Phenotypic Characterization of Astringent Persimmon Lines with Recessive Homozygosity at the <i>ASTRINGENCY</i> Marker Locus

Persimmon fruit synthesizes and accumulates proanthocyanidins (PAs), resulting in its astringent taste. The pollination-constant and non-astringent (PCNA) trait is conferred by recessive alleles at the ASTRINGENCY (AST) locus, which has been exploited to control PA accumulation of persimmon fruit. However, some individuals with recessive homozygosity at the AST marker locus in breeding populations produce mature fruit with astringency, thereby reducing the marker-selection efficiency for the PCNA trait. In this study, we genetically and physiologically characterized the predicted ast-homozygous individuals exhibiting strong astringency in a cross population of ‘Taigetsu’ (non-PCNA) and ‘Kanshu’ (PCNA). The fruit PA content of these astringent individuals was higher than that of the other PCNA fruit, but lower than that of the non-PCNA fruit. These astringent individuals were similar to the other PCNA plants in terms of tannin cell size. Gene expression analysis revealed that PA synthesis-related genes (e.g., DkMYB4, DkMYC1, and DkANR) were expressed at a higher level in the astringent individuals than in the other PCNA fruit during the early fruit development stage. Furthermore, in the presumed ast-homozygous individuals with various PA contents, the expression of cellular function-related genes was highly correlated with PA accumulation. These genes may be important for tannin cell development and PA synthesis, potentially offering a novel approach to further modulate astringency in persimmons.