Abstract:

The amino acid compositions and relative contents of phloem and xylem in different poplar strains, including 35-yr-old Populus pseud-simonii，24-yr-old P. pseudo-simonii×P. nigra，24-yr-old P. simonii×P. nigra，16-yr-old P. koreana，27-yr-old P. simonii and 40-yr-old P. simonii, were detected by high performance liquid chromatography method with AccQ\5Tag precolumn derivatization. The relationship between amino acid and the damage of Xylotrechus rusticus to poplars was also evaluated. The results showed that fifteen amino acids including Ala，Arg，Asp，Cys，Cyss，Glu，Gly，Ile，Leu，Lys，Phe，Pro，Ser, Thr and His were detected in the phloem at 2.5 m height of stem of tested poplar strains; the kinds of amino acids in the xylem were similar to that in the phloem, except that Val instead of His was present in the xylem. In the phloem, the relative contents of the same amino acids in different poplar strains were remarkably different, but there was no significant correlation between amino acid relative contents and the ratio of damaged trees. In xylem, the relative contents of the same amino acids in different poplar strains were also remarkably different, but there was significant positive correlation between amino acid relative contents and the ratio of damaged trees. The results suggested that the higher the amino acid relative contents in xylem, the better for the growth and development of Xylotrechus rusticus larvae. In P. pseud-simonii, the 15 kinds of amino acids were all present with their contents in rather balanced level in the xylem, and the rate of damaged trees was as high as 84%. In P. simonii× P. nigra, only 4 kinds of amino acids were present with their contents in relatively lower level, and in P. koreana, 13 kinds of amino acids were present with their relative contents not balanced; the both strains showed high resistance to Xylotrechus rusticus. The rate of damaged trees showed no correlation with  the relative contents of amino acids in different heights of trees examined, and this may be related to the oviposition habit of Xylotrechus rusticus L., which only lays eggs in cracks of old bark.

Key words: Xylotrechus rusticus, phloem, xylem, amino acid, high performance liquid chromatography, resistance to insects