目前所进行的优树选择育种仅1代是不能完成的。用种子园种苗造林,再在这些造林地上作下一代优树选择需要多代。象这类方法,为了尽可能地降低子代个体间的亲缘率,一般认为:定值于种子园中的无性系数越多越好。就其数目而言,Stern(1959)认为40—50个无性系就够了,在他研究的当时,由干群体遗传学尚未很好地整理的缘故,报告内容不够明 At present, only one generation of elite tree selection breeding can not be completed. Planting seedlings with seed orchard, and then in these afforestation sites for next generation superior tree selection requires multiple generations. Like this kind of method, in order to reduce the kinship rate among the offspring individuals as much as possible, it is generally believed that the more asexual coefficients are set in the seed orchard, the better. In terms of numbers, Stern (1959) concluded that 40-50 clones would suffice, and at the time of his study, the genetics of the population had not been well organized, and the report was not informative