A. Salas

Assessing changes in the genetic diversity of potato gene banks. 2. In situ vs ex situ

Abstract An important question in the conservation of potato germ plasm is whether germ plasm in the gene bank, although stable, still represents the in situ populations from which it was collected, sometimes many decades ago. The answer would direct objective decisions regarding the value of re-collections and in situ preservation. The present study was undertaken as a project of the Association of Potato Inter-gene-bank Collaborators (APIC). It measured genetic differentiation between potato germ plasm maintained in the US gene bank for many years and current in situ populations re-collected from the same original sites in the wild. Solanum jamesii and Solanum  fendleri from the United States were used as representatives of potato germ plasm. Re-collections were carried out in 1992 at the same locations at which gene bank-conserved accessions had been collected in 1958 and 1978. RAPD markers revealed significant genetic differences between gene bank-conserved and re-collected in situ populations for all seven comparisons of S. jamesii (diploid outcrosser), and 12 of 16 comparisons within S.  fendleri (tetraploid inbreeder). The average genetic similarities were 65.2% for S.  jamesii and 80.4% for S.  fendleri. Possible explanations and consequences of these unexpectedly large differences are discussed.

A decade of collecting and research on wild potatoes of the Southwest USA

Potato is an important world crop with an abundant diversity of wild relatives for research and breeding. About 200 tuber-bearingSolarium relatives of the cultivated potato are distributed from southern Chile to the southwest USA. Only five of these have been reported in the USA, and only two exist with certainty (S. fendleri andS. jamesii). This paper reviews the procedures and outcome of 12 expeditions by the authors to the Southwest USA from 1992 to 2001 that resulted in 132 new germplasm accessions. Previously published information allowed successful collection from many documented sites, and many new sites were discovered and sampled. Incomplete or inaccurate records were improved and refined, making it possible for others to easily find these sites. When assessed for genetic diversity, re-collections from the same site were found to be nearly as genetically different as samples from different sites, and genetic differences between sites could not be linked with any ecogeographic parameter, even physical distance of separation. In conclusion, wild potato germplasm from the USA and associated knowledge was greatly expanded, but reaching the goal of obtaining and keeping the most complete sample possible of the genetic diversity will involve additional collecting and continued research on the reproductive behavior of these plants.ResumenLa papa es un cultivo importante a nivel mundial; con una gran diversidad de formas silvestres que han sido importantes para realizar investigaciones y trabajos de majoramiento genético. Existen alrededor de 200 especies deSolanum que producen tubérculos, ellas estait distribuídas desde el sur de Chile hasta el sudoeste de EE UU. Cinco de estas especies han sido reportadas en EE UU pero, probablemente, solo existen dos de ellas (S. fendleri y S. jamesii). Este artículo es una revisión de los detalles y los resultados de 12 expediciones llevadas a cabo por los autores en el sudoeste de EE UU desde 1992 hasta el 2001, las cuales permitieron colectar 132 accesiones nuevas de germoplasma. Gracias a publicaciones hechas anteriormente, las colecciones en los lugares previamente descritos fueron exitosas, asimismo muchos lugares nuevos fueron encontrados y muestreados. Los registros de colección que estaban incompletos o equivocados fueron corregidos y mejorados, haciendo de ellos fácilmente ubicables para cualquiera. La evaluación de la diversidad genética determinó que las re-colecciones hechas en el mismo lugar eran genéticamente tan diferentes como las colecciones hechas en diferentes lugares, que diferencias genéticas entre lugares no estaban asociadas a ningún parámetro ecogeográfico, incluyendo separación física. En conclusión, el germoplasma silvestre de papa de EE UU asi como el conocimiento asociado a este ha sido expandido enormemente, sin embargo la meta de colectar y mantener la mayor cantidad de diversidad genética va a requerir de más colecciones e investigación contínua sobre el comportamiento reproductivo de estas plantas.

Ex Situ Conservation Priorities for the Wild Relatives of Potato (Solanum L. Section Petota)

Crop wild relatives have a long history of use in potato breeding, particularly for pest and disease resistance, and are expected to be increasingly used in the search for tolerance to biotic and abiotic stresses. Their current and future use in crop improvement depends on their availability in ex situ germplasm collections. As these plants are impacted in the wild by habitat destruction and climate change, actions to ensure their conservation ex situ become ever more urgent. We analyzed the state of ex situ conservation of 73 of the closest wild relatives of potato (Solanum section Petota) with the aim of establishing priorities for further collecting to fill important gaps in germplasm collections. A total of 32 species (43.8%), were assigned high priority for further collecting due to severe gaps in their ex situ collections. Such gaps are most pronounced in the geographic center of diversity of the wild relatives in Peru. A total of 20 and 18 species were assessed as medium and low priority for further collecting, respectively, with only three species determined to be sufficiently represented currently. Priorities for further collecting include: (i) species completely lacking representation in germplasm collections; (ii) other high priority taxa, with geographic emphasis on the center of species diversity; (iii) medium priority species. Such collecting efforts combined with further emphasis on improving ex situ conservation technologies and methods, performing genotypic and phenotypic characterization of wild relative diversity, monitoring wild populations in situ, and making conserved wild relatives and their associated data accessible to the global research community, represent key steps in ensuring the long-term availability of the wild genetic resources of this important crop.

Periderm- and cortex-based resistance to tuber-feeding Phthorimaea operculella in two wild potato species

The trichome‐bearing wild potatoes Solanum berthaultii (Hawkes) and Solanum tarijense (Hawkes) (Solanaceae) have noted resistance to leaf‐feeding insect herbivores; however, little is known about their resistance to tuber‐feeding herbivores. This study evaluates resistance in tubers of these two species to attack by the potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae). Tubers from a range of accessions were presented to recently emerged neonate tuber moth larvae. Resistance to neonates varied between accessions and was generally higher in accessions of S. tarijense. The contribution to observed resistance of periderm vs. cortex factors was assessed by perforating tuber periderm in paired‐tuber experiments. Across species and accessions, an average of 62% of resistance was attributed to periderm‐related factors. All larvae entered tubers through the eyes. Unidentified cortex‐related factors affected larval development time and pupal weight. Sprouting compromised resistance by reducing the protective value of the periderm. The degree of sprouting also decreased larval development times and increased pupal weights in one of two accessions examined. These results demonstrate the potential of S. berthaultii and S. tarijense as sources of tuber‐resistance and identify accessions of both species with notably high periderm‐based protection. Levels of periderm resistance were not correlated to levels of cortex resistance and represent an independent resistance source compatible with the food value of crop potato.

Taxonomy and new collections of wild potato species in Central and Southern Peru in 1999

Peru contains about half of the described wild potato taxa, and many of these are not yet preserved in genebanks. This paper reports results of the second of a series of five planned collecting expeditions to Peru. Collections were made in the central Peruvian departments of Ancash, Huancavelica, La Libertad, and Lima, from March 8 to April 25,1999. They follow collections in 1998 in the southern Peruvian departments of Apurimac, Arequipa, Cusco, Moquegua, Puno, and Tacna. We collected 101 germplasm accessions, including first germplasm collections of the following 22Solanum taxa:Solanum amayanum, S. anamatophilum, S. arahuayum (lost in germplasm increase),S. augustii, S. bill- hookeri, S. cantense, S. chavinense, S. chomatophilum var. subnivale, S. chrysoflorum, S. gracilifrons, S. hapalos um, S. huarochiriense, S. hypacrarthrum, S.jalcae, S. moniliforme, S. multiinterruptum f. longipilosum, S. multiinterruptum var. machaytambinum, S. peloquinianum, S. rhombilanceolatum, S. simplicissimum, S. taulisense (lost in germplasm increase), andS. wittmackii. In addition, new collections were made of the under-collected speciesS. hastiforme (three collections). The above taxonomy is that used in planning our expedition, that we compare to a new treatment of Peruvian wild potatoes published by C. Ochoa in 1999. This paper reports the collection and new species identifications of the 1999 collections, and germplasm conservation and survival of the 1998 and 1999 collections. In addition, chromosome counts are provided for 134 accessions from the 1998 and 1999 expeditions, including first reports forS. chomatophilum var. subnivale (2n = 2x = 24),S. megistacrolobum subsp.purpureum (2n = 2x = 24), andS. multiinterruptum var.multiinterruptum f.albiflorum (2n = 2x = 24); we also report the first triploid count of an accession ofS. immite.ResumenEl Perú tiene aproximadamente la mitad de las taxa de papa silvestre descrita, muchas de las cuales aún no están conservadas en bancos genéticos. Este articulo consigna los resultados de la segunda de una serie de cinco expediciones planificadas de recolección en el Perú. Se colectó en los departamentos de Ancash, Huancavelica, La Libertad y Lima, entre el 8 de marzo y el 25 de abril de 1999. Fueron la continuatión de colecciones realizadas en 1998 en el sur del Perú, en los departamentos de Apurímac, Arequipa, Cusco, Moquegua, Puno y Tacna. Recolectamos 101 accesiones de germoplasma, incluyendo las primeras colecciones de germoplasma de las siguientes 22 taxa deSolanum: Solanum amayanum,S. anamatophilum, S. arahuayum (perdida al incrementar germoplasma),S. augustii, S. bill- hookeri, S. cantense, S. chavinense, S. chomatophilum var.subnivale, S. chrysoflorum, S. gracllifrons, S. hapalosum, S. huarochiriense, S. hypacrarthrum, S.jalcae, S. moniliforme, S. multiinterruptumf. longipilosum, S. multiinterruptum var.machaytambinum, S.peloquinianum, S. rhombilanceolatum, S. simplicissimum, S. taulisense (perdida al incrementar germoplasma) yS. wittmackii. Además, colectamos una especie poca colectada:S. hastiforme (tres colecciones). La taxonomía aquí usada es la del planeamiento la expedicién que fue comparada con el nuevo tratamiento de papas silvestres peruanas publicado por Carlos Ochoa en 1999. Este articulo informa sobre la colección y la identificación de nuevas especies de las colecciones de 1999 y de la conservación y supervivencia del germoplasma de las colecciones de 1998 y 1999. Asimismo, se proporciona el conteo de cromosomas de 134 accesiones de las expediciones de 1998 y 1999, incluido el primer reporte deS. megistacrolobum subsp.purpureum (2n = 2x = 24), S.multiinterruptum var.multiinterruptum f.albiflorum (2n = 2x = 24) yS. velardei (2n = 2x =24); también informamos sobre el primer conteo de triploide de una accesión deS. immite.

Variations in resistance against Phthorimaea operculella in wild potato tubers.

Tuber resistance can contribute to current management strategies against the potato tuber moth, Phthorimaea operculella Zeller (Lepidoptera: Gelechiidae), in field and stored potatoes. Wild potatoes represent a potential source of novel resistance traits against the moth. We assessed resistance in three wild potato species, Solanum multiinterruptum Bitt., Solanum sparsipilum (Bitt.) Juz. & Buk., and Solanum wittmackii Bitt. against neonate and developing tuber moth larvae. All three species had high levels of resistance but accessions of S. sparsipilum and S. wittmackii were significantly more resistant. Resistance in S. multiinterruptum was generally concentrated in the tuber periderm, whereas in S. sparsipilum and S. wittmackii resistance was mainly cortex‐based. Unidentified cortex‐resistance factors in all three species reduced survival and increased larval and pupal development times, but had no apparent effects on the pupal weights of survivors. A high proportion of larvae abandoned or died within tubers of S. wittmackii, which has particularly high levels of unidentified cortex‐based defenses. Resistance decreased in S. multiinterruptum and S. sparsipilum as tubers sprouted but was more stable in S. wittmackii. Periderm‐based resistance was more stable than cortex‐based resistance in S. multiinterruptum during sprouting. In contrast, cortex‐based resistance was stable in tubers of S. wittmackii as these sprouted, and resistance may have increased on some older sprouting tubers. Solanum multiinterruptum and S. sparsipilum are proposed as potential sources of resistance against the potato tuber moth.

A Morphometric Study of Species Boundaries of the Wild Potato Solanum Series Piurana (Solanaceae) and Putatively Related Species from Seven Other Series in Solanum Sect. Petota

Abstract There are about 190 wild potato (Solanum L. section Petota Dumort.) species distributed from the southwestern United States to central Argentina and adjacent Chile and Uruguay. The morphological similarity of many of its constituent species has led to widely conflicting taxonomic treatments. Solanum series Piurana Hawkes is one of 21 series recognized in section Petota in the latest comprehensive taxonomic treatment by Hawkes in 1990. They are distributed from southern Colombia, south through Ecuador to central Peru. The limits of the series and validity of its constituent species are unresolved. We provide the first comprehensive morphological phenetic study of the series, to include putatively related species in ser. Conicibaccata, Cuneoalata, Ingifolia, Megistacroloba, Simplicissima, Tuberosa, and Yungasensa, through an examination 188 living germplasm accessions of 33 species, planted in replicated plots in a field station in Andean Peru. Only four morphologically well-defined groups were supported. Continuing work is exploring molecular support for these species in these eight series.

Comparison of "remote" versus "easy" in situ collection locations for USA wild Solanum (potato) germplasm.

A basic question in germplasm collecting is whether the in situ genetic diversity in a given geographic range has been adequately sampled. While one would ideally sample all diverse sites with appropriate habitat, there is usually a practical bias against visiting relatively inaccessible sites. For wild potato in the USA, mountain habitats often include easy access locations (near roads, usually at lower altitudes), and relatively remote locations (usually high altitude crests that can be accessed only by trail hiking and camping). This work used AFLP markers to compare three southeastern Arizona mountain ranges for which multiple “easy” and “remote” Solanum fendleri populations had been collected. Of the total markers detected, 24%, 6% and 3% were unique to the “remote” locations, and 3%, 21% and 34% were unique to “easy” locations. This case study demonstrates that populations at such locations are not identical, but the most unique alleles are sometimes captured at the remote location, sometimes at the easy. The practical conclusion is that both locations need to be sampled and compared empirically in the lab for unique allele richness to identify locations with highest priority for additional collecting.ResumenUna pregunta básica que se hace cuando se colecta germoplasma, es si la diversidad genética in situ dentro de un area geográfica determinada ha sido muestreada adecuadamente. Mientras que idealmente es posible muestrear todos los sitios diversos con el hábitat apropiado, generalmente hay una predisposición práctica en contra de visitar sitios relativamente inaccesibles. En cuanto a especies silvestres de papa en los EUA, los hábitats montañosos a menudo incluyen localidades de fácil acceso (cerca de caminos, generalmente a altitudes bajas), y los lugares relativamente remotos (generalmente lugares de gran altura a los que se tiene acceso solo por rutas de a pie y acampando). En este trabajo se usaron marcadores AFLP para comparar tres montañas del sureste de Arizona en donde se colectaron poblaciones múltiples “fáciles” y “remotas” de Solanum fendleri. Del total de marcadores detectados, 24%, 6% y 3% fueron únicos de las localidades “remotas”, y 3%, 21% y 34% fueron únicas de los lugares “fáciles”. Este estudio demuestra que las poblaciones de tales localidades no son idénticas, pero los alelos mas exclusivos se captan algunas veces en la localidad remota y en otras ocasiones en la fácil. La conclusión práctica es que ambas localidades necesitan muestrearse y compararse empíricamente en el laboratorio, para determinar abundancia de alelos únicos e identificar lugares de la más alta prioridad para colectas adicionales.

A Morphometric Study of Species Boundaries of the Wild Potato Solanum Series Conicibaccata: a Replicated Field Trial in Andean Peru

Abstract Solanum series Conicibaccata contains about 40 wild potato (section Petota) species distributed from southern Mexico to central Bolivia. It contains diploids (2n = 2x = 24), tetraploids (2n = 4x = 48) and hexaploids (2n = 6x = 72) and some polyploids are likely allopolyploids. Our morphological phenetic study in an Andean site in central Peru (12°S, 3200 m altitude) is a replicated study from one done in the north central United States (45°N, 180 m elevation) but uses more species (28 vs. 25), accessions (173 vs. 100), and morphological characters (72 vs. 45) and also includes members of related series Piurana. Both US and Peruvian studies provide phenetic support with Canonical Discriminant Analyses (but poorly if at all with Principal Components Analyses) to distinguish the following species or species groups in series Conicibaccata: 1) S. agrimonifolium and S. oxycarpum as a possible single species, and 2) S. longiconicum (tetraploids from Mexico and Central America), 3) the South American Conicibaccata diploids as a possible single species, except for 4) S. trinitense that is distinctive, 5) the South American tetraploids as a group except for 6) S. flahaultii that is distinctive. However, character states among these species or species groups are often present only by using a range of widely overlapping character states (polythetic support). We suspect that our continuing molecular studies will support the synonymy of many of these species.

The discovery and phylogenetic implications of a novel 41 bp plastid DNA deletion in wild potatoes

Insertions and deletions (indels) are common in intergenic spacer regions of plastid DNA and can provide important phylogenetic characters for closely related species. For example, a 241-bp plastid DNA deletion in the trnV-UAC/ndhC intergenic spacer region has been shown to have major phylogenetic importance in determining the origin of the cultivated potato. As part of a phylogenetic study of the wild potato Solanum series Piurana group we screened 199 accessions of 38 wild potato species in nine of the 19 tuber-bearing (Solanum section Petota) series that have not been examined before for indels in the trnV-UAC/ndhC intergenic spacer region. A novel 41 bp deletion (but no 241 bp deletion) was discovered for 30 accessions of three species: S. chiquidenum (5 of 10 accessions), S. chomatophilum (19 of 28), and S. jalcae (6 of 6). Accessions with and without this deletion are found throughout much of the north-south range of all three species in northern and central Peru, but not east of the Marañón River. Multivariate morphological analyses of these 44 accessions showed no morphological associations to the deletion. The results suggest extensive interspecific gene flow among these three species, or a common evolutionary history among species that have never been suggested to be interrelated.