The aim of this study was to investigate variability in the sorbitol: sucrose ratio (SSR) in source leaves of different peach [Prunus persica (L.) Batsch] cultivars. Four- and 5-year-old trees of 58 cultivars were examined. Mature leaves were sampled on three dates in middle to late summer and analyzed for neutral soluble sugars using high-performance liquid chromatography. Differences in SSRs were observed. In most cultivars, the sorbitol content was at least twice that of sucrose. The maximal range of SSR occurred on the third date and ranged from 1.5 to 4.3. There was a date × genotype interaction (P < 0.01). When cultivars were grouped by country of origin, the mean ratios of the Japanese group were lower than those of the Italian and American groups for all three sampling dates. The SSRs of nectarines were higher than those of peach and canning clingstone-type cultivars. In general, variations in SSR were due mostly to differences in sucrose content. The SSR was negatively correlated with flowering date. These results indicate variability in SSR in peach germplasm, variability that seems to be related to the geographical origin of the cultivars.
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