Anne-Michelle Faux

Congruence between morphological and molecular markers inferred from the analysis of the intra-morphotype genetic diversity and the spatial structure of Oxalis tuberosa Mol.

Oxalis tuberosa is an important crop cultivated in the highest Andean zones. A germplasm collection is maintained ex situ by CIP, which has developed a morphological markers system to classify the accessions into morphotypes, i.e. groups of morphologically identical accessions. However, their genetic uniformity is currently unknown. The ISSR technique was used in two experiments to determine the relationships between both morphological and molecular markers systems. The intra-morphotype genetic diversity, the spatial structures of the diversity and the congruence between both markers systems were determined. In the first experience, 44 accessions representing five morphotypes, clearly distinct from each other, were analyzed. At the molecular level, the accessions exactly clustered according to their morphotypes. However, a genetic variability was observed inside each morphotype. In the second experiment, 34 accessions gradually differing from each other on morphological base were analyzed. The morphological clustering showed no geographical structure. On the opposite, the molecular analysis showed that the genetic structure was slightly related to the collection site. The correlation between both markers systems was weak but significant. The lack of perfect congruence between morphological and molecular data suggests that the morphological system may be useful for the morphotypes management but is not appropriate to study the genetic structure of the oca. The spatial structure of the genetic diversity can be related to the evolution of the species and the discordance between the morphological and molecular structures may result from similar selection pressures at different places leading to similar forms with a different genetic background.

Evidence of intra-varietal genetic variability in the vegetatively propagated crop oca (Oxalis tuberosa Mol.) in the Andean traditional farming system

Oxalis tuberosa is a vegetatively propagated tuber crop in the Andes. The peasants cultivate a great number of varieties for which genetic homogeneity has never been demonstrated. Morphological descriptors and ISSR markers were used to determine the intra-varietal diversity and the influence of the mode of conservation ex-situ vs in-situ. Molecular markers revealed an intra-varietal genetic diversity attesting that oca varieties are not pure clones. The morphological analysis was congruent with the peasant classification, contrary to the molecular markers. The comparison between both conservation strategies revealed a larger intra-varietal diversity in in-situ conditions and a genetic divergence between plants. The traditional practices are likely to be responsible of the intra-varietal polymorphism since the oca is propagated almost exclusively vegetatively. At the conservation level, differences could be explained by the sampling methods. A more integrated approach between genebanks and in-situ conservation is recommended to maintain the genetic resources of the species.