Assessment of genetic variability of olive varieties by microsatellite and AFLP markers

Fourteen developed microsatellite markers were characterized for their use in genotyping and diversity studies of olive varieties. After optimisation of microsatellite assay and allele sizing, ninety-six alleles were found in nineteen varieties, with an average of 6.8 alleles per locus. The characteristics of the microsatellite markers were used to identify markers that can be reliably applied for variety genotyping. Such features were the generation of complex banding patterns supported by underlying allele sequences, `short allele dominance', an unstable repeat structure and a low number of alleles. AFLP analysis was performed on the same set of olive varieties using eight primer pair combinations. The genetic relationships among nineteen olive varieties were compared on the basis of microsatellite and AFLP polymorphisms. Genetic distances between all pairwise combinations of the varieties were calculated using Jaccard's coefficient of similarity and dendrograms were constructed by the UPGMA method. The results of clustering analysis with both molecular systems showed the common genetic background of Tuscan varieties, and genetic divergence within Slovene olive germplasm. Slovenian varieties ‘Buga’, ‘Štorta’ and ‘Samo’ might represent regionally selected olives, while ‘Zelenjak’ and ‘Črnica’ are probably derived from the Central Italian region. The predominant local ‘Istrska belica’ was introduced to Slovenia independently from the other regional varieties and showed the lowest genetic similarity with the other regional varieties. This revised version was published online in August 2006 with corrections to the Cover Date.     

Penetrance of creeping-rootedness in clonal progenies of lucerne and observations on underground morphology of plants differing for this character

Elaeis oleifera or ‘caiaué’, a close relative of oil palm (E. guineensis), has some agronomic traits of great interest for the oil palm genetic breeding such as slow growth, oil quality (mostly unsaturated) and disease resistance. An analysis of a Brazilian oil palm germplasm collection was carried out using RAPD (Random Amplified Polymorphic DNA) markers with the objective of understanding the genetic variation of ‘caiaué’ accessions collected in the Amazon Forest in the last two decades. A sample of 175 accessions obtained along the Amazon River Basin was analyzed and compared to 17 accessions of oil palm from Africa. Ninety-six RAPD markers were used in the analysis, of which fourteen were shown to be specific to oil palm, while twelve were specific to ‘caiaué’. Results showed that the Brazilian ‘caiaué’ accessions studied have moderate levels of genetic diversity as compared to oil palm accessions. The data allowed the establishment of similarity groups for ‘caiaué’ accessions, which is useful for selecting parental plants for population breeding. Cluster analysis showed that, in general, genetic similarities are not correlated to geographical distances, but consistent with geographical dispersal along the Amazon River network. AMOVA showed that most of the genetic variation is found within populations, as expected for anallogamous and long-lived perennial species. The study provides important information to define strategies for future collection expeditions, for germplasm conservation and for the use of E. oleifera in breeding programs. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ecotypic differentiation in Medicago polymorpha L. along an environmental gradient in central Chile. RAPDs studies show little genetic divergence

Burr medic (Medicago polymorpha) is distributed in a wide range of bioclimatic and edaphic conditions throughout the mediterranean-climate region of Chile. Previous studies on populations of M. polymorpha collected along this gradient revealed a remarkable ecotypic differentiation in many adaptive traits. Random amplified polymorphic DNA (RAPD) was used to evaluate genetic divergence in 36 accessions collected along the entire gradient. Three Australian commercial cultivars were also included in the study, of which two originated in Chile. The 40 RAPD primers used revealed a high degree of polymorphism and generated a total of 295bands, of which 78% were polymorphic. Degrees of similarity, based on Nei's genetic distance, identified one group of accessions (22 of the 39studied) with an index of similarity = 100% centered in the semiarid and arid zones of the study region. The remaining 17 accessions (from more mesic zones and one commercial cultivar) were more diverse. Only 91%similarity was found for the combined 39 accessions, indicating a low degree of genetic divergence. Biogeographical and life history strategy aspects of the results are discussed, including the notion of a suite of ‘arid-adapted’ characteristics arising in annual legumes under arid /semiarid conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fingerprinting temperate <Emphasis Type="Italic">japonica</Emphasis> and tropical <Emphasis Type="Italic">indica</Emphasis> rice genotypes by comparative analysis of DNA markers

This paper describes the relative efficiency of three marker systems, RAPD, ISSR, and AFLP, in terms of fingerprinting 14 rice genotypes consisting of seven temperatejaponica rice cultivars, three indica near-isogenic lines, three indica introgression lines, and one breeding line of japonica type adapted to high-altitude areas of the tropics with cold tolerance genes. Fourteen RAPD, 21 ISSR, and 8 AFLP primers could produce 970 loci, with the highest average number of loci (92.5) generated by AFLP. Although polymorphic bands in the genotypes were detected by all marker assays, the AFLP assay discriminated the genotypes effectively with a robust discriminating power (0.99), followed by ISSR (0.76) and RAPD (0.61). While significant polymorphism was detected among the genotypes of japonica and indica through analysis of molecular variance (AMOVA), relatively low polymorphism was detected within the genotypes of japonica rice cultivars. The correlation coefficients of similarity were significant for the three marker systems used, but only the AFLP assay effectively differentiated all tested rice lines. Fingerprinting of backcross-derived resistant progenies using ISSR and AFLP markers easily detected progenies having a maximum rate of recovery for the recurrent parent genome and suggested that our fingerprinting approach adopting the ‘undefined-element-amplifying’ DNA marker system is suitable for incorporating useful alleles from the indica donor genome into the genome of temperate japonica rice cultivars with the least impact of deleterious linkage drag.     

Classification of cassava into ‘bitter’ and ‘cool’ in Malawi: From farmers' perception to characterisation by molecular markers

Cassava roots, a major food in Africa, contain cyanogenic glucosides that may cause toxic effects. Malawian women farmers considered fields of seemingly similar cassava plants to be mixes of both ‘cool’ and ‘bitter’ cultivars. They regard roots from ‘cool’ cultivars as non-toxic. Roots of ‘bitter’ were considered to require extensive traditional processing done by women to be safe for consumption. But curiously, these women farmers preferred ‘bitter’ cultivars since toxicity confers protection against theft, which was a serious threat to the food security of their families. We studied how well these farmers comprehend the effects of genetic variations in cassava when dealing with cyanogenesis in this complex system. Using molecular markers we show that most plants farmers identified as belonging to a particular named cultivar had a genotype typical of that cultivar. Farmers' ethno-classification into ‘cool’ and ‘bitter’ cultivars corresponded to a genetic sub-division of the typical genotypes of the most common cultivars, with four-fold higher cyanogenic glucoside levels in the bitter cultivars. Examining morphology, farmers distinguished genotypes better than did the investigators when using a standard botanical key. Undoubtedly, these women farmers grasp sufficiently the genetic diversity of cassava with regard to cyanogenesis to simultaneously benefit from it and avoid its dangers. Consequently, acyanogenic cassava – the breeding of which is an announced good of some cassava genetic improvement programmes – is not a priority to these farmers. Advances in molecular genetics can help improve food supply in Africa by rapid micropropagation, marker assisted breeding and introduction of transgenic varieties, but can also help to elucidate tropical small-scale farmers' needs and skills. This revised version was published online in August 2006 with corrections to the Cover Date.     

RAPD genetic diversity of Albanian olive germplasm and its relationships with other Mediterranean countries

RAPD markers were used for the study of 19Albanian olive cultivars and two wild olives (oleasters). A total of 76polymorphic bands (4.8 polymorphic markers per primer) out of 107 reproducible were obtained using 16 primers. The number of bands per primer ranged from 4 to 10,whereas the number of polymorphic bands ranged from 1 to 9, corresponding to 71%of the total amplification products. All the accessions could be identified by the combination of four primers: OPA-19;OPA-02; OPK-16 and OPP-19. The dendrogram,based on Jaccard's index, included three major groups according to their origin: 1)most of the cultivars from the area of Berat (South of Albania) 2) cultivars from the Centre and Centre-North of Albania and3) cultivars from the Centre and North-West of Albania along with the oleaster from Elbasan. In order to evaluate the origin of Albanian cultivars they were compared to those diffused in other countries like Greece, Italy and Turkey, due to geographical and historical affinity among these countries, by using a one way AMOVA. Although most of the genetic diversity was attributable to differences among cultivars within each country (91.47%) significantφ-values among countries(φ_st = 0.085; p < 0.001)suggested the existence of RAPD phenotypic differentiation. Significant φ-values in all pairs formed by Albania with the other countries were observed. These results are consistent with the autochthonous origin of Albanian cultivars. This revised version was published online in August 2006 with corrections to the Cover Date.     

Morphological and molecular characterization of melon accessions resistant to Fusarium wilts

Fusarium wilt incited by Fusarium oxysporum f. sp. melonis (F.o.m) is one of the most widespread and devastating melon diseases. While resistance to physiological races 0, 1, and 2 is relatively frequent in different botanical varieties, sources of resistance to race 1,2 are restricted to a few Far-Eastern accessions. In this work, the results of a screening for resistance to F.o.m. race 1,2 among 32 accessions are presented. Three Japanese accessions (‘Kogane Nashi Makuwa’, ‘C-211’, and ‘C-40’) showed the highest resistance levels, but useful levels of resistance were also detected in one Russian ‘C-160’ and two Spanish (‘C-300’ and ‘Mollerusa-7’) accessions. These resistant materials, together with other accessions previously described as resistant to F.o.m. races 0, 1, and/or 2 have been morphologically and molecularly characterized. Based on cluster analysis, these accessions have been grouped according to the botanical subspecies they belong to. Assessment of genetic diversity indicated that the resistant accessions to races 0, 1 and 2, are scattered along the established clusters. On the other hand, high levels of resistance to the race 1,2 could be found only among accessions belonging to Cucumis melo subsp. agrestis, nevertheless, a certain degree of resistance to this race could also be found within some accessions belonging to subsp. melo. As far as we know, this is the first report of resistance to F.o.m race 1,2 found out from the Far-Eastern melon material. Based on fruits characteristics, it appears that several inodurus and cantalupensis accessions could be exploited in breeding programs as resistance sources to F.o.m races 0, 1 and/or 2 for the improvement of these melon types. The accessions with the highest levels of resistance to the race 1,2 appeared to be very distant both molecularly and morphologically from the commercial types. Nevertheless ‘C-160’, ‘C-300’, and ‘Mollerusa-7’ classified as var. inodorus are morphologically very similar to the Spanish commercial types and might be used as resistant sources in breeding these melon types.     

A molecular technique for selection of self-compatible varieties of Japanese pear (Pyrus pyrifolia Nakai)

The pear cultivar ‘Osa-Nijisseiki’ (S₂S^sm ₄; sm = stylar-part mutant) has been used as a parent to breed self-compatible cultivars that produce excellent fruits. However, determination of the self-compatibility of ‘Osa-Nijisseiki’ offspring requires a lot of time, 6 years or more, by conventional cross breeding. We have designed a rapid reliable method for the identification of self-compatible varieties of ‘Osa-Nijisseiki’ offspring based on the polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) with S-allele specific restriction endonucleases. By using this method, 8 self-compatible varieties were selected among 16 selections resulting from a cross between the self-compatible cultivar ‘Osa-Nijisseiki’ (S₂S^sm ₄) and the self-incompatible cultivars ‘Niitaka’ (S₃S₉), ‘Whasan’ (S₃S₅), ‘Chuwhangbae’ (S₄S₆). The S-genotypes of 16 ‘Osa-Nijisseiki’ offsprings were also determined. This revised version was published online in August 2006 with corrections to the Cover Date.     

Assessment of genetic diversity in cabbage cultivars using RAPD and SSR markers

Genetic relationship and diversity among seven cabbage cultivars were analyzed using RAPD and SSR markers. These cultivars are of great commercial value in India and are confirmed for their reaction to black rot caused by Xanthomonas campestris pv. campestris. However, so far the extent of genetic diversity and relatedness has not been studied in these cultivars. A total of 17 selected RAPD primers generated 90 bands, 76 of which were polymorphic (84.44%). In addition, 27 selected SSR primers generated 67 amplified bands with 59 of which were polymorphic (87.6%). Though both the marker techniques were able to discriminate the cultivars effectively, analysis of combined data of markers (RAPD and SSR) resulted in better distinction of cultivars. By combining both the markers, a total of 157 bands were detected of which 135 bands (85.98%) were polymorphic, i.e. an average of 5.95 bands per primer. High level of polymorphism (> 85%) recorded with two different marker systems indicated a high level of genetic variation existing among the cultivars. Genetic relationship estimated using similarity co-efficient (Jaccard’s) values between different pairs of cultivars varied from 0.21 to 0.77 in RAPD, 0.42 to 0.82 in SSR, and 0.43 to 0.89 with combined markers. A high correspondence had been recorded between the values of genetic variations generated by UPGMA, clustering, and scatter plot diagrams. The cultivars ‘January King Sel. Improved’ and ‘Golden Acre’ are highly divergent cultivars as demonstrated by both the marker systems.     

Discovery of single nucleotide polymorphism in <Emphasis Type="Italic">Capsicum</Emphasis> and SNP markers for cultivar identification

Molecular markers based on single nucleotide polymorphisms (SNPs) are abundant and evenly distributed in a whole genome enough to distinguish individuals in a population. In recent years, sets of SNP markers have been designed and applied for cultivar identification in various crop species. This paper is the first to report the development of a panel of SNP markers for variety identification in peppers. We used conserved ortholog set II (COSII) markers developed from conserved unigenes between tomato and Arabidopsis to identify SNPs in peppers. We tested 438 COSII primer sets amplified as single PCR products out of a total 600 COSII primer sets. Among the 438 COSII primers, 170 primer sets (38.8%) showed polymorphisms between Capsicum annuum ‘RNaky (RN)’and C. chinense ‘PI 159234 (234)’. In contrast, only 48 primer sets (11.0%) out of 438 primers sets were polymorphic between C. annuum ‘Perennial (PER), and ‘Dempsey (DEMP)’. The average frequency of SNPs plus InDels between C. annuum and C. chinense was 1/189 bp and between C. annuum spp. was 1/948 bp. Primer sets showing SNP between C. annuum PER and DEMP were re-designed to Allele Specific PCR (AS-PCR) primers and we finally selected a total of 40 SNP markers for cultivar identification. As the result, we were able to discriminate 97.5% of the 81 commercial hot cultivars and 100% of the 17 sweet pepper cultivars. We conclude the paper by discussing the use of the SNP marker set for cultivar identification and other applications.     

Interaction of border and center rows of multiple row plots in watermelon yield trials

Researchers interested in evaluating watermelon (Citrullus lanatus(Thunb.) Matsum. & Nakai) cultivars for yield often use multiple-row plots to simulate the monoculture system growers use or ingle-row plots to save on land, labor, and seeds. An important question is whether there is significant interaction of border rows with center rows when diverse cultivars are planted in adjacent rows. Based on recommendations from watermelon researchers in the U.S., ‘Charleston Gray’, ‘Crimson Sweet’, and ‘Sugar Baby’ were chosen to represent long, medium, and short-vined cultivars, respectively. Cultivars were planted in three-row plots with all nine combinations of the three represented in border and center rows. The experiment was a randomized complete block with the nine border by center plot combinations, two locations (Kinston, Clinton), and three replications at each location. Vine length was measured during the season, and fruit from four harvests were graded (marketable and cull), counted and weighed. Results showed that ‘Charleston Gray’ had the longest vines, followed by ‘Crimson Sweet’ and ‘SugarBaby’. In the analysis of variance, the largest effects (F ratio) on yield were from cultivar, location, and the interaction of the two. The smallest effects were border row and the interaction of center with border row. Center by border interactions were significant (5%level) in some cases, but were usually small and did not involve change in rank. Therefore, researchers interested in running trials with many cultivars and small seed quantities can obtain good data using single-row plots. However, there is a small (but significant) interaction of center with border rows in some cases, so testing at the final stage should be with trials having multiple-row plots or with cultivars grouped by vine length. Additional research is needed to determine the effect of cultivars having extreme plant types, for example dwarf cultivars in bordering rows with long-vined cultivars. This revised version was published online in July 2006 with corrections to the Cover Date.     

Carbamate-induced flowering in asparagus (Asparagus officinalis L.) seedlings: optimization of treatment and cultivar variation in flowering response and pollen germination

Optimal carbamate treatment conditions were studied for flower induction in seedlings of an asparagus cultivar ‘Mary Washington 500 W’. Flower induction was most accelerated by soaking seeds in 50 mg l⁻¹ carbamate solution for 12 days at 25 ^°C under the fluorescent light. Longer exposure to carbamate over a 12 day period induced a higher percentage of seedlings to flower. A higher percentage of flowering seedlings were male. Flower induction frequency among seven cultivars through carbamate treatment widely ranged from 13 to 67%. ‘Geynlim’, ‘Mary Washington 500 W’ and ‘Welcome’ exhibited a high percentage of flowering seedlings, while ‘Larac’ and ‘Vulkan’ showed low values. Only male flowers were induced in all-male cultivars. Variation in pollen germination was found within all cultivars. ‘Geynlim’, ‘Cito’ and ‘Mary Washington 500 W’ showed high values of average pollen germination. Application of carbamate compound to induce flower production can rapidly produce homogenic cultivars which include both sexes. This is necessary for genetic studies and breeding purposes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Identification and mapping of a quantitative trait locus controlling extreme late bolting in Chinese cabbage (Brassica rapa L. ssp. pekinensis syn. campestris L.) using bulked segregant analysis

DNA markers linked to a locus controlling an extreme late bolting trait, which was originally found in a local cultivar of a non-heading leafy vegetable,‘Osaka Shirona Bansei’ (Brassica rapa L. ssp. pekinensis syn. campestris L.) were identified using bulked segregant analysis. A doubled haploid (DH) line, DH27, which is a progeny of ‘Osaka Shirona Bansei’, shows extreme late bolting, and bolts without vernalization. DH27 was crossed with a normal bolting DH line, G309. The plantlets of the parents, F₁ and F₂, were vernalized and then grown in a greenhouse. The bolting time of F₂ plants showed a continuous distribution from 19 to 231 days after vernalization (DAV), suggesting the effects of a few major genes and polygenes. Possible linkage markers for this trait were screened by modified bulked segregant analysis (BSA). The BSA using four bulks suggested that a 530-bp RAPD band RA1255C was linked to a locus controlling the bolting trait. The RAPD band was cloned and used as a probe to detect RFLP. The fragment detected a single locus, BN007-1,the segregation of which in the F₂ population matched that of RA1255C. Three other RAPDs were found to be linked to BN007-1. A quantitative trait locus(QTL) affecting the bolting time was detected around BN007-1 using MAPMAKER/QTL. Since the difference between bolting times of both the parental genotypes in the F₂ was 138 days, these markers may be useful for a marker-assisted selection (MAS) in the breeding program for late bolting or bolting-resistant cultivars in B. rapa crops. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pear mutagenesis: In vitro treatment with gamma-rays and field selection for productivity and fruit traits

In vitro shoots of six pear (Pyrus communis L.) cultivars, ‘Conference’, ‘Doyennéd'Hiver’, ‘Passe Crassane’, ‘Bartlett’, ‘AbbéFetel’ and ‘Butirra Precoce Morettini’ were irradiated with gamma rays (3.5 Gy). After three subcultures, microcuttings from the irradiated shoots and from additional non-irradiated microcuttings were rooted to establish plants for survey orchards. All trees were individually observed for variation in fruit traits and for productivity. Trees were selected for improved characters related to production such as early bearing and consistent productivity. Variations observed in fruit appearance concerned degree of russeting, fruit shape and size. The frequencies of the observed variations in fruit traits depended on the cultivar, ranging from 0.81% in ‘Doyennéd'Hiver’ to 3.64% in ‘Passe Crassane’. Of the 97 variants selected, only two showed chimeral behavior. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic diversity and identification of cymbidium cultivars as measured by random amplified polymorphic DNA (RAPD) markers

DNA from thirty-six cymbidium cultivars was examined using polymerase chain reaction (PCR) to determine the efficiency of randomly amplified polymorphic DNA (RAPD) markers in identifying cultivars and determining levels of genetic variability. A total of 132 RAPD markers, 78% of which were polymorphic, were produced from 15 10mer arbitrary primers. All the cultivars were distinguishable when a number of primers was considered. One cultivar, Blue Smoke ‘Green Meadow’ could be distinguished from all the rest based only on lack of the OPA5-370 fragment. Genetic distances among the cultivars were estimated based on the amount of band sharing and ranged from 0.08–0.50 with an average of 0.29. Cluster analysis of genetic distance estimates grouped siblings together with each other and parents with offsprings, thereby agreeing with known parentage information and corroborating isozyme data obtained from a separate study. The possible application of the observed polymorphism and variation to cymbidium breeding is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Potato Virus Y Resistance Gene, Ry chc, Mapped to the Distal End of Potato Chromosome 9

Summary A Japanese leading cultivar ‘Konafubuki’ has an extreme resistance gene Ry _chc to Potato virus Y (PVY) in a simplex fashion. To reduce complexity of the highly heterozygous autotetraploid genome and map the Ry _chc gene, haploid plants were parthenogenetically induced from ‘Konafubuki’. The ratio of 7 resistant: 5 susceptible haploids confirmed the single dominant, simplex genotype of ‘Konafubuki’. A selected resistant haploid 98H20-5 was crossed with a susceptible diploid, resulting in 119 F ₁ plants. Using RFLP and RAPD markers, Ry _chc was mapped to the most distal end of the chromosome 9 where the recovery of recombinant genotypes was extremely reduced in this mapping population possibly due to the linked inferiority factor. The location of Ry _chc is different from those of the other extreme resistance genes to PVY, but possibly resides in one of resistance gene clusters.     

Genetic diversity of plums characterized by random amplified polymorphic DNA (RAPD) analysis

We investigated the genetic diversity of 42 plum varieties by RAPD analysis. Twenty primers discriminated all plum varieties excepting two synonymous pairs: 'Botankyou and ‘Kelsey’, and ‘Chairn’ and ‘Tragedy’. Two North American plums, ‘Beach Plum’ and ‘Glow’, were genetically distinct from the other plums by cluster analysis. Overlaps observed between the ‘European plum group’ and the ‘Japanese plum group’, were perhaps due to intercrossing. We could also discriminate ‘Sordum’ from 'Late Sordum and ‘Bansei Sordum’, although ‘Late Sordum’ and ‘Bansei Sordum’ are thought to be derived from bud mutants of ‘Sordum’. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heritability and gain from selection for field resistance against multiple root-knot nematode species (Meloidogyne incognita race 1 and M. javanica) in carrot

Heritability and gain from selection of traits associated with field resistance to multiple root-knot nematode species were estimated in carrot (Daucus carota L.). Experimental plots were uniformly and simultaneously infested with Meloidogyne incognita race 1 and M. javanica. Forty-seven half-sib families derived from the cv. ‘Brasília’ were evaluated for: (1) percentage of commercial roots with non-galling symptoms (%RNG); (2) percentage of commercial roots with gall symptoms (%RGS) and (3) percentage of non-commercial roots (%NCR). The cultivars ‘Brasília’ (resistant), ‘Carandaí’ (intermediate) and ‘Nova Kuroda’ (susceptible) were employed as standards. Broad-sense heritability estimates were 61.9 % for %RNG; 30.6 % for %RGS and 67.9 % for %NCR. However, the gains from selection were very small for all traits. The genotypic correlation between %RGS and %NCR was –0.38 and the correlation between %RNG and %RGS was 0.13. Selection on increasing %RNG resulted in a negative correlated response on %NCR (genotypic correlation = –0.99) indicating repulsion phase linkage(s) between the genetic factor(s) controlling these traits. The phenotypic correlation of –0.88 between %RNG and %NCR suggested that incomplete penetrance and dosage effects might be involved in the expression of these traits. Selection of superior genotypes (i.e. high %RNG, low %RGS, and low %NCR) can be achieved. ‘Brasília’ was among the genotypes selected for the following cycle of recombination reinforcing the notion that this cultivar is one of the most promising sources of stable, wide-spectrum field resistance to Meloidogyne species in D. carota. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genetic variation of sweet potatoes (Ipomoea batatas L.) cultivated in Chile determined by RAPDs

RAPD (randomly amplified polymorphic DNA) technology was applied to analyze the genetic variability of sweet potato germplasm existing in Chile and elsewhere. Analysis of 28 cultivars from all over the world showed polymorphic bands with all 18 primers tested. A total of 124 RAPD bands were scored with an average of 6.9 polymorphic bands per primer. These results confirm that sweet potato exhibits high genetic variation. Two groups were distinguished: one containing Peruvian cultivars, and another containing cultivars from the rest of the world. Analysis of 14 accessions from Central Chile and one from Northern Chile showed polymorphic bands with 24 of 26 primers tested, but almost all of the 140 polymorphic bands merely showed the distinctness of the Northern accession. The almost complete uniformity of the other 14 accessions shows that sweet potato germplasm collected in Central Chile has very little genetic variability and may be derived from a single cultivar. Based on these results and on historical records, some hypotheses are proposed to explain the origin of sweet potatoes cultivated in Chile. This revised version was published online in July 2006 with corrections to the Cover Date.