Correlation between phosphorus content and fruit quality in strawberries

The effects of phosphorus (P) on quality of strawberry fruits have received little attention. In a previous study we found that the fruit of white-flesh mutant of strawberry cultivar 'Sachinoka' was sweeter than the fruit of wild type, and the total soluble sugar content in mutant fruits was significantly higher than that in wild type fruit. At the same time, the content of P in mutant fruits was significantly higher than that in wild type fruits. So we speculate that there is a positive correlation of sugar with P content in strawberry fruits, and increasing P content in strawberries can result in sweeter strawberries. To verify this hypothesis, we measured P and soluble solids content (SSC) in different kinds of strawberry fruits. The positive correlation between SSC and P content was first verified among 24 strawberry cultivars with the correlation coefficient r=0.95. Furthermore it was also verified among different parts (top, middle and bottom) of strawberry fruits (r=0.87). We found that both P content and SSC in fruits increased after strawberry plants were irrigated with 6.0 mM phosphoric acid, and the most effective way to improve strawberry quality is to apply KH₂PO₄ solution.