A Genetic Analysis of Fruit Firmness in Strawberry

The University of Florida strawberry breeding program regularly generates information on genetic parameters for fruit quality traits in order to inform crossing and selection decisions.  The main objectives of this study were to determine heritabilities and multiple correlations (additive, genotypic, and phenotypic) among traits for marketable yield, average fruit weight (fruit size), soluble solids content (SSC) and fruit firmness in the main breeding population during the 2012-2013 and 2013-2014 seasons.  A partial diallel mating design of 76 full-sib families from 27 parents in 2012 and of 63 full-sib families from 19 parents in 2013 was used to establish a cloned progeny trial in each season at the UF/IFAS Gulf Coast Research and Education Center at Wimauma, FL.  Narrow-sense heritabilities were estimated as  h²= 0.30 to 0.33 for marketable yield, h²= 0.53 to 0.45 for average fruit weight, h²= 0.16 to 0.33 for SSC and h²= 0.24 to 0.41 for fruit firmness. Broad-sense heritabilities for all four traits varied from H²= 0.31 to 0.67, showing large estimates of dominance variance for marketable yield in both seasons and of epistatic variance for average weight, SSC and fruit firmness.   Phenotypic, additive and genotypic correlations between firmness and other traits were small, but moderate and favorable additive (r_a= 0.40 ± 0.24) and genotypic correlations (r_g= 0.35 ± 0.09) were found between marketable yield and average weight in season 2013-2014.  Large unfavorable additive (r_a= -0.69 ± 0.18 and -0.86 ± 0.11)   and genotypic correlations (r_g= -0.47 ± 0.07 and -0.52 ± 0.09) were obtained between marketable yield and SSC in both seasons.   Moderate genetic gains should be obtained from recurrent selection based on breeding values for all four traits, using a selection index that appropriately weights each trait according to its economic value.