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Journal of Selection for both growth and wood properties in hybrid Forestry Research 14(3): 225–229. poplar clones. For. Sci. 49: 901–908. RAJORA, O. P., L. ZSUFFA and F. C. YEH (1994): Variation, ZOBEL, B. J. and J. B. JETT (1995): Genetics of Wood Pro- inheritance and correlations of growth characters and duction. Springer Verlag, Berlin, Heidelberg, New York. Crossability of Pinus sibirica and P. pumila with their hybrids By G. V. VASILYEVA1) and S. N. GOROSHKEVICH Institute of Monitoring of Climatic and Ecological Systems, Siberian Branch of the Russian Academy of Sciences, 10/3, Academichesky Ave., Tomsk, Russia (Received 4th June 2012) Abstract species introgression. The hybrids probably contribute to interspecies genetic exchange both through hybrid Crossability of Pinus sibirica and P. pumila hybrids and their parental species was studied using the con- seed production following pollination by parental species and by hybrid pollen distribution. trolled pollination method. Pinus sibirica and its hybrids were represented by grafts at the “Kedr” field Key words: hybridization, Pinus sibirica, P. pumila, controlled station southeast of Tomsk Oblast, Russia; the parental pollination, reproductive isolation. species was of local provenance, with its hybrids obtained from the Southern Baikal region. In the case of P. pumila, trees were pollinated in a wild stand located Introduction in the Upper Angara River delta. Parental species had Interspecies hybridization is common in plants, and the highest number of filled seeds under open pollina- quite frequently contributes to their evolution (RIESE- tion. When they were pollinated with hybrid pollen, the BERG, 1997; RIESEBERG and CARNEY, 1998; ARNOLD et al., trees showed nearly two-fold reductions in the number of filled seeds. Hybrids tended to abort most ovules dur- 1999). In woody plants, the widespread occurrence of ing the first year of female cone development, resulting natural hybridization is closely connected with in a high seed abortion rate and consequent low seed anemophily, a non-specialized type of pollination production. The number of filled seeds obtained from (KOROPACHINSKIY and MILYUTIN, 1979; 2006). In conifers, hybrids was low, with levels ranging from 8.2 to 24.3%. natural hybridization usually leads to introgression, i.e., Because of weak reproductive isolation between hybrids genetic exchange between species (GRANT, 1981; and parental species, crosses are inevitable and lead to KOROPACHINSKIY, 1992; KOROPACHINSKIY and MILYUTIN, 2006). 1) Corresponding author: GALINA VASILYEVA. Telephone: +7(3822) Among five-needle pines, Siberian stone pine (Pinus 491907, Fax: +7(3822) 491950. E-mail: [email protected] sibirica Du Tour) and Siberian dwarf pine (P. pumila Silvae Genetica 62, 1–2 (2013) 61 DOI:10.1515/sg-2013-0008 edited by Thünen Institute of Forest Genetics Vasilyeva et. al.·Silvae Genetica (2013) 62/1-2, 61-68 [Pall.] Regel) have the largest natural habitats, occupy- strength of genetic barriers between species and/or ing about 5 and 6 million km2, respectively (CRITCHFIELD hybrids. These crossing techniques have been widely and LITTLE, 1966). Pinus sibirica is widely distributed applied to investigate affinity and incompatibility throughout Russia. Its northern border extends from the sources in conifers, especially in larches (AVROV, 1982), Izhma River to the middle course of the Pechora River silver firs (KORMUTAK et al., 2008), spruces (FOWLER, and the Northern Urals, then east to the Yenisei River 1987; MAJOR et al., 2005), two-needle pines (MCWILLIAM, (up to 68°N), and then slightly south to the upper reach- 1959; CRITCHFIELD, 1966; WACHOWIAK et al., 2005; KOR- es of the Aldan River. Its eastern border is in Trans- MUTAK et al., 2005; LEWANDOWSKI and WISNIEWSKA, baikalia, stretching along the Yablonovy Range into 2006), and five-needle pines (KRIEBEL, 1972; CRITCH- P. sibirica’s southernmost point in northern Mongolia FIELD, 1975; TITOV, 1977; BLADA, 1994; FERNANDO et al., (about 46°30’ N). The southern border encompasses the 2005). Altai Mountains and extends westward to the southern The earliest studies of natural hybridization between part of the West Siberian Plain and thence to its west- and focused solely on morphology of ern border in the Ural Mountains (Flora of USSR, 1934). P. sibirica P. pumila a few putative hybrids (POZDNYAKOV, 1952; GALAZIY, is distributed between 69° and 35°N, Pinus pumila 1954; MOLOZHNIKOV, 1975). Hybridization between these i.e., from the northern timberline in Yakutia to Honshu species was confirmed by isoenzyme analysis (POLITOV Island. From west to east, its range extends from Lake et al., 1999). Natural hybrids between P. sibirica and Baikal to the Kamchatka Peninsula, although the mid- P. pumila are now known to frequently occur in areas dle portion of its western border deviates strongly to the where their habitats overlap (GOROSHKEVICH, 1999; east. This deviation is due to low snowfall in winter and GOROSHKEVICH et al., 2008a,b). The hybrids are fertile, the centuries-old impact of forest fires (UTKIN et al., and are characterized by intermediate-sized cones and 2001). seeds and considerably reduced seed efficiency com- Pinus sibirica and P. pumila have extensively overlap- pared with the parental species (GOROSHKEVICH et al., ping ranges, with areas of sympatry encompassing near- 2008a). In previous studies, hybrid seed efficiency var- ly 1 million km2 (Fig. 1). This overlapping territory ied depending on terrain and year of collection, with includes the Aldan Uplands, the Stanovoye Uplands, the 1.8–25.1% of ovules growing into filled seeds with well- Vitim Plateau, the Khentei-Chikoiskoye Uplands, and developed embryos (GOROSHKEVICH, 2004; VASILYEVA et the mountain ridges surrounding Lake Baikal, exclud- al., 2006; PETROVA et al., 2007). When studying hybrid ing its western shores. reproductive performance, knowledge of the degree of Hybrids are frequently found in their parental species’ their reproductive isolation from parental species is communities. The effect of these hybrids on population needed to determine the intensity, direction, and proba- processes is determined by their fertility and ability to ble results of hybridization. The aim of our study was to backcross with parental species (GRANT, 1981; RIESE- determine crossability of P. sibirica and P. pumila BERG, 2001). Controlled crossing experiments can be hybrids and their parental species using the controlled used to study reproductive isolation and estimate the pollination method. Figure 1. – Geographic distribution of P. sibirica and P. pumila. 1 – “Kedr” field station, 2 – Upper Angara River delta where controlled pollination of P. pumila was conducted, 3 – northern macroslope of Khamar-Daban Ridge is point of origin of hybrids used in the experiment. 62 DOI:10.1515/sg-2013-0008 edited by Thünen Institute of Forest Genetics Vasilyeva et. al.·Silvae Genetica (2013) 62/1-2, 61-68 Materials and Methods coefficient 0.6 represents the average fraction of fertile The study was carried out from 2005 to 2011 at two scales in P. sibirica cones (GOROSHKEVICH and locations in Russia. The first location was the “Kedr” KHUTORNOY, 1996). Seeds were categorized as either field station, managed by the Institute of Monitoring of full-grown or aborted, with the quality of full-grown Climatic and Ecological Systems and situated 30 km seeds checked using X-ray analysis (SHCHERBAKOVA, south of Tomsk (56°13 N 84°51 E, 78 m above sea level). 1965). The second location was a wild stand of P. pumila in the Collected data were statistically analyzed using Sta- Upper Angara River delta near Nizhneangarsk (55°47 N tistica 6.0 software. Mean, standard deviation, and max- 109°33 E, 487 m above sea level). Grafts of eight P. sibir- imum and minimum values were calculated. Compari- ica clones of local provenance were used as maternal son of means of cones taken from different crosses was plants.