Fruit misshapen in strawberry cultivars (Fragaria x ananassa) is related to achenes functionality

Fruit deformation is a phenomenon commonly observed in commercial strawberry cultivars (Fragaria xananassa) with a negative impact on the economic benefit of crop production. To better understand this physiopathy, we evaluated fruit size and the relative amount of 'small' (< 0.4 mm) and 'big' achenes (> 0.6 mm) in misshapen (MF) and well-formed (WF) fruits from 'Camarosa', 'Ventana' and 'Medina' strawberry cultivars growing in the field. In 'Camarosa', size-dependent achenes functionality was assessed by analysing achenes germinability and differences in time to ripening between MF and WF. We found that the occurrence of fruit deformation was not only strongly dependent on the cultivar (i.e. genetic factor) but also was promoted by low temperatures (i.e. environmental factor). Regardless of the cultivar, MF showed higher percentage of 'small' non-functional achenes than WF, indicating a failure in achene development, which could be related to the functional integrity of reproductive structures. To test this hypothesis, we performed an experiment by pollinating strawberry flowers with pollen developed under low and mild temperatures. Low temperatures reduced pollen viability, and flowers pollinated with low quality pollen led to a higher amount of MF. However, fruit deformation was not completely explained by differences in pollen quality, neither by differences in pistil maturity and receptivity nor ovule viability, suggesting that non-functional achenes might result from a disruption in postfertilisation processes such as embryo abortion as a consequence of low temperatures.