Comparative anatomy of the conductive tissues of the scions of Pinus sibirica Du Tour, P. cembra L. and their rootstocks P. sylvest

To study the appearance of incompatibility in adult graft trees, we studied the anatomical characteristics ofconducting phloem and sapwood in 55-year-old scions of Pinus sibirica Du Tour and Pinus cembra L. and their rootstocks –Scots pine (Pinus sylvestris L.). It was found that in all variants the width of the sapwood in the rootstock is significantlyhigher than in the scion; however, when only the early tracheids are taken into account, the differences between the scionand the rootstock are not significant, and the total width of the early tracheids from the sapwood is some higher in theP. cembra trees. In the place of rootstock and scion union, the width of the rootstock sapwood decreases due to a decreasein the proportion of late tracheids, while the sapwood of the scion remains almost unchanged. The variability of the sapwood width in scions and rootstocks of the P. cembra is lower and it is less sensitive to the reduction of increments thanin the P. sibirica, it indicates interspecific differences. The average width of the conducting phloem for the growing seasonalso varies less in the P. cembra, and in individuals of the P. sibirica with small xylem increments it approaches the widthof the current xylem increment. The relationship between the width of the conducting phloem and the width of the sapwood is weak; the width of the phloem depends more on the current growth of the xylem. The quantitative differencesin the width of the sapwood and the conducting phloem make it possible to judge the preservation of their species-specificity during long-term coexistence of the scion and the rootstock, as well as the effect of the scion on to the rootstock.