Abstract: Based on the investigation of symptoms of the infected Chinese pine tree and the amount of their nymph, the infected trees are graded into four classes. There is in the ratio of 9:3:3:1 among the four classes of trees. The gradation is not related to the environment. There is a negative correlation between the tree growing capacity and the amount of the nymph, but not significant. The trees of class Ⅰ grow normally without symptoms. The difference of growth between Ⅰ and Ⅲ, Ⅳ class of trees is very significant. The symptoms occured on the infected trees which are six years old. If no symptoms occured on such trees they will not occur ever. The chances of infection will become much less when the trees are over 15 years old. For this reason, the age of stand in which the plus trees with the resistance are selected will be over 15 years old. By using the method of 5 dominant trees, the plus trees shall be selected among the trees of class Ⅰ and its DBH and H must be larger than the average by 15% and 5% respectively.

Key words: Dominant tree, Allele, Dominant gene