Isozyme diversity and analysis of the mating system of the wild rice Oryza latifolia Desv. in Costa Rica

Oryza latifolia is the most abundant and widespread wild relative of rice in the lowlands of Costa Rica. It also has the most diverse morphology. However, little is known about the genetic diversity and mating system of this allotetraploid species. Genetic analyses of nine populations from different life zones from the Pacific and Atlantic slopes were performed using six isozyme loci. Differences in genetic variability were observed among populations, of which Palo Verde and Santa Rosa were the most diverse. Most Atlantic populations clustered together, and a similar result was obtained with the Pacific populations. High levels of interpopulation diversity were observed while most populations were monomorphic for at least one genotype, suggesting little genetic flow within populations. Even in polymorphic populations no variation was observed within progeny groups, combined with Hardy-Weinberg disequilibria in most populations, commonly observed in autogamous species or in species with clonal reproduction. However, the high frequency of heterozygous-like patterns may suggest that the reproductive system of O. latifolia might be more complex. Future research may explain the genetic patterns as well as the reproductive biology of this species. The knowledge of the genetic diversity and mating system of O. latifolia could contribute to the implementation of genetic resource conservation strategies and gene flow analyses, as well as of breeding programs for rice improvement.     

The Weedy Rice Complex in Costa Rica. I. Morphological Study of Relationships Between Commercial Rice Varieties,Wild <Emphasis Type="Italic">Oryza</Emphasis> Relatives and Weedy Types

Weedy rice is a complex of Oryza morphotypes widely distributed in commercial rice fields, which interfere with rice cultivation, seed production, industrial processing and commercialization of this crop in several countries. The objective of this study was to characterize the weedy rice complex of Costa Rica by comparing it with the cultivated and wild rice species found in the country. A collection of weedy rice accessions, representative of the morphotypes found in the country, was established and characterized. Their morphometric relationships were established by comparing 27 morphological traits with commercial rice cultivars, landraces and wild Oryza species and by performing a multivariate analysis. Twenty-one weedy rice morphotypes were identified among 735 weedy accessions by using a three-digit code based on seed characters. Three principal components (PCs) explained 66.25% of the variation observed. The first PC accounted for 36.21% of the variation and separated CCDD genome type Oryza latifolia and O. grandiglumis from AA genome species O. sativa, O. glumaepatula, O. rufipogon and O. glaberrima. The second (18.9%) and third (11.14%) PCs separated the weedy morphotype groups from the AA genome species O.sativa, O. glaberrima and O. rufipogon. The weedy morphotypes were scattered between the indica commercial rice varieties, the cluster landraces–glaberrima and O. rufipogon. Additionally, a group of morphotypes showed intermediate characteristics between O. sativa and O. rufipogon, suggesting that hybridization could have taken place in the past between these species. None of the morphotypes collected in Costa Rica clustered with the allotetraploids CCDD species or O. glumaepatula.     

The fragrance (fgr) gene in natural populations of wild rice (Oryza rufipogon Griff.)

The Asian cultivated rice, Oryza sativa L. (spp. indica or japonica), is assumed to have originated from one or both of the two wild Asian species, O. rufipogon Griff. and O. nivara Sharma and Shastry. They occur throughout the monsoon Asia and west Oceania. Fragrance is the most important trait among the domesticated characters of basmati and jasmine rice of Asia. The gene for fragrance in a scented rice shows the presence of a mutated portion (i.e., an eight base pair deletion in exon 7) that result in its loss of fragrance. In the present study, 229 wild rice O. rufipogon accessions were genotyped for this locus using a PCR assay. The wild rice species contained the mutated allele of the fgr gene at a low frequencies of 0.23. The surveyed populations were in Hardy–Weinberg equilibrium. This observation supports the hypothesis that the allele for fragrance was already present in the wild rice, and that this trait appeared in scented rice cultivars because of selection by the farmers of genotypes possessing this character during the process of domestication.     

Genetic Diversity in Accessions of Wild Rice Oryza granulata from South and Southeast Asia

Oryza granulata, an upland wild rice species, represents an unique germplasm for possessing abilities of tolerance to shade and drought, immune to bacterial blight and resistance to brown planthopper. Although low degree of genetic variability has been revealed within its populations, little genetic information at the species level is available in determining rational conservation strategies. Here we used dominant DNA marker random amplified polymorphism DNA (RAPD) to assess the genetic variability among 23 accessions of O. granulata that collected from main distribution areas worldwide. Twenty decamer primers generated a total of 243 bands, with 83.5% of them (203 bands) being polymorphic. Calculation of Shannon index of diversity revealed an average value of 0.42 ± 0.25, indicating that O. granulata maintains a relatively high degree of genetic diversity on the species level. Analysis of genetic dissimilarity (GD) showed that genetic differentiation occurred among studied accessions, which supports the feasibility of current ex situ conservation strategies. We also suggested that information based on population studies, which could be achieved by international co-operation, is needed to conserve this widespread germplasm more effectively.     

Evaluation of Genetic Diversity of Wild Rice (Oryza rufipogon Griff.) in Myanmar using Simple Sequence Repeats (SSRs)

As a part of an in situ survey of wild rice (Oryza rufipogon Griff.) in Myanmar (Burma), 16 strains of wild rice were collected, and analyzed for allelic diversity over 74 loci with simple sequence repeat (SSR) markers to obtain a basic information for their conservation. Three each of indica and japonica cultivars were added for a comparison. In the six cultivars and 16 strains of wild rice, three to 15 alleles were detected per locus with an average of 7.9. The wild rice revealed a large number of unique alleles throughout their chromosomes with much wider ranges of variation than those detected in the six cultivars of O. sativa L.. The alleles found in the wild rice were classified into those specific to wild rice, common to wild rice and cultivars, and those similar to indica or japonica cultivars. According to the classification, the genotype of each of the 16 strains of wild rice was schematically depicted. The genetic variation among individual strains within a collection site was larger than the variation among the collection sites.     

Observations on the geographic distribution, ecology and conservation status of several Phaseolus bean species in Costa Rica

Interest in bean genetic resources of Central America has resumed because of disease pressures (e.g., web blight, BGMV) and limitations of current bean varieties. As most of the diversity in landraces has been explored, focus is now on the exploration of wild forms of the primary gene pool and wild species of the secondary gene pool. A germplasm collection was carried out in the field and resulted in the collection of 29 wild populations for six Phaseolus species; it complemented field work done in 1987. Nine more populations were found for P. costaricensis, 10 for wild P. lunatus, one for P. oligospermus, one for P. tuerckheimii, four for wild P. vulgaris and four for P. xanthotrichus. Ninety-three herbarium voucher specimens were collected for 19 populations of the six species (deposited at CR). These results confirm the presence of wild P. vulgaris on both slopes of the central valley of Costa Rica, namely in the life zones bh-MB and bmh-P, and of P. costaricensis in the life zone bmh-MB. These life zones of limited range in Costa Rica have been heavily modified, thus fully justifying the germplasm collection for ex situ conservation. For both species the range of distribution in Costa Rica has been almost completely sampled. The life characteristics of each species that are relevant for their conservation in situ are briefly reviewed. Distribution ranges of each wild bean species are compared with the present extension of national parks, protected areas and fauna/flora sanctuaries, and suggestions for expanding such protected areas are made.     

Selection of efficient vesicular-arbuscular mycorrhizal fungi for wetland rice (Oryza sativa L.)

Summary We tested the response of the wetland rice cultivar Prakash to inoculation with ten vescular-arbucular mycorrhizal (VAM) fungi (three selected from the first screening and seven isolated from local paddy fields) in a pot experiment under flooded conditions in order to select the most efficient mycorrhizal fungi to inoculate the rice nursery. A sandy clay loam soil was used as the substrate, fertilized with the recommended N and K levels (100 kg N ha^–1 as ammonium sulphate and 50 kg K ha^–1 as muriate of potash) and half the recommended level of P (25 kg ha^–1 as super phosphate). The inoculation was made into dry nursery beds and the beds were flooded when the seedlings were about 25 cm high, in 15 days. Twenty-eight-day old seedlings were transferred to pots filled with well puddled soil flooded with 5 cm of standing water. Based on the increase in grain yield and total biomass, Glomus intraradices and Acaulospora sp. were considered efficient and suitable for inoculation into rice nurseries.     

Dual origin of the cultivated rice based on molecular markers of newly collected annual and perennial strains of wild rice species, Oryza nivara and O. rufipogon

The direct ancestor of rice (Oryza sativa L.) is believed to be AA genome wild relatives of rice in Asia. However, the AA genome wild relatives involve both annual and perennial forms. The distribution of the retrotransposon p-SINE1-r2, a short interspersed nuclear element (SINE) at the waxy locus was analyzed in diverse accessions of the AA genome wild relatives of rice (O. rufipogon sensu lato). Most annual wild rice accessions had this retrotransposon, while most perennial types lacked this element, contradicting results to the previous studies. Results presented here suggest that O. sativa has dual origin that lead to indica-japonica differentiation. Results suggest the indica line of rice varieties evolved from the annual genepool of AA genome and the japonica varieties from the perennial genepool of AA genome wild rice.     

Diversity and genetic resources of wild <Emphasis Type="Italic">Vigna</Emphasis> species in India

Diversity in morphological characters of 206 accessions of 14 wild Vigna species from India was assessed. Of these, 12 species belonged to Asian Vigna in the subgenus Ceratotropis and two were V. vexillata and V. pilosa belonging to subgenus Plectotropis and Dolichovigna, respectively. Data on 71 morphological traits, both qualitative and quantitative, were recorded. Data on 45 qualitative and quantitative traits exhibiting higher variation were subjected to multivariate analysis for establishing species relationships and assessing the pattern of intraspecific variation. Of the three easily distinguishable groups in the subgenus Ceratotropis, all the species in mungo-radiata group, except V. khandalensis, viz. V. radiata var. sublobata, V. radiata var. setulosa, V. mungo var. silvestris and V. hainiana showed greater homology in vegetative morphology and growth habit. The species, however, differed in other plant, flower, pod and seed characteristics. Within species variation was higher in V. mungo var. silvestris populations and three distinct clusters could be identified in multivariate analysis. V. umbellata showed more similarity to V. dalzelliana than V. bourneae and V. minima in the angularis-umbellata (azuki bean) group. Within species variations was higher in V. umbellata than other species in the group. In the aconitifolia-trilobata (mothbean), V. trilobata populations, were more diverse than V. aconitifolia. The cultigens of the conspecific wild species were more robust in growth, with large vegetative parts and often of erect growth with three- to five-fold increase in seed size and seed weight, except V. aconitifolia, which has still retained the wild type morphology to a greater extent. More intensive collection, characterisation and conservation of species diversity and intraspecific variations, particularly of the close wild relatives of Asian Vigna with valuable characters such as resistance to biotic/abiotic stresses, more number of pod bearing clusters per plant etc. assumes great priority in crop improvement programmes.     

Chromosome numbers and ploidy levels of<Emphasis Type="Italic"> Paspalum</Emphasis> species from subtropical South America (Poaceae)

Somatic chromosome numbers of 131 accessions belonging to 55 Paspalum species from subtropical South America have been determined. All species had x = 10 as a basic chromosome number, except P. almum which had x = 6. Six ploidy levels were found among species with tetraploidy as the most frequent condition. New diploid and octoploid counts were reported. For Paspalum lilloi and P. glabrinode (both 2n = 2x = 20), and for P. ellipticum, P. erianthoides, P. ovale and P. remotum (all 2n = 8x = 80) sporophytic chromosome numbers are presented for the first time. Records that differ from previously reported counts are given for the following species: P. paucifolium (2n = 2x = 20), P. ceresia (2n = 6x = 60), P. conjugatum (2n = 6x = 60), P. alcalinum (2n = 6x = 60) and P. aff. arundinellum (2n + 1 = 5x + 1 = 51). These chromosome data are discussed in light of ploidy-level variation and implications for breeding systems within and among species.     

Case studies on breeding systems and its consequences for germplasm conservation: 3. Electrophoretic mobility of phaseolins in wild populations of Lima beans (Phaseolus lunatus L.) in the Central Valley of Costa Rica

We studied the variation in the electrophoretic mobility of phaseolins of 202 individual seeds from thirty-eight wild populations of Lima beans (Phaseolus lunatus) in the Central Valley of Costa Rica. We found four main polypeptides or banding regions with molecular weights which ranged from 21.5 to 31 kDaltons. Two of these peptides were polymorphic, and their combination resulted in four distinct genotypes. The frequency of the different genotypes varies among populations, but two of them, namely B¹¹C¹¹, B²²C²², were found in most of the populations studied (37 out of 38 populations examined). Overall, there was a lack of heterozygotes among the individuals examined, which strongly suggests that there is gametic disequilibrium for the encoding regions involved in the synthesis of these polypeptides. When we arranged the populations into eight groups according to their proximity and phenology, we found that the distribution of the peptides was also variable among them. The possible association between the distribution of the patterns of electrophoretic mobility observed and climatic factors, such as mean annual rainfall, mean annual temperature and mean annual relative humidity is discussed.     

Uptake and metabolism of isouron in rice (Oryza sativa L.) seedlings

Summary Isouron, a pre-emergence herbicide, inhibited the growth of rice seedlings in a nutrient solution; the critical concentration was about 0.10 mg l^-1. Isotope studies showed that isouron, added to the nutrient solution, was observed by the rice roots and translocated rapidly to the shoot. In rice seedlings, isouron was converted to six known metabolites, 3-(5-(1-dimethyl-2-hydroxy-ethy)-3-isoxazolyl]urea, 3-(5-tert-butyl-3-isoxazolyl)-1-methylurea, 3-(5-tert-butyl-3-isoxazolyl)ure, 3-amino-5-tert-butylisoxazole, 3-[5-(1,1-dimethyl-2-hydroxyethyl)-3-isoxazolyl]-1-dimethylurea, and 3-[5-(1,1-dimethyl-2-hydroxyethyl)-3-isoxazolyl]-1-methylurea, and two unknown metabolites.     

Genetic Diversity in Tunisian Ceratonia siliqua L. (Caesalpinioideae) Natural Populations

The last two centuries witnessed the human-caused fragmentation of Tunisian Ceratonia siliqua L. (Caesalpinoideae) populations which were often represented by scattered individuals. Seventeen populations growing in four bioclimatic zones: sub-humid, upper semi-arid, mean semi-arid and lower semi-arid zones, were sampled for allozyme diversity to assess their genetic diversity and structuration using eight isozymes revealed by starch gel electrophoresis. The species showed high diversity within populations. The average number of alleles per polymorphic locus was 1.98, the percentage of polymorphic loci was 83.4% and the mean observed heterozygosity (Ho) and expected heterozygosity (He) under Hardy–Weinberg equilibrium were respectively 0.247 and 0.316. A substantial level of inbreeding within populations induced by Wahlund effect, was observed (F_IS = 0.231). High diversity resulted from the great number of genotypes in the ancestral population before fragmentation, favoured by the outbreeding of the species. High differentiation and low gene flow were detected among populations (F_ST = 0.200) and among pairs of ecological zones (0.113< F_ST <0.198). However, the differentiation coefficient of the four zones was low (F_ST = 0.085) and similar to the average F_ST for forest trees. Population structuration depends on geographic distance between sites rather than bioclimate, indicating that structuration has occurred slowly and that climatic conditions have had little effect. Nei's genetic distances (D) between populations were low and ranged from 0.004 to 0.201. Mean D value for all population was 0.087. The UPGMA clustering established for all populations through Nei's genetic distances did not clearly show that, for the majority of populations, grouping had resulted from ecological factors or geographic location. The substantial differentiation and the high genetic similarities between populations indicate that populations have been recently isolated as a result of anthropic pressure. In-situ conservation strategies must first focus on populations with a high level of genetic diversity and rare alleles. Appropriate conservation action should take account of bioclimatic zones. Ex-situ preservation should be based on a maximum number of individuals collected within populations in each ecological group and their propagation in different bioclimates by means of cuttings.     

Fate and interaction with native soil N of ammonium N applied to wetland rice (Oryza sativa L.) grown under saline and non-saline conditions

Summary The effect of salts on the balance of fertilizer N applied as ¹⁵N-labelled ammonium sulphate and its interaction with native soil N was studied in a pot experiment using rice (Oryza sativa L.) as a test crop. The rice crop used 26%–40% of the applied N, the level of applied N and salts showing no significant bearing on the uptake of fertilizer N. Losses of fertilizer N ranged between 54% and 68% and only 5%–8% of the N was immobilized in soil organic matter. Neither the salts nor the rate of N application had any significant effect on fertilizer N immobilization. The effective use of fertilizer N (fertilizer N in grain/fertilizer N in whole plant) was, however, better in the non-saline soil. The uptake of unlabelled N (N mineralized from soil organic matter and that originating from biological N₂ fixation in thes rhizosphere) was inhibited in the presence of the salts. However, in fertilized soil, the uptake of unlabelled N was significantly enhanced, leading to increased A values [(1-% Ndff/% Ndff)x N fertilizer applied, where Ndff is N derived from fertilizer], an index of interaction with the added N. This added N interaction increased with increasing levels of added N. Since the extra unlabelled N taken up by fertilized plants was greater than the fertilizer N immobilized, and the root biomass increased with increasing levels of added N, a greater part of the added N interaction was considered to be real, any contribution by an apparent N interaction (pool substitution or isotopic displacement) to the total calculated N interaction being fairly small. Under saline conditions, for the same level of fertilizer N addition, the added N interaction was lower, and this was attributed to a lower level of microbial activity, including mineralization of native soil N, rootdriven immobilization of applied N, and N₂ fixation.     

Soil ciliates (Protozoa: Ciliophora) from evergreen rain forests of Australia, South America and Costa Rica: diversity and description of new species

This paper provides, for the first time, comprehensive data on alpha diversity of soil ciliates from evergreen tropical and temperate rain forests. Thirty-three samples were collected in Australia, Tasmania, Amazonia and Costa Rica and analysed with the non-flooded Petri dish method, which reactivates the ciliates’ resting cysts from air-dried samples. The 175 taxa found contained 34 new species, 4 of which are described in this paper, viz. Platyophrya paoletti n. sp., Lamtostyla abdita n. sp., L. granulifera n. sp., and Apoamphisiella tihanyiensis (Gellért and Tamás 1958) n. gen., n. comb. Although this is a considerable number, it is much lower than one would expect. The data would be even more perplexing if the four rich samples (up to 90 species/sample) from the Manaus floodplain were excluded. We then would be confronted with about 90 taxa in 29 samples, of which 13 contained fewer than ten species. A hypothesis is put forward that the non-flooded Petri dish method is inappropriate for studying soil ciliate diversity in evergreen rain forests because most species have a reduced capacity to produce dry-resistant (protective) resting cysts due to the permanent wetness of their habitats. This view is supported by a comparative analysis of a fresh (containing 40 species) and air-dried/rewetted (2 species only) sample from a cloud rain forest near Merida (Venezuela), and the observation that the capacity of soil ciliates to produce resting cysts often dramatically decreases after prolonged laboratory cultivation in liquid media. Direct microscopy of fresh samples seems to be an appropriate alternative because specimens can be easily collected due to their considerable abundance (≥1000 individuals/g wet mass of litter). Received: 8 April 1997     

水稻与慈姑间作栽培对水稻病虫害和产量的影响

合理的间套作种植能够显著降低病虫害的发生,但已有相关研究主要集中在旱地作物种类或旱稻上,而水田环境下水稻间作体系的作物搭配及种植模式研究目前还十分缺乏。本文通过田间对比试验研究了水稻与慈姑间作栽培对水稻病虫害、微环境以及水稻产量的影响效应。结果表明,间作栽培模式对稻飞虱和稻纵卷叶螟无显著的防控效果。但在拔节期和抽穗期期间,间作栽培模式下水稻纹枯病病丛率分别比单作处理低64.3%和88.2%,稻瘟病病叶率在灌浆期和乳熟期显著低于单作,表明间作栽培模式显著降低了水稻稻瘟病和纹枯病的发生。间作栽培模式下水稻叶片POD、SOD和CAT酶活性与单作模式相比出现了不同程度降低,单作模式下水稻较高的病害发生程度可能是导致叶片保护酶活性增高的原因;间作栽培在早午时段降低了水稻叶片表面的空气湿度,且水稻叶片光合有效辐射强度在多数时段均高于单作栽培,说明间作栽培模式改善了稻田小气候环境,有利于降低病菌的滋生和传播;光合气体交换日进程测定结果表明,灌浆期间水稻/慈姑间作栽培模式下水稻叶片净光合速率、蒸腾速率以及气孔导度在日间大部分时段均高于单作水稻,说明间作栽培模式提高了水稻的群体光能利用率以及群体光合效率;间作栽培模式下的土地当量比为1.17,表明水稻与慈姑间作栽培模式不仅能有效控制水稻病虫害的发生,同时能起到良好的增产效果。     

A Preliminary Comparative Evaluation of Genetic Diversity between Chinese and Japanese Wild Soybean (<Emphasis Type="Italic">Glycine soja</Emphasis>) Germplasm Pools using SSR markers

The wild soybean, an annual self-pollinating plant, is the progenitor of soybeans and is extensively distributed in the Far East of Russia, the Korea peninsula, China and Japan. Geographically, Japan is surrounded by sea and insulated from China. We preliminarily evaluate whether the Japanese and Chinese wild soybean germplasm pools are genetically differentiated from each other using SSR markers. The results showed that the two pools have great genetic differentiation. Some loci presented obvious differences in mean genetic divergence (G_ST) value between the two pools. The G_ST among the geographic regions in China was higher than that in Japan. The average within-geographic region gene diversity values (H_S) in the two pools were completely identical and thus the genetic difference between the two pools was mostly attributed to the relatively high level of between-geographic region gene diversity (D_ST) in China. We suggest that Japanese and Chinese wild soybeans should be comparatively independently evolving in phylogeny.     

Differential heterosis in a natural population of Asian wild rice (<Emphasis Type="Italic">Oryza rufipogon</Emphasis> Griff.) due to reproductive strategy and edge effect

Asian common wild rice (Oryza rufipogon) is a polycarpic perennial plant with a mixed inbreeder/outbreeder strategy. Seeds and clones are both reproductive components of the population. However, when collected in the flowering stage, the two differ substantially as to whether they have experienced natural selection directly or not. This study is aimed at evaluating mechanisms for the survival of a population by comparing genetic structure among subpopulations that are classified in terms of: (1) reproductive systems (clones or seeds); and also (2) location (fringe or inside). First, the genotypes determined at seven SSR (Simple Sequence Repeat) loci showed that parameters of observed heterozygosity (H_O) and outcrossing rate (t) were clearly higher in clones (H_O = 0.609, t = 82.4%) than in seeds (H_O = 0.346, t = 35.5%), although the two had approximately the same values for the number of alleles (A) and expected heterozygosity (H_E)(A = 4.43 in both clones and seeds, H_E = 0.709, 0.692 in clones and seeds, respectively). This result indicates that the individuals showing heterosis, with high numbers of heterozygous loci and outcrossing rates, are more likely to survive in the natural habitat. Secondly, parameters of observed heterozygosity and outcrossing rates were lower for seeds from the fringe area (H_O = 0.238, t = 24.6%) compared to seeds from the inside area (H_O = 0.443, t = 60.7%), although values were similar in clones of both the fringe and inside areas. This result suggests that the edge effect might be due mainly to the restriction of wind strength in fringe area of the forested swamp.     

Application of random amplified polymorphic DNA markers to evaluate intraspecific genetic variation in the Elymus alaskanus complex (Poaceae)

Random amplified polymorphic DNA (RAPD) markers were used to evaluatethe levels and patterns of genetic diversity in ten Elymusalaskanus populations, which were collected from Canada, USA,Greenland and Russia. Ten arbitrarily chosen decamer primers were used in thisstudy. The results revealed high levels of variation. The mean number of allelesper locus (Ap) was 1.5, ranging from 1.4 to 1.6, the meanpercent of polymorphic loci (Pp) was 49.5%, ranging from35.1% to 64.9%, and the mean gene diversity (Hep) was0.162, varying from 0.142 to 0.262. The total variation wasH _T = 0.403. When partitioned(G _ST), 60% of the total variation was foundamong the populations. Although the genetic diversity values obtained with RAPDsare much higher than for allozymes, they are similar regarding how the geneticvariation is distributed among populations. In addition, a similar geneticpattern of population differentiation, where populations from Greenland andthe USA (violaceus and latiglumis)were clearly separated from the others (hyperarcticus,komarovii and sajanensis), wasrevealed by both the cluster and principal coordinates analyses.     

Genetic diversity of the African hexaploid species Solanum scabrum Mill. and Solanum nigrum L. (Solanaceae)

Two hexaploid species of Solanum sect. Solanum are present in Africa: Solanum scabrum and S. nigrum. Solanum scabrum is a widely cultivated species and is used as a leafy vegetable, as a source of medicine and as a source of ink dye. In previous studies a wide range of morphological diversity has been reported in this species and in some studies subspecies have been proposed. Subspecies are also recognized in S. nigrum. However, it has not been established whether or not the morphological differences are reflected at the genomic level. The present study applies AFLPs to study the genetic diversity in S. scabrum and its relationship to geographical provenance, morphological differences and the possible existence of subspecies within S. scabrum and S. nigrum. The data obtained were analyzed with cluster analysis (using UPGMA and NJ). The results indicate that the genetic variation within S. scabrum was higher within accessions than between accessions. Accessions did not cluster according to their geographical provenance, indicating that accessions from different geographical areas were not significantly different genetically. The clustering reflected neither morphological differences nor domestication status (cultivated or wild). The morphological differences exhibited by S. scabrum could be due to selection by farmers for different plant types. The AFLP derived clustering pattern did not segregate the subspecies recognized in S. scabrum and S. nigrum into separate subclusters.