biaxial tensile tests such as were first described by Bargel et al. (2004) . In this test, an excised segment of the fruit surface is pressurized from its inner side. As a result, the segment bulges and its surface area increases thereby mimicking the
tensile testing device. This cut stem was used to measure the stem diameter, and the seedling height was measured from the point where the stem was cut to the tips of the buds, excluding leaves. After each measurement, seedlings were completely dried (48 h
microscope (MZ10F; Leica Microsysteme GmbH, Wetzlar, Germany; camera DP71; Olympus) and image analysis (Software Cell^P; Olympus). The release of biaxial strain ( ; %) was calculated as: Tensile test. Strips (5 mm wide) were excised from CM or DCM discs (24
of epidermal segments (ES) of the fruit skin for tensile testing. At 141 DAFB when fruit were commercially mature, all fruit were harvested and put into cold storage [1.7 °C, 92% relative humidity (RH)] for up to 118 d (equivalent to 259 DAFB). At
the physiological inside to prevent uncontrolled water uptake from that side—this could have confounded the test results ( Simon, 1977 ). In contrast to the more common, uniaxial tensile tests of engineering, biaxial tensile tests better mimic the
The tensile properties of european pear (Pyrus communis L. `Beurre Bosc') and asian pear (Pyrus pyrifolia Nakai `Choguro') were examined using a microscope-mounted apparatus that allowed direct observation and recording of cell and tissue changes during testing. To manipulate turgor potential, tissue slices from fruit of different firmness (ripeness) were incubated in sucrose solutions of differing water potential. Solution water potentials were adjusted for individual fruit, and varied between -2.5 and 1 MPa from the water potential of the expressed juice. Fruit firmness declined from 100 to 20 N and from 60 to 25 N during ripening of european and asian pears, respectively. For both european and asian pears the relationship between fruit firmness and tensile strength of tissue soaked in isotonic solutions was sigmoidal, with the major mechanism of tissue failure being cell wall failure and cell fracture at high firmness and intercellular debonding at low firmness. In the intermediate zone, where fruit firmness and tissue tensile strength decreased simultaneously, a mixture of cell wall rupture and intercellular debonding could be observed. Tissue and cell extension at maximum force both declined similarly as fruit softened. Tensile strength of tissue from firm pears (>50 N firmness, >0.8 N tensile strength) decreased by as much as 0.6 N during incubation in solutions that were more concentrated than the cell sap (hypertonic solutions). When similar tissue slices were incubated in solutions that were less concentrated than the cell sap (hypotonic solutions), the tensile strength increased by up to 0.4 N. This is interpreted as stress-hardening of the cell wall in response to an increase in cell turgor. Tensile strength of tissue from soft pears was not affected by osmotic changes, as the mechanism of tissue failure is cell-to-cell debonding rather than cell wall failure.
The relationships between cellular characteristics of cortical tissue from `Braeburn' apple fruit (Malus domestica Borkh.) that had been harvested at two maturities and changes in texture that occurred during storage at 0C were studied. Tensile tests were used to measure adhesion between neighboring cells, and turgor pressure was manipulated to determine the pressures required to burst cells. Apples of advanced maturity became mealy during cool storage, while those of less advanced maturity did not. Mealiness was associated with low adhesion between neighboring cells, and a relatively high resistance to cell rupture.
“Effects of selected herbicides on sod tensile strength and rooting of mature and immature turf of common centipedegrass [Eremochloa ophiuroides (Munro.) Hack] were studied in field experiments. Herbicides evaluated were atrazine, atrazine + tridiphane, bensulide, DCPA, DPX-6316, imazapyr, imazaquin, napropamide, oxadiazon, pendimethalin, sethoxydim, simazine, and sulfometuron. At 2, 4, and 8 weeks after treatment (WAT), sod tensile strength was determined, and root length and number were measured 7 to 10 days later. In 1986 sod tensile strength was not affected, but in 1987 the tensile strength of the immature turf was reduced at 8 WAT by bensulide and imazapyr. Rooting was suppressed most by benstdide, imazapyr, napropamide, and sulfometuron at most rates and dates tested. By 8 WAT, root length, root number, and tensile strength of herbicide-treated centipedegrass sod did not differ from that of the untreated sod except for those plots treated with bensulide or imazapyr. Chemical names used: 6-chloro-N-ethyl-N' -(1-methylethyl) -1,3,5-triazine-2,4 -diamine (atrazine); 2-(3,5-dichlorophenyl) -2-(2,2,2-trichloroethyl) oxirane (tridiphane); O,O -bis(l-methylethyl)S-[2-[(phenylsulfonyl) amino] ethyl] phosphorodithioate (bensulide); dimethyl 2,3,5,6 -tetrachloro-1,4 -benzenedicarboxylate (DCPA); methyl 3-[[(4-methoxy-6-methyl-1,3,5-triazin-2-ylaminocarbonyl]aminosulfonyl]-2-thiophenecarboWlate (DPX-6316); (&)-2-[4,5 -dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl] -3-pyridinecarbolic acid (imazapyr); 2-[4,5-dihydro-4 -methyl-4 -(1-methylethyl) -5-oxo-W-imidazol-2-yl]-3 -quinolinecarboxylic acid (imazaquin); N,N-diethyl-2-(1-naphthalenyloxy)propanamide (napropamide); 3-[2,4-dichloro-5 -(1-methylethoxy) phenyl]-5-(l,l-dimethylethyl)-1,3,4 -oxadiazol-2-(3H) -one (oxadiazon); N-(1 -ethylpropyl)-3, 4-dimethyl-2,6-dinitrobenzenamine (pendimethalin); .2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio) propyl]-3-hydroxy-2 -cyclohexen-1-one (sethoxydim); 6-chloro-N,N'-diethyl-1,3,5-triazine-2)4-diamine (simazine); 2-[[[[(4,6-dimethyl-2-pyrimidinyl)amino]carbonyl] amino] sulfonyl] benzoic acid (sulfometuron).
Kiwifruit [Actinidia deliciosa (A. Chev) C.F. Liang et A.R. Ferguson] flesh firmness can decline by as much as 94% during fruit ripening. This phenomenon was investigated at the cellular level, with the aim of characterizing changes in the physiological condition and mechanical properties of cells. The tensile strength of kiwifruit outer pericarp tissue was measured, and low-temperature scanning electron microscopy was used to examine the mode of cell failure at fracture surfaces. The propensity with which cells ruptured was determined by incubating tissue discs in hypertonic and hypotonic solutions, and water potentials, osmotic potentials, turgor pressures, and tissue density were measured. An initial rapid reduction in flesh firmness—from 80 to 27 N during 6 weeks of storage at 0C—was related to a reduction in the adhesion between neighboring cells. Following tensile tests, an examination of fracture surfaces indicated that cells from freshly harvested fruit had ruptured, exposing the cell interior. After 6 weeks of storage, neighboring cells separated from each other without breaking open. With 23 additional weeks of storage at 0C, flesh firmness decreased from 27 to 5 N. The final softening stage was associated with an increase in the proportion of cells that separated at the middle lamella and an increase in the plasticity of the cell wall.
used to test new containers. Tensile strength of new or used containers was tested by suspending the containers 12 cm above a catch basin. The containers were leveled and increasing amounts of weight using 4.5-mm diameter steel balls (354 mg each) were