CHARACTERIZATION OF DETERMINANTS OF FRICTION DISCOLOURATION IN PEARS

Friction discolouration (FD) of pears is an important postharvest disorder responsible for significant consumer discontent in markets because of the unattractive appearance of the fruit surface. Control of this problem is essential to increase profitability of the pear industry. There is no single factor known to act as a limiting factor in incidence of FD; however, certain biochemical constituents (polyphenol oxidase, phenolic compounds and ascorbic acid) and skin anatomy have been reported to play important roles in this mechanism. Identification of determinants likely to play a role in the incidence of FD is a prerequisite for identifying molecular markers which can be used in pear breeding programmes to identify susceptible individuals and discard them early in the breeding cycle. For this purpose, 250 seedlings from two segregating populations for FD derived from interspecific crosses between Asian and European pear were selected. Out of 22 variables studied, a few consistent predictors were observed in relation to FD index of seedlings. All these variables were phenolic compounds. The study showed that the concentrations of procyanidin dimer B2 and isorhamnetin 3-galactoside/ glucoside were negatively correlated, while epicatechin and quercetin-3-O-glucoside were positively correlated, with susceptibility to FD. In addition, there was clear evidence of the influence of environmental factors (fruit size, harvest date, time in storage) on FD. These data will be used to accelerate the search for molecular markers which can be used to reduce FD-susceptibility in the pear breeding programme.