HORTSCIENCE 47(2):164–170. 2012. pathogens have been reported in grafted sola- naceous and cucurbitaceous crops. Moreover, certain foliar fungal and viral diseases were Defense Mechanisms Involved suppressed when susceptible scions were grafted onto specific rootstocks (Louws et al., in Disease Resistance of 2010). Diseases controlled by grafting in dif- ferent vegetable crops are listed in Table 1. Grafted Vegetables Soilborne fungal and oomycete diseases. The earliest reported use of vegetable graft- Wenjing Guan and Xin Zhao1 ing for disease control was for management Horticultural Sciences Department, University of Florida, 1301 Fifield Hall, of fusarium wilt in cucurbits (Sakata et al., Gainesville, FL 32611 2005). Commonly used cucurbitaceous root- stocks are non-hosts to most formae speciales Richard Hassell of F. oxysporum, and thus grafting has been Clemson University CREC, 2700 Savannah Highway, Charleston, SC 29414 successfully used to control fusarium wilt in cucurbit production (Louws et al., 2010). Judy Thies Verticillium wilt, primarily caused by Verti- USDA ARS U.S. Vegetable Laboratory, 2700 Savannah Highway, Charleston, cillium dahliae, is another vascular wilt disease that often affects Solanaceae and Cucurbita- SC 29414 ceae. Studies with plants grafted onto com- Additional index words. Cucurbitaceae, induced resistance, microbial community, nutrient mercial rootstocks and subjected to infection uptake, rootstock, Solanaceae with V. dahliae indicated that both scions and rootstocks contributed to disease resistance Abstract. Grafting with resistant rootstocks is an effective strategy to manage a variety of of the grafted combinations in watermelons, soilborne diseases and root-knot nematodes in solanaceous and cucurbitaceous vegeta- melons (Cucumis melo L.), cucumbers bles. In addition, improved resistance to some foliar diseases and viruses has also been (Cucumis sativus L.), and tomatoes (Solanum reported in grafted plants. Hence, grafting technology is considered an important and lycopersicum L.) (Paplomatas et al., 2002). innovative practice of integrated pest management and a promising alternative for soil Monosporascus sudden wilt, caused by fumigants in vegetable production. Inherent resistance within rootstocks and improved Monosporascus cannonballus, is an impor- plant nutrient uptake are generally suggested as the main reasons for improved disease tant soilborne disease of melon and water- control in grafted vegetables. However, increasing evidence indicated that systemic defense melon in hot and semiarid areas. Grafting mechanisms may also play an important role in plant defense as a result of grafting. This scions of susceptible melon cultivars onto C. review analyzes current literature on the use of grafting techniques for disease manage- maxima Duch. and C. maxima · C. moschata ment in vegetable crops, discusses potential mechanisms associated with grafting-conferred rootstocks improved resistance of melon plant defense, and identifies needs for future research to promote more effective and (Edelstein et al., 1999) although Cucurbita efficient use of grafting technology to support sustainable vegetable production. is normally regarded as a host for M. can- nonballus (Mertely et al., 1993). However, Grafting, with selected resistant root- A few reviews have been published re- the improved resistance and better yield with stocks, for the purpose of controlling diseases cently, which address the integrated use of grafted plants was inconsistent. The variable and pests is an ancient practice widely used in grafting techniques in vegetable production. results might be attributed to differences in cultivating a variety of woody trees. Some of Among them, a review by Lee and Oda (2003) rootstock–scion combinations and growing the well-known examples include controlling covered topics including grafting methods and conditions. Phytophthora blight, caused by tristeza on citrus, fireblight and collar rot on procedures, grafting physiology, and produc- Phytophthora capsici, is regarded as one of apples, and nematodes on peaches and wal- tion status of grafted vegetables and orna- the most destructive diseases in production of nuts (Mudge et al., 2009). mental crops. Cucurbit grafting including the cucurbits. In P. capsici-infested fields, yields Research on herbaceous vegetable grafting history, current status, and benefits of vege- of cucumbers grafted on bottle gourd [Lage- began in the 1920s with watermelon [Citrullus table grafting were well documented by Davis naria siceraria (Mol.) Standl.], C. moschata lanatus (Thunb.) Matsum. & Nakai] grafted and colleagues (2008). Louws and coauthors Duch., and wax gourd [Benincasa hispida onto squash rootstocks (Cucurbita moschata (2010) summarized current literature on use (Thunb.) Cogn.] rootstocks were significantly Duch.) to overcome yield loss caused by of grafting technology to manage diseases and increased and vegetative growth was more fusarium wilt (Sato and Takamatsu, 1930). pests in vegetable production. The review pro- vigorous (Wang et al., 2004). Watermelons Since then, grafting has been widely used in vided up-to-date information on disease cy- grafted onto selected bottle gourd rootstocks Asia and European countries as an effective cles, current disease management practices, and also exhibited resistance to P. capsici (Kousik tool for managing several soilborne diseases effects of rootstocks on controlling different and Thies, 2010). Corky root disease caused and root-knot nematodes in the Solanaceae pathotypes. Some important disease resistance by Pyrenochaeta lycopersici is a severe prob- and Cucurbitaceae. Interest in vegetable graft- mechanisms were mentioned, whereas system- lem for Solanaceae. Tomatoes grafted onto ing has recently grown in the United States as atic discussion of this topic was rather limited. ‘Beaufort’ rootstocks (S. lycopersicum · S. an alternative to soil fumigants and as an Unlike previous work, the current review habrochaites S. Knapp & D.M. Spooner) had integrated pest management practice in var- explores specifically the defense mechanisms lower disease incidence, higher yield, and ious crop production systems (Kubota et al., in grafted vegetable plants and discusses fu- larger fruit (Hasna et al., 2009). Similar re- 2008). ture research initiatives needed to advance sults were also found in grafted eggplants our understanding of the underlying grafting (S. melongena L.) (Iouannou, 2001). mechanisms and to enhance vegetable root- Soilborne bacterial diseases. Tomato bac- stock breeding programs. terial wilt, caused by Ralstonia solanacea- rum, is one of the most destructive diseases of Received for publication 6 Sept. 2011. Accepted tomato. Resistance to bacterial wilt in toma- for publication 13 Dec. 2011. We thank Drs. Peter J. Dittmar and Guodong Liu Diseases Controlled by Grafting toes is a quantitative trait and is closely associ- for providing comments before the original manu- in Vegetable Production ated with small fruit size (Louws et al., 2010). script was submitted. Thus, few resistant tomato cultivars are com- 1To whom reprint requests should be addressed; Improved resistances to many soilborne mercially available (King et al., 2010). Grafting e-mail zxin@ufl.edu. fungal, oomycete, bacterial, and nematode scions of susceptible tomato cultivars onto 164 HORTSCIENCE VOL. 47(2) FEBRUARY 2012 REVIEW Table 1. Diseases reported to be controlled by grafting in different vegetable crops. Colletotrichum coccodes) on tomatoes and Disease and pest Pathogen Crops eggplants, and Rhizoctonia damping off Fungal and oomycete diseases (caused by Rhizoctonia solani) on tomatoes Fusarium wilt Fusarium oxysporum Tomato, pepper, watermelon, (King et al., 2008; Louws et al., 2010) (Table melon, cucumber 1). Grafting has also been reported to im- Fusarium crown and root rot Fusarium oxysporum; Tomato, pepper, watermelon prove crop resistance to the foliar fungal Fusarium solani diseases such as powdery mildew (caused Verticillium wilt Verticillium dahliae Tomato, eggplant, watermelon, by Podosphaera xanthii) and downy mildew melon, cucumber (caused by Pseudoperonospora cubensis)on Monosporascus sudden wilt Monosporascus cannonballus Watermelon, melon Phytophthora blight Phytophthora capsici Tomato, pepper, watermelon, cucumbers, when certain rootstocks were cucumber used (Louws et al., 2010; Sakata et al., 2006). Corky root Pyrenochaeta lycopersici Tomato, eggplant Target leaf spot Corynespora cassiicola Cucumber Inherent Resistance within Rootstocks Black root rot Phomopsis sclerotioides Cucumber, melon as the First Line of Defense Gummy stem blight Didymella bryoniae Melon Southern blight Sclerotium rolfsii Tomato Because grafting is used primarily for con- Brown root rot Colletotrichum coccodes Tomato, eggplant trolling soilborne diseases, the defense mech- Rhizoctonia damping off Rhizoctonia solani Tomato anisms are generally associated with inherent Powdery mildew Podosphaera xanthii Cucumber Downy mildew Pseudoperonospora cubensis Cucumber resistance within rootstocks (King et al., Bacterial diseases 2008). Rootstock selection and breeding has Bacterial wilt Ralstonia solanacearum Tomato, pepper, eggplant targeted both non-host and host resistance. Nematodes Using non-host resistance. Non-host dis- Root-knot Meloidogyne spp. Cucumber, melon, watermelon, ease resistance refers to the resistance pro- tomato, eggplant, pepper vided by all members of a plant species Viral diseases against all races of a certain pathogen and