Planting Year Prohexadione-Calcium Treatment Increases the Cropping Potential and Yield of Strawberry

The yield of strawberry (Fragaria x ananassa Duch.) is dependent on the number of inflorescences initiated in the apical meristems of the main and branch crowns. Branch crown formation is enhanced by short-day (SD) conditions while long-day (LD) conditions promote runner formation from the axillary buds of the main crown. Gibberellin (GA) and GA biosynthesis inhibitor application studies indicate that the fate of axillary buds is also affected by GA. We tested if prohexadione-calcium (ProCa), the inhibitor of GA biosynthesis, could be used to regulate vegetative and generative growth of strawberry in northern European conditions. SD cultivars 'Polka' or 'Honeoye' were sprayed with 0-200 mg/L ProCa concentrations during the planting year in six experiments. ProCa had a positive effect on both cultivars, but the results varied between the experiments. ProCa reduced the number of runners in five experiments and increased crown branching in three experiments during the treatment year. Reduced runnering and/or increased number of crown branches correlated with 23-53% increase on the number of inflorescences and, consequently, berry yield in four cases during the following year. In conclusion, in the northern European climate runner and branch crown formation can be controlled with single timely ProCa treatment during the planting year resulting in a significant increase of the yield during the following season.