Evaluation of Sweet Cherry Fruit Firmness by Compression Testing and Penetrometer

Sweet cherry (Prunus avium L.) is considered a premium quality temperate fruit. Firmness is one of the most important fruit quality traits in sweet cherry, as it is a component of both consumer acceptance and storability. The traditional method utilized to determine firmness is by compression. We evaluated the relationship between a traditional compression-type firmness tester (Firmtech 2) and a programmable penetrometer (Mohr MDT-2). Firmness data from both instruments was successfully used to detect the combined effects of rootstock and spacing on firmness in a grower-focused trial. However, data from the Firmtech 2 was superior based on adjusted R2 values of treatment effects models. Correlation analysis between the Firmtech 2 and MDT-2 revealed that the linear relationship between the firmness data was moderate overall and varied considerably between genotypes and between trees of the same genotype. This indicates that the two instruments are measuring different components of fruit firmness and suggests multiple genetic and environmental factors are involved. Fruit sampled later in the season in 2021 after a severe heat wave had no significant relationship between perceived texture and measurements from either instrument (nor between instruments), likely due to heat damage. The high throughput and non-destructive analysis of the compression test is better suited for use in early-stage selection in breeding programs or for commercial use to discard soft fruit. The penetrometer provides higher-dimensional data that may be useful for more thorough analysis of sweet cherry texture for research purposes.