Genepool Variation in Genus Glycine Subgenus Soja Revealed by Polymorphic Nuclear and Chloroplast Microsatellites

A combination of nuclear and chloroplast simple sequence repeats (SSRs) have been used to investigate the levels and pattern of variability detected in Glycine max and G. soja genotypes. Based on the analysis of 700 soybean genotypes with 115 restriction fragment length polymorphism (RFLP) probes, 12 accessions were identified that represent 92% of the allelic variability detected in this genepool. These 12 core genotypes together with a sample of G. max and G. soja accessions were evaluated with 11 nuclear SSRs that detected 129 alleles. Compared with the other G. max and G. soja genotypes sampled, the core genotypes represent 40% of the allelic variability detected with SSRs. Despite the multi-allelic nature of soybean SSRs, dendrograms representing phenetic relationships between accessions clustered according to their subspecies origin. In addition to biparentally inherited nuclear SSRs, two uniparentally (maternally) transmitted chloroplast SSRs were also studied. A total of seven haplotypes were identified, and diversity indices of 0.405 +/- 0.088 and 0.159 +/- 0.071 were obtained for the two chloroplast SSRs. The availability of polymorphic SSR loci in the chloroplast genome provides new opportunities to investigate cytonuclear interactions in plants.     

PCR‐based markers detect genetic variation at growth and immune function‐related loci in chinook salmon (Oncorhynchus tshawytscha)

We developed seven polymerase chain reaction (PCR) based markers that detect genetic variation at loci related to growth (four) and immune function (three) in chinook salmon. One assay shows a length polymorphism following PCR; the others show restriction fragment length polymorphisms (PCR‐RFLP). Two alleles were detected in each assay, and the common alleles were found at frequencies of 0.67–0.95 in seven wild populations in British Columbia, Canada. These loci also amplified in other salmonid species. These markers, by detecting variation linked to genes with high fitness relevance, are expected to be useful in a range of theoretical and applied studies.     

Restriction fragment length polymorphism diversity in soybean

Summary Fifty-eight soybean accessions from the genus Glycine, subgenus Soja, were surveyed with 17 restriction fragment length polymorphism (RFLP) genetic markers to assess the level of molecular diversity and to evaluate the usefulness of previously identified RFLP markers. In general, only low levels of molecular diversity were observed: 2 of the 17 markers exhibited three alleles per locus, whereas all others had only two alleles. Thirty-five percent of the markers had rare alleles present in only 1 or 2 of the 58 accessions. Molecular diversity was least among cultivated soybeans and greatest between accessions of different soybean species such as Glycine max (L.) Merr. and G. soja Sieb. and Zucc. Principal component analysis was useful in reducing the multidimensional genotype data set and identifying genetic relationships.     

基于大豆胞囊线虫病抗性候选基因的SNP位点遗传变异分析

以我国363份栽培和野生大豆资源为材料, 对大豆胞囊线虫抗性候选基因(rhg1和Rhg4)的SNP位点(8个)进行遗传变异分析, 以期阐明野生和栽培大豆间遗传多样性及连锁不平衡水平差异。结果表明, 与野生大豆相比, 代表我国栽培大豆总体资源多样性的微核心种质及其补充材料的连锁不平衡水平较高(R²值为0.216)。在栽培大豆群体内, 基因内和基因间分别有100％和16.6％的SNP位点对连锁不平衡显著, 形成两个基因特异的连锁不平衡区间(Block)。在所有供试材料中共检测到单倍型46个, 野生大豆的单倍型数目(27)少于栽培大豆(31), 但单倍型多样性(0.916)稍高于栽培大豆(0.816)。单倍型大多数(67.4％)为群体所特有(31个), 其中15个为野生大豆特有单倍型。野生大豆的两个主要优势单倍型(Hap_10和Hap_11)在栽培大豆中的发生频率也明显下降, 推测野生大豆向栽培大豆进化过程中, 一方面形成了新的单倍型, 另一方面因为瓶颈效应部分单倍型的频率降低甚至消失。     

Inheritance of restriction fragment length polymorphisms and random amplified polymorphic DNAs in coastal Douglas-fir

A total of 225 new genetic loci [151 restriction fragment length polymorphisms (RFLP) and 74 random amplified polymorphic DNAs (RAPD)] in coastal Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco var. menziesii] have been identified using a three-generation outbred pedigree. The Mendelian inheritance of 16 RFLP loci and 29 RAPD loci was demonstrated based on single-locus segregation in a sample of F₂ progeny. One RFLP locus, PtIFG2025, showed segregation distortion. Probe pPtIFG2025 is a loblolly pine cDNA probe encoding for rbcS. The 16 RFLP loci and 23 allozyme loci were also assayed in a sample of 16 Douglas-fir seed-orchard clones. Allelism was determined at 11 of the 16 RFLP loci. RFLPs were able to detect slightly more variation (4.0 alleles per locus) than allozymes (3.1 alleles per locus). The inheritance of an additional 80 RAPD loci was determined based on haploid segregation analysis of megagametophytes from parent tree 013-1. Once 200–300 markers are identified and placed on a genetic map, quantitative trait loci affecting bud phenology will be mapped.     

Automated sizing of fluorescent-labeled simple sequence repeat (SSR) markers to assay genetic variation in soybean

 Simple Sequence Repeat (SSR) allele sizing provides a useful tool for genotype identification, pedigree analysis, and for estimating genetic distance between organisms. Soybean [Glycine max (L.) Merr.] cultivars are identified for Plant Variety Protection (PVP) purposes by standard pigmentation and morphological traits. However, many commercial soybeans arise from a limited number of elite lines and are often indistinguishable based on these traits. A system based on SSR markers would provide unique DNA profiles of cultivars. Fluorescent labeling of alleles combined with automated sizing with internal size standards in each gel lane was used as an alternative to standard [³²P] labeling to assess genetic variability in soybean. Allelic frequencies at 20 SSR loci were determined in 35 soybean genotypes that account for greater than 95% of the alleles in North American soybean cultivars based upon pedigree analysis. An average of 10.1 alleles per locus (range: 5–17), with a mean gene diversity of 0.80 (range: 0.50 to 0.87) were observed at the 20 SSR loci. The 20 loci successfully distinguished modern soybean cultivars that are identical for morphological and pigmentation traits, as well as 7 soybean genotypes reported to be indistinguishable using 17 RFLP probes. Pedigrees of 7 cultivars were studied to estimate stability of SSRs in soybean across generations. Of the 7 pedigrees 6 had one locus in the progeny with an allele(s) that was not present in either parent. These new alleles are most likely the result of mutation. The mutation rate of SSR alleles in soybean was similar to that reported in humans. To avoid difficulty associated with mutation, DNA fingerprint data should be determined from the bulk of 30-50 plants of a cultivar. Received: 24 March 1997 / Accepted: 4 April 1997     

DNA Sequence Variation within Maize and Melon: Observations from Polymerase Chain Reaction Amplification and Direct Sequencing

While compiling genetic linkage maps in several plant species based upon restriction fragment length polymorphisms (RFLPs), it was noted that the incidence of polymorphism differs among species. The basis of this disparity was investigated in this study by examining the nucleotide sequence at homologous loci among distinct cultivars within two species which exhibit considerably different levels of RFLPs. Using the polymerase chain reaction, homologous regions from different cultivars were first amplified and the nucleotide sequence of the products were determined. Four genomic regions of seven maize cultivars and three genomic regions of eight melon cultivars were examined to compare the respective levels of sequence variation between the two species. Levels of variation for both base substitutions and insertions/deletions varied widely among the maize sequences and between maize and melon for base substitutions. Estimates of theta (a measure of polymorphism) ranged from 0 to 0.002 in melon and from 0.006 to 0.040 for base substitutions and from 0.002 to 0.023 for insertions/deletions in maize. Critical value tests and chi-squared tests suggested that in maize the underlying processes generating and maintaining neutral mutations differ among the regions. The results not only suggest that several mechanisms are necessary to explain the variation seen in these two species, but also point to some basic dissimilarities in the organization and maintenance of the genomes of different plant species.     

Restriction fragment variation in the nuclear and chloroplast genomes of cultivated and wild Sorghum bicolor

Summary Fifty-six accessions of cultivated and wild sorghum were surveyed for genetic diversity using 50 low-copy-number nuclear DNA sequence probes to detect restriction fragment length polymorphisms (RFLPs). These probes revealed greater genetic diversity in wild sorghum than in cultivated sorghum, including a larger number of alleles per locus and a greater portion of polymorphic loci in wild sorghum. In comparison to previously published isozyme analyses of the same accessions, RFLP analysis reveals a greater number of alleles per locus. Furthermore, many RFLP alleles have frequencies between 0.25–0.75, while the vast majority of isozyme alleles are either rare (< 0.25) or near fixation (> 0.75). Correlations between genetic and geographic distances among the accessions were stronger when calculated with RFLP than with isozyme data. Systematic relationships revealed by nuclear and chloroplast restriction site analysis indicate that cultivated sorghum is derived from the wild ssp. arundinaceum. The portion of the wild gene pool most genetically similar to the cultivars is from central-northeastern Africa. Previous published data also suggested that this is most likely the principal area of domestication of sorghum. Introgression between wild and cultivated sorghum was inferred from disconcordant relationships shown by nuclear and chloroplast DNA markers. Introgression apparently occurs infrequently enough that the crop and its wild relatives maintain distinct genetic constitutions.     

Reevaluating the origin of domesticated cotton (Gossypium hirsutum; Malvaceae) using nuclear restriction fragment length polymorphisms (RFLPs)

The origin of domestication in Mesoamerican G. hirsutum populations is obscured by several factors, including the absence of a clearly identified wild progenitor, a complex population genetic structure, and many centuries of human-mediated dispersal and gene flow. Phenetic and phylogenetic analyses of allelic variation at 205 restriction fragment length polymorphism (RFLP) loci were conducted in an effort to unravel this complicated history. The RFLP data, in conjunction with previously published molecular, morphological, and anthropological information, suggest that coastal Yucatan populations are truly wild rather than reestablished feral derivatives. The geographical proximity of these wild coastal populations to agronomically primitive forms of G. hirsutum implicates the Yucatan peninsula as the primary site for the earliest stages of domestication. Agronomically advanced cultigens developed in southern Mexico and Guatemala appear to have been derived from introduced Yucatan peninsular forms, thereby creating the secondary center of diversity that has traditionally been interpreted as the geographical point of origin of domesticated G. hirsutum. The gene pool of modern, improved (Upland) cultivars derives from Mexican highland populations that, in turn, trace their origins to southern Mexico and Guatemala. Gossypium hirsutum is the first tetraploid perennial surveyed for RFLP variation. Levels of RFLP variation in G. hirsutum (H_T = 0.048, A = 1.24, and P = 22%) are low relative to other plant taxa, and, in contrast to the few comparable studies, levels of allozyme variation are higher than levels of RFLP variation. Despite assaying 205 loci, only six of the 23 Upland cultivars were found to have unique multilocus genotypes.     

The comparison of RFLP,RAPD, AFLP and SSR (microsatellite) markers for germplasm analysis

The utility of RFLP (restriction fragment length polymorphism), RAPD (random-amplified polymorphic DNA), AFLP (amplified fragment length polymorphism) and SSR (simple sequence repeat, microsatellite) markers in soybean germplasm analysis was determined by evaluating information content (expected heterozygosity), number of loci simultaneously analyzed per experiment (multiplex ratio) and effectiveness in assessing relationships between accessions. SSR markers have the highest expected heterozygosity (0.60), while AFLP markers have the highest effective multiplex ratio (19). A single parameter, defined as the marker index, which is the product of expected heterozygosity and multiplex ratio, may be used to evaluate overall utility of a marker system. A comparison of genetic similarity matrices revealed that, if the comparison involved both cultivated (Glycine max) and wild soybean (Glycine soja) accessions, estimates based on RFLPs, AFLPs and SSRs are highly correlated, indicating congruence between these assays. However, correlations of RAPD marker data with those obtained using other marker systems were lower. This is because RAPDs produce higher estimates of interspecific similarities. If the comparisons involvedG. max only, then overall correlations between marker systems are significantly lower. WithinG. max, RAPD and AFLP similarity estimates are more closely correlated than those involving other marker systems.Abbreviations RFLP restriction fragment length plymorphism - RAPD random-amplified polymorphic DNA - AFLP amplified fragment length polymorphism - SSR simple sequence repeat - PCR polymerase chain reaction - TBE Tris-borate-EDTA buffer - MI marker index - SENA sum of effective numbers of alleles     

An RFLP linkage map for loblolly pine based on a three-generation outbred pedigree

A genetic linkage map for loblolly pine (Pinus taeda L.) was constructed using segregation data from a three-generation outbred pedigree consisting of four grandparents, two parents, and 95 F₂ progeny. The map was based predominantly on restriction fragment length polymorphism (RFLP) loci detected by cDNA probes. Sixty-five cDNA and three genomic DNA probes revealed 90 RFLP loci. Six polymorphic isozyme loci were also scored. One-fourth (24%) of the cDNA probes detected more than 1 segregating locus, an indication that multigene families are common in pines. As many as six alleles were observed at a single segregating locus among grandparents and it was not unusual for the progeny to segregate for three or four alleles per locus. Multipoint linkage analysis placed 73 RFLP and 2 isozyme loci into 20 linkage groups; the remaining 17 RFLP and 4 isozyme loci were unlinked. The mapped RFLP probes provide a new set of codominant markers for genetic analyses in loblolly pine.     

RFLP tagging of QTLs conditioning specific leaf weight and leaf size in soybean

 Selection for high specific leaf weight (SLW) in soybean [Glycine max (L) Merr.] may increase apparent photosynthetic rate per unit leaf area (AP), which in turn may improve seed yield. In general, the SLW and leaf size are negatively correlated in soybean. To maximize total photosynthetic performance, and perhaps the seed yield, of a soybean cultivar, it would be necessary to establish a large leaf area rapidly while maintaining a high SLW. The objective of the present study was to identify quantitative trait loci (QTLs) conditioning SLW and leaf size in soybean. One hundred and twenty F₄-derived lines from a ‘Young’×PI416937 population were evaluated using restriction fragment length polymorphism (RFLP) markers. The genetic map consisted of 155 loci on 33 linkage groups (LGs) covering 973 cM of map distance. The phenotypic data were collected from two different environments – a greenhouse at Athens, Ga. and a field site at Windblow, N.C. The SLW and leaf-size measurements were made on leaves from the 8th and 9th node of soybean plants at the V12 stage of development. Combined over environments, six putative independent RFLP markers were associated with SLW, and four of these loci were consistent across environments. Individually, the six markers each explained between 8 and 18% of the phenotypic variation among lines for SLW. The Young alleles contributed to a greater SLW at four of the six independent marker loci, and transgressive segregation occurred among the progeny for SLW. Three putative independent RFLP markers were associated with leaf size, each explaining between 6 to 11% of the phenotypic variation in the trait, and one of these markers was identified in both environments. There was no correlation between SLW and leaf size in this population. Similarly, none of the six QTLs conditioning SLW were linked to any of the three QTLs for leaf size. In this soybean population, it is possible to select for progeny lines with greater SLW than either parent perhaps without affecting the leaf size. It is feasible to pyramid all of the desirable alleles for greater SLW and large leaf size in a single genetic background. Received: 16 August 1997 / Accepted: 20 October 1997     

Correlation of DNA fragment sizes within loci in the presence of non-detectable alleles

At present most forensic databases of DNA profiling of individuals consist of DNA fragment sizes measured from Southern blot restriction fragment length polymorphism (RFLP) analysis. Statistical studies of these databases have revealed that, when fragment sizes are measured from RFLP analysis, some of the single-band patterns of individuals may actually be due to heterozygosity of alleles in which fragment size resulting from one allele remains undetected. In this work, we evaluate the effect of such allelic non-detectability on correlation of fragment sizes within individuals at a locus, and its impact on the inference of independence of fragment sizes within loci. We show that when non-detectable alleles are present in a population at a locus, positive correlations of fragment sizes are expected, which increase with the proportion of non-detectable alleles at the locus. Therefore, a non-zero positive correlation is not a proof of allelic dependence within individuals. Applications of this theory to the current forensic RFLP databases within the US show that there is virtually no evidence of significant allelic dependence within any of the loci. Therefore, the assumption that DNA fragment sizes within loci are independent is valid, and hence, the population genetic principles of computing DNA profile frequencies by multiplying binned frequencies of fragment sizes are most likely to be appropriate for forensic applications of DNA typing data.Editor's commentsThe presence of non-detectable alleles for VNTR loci has plagued the use of these highly-discriminating systems in human identification. The authors take explicit account of these alleles, and are able to show independence of the frequencies of detectable alleles. They raise the troubling issue of how to account for occasional significant results when multiple tests are performed. By invoking Bonferroni corrections, they regard all tests, even those performed on different loci, as addressing the same hypothesis—the absence of dependence at any VNTR locus.     

Population genetics of the yellow fever mosquito in Trinidad: comparisons of amplified fragment length polymorphism (AFLP) and restriction fragment length polymorphism (RFLP) markers

Recent development of DNA markers provides powerful tools for population genetic analyses. Amplified fragment length polymorphism (AFLP) markers result from a polymerase chain reaction (PCR)-based DNA fingerprinting technique that can detect multiple restriction fragments in a single polyacrylamide gel, and thus are potentially useful for population genetic studies. Because AFLP markers have to be analysed as dominant loci in order to estimate population genetic diversity and genetic structure parameters, one must assume that dominant (amplified) alleles are identical in state, recessive (unamplified) alleles are identical in state, AFLP fragments segregate according to Mendelian expectations and that the genotypes of an AFLP locus are in Hardy-Weinberg equilibrium (HWE). The HWE assumption is untestable for natural populations using dominant markers. Restriction fragment length polymorphism (RFLP) markers segregate as codominant alleles, and can therefore be used to test the HWE assumption that is critical for analysing AFLP data. This study examined whether the dominant AFLP markers could provide accurate estimates of genetic variability for the Aedes aegypti mosquito populations of Trinidad, West Indies, by comparing genetic structure parameters using AFLP and RFLP markers. For AFLP markers, we tested a total of five primer combinations and scored 137 putative loci. For RFLP, we examined a total of eight mapped markers that provide a broad coverage of mosquito genome. The estimated average heterozygosity with AFLP markers was similar among the populations (0.39), and the observed average heterozygosity with RFLP markers varied from 0.44 to 0.58. The average FST (standardized among-population genetic variance) estimates were 0.033 for AFLP and 0.063 for RFLP markers. The genotypes at several RFLP loci were not in HWE, suggesting that the assumption critical for analysing AFLP data was invalid for some loci of the mosquito populations in Trinidad. Therefore, the results suggest that, compared with dominant molecular markers, codominant DNA markers provide better estimates of population genetic variability, and offer more statistical power for detecting population genetic structure.     

Genetic Population Structure and Gene Flow in the Atlantic Cod Gadus Morhua: A Comparison of Allozyme and Nuclear RFLP Loci

High levels of gene flow have been implicated in producing uniform patterns of allozyme variation among populations of many marine fish species. We have examined whether gene flow is responsible for the limited population structure in the Atlantic cod, Gadus morhua L., by comparing the previously published patterns of variation at 10 allozyme loci to 17 nuclear restriction fragment length polymorphism (RFLP) loci scored by 11 anonymous cDNA clones. Unlike the allozyme loci, highly significant differences were observed among all populations at the DNA markers in a pattern consistent with an isolation-by-distance model of population structure. The magnitude of allele frequency variation at the nuclear RFLP loci significantly exceeded that observed at the protein loci (χ(2) = 24.6, d.f. = 5, P < 0.001). Estimates of gene flow from the private alleles method were similar for the allozymes and nuclear RFLPs. From the infinite island model, however, estimates of gene flow from the DNA markers were fivefold lower than indicated by the proteins. The discrepancy between gene flow estimates, combined with the observation of a large excess of rare RFLP alleles, suggests that the Atlantic cod has undergone a recent expansion in population size and that populations are significantly displaced from equilibrium. Because gene flow is a process that affects all loci equally, the heterogeneity observed among populations at the DNA level eliminates gene flow as the explanation for the homogeneous allozyme patterns. Our results suggest that a recent origin of cod populations has acted to constrain the extent of population differentiation observed at weakly polymorphic loci and implicate a role for selection in affecting the distribution of protein variation among natural populations in this species.     

Phenetic relationships and levels of variability detected by restriction fragment length polymorphism and random amplified polymorphic DNA analysis of cultivated and wild accessions of Lycopersicon esculentum.

Random amplified polymorphic DNA (RAPD) and restriction fragment length polymorphism (RFLP) markers were used to assess the variability in tomato germplasm (Lycopersicon esculentum Mill.), which included 46 accessions from the following groups: vintage cultivars, modern cultivars, South American regional cultivars, and wild L. esculentum van cerasiforme. Two L. cheesmanii accessions served as an outgroup. The 48 accessions were monomorphic at 135 of the 215 RAPDs loci and 31 of the 48 RFLP loci that were assayed. Alleles were identified that distinguished the five groups and many of the cultivars. The frequency of polymorphic loci was low in vintage cultivars, with less than 2.8% of the loci being variable within the group. In contrast, introgression of wild germplasm into modern cultivars has increased the polymorphic loci to 11.6%, whereas within the group of regional cultivars linkage drag and outcrossing may be responsible for the further increase to 20.3%. These levels of genetic variability were lower in comparison to the 24.5% polymorphic loci of cerasiforme, a group that may contain unutilized desirable traits. The small genetic distance from the vintage cultivars to several of the widely distributed regionals and cerasiformes indicated that proximity of vintage cultivars in Latin America may have resulted in intercrossing of these materials with the wilder germplasm. RAPDs appear promising for both germplasm fingerprinting and as a predictor of genetic diversity for plant breeding applications.     

Genotypic characteristics of the rrn operon and genome of indigenous soybean Bradyrhizobia in cropping zones of China

Four genetic assays, 16S rRNA restriction fragment length polymorphism (RFLP), 16S rRNA sequencing, 16S-23S rRNA intergenetic spacer (IGS) RFLP, and amplified fragment length polymorphism (AFLP), were conducted to determine the genotypic characteristics of 44 indigenous strains of Bradyrhizobium from soybean (Glycine max L.) cropping zones of China. The results generated from different assays showed that soybean bradyrhizobial isolates comprised four genomic groups. Group I was composed of strains mainly isolated from the North and Northeast plains of China. All four assays confirmed this group as phylogenetically divergent from all the reference strains. Strains of the group may represent a new species. Strains in Group II isolated from a variety of geographic regions were ascribed to B. liaoningense. Strains in Group III, mainly isolated from Central and East China, were closely related to the reference strains of B. japonicum. Strains in Group IV belonged to B. elkanii.     

Construction of genetic linkage maps in maize and tomato using restriction fragment length polymorphisms

Summary Genetic linkage maps were constructed for both maize and tomato, utilizing restriction fragment length polymorphisms (RFLPs) as the source of genetic markers. In order to detect these RFLPs, unique DNA sequence clones were prepared from either maize or tomato tissue and hybridized to Southern blots containing restriction enzyme-digested genomic DNA from different homozygous lines. A subsequent comparison of the RFLP inheritance patterns in F2 populations from tomato and maize permitted arrangement of the loci detected by these clones into genetic linkage groups for both species.     

Genetic divergence between North American ancestral soybean lines and introductions with resistance to soybean cyst nematode revealed by chloroplast haplotype

Domesticated soybean [Glycine max (L.) Merr.] is a major crop with an established ancestral relationship to wild soybean (Glycine soja Sieb. & Zucc.) native to Asia. Soybean genetic diversity can be assessed at different levels by identification of polymorphic alleles at genetic loci, in either the plastid or nuclear genomes. The objective of this study was to evaluate genetic diversity based on chloroplast haplotypes for soybean genotypes present in the USDA germplasm resource collection. Shared chloroplast haplotypes represent broad groups of genetic relatedness. Previous work categorized three-quarters of the cultivated soybeans from Asia into a single haplotype group. Our results confirmed the close relationship of North American soybean ancestors and G. max plant introductions previously identified as representing potential sources of soybean genetic variation with the finding that these genotypes belonged to a single chloroplast haplotype group. Genetic diversity was identified in soybean genotypes determined to have a high density of single nucleotide polymorphisms and in a screen of accessions with resistance to soybean cyst nematode. Characterization of soybean plant introduction lines into chloroplast haplotype group may be an important initial step in evaluating the appropriate use of particular soybean genotypes.     

Genetic diversity of Ustilago maydis strains

Thirty wild isolates belonging to five different locations in Mexico plus two laboratory strains of Ustilago maydis were characterized by restriction fragment length polymorphism (RFLP) analysis using 23 different clones as probes derived from a PstI library and two restriction enzymes. All loci analysed presented a high level of polymorphism, including one locus with thirty one different alleles. Geographical grouping of the populations was based on Nei's genetic distance and there was no correlation between genetic and geographic distances among these isolates. Our results suggest that DNA fingerprinting is a useful method for detecting genetic variation in populations of U. maydis. This work demonstrated that considerable genetic variation may be present within field populations of U. maydis.