Resolution of quantitative trait loci for mechanical measures accounting for genetic variation in fruit texture of apple (Malus pumila Mill.)

Different attributes of fruit flesh texture contribute to consumer preference for eating quality in apple. We extended previous studies in order to determine whether a range of mechanical measures could resolve further the genetic contribution to variation in the physical attributes of apple fruit flesh. In particular we were interested in accounting for variation of the sensory traits crispness and juiciness. A quantitative genetic analysis of mechanical measures derived from compression and wedge fracture tests was carried out. This was based on segregation in an unselected mapping population which had previously been used to identify QTLs associated with penetrometer readings, stiffness by acoustic resonance, and a range of sensory descriptors. For wedge fracture tests significant QTLs were detected on L16 and L01. Those on L16 corresponded with positions previously determined for sensory measures of crispness and juiciness. Distance at maximum force was accounted for by a single QTL on L16 and correlated well with crispness and juiciness, suggesting that it may be appropriate for the selection of genotypes with fruit posessing desirable texture attributes. We established that the association of the sensory texture QTL on L16 is unlikely to be due to perceptual interactions with the Ma acidity locus. For compression measures, QTLs were detected on L01, L06, L08 and L15. Specific gravity is well-correlated with compression stiffness modulus, and both have a significant QTL on L06. Measures of cell size and shape determined across the population failed to detect any significant QTLs.