Open access publications in the SLU publication database

Abstract

The aim of this study was to investigate how to incorporate molecular genetics into the tree breeding program for E. urophylla. The material was a combined provenance and progeny trial, initially including 144 families from open-pollinated trees of nine provenances. It was selectively thinned in year 2 removing 75% of the trees in each family and again in year 5. The population structure was studied with SSR markers after the second thinning. The inbreeding coefficients (FIS) within provenances ranged from 0.069 to 0.198, relatively low values suggesting that selection at the first thinning favoured heterozygosity. Most of the molecular variation was within provenances in (FST = 0.023). The quantitative differentiation for growth traits (QST) among provenances after the second thinning was low since selection tended to equalize the performance of the provenances. The results support the general strategy of the breeding program to improve objective traits while retaining genetic variation. Wood properties (basic wood density, cellulose and lignin contents) were determined in a group of fast-growing and a group of slow-growing families. The cellulose content of the fast group was significantly higher than that of the slow group (40.0% and 37.1%, respectively) and cellulose content was significantly correlated phenotypically with DBH. High growth rate can be combined with high cellulose content for trees intended for pulping. This conclusion was consistent with the non-significant genetic correlations between growth traits and cellulose content or wood basic density based on larger samples. Expression in scrapes of secondary xylem of genes of cellulose and lignin synthesis were related to wood properties. Cellulose synthase A4 (EuCesA4) expression was significantly correlated with cellulose content. Since EuCesA4 is a potential marker of cellulose content, we sampled 60 trees to investigate the occurrence of polymorphism in the DNA sequence. In a 2 kb sequence through six exons and six introns, the polymorphism density was 23 per kb.