) Influence of grafting and plant-and-fruit pruning in ‘Prince’ melon. Bull. Veg. Ornam. Crops Res. Stn. Japan. C5:31-50. (in Japanese with English summary) Mian, I.H., Ali, M. and Akhter, R. 1995. Grafting of Solanum rootstocks to control rootknot of tomato and bacterial wilt of eggplant. Bull. Inst. Tropic. Agric. Kyushu Univ. 18:41-47. Monma, S., Akazawa, S., Shimosaka, K., Sakata, Y. and Matsunaga, H. 1997. ‘Daitaro’, a bacterial wilt- and fusarium wilt-resistant hybrid eggplant for rootstock. Bull. Natl. Res. Inst. Veg. Ornam. Plants and Tea Japan. 12:73-83. (in Japanese with English summary) Morra, L. 1998. Potential and limits of grafting in horticulture. Informatore Agrario 54:39-42. Oda M, Tsuji K, Sasaki H. 1993. Effect of hypocotyls morphology on survival rate and growth of cucumber seedlings grafted on Cucurbita spp. JARQ 26:259-263. Okimura, M., Matsou, S., Arai, K. and Okitsu, S. 1986. Influence of soil temperature on the growth of fruit vegetable grafted on different stocks. Bull. Veg. Ornam. Crops Res. Stn. Japan. C9:43-58. (in Japanese with English summary) Pavlou, G.C., Vakalounakis, D.J. and Ligoxigakis, E.K. 2002. Control of root and stem rot of cucumber, caused by Fusarium oxysporum f. sp. Radicis-cucumerinum, by grafting onto resistant roostocks. Plant Dis. 86:379-382. Romero, L., Belakbir, A., Ragala, L. and Ruiz M.J. 1997. Response of plant yield and leaf pigments to saline conditions: effectiveness of different rootstocks in melon plant (Cucumis melo L.). Soil Sci. Plant. Nutr. 43:855-862. Shimada, N. and Moritani, M. 1977. Nutritional studies on grafting of horticultural crops. (2) Absorption of minerals from various nutrient solutions by grafted cucumber and pumpkin plants. J. Japan Soc. Soil Sci. Plant Nutr. 48:396-401. Stigter, H.C.M. 1971. Some aspects of the physiological functioning of the graft muskmelon/Cucurbita ficifolia. Pflanzenphysiologie 65:223-231. Takahashi, K. 1984. Problems in vegetable cultivation using grafted plants. Yasaishikenjo Kenk yushiryo 11. NIVOT, Ano. (in Japanese) Tikoo, S.K., Mathai, P.J. and Kishan, R. 1979. Successful graft culture of tomato in bacterial wilt sick soil. Current Sci. 48:259-260. Traka-Mavrona, E., Koutsika-Sotiriou, M., Pritsa, T. 2000. Response of squash (Cucurbita spp.) as rootstock for melon (Cucumis melo L.). Sci. Hort. 83:353-362. White, R.A.J. 1963. Grafted glasshouse tomatoes give heavier crops. N.Z.J. Agric. 106:247-248.
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