65 research outputs found

    Russeting in apple and pear: A plastic periderm replaces a stiff cuticle

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    Background and aims Russeting in apples (Malus domestica Borkh.) and pears (Pyrus communis L.) is a disorder of the fruit skin that results from microscopic cracks in the cuticle and the subsequent formation of a periderm. To better understand russeting, rheological properties of cuticular membranes (CM) and periderm membranes (PM) were studied from the russet-sensitive apple 'Karmijn de Sonnaville' and from 'Conference' pear. Methodology The CM and PM were isolated enzymatically, investigated by microscopy and subjected to tensile tests, creep/relaxation tests and to stepwise creep tests using a material testing machine. Principal results The isolated CM formed a continuous polymer, whereas the PM represented a cellular structure of stacked cork cells. Tensile tests revealed higher plasticity of the hydrated PM compared with the CM, as indicated by a higher strain at the maximum force (1max) and a lower modulus of elasticity (E). In apple, the maximum force (Fmax) was higher in the CM than in the PM but in pear the higher Fmax value was found for the PM. In specimens obtained from the CM : PM transition zone, the weak point in apple was found to be at the CM : PM borderline but in pear it was within the CM. In both apple and pear, creep/relaxation tests revealed elastic strain, creep strain, viscoelastic strain and viscous strain components in both the PM and CM. For any particular force, strains were always greater in the PM than in the CM and were also greater in pear than in apple. The 1max and Fmax values of the CM and PM were lower than those of nonrusseted and russeted whole-fruit skin segments, which included adhering tissue. Conclusions In russeting, stiff CM are replaced by more plastic PM. Further, the cell layers underlying the CM and PM represent the load-bearing structure in the fruit skin in apple and pear.Niedersächsisches Ministerium für Wissenschaft und Kultur/76251-17-4/09/ZN254

    Progressive Decline in Xylem Inflow into Developing Plums

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    Recent evidence suggests xylem functionality may decline in developing European plums. Loss of xylem function may have negative consequences for fruit quality. The aim of this study was to establish and localize the loss of xylem functionality, both spatially and temporally using detached fruit. Fruit were detached from the tree under water and fed through a capillary mounted on the cut end of the pedicel. The rate of water movement through the capillary was recorded. Fruit were held above dry silica gel [≈0% relative humidity (RH)] or above water (≈100% RH) to maximize or minimize transpiration, respectively. Water inflow rate depended on developmental stage. It increased from stage I to a maximum at early stage III and then decreased until maturity. Feeding acid fuchsin to developing fruit revealed a progressive decline in dye distribution. The decline progressed basipetally, from the stylar end toward the stem end. At the mature stage III, only the pedicel/fruit junction was stained. The same pattern was observed in four further plum cultivars at the mature stage III. The inflow into early stage III fruit decreased as the RH increased. In contrast, the inflow was less dependent of RH at the mature stage III. Abrading the fruit skin cuticle had no effect on water inflow during early and mature stage III but did markedly increase fruit transpiration rate. Decreasing the osmotic potential (more concentrated) of the feeding solution decreased the water inflow. Our results indicate a progressive loss of xylem functionality in European plum. Transpiration and osmotic pull are the main drivers of this xylem inflow

    Low cuticle deposition rate in ‘Apple’ mango increases elastic strain, weakens the cuticle and increases russet

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    Russeting compromises appearance and downgrades the market value of many fruitcrops, including of the mango cv. ‘Apple’. The objective was to identify the mechanistic basis of ‘Apple’ mango’s high susceptibility to russeting. We focused on fruit growth, cuticle deposition, stress/strain relaxation analysis and the mechanical properties of the cuticle. The non-susceptible mango cv. ‘Tommy Atkins’ served for comparison. Compared with ‘Tommy Atkins’, fruit of ‘Apple’ had a lower mass, a smaller surface area and a lower growth rate. There were little differences between the epidermal and hypodermal cells of ‘Apple’ and ‘Tommy Atkins’ including cell size, cell orientation and cell number. Lenticel density decreased during development, being lower in ‘Apple’ than in ‘Tommy Atkins’. The mean lenticel area increased during development but was consistently greater in ‘Apple’ than in ‘Tommy Atkins’. The deposition rate of the cuticular membrane was initially rapid but later slowed till it matched the area expansion rate, thereafter mass per unit area was effectively constant. The cuticle of ‘Apple’ is thinner than that of ‘Tommy Atkins’. Cumulative strain increased sigmoidally with fruit growth. Strains released stepwise on excision and isolation (εexc+iso), and on wax extraction (εextr) were higher in ‘Apple’ than in ‘Tommy Atkins’. Membrane stiffness increased during development being consistently lower in ‘Apple’ than in ‘Tommy Atkins’. Membrane fracture force (Fmax) was low and constant in developing ‘Apple’ but increased in ‘Tommy Atkin’. Membrane strain at fracture (εmax) decreased linearly during development but was lower in ‘Apple’ than in ‘Tommy Atkins’. Frequency of membrane failure associated with lenticels increased during development and was consistently higher in ‘Apple’ than in ‘Tommy Atkins’. The lower rate of cuticular deposition, the higher strain releases on excision, isolation and wax extraction and the weaker cuticle account for the high russet susceptibility of ‘Apple’ mango

    Neck shrivel in European plum is caused by cuticular microcracks, resulting from rapid lateral expansion of the neck late in development

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    Susceptibility to the commercially important fruit disorder ‘neck shrivel’ differs among European plum cultivars. Radial cuticular microcracking occurs in the neck regions of susceptible cultivars, but not in non-susceptible ones, so would seem to be causal. However, the reason for the microcracking is unknown. The objective was to identify potential relationships between fruit growth pattern and microcracking incidence in the neck (proximal) and stylar (distal) ends of selected shrivel-susceptible and non-susceptible cultivars. Growth analysis revealed two allometric categories: The first category, the ‘narrow-neck’ cultivars, showed hypoallometric growth in the neck region (i.e., slower growth than in the region of maximum diameter) during early development (stages I + II). Later (during stage III) the neck region was ‘filled out’ by hyperallometric growth (i.e., faster than in the region of maximum diameter). The second category, the ‘broad-neck’ cultivars, had more symmetrical, allometric growth (all regions grew equally fast) throughout development. The narrow-neck cultivars exhibited extensive radial cuticular microcracking in the neck region, but little microcracking in the stylar region. In contrast, the broad-neck cultivars exhibited little microcracking overall, with no difference between the neck and stylar regions. Across all cultivars, a positive relationship was obtained for the level of microcracking in the neck region and the difference in allometric growth ratios between stage III and stages I + II. There were no similar relationships for the stylar region. The results demonstrate that accelerated stage III neck growth in the narrow-neck plum cultivars is associated with more microcracking and thus with more shrivel

    Russet Susceptibility in Apple Is Associated with Skin Cells that Are Larger, More Variable in Size, and of Reduced Fracture Strain

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    Russeting is an economically important surface disorder in apple (Malus × domestica Borkh). Indirect evidence suggests an irregular skin structure may be the cause of the phenomenon. The objective of this study was to characterize epidermal and hypodermal cell morphology and the mechanical properties of the skins of apple cultivars of differing russet susceptibility. Dimensions of epidermal and hypodermal cells were determined using microscopy. Stiffness (S), maximum force (Fmax), and maximum strain (εmax) at failure were quantified using uniaxial tensile tests of skin strips. Particularly during early fruit development, epidermal cells (EC) and hypodermal cells (HC) in russet non-susceptible cultivars occurred in greater numbers per unit area than in russet-susceptible ones. The EC and HC were lower in height, shorter in length, and of reduced tangential surface area. There were little differences in S or Fmax between non-susceptible and susceptible cultivars. However, the εmax were higher for the skins of non-susceptible cultivars, than for those of susceptible ones. This difference was larger for the young than for the later growth stages. It is concluded that russet-susceptible cultivars generally have larger cells and a wider distribution of cell sizes for both EC and HC. These result in decreased εmax for the skin during early fruit development when russet susceptibility is high. This increases the chances of skin failures which is known to trigger russeting

    Energy Gardens for Small-Scale Farmers in Nepal Institutions, Species and Technology. Field Work Report

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    The Nepal Energy Garden forges new links across disciplines by integrating research on the institutional economics of energy and technology transfer with the knowledge of botanists and engineers. The objectives are fourfold: to investigate the institutional economics of energy biomass and biofuel production from local to national and global scales to undertake a technical assessment of resources and conversion routes to combine the institutional and technical analyses to devise ways for community cooperation on sustainable energy production to transfer the knowledge gained to a wide international audience. The energy garden concept originates from an idea developed by the Hassan Biofuels Park in India and will follow their approach for using local plant species as the source of biofuels, thereby avoiding loss of biodiversity as much as possible, and using marginal land to avoid competition with food crops. The project is a partnership of four organisations in Nepal and the Hassan Biofuels Park. The objectives will be achieved through a combination of policy analysis, reviews of plant species, analysis of technical options and field work in the villages. The aim is to test the feasibility of expanding the successful Energy Garden approach to Nepal and worldwide

    Direct Evidence for a Radial Gradient in Age of the Apple Fruit Cuticle

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    The pattern of cuticle deposition plays an important role in managing strain buildup in fruit cuticles. Cuticular strain is the primary trigger for numerous fruit-surface disorders in many fruit crop species. Recent evidence indicates a strain gradient may exist within the apple fruit cuticle. The outer layers of the cuticle are more strained and thus more susceptible to microcracking than the inner layers. A radial gradient in cuticle age is the most likely explanation. Our study aimed to establish whether (or not) deposition of new cutin in a developing apple fruit occurs on the inner surface of the cuticle, i.e., immediately abutting the outward-facing epidermal cell wall. Developing apples were fed with 13C oleic acid through the skin. Following a 14-d period for incorporation, the fruit was harvested and the cuticular membranes (CMs) isolated enzymatically. The CMs were then ablated to varying extents from the inner or the outer surfaces, using a cold atmospheric pressure plasma (CAPP). Afterwards, the ablated CMs were dewaxed and the 13C contents were determined by mass spectrometry. The incorporation of 13C in the cutin fraction was higher than in the wax fraction. The 13C content was highest in non-ablated, dewaxed CM (DCM) and decreased as ablation depth from the inner surface increased. There was no change in 13C content when ablation was carried out from the outer surface. As fruit development proceeded, more 13C label was found towards the middle of the DCM. These results offered direct evidence for deposition of cutin being on the inner surface of the cuticle, resulting in a radial gradient in cuticular age—the most recent deposition (youngest) being on the inner cuticle surface (abutting the epidermal cell wall) and the earliest deposition (oldest) being on the outer surface (abutting the atmosphere). Copyright © 2021 Si, Khanal, Schlüter and Knoche
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