Article pubs.acs.org/JAFC
Leaf Metabolic, Genetic, and Morphophysiological Profiles of Cultivated and Wild Rocket Salad (Eruca and Diplotaxis Spp.) Francesca Taranto, Gianluca Francese, Francesco Di Dato, Antonietta D’Alessandro, Barbara Greco, Vincenzo Onofaro Sanajà, Alfonso Pentangelo, Giuseppe Mennella, and Pasquale Tripodi* Consiglio per la ricerca in agricoltura e l’analisi dell’economia agrariaCentro di Ricerca per l’Orticoltura (CREA-ORT), Via dei Cavalleggeri 25, 84098 Pontecagnano-Faiano, Salerno, Italy S Supporting Information *
ABSTRACT: Rocket salad (Diplotaxis spp., Eruca spp.) is a leafy vegetable rich in health-promoting compounds and widely consumed. In the present study, metabolic profiles of 40 rocket accessions mainly retrieved from gene banks were assessed. Seven glucosinolates (GLSs) and 15 flavonol compounds were detected across genotypes. Dimeric 4-mercaptobutyl-GLS and 4-(β-D-glucopyranosyldisulfanyl)butyl-GLS were the major components of the total glucosinolate content. Flavonols were different between genera, with the exception of isorhamnetin 3,4′-diglucoside. Morphoagronomic traits and color coordinates were also scored. Results showed a negative correlation between color and GLSs, indicating these last as responsible for the increase of the intensity of green and yellow pigments as well as for the darkness of the leaf, whereas agronomic traits showed positive correlation with GLSs. Genetic diversity was assessed using inter simple sequence repeat (ISSR) markers, allowing separation of the accessions on the basis of the species and elucidating the observations made by means of phenotypic data. KEYWORDS: rocket salad, Eruca spp., Diplotaxis spp., glucosinolates, flavonols, morphoagronomic traits, leaf color, genetic diversity
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INTRODUCTION Rocket is a common name used for herbaceous plants belonging to the Brassicaceae family, whose leaves have similar morphology and pungent taste. This crop, which comprises different species belonging to the Eruca and Diplotaxis genera, was known since Roman times, where citizens utilized it as a vegetable and condiment plant. To date other uses concern the production of oil and cosmetics as well as medical purposes.1,2 The production of rocket has been particularly concentrated in the Mediterranean basin and Western Asia, which are also considered the center of origin.3 In Europe, Italy and Spain are the largest producers thanks to the geographical position and mild climatic conditions. Recently the consumption has gradually spread to other latitudes principally as ready-to-use salads. For human consumption, three species are mainly used.4 Diplotaxis tenuifolia (L.) DC and Diplotaxis muralis (L.) DC are diploid and polyploid species, respectively, and both are perennial, which means that they can be cultivated in the winter and produce new sprouts in the spring, being very well adapted in harsh and poor soils. Eruca sativa Miller is a diploid, annual species, which flowers in spring, and whose seeds are ready for collecting in late spring; it can be cultivated in marginal areas although several cultivars seem to prefer rather rich soils. In the past years, several studies have focused attention on bioactive compounds produced by plants and their benefits on human health. Rocket contains a range of health-promoting phytochemicals including carotenoids, vitamin C, fiber, polyphenols, and glucosinolates.5,6 Several investigations have shown the potential role of phytochemicals, present in Brassicaceae, in the prevention of certain diseases and types of cancer;7 in particular, the health-promoting activities, including tumorigenesis inhibition and hepatoprotective effects, are more often attributed to substances contained in rocket plants.1,2,8 © XXXX American Chemical Society
Glucosinolates (GLSs) represent the major class of compounds in rocket, and their contents have been well documented in the literature.9,10 GLSs and their hydrolysis products are responsible of the typical pungent aromas and flavors11 whereas volatiles, such as isothiocyanates and indoles, have been consistently linked with anticarcinogenic activity in mammalian tissues.8 Furthermore, leaves of Eruca and Diplotaxis taxa so far investigated also contain significant levels of polyglycosylated flavonoids, which are antioxidants poorly absorbed in the proximal gastrointestinal tract and are therefore likely to reach the colon in substantial quantities, protecting the colonic epithelium from free radical attack.12 Additionally, it is wellknown that the content of bioactive compounds, hence the nutritional quality of food, can be influenced by several factors such as genetics, degree of ripeness, agronomic and environmental conditions during growth, food preparation, and processing. Dissecting the genetic diversity in crops is essential for the unequivocal germplasm identification in order to establish innovative crop improvement programs. For genetic studies and molecular breeding of crop plants, several typologies of markers are available which can be classified into different categories based on hybridization techniques, polymerase chain reaction (PCR), and sequencing technologies. The inter simple sequence repeat (ISSR) PCR based markers13 represent a powerful strategy to investigate the genetic diversity of crops particularly in species for which no information concerning the target sequence on the genome is available. The technique consists of amplification of DNA segments between Received: April 19, 2016 Revised: June 28, 2016 Accepted: June 30, 2016
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DOI: 10.1021/acs.jafc.6b01737 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
32.38 ± 0.59 g 11.03 ± 0.13 ef
9.43 ± 0.20 g 0.90 ± 0.05 d 2.77 ± 0.01 j−l 2.03 ± 0.15 l−o 0.28 ± 0.03 pq IPK ERU158 Eruca sativa Mill. 436-Es
Portugal
2.35 ± 0.18 n−r
6.00 ± 0.16 ij
12.61 ± 0.40 a−c 36.48 ± 0.30 cd 0.91 ± 0.02 d
1.84 ± 0.17 b 6.10 ± 0.96 g
7.78 ± 0.42 de 3.90 ± 0.06 ef
3.12 ± 0.03 hi 7.70 ± 0.26 d−g 1.94 ± 0.04 q−s
8.06 ± 0.07 c−f 0.72 ± 0.01 h−k
0.65 ± 0.08 j−l
2.51 ± 0.13 m−p
na IPK ERU151 Eruca sativa Mill. 435-Es
IPK ERU143 Eruca sativa Mill. 434-Es
Russia
37.94 ± 0.54 bc
2.10 ± 0.20 r
