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.
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