Characterization of genetic resources of onion (Allium cepa L.) from the Spanish secondary centre of diversity

Abstract

Onions are the second most-valuable vegetable in the world. Despite its global culinary and economic significance, the knowledge of genetic diversity and resources is limited. The aim of this study was to morphologically and physico-chemically characterize eighty-six onion landraces from Spain, part of the secondary Mediterranean Centre of diversity. The evaluated traits in the bulb included: weight, shape, firmness, soluble solids content (SSC), pungency and sugars content (glucose, fructose and sucrose). The results evidenced a great variability in all the evaluated traits. Correlations were significant between pungency and SSC (r = 0.34), firmness (r = 0.32), and sucrose content (r = 0.34); between fructose and glucose contents (r = 0.79); between sucrose content and SSC (r = 0.57); between SSC and weight (r = -0.35); between fructose and sucrose contents (r = -0.22); and between weight and sucrose content (r = -0.43). The combination of cluster and discriminant analyses resulted in a classification into four clusters (95.3% fit). Cluster 1 is represented by firm, pungent and large-sized bulbs; cluster 2 consists of large-sized, mild and sweet onions; cluster 3 is constituted by pungent, high-SSC and small-sized bulbs and cluster 4 is made up by elongated bulbs. The variability in important agronomical traits found point out that these onion accessions could be candidates for future breeding programs. In addition, the clustering could make the initial plant material selection easier and the correlations among the evaluated traits found could help to establish adequate selection strategies.Additional key words: cluster analysis; firmness; genetic diversity; pungency; soluble solids; sugars. Resumen Caracterización de los recursos genéticos de cebolla (Allium cepa L.) procedentes del centro secundario de diversificación de EspañaLa cebolla es el segundo cultivo hortícola a nivel mundial. Sin embargo, el conocimiento sobre los recursos y la diversidad genética de esta especie es limitado. Por ello, el objetivo del presente trabajo consistió en el estudio morfológico y físico-químico de una colección de 86 cultivares de cebolla procedentes de España (que forma parte del centro secundario de diversificación). Los caracteres evaluados en el bulbo incluyeron: peso, forma, firmeza, contenido en sólidos solubles (SSC), pungencia y contenido en azúcares (glucosa, fructosa y sacarosa). Los resultados evidenciaron una gran variabilidad en todos los caracteres evaluados. Las correlaciones fueron significativas entre la pungencia y SSC (r = 0,34), firmeza (r = 0,32) y contenido en sacarosa (r = 0,34); entre contenido en fructosa y glucosa (r = 0,79); entre contenido en sacarosa y SSC (r = 0,57); entre SSC y peso (r = -0,35); entre contenido en fructosa y sacarosa (r = -0,22) y entre el peso y contenido en sacarosa (r = -0,43). El análisis discriminante dio lugar a la formación de cuatro grupos con un ajuste del 95,3%. El grupo 1 está formado por bulbos grandes, firmes y picantes, el grupo 2 por cebollas grandes, su...

Effect of prolonged storage in controlled atmospheres on the conservation of the onion (Allium cepa L)quality

“…Although the TSS content of onion was reduced during storage, the average range obtained from the three treatments (TC, T1 and T2) can be considered acceptable for onion, due to they are within the range of TSS reported by other authors for this crop (Petropoulos et al, 2016a;Mallor et al, 2011b;Chope et al, 2007). These results were higher than those values reported by Malek and Heidarisoltanabadi (2015) in Spanish sweet onion cultivars.…”

Assessing the genetic diversity of Spanish Allium cepa landraces for onion breeding using microsatellite markers

“…The results shown here also demonstrate that the used EST-SSRs were useful to distinguish between onion accessions. Both the previously reported morphological characterization (Mallor et al, 2011) and the molecular analysis performed in this study provide valuable information for curators and for increasing germplasm use by researchers and plant breeders requesting samples.…”

“…All of them could be distinguished, although the branches were not clearly defined according to relevant onion characteristics, such as pungency, day length requirements, and skin colour (Table 1). These Spanish onion landraces were clustered by their morphological and physico-chemical characteristics in our earlier study (Mallor et al, 2011), however a clear relation among molecular and morphological/physico-chemical clusters has not proven to be clearly established. A similar result has been reported by Khar et al (2011) for Indian onions in which the clustering was not made on the basis of colour, growing season or geographical origin.…”

“…Spanish onion accessions are local landraces collected as seeds from farmers in the main growing regions of Spain between 1981 and 2006. All accessions were supplied by the BGHZ (Spain) and all of them have been previously characterized by using morphological and physico-chemical descriptors (Mallor et al, 2011). The onion seeds were grown in the same season in a randomized block design with three replications at the CITA de Aragon (Spain) (latitude 41 • 39 N), where soils have a loamy texture, moderately basic pH and relatively high salt contents.…”

“…Some of these traditional onion landraces are still grown in some regions of Spain due to their high quality and acceptance by local markets, but others have already disappeared (Mallor and Sales, 2012). A representative sample of the BGHZ onion collection has already been characterized using morphological and physico-chemical descriptors (Mallor et al, 2011). Thus, the goal of this study was to explore for the first time the genetic diversity of Spanish onion landraces using SSR markers, including 85 accessions supplied by the BGHZ.…”