Genetic Equivalence of Putative Duplicate Germplasm Collections Held at CIP and US Potato Genebanks

American Journal of Potato Research, May/Jun 2006 by Rio, A H del, Bamberg, J B, Huaman, Z

ABSTRACT

A common effort among members of the Association of Potato Inter-Genebank Collaborators (APIC) has yielded a global inventory of wild potato genetic resources that is freely accessible to researchers and breeders. In that database there are a number of accessions that originated from distributed progeny of a single original germplasm collection. The logical assumption has been that although these samples are in different locations, they should be genetically equivalent. This study tests this hypothesis by comparing 17 pairs of accessions of 16 different potato species, which are reputed duplicates preserved in the potato genebanks of The International Potato Center (CIP) in Peru and of the U.S.A. (USPG). The RAPD marker analysis revealed that even though the average genetic similarity of reputed duplicates was quite high, there were a few with significant differences. Similarly, SSR markers identified three reputed duplicates that were genetically different. SSRs revealed a loss of markers for some inter-genebank comparisons, a probable indication of genetic drift. Duplicate potato collections between CIP and USPG are in most cases genetically identical. The few exceptions merit further investigation regarding causes and the impact on useful traits.

RESUMEN

Un esfuerzo com�n entre los miembros de la Asociaci�n de Colaboradores de Bancos de Germoplasma de Papa (APIC) ha dado como resultado un inventario global de recursos gen�ticos de papa silvestre, de libre acceso a investigadores y mejoradores. En la base de datos existe un n�mero de accesiones que se han generado a partir de la progenie distribuida de la colecci�n original. La suposici�n l�gica ha sido que aunque estas muestras est�n en diferentes lugares, deber�an ser gen�ticamente equivalentes. Este estud�o prueba esta hip�tesis al comparar 17 pares de accesiones de 16 especies diferentes de papa, las cuales son consideradas como duplicados mantenidos en el banco de germoplasma del Centre Internacional de la Papa (CIP) en Per� y en los Estados Unidos de Am�rica (USPG). El analisis con el marcador RAPD revelo que a pesar de que la similaridad gen�tica de duplicados putatives fue bastante alta, sin embargo, hubo algunos con diferencias significativas. Igualmente los marcadores SSR identificaron tres duplicados putatives gen�ticamente diferentes. Los SSR revelaron una p�rdida de marcadores para algunas comparaciones entre bancos de genes, probable indicacion de deriva gen�tica. Los duplicados de las colecciones entre CIP y USPG son, en la mayor�a de los casos, gen�ticamente id�nticos. Las pocas excepciones que existen ameritan investigaci�n futura para determinar las causas y su efecto en caracteres de inter�s.

Accepted for publication 20 January 2006.

ADDITIONAL KEY WORDS: duplicate collections, genetic drift, potato genebanks, potato germplasm, RAPD markers, SSRs

ABBREVIATIONS: APIC, Association of Potato Intergenebank Collaborators; CIP, Tlip International Potato Center; GS, genetic .similarity; GA^sub 3^, giberellir acid; RAPD, random amplified polymorphic DNA; SSR, simple sequence repeats; USPG, US Potato Genebank; VIR, Vavilov Institute Potato Genebank

DISCLAIMER: Reported use of brand name products does not imply an endorsement by USDA, the University of Wisconsin-Madison, or The International Potato Center.

INTRODUCTION

In recent decades, a number of reports have indicated a progressive reduction and/or deterioration of natural environments that native plant species inhabit. Several factors contributing to this habitat attrition have been documented, ranging from urban expansion to global wanning (Rosenzweig 2001; Tllman and Lehman 2001). Reduction of habitats has obviously jeopardized the continued existence of many plant species, and in fact, many of them already face extinction. Conservation of plant species, therefore, has become a priority task. One option to safely conserve and protect plant diversity is to maintain samples of populations collected in situ outside of their natural habitats (ex situ). For instance, for several decades, potato genebanks worldwide have undertaken the task of collecting and preserving potato populations from different geographical origins (Hanneman 1989). There are nearly 200 different species spread along the American continent (Hijmans and Spooner 2001), which include a wide range of ecological niches and geographical settings; many of these habitats are certainly vulnerable.

Potato genebanks initiated a formal network to exchange information and methods as well as to coordinate research on problems of common interest (Bamberg et al. 1995). One accomplishment has been the creation of a comprehensive database of passport and evaluation records to consolidate information of wild potato species maintained in different potato genebanks. It shows that there was a single, original germplasm collection that was shared and separately multiplied at two or more genebanks (Huaman et al. 2000). The assumption has been that any assessment or characterization gathered at one genebank can be extrapolated to the presumed duplicate accession preserved at another genebank. However, all genebanks do not use the same procedures for seed increase, which might have an influence in modifying the genetic structure of germplasm populations preserved at genebanks (Schoen et al. 1998; Widrlechner et al. 1989). Genetic drift can potentially be generated by deficient sampling, seed contamination, environmental selection, and/or imperfect seed multiplication. For instance, Borner et al. (2000) indicated that genetic drift was observed for one of the wheat accessions maintained and regenerated at the genebank for very long time.