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

Abstract

Siberian stone pine (Pinus sibirica Du Tour) in Russia is primarily valued as a nut-bearing species. Therefore, intra-stand variation in its cone structure and seed production have been actively studied during the last 50 years. However, these studies are poorly related to practical breeding. We used a novel system of traits to characterize yearly seed crops at the different levels of its structural organization. The purpose is to analyze the results of long-term observations of the intra-stand variation of the reproductive features complex, and to reveal the pattern and character of its diversity. This information would be useful to develop the method of searching the initial material for breeding. The research plot is established in the Nizhne-Sechenovo forest located 25 km from 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 between 40-120 among years. The registration of seed crop and analysis of its structure was conducted every year from 1990 to 2005. The intra-stand variation of the traits' level was determined as a standard deviation in percent from the simple average. The level of variability rose sharply and the correlations between them decreased in the years of the low crops. The results concerning variation in seed and cone traits are listed in the next table. The number of full seeds depended rather on losses in the processes of development (r = 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 the ovules, which were lost at the earlier stages 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 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.