Pre-harvest factors affecting fruit quality in sweet oranges with an emphasis on albedo breakdown

Abstract

Albedo breakdown known as creasing, a physiological disorder, due to abnormal separation of cells leading to the formation of irregular fractures in the white tissue (albedo) causing the creases of sweet orange rind. It causes serious economic losses to the sweet orange growers in Australia and in other orange producing areas of the world.Fruit quality, particularly albedo breakdown has been influenced by various factors such as plant water relations, genetic factors, plant nutritional status and plant growth regulators. My research investigated the development of the incidence and the severity of albedo breakdown during fruit maturation and ripening, the effects of severity of albedo breakdown on fruit quality among locations and cultivars of ‘Navel’ sweet orange. I also elucidated the influence of deficit regulated irrigation, exogenous application of surfactants added in calcium solution, exogenous application of boron and the role of ethylene in the incidence of albedo breakdown, textural properties of the rind and fruit quality of ‘Navel’ sweet oranges.The incidence and the severity of albedo breakdown increased rapidly after commercial harvest. The incidence and severity of albedo breakdown in ‘Washington Navel’ orange differed from location to location, with the lowest at Harvey as compared to three other locations. Regardless of locations and cultivars, the severity of albedo breakdown did not affect juice content, soluble solids concentration, titratable acidity, ascorbic acid, citric acid and malic acid except for decreasing succinic acid and increasing tartaric acid. Locations and cultivars significantly influenced these fruit quality parameters.The application of deficit irrigation (50% and 75% water supply of control trees) improved fruit quality in terms of increased soluble solids concentrations and acidity levels without affecting percentage of juice, pH of juice, ascorbic acid and individual organic acids in ‘Navelina’ sweet orange. The enhancement of the uptake of Ca in leaf, rind, and pulp of the fruit and the reduction in the incidence of albedo breakdown were obtained with the application of different surfactants added into aqueous solutions of 2% Ca(NO[subscript]3)[subscript]2 starting from 81 days after full bloom (DAFB) at 10-day intervals. Among four tested surfactants, ‘Tween 20’ (0.05%) was the most effective in enhancing Ca uptake, reducing albedo breakdown and improving textural properties of rind and fruit firmness while maintaining the other important fruit quality attributes in ‘Washington Navel’ sweet orange.The foliar application of boron enhanced the concentration of boron and calcium in the leaf, rind and pulp. The single spray application of boron in early summer at 600 mg.L[superscript]-1 was the most effective in increasing boron concentration in the leaf, rind and pulp of fruit, reducing the incidence of albedo breakdown and improving textural properties of rind and fruit firmness without affecting any the other fruit quality attributes in ‘Washington Navel’ sweet orange.Rind of fruit with albedo breakdown produced the higher ethylene production than the normal fruit. The exogenous application of ethylene inhibitors including AVG (200 mg.L[superscript]-1) and CoSO[subscript]4 (300 mg.L[superscript]-1) reduced the incidence of albedo breakdown and improved the rind textural properties in ‘Washington Navel’ sweet orange. Ethylene seems to be involved in the incidence of albedo breakdown.In conclusion, the severity of albedo breakdown did not affect the major attributes of fruit quality in ‘Navel’ sweet oranges. The applications of deficit irrigation, exogenous 2% Ca(NO[subscript]3)[subscript]2 containing ‘Tween 20’ as a surfactant and the exogenous spray application of boron (600 mg.L[superscript]-1) influenced the incidence and severity of albedo breakdown without affecting other fruit quality parameters. Ethylene seems to be associated with the incidence of albedo breakdown in ‘Washington Navel’ sweet orange.