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Maribor, Slovenia

Tijskens L.M.M.,Wageningen University | Schouten R.E.,Wageningen University | Walsh K.B.,Central Queensland University | Zadravec P.,Fruit Growing Center | And 3 more authors.
Acta Horticulturae

Size increase (expressed as diameter) of four apple cultivars in five seasons during about 130 days before harvest, was analysed with a simple first order production mechanism. All variation in diameter among individual fruit could be attributed to the same origin (development stage or biological age), with explained parts (R2 adj) of more than 98%. The same general behaviour of diameter development was observed in two tomato cultivars whose fruits where grown at two different temperatures. These data were also analysed using the same model with explained parts (R2 adj) of about 90%. Converting diameter into volume (assuming a perfect sphere), the usually observed asymmetrical sigmoidal behaviour was obtained, frequently described in growth modelling with the Richard's curve. A similar sigmoidal behaviour was also observed in the accumulation of dry matter (DM), as measured with NIR technology in growing mangoes. The cubic root of these data on DM could be analysed using the same model formulation, including the variation between individual fruit, with R2 adj well over 90%. Accumulation of DM ends at harvest, so the mechanism of DM production can very well define the final level of DM obtained in harvested fruit. Since sugars and DM are strongly related (e.g., conversion of starch into sugars, Brix values), a very similar mechanism could govern the accumulation of sugars. Destructively measured data on sugars were collected in nectarines, showing indeed a very similar overall behaviour and variation. This indicates that growth (diameter, mass) and quality increase (DM, sugars) could be described by a very similar mechanism, providing the first tools in the quest to harvest quality. Source

Unuk T.,University of Maribor | Tijskens L.M.M.,Wageningen University | Germsek B.,University of Maribor | Zadravec P.,Fruit Growing Center | And 4 more authors.
Journal of the Science of Food and Agriculture

BACKGROUND: Homogeneity in appearance is one of the quality aspects asked for in the supply chain. Decreasing the biological variation in batches of harvested apples (cultivars Braeburn, Fuji and Gala) becomes increasingly important. Skin colour is one of the aspects that determine both optimal harvest and stage of development. Skin colour is affected by location in the canopy. The rules of development of biological variation are now established and will be used on skin colour data. RESULTS: The Minolta colour aspects a*, b* and L* measured before commercial harvest change in a sigmoidal fashion and can be analysed including the biological variation, with a logistic model in indexed nonlinear regression, obtaining explained parts of above 90%. The mechanism of colour change is not affected by state of development or location in the canopy. The location in the canopy affects the intensity of both red and green colouring compounds. The variation in colouration is not affected by the location in the canopy. CONCLUSION: The red-coloured apple cultivar (Gala) depends more on the location in the canopy than the less-coloured cultivars (Fuji and Braeburn). The colour development in Fuji apples is considerably slower, with a much larger variation in stage of development. The location in the canopy affects all aspects of biological variation (biological shift factor and asymptotic starting level of colouration) for all three colour aspects L*, a* and b*, but only the mean value, not the standard deviation. The biological shift factors per colour aspects are linearly related. Once induced, variation remains constant during development. © 2012 Society of Chemical Industry. Source

Stajnko D.,University of Maribor | Rozman T.,University of Maribor | Pavlovic M.,University of Maribor | Beber M.,Fruit Growing Center | Zadravec P.,Fruit Growing Center
Scientia Horticulturae

A long-term growth curves usually describes the development of fruits insufficiently for a particular season hence it might cause severe discrepancies between the forecasted and harvested characteristics. For improving the early yield forecasts of 'Gala Schniga'/MM9 apples (Malus×domestica Borkh) the diameter of fruits on different abounded trees; low (L) 4fruits/cm2, medium (M) 7fruits/cm2 and high (H) 9fruits/cm2 was measured in three successive growing seasons (2009, 2010 and 2011) every two weeks from the T-stage till picking fruits. The fruits' development was observed on the terminal (TL), 2-years (2L) and 3-years old shoots (3L). The input data were transformed over natural logarithm and regression analyzes into modified Gompertz function (models) describing the fruit growth on different abounded trees and different position of shoots on the trees. The use of specific models improves annual yield forecasts of 28 commercial 'Gala' orchards over the long-term model significantly. On that way the minimal difference of 200kg/ha was calculated with middle-loaded 2L model in 2009, 510kg/ha with low-loaded TL model in 2010 and 156kg/ha with middle-loaded 3L model in 2011, respectively. © 2013 Elsevier B.V. Source

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