The Implications of a Growing Agronomic Imperative for Vegetable Fruit Quality and Nutritive Value

fpls-08-00741 May 10, 2017 Time: 15:0 # 1 REVIEW published: 12 May 2017 doi: 10.3389/fpls.2017.00741 Vegetable Grafting: The Implications of a Growing Agronomic Imperative for Vegetable Fruit Quality and Nutritive Value Marios C. Kyriacou1, Youssef Rouphael2, Giuseppe Colla3, Rita Zrenner4 and Dietmar Schwarz4* 1 Department of Vegetable Crops, Agricultural Research Institute, Nicosia, Cyprus, 2 Department of Agricultural Sciences, University of Naples Federico II, Naples, Italy, 3 Department of Agricultural and Forestry Sciences, University of Tuscia, Viterbo, Italy, 4 Leibniz Institute of Vegetable and Ornamental Crops, Großbeeren, Germany Grafting has become an imperative for intensive vegetable production since chlorofluorocarbon-based soil fumigants were banned from use on grounds of environmental protection. Compelled by this development, research into rootstock– scion interaction has broadened the potential applications of grafting in the vegetable Edited by: Nadia Bertin, industry beyond aspects of soil phytopathology. Grafting has been increasingly tapped Plantes et Système de Cultures for cultivation under adverse environs posing abiotic and biotic stresses to vegetable Horticoles (INRA), France crops, thus enabling expansion of commercial production onto otherwise under- Reviewed by: Yuksel Tuzel, exploited land. Vigorous rootstocks have been employed not only in the open field Ege University, Turkey but also under protected cultivation where increase in productivity improves distribution Georgia Ntatsi, of infrastructural and energy costs. Applications of grafting have expanded mainly in Agricultural University of Athens, Greece two families: the Cucurbitaceae and the Solanaceae, both of which comprise major *Correspondence: vegetable crops. As the main drives behind the expansion of vegetable grafting have Dietmar Schwarz been the resistance to soilborne pathogens, tolerance to abiotic stresses and increase [email protected] in yields, rootstock selection and breeding have accordingly conformed to the prevailing Specialty section: demand for improving productivity, arguably at the expense of fruit quality. It is, however, This article was submitted to compelling to assess the qualitative implications of this growing agronomic practice Crop Science and Horticulture, a section of the journal for human nutrition. Problems of impaired vegetable fruit quality have not infrequently Frontiers in Plant Science been associated with the practice of grafting. Accordingly, the aim of the current Received: 03 March 2017 review is to reassess how the practice of grafting and the prevalence of particular Accepted: 20 April 2017 Published: 12 May 2017 types of commercial rootstocks influence vegetable fruit quality and, partly, storability. Citation: Physical, sensorial and bioactive aspects of quality are examined with respect to grafting Kyriacou MC, Rouphael Y, Colla G, for watermelon, melon, cucumber, tomato, eggplant, and pepper. The physiological Zrenner R and Schwarz D (2017) mechanisms at play which mediate rootstock effects on scion performance are Vegetable Grafting: The Implications of a Growing Agronomic Imperative discussed in interpreting the implications of grafting for the configuration of vegetable for Vegetable Fruit Quality fruit physicochemical quality and nutritive value. and Nutritive Value. Front. Plant Sci. 8:741. Keywords: carotenoids, Cucurbitaceae, flavor, functional compounds, physiological mechanism, mRNA doi: 10.3389/fpls.2017.00741 transport, rootstock, Solanaceae Frontiers in Plant Science| www.frontiersin.org 1 May 2017| Volume 8| Article 741 fpls-08-00741 May 10, 2017 Time: 15:0 # 2 Kyriacou et al. Vegetable Grafting: Fruit Quality INTRODUCTION been increasingly tapped for cultivation under adverse environments posing abiotic and biotic stresses to vegetable Retail cost for fresh horticultural products reflects capital crops, thus enabling expansion of commercial production investment in developing suitable plant stock, in fostering onto otherwise under-exploited land. The ability of its cultivation, and in product storage and handling along taping wild genetic resources for exploiting traits of root the food supply chain. Although a multifaceted concept physiological tolerance to stress independently to scion drawing on various implicated stakeholders, quality is characteristics has facilitated the application of grafting ultimately what captures the expectations to be met at the for the cultivation of annual fruit crops under marginal retail customer’s end of the agroindustry spectrum. The conditions of salinity, nutrient stress, water stress, organic perception of quality is dependent on intrinsic traits of pollutants, and alkalinity (Savvas et al., 2010; Schwarz et al., horticultural commodities, shaped by genotypic, cultural and 2010; Borgognone et al., 2013). Moreover, the economic ecophysiological effects, and on extrinsic traits formulated by implications of the significant yield increase imparted by select the socio-economic and marketing environment (Schreiner vigorous commercial rootstocks has encouraged their use et al., 2013). Multidisciplinary studies have highlighted under protected cultivation where increase in productivity that quality is more important to consumers than price improves distribution of infrastructural and energy costs when the latter varies within the anticipated range (Harker (Colla et al., 2011). Provided the anatomical and physiological et al., 2003). Although consonance of quality with the compatibility of the graft combinations, rootstock effects cost of purchase influences consumer behavior, quality on plant performance under soil biotic and abiotic stress is that which largely commands recurring customers. conditions clearly outweigh those of the scion. Moreover, In regulatory context, the issue of quality is addressed there is evidence of rootstock mediation in the configuration chiefly by crop-specific class standards based on limited of scion fruit quality characteristics, widely reported in a key visual and organoleptic characteristics (Commission range of crops but confounded with frequent rootstock– Implementing Regulation (EU) No 543/2011, 2011). Quality scion interaction which cannot always be explained in the standards thus tend to define class criteria for minimum context of narrow rootstock–scion specificity (Rouphael et al., acceptability and provide practical, effective, mostly non- 2010). destructive means for standardization procedures. They As the main drives behind the expansion of vegetable fail, however, to address complex compositional aspects of grafting have been the resistance to soilborne pathogens quality pertaining to flavor, particularly the volatile aroma (Louws et al., 2010), tolerance to abiotic stresses (Schwarz fraction, or to nutritional and bioactive value which consumers et al., 2010; Kumar et al., 2015; Rouphael et al., 2016) are becoming increasingly conscious of Schreiner et al. and increase in yields (Lee et al., 2010), rootstock selection (2013). and breeding have accordingly conformed to the prevailing Plant breeding on the other hand, has aimed preeminently at demand for improving productivity, arguably at the expense improving yield, endowing plant stock with disease resistance, of fruit quality. Thus, grafting has not been employed as at providing resilience to mechanical injury and improving a method for improving vegetable fruit quality. Quite the overall postharvest performance, and to a lesser extent at contrary, often yield and quality are contradictory traits (Klee improving sensory quality traits (Bai and Lindhout, 2007). and Tieman, 2013). Considering the rapid expansion of the However, the configuration of important sensory traits, such vegetable grafting industry, understanding the implications of as volatile aroma components, seems mediated by ethylene- grafting for fruit quality is imperative, and equally pressing is dependent biosynthetic pathways linked also to shelf-life the unraveling of the mechanisms involved. Possible factors performance (Pech et al., 2008), and to textural changes engaged in rootstock mediation of quality include changes associated with cell wall matrix solubilization events (Dos-Santos in water and nutrient uptake efficiency, indirect effects on et al., 2013). Hence breeding for shelf-life may elicit adverse ripening behavior resulting from altered crop load and source– pleiotropic effects on desirable sensory attributes (Causse et al., sink balance, and even an epigenetic component to the 2002). This is particularly critical in fruits characterized by grafting process involving transfer of genetic material from autocatalytic climacteric ripening, as aptly exemplified by the rootstock to scion (Savvas et al., 2010; Soteriou et al., 2014; distinct sensory profile of odorous climacteric vs. inodorous Avramidou et al., 2015). Previous reviews on the grafting non-climacteric melons (Verzera et al., 2011). Collecting of annual fruit crops that have covered aspects relating to desirable traits while avoiding undesirable combinatorial effects fruit quality were published by Davis et al.(2008a, only complicates breeding efforts. In this respect, grafting may Cucurbitaceae), Flores et al.(2010 only tomato), and Rouphael provide expedient means of selecting independently for rootstock et al.(2010). The current review aims at providing an updated and scion traits, provided the compatibility of the graft critical review of scientific advances addressing grafting effects combination. on the fruit quality of annual

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