Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] is an important specialty crop in Florida, a leading watermelon producer in the United States, with an average production value exceeding $80 million each year (USDA, 2017). Seedless cultivars are commonly grown by Florida growers, in response to the increasing market demand for seedless watermelon in the United States (Elwakil et al., 2017; Ferreira and Perez, 2016). The tetraploids used in developing triploid watermelons usually have very limited resistance to fusarium wilt and this may have resulted in most of common seedless watermelon cultivars being susceptible to fusarium wilt (Bruton et al., 2007).
Fusarium wilt of watermelon, caused by FON, is a reemerging pathogen that can cause 100% yield losses in extreme cases (Bruton, 1998). Among the first described fusarium wilt diseases, fusarium wilt of watermelon is still economically important as it occurs worldwide and the pathogen continues to evolve into new and more aggressive races, for which most commercial cultivars lack or have limited resistance (Egel and Martyn, 2013). The phaseout of the broad-spectrum soil fumigant methyl bromide has made it more difficult to manage fusarium wilt (King et al., 2008), thus, requiring producers to use more integrated management strategies including host resistance, biological and chemical controls, crop rotation, and grafting (Everts and Himmelstein, 2015).
Grafting has been widely used in solanaceous and cucurbitaceous crops as a novel integrated disease management strategy, especially when the availability of resistant cultivars is limited. By using selected rootstocks, grafting can efficiently control the soil-borne diseases caused by a wide range of pathogens including nematodes (e.g., root-knot, Meloidogyne), fungi (e.g., Verticillium, Fusarium, Pyrenochaeta, and Monosporascus), oomycetes (e.g., Phytophthora), bacteria (e.g., Ralstonia), and several soil-borne viral pathogens (Louws et al., 2010; Thies et al., 2010). Because many commercial watermelon cultivars are susceptible to FON race 2 (Miguel et al., 2004) and race 3 (Egel and Martyn, 2013), interspecific and intergeneric grafting, and the use of interspecific hybrid rootstocks are commonly practiced (Keinath and Hassell, 2014; Louws et al., 2010). Grafting can provide other benefits (e.g., improved fruit yield and lycopene content) besides disease management to watermelon producers, but these benefits can vary depending on the plant material and production systems implemented (Kyriacou et al., 2017; Rouphael et al., 2010).
The vigorous root system from the rootstock can also help improve growth and fruit yield of grafted plants regardless of infections from soil-borne pathogens (Lee et al., 2010). Several studies have confirmed the positive impact of specific rootstocks on plant growth and fruit quality (Alan et al., 2007; Chouka and Jebari, 1997; Kyriacou et al., 2016; Yetisir and Sari, 2003). The use of ‘Shintoza’ (C. maxima × C. moschata) rootstock increased fruit size and yield stability of grafted plants without affecting fruit quality (Miguel et al., 2004). The interest in watermelon grafting as an effective tool for fusarium wilt control has been identified among growers in Florida; however, to date limited research-based information is available regarding the use of grafted plants in fusarium wilt management in the Florida watermelon production systems.
Depending on grafting skill, available space, and healing environment, different grafting techniques, including tongue approach, hole insertion, and one-cotyledon grafting, are commonly used for commercial production of grafted watermelon transplants (Davis et al., 2008). In addition, root excision with regeneration of adventitious roots has been used in cucurbit grafting especially when the grafting process is mechanized (Guan and Zhao, 2015). It has also been suggested that a primary nursery can conduct grafting and remove the root system of the grafted plants after healing, while a secondary nursery receiving the shipped grafted plants with root excision can re-root the plants and distribute the re-rooted grafted plants locally (Sabatino, 2013). Root excision could conserve rootstock hypocotyl carbohydrate to improve the healing process (Memmott, 2010). However, it is unclear whether re-rooted, grafted watermelon seedlings will differ from the grafted plants without root excision in terms of their effectiveness in suppressing FON.
It was hypothesized that seedless watermelon plants grafted with selected C. moschata and C. maxima × C. moschata hybrid squash rootstocks could be highly resistant to FON infection and that root excision and regeneration would not affect the performance of grafted plants. Specifically, the objectives of this study were to 1) assess the growth and yield performance of grafted and nongrafted seedless watermelon plants when inoculated with FON race 2 and 2) determine the effect of root excision and regeneration on grafted plant performance under FON race 2 inoculation.
Bekhradi, F., Kashi, A. & Delshad, M. 2011 Effect of three cucurbits rootstocks on vegetative and yield of ‘Charleston Gray’ watermelon Intl. J. Plant Prod. 5 105 110
Bruton, B.D. 1998 Soilborne diseases in Cucurbitaceae: Pathogen virulence and host resistance, p. 143–146. In: J. McCreight (ed.). Cucurbitaceae’98. Amer. Soc. Hort. Sci. Press, Alexandria, VA
Bruton, B.D., Fish, W.W., Zhou, X.G., Everts, K.L. & Roberts, P.D. 2007 Fusarium wilt in seedless watermelons. 2007 Southeast Regional Veg. Conf. Proc., Savannah, GA. p. 93–98
Chouka, A. & Jebari, H. 1997 Effect of grafting on watermelon vegetative and root development, production and fruit quality. Intl. Symp. Cucurbits. 492
Coolong, T. 2015 Trial report: Seedless watermelon variety evaluation 2015. 25 May 2018. <https://site.extension.uga.edu/colquittag/files/2016/01/2015-UGA-Tifton-Watermelon-Variety-Trial-Results.pdf>.
Davis, A.R., Perkins-Veazie, P., Sakata, Y., López-Galarza, S., Maroto, J.V., Lee, S.G., Huh, Y.C., Sun, Z., Miguel, A., King, S.R., Cohen, R. & Lee, J.M. 2008 Cucurbit grafting Crit. Rev. Plant Sci. 27 50 74
Elwakil, W.M., Dufault, N.S., Freeman, J.H. & Mossler, M.A. 2017 Florida crop/pest management profile: Watermelon. UF/IFAS EDIS publication CIR1236. 25 May 2018. <http://edis.ifas.ufl.edu/pdffiles/PI/PI03100.pdf>.
Everts, K.L. & Himmelstein, J.C. 2015 Fusarium wilt of watermelon: Towards sustainable management of a re-emerging plant disease Crop Protection 73 93 99
Ferreira, G. & Perez, A. 2016 Fruit and tree nuts outlook. 21 Sept. 2018. <http://usda.mannlib.cornell.edu/usda/ers/FTS//2010s/2016/FTS-03-31-2016.pdf>.
Freeman, J.H., Dittmar, P.J. & Vallad, G.E. 2015 Commercial vegetable production in Florida. UF/IFAS EDIS Publication. 25 May 2018. <http://edis.ifas.ufl.edu/cv100>.
Guan, W. & Zhao, X. 2015 Effects of grafting methods and root excision on growth characteristics of grafted muskmelon plants HortTechnology 25 706 713
Huang, Y., Jiao, Y., Nawaz, M.A., Chen, C., Liu, L., Lu, Z., Kong, Q., Cheng, F. & Bie, Z. 2016 Improving magnesium uptake, photosynthesis and antioxidant enzyme activities of watermelon by grafting onto pumpkin rootstock under low magnesium Plant Soil 409 229 246
Huitrón, M.V., Diaz, M., Dianez, F. & Camacho, F. 2007 The effect of various rootstocks on triploid watermelon yield and quality J. Food Agr. Environ. 5 344 348
Ioannou, N., Ioannou, M. & Hadjiparaskevas, K. 2002 Evaluation of watermelon rootstocks for off-season production in heated greenhouses Acta Hort. 579 501 506
Keinath, A.P. & Hassell, R.L. 2014 Control of Fusarium wilt of watermelon by grafting onto bottlegourd or interspecific hybrid squash despite colonization of rootstocks by Fusarium Plant Dis. 98 255 266
Komada, H. 1975 Development of a selective medium for quantitative isolation of Fusarium oxysporum from natural soils Rev. Plant Protection Res. 8 114 124
Kyriacou, M.C., Rouphael, Y., Colla, G., Zrenner, R. & Schwarz, D. 2017 Vegetable grafting: The implications of a growing agronomic imperative for vegetable fruit quality and nutritive valueFront. Plant Sci. doi: 10.3389/fpls.2017.00741
Kyriacou, M.C., Soteriou, G.A., Rouphael, Y., Siomos, A.S. & Gerasopoulos, D. 2016 Configuration of watermelon fruit quality in response to rootstock-mediated harvest maturity and postharvest storage J. Sci. Food Agr. 96 2400 2409
Lee, J.M., Kubota, C., Tsao, S.J., Bie, Z., Echevarria, P.H., Morra, L. & Oda, M. 2010 Current status of vegetable grafting: Diffusion, grafting techniques, automation Scientia Hort. 127 93 105
Ling, N., Zhang, W., Wang, D., Mao, J., Huang, Q., Guo, S. & Shen, Q. 2013 Root exudates from grafted-root watermelon showed a certain contribution in inhibiting Fusarium oxysporum f. sp. niveum PLoS One 8 e63383
Liu, Q., Zhao, X., Brecht, J.K., Sims, C.A., Sanchez, T. & Dufault, N.S. 2017 Fruit quality of seedless watermelon grafted onto squash rootstocks under different production systems J. Sci. Food Agr. 97 4704 4711
Liu, Y., Qi, H., Bai, C., Qi, M., Xu, C., Hao, J., Li, Y. & Li, T. 2011 Grafting helps improve photosynthesis and carbohydrate metabolism in leaves of muskmelon Intl. J. Biol. Sci. 7 1161 1170
Louws, F.J., Rivard, C.L. & Kubota, C. 2010 Grafting fruiting vegetables to manage soilborne pathogens, foliar pathogens, arthropods and weeds Scientia Hort. 127 127 146
Malcolm, G.M., Kuldau, G.A., Gugino, B.K. & Jiménez-Gasco, M.M. 2013 Hidden host plant associations of soilborne fungal pathogens: An ecological perspective Phytopathology 103 538 544
Memmott, F. 2010 Refinement of innovative watermelon grafting methods with appropriate choice of developmental stage, rootstock type, and root treatment to increase grafting success. Clemson Univ., Clemson, SC, MS Thesis
Miguel, A., Maroto, J.V., Bautista, A.S., Baixauli, C., Cebolla, V., Pascual, B., Lopez, S. & Guardiola, J.L. 2004 The grafting of triploid watermelon is an advantageous alternative to soil fumigation by methyl bromide for control of Fusarium wilt Scientia Hort. 103 9 17
Miller, G., Khalilian, A., Adelberg, J.W., Farahani, H.J., Hassell, R.L. & Wells, C.E. 2013 Grafted watermelon root length density and distribution under different soil moisture treatments HortScience 48 1021 1026
Moreno, B., Jacob, C., Rosales, M., Krarup, C. & Contreras, S. 2016 Yield and quality of grafted watermelon grown in a field naturally infested with fusarium wilt HortTechnology 26 453 459
Sabatino, L. 2013 Advances in vegetable grafting and new nursery patterns for grafted plant production. Università degli Studi di Palermo, Italy, PhD Diss
Thies, J.A., Ariss, J.J., Hassell, R.L., Olson, S., Kousik, C.S. & Levi, A. 2010 Grafting for management of southern root-knot nematode, Meloidogyne incognita, in watermelon Plant Dis. 94 1195 1199
USDA 2017 Vegetables 2016 summary. <http://usda.mannlib.cornell.edu/usda/nass/VegeSumm//2010s/2017/VegeSumm-02-22-2017_revision.pdf>.