BWB-assisted plus tree selection and deployment design for bulked progenies of the first-cycle Chinese pine seed orchard

Genetic improvement of Chinese pine in Zhongwan Improved Variety Base, Gansu Province of northwestern China, is in the key transition period from the first breeding cycle to the second breeding cycle. How to effectively select and utilize germplasm resources of the second breeding cycle, based on the previous improvement results and combined modern theories and technologies in tree breeding, has become important issues to be addressed immediately. Using large-scale no-peditree open-pollinated bulked progeny population from the first-generation seed orchard of Chinese pine in Zhongwan Improved Variety Base, Gansu Province, as study materials, this study elaborates issues about open-pollinated bulked progenies based elite germplasm resource selection, evaluation and utilization strategies for advanced cycle improvement of Chinese pine. Results showed that 40 superior individuals were selected based on the relative growth of stem volume, with the mean volume dominance ratio of 0.83. Population consisting 40 individuals had high levels of genetic diversity, with the mean polymorphism information content of 0.620 2. Results from SSR molecular markers based phylogenetic analysis showed that the 40 individuals had varying phylogenetic relationships, belonged to 23 homogenous groups. To effectively control inbreeding, the 40 individuals were conducted within-homogenous group selection and finally only 23 superior individuals were remained and used for parents of seed orchard in the second breeding cycle. Combined with the results of volume dominance ratios and phylogenetic analysis of these parents, seed orchard in the second breeding cycle of Zhongwan Improved Variety Base was suggested to adopt the grouped, unbalanced, complete, fixed block design, which had taken the increase of volume genetic gain and the maintenance of genetic diversity of seed orchrd progenies into consideration simultaneously. Results from this study will provide new insights into effective selection and rational utilization of elite germplasm resources in advanced breeding cycles of Chinese pine, and will lay the foundation for shortening breeding cycle and increasing breeding efficiency in genetic improvement of Chinese pine.