Potato germplasm collecting expedition to Mexico in 1997: Taxonomy and new germplasm resources

Wild potato (Solanum sect.Petota) germplasm has been collected in Mexico on nine major expeditions, as determined by 20 collections or more from each expedition currently at the United States potato genebank, the National Research Support Program-6 (NRSP-6). These have resulted in 609 accessions with good collection data. In addition, NRSP-6 has germplasm of approximately 90 other Mexican collections that are unspecific regarding date or place of collection. This expedition was funded to collect those remaining collections with no or little germplasm:Solanum clarum,S. xedinense, S. hintonii, S. hjertingii var.physaloides, S. leptosepalum, S. lesteri, S. macropilosum, S. xmichoacanum, S. xsambucinum, andS. stenophyllidium. In addition, some species and species groups (species groups indicated in parentheses) have unresolved taxonomic problems that needed clarification by additional field collections. These are (S. agrimonifolium and S.oxycarpum), (S. brachycarpum, S. guerreroense, S. hougasii, andS. iopetalum - theS. brachycarpum complex), (S. fendleri, S. papita, S. stoloniferum - theS. stoloniferum complex),S. leptosepalum, andS. macropilosum. We conducted a wild potato germplasm collecting expedition in Mexico from August 22 to October 31, 1997. Our 103 collections, 71 as germplasm collections, provide the first germplasm samples forS. hjertingii var.physaloides,S. leptosepalum, andS. macropilosum. They provide additional germplasm of the rare speciesS. clarum, S. xedinense, S. lesteri, S. xmichoacanum, S. xsambucinum, andS. stenophyllidium. We additionally gathered germplasm and field data to help resolve taxonomic difficulties inS. agrimonifolium andS. oxycarpum, theS. brachycarpum complex, and theS. stoloniferum complex.     

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.     

Wild potato (Solanum sect.Petota) germplasm collecting expedition to Argentina in 1990, and status of Argentinian potato germplasm resources

Summary A joint Argentina/United States expedition collected wild potato (Solanum sect.Petota) germplasm in Argentina between February 4–28 and March 28–April 18, 1990. This was followed by a short expedition between February 27 and March 3, 1991. Collections were made in the Andes Mountains from southern Tucumán Province (27°20′S), south to southern Rio Negro Province (40°52′S) and comprised 88 lots of germplasm of ten species, 76 as true-seed and 12 as tubers. The most important new collections included germplasm ofS. brevidens, S. maglia, S. x rechei andS. venturii. By summarizing details of these collections with those of existing collections, we have been able to suggest future collecting in Argentina.     

Wild potato (Solanum sect.Petota) germplasm collecting expedition to Mexico in 1993, with special reference toSolanum bulbocastanum Dunal andS. cardiophyllum Lindley

Summary A joint Mexico/United States expedition collected wild potato (Solanum sect.Petota) germplasm in Mexico between August 1–31, 1993. The purpose of the expedition was to expand germplasm and herbarium collections ofS. bulbocastanum andS. cardiophyllum. Collections were made from west-central to southern Mexico, and comprised 19 true seed and 37 tuber collections (45 collections in total) of 9 species and two putative natural hybrids.     

Solanum sect. petota in Guatemala; Taxonomy and genetic resources

There are five wild potato species in Guatemala:Solanum agrimonifolium,S. bulbocastanum,S. clarum,S. demissum, andS. morelliforme. We conducted a collecting expedition there from September 11 to November 5, 1995. The goals of the expedition were to gather field data for taxonomic studies of the five species of Guatemalan wild potatoes and to collect potato germplasm. Our 43 true seed collections nearly quadruple the available wild potato germplasm for Guatemala, provide germplasm from most previously known localities, and add new ones. We provide a systematic treatment of Guatemalan wild potatoes, geographic and logistical data for collecting wild potatoes in Guatemala, statistics on human population growth and deforestation to help explain decline of wild potato populations, recommend areas for future collecting, and suggest two areas as in-situ reserves for wild potatoes     

Wild potato collecting expedition in Southern Peru (Departments of Apurímac, Arequipa, Cusco, Moquegua Puno, Tacna in 1998: Taxonomy and new genetic resources

Peru has 103 taxa of wild potatoes (species, subspecies, varieties, and forms) according to Hawkes (1990; modified by us by a reduction of species in theSolanum brevicaule complex) and including taxa described by C. Ochoa since 1989. Sixty-nine of these 103 taxa (67% ) were unavailable from any of the world’s genebanks and 85 of them (83%) had less than three germplasm accessions. We conducted a collaborative Peru (INIA), United States (NRSP-6), and International Potato Center (CIP) wild potato (Solanum sect.Petota) collecting expedition in Peru to collect germplasm and gather taxonomic data. This is the first of a series of planned expeditions from 1998–2002. We collected from February 18 to April 18, 1998, in the southern departments of Apurímac, Arequipa, Cusco, Moquegua, Puno, and Tacna. We made 57 germplasm collections, including 14 taxa that are the first available as germplasm for any country (Solanum aymaraesense, S. chillonanum, S. incasicum, S. megistacrolobum subsp.megistacrolobum f. purpureum, S. longiusculus, S. multiflorum,S. pillahuatense, S. sawyeri, S. sandemanii, S. tacnaense, S. tarapatanum, S. urubambae, S. velardei, S. villuspetalum), and two additional taxa that are the first available for Peru but with germplasm from Bolivia (S. megistacrolobum subsp.toralapanum, S. yungasense). Collections also were made for the rare taxaS. acroscopicum, S. buesii, S. limbaniense, andS. santolallae. Our collections suggest the following minimum synonymy may be needed for Peruvian potatoes:S. sawyeri as a synonym ofS. tuberosum;S. hawkesii andS. incasicum as synonyms ofS. raphanifolium;S. multiflorum andS. villuspetalum as synonyms ofS. urubambae.     

Screening the U.S. potato collection for frost hardiness

Potato is one of the most important world vegetables with respect to value of production and nutritional impact. Frost susceptibility reduces or precludes production on millions of hectares worldwide. In contrast to disease and pest problems, cultural or chemical treatments are not likely to be helpful in combating frost, so genetic improvement must be sought. Fortunately, wild relatives of the cultivated potato have been shown to exhibit frost tolerance far superior to that of cultivated species. In this research, over 2,600 accessions representing 101 species in the US potato collection at Sturgeon Bay, Wisconsin were visually screened after natural frosts in a uniform field in 1992. This provided a more comprehensive survey of germplasm accessions, further characterized species’ hardiness and intraspecific variation. The most hardy species wereSolanum acaule, S. albicans, S. commersonii, andS. demissum. An additional previously unreported extremely frost hardy species (Solanum paucissectum) was discovered. This information should expand the insights and germplasm options available to those intent on breeding desirable varieties with high levels of frost hardiness.     

Foliar resistance toPhytophthora infestans (Mont.) de Bary (US-8) in 13 Mexican and South AmericanSolarium species having EBNs of 1, 2, and 4 and implications for breeding

The recent US-8 clonal lineage ofPhytophthora infestans, the pathogen causing late blight (LB) disease, is one of the most widespread and difficult to control. Sources of foliar resistance to US-8 were evaluated in 1927 seedling genotypes by sampling 49 plant introductions (PIs) representing 13 Mexican and South AmericanSolanum species having an Endosperm Balance Number (EBN) of 1, 2, or 4, and one species with an unknown EBN. Species evaluated were 2x(1EBN)S. bulbocastanum, S. cardiophyllum, S. commersonii, S. pinnatisectum, andS. trifidum; 2x(2EBN)S. berthaultii, S. megistacrolobum, S. microdontum, andS. verrucosum; 4x(2EBN)S. fendleri andS. stoloniferum; 6x(4EBN)S. guerreroense;2x unknown EBNS. polyadenium; as well as4x S. tuberosum families as controls. Foliar resistance in the field was monitored in 1998 and 1999. Resistance differed relative to species geographic origin, EBN, species themselves, PIs within a species, and genotypes within a PI. In 1998 Mexican germplasm had a lower area under the disease progress curve (AUDPC, 1140) and greater resistance than South American germplasm (1601), while the 1EBN (1119) and unknown EBN (1075) species had greater resistance than 2EBN (1470) and 4EBN (1888) species. AUDPC ranged among species from 555 (S. cardiophyllum) to 1932 (S. megistacrolobum) and among PIs within a species most widely forS. bulbocastanum (267–1007) and least widely forS.polyadenium (1019–1179). In 1999 LB symptoms were not observed on the species before an early freeze; however, all 1999S. tuberosum families showed LB symptoms and segregated for resistance, pointing to greater resistance in the species than in cultivated germplasm. Resistance found in diploid 2EBN germplasm is more accessible due to greater crossability with cultivated germplasm; however, though more difficult to introgress, resistance found in some of the more reproductively isolated 1EBN germplasm is worth pursuing.     

Solarium SectionPetota in Costa Rica: Taxonomy and genetic resources

Prior to 1996, worldwide holdings of germplasm of wild potatoes from Costa Rica amounted to just two collections; this country therefore formed a priority for collecting. We mapped all localities of wild potatoes from herbarium specimen data from Costa Rica and collected throughout the country. We made 13 collections, 10 of these with botanical seeds. These collections considerably extend the numbers of accessions and geographic range of the germplasm available from Costa Rica. The taxonomic identity of the species of wild potatoes (Solanum sect. Petota) in Costa Rica was previously unresolved. Our fieldwork supports the concept that Costa Rican wild potatoes belong to a single species,S. longiconicum.     

Potato germplasm collecting expedition to Chile, 1989, and utility of the Chilean species

A joint Chilean, United States potato (Solanum sect.Petota) germplasm collecting expedition was conducted in Chile between January 21–March 30, 1989. The trip resulted in collections ofSolanum brevidens (50 accessions),S. etuberosum (28 accessions),S. maglia (3 accessions) and indigenous primitive landraces ofS. tuberosum (24 accessions). Comments are presented on the habitats, distribution, and potential and realized breeding value of these species.     

Castor genetic resources: A primary gene pool for exploitation

Castor (Ricinus communis L., 2n = 2x = 20) is grown across the world in tropical, sub-tropical and warm temperate regions. Castor oil has more than 700 industrial uses and its global demand is rising constantly at 3-5% per annum. Vast castor germplasm collections are being conserved in more than 50 genebanks across the world. But consolidated reports on their status and value are not available to tap their potential. Utilization of vast global germplasm could only be enhanced when the information on germplasm is shared and seed are exchanged. Therefore, the review provides information on current status of global castor collections and an overall view of potential of these collections besides highlighting the challenges and opportunities facing germplasm. This report serves as a unique starting point for the global castor community to build strong multinational collaborations to facilitate knowledge and resource integration and coordinated research planning.     

Germplasm transfer from the wild tetraploid speciesSolanum acaule bitt. to the cultivated potato,S. tuberosum L. using 2N eggs

Solanum acaule Bitt. (acl ¹, 2n=4x=48 and 2n=6x=72) is a wild potato species in which resistance to adverse biotic and abiotic agents has been found. The tetraploid subspeciesacaule andaemulans cannot be easily crossed with the common potato,S. tuberosum L. Grouptuberosum (tbr, 2n=4x=48) because the development of the endosperm in the hybrid seed is abnormal. Since 4xacl behaves as a diploid in intra and interploidy crosses, it was postulated that the hybridization barrier withtbr could be overcome if the wild species produced 2n gametes. One hundred and ninety-seven plants of 4xacl (22 introductions) were screened for pollen of heterogeneous size; only two plants produced this type of pollen, with 3% and 5% of pollen in the large class, respectively. On the other hand, 427 plants (47 introductions) were screened for 2n eggs through controlled crosses withtbr. Forty-one plants (13 introductions) produced 219 berries of which 46 contained at least one plump seed. Seed from berries with low seed set gave rise to hexaploid hybrids possibly through the functioning of 2n eggs from 4xacl. A sample of these hybrids was successfully backcrossed as female parents totbr, giving rise to 5x BC₁ progenies. These BC₁ progenies could be easily back-crossed totbr, yielding tetraploid or near tetraploid BC₂ plants.     

Genetic heterogeneity estimated by RAPD polymorphism of four tuber-bearing potato species differing by breeding system

Most wild potato germplasm in genebanks is collected, preserved, and evaluated as botanical seed populations that may be highly heterozygous and heterogeneous. However, some species are selfers so potentially very homozygous, perhaps also homogeneous. Intrapopulation heterogeneity increases sampling error that can undermine consistency in seed regeneration in the genebank, screening results, germplasm collecting, and estimates of taxonomic relationships. Thus, knowledge of genetic heterogeneity (GH) can predict the need to commit more resources for larger sample sizes or replication when populations of a given species are being regenerated, evaluated, collected, and classified. This study investigated withinpopulation GH in 32 potato populations comprising four different breeding systems observed inSolatium species:S. fendleri (2n=4x=48, disomic selfer),S. jamesii (2n=2x=24, outcrosser),S. sucrense (2n=4x=48, tetrasomic outcrosser), andS. verrucosum (2n=2x=24, selfer). RAPD markers were used to estimate heterogeneity among 24 individuals per population. Populations ofS. verrucosum were quite homogeneous with an average GH of 6.0%. Similarly low heterogeneity was detected among the eight populations ofS. fendleri (average GH=7.1%). In contrast,S. jamesii andS. sucrense had a much higher GH of 29.4% and 44.1%, respectively. These results demonstrate and quantify the great difference in intrapopulation heterogeneity among wild potato species. Calculations based on intrapopulation heterogeneity indicate that samples should be composed of 25 to 30 random plants for low sample variation that is uniform for all species.     

Species relationships between a wild tetraploid potato species,Solanum acaule bitter, and its related species as revealed by rflps of chloroplast and nuclear DNA

Solanum acaule Bitter is a wild, disomic tetraploid potato species widely distributed in the South America. In this study, species relationships between eight accessions ofS. acaule and 108 accessions of 27 morphologically closely related species were investigated using chloroplast and nuclear DNA RFLPs. Chloroplast DNA types were determined for most of the accessions based on restriction digestion patterns of entire chloroplast DNA. C type chloroplast DNA was common inS. acaule andS. albicans (a hexaploid derivative fromS. acaule), which was also found inS. megistacrolobum, S. sanctae-rosae,S. raphanifolium, and several other Peruvian species in seriesTuberosa. Nuclear DNA was analyzed by Southern hybridization with 31 single-copy RFLP probes. One hundred and thirty-four bands were scored, from which a UPGMA dendrogram was constructed to show overall similarities among accessions.Solanum acaule andS. albicans (andS. demissum) formed a cluster with a high similarity, and then, this group was clustered withS. megistacrolobum andS. sanctae-rosae. The resulting cluster was well separated from other clusters. Thus, we suggest that an initial tetrasomic tetraploid arose from eitherS. megistacrolobum orS. sanctae-rosae. Interestingly, a Mexican hexaploid speciesS. demissum showed the closest similarity toS. acaule andS. albicans, suggesting that they shared a common ancestry.     

Pollen-pistil incompatibility in a diploid hybrid potato population with cultivated and wild germplasm

The basis of low seed set was investigated in a diploid hybrid population with germplasm from the cultivated speciesSolanum tuberosum spp.tuberosum andS. tuberosum ssp.phureja and the wild speciesS. chacoense. Controlled crosses were performed following an incomplete diallel mating design which included the hybrid population and the parental species. Pollen grain germination and pollen tube growth were observed with fluorescence microscopy in 174 intrapopulation and interspecific combinations of genotypes. Fifty percent of the combinations of genotypes within the hybrid population and 46% of those between this population and the parental species were incompatible; overall, 71% of the interspecific combinations of genotypes were compatible when plants of the hybrid population were used as females, vs. 5% when used as males. Although the site of reaction could vary in a given intrapopulation or interspecific cross with the combinations of genotypes, pollen tube inhibition occurred in the first third of the style in 42% of them. Since the gene pool of the hybrid population had been widened with germplasm from other geographic areas and the genotypes ofS. tuberosum ssp.tuberosum, S. chacoense andS. tuberosum ssp.phureja used in this study were not the ones involved in the original crosses, it is concluded that the S-locus is not controlling the incompatibility reaction but rather that a cross-incompatibility system, possibly governed by more than one locus, is acting.     

Some studies on the distribution and incidence of potato mop-top virus in Peru

Symptoms of PMTV are distributed widely in potatoes in the highlands (Andes) of Peru, but have not been found in coastal plantings; they were observed in 9 out of 22 Peruvian Departments. Incidences of over 10% of affected plants in one or more crops were found in 14 different localities. Thirteen cultivars with symptoms were observed, 9 wereSolanum tuberosum subsp.andigena Juz. & Buk., 3 were hybrids ofS. tuberosum subsp.andigena xS. tuberosum subsp.tuberosum L orS. Curtilobum Juz. & Buk. and 1 wasS. juzepczukii Buk. Symptoms were also seen in 29 clones of the potato germplasm collection of the International Potato Center. Distribution and prevalence of PMTV in Peru appear to be related to those rainfall and temperature conditions that favour its fungus vectorSpongospora subterranea (Wallr.) Lagerh.     

Evaluation for chipping and tuber soft rot (Erwinia carotovora) resistance in potato clones from unilateral sexual polyploidization (2x × 4x)

The aim of this work is the evaluation of tetraploid potato clones with germplasm fromS. chacoense andS. phureja for chipping and resistance to tuber soft rot (Erwinia carotovora subsp.carotovora). Tetraploid potato clones were obtained via 2n eggs through 2x–4x crosses. Cytological mechanisms were investigated in the diploid hybrid 2n-egg producer used as parent in the unilateral sexual polyploidization scheme; the omission of the second meiotic division and cytokinesis failure at the end of meiosis were identified with a genetic consequence equivalent to second division restitution (SDR). Tuber marketable yield, specific gravity and chip-processing ability evaluated at harvest and after cold storage with and without reconditioning were higher in some clones as compared to theS. tuberosum tetraploid parent. Tuber soft rot resistance, contributed byS. chacoense, was successfully transferred to the4x level. After inoculation withErwinia carotovora subsp.carotovora and estimation of the rotted area, one tetraploid clone proved to be resistant and three partially resistant. The genetic value of exotic germplasm and sexual polyploidization strategy are discussed in relation to potato improvement.     

Hybridization between Gp. Tuberosum Haploids and 1EBN wild potato species

Diploid wild potato species, classified as 1EBN (Endosperm Balance Number), do not cross with tetraploid or diploid forms ofS. tuberosum Gp. Tuberosum. The crossing of 2n pollen producing 1EBN clones as well as chromosome-doubled 1EBN clones with Gp. Tuberosum haploids was initiated to overcome this hybridization barrier. The screening of eleven 1EBN species,S. brachistotrichum, S. bulbocastanum, S. cardiophyllum, S. chancayense, S. commersonii, S. etuberosum, S. fernandezianum, S. jamesii, S. mochicense, S. pinnatisectum andS. trifidum, resulted in the identification of 2n pollen producers in eight of the species examined. Direct hybridization with Gp. Tuberosum haploids utilizing the above-mentioned crossing scheme was successful withS. chancayense andS. commersonii. The hybrids obtained, however, were male and female sterile. Abnormal microsporogenesis in the hybrids was postulated to be the result of an interaction between Gp. Tuberosum cytoplasm and nuclear genes contributed by the 1EBN male parent. Analyses of the growth of 1EBN species’ pollen tubes in the stigma/style of Gp. Tuberosum haploids were also conducted. Interspecific incompatibilities were observed with the most severe forms found with the use of species in the Series Etuberosa. The use of the Endosperm Balance Number theory can aid in designing crosses which overcome barriers to successful endosperm development. Sterilities in the hybrids obtained as well as interspecific incompatibilities will also need to be addressed, however, before 1EBN species germplasm can be successfully utilized for the improvement of the cultivated potato.     

Screening of exotic potato germplasm for nitrogen uptake and biomass production

Exotic potato germplasm may contain useful traits for improving nitrogen (N) use efficiency in cultivated potatoes (Solanum tuberosum L.). The objective of this study was to evaluate a “mini” core collection of wild germplasm for biomass production, N uptake, and N use efficiency. A field study was conducted during the 1993 growing season on a loamy sand soil at Becker, Minnesota. Uniform transplants for 39 wild accessions and 3 varieties were grown under greenhouse conditions, and after 40 days, they were transplanted to the field. Plants were subjected to two N treatments, 0 and 225 kg N ha¹, replicated three times in a split-plot design. Plant parts were collected separately 111 days after transplanting, dried, weighed, and analyzed for N concentration. Nitrogen rate and potato species had significant effects on total dry weight, N content, and tissue N concentration. The regression coefficient of N concentration on total dry weight was very low (r=0.22, NS), whereas the regression coefficient of total N content on total dry weight was high (r=0.94, P>0.001). At both low and high N environments, Russet Burbank had greater dry weight than all the accessions. Several wild accessions, especiallyS. chacoense, S. commersonii, S. kurtzianum, S. microdontum, andS.phureja, had equal to or greater dry weights than Russet Norkotah or Red Norland. For N uptake efficiency, 2,7, and 20 accessions were ranked better than Russet Burbank, Russet Norkotah, and Red Norland, respectively. Recovery of soil applied N by the varieties ranged from 16 to 36%; the top seven wild accessions recovered between 27 and 49%. Based on plant growth without added N fertilizer and relative response to N fertilizer, the species were categorized into four relative N use efficiency groups: good foragers with good response to N, poor foragers with good response to N, good foragers with poor response to N, and poor foragers with poor response to N.     

Response of six wild potato species to chloride and sulfate salinity

Eleven accessions belonging to six species ofSolanum (S. bulbocastanum,S. chacoense, S. gourlayi, S. microdontum, S. papita, and S.sparsipilum) were tested for resistance to salt. Resistance was measured by survival and growth (dry weight of tops) of plants treated with solutions of NaCl and Na₂SO₄. The six species could be grouped into four classes based on good to poor resistance to salt solutions (1.S. chacoense, 2.S. gourlayi, 3.S. microdontum, S. sparsipilum, S. bulbocastanum and 4.S. papita). There was a close relationship (r=0.94**) between the survival of plants and growth of surviving plants treated with salt solutions. There was no relationship between known heat or drought resistance of various accessions and salt resistance. Results indicate there is a large genetic base available to improve the salt resistance of the cultivated potato.