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Progeny testing of Scots pine in Latvia is carried out in only few locations, however, material from selections via seed orchards is deployed in various climatic and soil conditions, therefore concerns arise for influence of genotype environment interaction on levels of genetic gain. Problem is addressed based on 3 open pollinated progeny tests, consisting of 80 open pollinated families, located in 3 distant climatic regions in Latvia. Test age is 27 years, therefore not only growth, but also branch quality traits can be reliably analyzed. Strong genetic correlation (rb=0.80-0.94) among sites for tree height and diameter was found, but considerably weaker for branch traits like diameter of thickest branch (rb=0.52-0.67), average branch diameter, and sum of branch diameters (rb=0.41-0.49). Coefficients of additive genetic variation and coefficients of phenotypic variation among family means, determining potential of improvement via breeding, can be inflated by up to half, based on single site estimates for growth traits and double for quality traits. Backward selection based on results of several trials, in contrast to forward selection or utilization of single experiment results, could lead to improvement of branch traits close to the same as for growth traits (height and diameter). Single site narrow-sense heritability estimates for analyzed growth and quality traits are up to twice as large as across site estimates, indicating possibilities of serious bias in genetic gain estimates based on results from one test site. Testing at 4-5 sites for further breeding work is recommended.

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