Variation of growth and leaf color traits of Betula pendula ‘Purple Rain’ hybrid offsprings at seedling stage

  Objective  The gametophyte recombination and gene exchange of parents in the process of hybridization were used to create offspring groups with rich variation, which provided material basis for subsequent tree varieties and new variety breeding.

  Method  A total of 19 hybrid families were obtained by crossing 3 Betula pendula ‘Purple Rain’ as female parent and 7 B. platyphylla as male parent. The seedling height, ground diameter, leaf color traits including chlorophyll, anthocyanin and leaf color parameters (L^*, a^*, b^*) in different developmental stages from May to September and seedling preservation rate of purple leaf seedlings in 2 years in each family were investigated. The differences of each trait between their families were statistically analyzed.

  Result  The analysis results of each trait showed that: (1) mostly, there were significant ( P < 0.05) to extremely significant ( P < 0.01) differences in growth traits and leaf color traits among families. The variation range of traits was greatly different, the variation of seedling height and ground diameter was about 25.00%, the relative content of anthocyanin and yellow-blue saturation (b^*) varied from 33.67% to 53.20% and the coefficient of variation of other traits was about 15.00%; (2) the leaf color traits changed greatly with season. The anthocyanin and red-green saturation (a^*) were the highest in May and June, and significantly decreased in 7, 8 and 9 parts, which was consistent with the seasonal variation of purple leaf color in spring and gradually green in summer. The seasonal variation of yellow-blue saturation (b^*) showed an increasing trend, which was consistent with the trend of leaf color becoming blue; (3) the preservation rate varied greatly among families. The preservation rates of three families were 95.0%, 90.4% and 88.4%, respectively, 2.7 times the average of the three families with the lowest preservation rates. In each family, the preservation rate of the family with B. platyphylla from Daxing’an Mountains as the male parent was 12.2% higher than that of the family with B. platyphylla from seed orchard.

  Conclusion  There are abundant variations in growth traits, anthocyanin content, leaf color parameters and preservation rate between B. pendula ‘Purple Rain’ and B. platyphylla families, which lay a foundation for further screening excellent hybrid varieties of B. platyphylla. The cold resistance of filial generation is improved by cold temperate provenance B. platyphylla as male parent.