Evaluation of male flower production in Sugi (Cryptomeria japonica) plus tree clones selected from a Kanto breeding region

Male flower production was evaluated with gibberellin treatment in plus tree clones (a total of 765 clones and 2,205 individuals) of Sugi (Cryptomeria japonica D. Don) planted in the crossing garden at Forest Tree Breeding Center. All the individuals were genotyped with SSR markers. The male flower production of the individual trees was evaluated by nine evaluators using male flower index (from 1: no or very little male flowers setting to 5: abundant). The male flower indexes of the genotyped clones were distributed in a bell curve and the average was 3.06. The accuracy of the evaluation of the male flower index was decreased by the un-trained evaluators, while its accuracy was increased by an increase in the number of evaluators, suggesting the importance of the replication of evaluators. The correlation of the male flower production with Gibberellin treatment between years was high and it was rarely influenced the climate compared to natural flowering. Gibberellin treatment was considered to be appropriate for the evaluation of male flower production.