The Journal of Heredity 2001:92(6)
© 2001 The American Genetic Association 92:511-516
Brief Communication |
High Levels of Genetic Differentiation of Oryza officinalis Wall. ex Watt. From China
From the Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing, P. R. China. The authors are sincerely grateful to Dr. Yi Zhou, Dr. Shou-zhou Zhang (Institute of Botany, Chinese Academy of Sciences), Prof. Qing-yan Luo, and Prof. Jiong-wei Zhang (Simao Prefecture Institute of Agricultural Sciences, Yunnan Province) for their help in collecting field materials; to Prof. Zhong-ren Wang, Prof. Kai-yu Pan, Dr. Shi-liang Zhou, and Miss Ke-qing Wang for their help with various aspects in our lab, and to Mr. Ru-sun Lin (Southern China Botanical Garden, Chinese Academy of Sciences, Guangzhou City), Prof. Zai-fu Xu, Prof. Guo-da Tao, Mr. Qing-juan Li, and Miss Yong-mei Xia (Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, Yunnan Province) for their help in transplanting materials.
Address correspondence to Li-zhi Gao, Department of Genetics, University of Georgia, Life Sciences Building, Athens, GA 30602-7223, or e-mail: Lizhi_g{at}yahoo.com.
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Abstract |
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In order to determine the population genetic structure of wild rice (Oryza officinalis Wall. ex Watt.), an endangered tropical and subtropical species, allozyme diversity encoded by 24 loci was analyzed electrophoretically in 145 individuals of eight natural populations from Hainan, Guangxi, and Yunnan provinces, China. A fairly high genetic differentiation (FST = 0.882 and mean I = 0.786) was found among the studied populations. Our results suggest that restricted gene flow may play a significant role in shaping such a population genetic structure. In addition, high genetic differentiation among populations within a geographically limited region may stem from a reduced population size and consequent genetic drift.
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Introduction |
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The evolutionary dynamics of a species in natural conditions are mediated by the genetic structure of their populations (Wright 1977, 1988). The nonrandom distribution of genetic variation within and among populations is often called the genetic structure of populations (Loveless and Hamrick 1984), which is primarily affected by selection, genetic drift, recolonization, and gene flow. Thus studies of population genetic structure can be crucial for assessing the actions and interactions of these evolutionary forces in natural populations (Selander and Whittman 1983). A large amount of literature on the genetic structure of plant populations has been accumulated in recent decades (Clegg and Allard 1972; Dewey and Heywood 1988; Hamrick 1989; Schaal and Smith 1980; Soltis and Soltis 1988), but further studies, particularly on tropical and subtropical plants, are needed in order to outline a clear picture of how genetic structure is shaped.
Because O. officinalis Wall. ex Watt. has potentially useful genes for higher biomass production, resistance to several insects (Heinriches et al. 1985; Jena and Khush 1990), and tolerance to shade and dry land, it is one of the most important genetic resources for the improvement of cultivated rice in the world. As a wind-pollinated herbaceous species, O. officinalis is widely distributed in tropical and subtropical regions in the world (Vaughan 1989, 1994). In China, the species is found in southern and southwestern regions: Guangxi, Guangdong, Hainan, and Yunnan provinces (National Exploration Group of Wild Rices 1984). However, our recent field investigation suggests that a great number of populations have disappeared and the species is being seriously threatened (Gao et al. 1996; Hong 1995). As a species of one of our most precious genetic resources, but a little understood one with respect to genetic diversity (Vaughan 1989), it is of great importance to learn about its population genetic structure.
Starch-gel electrophoresis provides biologists with valuable genetic markers that are suitable for the study of population genetics and evolutionary processes (Hamrick 1989), and thus it has been successfully used to study the genetic structure of natural populations (Soltis and Soltis 1991; Soltis et al. 1992). In the present study, allozyme analyses were conducted to explore population genetic structure and explain the observed spatial patterns of genetic variability in terms of evolutionary factors.
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Materials and Methods |
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Eight populations of O. officinalis were sampled from Hainan, Guangxi, and Yunnan provinces in China in October 1994 (Figure 1 and Table 1). Because O. officinalis has clonal ability in the populations sampled, care was taken to prevent collecting multiple samples from a single genetic individual. Individual live ratoons were randomly collected at intervals of at least 1 m in the field, numbered, transplanted to pots, and maintained at the Xishuangbanna Tropical Botanical Garden (Mengla County, Yunnan) and South China Botanical Garden (Guangzhou City). Young leaves were individually collected in March 1995, stored in plastic bags on ice, and transported to the laboratory by airplane. For each individual, 0.05 g of fresh young leaf material was crushed in 100 µl of Tris-HCl buffer (pH 7.5; see Soltis et al. 1983). The extract was absorbed into 3 mm x 8 mm paper wicks and stored at -70°C until electrophoresis was conducted.
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Starch-Gel Electrophoresis
Fourteen enzymes were resolved and scored using starch-gel electrophoresis. The electrophoretic methods followed Glaszmann et al. (1988) and Soltis et al. (1983) with 12% starch gels. A modification of buffer system 1 (S1) was used to resolve malate dehydrogenase (MDH, EC 1.1.1.37), malic enzyme (ME, EC 1.1.1.40), and phosphogluconate dehydrogenase (6PGD, EC 1.1.1.44) (the electrode buffer was diluted two times before use); aspartate aminotransferase (AAT, EC 2.6.1.1), di aphorase (DIA, EC 1.6.2.2), aminopeptidase (LAP, EC 3.4.11.1), phosphogluco isomerase (PGI, EC 5.3.1.9), and triosephosphate isomerase (TPI, EC 5.3.1.1) were resolved on buffer system 6 (S6); alcohol dehydrogenase (ADH, EC 1.1.1.1), fructose-bisphosphate aldolase (FBA, EC 4.1.2.13), glutamate dehydrogenase (G3PDH, EC 1.4.1.2), isocitrate dehydrogenase (IDH, EC 1.1.1.42), phosphoglucomutase (PGM, EC 2.7.5.1), and shikimate dehydrogenase (SKD, EC 1.1.1.25) were resolved on buffer system 1 of Glaszmann et al. (1988) (G1). Staining procedures for all enzymes followed Soltis et al. (1983). When more than one isozyme was observed for an enzyme, isozymes were numbered sequentially with the most anodally migrating enzyme designated 1. Allelic variation at a locus was coded alphabetically, with the most anodally migrating allozyme designated a.
Data Analysis
Electrophoretic data were analyzed using the computer program Biosys-1 version 1.7 for the IBM-PC (Swofford and Selander 1989). Data were entered as genotype numbers from which allele frequencies were calculated; genetic similarities between the eight populations were estimated using Nei's (1978) method and the data were used to construct an UPGMA dendrogram. The levels of genetic variability within populations were estimated using four variables: the mean number of alleles per locus (A), percentage of polymorphic loci (P), observed heterozygosity (Ho), and expected heterozygosity (He). The deviation from Hardy–Weinberg equilibrium (fixation indices) and F statistics were calculated. Outcrossing rates (t) were estimated using fixation indices (F), and outcrossing rate and fixation index are related by t = (1 - F)/(1 + F) (Weir 1990).
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Results |
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Enzyme electrophoresis resulted in clear staining for 14 enzymes, encoded by 24 putative loci. All the enzymes migrated anodally. Aat-2, Fba, G3pdh, Idh, Mdh-1, Me-1, Me-2, Pgi-1, and Tpi-2 were monomorphic, with all individuals from the eight populations possessing a single enzyme band with identical mobility for each locus, and all the other loci were polymorphic in at least one population. Aat-1, Aat-3, Adh, Dia-1, Dia-2, Lap-1, Lap-2, Mdh-2, 6Pgd, Pgi-2, Pgm, and Tpi-1 each had two alleles, Mdh-3 and Pgi-3 each had three alleles, and Skd had four alleles. Although two isozymes of PGM are typically present in diploid seed plants (Gottlieb 1982), only one PGM isozyme was observed in O. officinalis. Two loci of G3PDH and PGD are typically reported (Second 1982), but only one locus was observed in this study; the banding patterns of Pgi-2 and Pgi-3 seemed to be apparent gene duplications.
It is apparent that significant allelic differences existed between Hainan and the other two regions, and the differences came mainly from the presence of 10 specific alleles in Guangxi and Hainan (Table 2). The three populations (populations 1, 2, and 3) from Guangxi had Aat-3a, Dia-1a, Mdh-2b, Mdh-3c, and Skd-c, while the four populations (populations 4, 5, 6, and 7) from Hainan had Aat-3b, Dia-1b, Mdh-2a, Mdh-3b, and Skd-b. All populations from Guangxi had Lap-1b except population 2, which possessed the same allele (Lap-1a) as the populations from other regions. Moreover, there were two specific alleles: the three populations from Guangxi had Pgm-a, while the four populations from Hainan had Pgm-b, except populations 4 and 5 which had Pgm-a with low frequencies of 0.025 and 0.167, respectively. In addition, all the populations except populations 4 and 5, which possessed Lap-2b, Pgd-a, and Tpi-1b at the frequencies of 0.025 and 0.167, respectively, were monomorphic at Lap-2, Pgd, and Tpi-1. Of interest, population 8 from Yunnan shared more alleles with the populations from Guangxi (Aat-3a, Dia-1a, Mdh-2b, and Mdh-3c) than with those from Hainan (Aat-1a), which was responsible for the higher genetic identity between the two regions. Two specific alleles were found in population 8: one was Skd-d (1.00), which was also found in population 1 from Guangxi at a much lower frequency of 0.438, and the other was Dia-2a, which occurred at a rather low frequency of 0.031. Finally, seven alleles (Adh-a, Adh-b, Pgi-2a, Pgi-2b, Pgi-3a, Pgi-3b, and Pgi-3c) were found among all the populations studied at variable frequencies, which might also contribute to genetic differentiation among populations to a certain extent.
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The values of genetic diversity varied among populations (Table 3). It is clear that populations 4 and 5 from Hainan showed relatively higher levels than others, while population 3 from Guangxi and population 7 from Hainan showed the lowest levels of genetic diversity. Moreover, the mean levels of genetic diversity for Hainan were relatively higher than those for Guangxi as well as those for Yunnan. At the species level, genetic diversity was higher than that at the population level.
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The above results were further demonstrated by Wright's F statistics (Table 4). The high, statistically significant FST values observed at most of the polymorphic loci indicate a considerable genetic differentiation among populations of O. officinalis. The statistically significant average FST value of 0.882 suggests that 88.20% of the total genetic variation existed among popu lations. On a regional level, the statistically significant FST average value from Guangxi (FST = 0.615) was higher than that from Hainan (FST = 0.415) (not shown), indicating that there existed more genetic differentiation among Guangxi populations than among Hainan populations. FIS was 0.899, suggesting that most of the populations deviated from Hardy–Weinberg expectation within populations and that there was a deficiency of heterozygotes. Table 3 also gives the fixation indices for all the populations studied, suggesting most of the populations deviated from Hardy–Weinberg expectation. In general, the populations studied showed a deficiency of heterozygotes, with a mean fixation index of 0.520. The outcrossing rate (t) was also estimated to obtain preliminary insights into the mating system of the species; the populations of O. officinalis possessed an average estimated outcrossing rate of 31.6%.
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Nei's (1978) unbiased genetic identity values varied between the pairs of populations (data not shown). The mean of all pairwise comparisons of 0.786 suggests a fairly low genetic similarity and corresponds to the high level of FST observed. The mean genetic identity values estimated for the regions (Table 5) were somewhat lower than those among populations from both Hainan and Guangxi, indicating that high genetic differentiation in O. officinalis occurred between Hainan and the other two regions. The only population from Yunnan had a close genetic relationship with Guangxi despite the great geographic isolation and agreed with the difference of allelic frequencies observed. These results are shown in Figure 2, which not only shows the above relationships, but also indicates that pairs of populations that were geographically closer to each other had higher genetic identities than those separated by greater distances.
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Discussion |
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Levels of genetic variation are highly variable among plant populations (Hamrick 1989; Hamrick and Godt 1989), as is the case in O. officinalis. Compared to the mean estimate of allozyme diversity in the herbaceous perennial and wind-pollinated plant species reviewed by Hamrick and Godt (1989), O. officinalis possesses low levels of allozyme variation. The levels of genetic diversity in the species are much lower than those reported in O. rufipogon Griff. (Barbier 1989b; Second 1985a), and also lower than those in Chinese O. rufipogon (A = 1.3, P = 22.7%, and H = 0.068) according to our recent allozyme survey (Gao et al. 2000a). However, the species possesses a higher amount of genetic diversity than that of O. glumaepatula Steud. (Akimoto et al. 1995) and Chinese O. granulata Nees et Arn. ex Watt. (A = 1.09, P = 6.33%, and H = 0.016) (Gao et al. 2000b). The results therefore suggest that O. officinalis probably maintains a moderate level of genetic diversity in the genus Oryza. It is noteworthy that there exists a fairly high level of genetic differentiation, with the FST value (0.882) being much higher than the average for short-lived herbaceous perennials and wind-pollinated plants (Hamrick and Godt 1989) as well as gravity-dispersed plants (Loveless and Hamrick 1984). As compared to the other wild rice species studied, the genetic differentiation among populations of O. officinalis is not only much higher than that in O. rufipogon from Thailand (Barbier 1989b) and China (FST = 0.310) (Gao et al. 2000a), but it also seems somewhat higher than that in O. granulata from China (FST = 0.859) (Gao et al. 2000b). The level of mean genetic identity further supports the findings in the present study (I = 0.786), which is obviously lower than the mean I = 0.900 among populations within a species (Gottlieb 1981) and lower than those for other Oryza species studied, such as O. rufipogon from China (Gao et al. 2000a; Second 1985b) and Thailand (Barbier 1989a), O. granulata from China (I = 0.901) (Gao et al. 2000b), and O. glumaepatula from the Amazon basin (Akimoto et al. 1995).
The genetic differentiation of O. officinalis in this work exists not only between Hainan and the other two regions, but also within a geographically limited region. A possible explanation for the highly regional differentiation between Hainan and the other regions is that large populations might have been on Hainan Island before being isolated, and consequently geographical isolation between them has led to restricted gene flow. For immigrants that possibly arrived on the island before it was totally separated from the mainland, the founder effect may play a small role in its levels of genetic diversity. In addition, the tropical climate of the island might have advantages in maintaining the lower frequencies of genetic bottlenecks after establishment, and the influence of genetic bottleneck effects on outcrossing species with a large effective population size will be less than in smaller populations. These explanations are supported by the high level of genetic diversity observed within the populations of Hainan in the present study. Great geographical isolation and the channel barrier may have led to fairly restricted gene movement, and thus a great deal of specific alleles were fixed in the populations of different geographical regions and a high genetic differentiation was observed.
High genetic differentiation among populations of O. officinalis within a geographically limited region may stem from limited gene flow and genetic drift due to the smaller populations. Taking Guangxi as an example, relatively isolated natural habitats may play an important role in genetic differentiation. Most of the populations of O. officinalis grow in humid habitats beside streams in mountain valleys, and the water flow may act as a seed dispersal agent as well as live ratoons. It is possible that gene flow occurs along the same stream, but the populations along different streams are relatively isolated. In addition, although O. officinalis was widely distributed in Guangxi and once had a large population (Wu 1981), our recent field survey suggests that many populations of Guangxi have fallen into extinction, and the surviving ones have become fairly small in size and greatly isolated (Gao et al. 1996). The reduction in population size may lead to changes in allelic frequencies due to genetic drift (Ayala 1982), and very small, isolated populations in the respective streams may also reduce the chances of migration among populations. A high genetic identity between Yunnan and Guangxi, despite their distant geographical isolation, may be due to the same gene pool source that was shared by the populations in the two regions, as well as historical migration events.
Among the different causes proposed by Brown (1979), two may be used for the case of O. officinalis: selfing and isolation by distance. To explain the similar result that was observed in perennial populations of O. rufipogon from Thailand, Morishima and Barbier (1990) proposed that some inbreeding may occur in outcrossing asexual populations because of intraclonal outcrossing events. It is probably the case in O. officinalis in this study. In addition to regional geographic isolation, most of the populations studied are greatly isolated due to discrete natural habitats and human destruction (Gao et al. 1996), which has resulted in a deficiency of heterozygotes. Another possible explanation for the high differentiation observed in the present study may be that those lower sample sizes could tend to increase the FST estimates, since small sample sizes cause more deviant estimates of allele frequencies.
In conclusion, restricted gene flow as well as genetic drift may account for the high genetic differentiation of O. officinalis observed in the present study. However, the spatial distribution of genetic variation within plant populations results from the joint action of mutation, migration, selection, and genetic drift (Hamrick 1989). It should be noted that populations from other regions, such as Guangdong Province, as well as other worldwide regions, are not included in the present study. Therefore a full picture of population genetic structure for the species, as well as possible evolutionary causes, can be better outlined if extensive studies on these other populations are completed in the future. Further detailed information on the variation of reproductive and mating systems should also be helpful to explain the population genetic structure of O. officinalis. It is certainly a critical issue for the conservation of these wild genetic resources.
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Acknowledgments |
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We are grateful for Dr. James L. Hamrick for his careful review and valuable comments to improve the manuscript. This research was supported by the International Foundation for Sciences (IFS) (C/2378-2 to L.-Z.G.) and a grant of the President of the Chinese Academy of Sciences (to D.-Y.H.).
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Footnotes |
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Corresponding Editor: James L. Hamrick
Received July 16, 2000
Accepted September 5, 2001
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References |
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Akimoto M, Shimamoto Y, and Morishima H, 1995. Allozyme variation and genetic diversity of intra and inter populations of Oryza glumaepatula distributed in the Amazon basin. In: Abstracts of the Third International Rice Genetics Symposium. Manila, The Philippines: International Rice Research Institute.
Ayala FJ, 1982. Population and evolutionary genetics: a primer. Menlo Park, CA: Benjamin/Cummings; 73–78.
Barbier P, 1989a. Genetic variation and ecotypic differentiation in the wild rice species Oryza rufipogon. I. Population differentiation in life-history traits and isozymic loci. Jpn J Genet 64:259–271.
Barbier P, 1989b. Genetic variation and ecotypic differentiation in the wild rice species Oryza rufipogon. II. Influence of the mating system and life-history traits on the genetic structure of populations. Jpn J Genet 64:273–285.
Brown ADH, 1979. Enzyme polymorphism in plant populations. Theor Popul Biol 15:1–42.
Clegg MT and Allard RW, 1972. Patterns of genetic differentiation in the slender wild oat species Avena barbata. Proc Natl Acad Sci USA 69:1820–1824.
Dewey SE and Heywood JS, 1988. Spatial genetic structure in a population of Psychotria nerviosa. I. Distribution of genotypes. Evolution 42:834–838.
Fu LG, 1992. Endangered plant species in China, vol. 1. Beijing: Scientific Press; 314–316.
Gao LZ, Zhang SZ, Zhou Y, Ge S, and Hong DY, 1996. A survey of current status of wild rice in China. Chin Biodiv 4:162–166.
Gao LZ, Ge S, and Hong DY, 2000a. Allozymic diversity and genetic structure of common wild rice Oryza rufipogon Griff. in China. Theor Appl Genet 101:494–502.
Gao LZ, Ge S, and Hong DY, 2000b. Low levels of genetic diversity within populations and high differentiation among populations of a wild rice, Oryza granulata Nees et Arn. ex Watt. from China. Int J Plant Sci 161:691–697.
Glaszmann JC, de los Reyes BG, and Khush GS, 1988. Electrophoretic variation of isozymes in plumules of rice (Oryza sativa L.) a key to the identification to 76 alleles at 24 loci. IRRI Research Paper Series 134:1–14.
Gottlieb LD, 1981. Electrophoretic evidence and plant populations. Prog Phytochem 7:1–46.
Gottlieb LD, 1982. Conservation and duplication of isozymes in plants. Science 216:373–379.
Hamrick JL, 1989. Isozymes and the analysis of genetic structure in plant populations. In: Isozymes in plant biology (Soltis DE and Soltis PS, eds). Portland, OR: Dioscorides Press; 87–105.
Hamrick JL and Godt MJW, 1989. Allozyme diversity in plant species. In: Plant population genetics, breeding and genetic resources (Brown AHD, Clegg MT, Kahler AL, and Weir BS, eds). Sunderland, MA: Sinauer Associates; 43–63.
Heinriches EA, Medrano FG, and Rapusas HR, 1985. Genetic evaluation for insect resistance in rice. Manila, The Philippines: International Rice Research Institute.
Hong DY, 1995. Rescuing genetic resources of wild rices in China. Bull Chin Acad Sci 10:325–326.
Jena KK and Khush GS, 1990. Introgression of genes from Oryza officinalis Wall. ex Watt. to cultivated rice, O. sativa L. Theor Appl Genet 80:737–745.
Loveless MD and Hamrick JL, 1984. Ecological determinants of genetic structure in plant populations. Annu Rev Ecol Syst 15:65–95.[Web of Science]
Morishima H and Barbier P, 1990. Mating system and genetic structure of natural populations in wild rice Oryza rufipogon. Plant Species Biol 5:31–39.
National Exploration Group of Wild Rices, 1984. An investigation of genetic resources of wild rices in China. Acta Agric Sinica 6:3–10.
Nei TM, 1978. Estimation of average heterozygosity and genetic distance from a small number of individuals. Genetics 89:583–590.
Schaal BA and Smith WG, 1980. The apportionment of genetic variation within and among populations of Desmodium nudiflorum. Evolution 34:214–221.
Second G, 1982. Origin of the genetic diversity cultivated rice (Oryza spp.): study of the polymorphism scored at 40 isozyme loci. Jpn J Genet 57:25–57.
Second G, 1985a. Evolutionary relationships in the Sative group of Oryza based on isozyme data. Genet Sel Evol 17:89–114.
Second G, 1985b. A new insight into the genome differentiation in Oryza L. through isozymic studies. In: Advances in chromosome and cell genetics (Sharma AK and Sharma A, eds). Oxford: Blackwell Scientific Publications; 45–78.
Selander RK and Whittman TS, 1983. Protein polymorphism and the genetic structure of populations. In: Evolution of genes and proteins (Nei M and Koehn RK, eds). Sunderland, MA Sinauer Associates; 89–114.
Soltis DE, Haufler CH, Darrow DC, and Gastony GJ, 1983. Starch gel electrophoresis of ferns: a compilation of grinding buffers, gel and electrode buffers, and staining schedules. Am Fern J 73:9–29.[Web of Science]
Soltis PS and Soltis DE, 1988. Genetic variation and population structure in the fern Blechnum spicant (Blechnaceae) from western North America. Am J Bot 75:37–44.[Web of Science]
Soltis PS and Soltis DE, 1991. Genetic variation in endemic and widespread plant species, examples from Saxifragaceae and Polystiochum (Dryopteridaceae). Aliso 13:215–223.
Soltis PS, Soltis DE, Tucker TL, and Lang FA, 1992. Allozyme variability is absent in the narrow endemic, Bensonialla oregana (Saxifragaceae). Conserv Biol 6:131–134.
Swofford DL and Selander RB, 1989. Biosys-1, version 1.7. Champaign, IL: Illinois Natural History Survey.
Vaughan DA, 1989. The genus Oryza L.: current status of taxonomy. IRRI Research Paper Series 138:1–21.
Vaughan DA, 1994. The wild relatives of rice: a genetic resources handbook. Manila, The Philippines: International Rice Research Institute.
Weir BS, 1990. Genetic data analysis: methods for discrete population genetic data. Sunderland, MA: Sinauer Associates.
Wright S, 1977. The evolution and genetics of populations, vol. 3. Experimental results and evolutionary deductions. Chicago: University of Chicago Press.
Wright S, 1988. Surface of selective values revisited. Am Nat 134:115–123.
Wu MS, 1981. A preliminary survey of wild rices in Guangxi. Hereditas (Beijing) 3(3):36–37.
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