Biochemical studies on the development of aril browning in pomegranate

Abstract

Aril browning (AB) in pomegranate is a physiological disorder free of external symptoms. Browning of aril starts with a dark dot on the aril and spreads further to the entire aril. The incidence is at first observed at 50% fruit maturity near the calyx end just under the skin. Present studies showed that AB incidence was higher in panicles as compared to those on main shoots. Fruits exposed to sun showed lesser incidence. AB incidence also increased with fruit maturity. Biochemical studies revealed that sugars, TSS, starch and pH were higher in AB affected aril as compared to healthy arils whereas anthocyanin, polyphenols, titratable acidity, protein and ascorbic acid were less in AB affected aril. Enzyme activities like amylase, total dehydrogenase activity in seed were reduced in seed of AB affected aril compared to healthy, whereas enzyme activity like polyphenol oxidase was more in seed of AB affected aril as compared to seed of healthy aril. Healthy arils showed higher moisture content and the seed higher percentage and faster rate of germination as compared to seed of AB affected aril, revealing that seed of AB affected aril had lost moisture leading to reduction in seed viability. Field experiments with growth regulators showed that GA3 treatment reduced incidence of AB and PBZ treatment increased the incidence of browning as compared to control. These findings indicated that the development of AB in pomegranate is a result of combination of many factors like inter fruit competition, biochemical and physiological changes in aril during fruit growth.