Intra-stand variation of cone structure and seed production in Siberian stone pine: pattern and use for breeding

<p>Siberian stone pine (Pinus sibirica Du Tour) in Russia is primarily valued as a nut-bearing species. Therefore, intra-stand<br />variation in its cone structure and seed production have been actively studied during the last 50 years. However, these studies are<br />poorly related to practical breeding. We used a novel system of traits to characterize yearly seed crops at the different levels of its<br />structural organization. The purpose is to analyze the results of long-term observations of the intra-stand variation of the reproductive<br />features complex, and to reveal the pattern and character of its diversity. This information would be useful to develop the method of<br />searching the initial material for breeding. The research plot is established in the Nizhne-Sechenovo forest located 25 km from<br />Tomsk in the south part of the boreal zone (170 years old, mean height 22 m, mean d.b.h. 60 cm). The number of sampled trees varied<br />between 40-120 among years. The registration of seed crop and analysis of its structure was conducted every year from 1990 to 2005. The<br />intra-stand variation of the traits' level was determined as a standard deviation in percent from the simple average. The level of<br />variability rose sharply and the correlations between them decreased in the years of the low crops. The results concerning variation in seed<br />and cone traits are listed in the next table. The number of full seeds depended rather on losses in the processes of development (r =<br />0.80*-0.85*) than on their starting number (r =0.55*-0.60*). The mass of one seed with sound endosperm rose with an increase in the ratio of<br />the ovules, which were lost at the earlier stages<br />of development (r = 0.20-0.25*) and the flat seed ratio (r = 0.35*-0.40*). In year-to-year dynamics, the number of cones per tree is<br />positively connected with the number of filled seeds per cone (r = 0.78*) and with other indices characterizing 'the crop quality'.The breeding rank of trees by all important traits remains relatively stable from year to year. Consequently, even in the years of big crops even the most productive trees fully use its potential. A considerable increase in seed production by means of artificial selection of the best genotypes is therefore possible without a visible decrease in the crop quality and without intensification of the cone-bearing irregularity. Criteria and method of selection of the initial material for the Siberian stone pine breeding as nut-bearing species have been suggested.</p

Ecological and morphological studies in the hybrid zone between Pinus sibirica and Pinus pumila

In the Baikal Region, there is no phenological isolation between Siberian stone pine (P. sibirica Du Tour) and Siberian dwarf stone pine (P. pumila (Pall.) Regel) since the timing of their 'flowering' coincides. Morphologically intermediate individuals, supposedly natural hybrids,occur not very often. In the west half of Stanovoye upland area four regions were investigated: Barguzinskiy, Baikalskiy, Verchneangarskiy and the Severo-Myiskiy mountain ridges. Interspecific natural hybridization was found to take place in several overlapping regions of the species' ranges; however there are some differences in frequency of natural hybrid occurrence between regions as well as within each region. Great numbers of natural hybrids are found only in a specific habitat which occurs rarely and occupies a relatively small area. At the north-east coast of Lake Baikal the lakeside zone is occupied by Siberian stone pine forests with moderate participation of Siberian dwarf stone pine in the undergrowth. The natural hybrid are widespread everywhere. The ratio of fructiferous Siberian stone pine, Siberian dwarf stone pine and natural hybrid was found to be approximately 300:10:1. About 90% of the examined natural hybrids took an intermediate position between the two parental species by most features (structure of needles, shoots, and crown), i.e. representing putatively the first generation hybrids. Therefore, in contrast to the parental species they are subjected to the destructive effect of snowbreak (broken off or dislocated from part of the root system). Like the Siberian dwarf stone pine the natural hybrid has specific root sources forming from latent buds. Therefore, the hybrids are not subjected to ageing, as well as have no internal limitation of age and size. Siberian dwarf stone pine, Siberian stone pine and their natural hybrid grow together in the Upper Angara delta in the bog regions. In the most productive sites the ratio of fructiferous Siberian dwarf stone pine, Siberian stone pine and natural hybrid amounts approximately to 60:3:1. The ratio of fructiferous Siberian dwarf stone pine and natural hybrid reaches about 20:1 in the less productive sites where Siberian stone pine is sterile. Analysis of cone structure showed that the natural hybrid have substantially increased in comparison with the species' mortality and aplasia of reproductive structures at all stages of the generative cycle, from differentiation of the seed-bearing scales to differentiation of the embryo. The portion of the ovules, which develop into the valuable seed with differentiated embryo, amounted in Siberian dwarf stone pine to 69%, in Siberian stone pine to 44%, and in natural hybrid to 25%. Thus, the fertility of natural hybrid in the Upper Angara Delta substantially decreased in comparison with the pure species; however, it was demonstrated that natural hybridization between Siberian dwarf stone pine and Siberian stone pine species occurred.</span

Population genetic structure and mating system in the hybrid zone between Pinus sibirica Du Tour and P. pumila (Pall.) Regel at the Eastern Baikal Lake shore

<span style="font-family: Arial,Helvetica,sans-serif; font-size: small;">Genetic structure of sympatric Pinus sibirica Du Tour and P. pumila (Pall.) Regel populations and putative interspecific hybrids between them was analyzed in the Baikal Lake region (Barguzin Biosphere Natural Reserve, Davsha River basin) by means of 31 allozyme loci controlling 18 enzyme systems. Several alleles at loci Adh-1, Fest-2, Lap-3, Pgi-1, Sod-3 and Skdh-1 were diagnostic for P. sibirica, while alleles typical for P. pumila were detected at loci Gdh, Got-3, Lap-3, Mdh-2, Mdh-4, Pepca, Pgi-1, Pgd-2, Pgd-3, Pgm-1 and Pgm-2. All hybrids were heterozygous for the diagnostic Skdh-2 locus. Classification into hybrids and parental species using PCA analysis of multilocus allozyme genotypes had good correspondence with diagnoses made by morphological and anatomical analyses. Approximately 27% of embryos in P. pumila seeds had P. sibirica paternal contribution, and 8% of haplotypes in effective pollen pool combined alleles typical for P. pumila and P. sibirica, and therefore were classified as pollinated by the hybrids. About 83% of embryos in seeds from the hybrids most likely originated from fertilization by P. sibirica pollen, 14% from P. pumila and 3% from hybrid trees. This result favours the view that hybrids make both male and female contributions to the reproductive output of the population and confirm the presence of backcrosses and F2 hybrids.</span