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GENETIC EVIDENCE OF NATURAL HYBRIDIZATION BETWEEN SIBERIAN STONE , DU TOUR, AND DWARF SIBERlAN PINE, I? PUMILA (PALL.) REGEL

Dmitri V. Politov Is*, Maryana M. Belokon I, Oleg P. Maluchenkol, Yuri S. Belokon ', Vladimir N. MolozhnikovZ,Leon E. Mejnartowicz3 & Konstantin V. Krutovskii1~'

'' Laboratory of Population Genetics, Russian Academy of Sciences, N. I. Vavilov Institute of General Genetics, Gubkin Str. 3, GSP-1 Moscow 117809, Russia 2' Institute of Electron Beam Technology, Irkutsk 664000, Russia '' Laboratory of Biochemical Genetics, Polish Academy of Sciences, Institute of Dendrology, Parkowa Str. 5, PL-62-035 Kornik, Poland " Department of Science, Oregon State University, Corvallis, Oregon 97331-7501, U.S.A. *' To whom correspondence should be addressed

Received September 4, 1998; accepted January 20, 1999

ABSTRACT

Sympatric populations of two Eurasian bird-dispersed pine species Pincrs sibiricn and P pumila, and their putative natural hybrid were analyzed using 28 allozyme loci controlling 14 enzyme systems. The Aclll-I, Fe-2, and Lap3 loci in the hybrid had genotypes that are typical for P sibirica, but did not occur or are unlikely in I! p~rinila.The Grill, Got-2, Got-3, Pgnz-1 and Pg1t1~2loci had carried alleles and genotypes unknown for P sibiricn, but were common in P pztrda. The Skclh--2 locus was heterozygous for alleles, one of which was specific to P sibirica, the other to I! puti7ilu. Some embryos from of the hybrid were likely resulted from sclfing, while others from backcrosses with parental species. This is the first genetic evidence of natural hybridization and possible gene exchange between Siberian stone pine and dwarf Siberian pine.

Key words: Siberian stone pine, Pinit~sibiricn, dwarf Siberian pine, P pzcrizila, isozyme loci, natural hybridization

INTRODUCTION disputable in view of the recent data on genetic differ- entiation among of the section Strobus obtained Siberian stone pine (Pinus sibirica Du Tour) is a forest using isozymc loci (BELOKONeta/. 1998). tree widely distributed in and in the northeast of Unlike FI sibirica, which is typically a large tree up the . Its range extends eastward to the to 35 m tall, P p~~rnilaexists mainly as a shrub-like or Transbaikalia (the Baikal Lake region) and southern crawling form, only rarely displaying a tree-like pheno- -Yakutia, where it comes into contact with the type (Fig. 2). Some botanists studying stone pines (e.g., closely related dwarf Siberian pine (also known as SUKACHEV1929; GALAZII1954) have believed that the Japanese stone pine), P pimila (Pall.) Regel (Fig. 1). treelike form of FI pw7iila is mainly (though not These two species share several common evolutionary exclusively) attributed to the zone of sympatry between traits, such as large, wingless seeds, that are retained Siberian stone pine and dwarf Siberian pine. Based on within mature "indehiscent" cones, which promote bird- this fact, these authors assumed that upright forms of FI mediated dispersion (LANNEK1996). Though pumila are, in fact, inter-specific hybrids. This assump- some early botanical descriptions of F! pliinila (Flora tion could explain not only unusual living form, but Rossica 1784, cited in BOBROV1978) treated it as an also some other traits intermediate between these pine ecological or geographical variety of P sihirica, the species. However, to the best of our knowledge, there characteristic traits of this pine were later interpreted as are no genetic data or study proving the hybrid origin of distinct from P sibirica (REGEL1859, cited in BOBROV these suspected trees. The objective of this paper is to 1978), and since that time the species status of dwarf present genetic data confirming the hybrid origin (FI Siberian pine has been widely accepted. Both pines are punziln x P. sibirica) of a tree growing in the zone of traditionally included in the subsection Cembrae, contact of these two species using electrophoretic section Strobus, subgenus Strobus (CRITCHFIELD& analysis of seed isozymes. LITTLE1966), although this classification seems to be

0 ARHORA PUBLISHERS D. V. POLITOVETAL.: GENETICEVIDENCE OF NATURAL HYBRIDIZATION BETWEEN PINUSSIBIRICA AND P. PUMILA

Figure 1. Natural ranges and sympatry zone of the two stone pine species. The black dot indicates the location where the samples were collected

MATERIALS AND METHODS

Plant material

Open-pollinated seeds were collected from one sus- pected hybrid pine tree (referred to further as the "hybrid") grown on the territory of Barguzin Biosphere State Reserve (Buryat Republic, Russian Federation) in 1991 in the mixed stand among typical I? sibirica and I? pumila. The seeds were processed and stored at -20 "C in the Institute of Dendrology (Kornik, Poland) and part of them were handed over to the Institute of General Genetics (Moscow, Russia) by L. E. Mejnar- towicz in 1992. The sampled hybrid had morphological traits intermediate between P: sibirica and I? pumila A B C being a small tree about 4 m tall with broad open crown, and dark brown bark (Fig. 2B). Cones of the Figure 2. Typical Pinus sibirica (A), tree-like, supposedly hybrid (Fig. 3B) were smaller than those of P: sibirica hybrid, form of P. pumila (B) tree from the Barguzin (Fig. 3A) but larger and thicker and not as much Mountains, Malaya CheremshanaRiver drainage, and typical elongated as I? pumila cones (Fig. 3C). Size of the P. puntila (C) (A and C are taken from FARJON1984, and B seeds from the hybrid was also intermediate between from MOLOZHNIKOV1975). typical I? sibirica and I? pumila seeds, as shown in Fig. 3. Control seed samples were collected from 50 and 80 ingly, growing in the same region where the hybrid was typical I? sibirica and I? pumila pines, correspond- collected. In addition, extensive population genetic

D. V. POLITOVETAL.: GENETICEVIDENCE OF NATURAL HYBRIDIZATION BETWEEN PINUSSIBIRICA AND P. PUMILA

Table 1. Allele frequencies for 10 polymorphic loci averaged for all allopatric populations of P. sibirica and P. pumila studied in previous wide-scale population studies, for typical P. sibirica and P. pumila trees from neighboring stands surrounding the hybrid, and for the multilocus genotype of the hybrid.

P, sibirica P. pumila Locus/allele Hybrid allopatric neighbor neighbor allopatric

Adh -1 log Adh-1100 Adh-1/91 Adh-1/88 Fe-2/127 Fe -2/120 Fe-2/100 Fe -2/87 GdWl 11 Gdh.400 Got -2/112 Got-21100 Got-3/134 Got -3/lOO Got -3/53 Got -3/34 Lap -3/100 Lap -3/96 Lap -3/92 Lap -3/87 Pgm -]/I04 Pgm-1/100 Pgm -1196 Pgm-1/94 Pgm -2/lll Pgm-2/100 Pgm-2/97 Skdh-2/123 Skdh -211 10 Skdh -211 00 Skdh-2/95 Sod-1400 Sod-1/68 -- Note: Shaded raw cel show the unambiguous or the most likely origin of the allele in the hybrid. studies (KRUTOVSKIIet al. 1988, 1989, 1990, 1994, 109, 100 and 91. The hybrid had a heterozygote 1995; KRUTOVSKII& POLITOV1992; POLITOV1989; genotype 100191, typical for l? sibirica or very likely Po~rrovet a/. 1992; POLITOV & KRUTOVSKII1994; expected for hybrid, because allele 91 was almost fixed unpublished data), and for typical P sibirica and l? in !? pumila, and allele 100 was extremely rare and pamila trees from neighboring stands surrounding the found only once in a heterozygous tree in the popula- hybrid, and compare those to the multilocus genotype tion of the southern Sakha-Yakutia located far away of the hybrid inferred from segregation analysis of from the hybrid. haploid megagametophytes. Fe-2 was polymorphic in both species with alleles Adh-l was polymorphic in I? sibirica with 3 alleles: 127 and 100 found in l? sibirica, and 120 and 100 in !? Figure 4. The isozyme electrophoretic pattern of Skdh-2 alleles in megagametophytes of pure P, sibirica (1-6), hybrid (7-1 I), and pure P. pumila (12-16) trees. pumila. The hybrid was heterozygous 1271100, which is the only plausible explanation for its occurrence in would be likely for hybrid, but impossible for pure I? the studied tree (Fig. 4). pumila. Sod-1 has common allele 100 in l? pumila (fre- Gdh was almost monomorphic in l? sibirica, while quency 0.87-0.92), which is fixed in f? sibirica. two alleles, 100 and 11 1, were detected in I? pumila. Hybrid tree was homozygous for allele 100, but one Allele 100 was common in I? sibirica, but allele 111 embryo of this tree was heterozygote 100168. was not found in this species. The hybrid was hetero- Thus, some of the above-mentioned loci demon- zygous 1 111100, and therefore resembled l? punzila for strate genotypes typical for I? sibirica and impossible this locus, or obtained at least one allele from I? or very unlikely for l? purnila (Adh-I, Fe-2, and pumila. Lap-3), while others show a combination of alleles Got-2 was invariant in I? sibirica. The allele fixed impossible for l? sibirica (Gdh, Got-2, Got-3, Pgm-1, in this species was also the most common in I? punzila, and Pgnz-2), and, finally, the Skdh-2 locus gives a with an additional allele, 112, reaching frequency 0.25 straightforward evidence that the studied specimen did in stands surrounding the hybrid, which was heterozy- result from an inter-specific cross between Siberian gous 1121100. Thus, as for the Gdh locus, the hybrid stone pine and dwarf Siberian pine. However, we received at least one allele from l? punzila. cannot conclude whether it represents the first genera- Got-3 had only allele, 100, in I? sibirica, while four tion of inter-specific cross (F,),since the same geno- alleles were found in I? pumila, with 100 and 34 being type could occur in the next generation as a result of the most frequent. The hybrid was heterozygous either self-pollination of F, hybrid, cross between 100134, a genotype not observed in l? sibirica, but different hybrids, or backcross to I? pumila. frequent in I? pumila, and likely for hybrid. Considering the evolutionary significance of such Lap-3 was polymorphic in both species, but alleles inter-specific hybridization, it was also of interest to 100 and 87 were frequent in I? sibirica, while 96 and investigate the paternal contribution or effective pollen 92 were typical for l? pumila. The hybrid genotype pool that was responsible for developed embryos of this 1001100 occurs commonly in I? sibirica, but is rare in tree. For this purpose all eight viable embryos available pure l? punda. from the hybrid tree seeds were analyzed along with Pgnz-1 and Pgm-2, both have genotypes in the their megagametophytes. By assessing both the haploid hybrid that could result from either within I? pumila or megagametophyte and diploid embryo of a seed, we can inter-specific crosses, but not within I? sibirica. distinguish between maternal and paternal zygotic Skdh-2 is the only locus that shares no common contributions, and therefore, infer the source (i.e., one alleles in the two species and therefore it has the of parental species or hybrid) of the pollen that fertil- highest diagnostic value. l? pumila lacks allele 100, ized each particular ovule. Unfortunately, because of which is the only allele in I? sibirica. One could not an insufficient number of embryo-containing seeds, expect to find heterozygote 1001110 in pure I? sibirica precise quantification was impossible. However, or l? punzila, and therefore, inter-specific hybridization analysis of the paternal haplotypes in embryos of 8

O ARBORA PUBLISHERS D. V. POLITOVETAL. : GENETICEVIDENCE OF NATURAL HYBRIDIZATION BETWEEN PINUSSIBIRICA AND P. PUMILA

Table 2. Multilocus haplotypes of 8 pollen (PI-P8) fertilized the hybrid, and their inferred origin.

Locus P1 P2 P3 P4 P5 P6 P7 P8

sibirica or sibirica or sibirica or hybrid hybrid pumila Origin pumila hybrid hybrid hybrid

Note. Letters after allele names show the most likely origin of species-specific paternal allele (p - from , s - from P. sibirica). Conclusions on the assumed origin of the pollen is given in the last raw. available seeds from the hybrid revealed multiple them to be hybrids. It is unknown, however, how this source of pollen. At least 3 (-38%) embryos contained form corresponds to the tree-like P pumila found also a combination of paternal alleles characteristic of two on the Kamchatka Peninsula, far away from the Baikal different species, and therefore resulted either from Lake Region (MOLOZHNIKOV1975). self-pollination or from crosses with other unknown BOBROV(1961, 1972, 1978) studied the problem of hybrids (P3, P6, and P7, Table 2). Two other embryos introgressive hybridization and regarded the Trans- could not be result of selfing and very likely originated baikalia as a complex zone of introgression for many fromfertilization by P pumila pollen (PI and P8, Table taxa, both and angiosperms. However, in 2), since they contained alleles specific for this species spite of an occurrence of broad zone of sympatry and lacking in the studied hybrid. Parental haplotypes between P pumila and P sibirica, he emphasized that of the rest three embryos might have originated from P they occupy different elevations in the mountain taiga sibirica pollen (P2, P4, and P5, Table 2). However, in and subalpine ecosystems, and, therefore, do not these cases selfing also cannot be excluded since P hybridize. It is obvious that large-scale introgressive sibirica in general possesses fewer species-specific hybridization between them does not take place, other- alleles. wise one would have observed and described a variety of intermediate forms with different extents of similar- DISCUSSION ity to parental species over a large territory of their sympatry. However, a possibility of occasional hybrid- There are many instances of natural and artificial inter- ization exists in places of the species contact. P specific hybridization in most taxa, including pumila in the Baikal Lake region occupies mainly the cases confirmed by isozyme (e.g., WANGet al. 1990; upper mountain belt forming consistent dense popula- HACKER & BERGMANN199 I), cpDNA (WAGNERet al. tions there, and contacting P sibirica at the lower 1987; STINE et al. 1989; WATANOet al. 1995, 1996), elevations, at the lower limit of P pumila. These and mtDNA markers (WATANOet al. 1996). Authors mixed stands are at the upper elevation limit for P of numerous papers on hybridization in white pines of sibirica and represent . Another area of sympatry is attributed to the zone directly on the coast the section Strobus (e g., BLADA1994; MIRov 1967; of the Baikal Lake, where P pumila also often grows TITOV 1977; WATANOet al. 1995, 1996) as well as together with P sibirica (MOLOZHNIKOV1975). The CRITCHFIELD(1 986) who summarized available to date periods of pollination for these species overlap, so one information on hybridization in this section did not cannot expect strong phenological isolation. mention any case of P sibirica x P pumila hybridiza- As far as we are aware, the genetic evidence pre- tion. We are also unaware of any well documented sented here is the first direct confirmation of hybridiza- reports of recognized hybrids between these species, tion between the two species. Based on our preliminary although some researchers (e.g., SUKACHEV1929; data, we cannot conclude what generation the studied GALAZII1954; POZDNIAKOV1952) described forms of tree represents, F,, F,, or a backcross hybrid, or how a stone pine intermediate between P pumila and P well the offspring will survive a.nd compete. Although sibirica within the zone of their sympatry and believed the hybrid produced sound seeds with normal looking and potentially viable embryos, percentage of empty Baikal'skoi Sibiri (Introgressive hybridization in the flora seeds (about 25 5%) was relatively high compared to of the Baikal region in Siberia). Botanicheskii Zhurnal regular 15-2010 (authors' data) in pure P pumila (Botanical Journal) 46: 3 13-327 [In Russian]. stands. However, the limited number of available BOBROV, E. G. 1972: Introgressivnaia gibridizatsia, hybrid seeds did not allow us to make more vigorous formoobrazovanie i smeny rastitel'nogo pokrova. [Introgressive hybridization, speciation and succession in estimations and conclusions. ]. Botanicheskii Zhurnal (Botanical Journal) 57: Hypothetically, this particular gene exchange 865-879 [In Russian]. between P sibirica and P pumila may play a signifi- BOBROV,E. G. 1978: Lesoobrazujushie khvoinye SSSR cant adaptive role. The zone of sympatry in the Baikal [Forest-forming conifers of the USSR]. Nauka, Lenin- Region and Southern Yakutia is not optimal for both grad, 189 pp. [IN RUSSIAN] species and is intrinsically occupied by marginal CRITCHFIELD,W. B. 1986: Hybridization and classification of populations. These species are adapted to different the white pines (Pinus section Strobus). Taxon 35: environmental optima (BOBROV 1978), and their 647-656. survival outside the optimal zone may be promoted by CRITCHFIELD,W. B. & LITTLE,E. L. 1966: Geographic genes from related species coming from another side of distribution of the pines of the world. U.S. Dep. Agric., the sympatry zone with different environmental gradi- Washington, D. C. 98 pp. ents. It can be equally hypothesized that the sympatry FARJON,A. 1984: Pines: Drawings and descriptions of the zone plays only a transitional role and the hybrids are genus Pinus. Leiden: E. J. Brill. 204 p. Flora Rossica, 1784: l(1): 5 tab.2 fig. f-h. not adapted and occur only due to recurrent, sporadic GALAZII,G. I. 1954: Tree-line in the mountains of Eastern hybridization. However, occurrence of putative back- Siberia and its dynamics. Proceedings of Komarov crosses among open-pollinated progeny of the hybrid Botanical Institute, USSR Acad. Sci., V. 9, "Geobotanika" tree (Table 2) demonstrates the potential for gene [In Russian]. exchange and subsequent gene introgression. The HACKER,M. & BERGMANN,F. 1991: The proportion of frequency and distribution of hybrid-looking trees in hybrids in seed from a seed orchard composed of two the sympatry zone of Siberian stone pine and dwarf larch species (L. europaea and L. leptolepis). Ann. Sci. Siberian pine trees and their possible role in the species Fox 48: 63 1-640. adaptation and evolution are still largely unknown and KONNERT,M. & MAURER,W. 1995: Isozymic investigation set up the objectives of our future studies. Mitochon- on Norway spruce [Picea abies (L) Karst.] and European drial and chloroplast DNA markers, representing silver fir (Abies alba Mill.): Practical guide to separation maternal and paternal inheritance in conifers, respec- methods and zymogram evaluation. German Federal-State tively, can be applied to study direction of gene flow Working Group "Conservation of Forest Gene Re- and phenomenon of hybridization more comprehen- sources". 79 pp. KRUTOVSKII, K. V., POLITOV, D. V. & ALTUKHOV,YU. P. sively. 1987: Genetic variability in Siberian stone pine, Pinus sibirica Du Tour. I. Genetic control of isozyme systems. ACKNOWLEDGMENTS Genetika (Moscow) 23(12): 2216-2228 (translated in English as Soviet Genetics (1988) 23: 1568-1576). We thank Dr. W. Tom Adams and Dr. Frank Sorensen for KRUTOVSKII,K. V., POLITOV,D. V. & ALTUKHOV,Yu. P. very productive discussion that greatly helped us to improve 1988: Genetic variability in Siberian stone pine, Pinus manuscript. We also thank Dr. H. Wang and two anonymous sibirica Du Tour. 11. Level of allozyme variability in a reviewers for their reviews. This research was supported by natural population of Western Sayan. Genetika (Moscow) the grant 96-04-49465 of the Russian Foundation for 24(1): 118-124 (translated in English as Soviet Genetics Fundamental Research, and UNESCO 'Man and Biosphere' (1988) 24: 81-86). Young Scientist Research Award Scheme (to D. V. Politov). KRUTOVSKII,K. V., POLITOV, D. V., ALTUKHOV,Yu. P., MILUTINL. I., KUZNETSOVA,G. V., IROSHNIKOV,A. I., REFERENCES VOROBJEV,V. N. & VOROBJEVA,N. A. 1989: Genetic variability in Siberian stone pine, Pinus sibirica Du Tour. BELOKON',M. M., POLITOV,D. V., BELOKON',Yu. S., IV. Genetic diversity and differentiation between popula- KRUTOVSKII,K. V., MALUCHENKO0. P. & ALTUKHOV, tions. Genetika (Moscow) 25(11): 2009-2032 (translated Yu. P. 1998: Genetic differentiation in white pines of the in English as Soviet Genetics (1990) 25: 1343-1362). section Strobus: Isozyme analysis data. Doklady Biologi- KRUTOVSKII,K. V., POLITOV.D. V. & ALTUKHOV,Yu. P. cal Sciences 358: 8 1-84 (translated from the Proceedings 1990: Interspecific genetic differentiation of Eurasian of Russian Academy of Sciences: Doklady Akadernii Nauk stone pines for isoenzyme loci. Genetika (Moscow) 26(4): [In Russian] 358(5): 699-702). 694-707 (translated in English as Soviet Genetics (1990) BLADA,I. 1994: Interspecific hybridization of Swiss stone 26:440 -450). pine ( L.). Silvae Genetica 43: 15-20. KRUTOVSKII,K. V. & POLITOV,D. V. 1992: Study of intra- BOBROV,E. G., 1961 : Introgressivnaia gibridizatsia vo flore and interspecific genetic differentiation between Eurasian

O ARBORA PUBLISHERS 47 D.V. POLITOVETAL. : GENETICEVIDENCE OF NATURAL HYBRIDIZATION BETWEEN PINUSSIBIRICA AND P. PUMILA

stone pines using isozyme loci and multidimensional pines (Pinus, subsection Cembrae). In: Proceedings - analysis. In: Molecular Mechanisms of Genetic Processes. International Workshop on Subalpine Stone Pines and Proceedings of All Union Meeting, pp. 87-96. Moscow, Their Environment: the Status of Our Knowledge (W. C. Nauka Publishers [In Russian]. Schmidt & F,-K. Holtmeier, Comps.), St. Moritz, Switzer- KRUTOVSKII,K. V., POLITOV, D. V. & ALTUKHOV,Yu. P. land, Sept. 512, 1992. USDA For. Serv. Intermountain 1994: Study of genetic differentiation and phylogeny of Res. Stat. Gen. Tech. Rep. INT-GTR-309, pp. 36-42. stone pine species using isozyme loci. In: Proceedings - POZDNIAKOV,L. K. 1952: Drevovidnaia forma kedrovogo International Workshop on Subalpine Stone Pines and stlanika. [Tree-like form of dwarf Siberian pine]. Botani- Their Environment: the Status of Our Knowledge (W. C. cheskii Zhurnal (Botanical Journal) 37(5):688-691 [In Schmidt and F.-K. Holtmeier, Comps.), St. Moritz, Russian]. Switzerland, Sept. 5-12, 1992. USDA For. Serv. Inter- REGEL,Index Sem. Horti Petropol.1858: 23: 1859. mountain Res. Stat. Gen. Tech. Rep. INT-GTR-309, pp. RIDGWAY,G. L., SHERBURNE,S. W. & LEWIS, R. D. 1970: 19-30. Polymorphism in the serum esterase of Atlantic herring. KRUTOVSKII,K. V., POLITOV,D. V. & ALTUKHOV,Yu. P. Trans. Am. Fish Soc. 99: 147-151. 1995: Isozyme study of population genetic structure, STINE,M.,SEARS,B. B. &KEATHLEY,D. E. 1989: Inheritance mating system and phylogenetic relationships of the five of plastids in interspecific hybrids of blue spruce and stone pine species (subsection Cembrae, section Strobi, white spruce. Theor Appl. Genet. 78: 768-774. subgenus Strobus). In: Population Genetics and Genetic SUKACHEV,V. N. 1929: Predvaritel'nii otchet o Baikal'skoi Conservation of Forest Trees (Baradat, Ph., Adams, W. T. expeditcii AN v 1926 g. [Preliminary report on the Baikal & Miiller-Starck, G., Eds.). Proceedings of the Interna- Expedition of the Academy of Sciences in 1929). Otchety tional Symposium, Carcans Maubuisson, France, 24-28 o deiatel'nosti AN SSSR (Reports on the USSR Academy August 1992. SPB Academic Publishing, Amsterdam, of Sciences Activity), Leningrad 2: 10-18 [In Russian]. The Netherlands, pp. 279-304. TITOV,E. V. 1977: Opit skreschivanija kedra sibirskogo s LANNER,R. M. 1996: Made for Each Other: A Symbiosis of drugimi sosnami v uslovijakh severo-vostochnogo Altaia. Birds and Pines. Oxford University Press, Inc., New [Experimental crosses of Siberian stone pine with other York, Oxford, 160 pp. pines in the Northeast Altai]. Lesovedenie (Forestry) 4: MARKERT,C. L. & FAULHABER,I. 1965: Lactate dehydroge- 81 -87 [In Russian]. nase isozyme patterns in fish. J. Exp. Zool. 159(2): WAGNER,D. B., FURNIER,G. R., SAGHAI-MAROOF,M. A,, 3 19-332. WILLIAMS,S. M., DANCIK,B. P. & ALLARD,R. W. 1987: MIROV,N. T. 1967: The Genus Pinus. The Ronald Press Chloroplast DNA polymorphism in lodgepole and jack Company. New York. 577 pp. pines and their hybrids. Proc. Natl. Acad. Sci. USA 84: MOLOZHNIKOV,V. N. 1975: Kedrovii stlanik gornikh land- 2097 -2100. shaftov Severnogo Pribaikailia. [Dwarf Siberian pine in WANG,X.-R., SZMIDT,A.E., LEWANDOVSKI,A.& WANG,Z.- mountainous landscape of the North Baikal region]. R. 1990: Evolutionary analysis of Pinus densata Masters, Nauka, Leningrad, 203 pp. [In Russian]. a putative Tertiary hybrid. Theor Appl. Genet. 80: POLITOV,D. V. 1989: Allozyme polymorphism, genetic 635-640. differentiation and mating system of Siberian stone pine WATANO,Y., IMAZU,M. & SHIMIZU,T. 1995: Chloroplast Pinus sibirica Du Tour. Ph. D. Thesis. Moscow, 1989, DNA typing by PCR-SSCP in the Pinus pumila - I? 170 pp. (in Russian). parviflora var. pentaphylla complex (Pinaceae). Journal POLITOV,D. V., KRUTOVSKII,K. V. & ALTUKHOV,Yu. P. of Plant Research 108: 493-499. 1992: Isozyme loci characteristics of gene banks of WATANO,Y., IMAZU, M. & SHIMIZU,T. 1996: Spatial distri- populations of cedar pines. Genetika (Moscow) 27(1): bution of cpDNA and mtDNA haplotypes in a hybrid 93-1 14 (translated in English as Soviet Genetics (1992) zone between Pinus pumila and I? parviflora var. penta- 27: 76-95). phylla (Pinaceae). Journal of Plant Research 109: POLITOV,D. V. & KRUTOVSKII,K. V. 1994: Allozyme poly- 403-408. morphism, heterozygosity, and mating system of stone