Comparison studies on sucrose metabolism and phenolic content during fruit growth and maturation in pear cultivars

‘Patharnakh’ (Pyrus pyrifolia Burm.) (PN), a hard pear and ‘Punjab Beauty’ (Pyrus communis L. × Pyrus pyrifolia Burm.) (PB), a soft pear are dominant low-chill pear cultivars of subtropics of India. Present investigation reports the changes in sugar metabolism and related enzymatic activities in fruits of ‘PN’ and ‘PB’ cultivars harvested at different developmental stages from 45 to 150 days after fruit set. Total soluble sugars, fructose, and sucrose contents were higher in ‘PB’ as compared to ‘PN’ during fruit growth and maturation stages. Total phenols and flavanols increased initially and then showed a decreasing trend towards maturity. Sucrose synthase (SS) and sucrose phosphate synthase (SPS) activities strongly correlated to sucrose content in ‘PN’ but SPS was weakly related in ‘PB’ fruits. Acid and neutral invertases showed a negative correlation with sucrose content in ‘PN’, and a reverse trend in ‘PB’ cultivar was observed. It is concluded that SS and SPS are crucial for sucrose accumulation in ‘PN’, but invertase enzymes are also important for sucrose accumulation in ‘PB’ fruits.