BREEDING GOALS, TRAIT HEREDITY AND GENETIC IMPROVEMENT OF PERSIMMON IN JAPAN

The goal of persimmon breeding in Japan is to release new cultivars with improved fruit quality characteristics (non-astringency, high eating quality, commercially acceptable fruit size, the absence of cracks, long shelf-life, and good appearance), high and stable fruit yield, and disease and pest resistance. Of particular importance is the pollination-constant non-astringent (PCNA) trait, however, PCNA cultivars are very limited in the available germplasm. The PCNA trait is inherited qualitatively and the Japanese PCNA (J-PCNA) trait is controlled by recessive genes. Because the J-PCNA cultivars are closely related, repeated crossing among them has led to inbreeding depression for fruit weight and productivity. Consequently, the breeding approach has partly shifted to backcrossing (J-PCNA × non-PCNA) × J-PCNA since 1990, but two generations are generally needed to obtain a low percentage of PCNA offspring due to hexaploidy. Two astringent cultivars with high productivity and large fruit weight were released in 2007 from the PCNA × non-PCNA in this strategy. Unlike the J-PCNA trait, the Chinese PCNA (C-PCNA) trait is controlled by dominant genes, and approximately 50% of the offspring from C-PCNA × non-PCNA possessed this trait. However, the fruits of many C-PCNA offspring still have residual astringency. We developed DNA markers to distinguish the J-PCNA and C-PCNA genotypes, and marker-assisted selection is being effectively employed in PCNA × non-PCNA crosses. Other than the non-astringency trait, most economically-important traits are inherited quantitatively. Many of the traits including fruit ripening time, soluble solids concentration, and fruit cracking are controlled mainly by additive gene action. We predicted with high accuracy the distribution of genotypic values of the offspring for some of these traits. Gradual progress over generations has resulted in the release of new J-PCNA cultivars with early ripening, no calyx-end cracking, and/or high eating qualities.