Shoot zinc (Zn) concentration varies widely within Brassica oleracea L. and is affected by soil Zn and phosphorus (P) levels By MARTIN R. BROADLEY 1 * , SEOSAMH Ó LOCHLAINN 1 , JOHN P. HAMMOND 2 , HELEN C. BOWEN 2 , ISMAIL CAKMAK 3 , SELIM EKER 6 , HALIL ERDEM 6 , GRAHAM J. KING 4 and PHILIP J. WHITE 5 1 Plant and Crop Sciences Division, University of Nottingham, Sutton Bonington, Leicestershire, LE12 5RD, UK 2 Warwick HRI, University of Warwick,Wellesbourne,Warwick, CV35 9EF, UK 3 Sabanci University, Faculty of Engineering and Natural Sciences, Orhanli-Tuzla, 34956 Istanbul, Turkey 4 Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK 5 Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, UK 6 Cukurova University, Department of Soil Science, Faculty of Agriculture, 01330 Adana,Turkey (e-mail: martin.broadley@nottingham.ac.uk) (Accepted 25 April 2010) SUMMARY The low availability of zinc (Zn) in soils and crops affects dietary Zn intake worldwide.This study sought to determine if the natural genetic variation in shoot Zn concentrations ([Zn] shoot ) is sufficient to pursue a crop improvement breeding strategy in a leafy vegetable crop. The gene-pool of Brassica oleracea L. was sampled using a large (n = 376) diversity foundation set (DFS), representing almost all species-wide common allelic variation, and 74 commercial varieties (mostly F 1 ). The DFS genotypes were grown at low and high soil phosphorus (P) levels under glasshouse and field conditions, and also in a Zn-deficient soil, with or without Zn-fertilisation, in a glasshouse. Despite the large variation in [Zn] shoot among genotypes, environment had a profound effect on [Zn] shoot . The heritability of [Zn] shoot was significant, but relatively low, among 90 doubled-haploid (DH) lines from a mapping population. While several quantitative trait loci (QTL) associated with [Zn] shoot occurred on chromosomes C2, C3, C5, C7, and C9, these were generally weak and conditional upon growth conditions. Breeding for [Zn] shoot in B. oleracea is therefore likely to be challenging. Shoot P concentrations increased substantially in all genotypes under low soil Zn conditions. Conversely, only some genotypes had increased [Zn] shoot at low soil P levels. Sufficient natural genetic variation may therefore exist to study some of the interactions between Zn and P nutrition. Z inc (Zn) is an essential plant nutrient (Broadley et al., 2007). Worldwide, many soils have low Zn- availability, causing widespread yield losses and crops of low nutritional quality (Cakmak, 2008). Dietary Zn deficiencies can be alleviated by appropriate fertiliser inputs (i.e., agronomic biofortification) and, potentially, by crop improvement (genetic biofortification; Cakmak, 2008; White and Broadley, 2009). Several studies have reported variation in the Zn composition of the edible portions of crops (White and Broadley, 2009), including Brassica rapa ssp. pekinensis (Wu et al., 2007; 2008). However, most studies to date have focussed on the Zn composition of the grains of staple cereal crops as these are the major source of dietary energy. Zinc concentrations in leaves are typically greater than Zn concentrations in grain, tubers, and fruit, since the latter obtain most of their minerals via the phloem, and Zn is relatively non-mobile in the phloem. Leaves can therefore contribute substantially to dietary Zn intake, despite their low calorie content (Henderson et al., 2003). The aim of this study was to characterise, systematically and at a wider species level, the natural genetic variation in shoot Zn concentrations ([Zn] shoot ) in Brassica oleracea, and to determine if this variation was sufficient to pursue a crop improvement breeding strategy in a leafy vegetable crop. Plants typically have shoot Zn concentrations ([Zn] shoot ) < 100 mg Zn kg –1 dry weight (DW), although extensive natural genetic variation occurs (Broadley et al., 2007; Watanabe et al., 2007). A small but significant component (ca. 20%) of the natural genetic variation observed in [Zn] shoot values is associated with differences among families and higher-level taxonomic groups, probably reflecting evolutionary events during the diversification of early angiosperms. However, most variation in [Zn] shoot is due to recent evolutionary events among and within species. An example of wide among- species variation in [Zn] shoot occurs in members of the Brassicaceae, where a high [Zn] shoot (> 10,000 mg Zn kg –1 DW) has evolved independently in the Noccaea and Arabidopsis clades (Broadley et al., 2007). Within-species variation in [Zn] shoot has been reported in kale (B. oleracea var. acephala; 33 – 60 mg Zn g –1 DW; n = 22; Kopsell et al., 2004), B. rapa (23 – 156 mg Zn g –1 DW; n = 111; Wu et al., 2007), chickpea (Cicer arietinum; 56 – 137 mg Zn g –1 DW; n = 19; Ibrikci et al., 2003), and spinach *Author for correspondence. Journal of Horticultural Science & Biotechnology (2010) 85 (5) 375–380