Grafting of cucurbitaceous and solanaceous crops has become an established integrated pest management tool for the management of soilborne pathogens. The effectiveness of grafting for management of diseases relies on rootstocks that are either nonhost resistant or contain resistance genes for specific soilborne pathogens (Louws et al., 2010). Although the initial and main impetus for using grafted plants has been the ability to grow crops in fields that would otherwise be unsuitable as a result of disease pressure from soilborne pathogens (Lee and Oda, 2003), additional rootstock-derived benefits have been demonstrated.
Rootstock-imparted abiotic stress tolerance has been reviewed extensively (Rouphael et al., 2017; Schwarz et al., 2010). In cucurbit crops, certain rootstocks can improve growth and yield at suboptimal soil temperatures (Ahn et al., 1999; Zhou et al., 2007), reduced irrigation (Rouphael et al., 2008), and salinity (Colla et al., 2006; Huang et al., 2010). Research has focused on cucurbit rootstock root system physiology to help explain this improved tolerance; however, research has only been conducted with figleaf gourd (Cucurbita ficifolia) and is limited to suboptimal soil temperatures (Lee et al., 2005a, 2005b). Although root physiology is important for the maintenance of growth under limiting conditions, morphology should also be considered when investigating soil resource acquisition.
Substantial research has been conducted exploring root system morphology as it relates to resource uptake and use efficiency. Root morphologic and architectural traits such as diameter, length, and spatial distribution all affect water uptake (Comas et al., 2013; Ho et al., 2005; Mickelbart et al., 2015), phosphorus uptake (Hill et al., 2006; Zobel et al., 2007), and salinity tolerance (Lovelli et al., 2012). To date, little research has been conducted to compare cucurbit rootstock root systems. A survey of tomato (Solanum lycopersicum) rootstock root systems was conducted and showed that significant differences exist among commercially available rootstocks (Suchoff et al., 2017). Compared with tomato rootstocks, cucurbit rootstocks span a wider genetic range; in addition to exotic watermelon germplasm (Cohen et al., 2014), common rootstocks for watermelon scions include interspecific hybrids, bottle gourd, squash, and pumpkin (Lee and Oda, 2003). As such, there exists the potential for significant variation among cucurbit rootstock root system morphologies, which may explain some of the improved growth under limiting conditions.
The objectives of the study were 1) to determine if differences exist in root system morphologies among SG ‘Exclamation’, NG ‘Exclamation’, and nine cucurbit rootstocks grown in a solid, soilless medium; and 2) to determine whether these root system morphologies change or remain similar during the initial 3 WAT.
Ahn, S.J., Im, Y.J., Chung, G.C., Cho, B.H. & Suh, S.R. 1999 Physiological responses of grafted cucumber leaves and rootstock roots affected by low root temperature Scientia Hort. 81 397 408
Cohen, R., Tyutyunik, J., Fallik, E., Oka, Y., Tadmor, Y. & Edelstein, M. 2014 Phytopathological evaluation of exotic watermelon germplasm as a basis for rootstock breeding Scientia Hort. 165 203 210
Colla, G., Roupahel, Y., Cardarelli, M. & Rea, E. 2006 Effect of salinity on yield, fruit quality, leaf gas exchange, and mineral composition of grafted watermelon plants HortScience 41 622 627
Daley, S. & Hassell, R. 2014 Fatty alcohol application to control meristematic regrowth in bottle gourd and interspecific hybrid squash rootstocks used for grafting watermelon HortScience 49 260 264
Hill, J.O., Simpson, R.J., Moore, A.D. & Chapman, D.F. 2006 Morphology and response of roots of pasture species to phosphorus and nitrogen nutrition Plant Soil 286 7 19
Huang, Y., Bie, Z., He, S., Hua, B., Zhen, A. & Liu, Z. 2010 Improving cucumber tolerance to major nutrients induced salinity by grafting onto Cucurbita ficifolia Environ. Expt. Bot. 69 32 38
Keinath, A.P. & Hassell, R.L. 2014 Suppression of fusarium wilt caused by Fusarium oxysporum f. sp. niveum race 2 on grafted triploid watermelon Plant Dis. 98 1326 1332
Lee, S.H., Ahn, S., Im, Y.J., Cho, K., Cho, B., Chung, G. & Han, O. 2005a Differential impact of low temperature on fatty acid unsaturation and lipoxygenase activity in figleaf gourd and cucumber roots Biochem. Biophys. Res. Commun. 330 1194 1198
Lee, S.H., Chung, G. & Steudle, E. 2005b Gating of aquaporins by low temperature in roots of chilling-sensitive cucumber and chilling-tolerant figleaf gourd J. Expt. Bot. 56 985 995
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
Lovelli, S., Scopa, A., Perniola, M., Di Tommaso, T. & Sofo, A. 2012 Abscisic acid root and leaf concentration in relation to biomass partitioning in salinized tomato plants J. Plant Physiol. 169 226 233
Manavalan, L.P., Guttikonda, S.K., Nguyen, V.T., Shannon, J.G. & Nguyen, H.T. 2010 Evaluation of diverse soybean germplasm for root growth and architecture Plant Soil 330 503 514
Mickelbart, M.V., Hasegawa, P.M. & Bailey-Serres, J. 2015 Genetic mechanisms of abiotic stress tolerance that translate to crop yield stability Nat. Rev. Genet. 16 237 251
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
Pace, J., Lee, N., Naik, H., Ganapathysubramanian, B. & Lubberstedt, T. 2014 Analysis of maize (Zea mays L.) seedling roots with the high-throughput image analysis tool ARIA (automatic root image analysis) PLoS One 9 e108255
Petrie, C. & Hall, A. 1992 Water relations in cowpea and pearl millet under soil water deficits: I. Contrasting leaf water relations Austral. J. Plant Physiol. 19 577 589
Pornaro, C., Macolino, S., Menegon, A. & Richardson, M. 2017 WinRHIZO technology for measuring morphological traits of bermudagrass stolons Agron. J. 109 3007 3010
Pulgar, G., Villora, G., Moreno, D.A. & Romero, L. 2000 Improving the mineral nutrition in grafted watermelon plants: Nitrogen metabolism Biol. Plant. 43 607 609
Rouphael, Y., Cardarelli, M., Colla, G. & Rea, E. 2008 Yield, mineral composition, water relations, and water use efficiency of grafted mini-watermelon plants under deficit irrigation HortScience 43 730 736
Rouphael, Y., Venema, J.H., Edelstein, M., Savvas, D., Colla, G., Ntatsi, G., Ben-Hur, M., Kumar, P. & Schwarz, D. 2017 Grafting as a tool for tolerance of abiotic stress, p. 171–215. In: G. Colla, F. Pérez-Alfocea, and D. Schwarz (eds.). Vegetable grafting: Principles and practices. CAB International, Wallingford, UK
Sandhu, N., Raman, K., Torres, R., Audebert, A., Dardou, A., Kumar, A. & Henry, A. 2016 Rice root architectural plasticity traits and genetic regions for adaptability to variable cultivation and stress conditions Plant Physiol. 171 2562 2576
Schwarz, D., Rouphael, Y., Colla, G. & Venema, J.H. 2010 Grafting as a tool to improve tolerance of vegetables to abiotic stresses: Thermal stress, water stress and organic pollutants Scientia Hort. 127 162 171
Wijewardana, C., Reddy, K.R., Shankle, M.W., Meyers, S. & Gao, W. 2018 Low and high-temperature effects on sweetpotato storage root initiation and early transplant establishment Scientia Hort. 240 38 48
Zhou, Y., Huang, L., Zhang, Y., Shi, K., Yu, J. & Nogues, S. 2007 Chill-induced decrease in capacity of RuBP carboxylation and associated H2O2 accumulation in cucumber leaves are alleviated by grafting onto figleaf gourd Ann. Bot. 100 839 848
Zobel, R.W., Kinraide, T.B. & Baligar, V.C. 2007 Fine root diameters can change in response to changes in nutrient concentrations Plant Soil 297 243 254