Diversity in a clonally propagated crop: morphological characters in garlic compared with existing molecular classifications

A subset of 113 garlic accessions from the Gatersleben genebank collection was characterised using 16 morphological characters. The characterisation data were used for principal components and cluster analyses. Comparisons with existing RAPD and isozyme classifications were performed and gave high correlations especially in cases of the ophioscorodon and sativum groups. The morphological characterisation was used for the selection of a core collection which represents the greatest diversity of garlic in the northern part of Europe. Introduction Within the genus Allium , garlic is one of the larger crop species well represented in the collection of the Gatersleben gene bank. The garlic gene bank is especially valuable because of the high percentage of original material from collection missions. In the course of an EU-funded GenRes project, a priority subset out of all the Gatersleben accessions has been selected. The main selection criteria were the geographical representation in combination with already documented isozyme and RAPD data (MAASS and KLAAS, 1995). This subset has been characterised during four years by means of morphological markers. It has been introduced into virus-free in vitro storage and will be the research base for cryopreservation studies. It has been offered to other research groups and users as a reference collection for further studies on garlic. Material and methods The characterisation of the gene bank material has been done in co-ordination with the process of re-formulation of the minimum descriptors prepared for publication by IPGRI. 1 Institut für Pflanzengenetik und Kulturpflanzenforschung Gatersleben (IPK) Corrensstr. 3 D-06466 Gatersleben, Germany Morphological characters in garlic compared with existing molecular classifications 328 Fig. 1 a-c: Examples for characters used in morphological descriptions of garlic accessions a: scape; b: PRB/PRFL; c: BSTR The following 16 descriptors have been used for this study: BSTR bulb structure type (Fig. 1c) PD pseudostem diameter BW bulbil weight PH pseudostem height CC skin colour of the cloves PRB presence of bulbils (Fig. 1b) HM harvest maturity PRFL presence of flowers (Fig. 1b) FA foliage attitude SCAPE ability to form scapes (Fig. 1a) FC foliage colour SHSV side view shape of the compound bulb NRC number of cloves per bulb SHTV top view shape of full-grown bulbs OC outer skin colour of the bulb SZC size of the cloves For precise characterisation, the cloves were planted in field plots with planting distances of 15 cm within the lines and 62 cm between the rows. Of each accession 40 cloves were planted in the first year. For the repeated characterisation 10 cloves per accession were used in the next year. All characterisation data have been arranged in scores of 2 to 6 classes. Results and discussion The characterisation of the accessions in two successive years demonstrated similar results concerning the main characterisation parameters such as ability to produce scape, presence of bulbils and flowers, number of cloves, pseudostem height and bulb structure. Intra-clonal variability has been found in the character “Ability to produce scape” especially in the short-stalked forms. In this case, this character varied from scapes sitting only inside the bulb to the break of the bulbils through the leaf sheaths of the pseudostem in various heights from the soil level up to the end of the pseudostem. The characterisation data were used for principal components (Tables 1, 2) and cluster analyses. A. SENULA and E.R.J. KELLER 329 Tab. 1: Eigenvalue analysis of 16 morphological characters in garlic Principal component eigenvalue % variability accumulated variability 1 4.55 28.5 28.5 2 2.04 12.7 41.2 3 1.58 9.9 51.1 4 1.15 7.2 58.3 5 1.11 6.9 65.2 The first five principal components gave eigenvalues greater than 1.0 and explained together 65.2% of the accumulated variation. Correlations with values above / below ±0.6 were considered as most important for that principal component. The first component was associated mainly with SCAPE, BSTR, PRFL, PRB and PH. The second principal component was associated with SZC and BW. The third component was associated with SHSV (Table 2). Tab. 2: Correlation coefficients of 16 morphological characters Character PC 1 PC 2 PC 3 PC 4 PC 5 BSTR -0.825 0 0 0.180 0.175 BW -0.129 0.665 -0.338 -0.508 0 CC -0.113 0.187 0.483 -0.346 0.305 HM 0.575 -0.249 -0.480 0 0.118 FA -0.198 0.430 0 0.185 0.110 FC 0.503 -0.169 -0.346 0.149 0.287 NRC -0.586 -0.159 0 0.335 -0.131 OC 0.323 -0.175 0 0.151 -0.516 PD 0.181 0.692 0 0.379 -0.216 PH 0.630 0.285 0 0.471 0 PRB 0.787 0 0.352 0 0.169 PRFL 0.876 -0.173 0.287 0 0.113 SCAPE 0.870 0.115 0.192 -0.277 0 SHSV 0 0.189 0.694 0.106 -0.430 SHTV -0.318 0.145 0.345 0.297 0.547 SZC 0.314 0.754 -0.182 0 0.100 Morphological characters in garlic compared with existing molecular classifications 330 The cluster analysis identified five clusters containing between two and 59 accessions per cluster (Figure 2). Accessions of clusters 1 and 2 are characterised by the ability to produce a scape clearly longer than the pseudostem and possessing bulbils in the inflorescence only. Cluster 3 contained only four accessions with a tiny habit. Cluster 4 is characterised by two accessions without visible scape formation, irregular bulb structure and a small size of cloves. Cluster 5 covers mainly accessions which formed a scape shorter than the pseudostem. Fig. 2: Cluster analysis of 113 accessions of the garlic collection, calculated with complete linkage method (Euclidean distance) Several case studies were made to explain the interrelationships between the morphological marker trees and the already existing molecular marker dendrograms. According to MAASS and KLAAS (1995), the more basic (ancestral) groups (the longicuspis group) are scattered through their molecular dendrograms which makes them difficult for comparisons, whereas the ophioscorodon and sativum groups are sufficiently homogeneous to use them for comparisons (Figure 3). The analyses of the morphological parameters were used to select 25 accessions from the three main clusters 1 (48%), 2 (16%) and 5 (36%). These accessions represent the greatest diversity of garlic in the north of European Union and are the longday part of the core collection of garlic which has been established using funds of a European project aimed at preserving the genetic diversity of Allium. 0,00