Thinking about clonal breeding strategy of forest trees

With the rise of forest industry, clonal breeding of forest trees was born and developed rapidly. It played an important role in forest industry all over the world. Focused on the breeding objective of high-yield and high-quality, some individuals with high genetic gain were selected out from natural populations or artificially generated breeding offspring to meet the huge demand of society for forest products such as timber, dried fruits and medicines, after they were produced in a large scale and timely harvested. Compared with crops, it was necessary that different breeding strategies for forest trees were conducted owing to the limits of tree height, cross-pollination, late sexual maturity, long growth cycle, long testing period and large land occupation. Advances in modern biological sciences and breeding technologies make it possible to break through the genetic improvement strategy of cross breeding based on traditional mating designs. When cross breeding was conduced in interspecific hybrids or intraspecific hybrids in cross-pollinated tree species, a breeding strategy, combined gamete chromosome doubling for triploid production with construction of breeding parental group by screening SSR genetic distance and paternity identity of superior individual, could be adopted, which has been successfully applied in Populus tomentosa. In this strategy, genetic distance among parents in the germplasm bank was firstly estimated using SSR markers. Meanwhile, the paternal origin of superior half-sib individuals derived from the free-pollinated offspring in the germplasm bank was determined by SSR. Then, the breeding parental group would be constructed according to SSR genetic distance and paternity identity of superior individual in half-sib families. Parents with high combining ability were used to produce polyploid by sexual polyploidization. Therefore, the maximal utilization of ploidy vigor and heterosis would be achieved, and the process of forest clonal breeding would be also economically and efficiently promoted.