Russeting of Fruits: Etiology and Management

Abstract

The skin of a fruit protects the vulnerable, nutrient-rich flesh and seed(s) within from the hostile environment. It is also responsible for the fruit’s appearance. In many fruitcrop species, russeting compromises fruit appearance and thus commercial value. Here, we review the literature on fruit russeting, focusing on the factors and mechanisms that induce it and on the management and breeding strategies that may reduce it. Compared with a primary fruit skin, which is usually distinctively colored and shiny, a secondary fruit skin is reddish-brown, dull and slightly rough to the touch (i.e., russeted). This secondary skin (periderm) comprises phellem cells with suberized cell walls, a phellogen and a phelloderm. Russeted (secondary) fruit skins have similar mechanical properties to non-russeted (primary) ones but are more plastic. However, russeted fruit skins are more permeable to water vapor, so russeted fruits suffer higher postharvest water loss, reduced shine, increased shrivel and reduced packed weight (most fruit is sold per kg). Orchard factors that induce russeting include expansion-growth-induced strain, surface wetness, mechanical damage, freezing temperatures, some pests and diseases and some agrochemicals. All these probably act via an increased incidence of cuticular microcracking as a result of local concentrations of mechanical stress. Microcracking impairs the cuticle’s barrier properties. Potential triggers of russeting (the development of a periderm), consequent on cuticular microcracking, include locally high concentrations of O2, lower concentrations of CO2 and more negative water potentials. Horticulturists sometimes spray gibberellins, cytokinins or boron to reduce russeting. Bagging fruit (to exclude surface moisture) is also reportedly effective. From a breeding perspective, genotypes having small and more uniform-sized epidermal cells are judged less likely to be susceptible to russeting.

Solving the regulation puzzle of periderm development using advances in fruit skin

“…Partially russet development is stress inducible, and it can be repressed by rain sheltered cultivation and eliminated by fruit bagging ( Wang et al., 2016 ; Shi et al., 2019 ; Zhang et al., 2021 ). Similar effect of bagging has been observed in other fruits ( Winkler et al., 2022 ). These results suggest that expansion-growth-induced strain does not cause russeting independently in the absence of stress or certain environmental factors.…”

“…2015). The fruit susceptibility to russeting varies with developmental stages (Knoche et al, 2011;Khanal et al, 2021;Winkler et al, 2022). The de-differentiation potential of somatic cells to meristem depends on cell types and cell developmental stages, which can explain why periderm or russeting is more easily induced in the early developmental stage.…”

“…Orchard factors that induce fruit periderm development to russet include the expansion-growth-induced strain and environmental stresses ( Winkler et al., 2022 ). Partially russet development is stress inducible, and it can be repressed by rain sheltered cultivation and eliminated by fruit bagging ( Wang et al., 2016 ; Shi et al., 2019 ; Zhang et al., 2021 ).…”

Apple fruit periderms (russeting) induced by wounding or by moisture have the same histologies, chemistries and gene expressions

“…This requires some sort of signal which connects the two events. Potential signals resulting from impaired barrier properties include: (1) a decreased CO 2 concentration, (2) an increased O 2 concentration and (3) a more negative water potential of the flesh due to a more rapid dehydration at the fruit surface [ 8 , 11 , 22 ].…”

“…Russeting can be triggered by mechanical damage caused by external biotic factors, such as feeding insects [ 3 ] or external abiotic factors such as abrasion–e.g., leaf rub [ 4 ] or the use of some agrochemicals [ 5 ]. More commonly, the causes of russeting are developmental, the first visible symptoms of the disorder being the appearance of cuticular microcracks [ 6 – 8 ]. Such microcracks result from various sources including from strain of the fruit surface caused by growth [ 9 , 10 ] or exposure to surface moisture [ 11 – 15 ].…”