Evidence of intra-varietal genetic variability in the vegetatively propagated crop oca (Oxalis tuberosa Mol.) in the Andean traditional farming system A. Pissard 1 , J. A. Rojas-Beltran 2 , A.-M. Faux 1 , S. Paulet 1 , P. Bertin 1 1 De ´partement de Biologie applique ´e et Productions agricoles, Ecophysiologie et Ame ´lioration Ve ´ge ´tale, Universite ´ catholique de Louvain, Louvain-La-Neuve, Belgium 2 Fundacio ´n PROINPA (Promocio ´n e Investigacio ´n de Productos Andinos), Cochabamba, Bolivia Received 4 August 2006; Accepted 4 September 2007; Published online 4 December 2007 Ó Springer-Verlag 2007 Abstract. 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 morpholog- ical analysis was congruent with the peasant classi- fication, 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 prop- agated almost exclusively vegetatively. At the conser- vation level, differences could be explained by the sampling methods. A more integrated approach between genebanks and in-situ conservation is recom- mended to maintain the genetic resources of the species. Keywords: ISSR; oca; Oxalis tuberosa; genetic resources conservation Diverse tuber crops constitute the diet of many subsistence farmers through the Andes. The major crop, the potato, is associated in rotations with minor tubers, among which the oca, Oxalis tuberosa Mol., constitutes the most important species. Despite its clonal propagation for mil- lennia, the oca possesses an intact trimorphic system of genetic incompatibility. In fact, oca plants produce one of three types of flowers, which differ in style/stamen lengths. Incompati- bility reaction between pollen-stigma self and own-type promotes outcrossing and inhibits sel- fing (Gibbs 1976). The extent of both fruit and seed production seems to be controlled mainly by the expression of this tristylous system and the highest quantities of seeds may be obtained after legitimate pollinations (Trognitz et al. 1998, Trognitz and Hermann 2001). However, although seed set remains possible, oca is propagated essentially by tubers and botanical seed propa- gation by farmers has never been observed (Gibbs 1976, Trognitz et al. 1998). Correspondence: Audrey Pissard, Universite ´ catholique de Louvain, De ´partment de Biologie applique ´e et Productions agricoles, Ecophysiologie et Ame ´lioration Ve ´ge ´tale, Place Croix du Sud, 2 bte 11, 1348 Louvain-La-Neuve, Belgium e-mail: pissard@ecav.ucl.ac.be Pl Syst Evol 270: 59–74 (2008) DOI 10.1007/s00606-007-0605-3 Printed in The Netherlands Plant Systematics and Evolution