The mechanical properties and anatomy of fruit wall peels and their enzyme-isolated cuticular membranes (CM) are reported for three cherry tomato (Lycopersicon esculentum Mill.) cultivars that are crack-resistant, crack-intermediate, and crack-prone (i.e., Inbred 10, Sweet 100, and Sausalito Cocktail, respectively). The resistant and intermediate fruit peels strain-hardened when extended progressively; those of the crack-prone cultivar did so only modestly. The CM of all cultivars strain-hardened when extended with small forces; the CM of the intermediate and crack-prone cultivars strain-softened under tensile forces that did not strain-soften the crack-resistant cultivar. The peels and CM of the resistant cultivar were stiffer, stronger, and required more energy to break than crack-prone peels. The CM of crack-resistant peels developed deeper within the subepidermis than in the crack-prone or crack-intermediate peels. The CM in the outer epidermal periclinal walls of the crack-resistant and crack-intermediate cultivars was thicker than that of crack-prone peels. These data indicate that CM thickness can be used to gauge crack susceptibility among cherry tomato fruit, which can be useful in breeding programs and would facilitate QTL mapping of the underlying genetic factors.
Antonio J. Matas, Eward D. Cobb, Dominick J. Paolillo Jr., and Karl J. Niklas
Martin J. Bukovac, Alicia Pastor, Royal G. Fader, and Moritz Knoche
Morphological and physical characteristics of the cuticular membrane (CM) of selected cultivars of sweet cherry (Prunus avium L.) fruit were studied relative to rain-induced cracking. Two characteristics of the CM may be determinants in rain-induced fruit cracking. The surface morphology and chemistry determine surface wettability and water retention, and the morphology and physicochemical characteristics its water permeability. The fruit epidermis as well as the guard cell walls adjacent to the outer vestibule and stomatal pore are covered by a thin lipoidal CM. Stomata were present at a frequency of 0.1 to 2 per mm2 depending on cultivar and fruit surface position. However, most appeared nonfunctional with many pores partially or completely occluded with wax-like material. There was no evidence of water (containing fluorescein or AgNO3) penetration into stomatal pores following surface application or submerging fruit for short periods. There was stomatal pore penetration when submerged fruit were infiltrated by reduced pressure in the presence of 0.1% L-77. Preferential sorption of AgNO3 and fluorescein by cuticular ledges and guard cells was noted. The epicuticular wax (ECW) had no significant fine-structure. The CM was isolated enzymatically (cellulase/pectinase) and found to be 1 to 2 μm thick with an area weight of 1.2 to 2.3 g·m–2, of which 25% to 40% was chloroform/methanol (1: 1by vol.) soluble. Fractionation of the chloroform/methanol fraction indicated the presence of four groups of nonpolar constituents. The fruit surface was moderately difficult to wet, forming contact angles of 85% to 105%, and with an estimated critical surface tension in the range of 16-24 mN·m–1. Fruit water loss (transpiration) and uptake on submersion was followed and found to be complex. Transpiration increased with an increase in temperature, and both rate of transpiration and water uptake increased after removal of the epicuticular and cuticular waxes. Pathways of water uptake and the significance of our findings to rain-induced fruit cracking will be discussed.
Moritz Knoche, Bishnu P. Khanal, and Matej Stopar
in the cuticular membrane are the first detectable symptoms in russet development ( Faust and Shear, 1972a ; Hatch, 1975 ; Simons and Chu, 1978 ; Verner, 1938 ). A periderm is subsequently formed as a wound reaction that replaces the primary
Bishnu P. Khanal, Rejina Shrestha, Leonie Hückstädt, and Moritz Knoche
surface, they were all averaged. The mean of these scores was used in the subsequent correlative analyses ( Table 1 ). Table 1. Russeting susceptibility of 22 apple cultivars, mass of cuticular membrane (CM), dewaxed cuticular membrane (DCM) and wax
Eckhard Grimm, Stefanie Peschel, Tobias Becker, and Moritz Knoche
.8% in ‘Katalin’ ( Table 2 ). Strain measured in an exocarp segment was always lower than in a corresponding isolated CM. Table 2. Fruit mass and biaxial elastic strain ( ) in excised exocarp segments (ESs) and isolated cuticular membranes (CMs) from the
Stefanie Peschel and Moritz Knoche
/or 2) the mechanical constitution of the load-bearing peripheral structure, presumably the exocarp. Both groups of factors are mechanistically unrelated. The cuticular membrane plays an important role in cracking, because it represents the primary
Moritz Knoche and Eckhard Grimm
cracks in the cuticular membrane (CM) when fruit surfaces were exposed to water or high humidity ( Knoche and Peschel, 2006 ). These cracks were limited to the CM, did not traverse epidermal or hypodermal cell layers, and were only detectable by
Moritz Knoche and Stefanie Peschel
The cuticular membrane (CM) covers all aboveground, primary surfaces of terrestrial plants. It serves as a protective barrier against water loss, infection with pathogens, and mechanical damage. Maintaining these functions throughout development
Andreas Winkler, Eckhard Grimm, Moritz Knoche, Julian Lindstaedt, and Dirk Köpcke
Skin spot is a commercially important disorder of the fruit skin of ‘Elstar’ apples (Malus ×domestica Borkh.). The disorder is characterized by patches of small brownish dots (“skin spots”) that usually appear on the skin after fruit are removed from storage. Water-induced cuticular microcracks are implicated in the etiology of skin spot. The objectives of our study were 1) to establish the effect of surface wetness on the severity of skin spot; and 2) to identify possible relationships between meteorological records of rainfall over a number of seasons and the severity of skin spot in those seasons. Surface wetness treatments were imposed on fruit using overhead sprinklers installed above trees grown under a plastic rain shelter. During early fruit development [14 to 44 days after full bloom (DAFB)], surface wetness did not affect the severity of skin spot. However, during the later part of the growing season (greater than 44 DAFB), increased surface wetness increased the incidence and severity of skin spot and also the severity of cuticular microcracking. Most skin spots and microcracks were already present at harvest before storage, but skin spots and microcracking did increase slightly during subsequent controlled atmosphere (CA) storage. Over a 9-year period, the severity of skin spot in ‘Elstar’ apples grown and stored locally under standard orchard and storage conditions was positively correlated to the number of rainy days. This correlation was greater for the period between 1 Aug. to harvest than for periods 1 June to harvest or 1 July to harvest. Fruit treated with 1-methylcyclopropene (1-MCP) were more susceptible to skin spot than untreated control fruit. Calculating regression equations for the relationship between the severity of skin spot and the number of rainy days (period 1 Aug. and harvest) revealed that the (commercially important) threshold score for skin spot of 2 is predicted to occur after 44 rainy days for control fruit and after 34 rainy days for 1-MCP-treated fruit. Our data demonstrate that skin spot arises from cuticular microcracks, which in turn result from numerous exposures to surface wetness (rain, dew), especially those occurring during later stages of fruit development.
Christine Schumann, Henrik Jürgen Schlegel, Eckhard Grimm, Moritz Knoche, and Alexander Lang
Susceptibility of sweet cherry (Prunus avium L.) fruit to rain cracking increases toward maturity and is thought to be related to increases in both tissue pressure (