Estimation of the genetic parameters of boron and sorbitol concentration in fruit from a pear breeding population, and investigation of the relationship between these traits on the occurrence of flesh spot decay

Pears (Pyrus spp.) are among the oldest crops grown worldwide. They are cultivated in all temperate regions and world production is second only to apples among deciduous tree fruits. Flesh spot decay (FSD) is one of the most important physiological disorders of Asian pears. The causes of this disorder remain unclear and no single nutrient or factor has been identified as the causal factor; however FSD has been related to environmental conditions. This study was carried out to estimate genetic parameters, in particular narrow-sense heritabilities and additive genetic correlations, of boron (B) and sorbitol contents and FSD in pear fruit. Approximately ten trees from each of twenty families of a breeding population were used in this study. Approximately ten fruit from each tree were assessed for disorder after four weeks post-harvest storage, and a composite sample from each tree was subsequently analysed for B and sugar (including sorbitol) content. Symptoms of internal browning and cavities were independent and thus not considered to be the same disorder (FSD). The heritability estimates for the prevalence of browning and cavities were low (0.18 and 0.19 respectively). B and sorbitol contents showed a positive genetic correlation (0.38) supporting the argument that the translocation of B is facilitated by the formation of complexes with sorbitol. High heritability was estimated for B content (0.72); however, that for sorbitol content was relatively low (0.18). A negative genetic correlation was estimated between both B and sorbitol and the area of the fruit affected by browning (-0.28 and -0.44 respectively). However, the opposite effect was observed in relation to the occurrence of cavities (0.51 for B and 0.60 for sorbitol). Furthermore, a negative genetic correlation was estimated between fructose and the occurrence of cavities (-0.62). Given that sorbitol-B complexes releases B when sorbitol is converted to fructose, these results suggest that there might be a link between B, these sugars and the formation of cavities in the fruit. Further work examining the B content within various parts of the fruit is required to unravel this link.