Selection of elite lines of BpGH3.5-transgenic Betula platyphylla using growth adaptability analysis

White birch(Betula platyphylla)is precious material for pulpwood and widely distributed in 14 provinces of China.Previous study indicated that inhibited expression of a gene encoding an auxin amide synthase,BpGH3.5,in transgenic plants reduced the level of IAA–amino acid conjugation,resulting in more free IAA,thereby better growth of birch.Utilizing transgenic-B pGH3.5 lines to increase wood production in a wide range of environments is the goal for breeders.In three field trials here,we measured tree height,diameter at breast height,and volume of 16 BpGH3.5-transgenic 7-year-old white birch lines(including 12 antisense strand lines and 4 overexpression lines)and a wild-type white birch line from three sites that varied greatly in their environmental conditions.To select elite BpGH3.5-transgenic lines for each target environment,we used an additive main effects and multiplicative interaction model to analyze genotype by environment interaction,growth adaptability and stability.The selection criteria for elite transgenic lines were set as the average volume plus 0.75 times the standard deviation for the tested lines at each test site.Results showed that the effect of line and site for height was highly significant(P<0.01),and the effect of line×site was significant(P<0.05);selected as the elite lines were FG12,FG13 and FG27 at the Maoershan Experimental Forest Farm,FG13 and FG32 at the Shidaohe Forest Farm,and FG3 and FG31 at the Ecological Experiment Forest Farm.These seven high-yield,stable lines can now be tested in production trials or adjacent trial areas with similar environmental conditions,while the high-yield,unstable lines should be tested in production trials in areas deemed suitable for their growth.These results provide guidance on which released transgenic elite lines will grow best in a wide range of conditions.